Method and apparatus for performing handover in a wireless communication system

Abstract

The present disclosure relates to a method and device for performing handover in a wireless communication system. An operation method of a user equipment (UE) in a wireless communication system may include: receiving a radio resource control (RRC) reconfiguration message indicating handover from a source base station, the RRC reconfiguration message including data radio bearer (DRB) configuration information; generating a medium access control (MAC) entity of a target base station when the DRB configuration information includes an indicator indicating the configuration of a dual active protocol stack (DAPS) of at least one DRB; configuring the MAC entity of the target base station based on the MAC configuration information included in the RRC reconfiguration message indicating handover; suspending a signaling radio bearer (SRB) for the source base station; and establishing or configuring an SRB for the target base station.

Description

Technical Field

[0001] The present disclosure relates to a method and apparatus for performing handover in a wireless communication system. Background Art

[0002] In order to meet the growth in demand for wireless data services after the commercialization of the fourth generation (4G) communication system, considerable efforts have been made to develop an improved fifth generation (5G) communication system or a pre-5G communication system. For this reason, the 5G communication system or the pre-5G communication system is referred to as a 4G network communication system or a post-long term evolution (LTE) system. In order to achieve high data rates, it is being considered to implement a 5G communication system in an ultra-high frequency band (millimeter wave (mmWave)) (e.g., a 60GHz band). In order to reduce the path loss of radio waves and increase the propagation distance of radio waves in the millimeter wave band, technologies such as beamforming, massive multi-input multi-output (MIMO), full dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive antenna systems are being discussed for 5G communication systems. In addition, in order to improve the system network for 5G communication system, technologies such as evolved small cells, advanced small cells, cloud radio access networks (cloud RAN), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, mobile networks, cooperative communication, coordinated multi-point (CoMP), and reception interference elimination are being developed. In addition, for 5G communication system, hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) (FQAM) and sliding window superposition coding (SWSC) as advanced coding modulation (ACM) schemes have been developed, as well as filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as advanced access technologies.

[0003] The Internet has evolved from a human-centered connection network through which humans generate and consume information to an Internet of Things (IoT) network that exchanges and processes information between distributed elements such as objects. Internet of everything (IoE) technology is emerging, in which technologies related to IoT are combined with technologies such as processing big data by connecting to cloud servers. In order to realize IoT, various technical components are required, such as sensing technology, wired / wireless communication and network infrastructure, service interface technology, security technology, etc. In recent years, technologies including sensor networks for connecting objects, machine-to-machine (M2M) communication, machine type communication (MTC), etc. have been studied. In the IoT environment, smart Internet technology (IT) services can be provided to collect and interpret data obtained from objects connected to each other and create new value in human life. As existing information technology (IT) and various industries merge and combine with each other, IoT can be applied to various fields such as smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, health care, smart home appliances, high-quality medical services, etc.

[0004] Various attempts are being made to apply 5G communication systems to IoT networks. For example, technologies related to sensor networks, M2M communications, MTC, etc. are implemented by using 5G communication technologies including beamforming, MIMO, array antennas, etc. The above-mentioned application of cloud RAN as a big data processing technology may be an example of the fusion of 5G communication technology and IoT technology.

[0005] As various services may be provided according to the development of wireless communication systems, a method for seamlessly providing the services is required.

[0006] Public Content

[0007] Technical Solution

[0008] Based on the above discussion, the present disclosure provides an apparatus and method capable of effectively providing services in a mobile communication system.

[0009] Beneficial Effects

[0010] The disclosed embodiments provide an apparatus and method capable of providing services in a mobile communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1a is a diagram showing the architecture of an LTE system to which the present disclosure is applicable.

[0012] Figure 1b is a diagram showing a radio protocol architecture of an LTE system to which the present disclosure is applicable.

[0013] Figure 1c is a diagram showing the architecture of a next-generation mobile communication system to which the present disclosure is applicable.

[0014] Figure 1d is a diagram showing a radio protocol architecture of a next-generation mobile communication system to which the present disclosure is applicable.

[0015] Figure 1e is a diagram for describing a process in which a user equipment switches from a radio resource control (RRC) idle mode to an RRC connected mode and establishes a connection with a network in the present disclosure.

[0016] Figure 1f is a diagram showing a signaling procedure for performing a handover proposed in the present disclosure in a next generation mobile communication system.

[0017] Figure 1g The specific operation of the first embodiment of the effective switching method for minimizing the data interruption time caused by switching according to the embodiment of the present disclosure is shown.

[0018] Figure 1h The specific operation of the second embodiment of the effective switching method for minimizing the data interruption time caused by switching according to the embodiment of the present disclosure is shown.

[0019] Figure 1i is a diagram showing a structure of an effective packet data convergence protocol (PDCP) layer applied to a dual active protocol stack (DAPS) handover method, which is a second embodiment of an effective handover method proposed in the present disclosure, and a method of applying the structure.

[0020] Figure 1j is a diagram showing a structure of an effective service data adaptation protocol (SDAP) layer applied to a DAPS handover method which is a second embodiment of an effective handover method proposed in the present disclosure and a method of applying the structure.

[0021] Figure 1k is a diagram illustrating a method of applying bearer specific configuration information when configuring a DAPS switching method according to an embodiment of the present disclosure.

[0022] Figure 1l is a diagram illustrating the operation of a user equipment to which the embodiments proposed in the present disclosure are applicable.

[0023] Figure 1m is a diagram illustrating an operation of a user equipment performing a fallback procedure when a handover fails in a DAPS handover method proposed in the present disclosure.

[0024] Figure 1n is a block diagram showing the structure of a user equipment according to an embodiment of the present disclosure.

[0025] Figure 1o A block diagram configuration of a transmission and reception point (Tx / Rx point, TRP) in a wireless communication system according to an embodiment of the present disclosure is shown.

[0026] Implementation

[0027] According to an embodiment of the present disclosure, a method for operating a user equipment (UE) in a wireless communication system may include: receiving a switching command from a source base station; generating a protocol layer of a second bearer of a target base station based on information included in the switching command; performing random access to the target base station; and determining whether to maintain data transmission and reception with the source base station based on predetermined conditions.

[0028] According to an embodiment of the present disclosure, a method for operating a UE in a wireless communication system may include: receiving a radio resource control (RRC) reconfiguration message indicating a handover from a source base station, the RRC reconfiguration message including data radio bearer (DRB) configuration information; generating a medium access control (MAC) entity of a target base station when the DRB configuration information includes an indicator indicating the configuration of a dual active protocol stack (DAPS) of at least one DRB; configuring the MAC entity of the target base station based on the MAC configuration information included in the RRC reconfiguration message indicating the handover; suspending a signaling radio bearer (SRB) for the source base station; and establishing or configuring an SRB for the target base station.

[0029] According to the present disclosure, a UE in a wireless communication system may include: a transceiver; and at least one processor, configured to: receive a radio resource control (RRC) reconfiguration message indicating a handover from a source base station through the transceiver, the RRC reconfiguration message including data radio bearer (DRB) configuration information; generate a medium access control (MAC) entity of a target base station when the DRB configuration information includes an indicator indicating the configuration of a DAPS of at least one DRB; configure the MAC entity of the target base station based on the MAC configuration information included in the RRC reconfiguration message indicating the handover; suspend a signaling radio bearer (SRB) for the source base station; and establish or configure an SRB for the target base station. DETAILED DESCRIPTION

[0030] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. When describing the present disclosure, when a detailed description of a related known function or configuration is determined to unnecessarily obscure the main points of the present disclosure, its detailed description may be omitted herein. The terms used herein are defined by considering the functions in the present disclosure, but these terms may vary according to the intentions of the user or a person of ordinary skill in the art, precedents, etc. Therefore, the definition should be based on the content of the entire specification.

[0031] The effects and features of the present disclosure and the methods for realizing them will be explained with reference to the embodiments described in detail below with reference to the accompanying drawings. In this regard, the embodiments of the present disclosure may have different forms and should not be construed as being limited to the descriptions set forth herein. On the contrary, these embodiments are provided to make the present disclosure thorough and complete, and to fully convey the concepts of the embodiments of the present disclosure to those of ordinary skill in the art. Throughout the specification, the same reference numerals refer to the same elements.

[0032] It will be understood that the various blocks of the flowchart and the combination of the flowcharts can be performed by computer program instructions. Because these computer program instructions can be embedded in a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, the instructions executed by the processor of the computer or other programmable data processing device generate a module for performing the functions described in the (multiple) flowchart blocks. Because these computer program instructions can also be stored in a computer-usable or computer-readable memory, which can instruct the computer or other programmable data processing device to implement the functions in a specific manner, the instructions stored in the computer-usable or computer-readable memory can also produce an article containing instruction modules for performing the functions described in the (multiple) flowchart blocks. Because computer program instructions can also be embedded in a computer or other programmable data processing device, the instructions for generating a computer-implemented process by performing a series of operations on a computer or other programmable data processing device, thereby executing the computer or other programmable data processing device can provide operations for performing the functions described in the (multiple) flowchart blocks.

[0033] In addition, each block may represent a module, segment, or portion of code that includes one or more executable instructions for performing (multiple) specified logical functions. It should also be noted that in some alternative implementations, the functions described in the blocks may not occur in the order shown in the accompanying drawings. For example, two blocks shown in succession may actually be executed substantially simultaneously, or the blocks may sometimes be executed in reverse order, depending on the functions involved.

[0034] The term "machine / device" used herein refers to a software element or a hardware element, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), and a "module" or "machine / device" performs certain functions. However, the term "machine / device" is not limited to software or hardware. The term "machine / device" can be configured in an addressable storage medium, or can be configured to reproduce one or more processors. Therefore, for example, the term "machine / device" includes elements, such as software elements, object-oriented software elements, class elements and task elements, processes, functions, attributes, processes, subroutines, program code segments, drivers, firmware, microcodes, circuits, data, databases, data structures, tables, arrays and variables. The functions provided in the element and "machine / device" can be combined with fewer elements and "machine / device", or can be separated from additional elements and "machine / device". In addition, the element and "machine / device" can be implemented as one or more central processing units (CPUs) that are reproduced in a device or a secure multimedia card. In addition, in an embodiment of the present disclosure, "machine / device" can include one or more processors.

[0035] When describing the present disclosure, when the detailed description of related known functions or configurations is determined to unnecessarily obscure the main points of the present disclosure, the detailed description thereof may be omitted. Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0036] For the convenience of description, examples are given of terms used to identify access nodes, terms related to network entities, terms related to messages, terms related to interfaces between network entities, terms related to various identification information, etc. Therefore, the present disclosure is not limited to the terms described later, and other terms referring to entities with equivalent technical meanings may be used.

[0037] For the convenience of description, this document uses the terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard. However, the present disclosure is not limited to the terms and names, and can be equally applied to systems that comply with other standards. Specifically, the present disclosure can be applied to 3GPP new radio (NR) (fifth generation (5G) mobile communication standard). For the convenience of description, the term "eNB" used here can be used interchangeably with the term "gNB". That is, a base station described as an eNB can represent a gNB. In addition, the term "terminal" can refer not only to mobile phones, NB-IoT devices, and sensors, but also to other wireless communication devices.

[0038] Hereinafter, a base station allocates resources to a terminal, and may include at least one of a gNode B, an eNode B, a Node B, a BS, a radio access unit, a base station controller, and a node on a network. Examples of terminals may include user equipment (UE), a mobile station (MS), a cellular phone, a smart phone, a computer, a multimedia system capable of performing a communication function, etc. Of course, the present disclosure is not limited to the above examples.

[0039] The present disclosure proposes a seamless handover method capable of minimizing data interruption time due to handover or reducing the data interruption time to 0 ms in a next generation mobile communication system.

[0040] Specifically, the effective switching method proposed in the present disclosure may have one or more of the following features.

[0041] Furthermore, in the effective handover method proposed in the present disclosure, different handover methods can be applied to different bearers.

[0042] -When a UE that performs data transmission or reception (uplink or downlink data transmission and reception) with a source base station through the protocol layers (physical (PHY) layer, medium access control (MAC) layer, radio link control (RLC) layer, or PDCP layer) of multiple first bearers receives a switching command message (or a radio resource control (RRC) reconfiguration message) from the source base station, while continuously maintaining data transmission or reception with the source base station through the first bearers without interruption, the UE can establish multiple new protocol layers of second bearers corresponding to the protocol layers of the first bearers (for example, having the same bearer identifier), and can perform data transmission or reception (uplink or downlink data transmission and reception).

[0043] -After the UE receives the handover command message, the protocol layer (PHY layer, MAC layer, RLC layer or PDCP layer) of the newly established second bearer is configured to send or receive data with the target base station based on the bearer configuration information or protocol layer information included in the handover command message.

[0044] -When performing data transmission or reception (uplink or downlink data transmission and reception) with the source base station through the protocol layer of the first bearer, the UE performs a random access procedure to the target base station through the protocol layer (e.g., MAC layer) of the second bearer. The random access procedure may include preamble transmission, random access response reception, message 3 transmission, or message 4 reception (e.g., contention resolution MAC control element (CE) or uplink transmission resource reception).

[0045] -When performing data transmission or reception with the source base station through the protocol layer of the first bearer, the UE completes the random access process to the target base station through the protocol layer of the second bearer (for example, the MAC layer), and sends a switching completion message to the target base station through the protocol layer of the second bearer.

[0046] -When performing data transmission or reception with the source base station through the protocol layer of the first bearer, the UE completes the random access process to the target base station through the protocol layer of the second bearer (for example, the MAC layer), sends a switching completion message to the target base station through the protocol layer of the second bearer, and performs data transmission or reception (uplink or downlink).

[0047] -When the UE successfully completes the random access procedure to the target base station and receives uplink transmission resources from the target base station for the first time, the UE stops sending data to the source base station through the protocol layer of the first bearer and switches uplink transmission to send data to the target base station through the second bearer.

[0048] -When the UE receives the handover command message, the UE continues to perform data transmission or reception (uplink or downlink data transmission or reception) with the source base station through the protocol layer of the first bearer, and performs a random access process to the target base station through the protocol layer of the second bearer. When the UE successfully completes the random access process and receives uplink transmission resources from the target base station for the first time, the UE stops sending uplink data to the source base station through the protocol layer of the first bearer, and only sends uplink data to the target base station through the protocol layer of the second bearer. In addition, the UE can continue to receive downlink data from the source base station through the protocol layer of the first bearer, and can continue to receive downlink data from the target base station through the protocol layer of the second bearer.

[0049] The first bearer and the second bearer may be configured in a second PDCP layer structure. In the second PDCP layer structure, a first bearer (e.g., an RLC layer, a MAC layer, or a PHY layer) for a source base station and a second bearer (e.g., an RLC layer, a MAC layer, or a PHY layer) for a target base station may be connected to one PDCP layer. Uplink data may be transmitted via the PDCP layer through one of the first bearer and the second bearer. That is, the UE sends uplink data through the first bearer until the UE performs a random access process to the target base station, successfully completes the random access process, and receives uplink transmission resources from the target base station for the first time. When the UE performs a random access process to the target base station, successfully completes the random access process, and receives uplink transmission resources from the target base station for the first time, the UE may stop transmitting data through the first bearer and switch to transmitting uplink data to the target through the second bearer. In this case, in the second PDCP layer structure, the UE may receive downlink data from the source base station or the target base station through the first bearer or the second bearer.

[0050] Hereinafter, the present disclosure proposes an efficient switching process without data interruption time based on the above features.

[0051] When the UE performs the effective handover method without data interruption time proposed in the present disclosure, but the handover fails, the UE can reestablish the connection by quickly falling back to the source base station by using the features of the effective handover method proposed in the present disclosure. Specifically, the features of the effective handover method proposed in the present disclosure can mean that the connection with the source base station is maintained even when the UE performs the handover process. In addition, even when the UE fails to handover, the present disclosure also proposes a specific fallback method using a wireless connection connected to an existing source base station.

[0052] The present disclosure provides a method and apparatus for efficiently performing different handover methods for each bearer in a next generation mobile communication system.

[0053] The present disclosure relates to a method and apparatus for performing fallback when an effective handover method without interruption of data transmission and reception is performed but the handover fails in a next generation mobile communication system.

[0054] According to an embodiment, the next generation mobile communication system may require an efficient handover method to support services without data interruption and with low transmission delay. In the event of a handover failure, a method that can fall back while minimizing the data interruption time may be required.

[0055] The present disclosure can propose effective various handover methods, which can prevent the occurrence of data interruption time due to handover when performing handover in the next generation mobile communication system. In this way, services without data interruption can be supported. An effective method that allows the UE to quickly fall back to the source base station when the handover fails will be described.

[0056] Figure 1a is a diagram showing the architecture of an LTE system to which the present disclosure is applicable.

[0057] refer to Figure 1a The radio access network of the LTE system includes next-generation base stations (evolved node B, hereinafter referred to as ENB, node B or base station) 1a-05, 1a-10, 1a-15 and 1a-20, a mobility management entity (mobility management entity, MME) 1a-25 and a serving gateway (serving-gateway, S-GW) 1a-30. UE (or terminal) 1a-35 can access the external network through ENB 1a-05 to 1a-20 and S-GW 1a-30.

[0058] exist Figure 1aIn the LTE system, ENB 1a-05 to 1a-20 correspond to the existing node B of the universal mobile telecommunication system (UMTS). The ENB is connected to the UE 1a-35 through a radio channel and performs a more complex role than the existing node B. In the LTE system, all user services including real-time services, such as Voice over IP (VoIP) through the Internet Protocol, can be served through a shared channel. Therefore, a device for collecting and scheduling state information such as the buffer state of the UE, the available transmission power state, and the channel state may be required. This can be handled by ENB 1a-05 to 1a-20. One ENB can generally control multiple cells. For example, in order to achieve a transmission rate of 100Mbps, the LTE system can use, for example, an orthogonal frequency division multiplexing (OFDM) scheme in a 20MHz bandwidth as a radio access technology. In addition, a modulation scheme and an adaptive modulation and coding (AMC) scheme that determine the channel coding rate are applied according to the channel state of the UE. The S-GW 1a-30 is an entity that provides a data bearer, and can add or release a data bearer under the control of the MME 1a-25. The MME 1a-25 is an entity responsible for various control functions of the UE and a mobility management function, and is connected to a plurality of base stations.

[0059] Figure 1b is a diagram showing a radio protocol architecture of an LTE system to which the present disclosure is applicable.

[0060] refer to Figure 1b In the radio protocol of the LTE system, the UE and ENB include PDCP 1b-05 and 1b-40, RLC 1b-10 and 1b-35, and MAC 1b-15 and 1b-30, respectively. PDCP 1b-05 and 1b-40 may be responsible for operations such as IP header compression / decompression. The main functions of PDCP are summarized as follows.

[0061] - Header compression and decompression functions (Header compression and decompression: Robust header compression (ROHC) only)

[0062] -User data transmission function (user data transmission)

[0063] - In-sequence delivery function (in-sequence delivery of upper layer packet data units (PDUs) during PDCP re-establishment in RLC Acknowledged Mode (AM))

[0064] - Reordering functionality (for split bearers of DC (supports RLC AM only): PDCP PDU routing for transmission and PDCP PDU reordering for reception)

[0065] -Duplicate detection function (duplicate detection of lower layer SDU during PDCP reestablishment of RLC AM)

[0066] - Retransmission function (for split bearer of DC, retransmit PDCP SDU during handover, for RLC AM, retransmit PDCP PDU during PDCP data recovery)

[0067] -Encryption and decryption functions

[0068] -Timer-based SDU discard function (Timer-based SDU discard in uplink.)

[0069] RLC 1b-10 and 1b-35 perform automatic repeat request (ARQ) operations by reconfiguring PDCP PDUs to an appropriate size. The main functions of RLC are summarized as follows.

[0070] -Data transmission function (transmission of upper layer PDU)

[0071] -ARQ function (error correction through ARQ (only for AM data transmission))

[0072] - Connection, segmentation and reassembly functions (connection, segmentation and reassembly of RLC SDU (only for UM and AM data transmission))

[0073] -Resegmentation function (resegmentation of RLC data PDU (only for AM data transmission))

[0074] - Reordering function (reordering of RLC data PDU (only for UM and AM data transmission))

[0075] - Duplicate detection function (Duplicate detection (only for UM and AM data transmission))

[0076] - Error detection function (protocol error detection (for AM data transmission only))

[0077] -RLC SDU discard function (RLC SDU discard (only for UM and AM data transmission))

[0078] -RLC reconstruction function

[0079] MAC 1b-15 and 1b-30 may be connected to an RLC layer configured in one UE and perform operations of multiplexing RLC PDUs to MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. The main functions of MAC are summarized as follows.

[0080] - Mapping function (mapping between logical channels and transport channels)

[0081] -Multiplexing / demultiplexing function (multiplexing MAC SDUs belonging to one or different logical channels to the transport channel and delivering them to the transport block (TB) of the physical layer, / demultiplexing MAC SDUs belonging to one or different logical channels from the transport channel to the transport block (TB) of the physical layer)

[0082] -Scheduling information reporting function

[0083] -HARQ function (error correction through HARQ)

[0084] - Function to handle the priority between logical channels (priority handling between logical channels of a UE)

[0085] -Function of handling the priority between UEs (handling the priority between UEs through dynamic scheduling)

[0086] -MBMS service identification function

[0087] -Transmission format selection function

[0088] - Fill function

[0089] The PHY layers 1b-20 and 1b-25 perform operations of channel coding and modulating the upper layer data, forming the channel-coded and modulated upper layer data into OFDM symbols, and sending the OFDM symbols through the radio channel, or demodulating the OFDM symbols received through the radio channel, channel-decoding the demodulated OFDM symbols, and sending the channel-decoded OFDM symbols to the upper layer.

[0090] Figure 1c is a diagram showing the architecture of a next-generation mobile communication system to which the present disclosure is applicable.

[0091] refer to Figure 1c, the radio access network of the next generation mobile communication system (hereinafter referred to as NR or 5G) includes a next generation base station (NR Node B, hereinafter referred to as NR gNB or NR base station) 1c-10 and an NR core network (CN) 1c-05. NR UE (or terminal) 1c-15 can access an external network through NR gNB 1c-10 and NR CN 1c-05. NR UE 1c-15 can be located in area 1c-20.

[0092] exist Figure 1c In the present invention, NR gNB 1c-10 corresponds to the ENB of the existing LTE system. NR gNB 1c-10 can be connected to NR UE 1c-15 through a radio channel and can provide services superior to those of the existing Node B. In the next generation mobile communication system, all user services are served through shared channels. Therefore, a device for collecting and scheduling status information such as the buffer status of the UE, the available transmission power status, and the channel status is required. This can be handled by NR gNB 1c-10. One NR gNB 1c-10 generally controls multiple cells. Compared with the existing LTE, the next generation mobile communication system can have a bandwidth larger than the existing maximum bandwidth in order to achieve ultra-high-speed data transmission, and beamforming technology can be additionally used by using OFDM as a radio access technology. In addition, a modulation scheme and an adaptive modulation and coding (AMC) scheme that determine the channel coding rate are applied according to the channel status of the UE. NR CN 1c-05 performs functions such as mobility support, bearer configuration, and quality of service (QoS) configuration. NR CN 1c-05 is an entity responsible for various control functions and the mobility management function of the UE, and can be connected to multiple base stations. In addition, the next generation mobile communication system can interoperate with the existing LTE system, and the NR CN is connected to the MME 1c-25 through a network interface. The MME is connected to the ENB 1c-30 which is an existing base station.

[0093] Figure 1d is a diagram showing a radio protocol architecture of a next-generation mobile communication system to which the present disclosure is applicable.

[0094] Reference Figure 1d In the radio protocol of the next generation mobile communication system, UE and NR gNB include NR Service Data Adaptation Protocol (SDAP) 1d-01 and 1d-45, NR PDCP 1d-05 and 1d-40, NR RLC 1d-10 and 1d-35, and NRMAC 1d-15 and 1d-30, respectively.

[0095] The main functions of NR SDAP 1d-01 and 1d-45 may include some of the following.

[0096] -User data transmission function

[0097] - Mapping functionality between QoS flows and Data Radio Bearers (DRBs) for both DL and UL

[0098] - Functionality to mark QoS flow ID in uplink and downlink

[0099] -UL SDAP PDU reflective QoS flow to DRB mapping function

[0100] Regarding the SDAP layer, for each PDCP layer, each bearer or each logical channel, the UE can receive an RRC message to configure whether to use the header of the SDAP layer or the function of the SDAP layer. When configuring the SDAP header, the UE can instruct the UE to update or reconfigure the mapping information between the QoS flow and data bearer of the uplink and downlink by using a 1-bit non-access stratum (NAS) reflected QoS indicator and a 1-bit access stratum (AS) reflected QoS indicator of the SDAP header. The SDAP header may include QoS flow ID information indicating QoS. QoS information can be used as data processing priority, scheduling information, etc. to support effective services.

[0101] The main functions of NR PDCP 1d-05 and 1d-40 may include the following.

[0102] -Header compression and decompression function (Header compression and decompression: ROHC only)

[0103] -User data transmission function

[0104] - In-sequence delivery function (in-sequence delivery of upper layer PDU)

[0105] - Out-of-order delivery function (out-of-order delivery of upper layer PDUs)

[0106] - Reordering function (for reordering of received PDCP PDUs)

[0107] - Duplicate detection function (duplicate detection of lower layer SDU)

[0108] -Retransmission function (retransmission of PDCP SDU)

[0109] -Encryption and decryption functions

[0110] -Timer-based SDU discard function (Timer-based SDU discard in uplink.)

[0111] The reordering function of the NR PDCP layer may refer to a function of reordering PDCP PDUs received from a lower layer in sequence based on a PDCP sequence number (SN). The reordering function of the NR PDCP layer may include at least one of a function of sending data to an upper layer in a reordered order, a function of sending data immediately regardless of the order, a function of reordering PDCP PDUs and recording lost PDCP PDUs, a function of reporting the status of lost PDCP PDUs to a transmitter, and a function of requesting retransmission of lost PDCP PDUs.

[0112] The main functions of NR RLC 1d-10 and 1d-35 may include some of the following functions.

[0113] -Data transmission function (transmission of upper layer PDU)

[0114] - In-sequence delivery function (in-sequence delivery of upper layer PDU)

[0115] - Out-of-order delivery function (out-of-order delivery of upper layer PDUs)

[0116] -ARQ function (error correction through ARQ)

[0117] - Connection, segmentation and reassembly functions (connection, segmentation and reassembly of RLC SDU)

[0118] -Resegmentation function (re-segmentation of RLC data PDU)

[0119] - Reordering function (reordering of RLC data PDU)

[0120] - Duplicate detection function

[0121] -Error detection function (protocol error detection)

[0122] -RLC SDU discard function

[0123] -RLC reconstruction function

[0124] The in-sequence delivery function of the NR RLC layer may refer to a function of sending the RLC SDU received from the lower layer to the upper layer in sequence. The in-sequence delivery function of the NR RLC layer may include the following functions: in a case where one RLC SDU is received after being segmented into a plurality of RLC SDUs, a function of reassembling and sending the segmented and received RLC SDUs, a function of reordering the received RLC PDUs based on the RLC SN or PDCP SN, a function of reordering the RLC PDUs and recording the lost RLC PDUs, a function of reporting the status of the lost RLC PDUs to the sender, a function of requesting retransmission of the lost RLC PDUs, a function of transmitting only the RLC SDUs before the lost RLC SDUs to the upper layer in sequence when there are lost RLC SDUs, and in a case where there are lost RLC SDUs but a certain timer has expired, sending all RLC SDUs received before the timer is started in sequence to the upper layer, or in a case where there are lost RLC SDUs and a certain timer has expired, sending all RLC SDUs received so far in sequence to the upper layer. In addition, the NR RLC layer can process the RLC PDU in the order of reception (in the order of arrival, regardless of the order of sequence number and sequence number), and send the processed RLC PDU to the PDCP layer without considering the order (out-of-order delivery). In the case where the received RLC PDU is a segment, the segment stored in the buffer or to be received in the future can be received, reconfigured into a complete RLC PDU, processed and sent to the PDCP layer. The NR RLC layer may not include a connection function, and the connection function may be performed by the NR MAC layer, or may be replaced by the multiplexing function of the NR MAC layer.

[0125] The out-of-order delivery function of the NR RLC layer may refer to a function of directly sending the RLC SDU received from the lower layer to the upper layer without considering the order, and may include the following functions: in a case where one RLC SDU is received after being segmented into multiple RLC SDUs, reassembling and sending the segmented and received RLC SDUs, or storing the RLC SN or PDCP SN of the received RLC PDU, reordering the RLC PDUs, and recording the lost RLC PDUs.

