Method and apparatus for performing handover in wireless communication system

Abstract

A method performed by a terminal in a wireless communication system is provided. The method comprises receiving, from a source base station, a radio resource control (RRC) reconfiguration message comprising data radio bearer (DRB) configuration information, where the DRB configuration information comprises a DRB identifier and a dual active protocol stack (DAPS) handover indicator, and under the condition that the DRB configuration information comprises service data adaptation protocol (SDAP) configuration information and a target media access control (MAC) entity of the target base station indicates that random access to the target base station is completed, reconfiguring the SDAP entity based on the SDAP configuration information.

Description

Technical Field

[0001] The present disclosure relates to a method and apparatus for performing handover in a wireless communication system. More particularly, the present disclosure relates to a method for efficiently providing a service in a mobile communication system. Background Art

[0002] In order to meet the growing demand for wireless data services since the commercialization of the fourth generation (4G) communication system, efforts have been made to develop the fifth generation (5G) or quasi-5G communication system. Therefore, the 5G or quasi-5G communication system is called a "super 4G network" communication system or a "post-long term evolution (post-LTE)" system. The 5G communication system is considered to be implemented in a higher frequency (mmWave) band, for example, a 60GHz band, to achieve higher data rates. In order to reduce the propagation path loss of radio waves and increase the propagation distance of radio waves in the millimeter wave band, beamforming, massive multiple input multiple output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and large antenna technology in the 5G communication system are discussed. In addition, in the 5G communication system, the development of system network improvements based on advanced small cells, cloud radio access networks (RAN), ultra-dense networks, device-to-device (D2D) communications, wireless backhaul, mobile networks, cooperative communications, coordinated multi-point (CoMP), receiving-end interference elimination, etc. is underway. In 5G systems, hybrid FSK and FQAM modulation and sliding window superposition coding (SWSC) have been developed as advanced coded modulation (ACM), and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as advanced access technologies.

[0003] The Internet is a human-centered connectivity network where humans generate and consume information, and is now evolving into the Internet of Things (IoT), in which distributed entities such as things exchange and process information without human intervention. The Internet of Everything, which combines IoT technology and big data processing technology through connection with cloud servers, has occurred. In order to realize the IoT, technical elements such as "sensing technology", "wired / wireless communication and network infrastructure", "service interface technology", and "security technology" are required, and sensor networks, machine-to-machine (M2M) communication, machine-type communication (MTC), etc. have been studied recently. This IoT environment can provide intelligent Internet technology services to create new value for human life by collecting and analyzing data generated between connected things. Through the integration and combination between existing information technology (IT) and various industrial applications, IoT can be applied to various fields, including smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, health care, smart appliances, and advanced medical services.

[0004] Various attempts are being made to apply 5G communication systems to IoT networks. For example, technologies related to sensor networks, M2M communications, and MTC are being implemented by using 5G communication technologies that utilize beamforming, MIMO, and array antennas. The application of cloud RAN, which is the above-mentioned big data processing technology, can also be considered an example of the fusion between 5G technology and IoT technology.

[0005] As the above-mentioned development of wireless communication systems can provide various services, a method for efficiently providing these services is required.

[0006] Therefore, there is a need for an apparatus and method for efficiently providing services in a mobile communication system.

[0007] The above information is presented as background information only to assist in understanding the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with respect to the present disclosure. Summary of the invention

[0008] Aspects of the present disclosure are to address at least the above-mentioned problems and / or disadvantages and to provide at least the advantages described below. Therefore, one aspect of the present disclosure is to provide a method for efficiently providing a service in a mobile communication system.

[0009] Additional aspects will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The above and other aspects, features and advantages of certain embodiments of the present disclosure will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0011] Figure 1A is a diagram showing a configuration of a Long Term Evolution (LTE) system according to an embodiment of the present disclosure;

[0012] Figure 1B is a diagram showing a radio protocol architecture of an LTE system according to an embodiment of the present disclosure;

[0013] Figure 1C is a diagram showing a next generation mobile communication system according to an embodiment of the present disclosure;

[0014] Figure 1D is a diagram showing a radio protocol architecture of a new radio (NR) or fifth generation (5G) mobile communication system according to an embodiment of the present disclosure;

[0015] Figure 1E is a diagram showing a process in which a user equipment (UE) switches from a radio resource control (RRC) idle mode to an RRC connected mode and establishes a network connection according to an embodiment of the present disclosure;

[0016] Figure 1F is a diagram showing a signaling process for performing handover in a next generation mobile communication system according to an embodiment of the present disclosure;

[0017] Figure 1G Specific operations of Embodiment 1 of an efficient handover method for minimizing data interruption time due to handover according to an embodiment of the present disclosure are shown;

[0018] Figure 1H Specific operations of Embodiment 2 of an efficient handover method for minimizing data interruption time due to handover according to an embodiment of the present disclosure are shown;

[0019] Fig. 1I An architecture of an efficient packet data convergence protocol (PDCP) layer to be applied to a dual active protocol stack (DAPS) handover method of embodiment 2 as an efficient handover method according to an embodiment of the present disclosure, and a method of applying the architecture are shown;

[0020] Figure 1J An architecture of an efficient service data adaptation protocol (SDAP) layer to be applied to a DAPS handover method of embodiment 2 as an efficient handover method according to an embodiment of the present disclosure, and a method of applying the architecture are shown;

[0021] Figure 1K is a diagram illustrating a method of applying configuration information to each bearer when performing a DAPS switching method according to an embodiment of the present disclosure;

[0022] Figure 1L is a diagram illustrating the operation of a UE according to an embodiment of the present disclosure;

[0023] Figure 1M is a diagram illustrating an operation of a UE performing a fallback procedure when a handover fails in a DAPs handover method according to an embodiment of the present disclosure;

[0024] Figure 1N is a diagram showing a configuration of an LTE system according to an embodiment of the present disclosure;

[0025] Fig.1O is a diagram showing a radio protocol architecture of an LTE system according to an embodiment of the present disclosure;

[0026] Figure 1P is a diagram showing a next generation mobile communication system according to an embodiment of the present disclosure;

[0027] Figure 1Q is a diagram showing a radio protocol architecture of an NR or 5G mobile communication system according to an embodiment of the present disclosure;