[0126] NR MAC 1d-15 and 1d-30 can be connected to multiple NR RLC layers configured in one UE, and the main functions of NR MAC may include some of the following functions.

[0127] - Mapping function (mapping between logical channels and transport channels)

[0128] -Multiplexing and demultiplexing functions (MAC SDU multiplexing / demultiplexing)

[0129] -Scheduling information reporting function (Scheduling information reporting)

[0130] -HARQ function (error correction through HARQ)

[0131] - Function to handle the priority between logical channels (priority handling between logical channels of a UE)

[0132] -Function of handling the priority between UEs (handling the priority between UEs through dynamic scheduling)

[0133] -MBMS service identification function

[0134] -Transmission format selection function

[0135] - Fill function

[0136] The NR PHY layers 1d-20 and 1d-25 may perform the following operations: channel encode and modulate the upper layer data, form the channel-encoded and modulated upper layer data into OFDM symbols, and send the OFDM symbols through the radio channel, or demodulate and channel-decode the OFDM symbols received through the radio channel, and send the channel-decoded OFDM symbols to the upper layer.

[0137] Figure 1e is a diagram for describing a process in which a UE switches from an RRC idle mode to an RRC connected mode and establishes a connection with a network in the present disclosure.

[0138] exist Figure 1e In the RRC connection mode, when a UE that sends or receives data in RRC connection mode does not send or receive data for some reason or for a period of time, the gNB can send an RRCConnectionRelease message to the UE to switch the UE to RRC idle mode (1e-01). When data to be sent is generated, the UE that currently has no connection established (hereinafter, idle mode UE) performs an RRC connection establishment process with the gNB. The UE establishes reverse transmission synchronization with the gNB through a random access process and sends an RRCConnectionRequest message to the gNB (1e-05). The RRCConnectionRequest message contains a UE identifier and a connection establishment cause. The gNB sends an RRCConnectionSetup message so that the UE establishes an RRC connection (1e-10).

[0139] The RRCConnectionSetup message includes configuration information for each service / bearer / RLC layer, each logical channel or each bearer. Whether to use ROHC for each bearer / logical channel, ROHC configuration information (e.g., ROHC version, initial information, etc.), statusReportRequired information (information in which the gNB indicates the PDCP status report to the UE), drb-ContinueROHC information (configuration information to maintain the ROHC configuration information and use the ROHC configuration information as it is) can be sent by being included in the PDCP layer configuration information (pdcp-config). In addition, the RRCConnectionSetup message contains RRC connection establishment information, etc. The bearer used for the RRC connection is also called a signaling radio bearer (SRB) and is used to send or receive RRC messages, which are control messages between the UE and the gNB.

[0140] The UE that has established the RRC connection sends an RRCConnectionSetupComplete message (1e-15) to the gNB. The RRCConnectionSetupComplete message includes a SERVICE REQUEST control message in which the UE requests the MME to configure a bearer for a specific service. The gNB sends the service request message contained in the RRCConnectionSetupComplete message to the MME or AMF (1e-20), and the MME or AMF determines whether to provide the service requested by the UE. As a result of the determination, when the UE determines to provide the requested service, the MME or AMF sends an INITIAL CONTEXT SETUP REQUEST message (1e-25) to the gNB. The INITIAL CONTEXT SETUP REQUEST message includes QoS information to be applied when configuring DRB, security-related information applied to DRB (e.g., security keys, security algorithms, etc.), etc.

[0141] In addition, in the case where the gNB does not receive the UE capability information from the MME or AMF, the gNB may send a UE capability information request message to the UE to identify the UE capability information (1e-26). When the UE receives the UE capability information request message, the UE may configure and generate a UE capability information message and report the UE capability information message to the gNB (1e-27). The UE capability information message may include what type of switching method the UE supports. For example, the UE capability, i.e., information about whether the UE supports the effective switching method (dual active protocol stack (DAPS)) proposed in the present disclosure, may be reported to the gNB through an indicator. When the gNB identifies the UE capability information, the gNB may define an indicator for each switching method, and when instructing the UE to perform a switch, indicate to the UE in the switching command message which switch is indicated. For example, the gNB may indicate to the UE the effective switching method (DAPS switching method) proposed in the present disclosure. As another method, the DAPS switching method may be configured for each bearer (DRB or SRB) of the UE. When the gNB configures the DAPS switching method in the UE, other switching methods are indicated together to prevent data loss or transmission delay that may occur during the switching (examples of other switching methods include a conditional switching method (a method in which multiple target cells are set and multiple conditions are set in the UE, wherein when the above conditions are met during the cell selection or reselection process, the UE performs a switching process to one target cell) or a switching method without a random access process). The UE can perform a switching process to the target base station according to the switching method indicated in the switching command message.

[0142] The gNB exchanges SecurityModeCommand messages (1e-30) and SecurityModeComplete messages (1e-35) to set up security with the UE. When the security setup is complete, the gNB sends an RRCConnectionReconfiguration message (1e-40) to the UE.

[0143] The RRCConnectionReconfiguration message includes configuration information for each service / bearer / RLC layer, each logical channel or each bearer. Whether to use ROHC for each bearer / logical channel, ROHC configuration information (e.g., ROHC version, initial information, etc.), statusReportRequired information (information in which the gNB indicates the PDCP status report to the UE), drb-ContinueROHC information (configuration information that maintains the ROHC configuration information and uses the ROHC configuration information as is) can be sent by being included in the PDCP layer configuration information (pdcp-config). In addition, the RRCConnectionReconfiguration message contains RRC connection establishment information, etc. The bearer used for the RRC connection is also called SRB, and is used to send or receive RRC messages, which are control messages between the UE and the gNB.

[0144] In addition, the RRCConnectionReconfiguration message includes configuration information of the DRB in which user data will be processed, and the UE configures the DRB by applying the configuration information of the DRB and sends an RRCConnectionReconfigurationComplete message to the gNB (1e-45). The gNB that has completed the DRB configuration with the UE sends an initial context setup complete message to the MME or AMF (1e-50), and the MME or AMF that has received the initial context setup complete message exchanges an S1 bearer setup message and an S1 bearer setup response message to establish an S1 bearer with the S-GW (1e-55, 1e-60). The S1 bearer is a data transmission connection established between the S-GW and the gNB, corresponding one-to-one to the DRB. When all the above processes are completed, the UE sends or receives data through the gNB and the S-GW (1e-65, 1e-70). Therefore, the general data transmission process includes three steps: RRC connection configuration, security configuration, and DRB configuration. In addition, for some reason, the gNB can send an RRC Connection Reconfiguration message to reconfigure, add or change the configuration of the UE (1e-75).

[0145] In the present disclosure, a bearer may include an SRB and a DRB. SRB refers to a signaling radio bearer, and DRB refers to a data radio bearer. SRB is mainly used to send and receive RRC messages of the RRC layer, and DRB is mainly used to send and receive user layer data. UM DRB refers to a DRB using an RLC layer operating in unacknowledged mode (UM), and AM DRB refers to a DRB using an RLC layer operating in acknowledged mode (AM).

[0146] In the present disclosure, a bearer for which a DAPS switching method is configured may refer to or indicate at least one of a bearer in which a bearer identifier is included in a bearer list for which a DAPS switching method is configured or is not included in the bearer list for which a DAPS switching method is configured, a bearer in which a DAPS switching method configuration indicator is included in bearer-specific configuration information, and a bearer for which a DAPS switching method configuration indicator is configured in PDCP layer configuration information.

[0147] In the present disclosure, a bearer for which the DAPS switching method is not configured may refer to or indicate at least one of a bearer in which a bearer identifier is not included in a bearer list for which the DAPS switching method is configured or is included in a bearer list for which the DAPS switching method is not configured, a bearer in which a DAPS switching method configuration indicator is not included in bearer-specific configuration information, and a bearer for which a DAPS switching method configuration indicator is not configured in PDCP layer configuration information.

[0148] In the present disclosure, the source base station may be interpreted as a source cell (Pcell, Spcell or SCell) or a source cell group (cell group or main cell group), and the target base station may be interpreted as a target cell (pcell, Spcell or SCell) or a target cell group (cell group or main cell group).

[0149] Figure 1f is a diagram showing a signaling procedure for performing a handover proposed in the present disclosure in a next generation mobile communication system.

[0150] When a period or a specific event is met, the UE 1f-01 in RRC connected mode reports cell measurement information (measurement report) to the current source gNB (source ENB) 1f-02 (1f-05). The source gNB 1f-02 determines whether the UE 1f-01 performs handover to a neighboring cell based on the measurement information. Handover is a technology used to change the source gNB 1f-02 that provides services to the UE 1f-01 in the connected mode state to another gNB (or another cell of the same gNB). When the source gNB 1f-02 determines the handover, the source gNB 1f-02 requests the handover by sending a handover (HO) request message (e.g., a handover preparation information message) to the new gNB (i.e., the target gNB 1f-03 (1f-10)) that will provide services to the UE 1f-01. When the target gNB 1f-03 accepts the handover request, the target gNB 1f-03 sends a HO request confirmation message (e.g., a handover command message) to the source gNB 1f-02 (1f-15). The source gNB 1f-02, which has received the message, sends a handover command message (RRCReconfiguration message included in the dedicated control channel (DCCH) of the HO request confirmation message or the HO command message) to the UE 1f-01 (1f-20). The source gNB 1f-02 extracts the HO command message from the message received from the target gNB 1f-03 and sends the extracted HO command message to the UE 1f-01 by using the RRC connection reconfiguration message (1f-20).

[0151] The present disclosure proposes a method for determining the effective DAPS switching method proposed in the present disclosure by using two messages (the switching preparation information message (1f-10) and the switching command message (1f-15)) when the source gNB 1f-02 sends a switching preparation information message 1f-10, and in response thereto, the target gNB 1f-03 sends a switching command message 1f-15 to the source gNB 1f-02.

[0152] The first embodiment of the method for determining effective DAPS switching proposed in the present disclosure is as follows.

[0153] In the first embodiment, the subject that determines the DAPS switching method may be the source gNB 1f-02. In addition, in the first embodiment of the present disclosure, in the case where the source gNB 1f-02 requests the target gNB 1f-03 to use the DAPS switching method, the target gNB 1f-03 may always indicate or execute the DAPS switching method.

[0154] -The source gNB 1f-02 may define a new indicator in the handover preparation information message, may indicate to the target gNB 1f-03 that the source gNB 1f-02 will perform the DAPS handover method proposed in the present disclosure, and may request the DAPS handover method. The handover preparation information message may include current bearer configuration information, security key information of UE 1f-01, cell group configuration information, or capability information of UE 1f-01. The source gNB 1f-02 may know in advance whether the target gNB 1f-03 supports the DAPS handover method by sharing the capabilities of the target gNB 1f-03 in an implementation manner. The source gNB 1f-02 may instruct the target gNB 1f-03 to perform the DAPS handover method, may notify the target gNB 1f-03 that the source gNB 1f-02 may perform fast or early data forwarding, and may indicate that the target gNB 1f-03 is ready to receive and process fast or early data forwarding. The source gNB 1f-02 may request the DAPS handover method for each bearer (DRB or SRB).

[0155] -When the target gNB 1f-03 receives the handover preparation information message and identifies that an indicator for requesting a DAPS handover method is included, the target gNB 1f-03 may configure an RRCReconfiguration message including an indicator indicating a DAPS handover method when configuring an RRCReconfiguration message to indicate a handover to UE1f-01, and include the bearer configuration information, security key information, cell group configuration information, or system information required when UE 1f-01 performs the DAPS handover method. The target gNB 1f-03 may send the configured RRCReconfiguration message to the source gNB 1f-02 by including the configured RRCReconfiguration message in the DL-DCCH message of the handover command message. The target gNB 1f-03 may indicate the DAPS handover method (DRB or SRB) for each bearer.

[0156] -When the source gNB 1f-02 receives the handover command message, the source gNB 1f-02 may extract the RRCReconfiguration message included in the handover command message and indicate the handover by sending the RRCReconfiguration message to the UE 1f-01. The source gNB 1f-02 may identify the indicated DAPS handover method for each bearer and perform the DAPS handover method for each bearer (DRB or SRB).

[0157] The second embodiment of the method for determining effective DAPS switching proposed in the present disclosure is as follows.

[0158] In the second embodiment of the present disclosure, the subject that determines the DAPS switching method may be the target gNB 1f-03. In addition, in the second embodiment of the present disclosure, in the case where the source gNB 1f-02 requests the target gNB 1f-03 for the DAPS switching method by using an indicator, the target gNB 1f-03 may reject or accept the request, or instruct the source gNB 1f-02 by indicating another switching method in the switching command message.

[0159] The source gNB 1f-02 may define a new indicator in a handover preparation information message, may indicate to the target gNB 1f-03 that the source gNB 1f-02 will perform the DAPS handover method proposed in the present disclosure, and may request the DAPS handover method. The handover preparation information message may include the current bearer configuration information of the UE 1f-01, security key information, cell group configuration information, or capability information of the UE 1f-01. The source gNB 1f-02 may know in advance whether the target gNB 1f-03 supports the DAPS handover method by sharing the capabilities of the target gNB 1f-03 in an implementation manner. The source gNB 1f-02 may instruct the target gNB 1f-03 to perform the DAPS handover method, may notify the target gNB 1f-03 that the source gNB 1f-02 may perform fast or early data forwarding, and may indicate that the target gNB 1f-03 is ready to receive and process fast or early data forwarding. The source gNB 1f-02 may request the DAPS handover method for each bearer (DRB or SRB).

[0160] - In the case where the target gNB 1f-03 receives the handover preparation information message and identifies an indicator including a request for a DAPS handover method, the target gNB 1f-03 may reject or accept the DAPS handover request of the source gNB 1f-02, or indicate another handover method to the source gNB 1f-02, according to whether the DAPS handover method is supported, the amount or scheduling of current transmission resources. The target gNB 1f-03 may send an indicator for rejecting or accepting the DAPS handover request, or send an indicator indicating different types of handover methods by including the indicator in the handover command message. The target gNB 1f-03 may configure an RRCReconfiguration message to indicate a handover to the UE 1f-01, wherein the RRCReconfiguration message includes an indicator indicating the DAPS handover method when the request for DAPS handover is accepted, includes an indicator indicating another handover method when the request for DAPS handover is rejected, and includes necessary bearer configuration information, security key information, or cell group configuration information or system information when the UE 1f-01 performs the DAPS handover method or another handover method. In addition, the target gNB 1f-03 can send a configured RRCReconfiguration message to the source gNB1f-02 by including the configured RRCReconfiguration message in the DL-DCCH message of the handover command message. The target gNB 1f-03 can indicate the DAPS handover method for each bearer (DRB or SRB).

[0161] -When the source gNB 1f-02 receives the handover command message, the source gNB 1f-02 may identify whether the request for the DAPS handover method is accepted or rejected by identifying the indicator included in the handover command message. In the case where the request for the DAPS handover method is accepted, the source gNB 1f-02 may perform the DAPS handover method, may extract the RRCReconfiguration message included in the handover command message, and may indicate the handover by sending the RRCReconfiguration message to the UE 1f-01. When the indicator included in the handover command message is identified and the request for the DAPS handover method is rejected, or when another handover method is indicated, the source gNB 1f-02 may perform another handover method indicated by the target gNB 1f-03. In addition, the source gNB 1f-02 may extract the RRCReconfiguration message included in the handover command message and indicate the handover by sending the RRCReconfiguration message to the UE 1f-01. As another method, even when there is no separate indicator in the handover command message, the source gNB 1f-02 can read the RRCReconfiguration message included in the handover command message, can identify which handover method the target gNB 1f-03 indicates, and can identify whether the request for the DAPS handover method is accepted or rejected. The source gNB 1f-02 can perform the handover method indicated in the RRCReconfiguration message (e.g., the DAPS handover method or another handover method). The source gNB 1f-02 can identify the indicated DAPS handover method for each bearer and perform the DAPS handover method for each bearer (DRB or SRB).

[0162] The third embodiment of the method for determining effective DAPS switching proposed in the present disclosure is as follows.

[0163] In the third embodiment of the present disclosure, the subject that determines the DAPS switching method may be the target gNB. In addition, in the third embodiment of the present disclosure, the target gNB 1f-03 may identify the capabilities of the UE 1f-01, and may determine the switching method (e.g., DAPS switching method) based on whether the target gNB 1f-03 can support the DAPS switching method, the amount of current transmission resources, or scheduling.

[0164] -The source gNB 1f-02 may send a message for requesting handover to the target gNB 1f-03 by including the current bearer configuration information, security key information, cell group configuration information, or capability information of the UE 1f-01 in the handover preparation information message. The source gNB 1f-02 may know in advance whether the target gNB 1f-03 supports the DAPS handover method by sharing the capabilities of the target gNB 1f-03 in an implementation manner. In the case where the target gNB 1f-03 indicates to perform the DAPS handover method, the source gNB 1f-02 may perform fast or early data forwarding.

[0165] The target gNB 1f-03 may receive a handover preparation information message, and may determine a handover method (e.g., a DAPS handover method) based on capability information of the UE 1f-01, whether the target gNB 1f-03 is capable of supporting the DAPS handover method, and the amount or scheduling of current transmission resources. In the case where the target gNB 1f-03 determines the DAPS handover method, the target gNB 1f-03 may send a handover command message by including an indicator indicating the DAPS handover method in the handover command message. The target gNB 1f-03 may configure an RRCReconfiguration message to indicate a handover to the UE 1f-01, wherein the RRCReconfiguration message includes an indicator indicating the DAPS handover method when the DAPS handover is determined, includes an indicator indicating another handover method when a handover method other than the DAPS handover is determined, and includes bearer configuration information, security key information, or cell group configuration information or system information necessary when the UE 1f-01 performs the DAPS handover method or another handover method. The target gNB 1f-03 may send a configured RRCReconfiguration message to the source gNB 1f-02 by including the configured RRCReconfiguration message in the DL-DCCH message of the handover command message. The target gNB 1f-03 may indicate the DAPS handover method for each bearer (DRB or SRB).

[0166] -When the source gNB 1f-02 receives the handover command message, the source gNB 1f-02 may identify whether the DAPS handover is determined by identifying the indicator included in the handover command message. In the case where the DAPS handover method is indicated, the source gNB 1f-02 may perform the DAPS handover method, may extract the RRCReconfiguration message included in the handover command message, and may indicate the handover by sending the RRCReconfiguration message to the UE 1f-01. When the indicator included in the handover command message is identified and the DAPS handover method is not determined, or when another handover method is indicated, the source gNB 1f-02 may perform another handover method indicated by the target gNB 1f-03. In addition, the source gNB 1f-02 may extract the RRCReconfiguration message included in the handover command message and indicate the handover by sending the RRCReconfiguration message to the UE 1f-01. As another method, even when there is no separate indicator in the handover command message, the source gNB 1f-02 can read the RRCReconfiguration message included in the handover command message, can identify which handover method the target gNB 1f-03 indicates, can identify whether the DAPS handover method is determined, and in the case where another handover method is indicated, can execute the indicated handover method. The source gNB 1f-02 can identify the indicated DAPS handover method for each bearer and execute the DAPS handover method for each bearer (DRB or SRB).

[0167] The new embodiment may be expanded by combining the method of the first embodiment, the second embodiment, or the third embodiment of determining a valid DAPS switching method proposed in the present disclosure.

[0168] According to one embodiment, in the RRCReconfiguration message, the gNB may indicate to the UE 1f-01 the valid switching method (DAPS switching method) proposed in the present disclosure. As another method, the gNB may set the DAPS switching method for each bearer (DRB or SRB) of the UE 1f-01. For example, in the RRC message, a new indicator indicating the valid switching method (DAPS switching method) may be defined in the bearer configuration information, PDCP configuration information, or RLC configuration information for each bearer identifier or logical channel identifier, and the gNB may indicate the valid switching method to the UE 1f-01 for each bearer or each logical channel identifier by using the indicator. When the gNB configures the DAPS switching method in the UE, other switching methods are indicated together to prevent data loss or transmission delay that may occur during the switching (examples of other switching methods include conditional switching methods (a method in which multiple target cells are set and multiple conditions are set in the UE 1f-01, wherein when the above conditions are met during the cell selection or reselection process, the UE 1f-01 performs a switching process to one target cell) or a switching method without a random access process).

[0169] When receiving the RRCReconfiguration message, UE 1f-01 stops or continues to perform data transmission and reception with the source gNB 1f-02 according to the set method, and starts the T304 timer. In the case that UE 1f-01 does not successfully switch to the target gNB 1f-03 within a specific time (for example, when the T304 timer expires), T304 returns to the original setting of UE 1f-01 and switches UE 1f-01 to the RRC idle state. In addition, UE 1f-01 can trigger the RRC connection reestablishment process. When a valid switching method is configured and the connection with the source gNB 1f-02 is valid, UE 1f-01 can perform a fallback and report the switching failure to the source gNB 1f-02. The source gNB 1f-02 sends the sequence number (SN) status of the uplink / downlink data of each bearer (for example, each RLC UM bearer or each RLC AM bearer). When there is downlink or uplink data, the source gNB 1f-02 sends downlink or uplink data to the target gNB 1f-03 (1f-30, 1f-35). UE 1f-01 attempts to randomly access the target cell (1f-40) indicated by the source gNB 1f-02. Random access is used to notify the target cell that UE 1f-01 has moved through switching and matched uplink synchronization. For random access, UE 1f-01 sends a preamble ID provided from the source gNB 1f-02 or a preamble corresponding to a randomly selected preamble ID to the target cell. After a specific number of subframes have passed since the preamble was sent, UE 1f-01 monitors whether a random access response (RAR) message is sent from the target cell. The time interval for monitoring the RAR message is called the RAR window. When RAR is received during the monitoring time interval (1f-45), UE 1f-01 sends a HO completion message to the target gNB 1f-03 as an RRC reconfiguration completion message (1f-55). As described above, when UE 1f-01 successfully receives RAR from the target gNB 1f-03, UE 1f-01 stops the T304 timer (1f-50).

[0170] The target gNB 1f-03 requests the core network 1f-04 (i.e., MME / S-GW / AMF) to modify the path of the bearer to modify the path of the bearer set to the source gNB 1f-02 (1f-60, 1f-65), and notifies the source gNB 1f-02 to delete the UE context of UE 1f-01 (1f-70). The target gNB 1f-03 may send an RRC message (e.g., an RRCReconfiguration message) 1f-71 to the UE 1f-01 to indicate the release of the connection with the source gNB 1f-02 by using an indicator. According to another method, the target gNB 1f-03 may send MAC control information, RLC control information, or PDCP control information to the UE 1f-01 to indicate the release of the connection with the source gNB 1f-02. The UE 1f-01 attempts to receive data from the start time point of the RAR window relative to the target gNB 1f-03. After receiving the RAR, UE 1f-01 sends an RRC reconfiguration completion message to the target gNB 1f-03, receives downlink transmission resources or uplink transmission resources, and starts data transmission and reception with the target gNB 1f-03.

[0171] According to an embodiment, when the gNB configures or indicates the second embodiment (DAPS switching method) proposed in the present disclosure to the UE 1f-01 by using a switching command message or an RRC message (e.g., an RRCReconfiguration message), the applicable method is as follows. In the present disclosure, when the gNB configures the DAPS switching method in the UE 1f-01, or when the UE 1f-01 receives a switching command message configuring the DAPS switching method from the gNB, a method applied by applying one or more of the following methods may be performed.

[0172] -Method 1-1: When attempting to indicate or configure a handover to UE 1f-01, the gNB (source gNB 1f-02, target gNB 1f-03, LTE base station, or NR base station) may include mobility control information or reconfiguration with synchronization configuration information in the RRCReconfiguration message. The gNB may define an indicator in SRB-ToAddMod or SRB-ToAddModList or DRB-ToAddModList of the bearer configuration information (dedicated radio resource configuration or radio bearer configuration) of the RRCReconfiguration message, and may indicate the DAPS handover method for each bearer (each SRB or DRB) by the defined indicator. In addition, the gNB may define an indicator in the pdcp-config of SRB-ToAddMod or DRB-ToAddMod, and indicate the DAPS handover method for each bearer. In addition, in the case of LTE, when the LTE base station indicates or configures the handover in UE 1f-01 with the LTE RRCReconfiguration message, pdcp-config is not defined in SRB-ToAddMod, and the use of the default PDCP layer configuration is set. Therefore, the LTE base station can define the indicator in SRB-ToAddMod for SRB, can configure the DAPS handover method for each bearer, can define the indicator in pdcp-config of DRB-ToAddMod for DRB, and can configure the DAPS handover method for each bearer.

[0173] UE 1f-01 may perform a DAPS switching method for a bearer in which a DAPS switching method is configured for each bearer according to the configuration indicated in the received switching command message (RRCReconfiguration message), and may perform a general switching method for a bearer in which a DAPS switching method is not configured. In addition, when the mobility control information of the switching command message or the reconfiguration with synchronization configuration information includes an indicator indicating or configuring the type of switching method for UE 1f-01 (e.g., MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) and the DAPS switching method is configured for each bearer, when performing the switching process for each bearer, UE 1f-01 may apply the DAPS switching method in preference to other types of switching methods. For example, UE 1f-01 may perform a DAPS switching method for a bearer in which a DAPS switching method is configured for each bearer according to the configuration. For bearers for which the DAPS switching method is not configured, UE 1f-01 may perform a switching method (e.g., MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) configured according to an indicator indicating or configuring the switching method type of UE 1f-01 in the mobility control information of the switching command message or the reconfiguration with synchronization configuration information. In addition, in order to reduce the complexity of implementing UE 1f-01, when the DAPS switching method is configured in at least one bearer or a specific bearer, the types of other switching methods used for UE 1f-01 in the mobility control information of the switching command message or the reconfiguration with synchronization configuration information (e.g., MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) may be set not to be indicated or configured. In addition, when UE 1f-01 receives a switching command message (RRCReconfiguration message) and the DAPS switching method is configured for at least one bearer in the switching command message (RRCReconfiguration message) or for a specific bearer for each bearer, the RRC layer, SDAP layer, MAC layer, PHY layer or SRB processing method for performing the DAPS switching method proposed in the present disclosure may be applied. For each bearer for which the DAPS switching method is configured, the PDCP layer or RLC layer processing method for performing the DAPS switching method proposed in the present disclosure may be applied.

[0174] -Method 1-2: When attempting to indicate or configure a handover to UE 1f-01, the gNB (source gNB 1f-02, target gNB1f-03, LTE base station, or NR base station) may include mobility control information or a reconfiguration with synchronization configuration information in the RRCReconfiguration message. The base station may define an indicator in the DRB-ToAddMod-ToAddModList of the DRB in the bearer configuration information (dedicated radio resource configuration or radio bearer configuration) of the RRCReconfiguration message, and may indicate the DAPS handover method for each bearer (DRB) by the defined indicator. For SRBs, a separate indicator for configuring the DAPS handover method may not be introduced. That is, in the case where UE 1f-01 configures a DAPS handover method for at least one bearer (DRB) or a specific bearer (DRB) of each bearer in the received handover command message (RRCReconfiguration message), the SRB processing method for performing the DAPS handover method proposed in the present disclosure may be applied. In addition, the gNB can define an indicator in the pdcp-config of DRB-ToAddMod and indicate the DAPS switching method for each bearer.

[0175] UE 1f-01 can perform the DAPS switching method for the bearer for which the DAPS switching method is configured for each bearer according to the configuration indicated in the received switching command message (RRCReconfiguration message), and can perform the general switching method for the bearer for which the DAPS switching method is not configured. In addition, when the mobility control information of the switching command message or the reconfiguration with synchronization configuration information includes an indicator indicating or configuring the type of switching method for UE 1f-01 (for example, MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) and the DAPS switching method is configured for each bearer, when performing the switching process for each bearer, UE 1f-01 can apply the DAPS switching method in priority to other types of switching methods. For example, UE 1f-01 can perform the DAPS switching method for the bearer for which the DAPS switching method is configured for each bearer according to the configuration. For bearers for which the DAPS switching method is not configured, UE 1f-01 may perform a switching method (e.g., MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) configured according to an indicator indicating or configuring the switching method type of UE 1f-01 in the mobility control information of the switching command message or the reconfiguration with synchronization configuration information. In addition, in order to reduce the complexity of implementing UE 1f-01, when the DAPS switching method is configured in at least one bearer or a specific bearer, the types of other switching methods used for UE 1f-01 in the mobility control information of the switching command message or the reconfiguration with synchronization configuration information (e.g., MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) may be set not to be indicated or configured. In addition, when UE 1f-01 receives a switching command message (RRCReconfiguration message) and the DAPS switching method is configured for at least one bearer in the switching command message (RRCReconfiguration message) or for a specific bearer for each bearer, the RRC layer, SDAP layer, MAC layer, PHY layer or SRB processing method for performing the DAPS switching method proposed in the present disclosure may be applied. For each bearer for which the DAPS switching method is configured, the PDCP layer or RLC layer processing method for performing the DAPS switching method proposed in the present disclosure may be applied.

[0176] -Method 2-1: When attempting to indicate or configure a handover to UE 1f-01, the gNB (source gNB 1f-02, target gNB 1f-03, LTE base station, or NR base station) may include mobility control information or reconfiguration with synchronization configuration information in the RRCReconfiguration message. The gNB may define and include an indicator indicating or configuring a DAPS handover method in the mobility control information or synchronization reconfiguration, and may use the indicator to indicate that the DAPS handover method is configured for at least one bearer or a specific bearer. In addition, the gNB may define an indicator in SRB-ToAddMod or DRB-ToAddMod of SRB-ToAddModList or DRB-ToAddModList in the bearer configuration information (dedicated radio resource configuration or radio bearer configuration) of the RRCReconfiguration message, and may indicate a DAPS handover method for each bearer (each SRB or DRB). In addition, the gNB may define an indicator in pdcp-config of SRB-ToAddMod or DRB-ToAddMod, and indicate a DAPS handover method for each bearer. In addition, in the case of LTE, when the LTE base station indicates or configures the switching in UE 1f-01 with the LTE RRCReconfiguration message, pdcp-config is not defined in SRB-ToAddMod, and the use of the default pdcp layer configuration is set. Therefore, the LTE base station can define the indicator in SRB-ToAddMod for SRB, configure the DAPS switching method for each bearer, define the indicator in pdcp-config of DRB-ToAddMod for DRB, and configure the DAPS switching method for each bearer.

[0177] UE 1f-01 can perform a DAPS switching method for a bearer for which a DAPS switching method is configured for each bearer according to the configuration indicated in the received switching command message (RRCReconfiguration message), and can perform a general switching method for a bearer for which a DAPS switching method is not configured. In addition, when the mobility control information of the switching command message or the reconfiguration with synchronization configuration information includes an indicator indicating or configuring the type of switching method used for UE 1f-01 (e.g., MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) and the DAPS switching method is configured for each bearer, when performing a switching process for each bearer, UE 1f-01 can apply the DAPS switching method in preference to other types of switching methods. For example, UE 1f-01 can perform a DAPS switching method for a bearer for which a DAPS switching method is configured for each bearer according to the configuration. For bearers for which the DAPS switching method is not configured, UE 1f-01 may perform a switching method (e.g., MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) configured according to an indicator indicating or configuring the switching method type of UE 1f-01 in the mobility control information of the switching command message or the reconfiguration with synchronization configuration information. In addition, in order to reduce the complexity of implementing UE 1f-01, when the DAPS switching method is configured in at least one bearer or a specific bearer, the types of other switching methods used for UE 1f-01 in the mobility control information of the switching command message or the reconfiguration with synchronization configuration information (e.g., MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) may be set not to be indicated or configured. In addition, when UE 1f-01 receives a switching command message (RRCReconfiguration message) and an indicator indicating or configuring the DAPS switching method is included (or configured) in the mobility control information or synchronization reconfiguration in the switching command message (RRCReconfiguration message), the RRC layer, SDAP layer, MAC layer, PHY layer or SRB processing method for executing the DAPS switching method proposed in the present disclosure can be applied. For each bearer configured with the DAPS switching method, the PDCP layer or RLC layer processing method for executing the DAPS switching method proposed in the present disclosure can be applied.

[0178] -Method 2-2: When attempting to indicate or configure a handover to UE 1f-01, the gNB (source gNB 1f-02, target gNB 1f-03, LTE base station, or NR base station) may include mobility control information or reconfiguration with synchronization configuration information in the RRCReconfiguration message. The gNB may define and include an indicator indicating or configuring a DAPS handover method in the mobility control information or synchronization reconfiguration, and may use the indicator to indicate that the DAPS handover method is configured for at least one bearer or a specific bearer. In addition, the gNB may define an indicator in the DRB-ToAddMod-ToAddModList of the DRB in the bearer configuration information (dedicated radio resource configuration or radio bearer configuration) of the RRCReconfiguration message, and may indicate the DAPS handover method for each bearer (DRB). For SRBs, a separate indicator for configuring the DAPS handover method may not be introduced. That is, when UE 1f-01 receives a handover command message (RRCReconfiguration message) and a DAPS handover method is configured for at least one bearer (DRB) or for a specific bearer (DRB) of each bearer in the handover command message (RRCReconfiguration message), the SRB processing method for performing the DAPS handover method proposed in the present disclosure can be applied. In addition, gNB 1f-03 can define an indicator in the pdcp-config of DRB-ToAddMod and indicate the DAPS handover method for each bearer.

[0179] UE 1f-01 can perform the DAPS switching method for the bearer for which the DAPS switching method is configured for each bearer according to the configuration indicated in the received switching command message (RRCReconfiguration message), and can perform the general switching method for the bearer for which the DAPS switching method is not configured. In addition, when the mobility control information of the switching command message or the reconfiguration with synchronization configuration information includes an indicator indicating or configuring the type of switching method for UE 1f-01 (for example, MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) and the DAPS switching method is configured for each bearer, when performing the switching process for each bearer, UE 1f-01 can apply the DAPS switching method in priority to other types of switching methods. For example, UE 1f-01 can perform the DAPS switching method for the bearer for which the DAPS switching method is configured for each bearer according to the configuration. For bearers for which the DAPS switching method is not configured, UE 1f-01 may perform a switching method (e.g., MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) configured according to an indicator indicating or configuring the switching method type of UE 1f-01 in the mobility control information of the switching command message or the reconfiguration with synchronization configuration information. In addition, in order to reduce the complexity of implementing UE 1f-01, when the DAPS switching method is configured in at least one bearer or a specific bearer, the types of other switching methods used for UE 1f-01 in the mobility control information of the switching command message or the reconfiguration with synchronization configuration information (e.g., MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) may be set not to be indicated or configured. In addition, when UE 1f-01 receives a switching command message (RRCReconfiguration message) and an indicator indicating or configuring the DAPS switching method is included (or configured) in the mobility control information or synchronization reconfiguration in the switching command message (RRCReconfiguration message), the RRC layer, SDAP layer, MAC layer, PHY layer or SRB processing method for executing the DAPS switching method proposed in the present disclosure can be applied. For each bearer configured with the DAPS switching method, the PDCP layer or RLC layer processing method for executing the DAPS switching method proposed in the present disclosure can be applied.

[0180] -Method 3-1: When attempting to indicate or configure a handover to UE 1f-01, the gNB (source gNB 1f-02, target gNB 1f-03, LTE base station, or NR base station) may include mobility control information or reconfiguration with synchronization configuration information in an RRCReconfiguration message. The gNB may define and include an indicator indicating or configuring a DAPS handover method in the mobility control information or synchronization reconfiguration, and may use the indicator to indicate that the DAPS handover method is configured for at least one bearer or a specific bearer. In addition, the gNB may configure and include a list of bearers for which the DAPS handover method is configured in the mobility control information or synchronization reconfiguration, may include an identifier (SRB or DRB) of a bearer for which the DAPS handover method is configured in the bearer list, and may indicate whether the DAPS handover method is configured for each bearer. In addition, the gNB may configure and include a list of bearers for which the DAPS handover method is not configured in the mobility control information or synchronization reconfiguration, may include an identifier (SRB or DRB) of a bearer for which the DAPS handover method is not configured in the bearer list, and may indicate whether the DAPS handover method is configured for each bearer.

[0181] UE 1f-01 can perform the DAPS switching method for each bearer according to the configuration indicated in the received switching command message (RRCReconfiguration message), for a bearer configured with the DAPS switching method, a bearer whose identifier is included in the bearer list configured with the DAPS switching method, or a bearer whose identifier is not included in the bearer list not configured with the DAPS switching method, and UE 1f-01 can perform a general switching method for a bearer not configured with the DAPS switching method, a bearer whose identifier is not included in the bearer list configured with the DAPS switching method, and a bearer whose identifier is included in the bearer list not configured with the DAPS switching method. In addition, when the mobility control information of the handover command message or the reconfiguration with synchronization configuration information includes an indicator indicating or configuring the type of handover method for UE 1f-01 (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover CHO) and the DAPS handover method is configured for each bearer, when performing the handover process for each bearer, UE 1f-01 can apply the DAPS handover method in priority to other types of handover methods. For example, according to the configuration, for each bearer, UE 1f-01 can perform the DAPS handover method on a bearer configured with the DAPS handover method, a bearer whose identifier is included in a bearer list configured with the DAPS handover method, or a bearer whose identifier is not included in a bearer list not configured with the DAPS handover method. UE 1f-01 can perform a switching method on a bearer for which a DAPS switching method is not configured, a bearer whose identifier is not included in a bearer list for which a DAPS switching method is configured, or a bearer whose identifier is included in a bearer list for which a DAPS switching method is not configured, and the switching method is set according to an indicator (e.g., MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) indicating or configuring the type of switching method of UE 1f-01 in the mobility control information of the switching command message or the reconfiguration with synchronization configuration information. In addition, in order to reduce the complexity of implementing UE1f-01, in the case where the DAPS switching method is configured in at least one bearer or a specific bearer, the types of other switching methods for UE 1f-01 in the mobility control information of the switching command message or the reconfiguration with synchronization configuration information (e.g., MakeBeforeBreak switching, rach-skip switching, RACH-less switching, or conditional switching CHO) can be set not to be indicated or configured.In addition, when a switching command message (RRCReconfiguration message) is received and an indicator indicating or configuring the DAPS switching method is included (or configured) in the mobility control information or synchronization reconfiguration of the switching command message (RRCReconfiguration message), the UE 1f-01 can apply the RRC layer, SDAP layer, MAC layer, PHY layer or SRB processing method for executing the DAPS switching method proposed in the present disclosure. For each bearer, the UE 1f-01 can apply the PDCP layer or RLC layer processing method for executing the DAPS switching method proposed in the present disclosure to a bearer configured with the DAPS switching method, a bearer whose identifier is included in the bearer list configured with the DAPS switching method, or a bearer whose identifier is not included in the bearer list not configured with the DAPS switching method.

[0182] -Method 3-2: When attempting to indicate or configure a handover to UE 1f-01, the gNB (source gNB 1f-02, target gNB 1f-03, LTE base station, or NR base station) may include mobility control information or reconfiguration with synchronization configuration information in an RRCReconfiguration message. The gNB may define and include an indicator indicating or configuring a DAPS handover method in the mobility control information or synchronization reconfiguration, and may use the indicator to indicate that the DAPS handover method is configured for at least one bearer or a specific bearer. In addition, the gNB may configure and include a list of bearers for which the DAPS handover method is configured in the mobility control information or synchronization reconfiguration, may include an identifier (SRB or DRB) of a bearer for which the DAPS handover method is configured in the bearer list, and may indicate whether the DAPS handover method is configured for each bearer. In addition, the gNB may configure and include a list of bearers for which the DAPS handover method is not configured in the mobility control information or synchronization reconfiguration, may include an identifier (SRB or DRB) of a bearer for which the DAPS handover method is not configured in the bearer list, and may indicate whether the DAPS handover method is configured for each bearer. In addition, a separate indicator for configuring the DAPS switching method may not be introduced for the SRB. That is, when the UE 1f-01 receives a switching command message (RRCReconfiguration message) and the DAPS switching method is configured for at least one bearer (DRB) or for a specific bearer (DRB) of each bearer in the switching command message (RRCReconfiguration message), the SRB processing method for performing the DAPS switching method proposed in the present disclosure may be applied.

[0183] UE 1f-01 can perform the DAPS switching method for each bearer according to the configuration indicated in the received switching command message (RRCReconfiguration message), for a bearer configured with the DAPS switching method, a bearer whose identifier is included in the bearer list configured with the DAPS switching method, or a bearer whose identifier is not included in the bearer list not configured with the DAPS switching method, and UE 1f-01 can perform a general switching method for a bearer not configured with the DAPS switching method, a bearer whose identifier is not included in the bearer list configured with the DAPS switching method, and a bearer whose identifier is included in the bearer list not configured with the DAPS switching method. In addition, when the mobility control information of the handover command message or the reconfiguration with synchronization configuration information includes an indicator indicating or configuring the type of handover method for UE 1f-01 (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover CHO) and the DAPS handover method is configured for each bearer, when performing the handover process for each bearer, UE 1f-01 can apply the DAPS handover method in priority to other types of handover methods. For example, according to the configuration, for each bearer, UE 1f-01 can perform the DAPS handover method on a bearer configured with the DAPS handover method, a bearer whose identifier is included in a bearer list configured with the DAPS handover method, or a bearer whose identifier is not included in a bearer list not configured with the DAPS handover method. UE 1f-01 may perform a handover method on a bearer for which a DAPS handover method is not configured, a bearer whose identifier is not included in a bearer list for which a DAPS handover method is configured, or a bearer whose identifier is included in a bearer list for which a DAPS handover method is not configured, and the handover method is set according to an indicator (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover CHO) indicating or configuring the type of handover method of UE 1f-01 in the mobility control information of the handover command message or the reconfiguration with synchronization configuration information. In addition, in order to reduce the complexity of implementing UE1f-01, in the case where the DAPS handover method is configured in at least one bearer or a specific bearer, the types of other handover methods for UE 1f-01 in the mobility control information of the handover command message or the reconfiguration with synchronization configuration information (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover CHO) may be set not to be indicated or configured.In addition, when an indicator indicating or configuring the DAPS switching method is included (or configured) in the mobility control information or synchronous reconfiguration of the received switching command message (RRCReconfiguration message), the UE 1f-01 can apply the RRC layer, SDAP layer, MAC layer, PHY layer or SRB processing method for executing the DAPS switching method proposed in the present disclosure. For each bearer, the UE 1f-01 can apply the PDCP layer or RLC layer processing method for executing the DAPS switching method proposed in the present disclosure to a bearer configured with the DAPS switching method, a bearer whose identifier is included in the bearer list configured with the DAPS switching method, or a bearer whose identifier is not included in the bearer list not configured with the DAPS switching method.

[0184] Hereinafter, the present disclosure proposes a seamless handover method capable of minimizing a data interruption time due to handover or reducing the data interruption time to 0 ms in a next generation mobile communication system.

[0185] UE 1f-01 can configure multiple first bearers with the source gNB 1f-02, and can perform data sending and receiving (uplink or downlink data sending and reception) through the protocol layer of the bearer (PHY layer, MAC layer, RLC layer or PDCP layer), but for the convenience of description, it is assumed in the drawings and description that UE 1f-01 has one bearer.

[0186] Figure 1g The specific operation of the first embodiment of the effective switching method for minimizing the data interruption time caused by switching according to the embodiment of the present disclosure is shown.

[0187] According to an embodiment, in Figure 1g In a first embodiment of an effective handover method, in a first operation 1g-01, when UE1g-20 receives a handover command message from a source gNB 1g-05 while transmitting and receiving data with the source gNB 1g-05, UE 1g-20 may release the connection with the source gNB 1g-05 according to the handover method indicated in the handover command message (e.g., RRCReconfiguration message), may perform a random access procedure to the target gNB 1g-10, and may perform a handover procedure. According to another method, UE 1g-20 may continuously transmit and receive data to and from the source gNB 1g-05 so as to minimize a data interruption time occurring during the handover according to the indicated handover method.

[0188] According to an embodiment, in the second operation 1g-02, when UE 1g-20 performs a random access procedure to the target gNB 1g-10 according to the handover method indicated in the handover command message received from the source gNB 1g-05, when the leading code is sent to the target gNB 1g-10, or when data is sent for the first time through the uplink transmission resources on the PUCCH or PUSCH transmission resources, UE 1g-20 may stop data transmission and reception (uplink data transmission and downlink data reception) with the source gNB 1g-05.

[0189] According to an embodiment, in the third operation 1g-30, UE 1g-20 can complete the random access process to the target gNB 1g-10, can send a switching completion message to the target gNB 1g-10, and can start data transmission and reception (uplink data transmission and downlink data reception) with the target gNB 1g-10.

[0190] According to a first embodiment of an effective handover method of the present disclosure, a handover method performed when the DAPS handover method is not configured in the present disclosure will be described.

[0191] Figure 1h The specific operation of the second embodiment of the effective switching method for minimizing the data interruption time caused by switching according to the embodiment of the present disclosure is shown.

[0192] According to an embodiment, in Figure 1h In the second embodiment of the effective switching method, in the first operation 1h-01, the UE 1h-20 may receive a switching command message from the source gNB 1h-05 while sending and receiving data with the source gNB 1h-05. In the case where the source gNB 1h-05 indicates a switching method (e.g., a DAPS switching method) according to the second embodiment of the effective switching method proposed in the present disclosure or indicates an overhand of each bearer in the switching command message, the UE 1h-20 may continuously send and receive data to and from the source gNB 1h-05 through the protocol layer 1h-22 of the first bearer so as to minimize the data interruption time occurring during the switching even when the UE 1h-20 receives the switching command message.

[0193] In addition, when the RRC layer of the UE 1h-20 identifies an indication of a handover method (e.g., a DAPS handover method) according to the second embodiment of the effective handover method proposed in the present disclosure in the handover command message, or an indicator identifying the DAPS handover method of each bearer, the RRC layer may send the indicator to the PDCP layer corresponding to each bearer or the bearer indicating the DAPS handover method. When the PDCP layer receives the indicator, the PDCP layer may select the first PDCP layer structure ( Figure 1i 1i-11 or 1i-12) is transferred to the second PDCP layer structure ( Figure 1i 1i-20).

[0194] exist Figure 1h In the first operation 1h-01, UE 1h-20 receives a handover command message (RRCReconfiguration message) from the gNB. In addition, when handing over to the second PDCP layer structure according to the configuration included in the handover command message received by UE 1h-20, UE 1h-20 can pre-configure or establish the protocol layer (PHY layer, MAC layer, RLC layer or PDCP layer) 1h-21 of the second bearer of the target gNB 1h-10, can derive and update the security key of the target gNB 1h-10, and can configure the header (or data) compression context of the target gNB 1h-10. In addition, in the case where the UE 1h-20 receives a handover command message from the source gNB 1h-05 and the source gNB 1h-05 indicates the DAPS handover method proposed in the present disclosure in the handover command message, when the DAPS handover method is indicated for a specific bearer, or when the PDCP reordering timer value is newly set, the UE 1h-20 can be configured to perform a handover from the first PDCP layer structure or function ( Figure 1i 1i-11 or 1i-12) is transferred to the second PDCP layer structure or function ( Figure 1i 1i-20 in). When the first PDCP layer structure or function ( Figure 1i 1i-11 or 1i-12) is transferred to the second PDCP layer structure or function ( Figure 1i 1i-20), UE 1h-20 may update the reordering variable with the PDCP sequence number or count value expected to be received next, and may stop and restart the reordering timer.

[0195] In addition, when UE 1h-20 receives a handover command message (e.g., an RRC reconfiguration message), the RRC layer of UE 1h-20 may start a first timer (e.g., T304). When UE 1h-20 performs a random access procedure to the target gNB 1h-10 to perform handover and the random access procedure is successfully completed (e.g., when the first condition proposed in the present disclosure is met), the first timer may be stopped. When the handover fails and the first timer has expired, if the connection to the source gNB 1h-05 is valid, UE 1h-20 may perform a fallback, report the handover failure to the source gNB 1h-05, and attempt connection recovery. If the connection to the source gNB 1h-05 is invalid, UE 1h-20 may perform an RRC connection reestablishment procedure.

[0196] The handover command message received by the UE 1h-20 from the source gNB 1h-05 may include information for performing configuration and establishment so that the first bearer has the same bearer identifier as the second bearer, thereby preventing each bearer from experiencing a data interruption time. In addition, in the second embodiment of the present disclosure, the PDCP layer of the first bearer and the PDCP layer of the second bearer may logically operate as one PDCP layer, and the reference Figure 1i Describe its operation method in more detail.

[0197] In addition, in the second embodiment of the present disclosure, in the case where UE 1h-20 is allowed to send uplink data to both the source gNB 1h-05 and the target gNB 1h-10, UE 1h-20 may send uplink data to only one of the source gNB 1h-05 and the target gNB 1h-10, so as to prevent the problem of reduced coverage due to insufficient transmission power of UE 1h-20 when sending uplink data, or the problem of determining which gNB to request transmission resources and which gNB to send uplink data to (link selection). Specifically, in the second embodiment, when UE 1h-20 does not have the ability to send uplink data to different gNBs at the same time at different frequencies or the same frequency (dual uplink transmission), UE 1h-20 may send uplink data to only one of the source gNB 1h-05 and the target gNB 1h-10 in one time unit. Therefore, UE 1h-20 can perform a scheduling request only to one of the source gNB 1h-05 and the target gNB 1h-10, can send a report (e.g., a buffer status report) about the size of data to be sent in the PDCP layer only to one of the source gNB 1h-05 and the target gNB1h-10, and can receive uplink transmission resources and send uplink data only to one gNB. In addition, even when UE 1h-20 receives a switching command message from the source gNB 1h-05, the MAC layer of the first bearer is not reset, thereby preventing data loss due to HARQ retransmission by continuing data transmission and reception. In addition, in the case of the RLC layer in AM mode, RLC retransmission can be performed continuously.

[0198] According to another method, in a case where the second embodiment of the effective switching method proposed in the present disclosure (DAPS switching method) is indicated for each bearer in the switching command message, the UE may continuously send data to or receive data from the source gNB 1h-05 only for the PDCP layer, RLC layer, or MAC layer corresponding to the bearer or logical channel identifier indicated in the second embodiment (DAPS switching method) in the switching command message, or only for the data corresponding to the bearer or logical channel identifier. In addition, even when the first condition proposed in the present disclosure is satisfied (for example, when uplink data transmission is handed over to the target gNB 1h-10), the UE may continuously send or receive RLC control data (RLC status report), PDCP control data (ROHC feedback or PDCP status report), or HARQ retransmission to or from the source gNB 1h-05 only for the PDCP layer, RLC layer, or MAC layer corresponding to the bearer or logical channel identifier indicated in the switching command message in the second embodiment (DAPS switching method). In addition, in the case where the second embodiment of the effective switching method proposed in the present disclosure (DAPS switching method) is indicated for each bearer in the switching command message, the UE can stop data transmission or reception with the source gNB 1h-05 for the PDCP layer, RLC layer or MAC layer corresponding to the bearer or logical channel identifier not indicated in the second embodiment (DAPS switching method) in the switching command message.

[0199] The UE may receive a switching command message. In an embodiment, when the DAPS switching method proposed in the present disclosure is indicated in the switching command message, when the DAPS switching method is indicated for a specific bearer, when the DAPS switching method is configured for at least one bearer, when the DAPS switching method is configured for a specific bearer, or when mapping information between QoS flows and bearers is newly configured, the UE may switch from the first SDAP layer structure or function 1j-10 to the second SDAP layer structure or function 1j-20 proposed in the present disclosure for each bearer or with respect to the bearer indicated by the DAPS switching method.

[0200] In the second SDAP layer structure, the mapping information between the first QoS flow and the bearer of the existing source gNB is maintained, and the uplink data to be sent to the source gNB and the downlink data to be received from the source gNB are processed. The second mapping information between the QoS flow and the bearer newly configured in the handover command message can be configured for the target gNB, and can be used to process the uplink data to be sent to the target gNB and the downlink data to be received from the target gNB. That is, in the second SDAP layer structure proposed in the present disclosure, the first mapping information between the QoS flow and the bearer of the source gNB or the second mapping information between the QoS flow and the bearer is maintained, and the data of the source gNB and the data of the target gNB are processed separately.

[0201] According to an embodiment, the SDAP layer in the second SDAP layer structure can distinguish whether the data received from the lower layer is data received from the source gNB or data received from the target gNB through a 1-bit indicator of the SDAP header, a 1-bit indicator of the PDCP header, or information indicated by the PDCP layer. In the case where the gNB indicates the DAPS switching method for each bearer to the UE by using a switching command message, the gNB can always indicate the DAPS switching method for the default bearer (default DRB). In this way, in the case where data is generated in a new QoS flow that does not correspond to the mapping information between the QoS flow and the bearer during the DAPS switching process, the gNB can enable the UE to always send uplink data to the default bearer.

[0202] In the case where the DAPS switching method is not configured in the default bearer, uplink data transmission of the new QoS flow generated during the switching is not possible. Therefore, data interruption time may occur. According to another method, in the case where the UE receives a switching command message (e.g., an RRCReconfiguration message), the second embodiment (DAPS switching method) is indicated, and the SDAP layer configuration information of the target gNB or the second mapping information between the QoS flow and the bearer is configured in the RRC message, and when the first condition proposed in the present disclosure is met, the UE can apply the SDAP layer configuration information or the second mapping information between the QoS flow and the bearer. In addition, when the second embodiment (DAPS switching method) is indicated for each bearer in the switching command message, when the first mapping information between the QoS flow and the bearer of the source gNB is maintained, the UE can only maintain and apply the first mapping information between the QoS flow and the bearer corresponding to the bearer indicated in the second embodiment. The first mapping information between the QoS flow and the bearer corresponding to the bearer not indicated in the second embodiment may be released or not applied. When the SDAP layer configuration information of the target gNB or the second mapping information between the QoS flow and the bearer is configured in the RRC message, when the first condition proposed in the present disclosure is met, the UE applies the SDAP layer configuration information of the target gNB or the second mapping information between the QoS flow and the bearer to send or receive data with the target gNB.

[0203] According to an embodiment, in Figure 1h In a second embodiment of an effective switching method, in a second operation 1h-02, UE1h-20 can perform a random access procedure of the target gNB 1h-10 indicated in the switching command message through the protocol layer of the second bearer. Even when UE 1h-20 performs a random access procedure through the protocol layer of the second bearer, UE 1h-20 can continue to perform data transmission or reception (uplink data transmission or downlink data reception) with the source gNB 1h-05 through the protocol layer of the first bearer. In the second operation, UE 1h-20 performs a cell selection or reselection procedure and performs a random access procedure on the target cell indicated in the switching command message (RRCReconfiguration message) received from the source gNB 1h-05.

[0204] According to one embodiment, Figure 1hIn the second embodiment of the effective switching method, in the third operation 1h-03, when the first condition is met, the UE 1h-20 can stop sending uplink data to the source gNB 1h-05 through the protocol layer 1h-22 of the first bearer for which the DAPS switching method is configured, and can send uplink data to the target gNB 1h-10 through the protocol layer 1h-21 of the second bearer. At this time, the UE 1h-20 can continue to receive downlink data from the source gNB 1h-05 and the target gNB 1h-10 through the protocol layers of the first bearer and the second bearer. The third operation can be an operation in which the UE 1h-20 hands over the uplink transmission from the source gNB 1h-05 to the target gNB 1h-10 when the first condition is met. Specifically, UE 1h-20 sends uplink data to the source gNB 1h-05 through the first bearer until the first condition is met, and when the first condition is met, UE 1h-20 stops sending uplink data to the source gNB 1h-05 through the first bearer, and starts sending uplink data to the target gNB 1h-10 through the second bearer.

[0205] Specifically, in the second PDCP layer structure proposed for the bearer configured with the DAPS switching method in the present disclosure, when the first condition is satisfied when uplink data is sent through the first bearer, and an indicator is received from the lower layer (when the random access procedure from the MAC layer to the target gNB 1h-10 is successful) or the upper layer (when the first timer in the RRC layer has expired), the PDCP layer may stop uplink data transmission through the first bearer and hand over to start uplink data transmission through the second bearer. In addition, as in Figure 1i In the PDCP layer structure proposed in, the reception PDCP layer 1h-21 of the second bearer can be driven as a single device with the reception PDCP layer 1h-22 of the first bearer, and seamless data reception from the source gNB 1h-05 or the target gNB 1h-10 can be continuously performed by using the stored transmission / reception data, sequence number information, or information such as header compression and decompression context. The first condition can be one of the following conditions. The following first condition proposes an uplink data transmission handover time point at which transmission resources are most efficiently used and data interruption time is minimized as much as possible.