[0028] Figure 1R is a diagram showing a process in which a UE switches from an RRC idle mode to an RRC connected mode and establishes a network connection according to an embodiment of the present disclosure;

[0029] Figure 1S is a diagram showing a signaling process for performing handover in a next generation mobile communication system according to an embodiment of the present disclosure;

[0030] Figure 1T Specific operations of Embodiment 1 of an efficient handover method for minimizing data interruption time due to handover according to an embodiment of the present disclosure are shown;

[0031] Figure 1U Specific operations of Embodiment 2 of an efficient handover method for minimizing data interruption time due to handover according to an embodiment of the present disclosure are shown;

[0032] Figure 1V An architecture of an efficient PDCP layer to be applied to a DAPS handover method of Embodiment 2 as an efficient handover method according to an embodiment of the present disclosure, and a method of applying the architecture are shown;

[0033] Figure 1W is a diagram illustrating the operation of a UE according to an embodiment of the present disclosure;

[0034] Figure 1X is a diagram showing a configuration of a UE according to an embodiment of the present disclosure; and

[0035] Figure 1Y It is a diagram showing the configuration of a transmission point and a reception point (TRP / Tx / Rx point) in a wireless communication system according to an embodiment of the present disclosure.

[0036] Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures. DETAILED DESCRIPTION

[0037] According to one aspect of the present disclosure, a method performed by a terminal in a wireless communication system is provided. The method includes receiving a radio resource control (RRC) reconfiguration message including data radio bearer (DRB) configuration information from a source base station, wherein the DRB configuration information includes a DRB identifier and a dual active protocol stack (DAPS) switching indicator, and when the DRB configuration information includes service data adaptation protocol (SDAP) configuration information and a target medium access control (MAC) entity of a target base station indicates that random access to the target base station is completed, reconfiguring the SDAP entity based on the SDAP configuration information.

[0038] According to another aspect of the present disclosure, a terminal in a wireless communication system is provided. The terminal in the wireless communication system includes a transceiver and at least one processor. The at least one processor is configured to: receive a radio resource control (RRC) reconfiguration message including data radio bearer (DRB) configuration information from a source base station via the transceiver, wherein the DRB configuration information includes a DRB identifier and a dual active protocol stack (DAPS) switching indicator, and when the DRB configuration information includes service data adaptation protocol (SDAP) configuration information and the target media access control (MAC) entity of the target base station indicates that random access to the target base station is completed, reconfigure the SDAP entity based on the SDAP configuration information.

[0039] Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses various embodiments of the disclosure.

[0040] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of the various embodiments of the present disclosure as defined by the appended claims and their equivalents. The following description includes various specific details to assist in understanding, but these are to be regarded as merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications may be made to the various embodiments described herein without departing from the scope and spirit of the present disclosure. In addition, for the sake of clarity and conciseness, descriptions of well-known functions and configurations may be omitted.

[0041] The terms and words used in the following description and the attached claims are not limited to the written meanings, but are only used by the inventor to make the present disclosure clearly and consistently understood. Therefore, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustrative purposes only and is not intended to limit the present disclosure as defined by the attached claims and their equivalents.

[0042] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.

[0043] With reference to the embodiments of the present disclosure described below in conjunction with the accompanying drawings, the advantages and features of the present disclosure and the methods for implementing the same will become apparent. However, the present disclosure can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein, but rather these embodiments are provided so that the present disclosure will be thorough and complete and will fully convey to those skilled in the art the scope of the present disclosure which is limited only by the claims. In the specification, identical elements are represented by identical reference numerals.

[0044] Throughout the disclosure, the expression "at least one of a, b, or c" means only a, only b, only c, both a and b, both a and c, both b and c, all of a, b, and c, or variations thereof.

[0045] Examples of the terminal may include a User Equipment (UE), a Mobile Station (MS), a cellular phone, a smart phone, a computer, a multimedia system capable of performing a communication function, and the like.

[0046] In this disclosure, a controller may also be referred to as a processor.

[0047] Throughout the specification, a layer (or a layer device) may also be referred to as an entity.

[0048] It will be understood that each box shown in the flowchart and the combination of boxes shown in the flowchart can be implemented by computer program instructions. The computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, so that the instructions executed by the processor of the computer or other programmable data processing device generate a device for performing the functions specified in the flowchart box. The 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 operate in a specific manner, so that the instructions stored in the computer-usable or computer-readable memory generate a product including an instruction device for performing the functions specified in the flowchart box. The computer program instructions can also be loaded onto a computer or other programmable data processing device, causing a series of operations for generating a computer-implemented process to be performed on a computer or other programmable device, so that the instructions executed on the computer or other programmable device provide operations for implementing the functions specified in the flowchart box.

[0049] In addition, each frame shown in the flow chart may represent a module, a fragment or a portion of code, which includes one or more executable instructions for performing a specified logical function. It should also be noted that in some optional embodiments, the functions shown in the frame may not occur in order. For example, the two frames shown in the flow chart may be executed substantially simultaneously, or the frames may sometimes be executed in reverse order, depending on the functions involved.

[0050] The term "unit" as used in the embodiments of the present disclosure refers to a software or hardware component that performs certain tasks, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). However, the term "unit" is not meant to be limited to software or hardware. A "unit" may be configured to be in an addressable storage medium or configured to operate one or more processors. Therefore, as an example, a "unit" may include components such as software components, object-oriented software components, class components, and task components; processes, functions, attributes, procedures, subroutines, program code fragments, drivers, firmware, microcodes, circuits, data, databases, data structures, tables, arrays, and variables. The functions provided in components and "units" may be combined into fewer components and "units", or may be further separated into additional components and "units". In addition, components and "units" may be implemented as one or more central processing units (CPUs) in an operating device or a secure multimedia card. In addition, a "unit" may include one or more processors in the embodiments of the present disclosure.

[0051] Hereinafter, in order to avoid obscuring the present disclosure in unnecessary detail, well-known functions or configurations are not described. Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0052] Hereinafter, for the convenience of explanation, terms identifying access nodes, terms indicating network entities, terms indicating messages, terms indicating interfaces between network entities, and terms indicating various identification information as used in the following description are exemplified. Therefore, the present disclosure is not limited to the terms to be described below, and other terms indicating objects having equivalent technical meanings may be used.

[0053] For ease of description, the present disclosure uses terms and names defined in the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) standard. However, the present disclosure is not limited to these terms and names, and is equally applicable to communication systems that conform to other standards. In particular, the present disclosure may be applicable to 3GPP New Radio (NR), the fifth generation (5G) mobile communication standard. In the present disclosure, for ease of description, evolved Node B (eNB) may be used interchangeably with next generation Node B (gNB). For example, a BS described as an eNB may represent a gNB. In the present disclosure, the term "terminal" may refer not only to mobile phones, narrowband Internet of Things (NB-IoT) devices, and sensors, but also to other wireless communication devices.

[0054] Hereinafter, a base station is an entity that allocates resources to a terminal, and may be at least one of a gNodeB, an eNodeB, a Node B, a base station (BS), a radio access unit, a BS controller, or a node on a network. In the present disclosure, a terminal may include a user terminal (UE), a mobile station (MS), a cellular phone, a smart phone, a computer, or a multimedia system capable of performing a communication function. However, the present disclosure is not limited to the above examples.

[0055] In the present disclosure, provided is a hitless handover method capable of minimizing data interruption time due to handover or making the data interruption time 0 milliseconds in a next generation mobile communication system.

[0056] More specifically, the efficient switching method provided by the present disclosure may have one or more of the features described below.

[0057] In addition, for the efficient switching method proposed in the present disclosure, different switching methods can be applied to different bearers.

[0058] -When the UE receives a handover command message (e.g., a handover command message or a radio resource control (RRC) reconfiguration message) from the source BS, the UE performs data transmission or reception (uplink (UL) or downlink (DL) data transmission and reception) to or from the source BS by using each of the protocol layers (i.e., a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, and a packet data convergence protocol (PDCP) layer) for multiple first bearers, the UE can configure protocol layers corresponding to the protocol layers of the multiple first bearers for multiple new second bearers (e.g., having the same bearer identifier), and the UE can perform data transmission or reception (UL or DL ​​data transmission and reception) but does not interrupt but maintains data transmission or reception (UL or DL ​​data transmission and reception) to or from the source BS via the multiple first bearers.

[0059] -Based on the bearer configuration information or multiple protocol layer information included in the handover command message, after the UE receives the handover command message, the protocol layers (PHY layer, MAC layer, RLC layer and PDCP layer) of the newly configured multiple second bearers are configured to send data to and receive data from the target BS.

[0060] - In the aforementioned situation, the UE may be configured to perform data transmission or reception (UL or DL ​​data transmission and reception) to or from the source BS by using a protocol layer for a plurality of first bearers, and to perform a random access procedure on the target BS by using a protocol layer (e.g., a MAC layer) for a plurality of second bearers. In the aforementioned situation, the random access procedure may include transmission of a preamble, reception of a random access response, transmission of a message 3, reception of a message 4 (e.g., reception of a contention resolution MAC control element (CE) or a UL transmission resource), and the like.

[0061] -In the aforementioned situation, the UE may be configured to perform sending or receiving data to or from the source BS by using a protocol layer for multiple first bearers, and complete a random access procedure to the target BS by using a protocol layer (e.g., a MAC layer) for multiple second bearers, and send a switching completion message to the target BS by using a protocol layer for multiple second bearers.

[0062] -In the aforementioned situation, the UE may be configured to perform data transmission or reception to or from the source BS by using a protocol layer for multiple first bearers, and complete a random access procedure to the target BS by using a protocol layer (e.g., a MAC layer) for multiple second bearers, and send a switching completion message and perform data transmission and reception (UL or DL) by using a protocol layer for multiple second bearers.

[0063] -In the aforementioned situation, the UE may be configured in the following manner: when the UE successfully completes the random access procedure to the target BS and then initially receives UL transmission resources from the target BS, the UE interrupts sending data to the source BS by using a protocol layer for a plurality of first bearers, switches UL transmission, and then sends data to the target BS by using a plurality of second bearers.

[0064] - In the aforementioned situation, the UE may be configured in the following manner: when the UE receives the handover command message, the UE continuously performs data transmission to or reception from the source BS (UL or DL ​​data transmission and reception), and performs a random access procedure to the target BS by using a protocol layer for a plurality of second bearers; and when the UE successfully completes the random access procedure and then initially receives UL transmission resources from the target BS, the UE interrupts the transmission of data to the source BS by using a protocol layer for a plurality of first bearers, and performs the transmission of UL data to the target BS only by using a protocol layer for a plurality of second bearers. In addition, the UE may be configured to continuously receive DL data from the source BS by using a protocol layer for a plurality of first bearers, and continuously receive DL data from the target BS by using a protocol layer for a plurality of second bearers.

[0065] -In the aforementioned situation, the first bearer and the second bearer may be configured for a second PDCP layer architecture, and in the second PDCP layer architecture, the first bearer (e.g., RLC layer, MAC layer, or PHY layer) for the source BS and the second bearer (e.g., RLC layer, MAC layer, or PHY layer) for the target BS are both connected to one PDCP layer, and UL data may be sent via one of the first bearer or the second bearer by using the PDCP layer. For example, before the UE performs a random access procedure to the target BS, successfully completes the random access procedure, and initially receives UL transmission resources from the target BS, the UE sends UL data via the first bearer; and when the UE performs a random access procedure to the target BS, successfully completes the random access procedure, and initially receives UL transmission resources from the target BS, the UE may interrupt data transmission via the first bearer, may switch data transmission, and then may send UL data to the target BS via the second bearer. In this regard, the UE having the second PDCP layer architecture may be configured to receive DL data from the source BS or the target BS via the first bearer or the second bearer.

[0066] Hereinafter, based on the above features, the present disclosure provides an efficient switching process with no data interruption time.

[0067] When the UE performs the efficient handover method with no data interruption time proposed in the present disclosure, in the case of UE handover failure, the UE can use the features of the efficient handover method proposed in the present disclosure to reconfigure the link to the source BS by quickly falling back to the source BS. The features of the efficient handover method proposed in the present disclosure may specifically refer to the UE maintaining the link to the source BS even when the UE performs the handover process. In addition, the present disclosure proposes a specific method by which the UE can fall back to the source BS by using the previous radio link to the source BS even when the handover process performed by the UE fails.