[0206] -When UE 1h-20 successfully completes the random access procedure to the target gNB 1h-10 through the layer of the second bearer (e.g., the MAC layer), when UE 1h-20 successfully completes the random access procedure to the target gNB 1h-10 through the layer of the second bearer (e.g., the MAC layer) and the first uplink transmission resource is allocated from the target gNB 1h-10, or when the uplink transmission resource is indicated to UE 1h-20 for the first time, UE 1h-20 can determine that the first condition is met.

[0207] >For example, when UE 1h-20 receives a handover command message from source gNB 1h-05, and when random access to target gNB 1h-10 is indicated, the indicated random access is a contention free random access (CFRA) procedure (e.g., when a pre-specified preamble or UE (1h-20) cell identifier (e.g., cell-radio network temporary identifier (C-RNTI)) is allocated),

[0208] >>When UE 1h-20 sends a pre-specified preamble to the cell of the target gNB 1h-10 and receives a RAR message, UE 1h-20 can determine that the random access process has been successfully completed. Therefore, when the UE receives (or is allocated) the first uplink transmission resource allocated (or included or indicated) in the RAR message, the UE can determine that the first condition is met. According to another method, when the UE receives an uplink transmission resource for the first time after receiving the RAR, the UE can determine that the first condition is met.

[0209] >When the UE 1h-20 receives a Handover Command message from the source gNB 1h-05, and when random access to the target gNB 1h-10 is indicated, the indicated random access is a contention-based random access (CBRA) procedure (e.g., when a pre-specified preamble or UE (1h-20) cell identifier (e.g., C-RNTI) is not allocated),

[0210] >>When UE 1h-20 sends a preamble (e.g., a random preamble) to the cell of the target gNB 1h-10, receives a RAR message, sends message 3 (e.g., a handover completion message) to the target gNB by using the uplink transmission resources allocated (or included or indicated) in the RAR message, and receives a MAC CE (contention resolution MAC CE) indicating that the contention has been resolved by message 4 from the target gNB 1h-10, or when uplink transmission resources are received on the PDCCH corresponding to the C-RNTI of the UE 1h-20, the UE 1h-20 can determine that the random access procedure to the target gNB 1h-10 has been successfully completed. Therefore, when the UE 1h-20 monitors the PDCCH for the first time and receives uplink transmission resources on the PDCCH corresponding to the C-RNTI of the UE 1h-20 (or when indicated for the first time), the UE 1h-20 can determine that the first condition is satisfied. According to another method, when the size of the uplink transmission resource allocated in the RAR message is sufficient to send message 3 and the UE 1h-20 is allowed to send uplink data in addition, the UE 1h-20 can determine that the uplink transmission resource has been received for the first time, and can determine that the first condition is satisfied. That is, when the RAR is received, the UE can determine that the uplink transmission resource has been received for the first time and the first condition is satisfied.

[0211] - In the case where a handover method not requiring a random access procedure (RACH-less handover) is indicated together in the handover command message received by the UE 1h-20,

[0212] >When uplink transmission resources for the target gNB 1h-10 are included in the Handover Command message,

[0213] >>When UE 1h-20 sends message 3 (e.g., a handover complete message or an RRCReconfigurationComplete message) on the uplink transmission resources of the target gNB 1h-10 and receives a UE (1h-20) identity confirmation MAC CE (UE identity confirmation MAC CE) as message 4 from the gNB, or when uplink transmission resources are received on a PDCCH corresponding to the C-RNTI of UE 1h-20, UE 1h-20 can determine that the random access procedure has been successfully completed and the first condition is satisfied. According to another method, after the random access procedure is successfully completed, when the UE performs PDCCH monitoring and receives a first uplink transmission resource on a PDCCH corresponding to the C-RNTI of UE1h-20, UE 1h-20 can determine that the first condition is satisfied.

[0214] >When the uplink transmission resources for the target gNB 1h-10 are not included in the Handover Command message,

[0215] >>When UE 1h-20 performs PDCCH monitoring on the target gNB 1h-10 (or cell) and receives uplink transmission resources on the PDCCH corresponding to the C-RNTI of UE 1h-20, when UE 1h-20 sends message 3 (e.g., a handover completion message or an RRCReconfigurationComplete message) on the uplink transmission resources and receives a UE (1h-20) identity confirmation MAC CE (UE identity confirmation MAC CE) from the gNB, or when uplink transmission resources are received on the PDCCH corresponding to the C-RNTI of UE 1h-20, UE 1h-20 can determine that the random access procedure has been successfully completed and the first condition is satisfied. According to another method, after the random access procedure is successfully completed, when the UE performs PDCCH monitoring and receives the first uplink transmission resource on the PDCCH corresponding to the C-RNTI of UE1h-20, UE 1h-20 can determine that the first condition is satisfied.

[0216] In the following, an effective method for switching uplink data from the source gNB1h-05 to the target gNB 1h-10 in the DAPS switching method proposed in the present disclosure is proposed. For the target gNB 1h-10 corresponding to the second bearer, it can be identified in the MAC layer or the RRC layer according to one of the following methods or a combination thereof whether the above-mentioned first condition is met.

[0217] -First method: For example, in the case where DAPS switching is indicated in the RRCReconfiguration message received by the UE 1h-20, the UE 1h-20 may configure a MAC layer for the target gNB 1h-10 corresponding to the second bearer, and the MAC layer of the target gNB may perform a random access procedure and may identify whether the above-mentioned first condition is met. In addition, when the first condition is met, the MAC layer of the target gNB may indicate to the upper layer (e.g., PDCP layer) of the bearer configured with the DAPS switching method an indicator that uplink data transmission is handed over from the source gNB 1h-05 through the first bearer to the target gNB 1h-10 through the second bearer in the DAPS switching method proposed in the present disclosure.

[0218] -Second method: According to another method, for example, in the case where DAPS switching is indicated in the RRCReconfiguration message received by the UE 1h-20, the UE 1h-20 may configure a MAC layer for the target gNB 1h-10 corresponding to the second bearer, and the MAC layer of the target gNB may perform a random access procedure and identify whether the above-mentioned first condition is satisfied. In addition, when the first condition is satisfied, the MAC layer of the target gNB may indicate to the upper layer (e.g., RRC layer) that the first condition is satisfied. In addition, the upper layer (e.g., RRC layer) may indicate to the lower layer (e.g., PDCP layer) of the bearer for which the DAPS switching method is configured an indicator that uplink data transmission is handed over from the source gNB 1h-05 through the first bearer to the target gNB 1h-10 through the second bearer in the DAPS switching method proposed in the present disclosure. In the case where the first condition proposed in the present disclosure is satisfied, or in the case where the random access procedure to the target gNB 1h-10 is successfully performed, the upper layer (e.g., RRC layer) may stop the first timer. In the case where the first timer stops, the RRC layer may use an indicator to instruct the PDCP layer to hand over uplink data transmission to the bearer for which the DAPS switching method is intended.

[0219] -Third method: In the case where DAPS switching is indicated in the RRCReconfiguration message received by UE 1h-20, UE 1h-20 may configure a MAC layer for the target gNB 1h-10 corresponding to the second bearer. When an indicator indicating to the lower layer (e.g., MAC layer) that the RRC layer of UE 1h-20 performs DAPS switching is sent to the lower layer (e.g., MAC layer), the MAC layer of the target gNB may perform a random access procedure and identify whether the above-mentioned first condition is met. In addition, when the first condition is met, the MAC layer of the target gNB may indicate to the upper layer (e.g., PDCP layer) of the bearer configured with the DAPS switching method an indicator that uplink data transmission is handed over from the source gNB 1h-05 through the first bearer to the target gNB 1h-10 through the second bearer in the DAPS switching method proposed in the present disclosure.

[0220] -Fourth method: According to another method, in the case where DAPS switching is indicated in the RRCReconfiguration message received by the UE 1h-20, the UE 1h-20 may configure the MAC layer for the target gNB 1h-10 corresponding to the second bearer. When an indicator indicating that the RRC layer of the UE 1h-20 performs DAPS switching is indicated to the lower layer (e.g., the MAC layer), the MAC layer of the target gNB may perform a random access procedure and identify whether the above-mentioned first condition is met. In addition, when the first condition is met, the MAC layer may indicate to the upper layer (e.g., the RRC layer) that the first condition is met. In the case where the indicator is identified and the first condition proposed in the present disclosure is met, or when the random access procedure to the target gNB 1h-10 is successfully performed, the upper layer (e.g., the RRC layer) may stop the first timer. In addition, the upper layer (e.g., the RRC layer) may indicate to the lower layer (e.g., the PDCP layer) of the bearer for which the DAPS switching method is configured an indicator that uplink data transmission is handed over from the source gNB 1h-05 through the first bearer to the target gNB 1h-10 through the second bearer in the DAPS switching method proposed in the present disclosure.

[0221] According to the above-mentioned first method, second method, third method or fourth method, when the PDCP layer receives an indicator that the first condition is satisfied from an upper layer (e.g., RRC layer) or a lower layer (e.g., MAC layer), or an indicator to hand over uplink data transmission from the source gNB 1h-05 to the target gNB 1h-10 (e.g., in the case of indicating the DAPS switching method), the PDCP layer may perform the protocol layer operations proposed below to effectively perform the handover of uplink data transmission, and may perform one or more of the following operations to prevent data loss due to uplink data transmission.

[0222] The following operations may be applied to the PDCP layer (RLC layer operating in AM mode or RLC layer operating in UM mode) connected to an AM DRB or a UM DRB. Before the first condition is satisfied, or before an indicator that the first condition is satisfied is received, when there is data to be sent in the buffer, the PDCP layer may notify the MAC layer of the first bearer of the source gNB 1h-05 of the presence of data to be sent (e.g., PDCP data amount), and uplink data transmission to the source gNB 1h-05 may be performed. The MAC layer of the first bearer for the source gNB 1h-05 may perform a scheduling request or buffer status report procedure in order to receive uplink transmission resources allocated to the source gNB 1h-05. When the above-mentioned first condition is satisfied, or when an indicator that the first condition is satisfied is received, for a bearer configured with the DAPS switching method, uplink data transmission switching to the target gNB 1h-10 may be performed as follows.

[0223] -The UE may use the uplink or downlink ROHC context of the source gNB 1h-05 as is without initialization, may initialize the uplink or downlink ROHC context of the target gNB 1h-10, and may start from an initial state (e.g., IR state in U mode).

[0224] -In order to hand over uplink data transmission from the first bearer for the source gNB 1h-05 to the second bearer for the target gNB1h-10, the PDCP layer may indicate to the MAC layer of the first bearer for the source gNB 1h-05 that the size or amount of data to be transmitted is 0 (or does not exist). That is, the PDCP layer may indicate that there is no more data to be transmitted by indicating to the MAC layer of the first bearer that the PDCP data amount of the PDCP layer is 0 (even when there is actually data to be transmitted in the buffer, the PDCP layer may indicate to the MAC layer of the first bearer of the source gNB 1h-05 that there is no data to be transmitted in order to hand over uplink data transmission).

[0225] -However, as proposed in the present disclosure, in the case of a handover method (DAPS handover method) indicating the second embodiment of the present disclosure, in the case of a bearer indicating the handover method (DAPS handover method) of the second embodiment of the present disclosure, or in the case where the first condition is satisfied, when the RLC control data (RLC status report) or PDCP control data (PDCP status report or ROHC feedback) of the source gNB 1h-05 is generated, the PDCP layer of the bearer may indicate the amount of data corresponding to the RLC control data or PDCP control data to the MAC layer of the source gNB 1h-05, and data transmission to the source gNB 1h-05 or the RLC layer of the source gNB 1h-05 may be performed. However, as proposed in the present disclosure, in the case of indicating the handover method (DAPS handover method) of the second embodiment of the present disclosure, in the case of the bearer indicating the handover method (DAPS handover method) of the second embodiment of the present disclosure, and in the case where the first condition is satisfied, when the RLC control data (RLC status report) or PDCP control data (PDCP status report or ROHC feedback) of the target gNB 1h-10 is generated, the PDCP layer of the bearer may indicate the amount of data corresponding to the RLC control data or PDCP control data to the MAC layer of the target gNB 1h-10, and data transmission to the target gNB 1h-10 or the RLC layer of the target gNB 1h-10 may be performed. When the first condition is not satisfied, the PDCP layer may indicate the amount of data corresponding to the generated data (PDCP data PDU or PDCP control PDU) to the MAC layer of the source gNB 1h-05, and data transmission to the source gNB 1h-05 or the RLC layer of the source gNB 1h-05 may be performed. Therefore, in the structure of the second PDCP layer proposed for the bearer configured with the DAPS switching method, when an indicator that the first condition is satisfied is received, the second PDCP layer may indicate to the target gNB 1h-10 the bearer for the source gNB 1h-05, the PDCP control data or RLC control data to be sent to the MAC layer for the source gNB1h-05, or the amount of data excluding the data size when indicating the amount of data to the MAC layer of the target gNB 1h-10.

[0226] -The PDCP layer (RLC layer operating in AM mode) connected to the AM DRB (all PDCP PDUs stored in the past are discarded (e.g., PDCP SDUs are not discarded in order to prevent loss of original data)) may perform a new header compression procedure on data (buffered PDCP SDUs) starting from the first data (e.g., PDCP SDUs) for which successful delivery is not confirmed by a lower layer (e.g., RLC layer corresponding to the first bearer for the source gNB 1h-05) based on the header context of the target gNB 1h-10 before the first condition is satisfied or before receiving an indicator that the first condition is satisfied, in ascending order of the assigned count value (or PDCP sequence number). The PDCP layer may apply a security key for the target gNB 1h-10 to perform an integrity procedure or a ciphering procedure again, and may configure a PDCP header and send the configured PDCP header to the lower layer (RLC layer of the second bearer of the target gNB 1h-10) to perform retransmission or transmission. That is, the PDCP layer may perform cumulative retransmission starting from the first data for which successful delivery is not confirmed. According to another method, when performing retransmission, the PDCP layer may start performing retransmission only for data in which successful delivery is not confirmed from a lower layer (e.g., an RLC layer for a first bearer of the source gNB 1h-05). More specifically, the PDCP layer (RLC layer operating in AM mode) connected to the AM DRB (all previously stored PDCP PDUs for transmission to the source gNB 1h-05 through the first protocol layer connected to the PDCP layer are discarded (e.g., PDCP SDUs may not be discarded in order to prevent loss of original data)) may perform a new header or data compression process only for data (e.g., PDCP SDUs) in which successful delivery is not confirmed from a lower layer (e.g., RLC layer) of the first protocol layer of the source gNB 1h-05 by applying a header compression (or data compression) protocol context or security key corresponding to the target gNB 1h-10 based on an allocated count value (or PDCP sequence number) before a first condition is satisfied or before an indicator that the first condition is satisfied is received. The PDCP layer may perform the integrity process or the encryption process again, may configure the PDCP header, and may perform retransmission or transmission by sending the configured PDCP header to a lower layer, which is a second protocol layer for transmission to the target gNB 1h-10. That is, in order to prevent waste of transmission resources, the PDCP layer may perform selective retransmission only for data for which successful delivery is not confirmed. According to another method, a transmission or retransmission operation is performed by releasing a lower layer (e.g., a transmitting or receiving RLC layer or MAC layer) which is a first protocol layer for transmitting data to the source gNB 1h-05.When the transmission or retransmission process is extended to the UM DRB, the PDCP layer connected to the RLC layer operating in UM mode may treat data that has not been transmitted to the lower layer, data for which the PDCP discard timer has not expired, or data to which a PDCP sequence number (or count value) has been assigned as data received from an upper layer or newly received, and perform header (or data) compression on the data using the header (or data) compression context or security key of the target gNB 1h-10 without restarting the PDCP discard timer for each data. Alternatively, the PDCP layer may perform a ciphering or integrity protection process, may generate and connect a PDCP header, and may perform transmission or retransmission. The PDCP layer may process the data in ascending order of the count value assigned before the process is triggered, and may perform transmission or retransmission. The window state variable of the PDCP layer connected to the UM DRB or AM DRB may be maintained and used without initialization.

[0227] -When there is data to be transmitted in the buffer, the PDCP layer may notify the existence of data to be transmitted by indicating the size or amount of data to be transmitted (e.g., PDCP data amount) to the MAC layer of the second bearer of the target gNB 1h-10, and uplink data transmission handover to the target gNB 1h-10 may be performed. The MAC layer of the second bearer of the target gNB 1h-10 may perform a scheduling request or buffer status report procedure to receive uplink transmission resources allocated to the target gNB 1h-10.

[0228] -For the bearer indicated (or configured) in the second embodiment (or DAPS handover method), in the case where the first condition is satisfied, the configuration information or context for the data compression protocol (for the source gNB) (e.g., uplink data compression protocol) may be released. Alternatively, in the case where the first condition is satisfied, the upper layer (e.g., RRC layer) of the UE may instruct or reconfigure the PDCP layer to release the configuration information or context for the data compression protocol (e.g., uplink data compression protocol). However, for the bearer of the second embodiment (or DAPS handover method) that is not indicated (or configured), when the handover command message is received, the UE may release the configuration information or context for the data compression protocol (e.g., uplink data compression protocol). Alternatively, when the handover command message is received, the upper layer (e.g., RRC layer) of the UE may instruct or reconfigure the PDCP layer to release the configuration information or context for the data compression protocol (for the source gNB) (e.g., uplink data compression protocol). This is because, for bearers configured with the DAPS switching method, it is necessary to compress data and send the compressed data to the source gNB by using the configuration information or context of the data compression protocol of the source gNB until the first condition is met.

[0229] As described above, when the DAPS switching method is configured for at least one of the bearers configured in the UE, when the DAPS switching method is configured for a specific bearer, when the first condition is met, or when the UE receives an indicator indicating that the first condition is met, the UE may perform one of the following methods on a bearer for which the DAPS switching method is not configured.

[0230] -Method 1: In the case where condition 1 is satisfied as described above, the upper layer (e.g., RRC layer) of the UE may trigger or request a PDCP re-establishment procedure for one or more bearers for which the DAPS handover method is not configured (even when the target gNB configures the PDCP re-establishment procedure for the bearer in the handover command message, the PDCP re-establishment procedure may be performed when the first condition is satisfied). The PDCP layer receiving the PDCP re-establishment procedure request may perform a different PDCP re-establishment procedure for each bearer. For example, the PDCP layer may initialize a window state variable for a UM DRB, and may perform transmission or retransmission by compressing or encrypting data that has not been sent to a lower layer or data for which a PDCP discard timer has not expired, or by performing integrity protection, in ascending order of a count value based on a header (or data) compression context or security key of the target gNB. In addition, when a reordering timer is running, the PDCP layer may stop and initialize the reordering timer, may process the received data (PDCP SDU or PDCP PDU) sequentially, and may send the processed data to the upper layer. In addition, the PDCP layer may not initialize the window state variable of the AM DRB, and may perform transmission or retransmission by compressing or ciphering, or performing integrity protection on the first data (PDCP SDU or PDCP PDU) whose successful delivery is not confirmed from the lower layer in ascending order of the count value or PDCP sequence number based on the header (or data) compression context or security key of the target gNB. When the handover command message is received for the bearer for which the DAPS handover method is not configured, the PDCP re-establishment process is not performed, and when the first condition is satisfied, the reason why the PDCP re-establishment process is performed is that when the handover process from the UE to the target gNB fails, the UE may perform fallback to the source gNB, in the PDCP re-establishment process, the bearer compresses the data into the header (or data) compression context of the target gNB, and when the UE has to fall back, the data processed by ciphering or integrity protection using the security key of the target gNB may become useless and may be discarded. In addition, in the case where the UE has to fall back, the PDCP re-establishment process may be performed again for the bearer, thereby compressing the data using the header (or data) compression context of the source gNB of the data to be transmitted. Likewise, encryption or integrity protection has been performed again with the security key of the source gNB. Therefore, unnecessary processing may occur. Therefore, when the UE performs the DAPS handover method, for the bearer for which the DAPS handover method is not configured, the PDCP re-establishment procedure may not be triggered or performed when the UE receives the handover command message. Alternatively, the target gNB may not configure the PDCP re-establishment procedure for the bearer in the handover command message, and may trigger or perform the PDCP re-establishment procedure when the first condition is met. For the bearer for which the DAPS handover method is configured, the PDCP re-establishment procedure is not performed.

[0231] -Method 2: In the case of receiving a handover command message for a bearer for which the DAPS handover method is not configured, the upper layer (e.g., RRC layer) of the UE may trigger or request a PDCP re-establishment procedure. The PDCP layer receiving the request for the PDCP re-establishment procedure may perform a different PDCP re-establishment procedure for each bearer. For example, the PDCP layer receiving the request for the PDCP re-establishment procedure may initialize a window state variable for the UM DRB, and may perform transmission or retransmission by compressing or encrypting data that has not been sent to the lower layer or data that the PDCP discard timer has not expired, or by performing integrity protection, in ascending order of a count value based on a header (or data) compression context or security key of the target gNB. Optionally, when the reordering timer is running, the PDCP layer receiving the request for the PDCP re-establishment procedure may stop and initialize the reordering timer, may process the received data (PDCP SDU or PDCP PDU) sequentially, and may send the processed data to the upper layer. Alternatively, the PDCP layer receiving the request for the PDCP re-establishment procedure may not initialize the window state variable of the AM DRB, and may perform transmission or retransmission by performing compression or ciphering, or performing integrity protection, on the first data (PDCP SDU or PDCP PDU) for which successful delivery from the lower layer is not confirmed, in ascending order of the count value or PDCP sequence number, based on the header (or data) compression context or security key of the target gNB. In the case of receiving a handover command message for a bearer for which the DAPS handover method is not configured, the data is compressed using the header (or data) compression context of the target gNB through the PDCP re-establishment procedure, and the data is processed by performing ciphering or integrity protection using the security key of the target gNB. In the case of failure of the handover procedure from the UE to the target gNB (for example, in the case where the first timer has expired or the radio connection to the target gNB has failed), fallback to the source gNB is possible. Therefore, in order to discard the generated or processed data (e.g., PDCP PDU) for transmission from the bearer to the target gNB and reprocess the data (e.g., PDCP SDU) based on the header (or data) compression context or security key of the source gNB, when the UE performs fallback, the UE can request and instruct the upper layer (e.g., RRC layer) of the UE to reconfigure a discharge indication, a PDCP re-establishment procedure, or send the configuration information (security key or header (or data) compression context) of the source gNB of the data (PDCP PDU) processed based on the configuration information (security key or header (or data) compression context) of the target gNB to the bearer for which the DAPS switching method is not indicated, and generate and process again according to the data based on the source gNB configuration information.

[0232] In a second embodiment of the effective handover method proposed in the present disclosure (e.g., a DAPS handover method), even after the UE receives a handover command message (e.g., an RRCReconfiguration message), the UE can continue to receive downlink data from the source gNB 1h-05 or the target gNB 1h-10 through the protocol layer of the first bearer for the source gNB 1h-05 or the second bearer for the target gNB 1h-10. In an embodiment, in order for the UE to seamlessly receive downlink data from the source gNB 1h-05 (or the target gNB 1h-10), or in order for the source gNB 1h-05 (or the target gNB 1h-10) to seamlessly send downlink data, an RLC status report instead of data can be allowed to continuously perform uplink transmission to the source gNB 1h-05 (or the target gNB 1h-10) for the AM bearer through the protocol layer of the first bearer (or the second bearer). That is, even when the first condition is satisfied and the UE switches uplink data transmission to the target gNB 1h-10, in the case where the UE needs to send an RLC status report, HARQ ACK or NACK, or PDCP control data (PDCP ROHC feedback or PDCP status report) to the source gNB 1h-05, data transmission is allowed to be sent through the first bearer used for the source gNB 1h-05. This is because, in the case of an AM bearer, after the data is sent to the transmitting end, when the RLC status report does not indicate successful delivery (i.e., when the RLC status report is not received), the data may not be sent continuously thereafter. Specifically, in Figure 1h In the second embodiment of the effective switching method, in the third operation 1h-03, even when the first condition is met and the UE 1h-20 stops sending uplink data to the source gNB 1h-05 through the protocol layer 1h-22 of the first bearer and hands over to start sending uplink data to the target gNB 1h-10 through the protocol layer 1h-21 of the second bearer, the UE can continue to send HARQ ACK or HARQ NACK information, RLC status report (ACK or NACK information), or PDCP control data (for example, PDCP status report or ROHC feedback information) so as to seamlessly receive downlink data from the source gNB1h-05 (or target gNB 1h-10), or the source gNB 1h-05 (or target gNB 1h-10) effectively sends downlink data.

[0233] In addition, Figure 1hIn the second embodiment of the effective switching method, in the third operation 1h-03, even when the first condition is satisfied and the UE 1h-20 stops sending uplink data to the source gNB 1h-05 through the protocol layer 1h-22 of the first bearer and hands over to start sending uplink data to the target gNB 1h-10 through the protocol layer 1h-21 of the second bearer, the UE can continue to perform data transmission due to HARQ retransmission of the MAC layer, or continue to perform data transmission due to retransmission of the AM mode RLC layer to prevent data loss to the source gNB 1h-05. Figure 1h In a second embodiment of the effective switching method, in the third operation 1h-03, when the first condition is met and UE 1h-20 stops sending uplink data to the source gNB 1h-05 through the protocol layer 1h-22 of the first bearer and hands over to start sending uplink data to the target gNB1h-10 through the protocol layer 1h-21 of the second bearer, the source gNB 1h-05 or the target gNB 1h-10 can allocate transmission resources to the UE by dividing time to prevent conflicts between uplink transmission resources to the target gNB 1h-10 and uplink transmission resources to the source gNB 1h-05. In the case where the uplink transmission resources to the target gNB 1h-10 and the uplink transmission resources to the source gNB 1h-05 conflict and overlap with each other, the UE may give priority to the uplink transmission resources of the source gNB 1h-05 and perform data transmission to the source gNB 1h-05 in order to maintain downlink data transmission or continuously receive downlink data from the source gNB 1h-05 without problem. According to another embodiment, in the case where the uplink transmission resources to the target gNB 1h-10 and the uplink transmission resources to the source gNB 1h-05 conflict and overlap with each other, the UE may give priority to the uplink transmission resources of the target gNB 1h-10 and perform data transmission to the target gNB 1h-10 in order to maintain downlink data transmission from the target gNB 1h-10.

[0234] Specifically, in a case where a handover corresponding to the second embodiment of the present disclosure (e.g., DAPS handover) is indicated, the UE receives a handover command message, or indicates for each bearer, indicating the bearer of the DAPS handover or the UE may perform a scheduling request through the first protocol layer until the first condition is met, a buffer status report may be sent to the source gNB 1h-05, uplink transmission resources may be received, and uplink data may be sent. The UE may receive downlink data from the source gNB 1h-05. However, in a case where the first condition is met, the UE may no longer send data to the source gNB 1h-05, may hand over the uplink through the second protocol layer to perform a scheduling request, may send a buffer status report to the target gNB 1h-10, may receive uplink transmission resources, and may send uplink data to the target gNB 1h-10. However, the UE may continue to receive downlink data from the source gNB 1h-05. Even after uplink transmission handover, HARQ ACK or HARQ NACK, RLC status report or PDCP control data (e.g., PDCP status report or ROHC feedback information) corresponding to downlink data can be continuously sent. In addition, even when the first condition is met, the UE can continue to receive downlink data from the source gNB1h-05 or the target gNB 1h-10.

[0235] exist Figure 1h In a second embodiment of the effective switching method, in the fourth operation 1h-04, when the second condition is satisfied, the UE 1h-20 may stop receiving downlink data from the source gNB 1h-05 through the protocol layer 1h-22 of the first bearer, and may release the connection with the source gNB 1h-05. The second condition may be one of the following conditions. In addition, the PDCP layer 1h-21 of the second bearer may continue to perform seamless data transmission or reception with the target gNB 1h-10 by using information such as transmission or reception data, sequence number information, or header compression and decompression context stored in the PDCP layer 1h-22 of the first bearer.

[0236] -When the UE performs a random access procedure to the target gNB 1h-10 through layer 1h-21 of the second bearer and receives the RAR, the UE may determine that the second condition is satisfied.

[0237] -When the UE performs a random access procedure to the target gNB 1h-10 through the layer of the second bearer, receives the RAR, configures the switching completion message and sends it to the target gNB 1h-10, the UE can determine that the second condition is satisfied.

[0238] -When the UE completes the random access procedure to the target gNB 1h-10 through the layer of the second bearer and sends data on the PUCCH or PUSCH uplink transmission resource for the first time, or when the PUCCH or PUSCH uplink transmission resource is received for the first time, the UE can determine that the second condition is met.

[0239] -When the gNB sets a separate timer in the UE using an RRC message and the timer has expired, the UE may determine that the second condition is met.