[0068] The present disclosure provides a method and apparatus for applying configuration information to each of bearers in a dual active protocol stack (DAPS) handover method of a next generation mobile communication system.

[0069] The present disclosure relates to a method and apparatus for performing fallback in response to handover failure while performing an efficient handover method with no data interruption time during handover in a next generation mobile communication system.

[0070] According to the embodiments of the present disclosure, the next generation mobile communication system may require an efficient handover method to support services without data interruption and low transmission latency. When the handover fails, a method for performing fallback with minimal data interruption time may be required.

[0071] The present disclosure may propose various efficient handover methods, by which data interruption time due to handover does not occur during handover in the next generation mobile communication system. In this way, services without data interruption can be supported. In addition, an efficient method will be described in which the UE can quickly fall back to the source BS when the UE handover fails.

[0072] Figure 1A is a diagram showing a configuration of an LTE system according to an embodiment of the present disclosure.

[0073] refer to Figure 1A , the radio access network (RAN) of the LTE system includes multiple evolved Node Bs (eNBs) (or Node Bs or base stations) 1a-05, 1a-10, 1a-15, and 1a-20; a mobility management entity (MME) 1a-25 and a serving gateway (S-GW) 1a-30. UE (or terminal) 1a-35 can access an external network via eNB 1a-05, 1a-10, 1a-15, or 1a-20 and S-GW 1a-30.

[0074] refer to Figure 1A , eNB 1a-05, 1a-10, 1a-15 or 1a-20 may correspond to an existing Node B of a Universal Mobile Telecommunications System (UMTS). ENB 1a-05, 1a-10, 1a-15 or 1a-20 may be connected to UE 1a-35 via a wireless channel and may perform complex functions compared to an existing Node B. All user service data including real-time services such as Voice over Internet Protocol (VoIP) may be provided through a shared channel in an LTE system, so an entity for collating UE status information (e.g., buffer status information, available transmit power status information, and channel status information) and performing scheduling may be required, and eNB 1a-05, 1a-10, 1a-15 or 1a-20 may operate as such an entity. One eNB typically controls multiple cells. For example, an LTE system may use a radio access technology such as orthogonal frequency division multiplexing (OFDM) with a 20MHz bandwidth to achieve a data rate of 100Mbps. Adaptive modulation and coding (AMC) may be used to determine the modulation scheme and channel coding rate according to the channel state of the UE. S-GW 1a-30 is an entity that provides data bearers, and may establish and release data bearers under the control of MME 1a-25. MME 1a-25 is an entity for performing mobility management functions and various control functions for UE 1a-35, and is connected to multiple eNBs 1a-05, 1a-10, 1a-15, and 1a-20.

[0075] Figure 1B is a diagram showing a radio protocol architecture of an LTE system according to an embodiment of the present disclosure.

[0076] refer to Figure 1B , the radio protocol architecture of the LTE system may include packet data convergence protocol (PDCP) layers 1b-05 and 1b-40 for UE and eNB, respectively, radio link control (RLC) layers 1b-10 and 1b-35 for UE and eNB, respectively, and medium access control (MAC) layers 1b-15 and 1b-30 for UE and eNB, respectively. The PDCP layer 1b-05 or 1b-40 may, for example, perform IP header compression / decompression. The main functions of the PDCP layer 1b-05 or 1b-40 are summarized as follows.

[0077] -Header compression and decompression: Robust Header Compression Only (ROHC)

[0078] -User data transmission

[0079] - In-sequence delivery of upper layer packet data units (PDUs) during PDCP re-establishment procedure for RLC Acknowledged Mode (AM)

[0080] - For decentralized bearers in DC (supports RLC AM only): PDCP PDU routing for transmission, and PDCP PDU reordering for reception

[0081] - Duplicate detection of lower layer service data units (SDUs) during PDCP re-establishment for RLC AM

[0082] - For distributed bearers in DC, retransmit PDCP SDUs at handover; and for RLC AM, retransmit PDCP PDUs during PDCP data recovery procedure

[0083] -Encryption and decryption

[0084] - Timer-based SDU discard in uplink

[0085] The RLC layer 1b-10 or 1b-35 may perform an automatic repeat request (ARQ) operation by reconfiguring a packet data convergence protocol packet data unit (PDCP PDU) to an appropriate size. The main functions of the RLC layer 1b-10 or 1b-35 may be summarized as follows.

[0086] -Upper layer PDU transmission

[0087] - Error correction through ARQ (for AM data transmission only)

[0088] - Concatenation, segmentation and reassembly of RLC SDUs (only for negative acknowledgement mode (UM) and AM data transmission)

[0089] - Re-segmentation of RLC data PDU (only for AM data transmission)

[0090] - Reordering of RLC data PDUs (only for UM and AM data transmission)

[0091] -Duplicate detection (for UM and AM data transmission only)

[0092] -Protocol error detection (AM data transmission only)

[0093] -RLC SDU discard (only for UM and AM data transmission)

[0094] -RLC reconstruction

[0095] The MAC layer 1b-15 or 1b-30 may be connected to a plurality of RLC layers configured for one UE, and may multiplex the RLC PDU into the MAC PDU, and may demultiplex the RLC PDU from the MAC PDU. The main functions of the MAC layer 1b-15 or 1b-30 may be summarized as follows.

[0096] - Mapping between logical channels and transport channels

[0097] - Multiplex MAC SDUs belonging to one or different logical channels into a transport block (TB) delivered to the physical layer via a transport channel, or demultiplex the MAC SDUs from a transport block delivered from the physical layer via a transport channel

[0098] -Dispatch information report

[0099] - Error correction through Hybrid ARQ (HARQ)

[0100] - Priority handling between logical channels of a UE

[0101] - Priority handling between dynamically scheduled UEs

[0102] -Multimedia Broadcast / Multicast Service (MBMS) service identification

[0103] -Transmission format selection

[0104] -filling

[0105] The physical (PHY) layer 1b-20 or 1b-25 may encode and modulate an upper layer data channel into an OFDM symbol and send the OFDM symbol through a wireless channel; or may demodulate and channel-decode an OFDM symbol received through a wireless channel and transmit the OFDM symbol to an upper layer.

[0106] Figure 1C A next generation mobile communication system is shown according to an embodiment of the present disclosure.

[0107] refer to Figure 1CAs shown, the radio access network of the next generation mobile communication system (hereinafter referred to as NR or 5G communication system) includes a new radio node B (NR gNB, NR NB or gNB) 1c-10 and a new radio core network (NR CN) 1c-05. The NR UE (or terminal) 1c-15 located in the area 1c-20 accesses the external network via the NR gNB 1c-10 and the NR CN 1c-05.

[0108] refer to Figure 1C , NR gNB 1c-10 corresponds to the eNB of the conventional LTE system. NR gNB 1c-10 can be connected to NR UE 1c-15 through a wireless channel, and can provide superior services compared to the existing Node B. All user service data can be served through a shared channel in the NR or 5G mobile communication system, so an entity for collating the buffer status information, available transmission power status information and channel status information of the UE and performing scheduling may be required, and NR gNB 1c-10 can operate as such an entity. One NR gNB usually controls multiple cells. The NR or 5G communication system may have a bandwidth larger than the maximum bandwidth of the existing LTE system to achieve an ultra-high data rate, and compared to the existing LTE system, NR or 5G may use OFDM as a radio access technology, and may also use beamforming technology. In addition, NR gNB 1c-10 uses AMC to determine the modulation scheme and channel decoding rate according to the channel state of the NR UE 1c-15. 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 for performing mobility management functions and various control functions for NR UE 1c-15, and is connected to multiple base stations. The NR or 5G mobile communication system can cooperate with the existing LTE system, and the NR CN 1c-05 can be connected to the MME 1c-25 through a network interface. The MME 1c-25 is connected to the eNB 1c-30 which is a traditional base station.

[0109] Figure 1D is a diagram showing a radio protocol architecture of an NR or 5G mobile communication system according to an embodiment of the present disclosure.

[0110] refer to Figure 1D The radio protocol architecture of the NR or 5G mobile communication system may include NR service data adaptation protocol (SDAP) layers 1d-01 and 1d-45 for UE and NR gNB, respectively, NR PDCP layers 1d-05 and 1d-40 for UE and NR gNB, respectively, NR RLC layers 1d-10 and 1d-35, and NR MAC layers 1d-15 and 1d-30 for UE and NR gNB, respectively.

[0111] The main functions of NR SDAP layer 1d-01 or 1d-45 may include some of the following functions.

[0112] -User plane data transmission

[0113] - Mapping between DL and UL QoS flows and Data Radio Bearers (DRBs)

[0114] -Mark QoS flow identifier (ID) in DL and UL packets

[0115] -Mapping of reflective QoS flows of UL SDAP PDU to DRB

[0116] For the SDAP layer, the UE can be configured to use the header of the SDAP layer or use the SDAP layer function of each PDCP layer, each bearer or each logical channel through an RRC message. When the SDAP header is configured, the 1-bit non-access layer (NAS) reflection QoS indicator and the 1-bit access layer (AS) reflection QoS indicator of the SDAP header can indicate that the UE updates or reconfigures the mapping information of the UL and DL QoS flows and data bearers. The SDAP header may include QoS flow ID information indicating QoS. The QoS information can be used as data processing priority information or scheduling information to appropriately support services.

[0117] The main functions of NR PDCP layer 1d-05 or 1d-40 may include some of the following functions.

[0118] -Header compression and decompression: ROHC only

[0119] -User data transmission

[0120] - In-sequence delivery of upper layer PDUs

[0121] - Out-of-order delivery of upper layer PDUs

[0122] - Reordering of PDCP PDUs for reception

[0123] - Duplicate detection of lower layer SDU

[0124] -Retransmission of PDCP SDU

[0125] -Encryption and decryption

[0126] - Timer-based SDU discard in uplink

[0127] The reordering function of the NR PDCP layer 1d-05 or 1d-40 may indicate a function of reordering PDCP PDUs received from a lower layer based on a PDCP sequence number (SN). The reordering function may include: a function of delivering the reordered data to an upper layer in sequence or out of sequence, a function of recording lost PDCP PDUs by reordering received PDCP PDUs, a function of reporting status information of lost PDCP PDUs to a transmitter, or a function of requesting retransmission of lost PDCP PDUs.

[0128] The main functions of the NR RLC layer 1d-10 or 1d-35 may include some of the following functions.

[0129] -Transmission of upper layer PDU

[0130] - In-sequence delivery of upper layer PDUs

[0131] - Out-of-order delivery of upper layer PDUs

[0132] - Error correction via ARQ

[0133] - Concatenation, segmentation and reassembly of RLC SDU

[0134] - Re-segmentation of RLC data PDUs

[0135] - Reordering of RLC data PDUs

[0136] - Duplicate detection

[0137] -Protocol error detection

[0138] -RLC SDU discarded

[0139] -RLC reconstruction

[0140] The in-sequence delivery function of the NR RLC layer 1d-10 or 1d-35 may indicate a function of delivering the RLC SDU received from the lower layer to the upper layer in sequence. The in-sequence delivery function may include: a function of reassembling the RLC SDU and transmitting the reassembled RLC SDU when multiple RLC SDUs from one RLC SDU segment are received; a function of reordering the received RLC PDU based on the RLC SN or PDCP SN; a function of recording the lost RLC PDU by reordering the received RLC PDU; a function of reporting the status information of the lost RLC PDU to the transmitter; a function of requesting retransmission of the lost RLC PDU; a function of delivering only the RLC SDU before the lost RLC SDU to the upper layer in sequence when there is a lost RLC SDU; a function of delivering all RLC SDUs received before the timer is started in sequence to the upper layer even though there is a lost RLC SDU when a certain timer expires; or a function of delivering all RLC SDUs received until the current time in sequence to the upper layer even when there is a lost RLC SDU when a certain timer expires. The NR RLC layer 1d-10 or 1d-35 may process the RLC PDU in the order of reception and transmit the RLC PDU to the NR PDCP layer 1d-05 or 1d-40 regardless of the SN (out-of-order delivery); and when a fragment is received, the NR RLC layer 1d-10 or 1d-35 may reassemble the fragment with other fragments stored in the buffer or received subsequently into a complete RLC PDU, and may transmit the RLC PDU to the NR PDCP layer 1d-05 or 1d-40. The NR RLC layer 1d-10 or 1d-35 may not have a cascading function, and the cascading function may be performed by the NR MAC layer 1d-15 or 1d-30, or replaced by the multiplexing function of the NR MAC layer 1d-15 or 1d-30.