[0240] >The timer may be started when the UE receives a Handover Command message from the source gNB 1h-05, when random access to the target gNB 1h-10 is started (when a preamble is sent), when a RAR is received from the target gNB 1h-10, when a Handover Complete message is sent to the target gNB 1h-10, or when data is sent for the first time on a PUCCH or PUSCH uplink transmission resource.

[0241] -After the UE performs a random access procedure to the target gNB 1h-10 through the layer of the second bearer, receives the RAR, configures the handover completion message and sends it to the target gNB 1h-10, the UE can determine that the second condition is satisfied when the successful delivery of the handover completion message is confirmed in the MAC layer (HARQ ACK) or the RLC layer (RLC ACK).

[0242] -After the UE performs a random access procedure to the target gNB 1h-10 through the layer of the second bearer, receives the RAR, or configures the switching completion message and sends it to the target gNB 1h-10, the UE can determine that the second condition is satisfied when uplink transmission resources are allocated from the target gNB 1h-10 for the first time, or when uplink transmission resources are indicated for the first time.

[0243] -When the source gNB 1h-05 performs the valid handover proposed in the present disclosure, the source gNB 1h-05 can determine when to stop transmitting downlink data to the UE or when to release the connection with the UE. For example, this can be determined by a certain method (for example, when a certain timer expires (the timer can be started after the handover indication), or when the source gNB 1h-05 receives an indication from the target gNB1h-10 that the UE has successfully performed the handover to the target gNB 1h-10). When no downlink data is received from the source gNB 1h-05 within a specific time, the UE can determine that the second condition is met, can determine that the connection with the source gNB 1h-05 has been released, and can release the connection.

[0244] -When the UE receives an indication (e.g., an RRC message (e.g., an RRC configuration message), a MAC CE, an RLC control PDU, or a PDCP control PDU) from the target gNB 1h-10 to release the connection with the source gNB 1h-05, the UE may determine that the second condition is satisfied.

[0245] -When the UE receives an indication (e.g., an RRC message (e.g., an RRC configuration message), a MAC CE, an RLC control PDU, or a PDCP control PDU) from the source gNB 1h-05 to release the connection with the source gNB 1h-05, the UE may determine that the second condition is met.

[0246] -When the UE does not receive downlink data from the source gNB 1h-05 within a specific time, the UE may determine that the second condition is met.

[0247] -The UE can determine that the second condition is satisfied when the UE successfully completes a random access procedure to the target gNB 1h-10 through a layer of the second bearer (e.g., a MAC layer), when the UE successfully completes a random access procedure to the target gNB 1h-10 through a layer of the second bearer and a first uplink transmission resource is allocated from the target gNB 1h-10, or when the uplink transmission resource is indicated to the UE for the first time.

[0248] > For example, more specifically, when the UE receives a HANDOVER COMMAND message from the source gNB 1h-05, and when random access to the target gNB 1h-10 is indicated, the indicated random access is a CFRA procedure (e.g., when a pre-specified preamble or UE cell identifier (e.g., C-RNTI) is allocated),

[0249] >>When the UE sends a pre-specified preamble to the cell of the target gNB 1h-10 and receives the RAR message, the UE can determine that the random access procedure has been successfully completed. Therefore, when the first uplink transmission resource allocated, included or indicated in the RAR message is received, the UE can determine that the second condition is satisfied. According to another method, when the UE receives the uplink transmission resource for the first time after receiving the RAR, the UE can determine that the second condition is satisfied.

[0250] >When the UE receives a Handover Command message from the source gNB 1h-05, and when random access to the target gNB 1h-10 is indicated, the indicated random access is a CBRA procedure (e.g., when no pre-assigned preamble or UE cell identifier (e.g., C-RNTI) is allocated),

[0251] >>When the UE sends a preamble (e.g., a random preamble) to the cell of the target gNB 1h-10, receives a RAR message, sends message 3 (e.g., a handover complete message) by using the uplink transmission resources allocated (or included or indicated) in the RAR message, and receives a MAC CE (contention resolution MAC CE) from the target gNB 1h-10 indicating that the contention has been resolved by message 4, or when uplink transmission resources are received on the PDCCH corresponding to the UE's C-RNTI, the UE can determine that the random access procedure to the target gNB 1h-10 has been successfully completed. Therefore, when the UE monitors the PDCCH for the first time on the PDCCH corresponding to the UE's C-RNTI and receives uplink transmission resources (or when indicated for the first time), the UE can determine that the first condition is met. According to another method, in the case where the size of the uplink transmission resources allocated in the RAR message is sufficient to send message 3 and the UE is allowed to send uplink data in addition, the UE can determine that the uplink transmission resources have been received for the first time and can determine that the first condition is met. That is, when receiving the RAR, the UE may determine that the uplink transmission resource has been received for the first time and the first condition is satisfied.

[0252] - In the case where a handover method not requiring a random access procedure (RACH-less handover) is indicated together in the handover command message received by the UE 1h-20,

[0253] > In case the uplink transmission resources of the target gNB 1h-10 are included in the Handover Command message,

[0254] >>When the UE sends message 3 (e.g., a handover complete message or an RRCReconfigurationComplete message) on the uplink transmission resources of the target gNB 1h-10 and receives a UE identity confirmation MAC CE as message 4 from the gNB, or when uplink transmission resources are received on the PDCCH corresponding to the UE's C-RNTI, the UE can determine that the random access procedure has been successfully completed. The UE can determine that the second condition is met. According to another method, after the random access procedure is successfully completed, the UE can determine that the second condition is met when the UE performs PDCCH monitoring and receives the first uplink transmission resource on the PDCCH corresponding to the UE's C-RNTI.

[0255] >When the uplink transmission resources for the target gNB 1h-10 are not included in the Handover Command message,

[0256] >>When the UE performs PDCCH monitoring on the target gNB 1h-10 (or cell) and receives uplink transmission resources on the PDCCH corresponding to the UE's C-RNTI, when the UE sends message 3 (e.g., a handover complete message or an RRCReconfigurationComplete message) on the uplink transmission resources and receives a UE identity confirmation MAC CE from the gNB, or when uplink transmission resources are received on the PDCCH corresponding to the UE's C-RNTI, the UE can determine that the random access procedure has been successfully completed and the second condition is met. According to another method, after the random access procedure is successfully completed, when the UE performs PDCCH monitoring and receives a first uplink transmission resource on the PDCCH corresponding to the UE's C-RNTI, the UE can determine that the second condition is met.

[0257] In the case where the UE performs the second embodiment of the effective switching method proposed in the present disclosure (for example, the DAPS switching method), when the UE identifies that the RRC layer, MAC layer, RLC layer of the first bearer of the source gNB 1h-05 or the RRC layer, MAC layer or RLC layer of the second bearer of the target gNB 1h-10 satisfies the second condition proposed in the present disclosure, an indicator indicating that the second condition is satisfied may be indicated to the PDCP layer of the bearer or UE performing the DAPS switching method. When the PDCP layer of the UE receives an indication indicating that the second condition is satisfied from a lower layer or an upper layer, or when the second condition is satisfied, the second embodiment of the effective switching method proposed in the present disclosure may be successfully completed by performing one or more of the following processes on the bearer or UE configured with the DAPS switching method.

[0258] -The UE may release the first bearer for the source gNB 1h-05 and release the connection with the source gNB 1h-05. Before releasing the first bearer for the source gNB 1h-05, an RLC reestablishment procedure may be performed on the RLC layer corresponding to the first bearer for the source gNB 1h-05 (for example, when a reordering timer is running, the timer may be stopped or initialized, and when received data is stored in a buffer, the stored data may be processed and sent to an upper layer, or when there is data to be sent in the buffer, the data may be discarded), or the MAC layer may be reset.

[0259] -When the connection with the source gNB 1h-05 is released, the UE may trigger the PDCP status reporting procedure to report the reception status of the downlink data received from the source gNB 1h-05 to the target gNB 1h-10, may configure the PDCP status report, and may send the PDCP status report to the target gNB 1h-10.

[0260] - In the event that the second condition is satisfied, for each bearer or with respect to a bearer in which a DAPS switching method is indicated, the UE may hand over from the second PDCP layer structure or function 1i-20 to the first PDCP layer structure or function 1i-11 or 1i-12 proposed in the present disclosure, may initialize a reordering variable, and may stop and initialize a reordering timer. The UE may perform a decryption process or header (or data) decompression by applying a security key or header compression decompression context of the source gNB 1h-05 to data stored in a buffer for reordering (e.g., data received from the source gNB 1h-05), and may discard the security key or header decompression context of the source gNB 1h-05. The processed data may be sent to an upper layer in ascending order. That is, in the case where the second condition is satisfied, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source gNB 1h-05 to the data stored in the buffer for reordering (e.g., data received from the source gNB 1h-05), and may discard the security key or header decompression context of the source gNB 1h-05. According to another method, in the case where the second condition is satisfied, for each bearer or with respect to the bearer in which the DAPS switching method is indicated, the UE may hand over from the second PDCP layer structure or function 1i-20 to the third PDCP layer structure or function 1i-30 proposed in the present disclosure. In addition, the UE may continue to use the reordering variables and the reordering timer without stopping or initializing the reordering variables and the reordering timer. However, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source gNB 1h-05 to the data stored in the buffer for reordering (e.g., data received from the source gNB 1h-05), and may discard the security key or header decompression context of the source gNB 1h-05. The processed data may be sent to the upper layer in ascending order. That is, in the case where the second condition is satisfied, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source gNB 1h-05 to the data stored in the buffer for reordering (e.g., data received from the source gNB 1h-05), and may discard the security key or header decompression context of the source gNB 1h-05. The UE can release the QoS mapping information of the SDAP layer of the source gNB1h-05, the security key information of the source gNB 1h-05 of the PDCP layer, the header (or data) compression context information of the source gNB 1h-05, or the RLC layer or MAC layer of the source gNB 1h-05.For each bearer or with respect to a bearer in which a DAPS switching method is indicated, handing over from a second PDCP layer structure or function 1i-20 to a first PDCP layer structure or function proposed in the present disclosure may mean a reconfiguration of the PDCP layer. Such a reconfiguration may be performed when a reconfiguration indicator of the PDCP layer is received from an upper layer (e.g., an RRC layer). For example, the UE receives a switching command message, and the upper layer (e.g., the RRC layer) sends a PDCP layer reconfiguration indicator to the PDCP layer of the bearer for which the DAPS switching method is configured. In this way, the first PDCP layer structure or function may be reconfigured to a second PDCP layer structure or function. For example, when the second condition is met, the upper layer (e.g., the RRC layer) sends a PDCP layer reconfiguration indicator to the PDCP layer of the bearer. In this way, the second PDCP layer structure or function may be reconfigured to a first PDCP layer structure or function. For example, whenever a PDCP layer reconfiguration indicator is received from an upper layer (e.g., RRC layer) in a toggle manner, the bearer PDCP layer can reconfigure the first PDCP layer structure or function into a second PDCP layer structure or function, or can reconfigure the second PDCP layer structure or function into the first PDCP layer structure or function.

[0261] - In the case where the second condition proposed in the present disclosure is satisfied when performing the DAPS switching method proposed in the present disclosure, the UE may release the first bearer for the source gNB and may again hand over from the second SDAP layer structure and function 1j-20 applied to each bearer or the bearer in which the DAPS switching method is indicated to the first SDAP layer structure and function 1j-10. In the case where the second condition is satisfied, the UE may hand over from the second SDAP layer structure or function 1j-20 to the first SDAP layer structure or function 1j-10 proposed in the present disclosure for each bearer or with respect to the bearer in which the DAPS switching method is indicated. The UE may maintain the second bearer of the target gNB or the second mapping information between the QoS flow and the bearer. Before releasing the first bearer of the source gNB or the first mapping information between the QoS flow and the bearer, the UE may complete data processing by applying the first mapping information between the QoS flow and the bearer to the data received from the source gNB (e.g., all data received from the source gNB), and then, the first mapping information between the QoS flow and the bearer or the first bearer may be released. The UE may send the processed data to the upper layer in ascending order. That is, in the case where the second condition is satisfied, the UE may process the data (e.g., a process of reading SDAP header information, updating mapping information, configuring SDAP header, or routing or sending to an appropriate upper layer or lower layer based on the first mapping information between the QoS flow and the bearer) by applying the first mapping information between the QoS flow and the bearer of the source gNB to the data stored in the buffer (e.g., data received from the source gNB), and may discard the first mapping information between the QoS flow and the bearer of the source gNB. The SDAP layer may define and apply a 1-bit indicator of a new SDAP header, a 1-bit indicator of a PDCP header, SDAP control data (e.g., a downlink end marker), or information indicated by the PDCP layer. Based on this, the SDAP layer may identify which type of data the last data received from the source gNB is. Therefore, after performing data processing by applying the first mapping information between the QoS flow and the bearer of the source gNB to the last data received from the source gNB, the first mapping information between the QoS flow and the bearer of the source gNB may be discarded. The SDAP layer may continue to maintain the second mapping information between the QoS flow and the bearer, and process the uplink data or downlink data to the target gNB based on the mapping information.

[0262] -When the MAC layer for the source gNB 1h-05 is reset and the second PDCP layer structure for the bearer for which the DAPS switching method is configured is handed over to the first PDCP layer structure, an RLC layer reconstruction or release procedure may be performed for the RLC layer for the source gNB 1h-05 in the second PDCP layer structure.

[0263] >In the present disclosure, when the second condition is satisfied, or when an indicator indicating that the second condition is satisfied is received from an upper layer (e.g., RRC layer) or a lower layer (e.g., MAC layer), the PLC layer reestablishment or release procedure for the first bearer of the source gNB may follow one of the following methods.

[0264] >> First method: For a specific bearer configured with the DAPS switching method, in the case where the RLC layer of the first bearer of the source gNB is the LTE RLC layer, the upper layer (e.g., the RRC layer) may instruct the LTE RLC layer to perform a reestablishment process. Specifically, in the case where the reordering timer is running in the LTE RLC layer, the reordering timer may be stopped or initialized. Optionally, when there is stored data, the stored data is processed and sent to the upper layer, thereby reducing the transmission delay caused by the reordering timer. In addition, the variable may be initialized, and the data for transmission may be discarded. Then, the upper layer (e.g., the RRC layer) may instruct the release of the LTE RLC layer. However, in the case where the RLC layer of the first bearer for the source gNB is the NR RLC layer, the upper layer (e.g., the RRC layer) may instruct the NR RLC layer to be released immediately without reestablishment. This is because the NR RLC layer always performs out-of-order delivery, and therefore, there may be no stored data, and even when there is stored data, the data may be segmented data, and therefore, there is no problem even if the stored data is discarded. As described above, different procedures may be applied according to the RLC layer configured for each bearer.

[0265] >> Second method: For a specific bearer configured with the DAPS switching method, in the case where the RLC layer of the first bearer of the source gNB is the LTE RLC layer, the upper layer (e.g., the RRC layer) may instruct the LTE RLC layer to perform a reestablishment process. Specifically, in the case where the reordering timer is running in the LTE RLC layer, the reordering timer may be stopped or initialized. In addition, when there is stored data, the stored data is processed and sent to the upper layer, thereby reducing the transmission delay caused by the reordering timer. In addition, the variable may be initialized, and the data for transmission may be discarded. Alternatively, the upper layer (e.g., the RRC layer) may release the LTE RLC layer. However, in the case where the RLC layer of the first bearer for the source gNB is the NR RLC layer, the upper layer (e.g., the RRC layer) may instruct the NR RLC layer to be released immediately without reestablishment. This is because the NR RLC layer always performs out-of-order delivery, and therefore, there may be no stored data, and even when there is stored data, the data may be segmented data, and therefore, there is no problem even if the stored data is discarded. As described above, different procedures may be applied according to the RLC layer configured for each bearer.

[0266] >> Third method: For a specific bearer configured with the DAPS switching method, in a case where the RLC layer of the first bearer of the source gNB is the LTE RLC layer and the target gNB sends an RRC message (e.g., RRCReconfiguration) including an indicator of releasing the connection with the source gNB or the first bearer of the source gNB to the UE, an indicator for reestablishing the LTE RLC layer (e.g., reestablishRLC) (or an indicator that may include releasing the LTE RLC layer) may be sent by configuration information (e.g., rlc-config) of the LTE RLC layer for the bearer included in the RRC message. Therefore, in a case where an indication of releasing the connection with the source gNB is received, or in a case where the second condition is satisfied, the upper layer (e.g., RRC layer) may read the RRC message and may instruct the LTE RLC layer to perform a reestablishment process according to the indication for the LTE RLC reestablishment process (or release). Specifically, when the reordering timer is running in the LTE RLC layer, the reordering timer may be stopped or initialized. When there is stored data, the stored data is processed and sent to the upper layer, thereby reducing the transmission delay caused by the reordering timer. In addition, the variables may be initialized and the data for transmission may be discarded. Then, the upper layer (e.g., RRC layer) may release the LTE RLC layer. For a specific bearer configured with the DAPS switching method, in the case where the RLC layer of the first bearer of the source gNB is an NR RLC layer and the target gNB sends an RRC message (e.g., RRCReconfiguration) including an indicator of releasing the connection with the source gNB or the first bearer of the source gNB to the UE, the indicator of releasing the NR RLC layer may be sent by the configuration information (e.g., rlc-config) of the NR RLC layer of the bearer included in the RRC message. As described above, depending on the RLC layer configured for each bearer, the target gNB may indicate different procedures with an RRC message, and thus, the UE may apply these procedures for each bearer.

[0267] >> Fourth method: For a specific bearer configured with the DAPS switching method, in a case where the RLC layer of the first bearer of the source gNB is the LTE RLC layer and the target gNB sends an RRC message (e.g., RRCReconfiguration) including an indicator of releasing the connection with the source gNB or the first bearer of the source gNB to the UE, an indicator for reestablishing the LTE RLC layer (e.g., reestablishing RLC) (or an indicator that may include releasing the LTE RLC layer) may be sent by configuration information (e.g., rlc-config) of the LTE RLC layer for the bearer included in the RRC message. Therefore, in the case of receiving an indication to release the connection with the source gNB, or in the case where the second condition is satisfied, the upper layer (e.g., RRC layer) may read the RRC message and may instruct the LTE RLC layer to perform a reestablishment process according to the indication for the LTE RLC reestablishment process (or release). Specifically, when the reordering timer is running in the LTE RLC layer, the reordering timer may be stopped or initialized. When there is stored data, the stored data is processed and sent to the upper layer, thereby reducing the transmission delay caused by the reordering timer. In addition, a variable may be initialized and data for transmission may be discarded. Alternatively, an upper layer (e.g., an RRC layer) may release the LTE RLC layer. For a specific bearer configured with the DAPS switching method, when the RLC layer of the first bearer of the source gNB is the NR RLC layer and the target gNB sends an RRC message (e.g., RRCReconfiguration) including an indicator of releasing the connection with the source gNB or the first bearer of the source gNB to the UE, the indicator of releasing the NR RLC layer or the indicator of reestablishing the NR RLC layer may be sent by being included in the RRC message for the bearer. As described above, the target gNB may indicate different procedures with an RRC message according to the RLC layer configured for each bearer, and thus, the UE may apply these procedures for each bearer.

[0268] -The receiving PDCP layer may process or store data received due to the re-establishment process of the lower layer (e.g., RLC layer), or may perform a header decompression process based on the header compression context (ROHC or Ethernet Header Compression (EHC)) for the stored data for the UM DRB (received from the source gNB 1h-05) or all the stored data (for the source gNB1h-05).

[0269] -The receiving PDCP layer may process or store the data received due to the re-establishment procedure of the lower layer (e.g., RLC layer), or may perform a header decompression procedure based on the header compression context (ROHC or EHC) for the stored data for the AM DRB (received from the source gNB 1h-05) or all the stored data (for the source gNB1h-05).

[0270] -According to another method, the receiving PDCP layer may process or store data received due to a reestablishment procedure of a lower layer (e.g., RLC layer). In the case where an indicator (drb-Continue ROHC or drb-Continue EHC) for continuing to use the header compression context is not set for a UM DRB or an AM DRB, the receiving PDCP layer may perform a header decompression procedure on the stored data (received from the source gNB 1h-05) or all stored data based on the header compression context (ROHC or EHC).

[0271] After performing the above process, the sending or receiving PDCP layer can discard or release the security key or header compression context of the source gNB 1h-05.

[0272] In this disclosure Figure 1f In the present invention, when sending a handover command message 1f-20 to a UE, the gNB may define an indicator of an embodiment proposed in the present disclosure in a handover command message (e.g., an RRCReconfiguration message), and may indicate to the UE which embodiment of the handover process the trigger corresponds to. The UE may perform the handover process according to the handover method indicated in the handover command message. For example, by executing the second embodiment (DAPS handover method) of the effective handover method proposed in the present disclosure, the UE may perform handover to the target gNB 1h-10 while minimizing the data interruption time. According to another method, in the handover command message, an indicator of an embodiment proposed in the present disclosure may be defined for each bearer. It may be more specifically indicated which embodiment is applied to the bearer during handover, and which bearer the embodiment is applied to during handover. For example, it may be indicated that the second embodiment of the present disclosure is applied only to an AM bearer in which an RLC layer driven in an AM mode is running, or it may be extended and applied to a UM bearer in which an RLC layer driven in an UM mode is running. In addition, it may be assumed that the embodiment proposed in the present disclosure is applicable to DRBs. However, it can be extended and applied to SRB when necessary (for example, when the UE maintains the SRB of the source gNB 1h-05 and handover to the target gNB 1h-10 fails, and the handover failure message is reported or restored to the SRB of the source gNB 1h-05).

[0273] In an embodiment of the present disclosure, when the UE performs data transmission and reception with the source gNB 1h-05 through the protocol layer of the first bearer, and performs data transmission and reception with the target gNB 1h-10 through the protocol layer of the second bearer, the MAC layer of the first bearer and the MAC layer of the second bearer can each operate a separate discontinuous reception (DRX) cycle to reduce the battery consumption of the UE. That is, even after receiving the switching command message, the UE can continue to apply the DRX cycle of the MAC layer when sending and receiving data through the protocol layer of the first bearer. According to the first condition or the second condition of the present disclosure, the UE can stop DRX. In addition, the UE can separately operate the application of the DRX cycle to the MAC layer of the second bearer according to the indication of the target gNB 1h-10.

[0274] In addition, in the present disclosure, the UE stops sending uplink data to the source gNB 1h-05 through the protocol layer of the first bearer and stops receiving downlink data from the source gNB 1h-05, which means that the UE reconstructs, resets or releases the protocol layer (PHY layer, MAC layer, RLC layer or PDCP layer) of the first bearer.

[0275] In the embodiments of the present disclosure, for ease of explanation, it has been described that the UE configures the first bearer for the source gNB 1h-05 or the second bearer for the target gNB 1h-10. It can be easily extended to the case where the UE configures multiple first bearers for the source gNB 1h-05 or configures multiple second bearers for the target gNB 1h-10, and the same situation can be applied. According to another method, it can be easily extended to the case of configuring multiple bearers of multiple target GNBs 1h-10, and the same situation can be applied. For example, the UE may perform a handover process to the first target gNB 1h-10 to configure the second bearer. In the event of a handover failure, the UE performs a handover process to the second target gNB 1h-10 to configure the second bearer. The UE may search and determine a cell that meets its own specific conditions (for example, a specific signal strength or higher) from the target GNB 1h-10, and may perform a handover process on it.

[0276] Figure 1i is a diagram showing a structure of an effective PDCP layer applied to a DAPS handover method, which is a second embodiment of an effective handover method proposed in the present disclosure, and a method of applying the structure.

[0277] Figure 1iThe specific structure and function of the effective PDCP layer applied to the DAPS switching method are proposed, which is the second embodiment of the effective switching method proposed in the present disclosure, and when performing the DAPS switching process, the structure of the PDCP layer proposed below can be applied to different PDCP layer structures of each bearer at different times.

[0278] For example, before receiving a handover command message from the gNB, the UE processes, sends or receives data by applying the first PDCP layer structure and function 1i-11 or 1i-12 proposed in the present disclosure to each bearer (1i-01).

[0279] However, in the case where the UE receives a handover command message from the gNB and the DAPS handover method proposed in the present disclosure is indicated in the handover command message, or in the case where the DAPS handover method is indicated for a specific bearer, the UE processes, sends or receives data by applying the second PDCP layer structure and function 1i-20 proposed in the present disclosure to one or more bearers indicating the DAPS handover method (1i-02). That is, in the case where the UE receives a handover command message and the DAPS handover method proposed in the present disclosure is indicated in the handover command message, or in the case where the DAPS handover method is indicated for a specific bearer, the UE can be handed over from the first PDCP layer structure or function 1i-11 or 1i-12 that has been used for each bearer to the second PDCP layer structure or function 1i-20 proposed in the present disclosure for each bearer or with respect to the bearer indicating the DAPS handover method.

[0280] According to another method, when the first condition is met, for each bearer or with respect to the bearer in which the DAPS switching method is indicated, the UE can be handed over from the first PDCP layer structure or function 1i-11 or 1i-12 already used for each bearer to the second PDCP layer structure or function 1i-20 (1i-02) proposed in the present disclosure. In the case where the UE receives a handover command message and the DAPS switching method proposed in the present disclosure is indicated in the handover command message, in the case where the DAPS switching method is indicated for a specific bearer, or in the case where a PDCP reordering timer value is newly set, when the UE is handed over from the first PDCP layer structure or function 1i-11 or 1i-12 to the second PDCP layer structure or function 1i-20 proposed in the present disclosure, for each bearer or with respect to the bearer in which the DAPS switching method is indicated, the UE can update the reordering variable with the PDCP sequence number or count value expected to be received next, and can stop and restart the reordering timer.

[0281] In the case where the second condition proposed in the present disclosure is satisfied when performing the DAPS switching method proposed in the present disclosure, the UE may release the first bearer for the source gNB and may again hand over from the second PDCP layer structure and function 1i-20 applied to each bearer or the bearer in which the DAPS switching method is indicated to the first PDCP layer structure and function 1i-11 or 1i-12. In the case where the second condition is satisfied and the UE hands over from the second PDCP layer structure or function 1i-20 to the first PDCP layer structure or function 1i-11 or 1i-12 proposed in the present disclosure for each bearer or with respect to the bearer in which the DAPS switching method is indicated, the UE may initialize the reordering variable and stop and initialize the reordering timer. The UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source gNB to the data stored in the buffer for reordering (e.g., data received from the source gNB), and may discard the security key or header decompression context of the source gNB. The UE may send the processed data to the upper layer in ascending order. That is, in the event that the second condition is satisfied, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source gNB to the data (e.g., data received from the source gNB) stored in the buffer for reordering, and may discard the security key or header decompression context of the source gNB.

[0282] According to another embodiment, in the case where the second condition proposed in the present disclosure is satisfied when performing the DAPS switching method proposed in the present disclosure, the UE may release the first bearer for the source gNB and may be handed over from the second PDCP layer structure and function 1i-20 applied to each bearer or the bearer in which the DAPS switching method is indicated to the third PDCP layer structure and function 1i-30. In the case where the second condition is satisfied and the UE hands over from the second PDCP layer structure or function 1i-20 to the third PDCP layer structure or function 1i-30 proposed in the present disclosure for each bearer or with respect to the bearer in which the DAPS switching method is indicated, the UE may use the reordering variable and the reordering timer without stopping or initializing the reordering variable and the reordering timer. However, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source gNB to the data (e.g., data received from the source gNB) stored in the buffer for reordering, and may discard the security key or header decompression context of the source gNB. The UE may send the processed data to the upper layer in ascending order. That is, in the event that the second condition is satisfied, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source gNB to the data (e.g., data received from the source gNB) stored in the buffer for reordering, and may discard the security key or header decompression context of the source gNB.

[0283] As disclosed in this Figure 1i As proposed in the specification, when the UE performs switching by applying different first PDCP layer structures and functions 1i-11 or 1i-12, second PDCP layer structures and functions 1i-20 or third PDCP layer structures and functions 1i-30 of the first PDCP layer to each bearer at different times, the UE can minimize data interruption time without losing data.

[0284] Figure 1i The first PDCP layer structure 1i-11 or 1i-12 proposed in the disclosure may have a (1-1)th PDCP layer structure, a (1-2)th PDCP layer structure, a (1-3)th PDCP layer structure or a (1-4)th PDCP layer structure, and the embodiments of the present disclosure may have the following features.

[0285] 1> (In the case of the (1-1) PDCP layer structure) For example, when the UE applies the first PDCP layer structure and function 1i-11 to a PDCP layer (e.g., E-UTRA PDCP layer or LTE PDCP layer) connected to an AM RLC layer (e.g., E-UTRA AM RLC layer), it can have the following characteristics.

[0286] 2> The receiving PDCP layer may first perform out-of-window data detection or duplicate data detection on the received data. (Because RLC AM has retransmission and the sizes of LTE RLC SN and PDCP SN may be different from each other, duplicate data or out-of-window data may be received. The window indicates the area of ​​the PDCP sequence number or count value where valid data is received.)

[0287] 3> The UE performs a decryption process and a header decompression process, and then discards the data outside the window or duplicate data. (Because useful information of the header decompression process (e.g., IR packet or header compression information) can be included, the data outside the window or duplicate data can be identified and then discarded.)

[0288] 2> The UE can directly decrypt the received data that is not discarded without sorting, and can perform the header decompression process. This is because the E-UTRAAM RLC layer arranges the data in sequence and transmits the data to the PDCP layer.

[0289] 2> When data is transmitted to the upper layer, the data is transmitted in ascending order of the count value.

[0290] 1> (In the case of the (1-2) PDCP layer structure) For example, when the UE applies the first PDCP layer structure and function 1i-11 to a PDCP layer (e.g., E-UTRA PDCP layer or LTE PDCP layer) connected to a UM RLC layer (e.g., E-UTRA UM RLC layer), an embodiment of the present disclosure follows the following features.

[0291] 2> No out-of-window data detection or duplicate data detection procedures are performed. This is because the UM E-UTRA RLC layer has no retransmission process.

[0292] 2> Directly perform the decryption process on the received data and perform the header decompression process.

[0293] 2> A reordering process may be performed to transfer data to an upper layer (eg, in ascending order).

[0294] 1> (In the case of the (1-3) PDCP layer structure) For example, when the UE applies the first PDCP layer structure and function 1i-11 to a PDCP layer (for example, an E-UTRA PDCP layer or an LTE PDCP layer) configured as a separated bearer, a packet repetition bearer or an LWA bearer, an embodiment of the present disclosure always applies a reordering process and a reordering timer, and may have the following characteristics.

[0295] 2> Out-of-window data detection for duplicate data detection is first performed on the received data. (Because RLC AM has retransmissions, or data may be received from different RLC layers at different times, and the sizes of LTE RLC SN and PDCP SN may be different, out-of-window data or duplicate data may be received.)

[0296] 3> Perform the decryption procedure. However, do not perform the header decompression process. (This is because E-UTRA PDCP cannot set the header compression protocol for split bearers or LWQ bearers.)

[0297] 3> After performing integrity protection or verification procedures on the data, the data will be discarded. In the event of failure of the integrity verification process, the data can be discarded and reported to the upper layer.

[0298] 3>Out-of-window or duplicate data is discarded.

[0299] 2> When not discarded, the decryption process is performed directly without sorting the received data. In the case where integrity protection or verification is set, integrity verification is performed. After performing the integrity protection or verification procedure on the data, the data is discarded. When the integrity verification process fails, the data can be discarded and reported to the upper layer.

[0300] 2> When sorting is performed on the received data and the data is arranged in ascending order without gaps in the PDCP sequence number or count value, a header compression process is performed and (when the header compression process or decompression process is configured) the data is sent to the upper layer in ascending order.

[0301] 2>When the reorder timer is running,

[0302] 3> When data corresponding to a count value having the same value as a value obtained by subtracting 1 from a value held by a reordering variable is transmitted to an upper layer, or when data is entirely transmitted to an upper layer without a gap in a PDCP sequence number (or count value),

[0303] 4>The reordering timer is stopped and initialized.

[0304] 2> When the reorder timer is not running,

[0305] 3> When there is data stored in the buffer but not transmitted to the upper layer, or when there is a gap in the PDCP sequence number (or count value),

[0306] 4>The reordering timer starts.

[0307] 4> The reordering variable is updated with the PDCP sequence number or count value expected to be received next.

[0308] 2>When the reordering timer expires,

[0309] 3> In the case where the header decompression process is configured in ascending order of the PDCP sequence number or a count value less than the reordering variable value, the header decompression process is performed and the stored data is sent to the upper layer.

[0310] 3> When the header decompression process is configured continuously in ascending order of the PDCP sequence number or count value for a value equal to or greater than the reordering variable value of the stored data, the header decompression process is performed and the stored data is sent to the upper layer.

[0311] 3>The variable value of the data last sent to the upper layer is updated with the PDCP sequence number or count value of the data last sent.

[0312] 3> When there is data stored in the buffer but not transmitted to the upper layer, or when there is a gap in the PDCP sequence number (or count value),

[0313] 4>The reordering timer starts.

[0314] 4> The reordering variable is updated with the PDCP sequence number or count value expected to be received next.

[0315] 1> (In the case of the (1-4) PDCP layer structure) For example, when the UE applies the first PDCP layer structure and function 1i-12 to the NR PDCP layer, the reordering process and reordering timer are always applied, and an embodiment of the present disclosure may have the following characteristics.

[0316] 2>First, perform the decryption process on the received data.

[0317] 2> If the integrity protection or verification process is configured, the integrity protection or verification process can be performed on the received data, and when the integrity verification process fails, the data can be discarded and reported to the upper layer.

[0318] 2> Perform out-of-window data detection or duplicate data detection on the received data. (After performing the decryption process, perform out-of-window data detection or duplicate detection. According to another method, the decryption process is performed only when the integrity protection or verification process is configured, and then the out-of-window data detection or duplicate detection is performed. When the integrity protection or verification process is not configured, the out-of-window data detection or duplicate detection is performed, and then the decryption process is performed on the data that is not discarded.)

[0319] 3>Out-of-window or duplicate data is discarded.

[0320] 2> In the case where data is not discarded, the received data is sorted and the data is arranged in ascending order without gaps in the PDCP sequence number or count value, a header compression process is performed, and (when the header compression process or decompression process is configured) the data is sent to the upper layer in ascending order.

[0321] 2> When data is transmitted to the upper layer, the data is transmitted in ascending order of the count value.

[0322] 2>When the reorder timer is running,

[0323] 3> When data corresponding to a count value having the same value as a value obtained by subtracting 1 from a value held by a reordering variable is transmitted to an upper layer, when data is all transmitted to an upper layer without a gap in a PDCP sequence number (or count value), or when the value of a variable storing a PDCP sequence number or the count value of data to be transmitted to an upper layer is greater than or equal to the value of the reordering variable,

[0324] 4>The reordering timer is stopped and initialized.

[0325] 2> When the reorder timer is not running,

[0326] 3> When there is data stored in the buffer that has not been sent to the upper layer, when there is a gap in the PDCP sequence number (or count value), or when the variable value storing the count value of the first data that has not been sent to the upper layer is less than the reordering variable value,

[0327] 4> The reordering variable is updated with the PDCP sequence number or count value expected to be received next.

[0328] 4>The reordering timer starts.

[0329] 2>When the reordering timer expires,

[0330] 3> In the case where the header decompression process is configured in ascending order of the PDCP sequence number or a count value less than the reordering variable value, the header decompression process is performed and the stored data is sent to the upper layer.

[0331] 3> When the header decompression process is configured continuously in ascending order of the PDCP sequence number or count value for a value equal to or greater than the reordering variable value of the stored data, the header decompression process is performed and the stored data is sent to the upper layer.

[0332] 3> The variable value of the first data not transmitted to the upper layer is updated with the PDCP sequence number or count value of the first data not transmitted to the upper layer.

[0333] 3> When there is data stored in the buffer that has not been sent to the upper layer, when there is a gap in the PDCP sequence number (or count value), or when the variable value storing the count value of the first data that has not been sent to the upper layer is less than the reordering variable value,

[0334] 4> The reordering variable is updated with the PDCP sequence number or count value expected to be received next.

[0335] 4>The reordering timer starts.

[0336] Figure 1i The second PDCP layer structure 1i-20 proposed in the disclosure may have the (2-1)th PDCP layer structure or the (2-2)th PDCP layer structure proposed in the present disclosure, and may have the same features.

[0337] The present disclosure proposes a second PDCP layer structure 1i-20 that is effective in handover. The second PDCP layer structure can be applied to the second embodiment of the effective handover method for minimizing data interruption time proposed in the present disclosure.

[0338] In the second PDCP layer structure, the UE can perform data transmission or reception with the source gNB 1i-21 through the protocol layer of the first bearer (e.g., SDAP layer, PDCP layer, RLC layer, or MAC layer). The UE can perform data transmission or reception with the target gNB 1i-22 through the protocol layer of the second bearer (e.g., SDAP layer, PDCP layer, RLC layer, or MAC layer).

[0339] The PDCP layer of the first bearer and the PDCP layer of the second bearer may be configured in the UE separately, but logically, may be operated as a single PDCP layer device, as in 1i-20. Specifically, the single PDCP layer may divide the functions of the PDCP layer to implement the functions of the upper PDCP layer (e.g., sequence number allocation function, reordering function, in-order delivery function, or duplicate detection function) and the functions of the two lower PDCP layers (e.g., decryption or encryption function, header (or data) compression or header (or data) decompression function, integrity protection or verification function, or duplicate detection function) for each source gNB and each target gNB. In addition, as described above, in the DAPS switching method, when the UE satisfies the first condition when sending uplink data to the source gNB, the UE is handed over to the target gNB, and downlink data may be continuously received from the source gNB and the target gNB. Therefore, the header (or data) compression protocol context may maintain and apply only one context for the source gNB or target gNB for the uplink, and may maintain and apply two contexts for the source gNB or target gNB for the downlink.

[0340] Based on the second PDCP layer structure proposed above, the second PDCP layer structure proposed in the present disclosure (eg, the E-UTRA PDCP layer for the DAPS handover method) may have the following features.

[0341] The upper transmit PDCP layer may be used to assign a PDCP sequence number to data received from an upper layer. In two lower transmit PDCP layer functions 1i-21 and 1i-22 for each source gNB and each gNB, a separate security key set for each source gNB and each target gNB may be used to apply a header (or data) compression context or security key set of the source gNB to data to be sent to the source gNB, and to apply a header (or data) compression context or security key set of the target gNB to data to be sent to the target gNB. In the case where a header (or data) compression process is configured, the header (or data) compression process is applied. In the case where integrity protection is configured, the integrity protection process is applied to the PDCP header and data (PDCP SDU), the ciphering process is applied, the data to be sent to the source gNB is sent to the transmit RLC layer of the first bearer, and the data to be sent to the target gNB is sent to the transmit RLC layer of the second bearer. The two lower transmit PDCP layer functions 1i-21 and 1i-22 may perform parallel data processing, wherein header compression, integrity protection, or ciphering processes are performed in parallel to accelerate data processing speed. In the two lower transmission PDCP layer functions, integrity protection or encryption procedures can be performed by using different security keys. In addition, logically, different data compression, integrity protection or encryption procedures can be performed by applying different compression contexts, security keys or security algorithms within a single transmission PDCP layer.

[0342] In the receiving PDCP layer function, for the data received from each lower layer, specifically, for the data received from the two RLC layers of each source gNB and each target gNB, the out-of-window data detection or duplicate detection process can be independently performed on the data received from each RLC layer based on the PDCP sequence number or count value in the lower receiving PDCP layer functions 1i-21 and 1i-22 of the source gNB or the target gNB. According to another method, for ease of implementation, the out-of-window data detection or duplicate detection process can be performed on all received data without distinguishing the RLC layer based on the PDCP sequence number or count value. According to another method, for more accurate duplicate detection, out-of-window data detection can be performed on all received data without distinguishing the RLC layer based on the PDCP sequence number or count value, and the duplicate detection process can be independently performed on the data received from each RLC layer. According to another method, in the case where the data received from different GNBs overlap with each other, out-of-window data detection can be performed on all received data based on the PDCP sequence number or count value without distinguishing the RLC layer to prevent data loss of the header compression protocol. Furthermore, after performing a decryption process or an integrity protection process or a header (or data) decompression process on data received from each RLC layer, a duplication detection process may be performed on the entire data.

[0343] The lower functions of the receiving PDCP layer may directly apply the decryption procedure on the received data by using separate header (or data) compression context or security key set for each source gNB and each target gNB. In addition, when integrity protection is configured, the lower functions of the receiving PDCP layer may apply integrity verification procedures on the PDCP header and data (PDCP SDU).

[0344] In the (2-1) PDCP layer structure, the header (or data) decompression process can be directly performed on the data received from the RLC layer of the first bearer of each source gNB without sorting. In addition, the header (or data) decompression process can be directly performed on the data received from the RLC layer of the second bearer of each target gNB without sorting. In addition, in order to distinguish the data received from the RLC layer of the first bearer of each source gNB and the data received from the RLC layer of the second bearer of each target gNB, an indicator can be defined for each data to determine whether the data is received from the source gNB or the target gNB. According to another method, a 1-bit indicator of the PDCP header, SDAP header, or RLC header can be defined to determine whether the data is received from the source gNB or the target gNB. In addition, for data received from the RLC layer of the first bearer of the source gNB for which the header (or data) compression process has been completed and data received from the RLC layer of the second bearer of the target gNB, a duplicate detection process (a process of discarding all data except one data (applicable to including data previously received or sent to the upper layer) for each PDCP sequence number or count value) can be performed based on the PDCP sequence number or count value. For data received from the RLC layer of the first bearer for the source gNB and data received from the RLC layer of the second bearer for the target gNB, a reordering process can be performed in ascending order based on the PDCP sequence number or count value, and the data can be sent to the upper layer sequentially. Because a single PDCP layer may receive data from different GNBs, that is, receive data from the first bearer or the second bearer in any order, it may be necessary to always perform the reordering process.

[0345] The two low reception PDCP layer functions can perform parallel data processing, that is, perform header compression, integrity protection or encryption processes in parallel to speed up data processing based on the PDCP sequence number or count value. The integrity protection or encryption process or decompression process can be performed by using different header (or data) compression contexts or security keys. In addition, logically, different data integrity protection or encryption processes or decompression processes can be performed by applying different header (or data) compression contexts or security keys or security algorithms within a single transmission PDCP layer. In addition, in the low reception PDCP layer function, an out-of-order decryption or integrity verification process can be performed on each received data regardless of the order of the PDCP sequence number or count value.

[0346] When distinguishing between the layer of the first bearer and the layer of the second bearer, considering that they are connected to different MAC layers, considering that they have different logical channel identifiers or they are different RLC layers connected to different MAC layers, or considering that different encryption keys are used, a single PDCP layer can use different security keys for uplink data and downlink data to perform an encryption or decryption process in order to distinguish between the layer of the first bearer (or the first RLC layer) and the layer of the second bearer (or the second RLC layer), and compression or decompression can be performed by using different compression protocol contexts.

[0347] Based on the second PDCP layer structure proposed above, the second PDCP layer structure proposed in the present disclosure (e.g., the NR PDCP layer for the DAPS switching method) may have the following characteristics.

[0348] The upper transmit PDCP layer may be used to assign a PDCP sequence number to data received from the upper layer. In two lower transmit PDCP layer functions 1i-21 and 1i-22 for each source gNB and each gNB, a separate security key set for each source gNB and each target gNB may be used to apply the header (or data) compression context or security key set of the source gNB to the data to be sent to the source gNB, and to apply the header (or data) compression context or security key set of the target gNB to the data to be sent to the target gNB. When the header (or data) compression process is configured, the header (or data) compression process is applied. In the case where integrity protection is configured, the integrity protection process is applied to the PDCP header and data (PDCP SDU), the ciphering process is applied, the data to be sent to the source gNB is sent to the transmit RLC layer of the first bearer, and the data to be sent to the target gNB is sent to the transmit RLC layer of the second bearer.

[0349] The two low transmission PDCP layer functions 1i-21 and 1i-22 can perform parallel data processing, wherein header compression, integrity protection or encryption processes are performed in parallel to speed up data processing. In the two low transmission PDCP layer functions, the integrity protection or encryption process can be performed by using different security keys. In addition, logically, different data compression, integrity protection or encryption processes can be performed by applying different compression contexts, security keys or security algorithms within a single transmission PDCP layer.

[0350] In the receiving PDCP layer function, for the data received from each lower layer, specifically, for the data received from the two RLC layers of each source gNB and each target gNB, an out-of-window data detection or duplicate detection process may be independently performed on the data received from each RLC layer based on the PDCP sequence number or count value in the lower receiving PDCP layer functions 1i-21 and 1i-22 of the source gNB or the target gNB. According to another method, for ease of implementation, an out-of-window data detection or duplicate detection process may be performed on all received data without distinguishing the RLC layers based on the PDCP sequence number or count value. According to another method, for more accurate duplicate detection, the receiving PDCP layer may perform out-of-window data detection on all received data without distinguishing the RLC layers based on the PDCP sequence number or count value, and a duplicate detection process may be independently performed on the data received from each RLC layer. According to another embodiment, in the case where data received from different GNBs overlap with each other, the receiving PDCP layer function may perform out-of-window data detection on all received data without distinguishing the RLC layer based on the PDCP sequence number or count value to prevent data loss of the header compression protocol, and may perform a repeated detection process on the entire data after receiving the decryption process, integrity protection process or header (or data) decompression process of the data received from the RLC layer.

[0351] The lower functions of the receiving PDCP layer apply the decryption process directly to the received data by using a separate header (or data) compression context or security key set for each source gNB and each target gNB, and when integrity protection is configured, the integrity verification process can be applied to the PDCP header and data (PDCP SDU).

[0352] In the (2-2) PDCP layer structure, after applying a reordering process to data received from the RLC layer of the first bearer of each source gNB and data received from the RLC layer of the second bearer of each target gNB, a header (or data) decompression process may be performed by applying a header (or data) compression context of each gNB (source gNB or target gNB) to each data received from each gNB (source gNB or target gNB) in ascending order of a PDCP sequence number or count value. In addition, in order to distinguish between data received from the RLC layer of the first bearer of each source gNB and data received from the RLC layer of the second bearer of each target gNB, an indicator may be defined for each data to determine whether the data is received from the source gNB or the target gNB.

[0353] According to another method, a 1-bit indicator of a PDCP header, SDAP header, or RLC header may be defined to determine whether data is received from a source gNB or a target gNB. In addition, for data received from the RLC layer of a first bearer of a source gNB for which a header (or data) compression process has been completed and data received from the RLC layer of a second bearer of a target gNB, a duplicate detection process (a process in which all data except one data (applicable to data previously received or sent to an upper layer) is discarded for each PDCP sequence number or count value) may be performed based on a PDCP sequence number or count value. For data received from the RLC layer of a first bearer for a source gNB and data received from the RLC layer of a second bearer for a target gNB, the data may be sent to an upper layer in ascending order based on a PDCP sequence number or count value. Because a single PDCP layer may receive data from different GNBs, i.e., receive data from a first bearer or a second bearer in any order, it may be necessary to always perform a reordering process.

[0354] The two low reception PDCP layer functions can perform parallel data processing, that is, perform header compression, integrity protection or encryption processes in parallel, so as to speed up data processing based on the PDCP sequence number or count value. In addition, the two low reception PDCP layer functions can perform integrity protection or encryption processes or decompression processes by using different header (or data) compression contexts or security keys. In addition, logically, different data integrity protection or encryption processes or decompression processes can be performed by applying different header (or data) compression contexts or security keys or security algorithms within a single transmission PDCP layer. In addition, in the low reception PDCP layer function, an out-of-order decryption or integrity verification process can be performed on each received data, regardless of the order of the PDCP sequence number or count value.

[0355] When distinguishing between the layer of the first bearer and the layer of the second bearer, considering that they are connected to different MAC layers, considering that they have different logical channel identifiers or they are different RLC layers connected to different MAC layers, or considering that different encryption keys are used, a single PDCP layer can use different security keys for uplink data and downlink data to perform an encryption or decryption process in order to distinguish between the layer of the first bearer (or the first RLC layer) and the layer of the second bearer (or the second RLC layer), and compression or decompression can be performed by using different compression protocol contexts.

[0356] The present disclosure may propose a third PDCP layer structure 1i-30 that is effective in switching. The third PDCP layer structure may be applied to the second embodiment of the effective switching method for minimizing data interruption time proposed in the present disclosure. In addition, the PDCP layer function in the third PDCP layer structure proposed in the present disclosure may be the same as the second PDCP layer structure proposed in the present disclosure. However, the third PDCP layer structure may release the first bearer for the source gNB in ​​the second PDCP layer structure. Specifically, the third PDCP layer structure proposed in the present disclosure has the same function as the second PDCP layer structure proposed above, but may have a structure for releasing the first bearer for the source gNB (e.g., SDAP layer, PDCP layer, RLC layer, or MAC layer). Therefore, the third PDCP layer structure may release the QoS mapping information of the SDAP layer of the source gNB, the security key information of the source gNB of the PDCP layer, the header (or data) compression context information of the source gNB, or the RLC layer or MAC layer of the source gNB.

[0357] Figure 1j is a diagram showing a structure of an effective SDAP layer applied to a DAPS handover method which is a second embodiment of an effective handover method proposed in the present disclosure and a method of applying the structure.

[0358] Figure 1j The specific structure and function of the effective SDAP layer applied to the DAPS switching method are proposed, which is the second embodiment of the effective switching method proposed in the present disclosure, and when performing the DAPS switching process, the structure of the SDAP layer proposed below can be applied to different SDAP layer structures of each bearer at different times.

[0359] For example, before receiving a handover command message from the gNB, the UE processes, sends, or receives data by applying the first SDAP layer structure and function 1j-10 proposed in the present disclosure to each bearer (1j-01). In the first SDAP layer structure and function, the SDAP layer may maintain and apply first mapping information between a QoS flow and a bearer of a source gNB for sending uplink data or receiving downlink data (e.g., a process of reading SDAP header information, updating mapping information, configuring SDAP header, or routing or sending to an appropriate upper or lower layer based on the first mapping information between the QoS flow and the bearer).

[0360] However, in the case where the UE receives a handover command message from the gNB and the DAPS handover method proposed in the present disclosure is indicated in the handover command message, or in the case where the DAPS handover method is indicated for a specific bearer, the UE processes, sends or receives data by applying the second SDAP layer structure and function 1j-20 proposed in the present disclosure to one or more bearers indicating the DAPS handover method (1j-02). That is, in the case where the handover command message is received and the DAPS handover method proposed in the present disclosure is indicated in the handover command message, in the case where the DAPS handover method is indicated for a specific bearer, in the case where the DAPS handover method is configured for at least one bearer, or in the case where the DAPS handover method is configured for a specific bearer, for each bearer or with respect to the bearer in which the DAPS handover method is indicated, the UE can be handed over from the first SDAP layer structure or function 1j-10 already used for each bearer to the second SDAP layer structure or function 1j-20 proposed in the present disclosure.

[0361] According to another method, when the first condition proposed in the present disclosure (for example, when the random access procedure for the target gNB is completed or when the first timer stops) is met, the UE can be handed over from the first SDAP layer structure or function 1j-10 that has been used for each bearer to the second SDAP layer structure or function 1j-20 (1j-02) proposed in the present disclosure for each bearer or with respect to the bearer in which the DAPS switching method is indicated. In the case where the UE receives a switching command message and the DAPS switching method proposed in the present disclosure is indicated in the switching command message, when the DAPS switching method is indicated for a specific bearer, or in the case where the mapping information between the QoS flow and the bearer is newly configured, for each bearer or with respect to the bearer in which the DAPS switching method is indicated, the UE can be handed over from the first SDAP layer structure or function or 1i-10 to the second SDAP layer structure or function 1i-20 proposed in the present disclosure.

[0362] In the second SDAP layer structure, the first mapping information between the QoS flow and the bearer of the existing source gNB is maintained, and the uplink data to be sent to the source gNB and the downlink data to be received from the source gNB are processed. The second mapping information between the newly configured QoS flow and the bearer in the handover command message can be configured for the target gNB, and the UE can use the configured information to process the uplink data to be sent to the target gNB and the downlink data to be received from the target gNB. That is, in the second SDAP layer structure proposed in the present disclosure, the first mapping information between the QoS flow and the bearer of the source gNB or the second mapping information between the QoS flow and the bearer is maintained, and the data of the source gNB and the data of the target gNB are processed separately.

[0363] In addition, in the case where the first condition proposed in the present disclosure is satisfied, for the bearer in which the DAPS switching method is indicated, it is necessary to hand over the uplink data transmission to the target gNB. Therefore, the process of changing, handing over or reconfiguring the first mapping information between the QoS flow and the bearer of the source gNB to the second mapping information between the QoS flow and the bearer of the target gNB can be performed on the uplink. As described above, when the mapping information is changed from the first mapping information between the QoS flow and the bearer to the second mapping information between the QoS flow and the bearer, the UE sends the SDAP control data generated for each changed QoS flow (for example, an end mark indicating that the data is the last data of the changed QoS flow) to the target gNB. Therefore, when the target gNB receives uplink data from the UE, the UE can perform data processing by reflecting the change in the mapping information between the QoS flow and the bearer. The SDAP layer in the second SDAP layer structure can distinguish whether the data received from the lower layer is data received from the source gNB or data received from the target gNB through a 1-bit indicator of the SDAP header, a 1-bit indicator of the PDCP header, or information indicated by the PDCP layer. In the case where the gNB indicates the DAPS switching method for each bearer to the UE with a switching command message, the DAPS switching method is indicated for the default bearer (default DRB). Therefore, during the DAPS switching procedure, in the case where data is generated in a new QoS flow that does not correspond to the mapping information between the QoS flow and the bearer, the UE can always send uplink data to the default bearer. When the DAPS switching method is not configured in the default bearer, uplink data transmission of the new QoS flow generated during the switching is not possible. Therefore, data interruption time may occur.

[0364] In the case where the second condition proposed in the present disclosure is satisfied when executing the DAPS switching method proposed in the present disclosure, the UE may release the first bearer for the source gNB and may again hand over from the second SDAP layer structure and function 1j-20 applied to each bearer or the bearer in which the DAPS switching method is indicated to the first SDAP layer structure and function 1j-10. In the case where the second condition is satisfied, for each bearer or with respect to the bearer in which the DAPS switching method is indicated, the UE may hand over from the second SDAP layer structure or function 1j-20 to the first SDAP layer structure or function 1j-10 proposed in the present disclosure. The UE may maintain the second bearer of the target gNB or the second mapping information between the QoS flow and the bearer. Before releasing the first bearer of the source gNB or the first mapping information between the QoS flow and the bearer, the UE may complete data processing by applying the first mapping information between the QoS flow and the bearer to the data received from the source gNB (e.g., all data received from the source gNB), and then, the first mapping information between the QoS flow and the bearer or the first bearer may be released. The UE may send the processed data to the upper layer in ascending order. That is, in the event that the second condition is satisfied, the UE may process the data (e.g., read SDAP header information, update mapping information, configure SDAP header, or route or send to an appropriate upper layer or lower layer based on the first mapping information between the QoS flow and the bearer) by applying the first mapping information between the QoS flow and the bearer of the source gNB to the data stored in the buffer (e.g., data received from the source gNB), and may discard the first mapping information between the QoS flow and the bearer of the source gNB.

[0365] The SDAP layer may define and apply a 1-bit indicator of a new SDAP header, a 1-bit indicator of a PDCP header, SDAP control data (e.g., a downlink end marker), or information indicated by the PDCP layer. Based on this, the SDAP layer may identify which type of data the last data received from the source gNB is. Therefore, after performing data processing by applying the first mapping information between the QoS flow and the bearer of the source gNB to the last data received from the source gNB, the SDAP layer may discard the first mapping information between the QoS flow and the bearer of the source gNB. The SDAP layer may continue to maintain the second mapping information between the QoS flow and the bearer, and process the uplink data or downlink data to the target gNB based on the mapping information.

[0366] In the present disclosure, when the UE receives Figure 1f When a handover command message is received and the bearer configuration information included in the handover command message is applied, it is proposed to apply the bearer configuration information in different ways according to the handover type indicated in the handover command message.

[0367] -When the UE receives a handover command message and the first handover method (for example, the first embodiment of the present disclosure or the general handover method) is indicated in the handover command message, the ReconfigWithSync information, or the MobilityControlInfo information, when the second embodiment (DAPS handover method) proposed in the present disclosure is not configured, or when the bearer is not configured in the bearer configuration information of the second embodiment (DAPS handover method) proposed in the present disclosure,

[0368] >In case the default bearer is configured in the SDAP layer configuration information configured in the handover command message, the default bearer of the source gNB can be set to the default bearer of the target gNB indicated in the configuration information.