[0141] The out-of-order delivery function of the NR RLC layer 1d-10 or 1d-35 may include a function of directly delivering the RLC SDU received from the lower layer to the upper layer out of order; a function of reassembling multiple RLC SDUs from one RLC SDU segment and transmitting the reassembled RLC SDU when a segmented RLC SDU is received; or a function of recording lost RLC PDUs by storing the RLC SN or PDCP SN of the received RLC PDU and reordering the received RLC PDUs.

[0142] The NR MAC layer 1d-15 or 1d-30 can be connected to multiple NR RLC layers configured for one UE, and the main functions of the NR MAC layer 1d-15 or 1d-30 may include some of the following functions.

[0143] - Mapping between logical channels and transport channels

[0144] -Multiplexing / demultiplexing of MAC SDU

[0145] -Dispatch information report

[0146] - Error correction through HARQ

[0147] - Priority handling between logical channels of a UE

[0148] - Priority handling between dynamically scheduled UEs

[0149] -MBMS service identification

[0150] -Transmission format selection

[0151] -filling

[0152] The NR PHY layer 1d-20 or 1d-25 may encode and modulate the upper layer data channel into an OFDM symbol, and may send the OFDM symbol through a wireless channel; or may demodulate and channel-decode the OFDM symbol received through a wireless channel, and may transmit the OFDM symbol to an upper layer.

[0153] Figure 1E is a diagram illustrating a process in which a UE switches from an RRC idle mode to an RRC connected mode and establishes a network connection according to an embodiment of the present disclosure.

[0154] refer to Figure 1E , when a UE configured to send and receive data in RRC connected mode does not send or receive data due to a predetermined reason or within a predetermined time, the gNB may send an RRCConnectionRelease message to the UE to allow the UE to transition to RRC idle mode in operation 1e-01. Thereafter, when a UE that is not currently configured with a link (hereinafter also referred to as an idle mode UE) has data to send, the UE may perform an RRC connection establishment procedure for the gNB. The UE establishes reverse transmission synchronization with the gNB through a random access procedure, and sends an RRCConnectionRequest message to the gNB in ​​operation 1e-05. The RRCConnectionRequest message may include an identifier of the UE, an establishment cause, etc. In operation 1e-10, the gNB sends an RRCConnectionSetup message to allow the UE to establish an RRC connection.

[0155] The RRCConnectionSetup message includes configuration information for each service / bearer / RLC layer or each logical channel or each bearer, and the PDCP layer configuration information (pdcp-config) may include information on whether each bearer / logical channel uses ROHC, ROHC configuration information (e.g., ROHC version, initial information, etc.), statusReportRequired information (information used by the BS to indicate the PDCP status report to the UE), and drb-ContinueROHC information (configuration information indicating to continue to use the ROHC configuration information without change), and these information may be sent. In addition, RRCConnectionSetup may include RRC connection configuration information. The bearer of the RRC connection is called a signaling radio bearer (SRB) and is used to send and receive RRC messages as control messages between the UE and the gNB.

[0156] In operation 1e-15, the UE that has established the RRC connection sends an RRCConnectionSetupComplete message to the gNB. The RRCConnectionSetupComplete message may include a control message, such as a SERVICE REQUEST message in which the UE requests the MME or the Access and Mobility Management Function (AMF) to configure a bearer for a service. In operation 1e-20, the GNB sends a service request message included in the RRCConnectionSetupComplete message to the MME or AMF, and the MME or AMF may determine whether to provide the service requested by the UE. As a result of the determination, when the service requested by the UE is to be provided, the MME or AMF sends an INITIAL CONTEXT SETUP REQUEST message to the gNB in ​​operation 1e-25. The INITIAL CONTEXTSETUP REQUEST message may include QoS information to be applied when configuring the DRB, security information to be applied to the DRB (e.g., security keys, security algorithms, etc.), etc.

[0157] When 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 in operation 1e-26 to determine the UE capability information. When the UE receives the UE capability information request message, the UE may configure, generate and report the UE capability information message to the gNB in ​​operation 1e-27. The UE capability information may include information about which types of switching methods the UE supports. For example, the UE may report information about the UE capabilities to the gNB via an indicator, which indicates whether the UE supports the efficient switching method (i.e., the DAPS switching method) proposed in the present disclosure. When the gNB determines the UE capability information, according to each switching method, the gNB may instruct the UE to switch by defining an indicator, which indicates which type of switching is indicated in the switching command message. For example, the gNB may indicate the efficient switching method (DAPS switching method) proposed in the present disclosure to the UE, or may configure the DAPS switching method for the UE according to each bearer (DRB or SRB). When the gNB configures the DAPS handover method for the UE, the gNB also indicates other handover methods (e.g., a conditional handover method (a configuration of multiple target cells and multiple conditions is configured for the UE, and when the UE satisfies the conditions in the cell selection process or the cell reselection process, the UE performs a handover process on one target cell) or a handover method without a random access process) to prevent data loss or transmission delay that may occur during the handover. The UE may perform a handover process on the target gNB according to the handover method indicated in the handover command message.

[0158] To configure security with the UE, the gNB exchanges SecurityModeCommand messages in operation 1e-30 and SecurityModeComplete messages in operation 1e-35. When the security configuration is complete, the gNB sends an RRCConnectionReconfiguration message to the UE in operation 1e-40.

[0159] The RRCConnectionReconfiguration message includes configuration information for each service / bearer / RLC layer or each logical channel or each bearer, and the PDCP layer configuration information (pdcp-config) may include information on whether each bearer / logical channel uses ROHC, ROHC configuration information (e.g., ROHC version, initial information, etc.), statusReportRequired information (information with which the BS indicates a PDCP status report to the UE), and drb-ContinueROHC information (configuration information indicating that the ROHC configuration information is continued and used without change), and these information may be sent. In addition, the RRCConnectionReconfiguration message may include RRC connection configuration information. The bearer of the RRC connection is called an SRB and is used to send and receive RRC messages as control messages between the UE and the gNB.