[0369] > In the case where the second mapping information between the QoS flow and the bearer is configured in the SDAP layer configuration information configured in the handover command message, the first mapping information between the QoS flow and the bearer applied by the source gNB may be released, and the second mapping information between the QoS flow and the bearer may be applied. According to another method, the first mapping information between the QoS flow and the bearer applied by the source gNB may be replaced with the second mapping information between the QoS flow and the bearer.

[0370] >In the case where a data discard timer value is set in the PDCP layer configuration information configured in the handover command message, the discard timer value may be directly applied to the PDCP layer corresponding to the bearer identifier of the configuration information.

[0371] > In case the drb-ContinueROHC indicator is set to false in the PDCP layer configuration information configured in the handover command message, a header compression or decompression protocol context may be initialized in the PDCP layer corresponding to the bearer identifier of the configuration information. In case the drb-ContinueROHC indicator is set to true, a header compression or decompression protocol context is not initialized in the PDCP layer corresponding to the bearer identifier of the configuration information.

[0372] >In case the reordering timer value is set in the PDCP layer configuration information configured in the handover command message, the reordering timer value may be directly applied to the PDCP layer corresponding to the bearer identifier of the configuration information.

[0373] >When the handover command message is received, the PDCP layer may be rebuilt. For example, the window state variable may be initialized for the SRB, and the stored data (PDCP SDU or PDCP PDU) may be discarded. The window state variable of the UM DRB may be initialized, and transmission or retransmission may be performed by performing compression or ciphering or integrity protection on the data that has not been sent to the lower layer or the data that the PDCP discard timer has not expired in ascending order of the count value based on the header (or data) compression context or security key of the target gNB. When the reordering timer is running, the reordering timer is stopped and initialized. The received data (PDCP SDU or PDCP PDU) may be processed sequentially and sent to the upper layer. For the AM DRB, the window state variable is not initialized, and transmission or retransmission may be performed by performing compression or ciphering or integrity protection on the first data (PDCP SDU or PDCP PDU) that has not been confirmed to be successfully delivered from the lower layer in ascending order of the PDCP sequence number or count value based on the header (or data) compression context or security key.

[0374] >In the case where security key-related configuration information or security algorithm is set in the security configuration information configured in the handover command message, the UE may derive new security keys or security configuration information by using the configuration information, may release existing security keys or security configuration information, or may replace existing security keys or security configuration information with new security keys or security configuration information.

[0375] > In the event that a new logical channel identifier is configured in the RLC layer configuration information configured in the handover command message, the UE may release the existing logical channel identifier corresponding to the bearer identifier indicated in the RLC layer configuration information, or

[0376] An existing logical channel identifier may be replaced with a new logical channel identifier.

[0377] >In the case where the RLC reestablishment process is configured in the RLC layer configuration information configured in the handover command message, the UE may perform the RLC reestablishment process for the RLC layer corresponding to the bearer identifier indicated in the RLC layer configuration information. That is, specifically, the UE may perform the RLC reestablishment process, and the sending RLC layer may perform the process of discarding all stored data. In addition, in the case where the reordering timer is running, the receiving RLC layer may stop and initialize the reordering timer, and may process all stored data and send the processed data to the upper layer. In addition, the UE may reset the MAC layer. In addition, the UE may reset the MAC layer of the source gNB and use the MAC layer of the target gNB.

[0378] >The MAC layer may be reset, and data transmission or reception of the source gNB and each bearer may be stopped. In addition, the MAC layer may stop PDCCH monitoring of the first UE identifier (C-RNTI) assigned from the source gNB. In addition, the MAC layer may stop the process of requesting scheduling from the source gNB, or may release the transmission resources used for scheduling. The PHY or MAC layer may perform a random access procedure to the target gNB. When the handover procedure to the target gNB is successfully completed, the PHY or MAC layer may resume data transmission or reception to the target gNB, and may start PDCCH monitoring on the second UE identifier (C-RNTI) assigned from the target gNB. The PHY or MAC layer may receive a system frame number from the target gNB and perform synchronization. The PHY or MAC layer may start or perform a process of requesting scheduling from the target gNB.

[0379] >The PHY layer may stop performing the process of channel measurement, channel measurement reporting, or sending HARQ ACK or NACK to the source gNB. The PHY layer performs a downlink synchronization process with respect to the target gNB. The configuration information about the target gNB (or Spcell or pcell) received in the handover command message may be configured in the lower layer or the PHY layer. When the handover process to the target gNB is successfully completed, the PHY layer may start or send HARQ ACK or NACK information to the target gNB. The PHY or MAC layer may receive the system frame number from the target gNB and perform synchronization. The PHY or MAC layer may start or perform a process of requesting scheduling to the target gNB.

[0380] >In the case where the RLC layer configuration information configured in the handover command message is a new configuration, the UE may perform an RLC reestablishment procedure on the RLC layer corresponding to the bearer identifier indicated in the RLC layer configuration information.

[0381] >In the event that a second priority level of a logical channel is newly configured in the MAC layer configuration information configured in the handover command message, the UE may release the first priority level corresponding to the logical channel identifier indicated in the configuration information, or may replace the first priority level corresponding to the logical channel identifier with the second priority level newly configured above.

[0382] >In the case where the second priority bit rate (prioritisedBitRate, PBR) of the logical channel is newly configured in the MAC layer configuration information configured in the handover command message, the UE may release the first priority bit rate (prioritisedBitRate, PBR) corresponding to the logical channel identifier indicated in the configuration information, or may replace the first priority bit rate (prioritisedBitRate, PBR) corresponding to the logical channel identifier with the second priority bit rate (prioritisedBitRate, PBR) newly configured above. The priority bit rate is a value that increases for each logical channel at regular intervals (e.g., TTI). When receiving uplink transmission resources, the UE may perform a logical channel prioritization (LCP) procedure, may send data of the logical channel considering the priority and the priority bit rate, and may send more data as the priority is higher or the value of the priority bit rate is larger.

[0383] > In the case where the second bucket size (bucketSizeDuration) of the logical channel is newly configured in the MAC layer configuration information configured in the handover command message, the UE may release the first bucket size (bucketSizeDuration) corresponding to the logical channel identifier indicated in the configuration information, or may replace the first bucket size (bucketSizeDuration) corresponding to the logical channel identifier with the second bucket size (bucketSizeDuration) newly configured above. The bucket size (bucket size) indicates the maximum value that the priority bit rate can have when the priority bit rate is accumulated.

[0384] >When the second allowed SCell information, allowed subcarrier spacing information, maximum PUSCH period or logical channel group configuration information is configured in the MAC layer configuration information configured in the switching command message, the UE may release the previously configured first allowed SCell information, allowed subcarrier spacing information, maximum PUSCH period or logical channel group configuration information, or may replace the previously configured first allowed SCell information, allowed subcarrier spacing information, maximum PUSCH period, or logical channel group configuration information with the second allowed SCell information, allowed subcarrier spacing information, maximum PUSCH period, or the newly configured logical channel group configuration information above.

[0385] -When the UE receives a handover command message, when the second handover method (for example, the second embodiment of the present disclosure or the DAPS handover method) is indicated or configured in the handover command message, the ReconfigWithSync information, or the mobilityControlInfo information, when the DAPS handover method is indicated or configured for each bearer identifier, when the second embodiment (DAPS handover method) proposed in the present disclosure is configured for a specific bearer in the bearer configuration information, or when the second embodiment (DAPS handover method) proposed in the present disclosure is configured for at least one bearer in the bearer configuration information,

[0386] > In the case where the default bearer is configured in the SDAP layer configuration information configured in the handover command message, the UE may perform the DAPS handover method proposed above in the present disclosure, may apply the second SDAP layer structure to maintain the default bearer of the existing source gNB, and may configure the default bearer information indicated in the configuration information as the default bearer of the target gNB. According to another method, when the first condition proposed in the present disclosure is met, the UE may hand over the default bearer of the existing source gNB to the default bearer of the target gNB indicated in the configuration information.

[0387] > In the case where the second mapping information between the QoS flow and the bearer is configured in the SDAP layer configuration information configured in the handover command message, the UE may perform the DAPS handover method proposed above in the present disclosure, and may apply the second SDAP layer structure to maintain the first mapping information between the QoS flow and the bearer applied for the source gNB, and may apply the second mapping information between the QoS flow and the bearer to the data of the target gNB. According to another method, in the case where the first condition proposed in the present disclosure is met, the UE may apply the second mapping information between the QoS flow and the bearer of the target gNB.

[0388] >In the case where the data discard timer value is set in the PDCP layer configuration information configured in the handover command message, the UE can execute the DAPS handover method proposed above in the present disclosure and apply the second PDCP layer structure to directly apply the discard timer value to the PDCP layer corresponding to the bearer identifier of the configuration information.

[0389] >The PDCP layer indicating or configuring the DAPS handover method in the handover command message is not reestablished, and the following procedures may be performed. For example, for SRBs, the UE may initialize the window state variable (variable initialization may be omitted for fallback when DAPS handover fails) or may discard the stored data (PDCP SDU or PDCP PDU). For UM DRBs, the UE may continue to perform data transmission or reception with the source gNB for data that has not been sent to the lower layer or for which the PDCP discard timer has not expired, without initializing the window state variable. For AM DRBs, the UE may continue to perform data transmission or reception with the source gNB, without initializing the window state variable.

[0390] >The PDCP layer for which the DAPS handover method is not indicated or configured in the handover command message may reestablish the PDCP layer. For example, the UE may initialize the window state variable for the SRB and may discard the stored data (PDCP SDU or PDCP PDU). The UE may initialize the window state variable for the UM DRB and may perform transmission or retransmission by performing compression or ciphering or integrity protection on the data that has not been sent to the lower layer or the data for which the PDCP discard timer has not expired in ascending order of the count value based on the header (or data) compression context or security key of the target gNB. When the reordering timer is running, the UE may stop or initialize the reordering timer. The UE may process the received data (PDCP SDU or PDCP PDU) sequentially and send the processed data to the upper layer. For the AM DRB, the UE may not initialize the window state variable and may perform transmission or retransmission by performing compression or ciphering or integrity protection on the first data (PDCP SDU or PDCP PDU) that has not been confirmed to be successfully transmitted from the lower layer in ascending order of the PDCP sequence number or count value based on the header (or data) compression context or security key. In addition, the RLC layer may also perform the reestablishment process.

[0391] >In a case where the drb-ContinueROHC indicator is set to false in the PDCP layer configuration information in which the DAPS handover method is indicated or configured in the handover command message, the UE may perform the DAPS handover method proposed above in the present disclosure, and may apply the second PDCP layer structure to use the header compression or decompression protocol context of the source gNB, as in the PDCP layer corresponding to the bearer identifier of the configuration information, to initialize the header compression or decompression protocol context of the target gNB and start from an initial state (e.g., IR state). In a case where the drb-ContinueROHC indicator is set to true, the UE may perform the DAPS handover method proposed above in the present disclosure, and may apply the second PDCP layer structure to use the header compression or decompression protocol context of the source gNB, as in the PDCP layer corresponding to the bearer identifier of the configuration information, to apply the header compression or decompression protocol context of the target gNB identically to the header compression or decompression protocol context of the source gNB. For example, the header compression or decompression protocol context of the source gNB may be applied as is by being copied to the header compression or decompression protocol context of the target gNB. According to another approach, the same header compression or decompression protocol context may be applied to either the target gNB or the source gNB.

[0392] >In the case where the DAPS switching method is indicated in the switching command message, or when the reordering timer value is set in the configured PDCP layer configuration information, the UE can perform the DAPS switching method proposed above in the present disclosure, and can apply the second PDCP layer structure to directly apply the reordering timer value to the PDCP layer corresponding to the bearer identifier of the configuration information.

[0393] >In the case where security key-related configuration information or a security algorithm is configured in the security configuration information indicating or configuring the DAPS handover method in the handover command message, or in the case where there is an indicator indicating a new process in the PDCP layer configuration information, the UE can derive new security keys or security configuration information by using the configuration information, can perform the DAPS handover method proposed above in the present disclosure, can apply the second PDCP layer structure to maintain the existing security keys or security configuration information of the source gNB, and can configure the security keys or security configuration information of the target gNB as new security keys or security configuration information.

[0394] >In a case where a new logical channel identifier is configured in the RLC layer configuration information of a bearer for which a DAPS switching method is indicated in a switching command message or configured, the UE may perform the DAPS switching method proposed above in the present disclosure, may apply a second PDCP layer structure to maintain an existing logical channel identifier of the RLC layer or MAC layer of the first bearer of the source gNB corresponding to the bearer identifier indicated in the RLC layer configuration information, and may configure a new logical channel identifier indicated in the RLC layer or MAC layer configuration information for the second bearer of the target gNB.

[0395] >In the RLC layer configuration information of the bearer for which the DAPS switching method is indicated or configured in the switching command message, the UE may not perform the RLC layer RLC reestablishment process on the source gNB. Specifically, the sending RLC layer may continue to send the stored data without performing the RLC reestablishment process. In addition, the receiving RLC layer may continuously process the stored data and the received data, so that there is no data interruption time. However, in the case where the first condition proposed in the present disclosure is met, according to the method proposed in the present disclosure, the PDCP layer for which the DAPS switching method is configured may send a data discard indicator for PDCP user data (PDCP data PDU) to indicate the discard of data (PDCP data PDU) about the AM bearer or UM bearer to the RLC layer of the source gNB, so that the RLC layer of the source gNB discards the PDCP data PDU, but may send the PDCP control PDU without discarding the PDCP control PDU.

[0396] >The PLC reconstruction process may be performed on the RLC layer of the bearer, where the DAPS handover method configured in the handover command message is not indicated or configured. In the case where the RLC reconstruction process is configured, the RLC reconstruction process may be performed. That is, specifically, the RLC reconstruction process is performed so that the sending RLC layer may perform a process of discarding all stored data (PDCP data PDU or PDCP control PDU). In addition, in the case where the reordering timer is running, the receiving RLC layer may stop and initialize the reordering timer, and may process all stored data and send the processed data to the upper layer.

[0397] >In a case where a new logical channel identifier is configured in the RLC layer configuration information of a bearer for which a DAPS switching method is indicated in a switching command message or configured, the UE may perform the DAPS switching method proposed above in the present disclosure, may apply a second PDCP layer structure to maintain an existing logical channel identifier of the RLC layer or MAC layer of the first bearer of the source gNB corresponding to the bearer identifier indicated in the RLC layer configuration information, and may configure a new logical channel identifier indicated in the RLC layer or MAC layer configuration information for the second bearer of the target gNB.

[0398] > In the case where the RLC layer configuration information of the bearer for which the DAPS handover method is indicated or configured in the handover command message is newly configured, the DAPS handover method proposed above in the present disclosure may be performed and the second PDCP layer structure may be applied. Therefore, for the RLC layer of the first bearer of the source gNB corresponding to the bearer identifier indicated in the RLC layer configuration information, the existing RLC configuration information may be maintained. For the RLC layer of the second bearer of the target gNB, the new RLC layer configuration information indicated in the configuration information may be configured.

[0399] >The present disclosure can be implemented Figure 1k Method 1, method 2 or method 3 for configuring the MAC layer proposed in.

[0400] >Execute Figure 1k The MAC layer is configured according to method 1, method 2 or method 3 proposed in , and for the bearer in which the DAPS switching method is indicated or configured in the MAC layer, data transmission or reception can be continuously performed. The MAC layer is not reset, and for the bearer in which the DAPS switching method is not indicated or configured, data transmission or reception can be stopped.

[0401] >PDCCH monitoring of the first UE identifier (C-RNTI) assigned from the source gNB may be continuously performed without resetting the MAC layer of the source gNB. In addition, the MAC layer of the source gNB may continue to perform a scheduling request to the source gNB. The PHY or MAC layer of the target gNB may apply the configuration to the configuration information to be received in the handover command message and perform a random access procedure to the target gNB. When the handover procedure to the target gNB is successfully completed, the PHY or MAC layer of the target gNB may start data transmission or reception to the target gNB and may start PDCCH monitoring of the second UE identifier (C-RNTI) assigned from the target gNB. The PHY or MAC layer may receive a system frame number from the target gNB and perform synchronization. The PHY or MAC layer of the target gNB may start or perform a procedure to request scheduling to the target gNB. Until the connection with the source gNB is released or until the second condition proposed in the present disclosure is satisfied, the UE may perform PDCCH monitoring for the first UE identifier allocated from the source gNB in ​​the PHY or MAC layer of the source gNB, and may perform PDCCH monitoring for the second UE identifier allocated from the target gNB in ​​the PHY or MAC layer of the target gNB. When the connection with the source gNB is released, or when the second condition proposed in the present disclosure is satisfied, the UE may stop PDCCH monitoring for the first UE identifier allocated from the source gNB in ​​the PHY or MAC layer of the source gNB, or may release the transmission resources for the scheduling request.

[0402] >The PHY layer of the source gNB may continue to perform the process of maintaining configuration information, performing channel measurement of the source gNB, performing channel measurement reporting, or sending HARQ ACK or NACK. The PHY or MAC layer of the target gNB performs a downlink synchronization process with respect to the target gNB. The PHY or MAC layer of the target gNB may configure the configuration information about the target gNB (or Spcell or Pcell) received in the handover command message in the lower layer or PHY layer of the target gNB. When the handover process to the target gNB is successfully completed, the PHY or MAC layer of the target gNB may start or send HARQ ACK or NACK information to the target gNB. The PHY or MAC layer of the target gNB may receive the system frame number from the target gNB and perform synchronization. The PHY or MAC layer of the target gNB may start or perform a process of requesting scheduling to the target gNB, a process of performing channel measurement, or a process of reporting channel measurement results. Until the connection with the source gNB is released or until the second condition proposed in the present disclosure is satisfied, the UE may perform PDCCH monitoring for the first UE identifier allocated from the source gNB in ​​the PHY or MAC layer of the source gNB, and may perform PDCCH monitoring for the second UE identifier allocated from the target gNB in ​​the PHY or MAC layer of the target gNB. When the connection with the source gNB is released, or when the second condition proposed in the present disclosure is satisfied, the UE may stop PDCCH monitoring for the first UE identifier allocated from the source gNB in ​​the PHY or MAC layer of the source gNB, or may release the transmission resources for the scheduling request.

[0403] >The present disclosure can be implemented Figure 1k Method 1, method 2 or method 3 for configuring or processing SRB proposed in.

[0404] >In the case where the second priority of the logical channel is newly configured in the MAC layer configuration information configured in the handover command message, the DAPS handover method proposed above in the present disclosure may be performed and the second PDCP layer structure may be applied. The existing configuration information may be maintained for the MAC layer of the first bearer of the source gNB corresponding to the indicated bearer identifier, and the new logical channel identifier indicated in the configuration information may be configured for the MAC layer of the second bearer of the target gNB. The newly configured second priority corresponding to the logical channel identifier indicated in the configuration information may be configured. According to another method, when the first condition proposed in the present disclosure is met, for each logical channel identifier, the priority may be applied to the MAC layer of the second bearer of the target gNB.

[0405] > In the case where a second priority bit rate (priority bit rate, PBR) of a logical channel is newly configured in the MAC layer configuration information configured in the handover command message, the UE may perform the DAPS handover method proposed above in the present disclosure. A second PDCP layer structure may be applied, the existing configuration information may be maintained for the MAC layer of the first bearer of the source gNB corresponding to the indicated bearer identifier, and the new logical channel identifier indicated in the configuration information may be configured for the MAC layer of the second bearer of the target gNB. The newly configured second priority bit rate corresponding to the logical channel identifier indicated in the configuration information may be configured. According to another method, in the case where the first condition proposed in the present disclosure is met, the second priority bit rate may be started to be applied to the logical channel identifier in the MAC layer of the second bearer of the target gNB (so that uplink transmission resources can be fairly allocated when different handover methods are indicated for each bearer). When started to be applied to each logical channel identifier, the priority bit rate is a value that is increased for each logical channel every specific time (e.g., TTI). When uplink transmission resources are received, an LCP procedure may be performed. Data of the logical channel may be sent taking into account the priority and the priority bit rate. When the priority is higher or the value of the priority bit rate is larger, more data can be transmitted.

[0406] > In addition, in the case where the DAPS handover method is applied, when the first condition proposed in the present disclosure is not yet satisfied, and therefore the UE needs to send uplink data through the first bearer for the source gNB, when performing the LCP process, the MAC layer of the first bearer may select only the bearer or logical channel identifier in which the DAPS handover method (or the handover method that can continue to send data to the source gNB even after receiving the handover command message) is indicated as the target of the LCP process, and perform the LCP process. For the bearer or logical channel identifier to which the DAPS handover method is not applied, when the handover command message is received, the uplink data may not be sent to the source gNB. Therefore, the bearer or logical channel identifier should not be selected as the target of the LCP process.

[0407] >In the case where a second bucket size (bucketSizeDuration) of a logical channel is newly configured in the MAC layer configuration information configured in the handover command message, the UE may perform the DAPS handover method proposed above in the present disclosure. A second PDCP layer structure may be applied. The existing configuration information may be maintained for the MAC layer of the first bearer of the source gNB corresponding to the above-mentioned bearer identifier. The new logical channel identifier indicated in the configuration information may be configured for the MAC layer of the second bearer of the target gNB. The newly configured second bucket size corresponding to the logical channel identifier indicated in the configuration information may be configured. According to another method, when the first condition proposed in the present disclosure is met, the second bucket size may be applied to the logical channel identifier in the MAC layer of the second bearer of the target gNB (so that uplink transmission resources may be fairly allocated when different handover methods are indicated for each bearer). The bucket size indicates the maximum value that the priority bit rate may have when the priority bit rate accumulates.

[0408] >When the second allowed SCell information, allowed subcarrier spacing information, maximum PUSCH period or logical channel group configuration information is configured in the MAC layer configuration information configured in the switching command message, the UE executes the DAPS switching method proposed in the present disclosure, and can apply the second PDCP layer structure to maintain the existing configuration information of the MAC layer of the first bearer of the source gNB corresponding to the above-mentioned bearer identifier, and can configure the second allowed SCell information, allowed subcarrier spacing information, maximum PUSCH period or logical channel group configuration information indicated in the MAC layer configuration information of the second bearer of the target gNB.

[0409] Figure 1k is a diagram illustrating a method of applying bearer specific configuration information when configuring a DAPS switching method according to an embodiment of the present disclosure.

[0410] As disclosed in this Figure 1kAs proposed in the present disclosure, when the UE receives a handover command message (1k-01), when the second handover method (for example, the second embodiment of the present disclosure or the DAPS handover method) is indicated in the ReconfigWithSync information, when the DAPS handover method is indicated for each bearer identifier or logical channel identifier, when the DAPS handover method is configured for at least one bearer, or when the DAPS handover method is configured for a specific bearer, the UE may generate or establish a MAC layer for the target gNB (or target cell) when receiving the handover command message. From the time the handover command message is received until the first condition proposed in the present disclosure is met, the UE may continue to send or receive data with the source gNB only for the bearer (AM bearer or UM bearer) in which the DAPS handover method is indicated by the MAC layer of the source gNB (or source cell). When the first condition is met, the UE may hand over the uplink data to the target gNB and may receive the downlink data from the source gNB until the connection with the source gNB is released. However, for a bearer in which the DAPS switching method is not indicated, the UE can continuously perform data transmission or reception with the source gNB from the time the switching command message is received until the first condition proposed in the present disclosure is satisfied. Therefore, in order for the UE to perform the operation proposed in the present disclosure, one or more of the following methods may be applied and may be modeled as 1k-21 or 1k-22. When the second condition proposed in the present disclosure is satisfied and the source gNB is released, it may be modeled as 1k-31 or 1k-32.

[0411] -When the UE receives the handover command message proposed in the present disclosure and the second handover method (e.g., the second embodiment of the present disclosure or the DAPS handover method) is indicated in the ReconfigWithSync information, when the DAPS handover method is indicated for each bearer identifier or logical channel identifier, when the DAPS handover method is configured for at least one bearer, or when the DAPS handover method is configured for a specific bearer, the SRB configured for the source gNB in ​​the MAC layer may be stopped. The upper layer (e.g., RRC layer device) of the UE may instruct the MAC layer of the source gNB to perform reconfiguration (MAC reconfiguration) using configuration information other than configuration information related to the bearer for which the DAPS handover method is not indicated in the handover command message in the configuration information of the current MAC layer. According to another method, the upper layer (e.g., RRC layer) of the UE may instruct the MAC layer of the source gNB to perform reconfiguration (MAC reconfiguration) using configuration information that includes only configuration information related to the bearer for which the DAPS handover method is indicated in the handover command message in the configuration information of the current MAC layer. When the UE reconfigures the MAC layer for the source gNB, the MAC layer of the source gNB of the UE may maintain only the logical channel identifier indicating the DAPS switching method, or the priority bit rate or bucket size corresponding to the logical channel identifier, and may release, no longer use, or no longer apply the logical channel identifier corresponding to the bearer that does not indicate the DAPS switching method, or the priority bit rate or bucket size corresponding to the logical channel identifier. In addition, the upper layer of the UE (e.g., the RRC layer) may perform a PDCP reestablishment procedure or an RLC reestablishment procedure on the bearer that does not indicate the DAPS switching method, may apply the PDCP configuration information or RLC configuration information configured in the switching message, or may stop the bearer. Optionally, the upper layer of the UE may stop the bearer in the MAC layer of the source gNB, or may be configured in the MAC layer of the target gNB (when the first condition is met, it may be configured in the MAC layer of the target gNB). In the handover command message, the MAC layer of the target gNB may be indicated so that, for a bearer in which the DAPS handover method is not indicated, the bearer configuration information (such as a logical channel identifier, a priority bit rate, or a bucket size) configured for the target gNB is configured or applied to the MAC layer of the target gNB. Optionally, the upper layer of the UE may hand over the connection of the PDCP layer or the RLC layer corresponding to the bearer in which the DAPS handover method is not indicated from the MAC layer of the source gNB to the MAC layer of the target gNB. In this case, when the MAC layer of the source gNB for the UE performs an LCP procedure for data transmission from this point in time, only the logical channel identifier corresponding to the bearer in which the DAPS handover method is indicated is selected as a candidate group, and the LCP procedure may be performed thereon.The process of reconfiguring the MAC layer of the source gNB performed by the upper layer (e.g., the RRC layer) may partially reset the MAC layer of the source gNB (partial MAC reset) to perform the same process. For example, the configuration information of the MAC layer of the bearer in which the DAPS switching method is not indicated may be initialized or released, or its application may be stopped. Data transmission or reception with the source gNB may be performed until the first condition proposed in the present disclosure is met. For the logical channel identifier corresponding to the bearer in which the DAPS switching method is not indicated, the MAC layer of the source gNB may first initialize the bit rate, may no longer apply the priority bit rate accumulation calculation process, and may release or stop the bearer. In addition, for the logical channel identifier corresponding to the bearer indicating the DAPS switching method, the MAC layer of the source gNB may continue to maintain the priority bit rate, and may perform the accumulation calculation process. When the first condition is met, the data transmission may be handed over to the target gNB. The MAC layer of the target gNB may initialize a priority bit rate or may start cumulative calculation for a newly configured logical channel identifier (a logical channel identifier corresponding to a bearer indicating a DAPS switching method or a bearer not indicating a DAPS switching method) (according to another method, when a switching command message for the MAC layer of the target gNB is received, the priority bit rate may be initialized and the cumulative calculation may be started). When a bearer not indicating a DAPS switching method has been configured or has been stopped, the MAC layer of the target gNB may be configured or restored to perform data transmission or reception with the target gNB, and the priority bit rate may be initialized or cumulative calculation may be started. Data reception is performed from the source gNB or the target gNB until the second condition proposed in the present disclosure is met. When the second condition is met (1k-03), the MAC layer of the source gNB is reset. The RLC layer, the PDCP layer, or the bearer configuration information corresponding to the bearer in which the DAPS switching method connected to the MAC layer of the source gNB is not indicated may be released from the MAC layer of the source gNB. The RLC layer or bearer configuration information corresponding to the bearer indicating the DAPS switching method can be released from the second PDCP layer structure or MAC layer of the source gNB (1k-31 or 1k-32). In the case where the switching process fails and the connection with the source gNB is valid, as proposed below in the present disclosure, the UE can perform a fallback process to the source gNB (1k-02), can restore the SRB configured in the MAC layer of the source gNB, can report the switching failure, can apply the existing bearer configuration information of the source gNB before receiving the switching command message again, can apply the configuration information of the original MAC layer (for example, the RRC layer can reconfigure the MAC layer configuration information used before receiving the switching command message for MAC layer configuration), and can resume data transmission or reception with the source gNB for each bearer (1k-10).According to another method, an upper layer (e.g., an RRC layer) of the UE may indicate an RLC reestablishment procedure for a bearer indicating a DAPS switching method or a bearer not indicated. According to another method, when the source gNB performs a DAPS switching method, configuration information of the MAC layer of the source gNB to be applied may be set as an RRC message.

[0412] In the method proposed in the present disclosure, when the UE receives a switching command message, when a second switching method (for example, the second embodiment of the present disclosure or a DAPS switching method) is indicated in the ReconfigWithSync information, when a DAPS switching method is indicated for each bearer identifier or logical channel identifier, when the DAPS switching method is configured for at least one bearer, or when the DAPS switching method is configured for a specific bearer, the SRB configured in the MAC layer of the source gNB can apply one or more of the following methods.

[0413] - In a case where the UE receives a handover command message, when the second handover method (for example, the second embodiment of the present disclosure or the DAPS handover method) is indicated in the ReconfigWithSync information, when the DAPS handover method is indicated for each bearer identifier or logical channel identifier, when the DAPS handover method is configured for at least one bearer, or when the DAPS handover method is configured for a specific bearer,

[0414] >Method 1: The SRB may be stopped in the MAC layer of the source gNB. Alternatively, the window state variable may be initialized by performing an RLC layer reestablishment process or a PDCP layer reestablishment process for the SRB, and the stored data (PDCP SDU, PDCP PDU, RLC SDU, or RLC PDU) may be discarded. Alternatively, the SRB may be configured in the MAC layer of the target gNB according to the configuration received in the handover message. According to another method, the SRB of the MAC layer of the source gNB may be configured according to the configuration received in the handover message, and may be handed over and connected to the MAC layer of the target gNB. When the UE handover process fails and a fallback process is performed, the UE may restore the SRB stopped in the MAC layer of the source gNB, or reconfigure the SRB configured in the target gNB to the existing configuration of the source gNB, and may be handed over and connected to the MAC layer of the source gNB and restored.

[0415] >Method 2: The SRB in the MAC layer of the source gNB may be stopped. Optionally, the RLC layer re-establishment process or the PDCP layer re-establishment process of the SRB may be stopped and not performed. Alternatively, the SRB may be configured in the MAC layer of the target gNB according to the configuration received in the handover message. According to another method, the SRB of the MAC layer of the source gNB may be configured according to the configuration received in the handover message, and may be handed over and connected to the MAC layer of the target gNB. When the UE handover process fails and the fallback process is performed, the UE may restore the SRB stopped in the MAC layer of the source gNB, or reconfigure the SRB configured in the target gNB to the existing configuration of the source gNB, and may be handed over and connected to the MAC layer of the source gNB and restored.

[0416] >Method 3: The SRB may be stopped in the MAC layer of the source gNB. Optionally, the RLC layer reestablishment process of the PDCP layer reestablishment process of the SRB is not performed, and the window state variable is not initialized, but the stored data (PDCP SDU, PDCP PDU, RLC SDU, or RLC PDU) may be discarded (in order to prevent the unsent RRC message from being sent unnecessarily later). Alternatively, the SRB may be configured in the MAC layer of the target gNB according to the configuration received in the handover message. According to another method, the SRB of the MAC layer of the source gNB may be configured according to the configuration received in the handover message, and may be handed over and connected to the MAC layer of the target gNB. When the UE handover process fails and the fallback process is performed, the UE may restore the SRB stopped in the MAC layer of the source gNB, or reconfigure the SRB configured in the target gNB to the existing configuration of the source gNB, and may be handed over and connected to the MAC layer of the source gNB and restored.

[0417] The present disclosure proposes a method for quickly falling back to the source gNB and reconfiguring the connection by using the features of the DAPS handover method proposed above when the UE performs the second embodiment of the effective handover method proposed in the present disclosure (DAPS handover method) and the UE handover fails. Specifically, the features of the DAPS handover method proposed in the present disclosure may mean that data transmission or reception is performed while maintaining the connection with the source gNB even when the handover process is performed. In the following present disclosure, it is specifically proposed to use a fallback to a wireless connection connected to an existing source gNB even when the handover fails.

[0418] As referenced in this disclosure Figure 1hAs described, in the second embodiment of the effective handover method (DAPS handover method), even when the UE receives a handover command message from the source gNB, the UE can perform a handover process to the target gNB while maintaining data transmission or reception with the source gNB, as proposed in 1h-02. In addition, the present disclosure proposes a process of falling back to the source gNB when the handover process to the target gNB fails.

[0419] As described above, in the case where the handover process of the UE to the target gNB fails, a method of determining whether the radio connection between the UE and the source gNB is valid is required in order to fall back to the source gNB. In the case where the radio connection between the UE and the source gNB is invalid, the UE handover fails, and when the fallback to the source gNB is performed, the fallback to the source gNB also fails. As a result, the data interruption time is excessively increased, resulting in a large amount of data loss. In addition, in the case where the radio connection between the UE and the source gNB is valid, it is also necessary to maintain the SRB configured in the UE and the source gNB.

[0420] First, the present disclosure proposes a new timer applicable to a handover method and a specific operation of the timer. In addition, according to the present disclosure, the specific operation of the timer can be different from each other according to the type of handover method indicated by the handover command message in the gNB. In addition, a method of releasing or maintaining a connection with a source gNB or SRB configuration according to a handover method is proposed.

[0421] In the present disclosure, in order to effectively perform the switching process, a first timer (e.g., T304), a second timer (e.g., T310), a third timer (e.g., T312), or a fourth timer (e.g., a timer for fallback) can be introduced and can be driven and applied during the switching process. According to the type of switching method indicated by the switching command message, the first timer (e.g., T304), the second timer (e.g., T310), the third timer (e.g., T312), or the fourth timer (e.g., a timer for fallback) proposed in the present disclosure can perform different operations as follows. For example, the first timer (e.g., T304) is a timer for determining whether the switching has been successfully performed. In addition, the second timer (e.g., T310) is a timer for determining whether the wireless connection is valid. In addition, the third timer (e.g., T312) is an auxiliary timer for determining whether the wireless connection is valid, and a timer for triggering a frequency measurement process and reporting a frequency measurement result. The fourth timer (e.g., a timer for fallback) is a timer for performing a fallback procedure to the source gNB when a handover fails when performing the second embodiment (DAPS handover method) of the effective handover method proposed in the present disclosure, sending a message to the source gNB indicating that a handover failure has been performed, and determining whether the fallback procedure has been successfully performed or has failed.

[0422] According to the indicated switching method, the specific operation of the first timer (e.g., T304), the second timer (e.g., T310), the third timer (e.g., T312) or the fourth timer (e.g., a timer for fallback) proposed in the present disclosure to support an effective switching method is proposed as follows.

[0423] 1> The UE receives an out-of-sync indication indicating that the synchronization of the radio connection signal does not match a certain number of times (for example, this can be set by the gNB) from a lower layer (for example, the MAC layer or the PHY layer), and when a problem in the physical layer is detected, a second timer (for example, T310) can be started when the first timer is not running. When receiving an in-sync indication indicating that the synchronization of the radio connection signal matches well from the lower layer a certain number of times (for example, this can be set by the gNB), when the handover process is triggered (started), or when the RRC connection reestablishment process starts, the UE stops the second timer. When the second timer expires, the UE triggers or starts the RRC connection reestablishment process. Alternatively, the UE transitions to the RRC idle mode and triggers or starts the RRC connection reestablishment process.

[0424] 1> When a frequency measurement procedure is triggered for a frequency measurement identifier configured for a third timer while the second timer is running, the UE starts the third timer. When a synchronization indication indicating a good synchronization match of a radio connection signal is received from a lower layer a certain number of times (for example, this can be set by the gNB), when a handover procedure is triggered (started), or when an RRC connection reestablishment procedure is started, the UE stops the third timer. When the third timer expires, the UE triggers or starts an RRC connection reestablishment procedure. Alternatively, the UE transitions to RRC idle mode and triggers or starts an RRC connection reestablishment procedure.

[0425] 1> In a case where the first handover method (for example, the first embodiment or the general handover method) is indicated in a handover command message (a message including a mobility indication (MobilityControl info or ReconfigurationWithSync) or a handover indication in an RRC Reconfiguration message) received by the UE from the gNB, when the UE receives the handover command message and the first handover method (for example, when the second embodiment (DAPS handover method) proposed in the present disclosure is not configured, or when the second embodiment (DAPS handover method) proposed in the present disclosure is not configured for a specific bearer in the bearer configuration information,

[0426] 2> In the present disclosure, when receiving a handover command message (a message including a mobility indication (MobilityControl info or ReconfigurationWithSync) or a handover indication in a RRC Reconfiguration message), the UE triggers the handover process and starts a first timer.

[0427] 2> When the handover process is triggered, the UE releases the SRB configured for the source gNB (e.g., SRB1) and configures the SRB for the target gNB (e.g., SRB1) based on the configuration information configured in the handover command message.

[0428] 2> When the handover process is triggered, when the second timer is running, the UE stops the second timer. When the first timer is running, even if the condition for starting the second timer is met (when the asynchronous indicator of the radio connection signal is received from the lower layer a certain number of times), the second timer may not be started. That is, when the first timer is running, the second timer may not be used.

[0429] 2> When the handover process is triggered, when the third timer is running, the UE stops the third timer. Only when the second timer is running, the UE can start the third timer when the condition for starting the third timer is met (when the frequency measurement process is triggered for the frequency measurement identifier configured with the third timer). That is, because the second timer is not used when the first timer is running, the third timer may not be used.

[0430] 2> When the UE successfully completes the handover procedure to the target gNB, or when the UE successfully completes the random access procedure, the UE stops the first timer.

[0431] 2> When the first timer expires (for example, when the handover process to the target gNB fails), the UE performs the RRC connection reestablishment process (releases the connection with the gNB and performs the RRC connection process again from the beginning, i.e., a cell selection or reselection process may be performed, a random access process may be performed, and an RRC connection reestablishment request message may be sent).

[0432] 1> In a case where the second handover method (for example, the second embodiment or the DAPS handover method) is indicated in a handover command message (a message including a mobility indication (MobilityControl info or ReconfigurationWithSync) or a handover indication in a RRC Reconfiguration message) received by the UE from the gNB (or even when the conditional handover method is indicated together, it is extended and applied), when the second embodiment (DAPS handover method) proposed in the present disclosure is configured in the handover command message, the ReconfigWithSync information, and the MobilityControlInfo information, when the UE receives the handover command message, when the second embodiment (DAPS handover method) proposed in the present disclosure is a specific bearer configuration in the bearer configuration information, or when the second embodiment (DAPS handover method) proposed in the present disclosure is at least one bearer configuration in the bearer configuration information,

[0433] 2> In the present disclosure, when the UE receives a handover command message (a message including a mobility indication (MobilityControl info or ReconfigurationWithSync) or a handover indication in a RRC Reconfiguartion message), the UE triggers the handover process and starts the first timer. When the conditional handover method is indicated together, when the handover process starts or the random access process is performed, the UE can select a cell from multiple target cells and start the first timer.

[0434] 2> When the handover process is triggered, the UE maintains or stops the SRB (e.g., SRB1) configured for the source gNB at the start of the DAPS handover method, and can configure the SRB (e.g., SRB1) for the target gNB based on the configuration information configured in the handover command message. According to another method, when the handover process is triggered, the UE maintains or stops the SRB (e.g., SRB1) configured for the source gNB at the start of the DAPS handover method, initializes the window state variable by reestablishing the PDCP layer or reestablishing the RLC layer for the SRB of the source gNB, stops the timer and instructs the discarding of the stored data (PDCP SDU or PDCP PDU) (this can be performed when the fallback process proposed in the present disclosure is triggered), and configures the SRB (e.g., SRB1) of the target gNB based on the configuration information configured in the handover command message. According to another method, by applying the second PDCP layer structure proposed in the present disclosure to the SRB, the UE can configure a first bearer for the source gNB and a second bearer for the target gNB. According to another method, when the second PDCP layer structure is applied to the SRB, the UE may initialize the window state variable, stop the timer, and instruct the discarding of the stored data (PDCP SDU or PDCP PDU) by reestablishing the PDCP layer or reestablishing the RLC device for the first bearer (this may be performed when the fallback procedure proposed in the present disclosure is triggered). That is, according to another method, when the fallback procedure proposed in the present disclosure is triggered, the UE may perform a process of discarding the data (e.g., old RRC messages) remaining in the SRB of the source gNB or stored in the buffer. Alternatively, the UE may instruct or trigger a process of discarding the data (e.g., old RRC messages) remaining in the PDCP layer of the SRB or stored in the buffer, performed by an upper layer (e.g., RRC layer) of the UE. This is because it is necessary to prevent the old RRC message from being sent to the source gNB.

[0435] 2> When the UE triggers the DAPS handover method when triggering the handover process, the second timer for the source gNB cannot be stopped even if it is running. Even when the first timer is running (or not running), the second timer can be started when the condition for starting the second timer is met (when the asynchronous indicator of the radio connection signal is received from the lower layer a certain number of times). The second timer can be used for the wireless connection between the UE and the source gNB. According to another method, two second timers are operated, one of which is used for the wireless connection between the UE and the source gNB, and the other second timer is used for the wireless connection between the UE and the target gNB. That is, even when the first timer is running, the second timer can also be used for the wireless connection with the source gNB or the target gNB. However, even when the second timer expires, the UE will not trigger the RRC connection reestablishment process when the first timer has not expired and is running. That is, specifically, when the second timer for the source gNB expires, when the first timer has not expired and is running, or when a random access procedure is being performed on the target gNB even when a radio connection failure (RLF) occurs, or when a handover procedure is performed on the target gNB, the UE can release the radio connection with the source gNB without triggering the RRC connection reestablishment procedure. In addition, the UE does not release the RRC configuration information (e.g., bearer configuration information, etc.) configured from the source gNB, and can be reused when the RRC connection reestablishment procedure is triggered later. In addition, when the first timer has not expired and is running even if the second timer has expired, the UE can report to the source gNB or the target gNB that the source connection has failed without triggering the RRC connection reestablishment procedure, can release the connection with the source gNB (e.g., can release the first bearer for the source gNB), or can stop the first bearer for the source gNB. However, when the second timer has expired, the UE can trigger the RRC connection reestablishment procedure when the first timer has expired, has stopped, or has not started and is therefore not running. Even when the handover procedure is performed, the second timer operates so that when the radio connection between the UE and the source gNB or the target gNB is monitored to determine that a handover failure has occurred and the radio connection with the source gNB or the target gNB is valid, the UE performs the fallback procedure. In addition, when the second timer for the target gNB expires, when the radio connection with the target gNB fails, or when the random access procedure to the target gNB is successfully performed, the RRC connection reestablishment procedure may be triggered when the first timer expires, has stopped, or has not yet started and is therefore not running.

[0436] 2> When the UE triggers the DAPS handover method when triggering the handover process, the third timer for the source gNB cannot be stopped even if it is running. Only when the second timer is running, the UE can start the third timer when the condition for starting the third timer is met (when the frequency measurement process is triggered for the frequency measurement identifier configured with the third timer). That is, because the UE uses the second timer even when the first timer is running, the third timer can also be used. The third timer can be used for the wireless connection between the UE and the source gNB. According to another method, two third timers are operated, one of which is used for the wireless connection between the UE and the source gNB, and the other is used for the wireless connection between the UE and the target gNB. That is, even when the first timer is running, the third timer can also be used for the wireless connection with the source gNB or the target gNB. However, even when the third timer expires, the UE will not trigger the RRC connection reestablishment process when the first timer has not expired and is running. In addition, when the first timer has not expired and is running even when the third timer expires, the UE can report to the source gNB or the target gNB that the source connection has failed without triggering the RRC connection reestablishment process, the connection with the source gNB can be released (for example, the first bearer for the source gNB can be released), or the first bearer for the source gNB can be stopped. However, when the third timer has expired, the UE can trigger the RRC connection reestablishment process when the first timer has expired, has stopped, or has not started and is therefore not running. Even when performing a handover process, the third timer operates so that when the radio connection between the UE and the source gNB or the target gNB is monitored to determine that a handover failure has occurred and the radio connection with the source gNB is valid, a fallback process is performed and the frequency measurement result is reported during the fallback process.

[0437] 2> When the UE successfully completes the handover procedure to the target gNB, the UE stops the first timer.

[0438] 2> When the first timer has expired (for example, when the handover procedure to the target gNB fails), when the maximum number of retransmissions to the target gNB has been exceeded in the RLC layer, when a handover command message is received but the UE fails to handover because the configuration information of the handover command message exceeds the capabilities of the UE or an error occurs in the application of the configuration information, when a problem occurs in random access to the target gNB and the random access procedure is continuously attempted, but the first timer has expired and the handover procedure fails, when the second timer or the third timer is driven for the target gNB, or when the second timer or the third timer has expired before the handover procedure is completed, or when the T304 timer stops or expires and it is determined that the handover procedure has failed,

[0439] 3> When the second timer or the third timer for the radio connection between the UE and the source gNB has not expired (or when the second timer or the third timer for the radio connection between the UE and the source gNB is not started or is running) or when the radio connection between the UE and the source gNB is valid,

[0440] 4>The UE may determine that the radio connection between the UE and the source gNB is valid and may perform the fallback procedure proposed in the present disclosure.

[0441] 4> When the UE starts the fallback process, when the SRB configured for the source gNB (e.g., SRB1 or the MAC, RLC, or PDCP layer of SRB1) stops, the UE can restore or newly configure the SRB, and can perform the fallback process on the SRB (e.g., SRB1). According to another method, when the second PDCP layer structure proposed in the present disclosure is applied to the SRB, the UE can perform the fallback process through the first bearer for the source gNB, and can release the second bearer for the target gNB. For example, the UE can hand over uplink data transmission to the first bearer for the source gNB, can indicate that there is data to be sent to the RLC layer or MAC layer of the first bearer, and can send a handover failure report message for the fallback process through the first bearer. In addition, when the fallback process is triggered, the UE can perform a process of discarding data (e.g., old RRC messages) remaining in the SRB of the source gNB or stored in the buffer, or the upper layer (e.g., RRC layer) of the UE can indicate or trigger a process of discarding data (e.g., old RRC messages) remaining in the PDCP layer of the SRB or stored in the buffer. This is because it is necessary to prevent old RRC messages from being sent to the source gNB.

[0442] 4> During the fallback process, the UE configures a report message indicating the handover failure through the SRB (e.g., SRB1) configured by the source gNB, and reports the handover failure to the source gNB. When the UE sends the report message indicating the handover failure to the source gNB, the frequency measurement result measured by the UE is reported together to help quickly restore the connection with the source gNB. According to another method, the UE may define and send MAC control information (e.g., it may indicate that there is data to be sent in a new MAC control information or buffer status report, or by defining a special value to indicate the handover failure), RLC control information, or PDCP control information, and indicate to the source gNB that the handover has failed. According to another method, the UE may send an RRC connection reestablishment request message to the SRB (e.g., SRB0 or ​​SRB1) of the source gNB. According to another embodiment, the fallback process may be a process of releasing a second bearer for the target gNB for each bearer when the handover fails, or in a second PDCP layer structure of a bearer for which the DAPS handover method is configured, or switching to a first PDCP layer structure, and allowing the UE to resume data transmission or reception through the first bearer for the source gNB. It may be indicated that there is data to be sent to the MAC layer of the first bearer, and the UE may report to the source gNB that there is a scheduling request or data to be sent (e.g., a buffer status report), or send a new MAC CE, RLC control data, or PDCP control data to fall back to the source gNB, and instruct the source gNB to resume data transmission. The SRB of the source gNB may be newly configured or restored. In addition, when the handover fails, the fallback process is pre-configured for each bearer, or the bearer for which the DAPS handover method is not configured does not have a second PDCP layer structure. The UE may release the PDCP layer, RLC layer, or bearer configuration information from the MAC layer of the target gNB, or the logical channel identifier information reconfigured in the configuration information of the handover command message, or may be handed over, connected, and configured to the MAC layer of the source gNB, and then data transmission or reception of each bearer to the source gNB may be resumed. This is because, when the UE receives the handover command message, the UE can apply the bearer configuration information configured in the handover command message to the MAC layer of the target gNB relative to the bearer in which the DAPS handover method is not indicated, and can hand over the connection of the PDCP layer or the RLC layer corresponding to the bearer in which the DAPS handover method is not indicated from the MAC layer for the source gNB to the MAC layer for the target gNB, and its connection. For example, when receiving the handover command message, the upper layer (e.g., RRC layer) of the UE can instruct the current MAC layer of the source gNB to perform reconfiguration (MAC reconfiguration) by using configuration information other than the configuration information related to the bearer in which the DAPS handover method is not indicated in the handover command message in the configuration information of the current MAC layer of the source gNB.Alternatively, the upper layer (e.g., RRC layer) of the UE may instruct the MAC layer of the source gNB to perform reconfiguration (MAC reconfiguration) by using configuration information, which includes only configuration information related to the bearer indicating the DAPS switching method in the handover command message in the configuration information of the current MAC layer. That is, when the handover command message is received, the configuration information of the PDCP layer, RLC layer, or MAC layer in which the bearer in which the DAPS switching method is not indicated is released in the MAC layer of the source gNB, and the MAC layer of the target gNB may be applied or connected to according to the bearer configuration of the target gNB. Therefore, when the UE performs the fallback procedure, the bearer in which the DAPS switching method is not configured must be reconfigured in the MAC layer of the source gNB. For example, when the UE performs the fallback procedure, the upper layer (e.g., RRC layer) of the UE may instruct the MAC layer of the source gNB to perform reconfiguration (MAC reconfiguration) by using configuration information and bearer configuration information indicating the DAPS switching method, which includes configuration information related to the bearer in which the DAPS switching method is not indicated in the handover command message in the configuration information of the current MAC layer. Alternatively, when performing the fallback procedure, the UE may reconfigure or restore the bearer configuration (e.g., PDCP layer configuration information, RLC layer configuration information, MAC layer configuration information, or PHY layer configuration information) before receiving the handover command message, and may apply to the bearer of the source gNB (PDCP layer configuration information, RLC layer configuration information, MAC layer configuration information, or PHY layer of SRB or AM DRB or UM DRB).

[0443] 4> During the fallback process, when the UE sends a report message (e.g., an RRC message, MAC CE or RLC control data, or the PDCP control data proposed above) to the source gNB indicating that the handover has failed, a fourth timer may be started. When the UE receives an indication or message from the source gNB in ​​response to the report message sent by the UE indicating that the handover has failed, the UE may stop the fourth timer. However, when the fourth timer expires, or when no response message is received until the fourth timer expires, the UE performs an RRC connection reestablishment process (the connection with the gNB may be released, and the RRC connection process may be performed again from the beginning, i.e., a cell selection or reselection process may be performed, a random access process may be performed, and an RRC connection reestablishment request message may be sent). When the RRC connection reestablishment process is triggered due to the expiration of the fourth timer, the second timer or the third timer may be stopped when the second timer or the third timer is running.

[0444] 3> When the second timer or the third timer for the radio connection between the UE and the source gNB or the target gNB expires, or when the radio connection between the UE and the source gNB or the target gNB is invalid,

[0445] 4> The UE performs the RRC connection reestablishment procedure (the connection with the gNB may be released, and the RRC connection procedure may be performed again from the beginning, i.e., a cell selection or reselection procedure may be performed, a random access procedure may be performed, and an RRC connection reestablishment request message may be sent).

[0446] 2> When the UE performs a DAPS handover process and the second condition proposed in the present disclosure is satisfied, the connectio...

Claims

1. A method for operating a user equipment UE in a wireless communication system, the method comprising: receiving a first radio resource control (RRC) reconfiguration message indicating the handover from the source base station, the first RRC reconfiguration message including data radio bearer (DRB) configuration information, the DRB configuration information including an indicator indicating that a dual active protocol stack (DAPS) is configured for at least one DRB; In case the indicator indicates that DAPS is configured for at least one DRB, generating a medium access control MAC entity of the target base station; configuring a MAC entity of the target base station based on the MAC configuration information included in the first RRC reconfiguration message indicating the handover; Suspending a signaling radio bearer SRB used for the source base station; Establishing or configuring an SRB for a target base station; receiving a second RRC reconfiguration message from the target base station; as well as In case that the second RRC reconfiguration message received from the target base station includes an indicator for releasing the source base station, a radio link control RLC entity of the source base station is released for the at least one DRB.

2. The method according to claim 1, further comprising: In a case where the indicator indicates that DAPS is configured for the at least one DRB, for the at least one DRB for which DAPS is configured, a Packet Data Convergence Protocol PDCP entity is reconfigured, and the PDCP entity is not reestablished.

3. The method according to claim 2, wherein: Reconfiguring the PDCP entity includes: An RLC entity of the target base station is established or configured for the at least one DRB for which DAPS is configured, based on the radio link control RLC configuration information included in the first RRC reconfiguration message indicating the handover.

4. The method according to claim 2, wherein: Reconfiguring the PDCP entity includes configuring the PDCP entity using header compression and decompression functions and security functions of the target base station.

5. The method according to claim 1 further includes, when the DRB configuration information includes an indicator indicating the configuration of the DAPS of the at least one DRB, applying a new radio network temporary identifier RNTI value indicated by the first RRC reconfiguration message indicating the handover to the MAC entity of the target base station.

6. The method according to claim 1, wherein: In a case where the second RRC reconfiguration message received from the target base station includes an indicator for releasing the source base station and the source base station is a base station related to the new radio interface NR, for the at least one DRB, releasing the RLC entity of the source base station without reestablishing the RLC entity; and In the case that the source base station is a base station related to Long Term Evolution (LTE), for the at least one DRB, the RLC entity of the source base station is reestablished.

7. The method according to claim 1, wherein: The first RRC reconfiguration message indicating the handover includes an indicator indicating that DAPS is configured for the at least one DRB, and does not include an indicator indicating that DAPS is configured for at least one SRB.

8. The method of claim 1, further comprising, if DRB is not configured for DAPS, resetting a MAC entity of the UE.

9. The method according to claim 1, further comprising, when the DRB is not configured for DAPS, re-establishing the PDCP entity or the RLC entity for the SRB of the UE or at least one DRB for which DAPS is not configured.

10. A user equipment UE in a wireless communication system, the UE comprising: Transceiver; and At least one processor configured to: receiving, by a transceiver, a first radio resource control (RRC) reconfiguration message from a source base station indicating a handover, the RRC reconfiguration message comprising data radio bearer (DRB) configuration information, the DRB configuration information comprising an indicator indicating that a dual active protocol stack (DAPS) is configured for at least one DRB; In case the indicator indicates that DAPS is configured for at least one DRB, generating a medium access control MAC entity of the target base station; configuring a MAC entity of the target base station based on the MAC configuration information included in the first RRC reconfiguration message indicating the handover; Suspending a signaling radio bearer SRB used for the source base station; Establishing or configuring an SRB for a target base station; receiving a second RRC reconfiguration message from the target base station; as well as In case that the second RRC reconfiguration message received from the target base station includes an indicator for releasing the source base station, a radio link control RLC entity of the source base station is released for the at least one DRB.

11. The UE according to claim 10, wherein: In a case where the indicator indicates that DAPS is configured for the at least one DRB, the at least one processor is further configured to reconfigure a Packet Data Convergence Protocol PDCP entity for the at least one DRB for which DAPS is configured, and the PDCP entity is not reestablished.

12. The UE according to claim 11, wherein: The at least one processor is further configured to: establishing or configuring an RLC entity of the target base station for at least one DRB for which DAPS is configured, based on the radio link control RLC configuration information included in the first RRC reconfiguration message indicating the handover; as well as The PDCP entity is configured with the header compression and decompression functions and security functions of the target base station.

13. The UE according to claim 10, wherein: The at least one processor is further configured to: In a case where the second RRC reconfiguration message received from the target base station includes an indicator for releasing the source base station and the source base station is a base station related to the new radio interface NR, for the at least one DRB, releasing the RLC entity of the source base station without reestablishing the RLC entity; and In the case that the source base station is a base station related to Long Term Evolution (LTE), for the at least one DRB, the RLC entity of the source base station is reestablished.

14. The UE according to claim 10, wherein: In a case where the DRB is not configured for DAPS, the at least one processor is further configured to reset a MAC entity of the UE.

15. The UE according to claim 10, wherein: In a case where the DRB is not configured for DAPS, the at least one processor is further configured to re-establish a PDCP entity or an RLC entity for an SRB of the UE or at least one DRB for which DAPS is not configured.

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