[0160] The RRCConnectionReconfiguration message includes configuration information of the DRB where user data is to be processed, and the UE configures the DRB by using the configuration information of the DRB, and sends an RRCConnectionReconfigurationComplete message to the gNB in ​​operation 1e-45. When the DRB configuration about the UE is completed, the gNB sends an INITIAL CONTEXT SETUP COMPLETE message to the MME or AMF in operation 1e-50, and upon reception, the MME or AMF may exchange an S1 bearer setup (BEARER SETUP) message and an S1 bearer setup (BEARER SETUP RESPONSE) message with the S-GW in operations 1e-55 and 1e-60 to configure the S1 bearer. The S1 bearer refers to a link for data transmission, which is configured between the S-GW and the eNB and corresponds one-to-one to the DRB. After the above process is completed, the UE may send data to or receive data from the gNB through the S-GW in operations 1e-65 and 1e-70. Therefore, the general data transmission process mainly includes three operations: RRC connection establishment, security setup and DRB configuration. In addition, the gNB may send an RRCConnectionReconfiguration message to the UE in operation 1e-75 for some reason to update, add or change the configuration.

[0161] In the present disclosure, a bearer may include an SRB and a DRB, where SRB stands for signaling radio bearer, and DRB stands for 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 multiple items of user plane data. UM DRB indicates a DRB configured to use an RLC layer operating in a negative acknowledgement mode (UM), and an acknowledgement mode (AM) DRB indicates a DRB configured to use an RLC layer operating in an AM.

[0162] In the present disclosure, a bearer configured with a DAPS switching method may refer to or indicate a bearer whose identifier is included in a bearer list configured with a DAPS switching method, a bearer whose identifier is not included in a bearer list not configured with a DAPS switching method, a bearer whose bearer configuration information includes a DAPS switching method configuration indicator, or at least one bearer from bearers having a DAPS switching method configuration indicator configured in PDCP layer configuration information.

[0163] In the present disclosure, a bearer not configured with the DAPS switching method may refer to or indicate a bearer whose identifier is not included in the bearer list configured with the DAPS switching method, a bearer whose identifier is included in the bearer list not configured with the DAPS switching method, a bearer whose bearer configuration information does not include a DAPS switching method configuration indicator, or at least one bearer from bearers having a DAPS switching method configuration indicator not configured in the PDCP layer configuration information.

[0164] In the present disclosure, the source BS may be interpreted as a source cell (PCell, SpCell or SCell) or a source cell group (cell group or primary cell group), and the target BS may be interpreted as a target cell (PCell, SpCell or SCell) or a target cell group (cell group or primary cell group).

[0165] Figure 1F is a diagram illustrating a signaling procedure for performing handover in a next generation mobile communication system according to an embodiment of the present disclosure.

[0166] refer to Figure 1F In operation 1f-05, UE 1f-01 in RRC_connected mode state reports cell measurement reports to the current source gNB 1f-02 in a periodic manner or when a specific event is met.

[0167] According to the present disclosure, the source gNB may be referred to as a source base station, and the target gNB may be referred to as a target base station. The source gNB 1f-02 determines whether the UE 1f-01 is to perform a handover to a neighboring cell based on a cell measurement report. Handover refers to a technique of switching the source BS to another BS (or another cell in the same BS), and the source gNB 1f-02 provides services to the UE 1f-01 in a connected mode state. When the source gNB 1f-02 determines the handover, in operation 1f-10, the source gNB 1f-02 requests the handover by sending a handover request message (e.g., a handover preparation information message) to the target gNB 1f-03, which is a new BS providing services to the UE 1f-01. When the target gNB 1f-03 accepts the handover request, the target gNB 1f-03 sends a handover request positive acknowledgment (Ack) message (e.g., a handover command message) to the source gNB 1f-02 in operation 1f-15. After receiving the message, the source gNB 1f-02 sends a handover command message (including an RRC Reconfiguration message in a dedicated control channel (DCCH) of a handover request Ack message) to UE 1f-01 in operation 1f-20. The source gNB 1f-02 extracts the handover command message from the message received from the target gNB 1f-03 and sends the handover command message to UE 1f-01 by using an RRCConnectionReconfiguration message in operation 1f-20.

[0168] In the present disclosure, a method for determining an efficient DAPS switching method is provided as follows: when the source gNB 1f-02 sends a switching preparation information message in operation 1f-10, and in response thereto, the target gNB 1f-03 sends a switching command message to the source gNB 1f-02 in operation 1f-15, an efficient DAPS switching method is determined by using two messages (i.e., the switching preparation information message in operation 1f-10 and the switching command message in operation 1f-15).

[0169] Embodiment 1 of the method for determining an efficient DAPS switching provided by the present disclosure will now be described.

[0170] In embodiment 1 of the present disclosure, the entity for determining the DAPS switching method may be the source gNB 1f-02. In addition, in embodiment 1 of the present disclosure, when 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.

[0171] -The source gNB 1f-02 may indicate to the target gNB 1f-03 that the source gNB 1f-02 is to perform the DAPS handover method proposed in the present disclosure and may request the DAPS handover method by defining a new indicator in the handover preparation information message. The handover preparation information message may include the current bearer configuration information of UE 1f-01, security key information, cell group configuration information, capability information of UE 1f-01, etc. The source gNB 1f-02 is configured to pre-share the capabilities of the target gNB 1f-03, so it can know in advance whether the target BS supports the DAPS handover method. The source gNB 1f-02 may indicate to the target gNB 1f-03 that the source gNB 1f-02 is to perform the DAPS handover method, may indicate to the target BS that the source gNB 1f-02 may quickly or pre-perform early data forwarding, and may indicate to the target gNB 1f-03 that it is ready to receive data forwarding and perform processing. The source gNB 1f-02 can request a DAPS switching method for each bearer (DRB or SRB).

[0172] -When the target BS1f-03 receives the handover preparation information message and recognizes that the indicator requesting the DAPS handover method is included therein, when the target BS1f-03 configures the RRC Reconfiguration message to indicate the handover to the UE 1f-01, the target BS1f-03 may add the indicator indicating the DAPS handover method, the bearer configuration information required for the UE 1f-01 to perform the DAPS handover method, the bearer configuration information, the security key information, the cell group configuration information, or the system information to the RRC Reconfiguration message. In addition, the target BS1f-03 may add the RRC Reconfiguration message to the DL-DCCH message in the handover command message, and may send the handover command message to the source BS1f-02. The target BS1f-03 may perform the indication of the DAPS handover method for each bearer (DRB or SRB).

[0173] -When the source BS1f-02 receives the handover command message, the source BS1f-02 may extract the RRC Reconfiguration message included in the handover command message, and may send the RRC Reconfiguration message to the UE 1f-01, thereby indicating the handover. The source BS1f-02 may identify the DAPS handover method for each bearer indicated, and may perform the DAPS handover method for each bearer (DRB or SRB).

[0174] Embodiment 2 of the method for determining an efficient DAPS switching provided by the present disclosure will now be described.

[0175] In embodiment 2 of the present disclosure, the entity used to determine the DAPS switching method may be the target BS1f-03. In addition, in embodiment 2 of the present disclosure, when the source BS1f-02 requests the target BS1f-03 for the DAPS switching method, the target BS1f-03 may reject or accept the request from the source BS1f-02, or may indicate another switching method to the source BS1f-02 via a switching command message indicating another switching method.

[0176] -The source BS1f-02 may indicate to the target BS 1f-03 that the source BS1f-02 is to perform the DAPS switching method proposed in the present disclosure and may request the DAPS switching method by defining a new indicator in the switching preparation information message. The switching preparation information message may include the current bearer configuration information, security key information, cell group configuration information, capability information of UE 1f-01, etc. The source BS 1f-02 is configured to pre-share the capabilities of the target BS1f-03, so it can know in advance whether the target BS1f-03 supports the DAPS switching method. The source BS1f-02 may indicate to the target BS1f-03 that the source BS1f-02 will perform the DAPS switching method, may indicate to the target BS1f-03 that the source BS1f-02 can perform early data forwarding, and may indicate that the target BS1f-03 is ready to receive data forwarding and perform processing. The source BS1f-02 may request each bearer (DRB or SRB) to request the DAPS switching method.

[0177] -When the target BS1f-03 receives the switching preparation information message and identifies that it includes an indicator requesting the DAPS switching method, the target BS1f-03 may reject or accept the request for the DAPS switching method from the source BS1f-02, or may indicate another switching method to the source BS1f-02 based on whether the target BS1f-03 can support the DAPS switching method, the amount of current transmission resources, or scheduling.

[0178] -The target BS1f-03 may add an indicator of rejecting the request for the DAPS switching method, an indicator of accepting the DAPS request for the switching method, or an indicator indicating another switching method to the switching command message, and may send the switching command message. In the case where the target BS1f-03 configures the RRC Reconfiguration message to indicate the switching to the UE 1f-01, the target BS1f-03 may configure the RRC Reconfiguration message as follows: when the DAPS switching request is accepted, the RRCReconfiguration message includes an indicator indicating the DAPS switching method; or when the DAPS switching request is rejected, the RRCReconfiguration message includes an indicator indicating another switching method, and the RRC Reconfiguration message includes the bearer configuration information, bearer configuration information, security key information, cell group configuration information, or system information required for the UE 1f-01 to perform the DAPS switching method or the other switching method. In addition, the target BS1f-03 may add the RRC Reconfiguration message to the DL-DCCH message in the switching command message, and may send the switching command message to the source BS1f-02. The target BS1f-03 can perform instructions for the DAPS switching method for each bearer (DRB or SRB).

[0179] -When the source BS1f-02 receives the handover command message, the source BS1f-02 may determine the indicator included in the handover command message, and thus may identify whether the request for the DAPS handover method is accepted or rejected. When the request for the DAPS handover method is accepted, the source BS1f-02 may execute the DAPS handover method, may extract the RRCReconfiguration message included in the handover command message, and may send the RRC Reconfiguration message to the UE 1f-01, thereby indicating the handover. When the source BS1f-02 determines the indicator included in the handover command message, when the request for the DAPS handover method is rejected or another handover message is indicated, the source BS1f-02 may execute another handover method indicated by the target BS1f-03. In addition, the source BS1f-02 may extract the RRC Reconfiguration message included in the handover command message, and may send the RRCReconfiguration message to the UE 1f-01, thereby indicating the handover. As another method, when a separate indicator is not included in the handover command message, the source BS1f-02 may determine the type of handover message indicated by the target BS1f-03 by reading the RRCReconfiguration message included in the handover command message, and may identify whether to accept or reject the request for the DAPS handover method. The source BS1f-02 may execute the handover method (e.g., the DAPS handover method or another handover method) indicated in the RRC Reconfiguration message. The source BS1f-02 may identify the indicated DAPS handover method for each bearer, and may execute the DAPS handover method for each bearer (DRB or SRB).

[0180] Embodiment 3 of the method for determining an efficient DAPS switching provided by the present disclosure will now be described.

[0181] In embodiment 3 of the present disclosure, the entity for determining the DAPS switching method may be a target BS. In addition, in embodiment 3 of the present disclosure, the target BS 1f-03 may determine the capability of UE 1f-01, and may determine the switching method (e.g., DAPS switching method) based on whether the target BS can support the DAPS switching method, the amount of current transmission resources, or scheduling.

[0182] -The source BS1f-02 may add the current bearer configuration information, security key information, cell group configuration information, capability information of UE 1f-01, etc. of UE 1f-01 to the switching preparation information message, and may send a switching preparation information message to request the target BS1f-03 to switch. The source BS1f-02 is configured to pre-share the capabilities of the target BS1f-03, so it can know in advance whether the target BS1f-03 supports the DAPS switching method. When the target BS1f-03 indicates to execute the DAPS switching method, the source BS1f-02 may quickly or pre-perform early data forwarding.

[0183] -The target BS1f-03 may receive the switching preparation information message, and may determine the switching method (e.g., DAPS switching method) based on the capability information of UE 1f-01, whether the target BS1f-03 can support the DAPS switching method, the amount of current transmission resources, or scheduling. When the target BS1f-03 determines the DAPS switching method, the target BS1f-03 may add an indicator indicating the DAPS switching method to the switching command message, and may send the switching command message to UE 1f-01. In the case where the target BS1f-03 configures the RRCReconfiguration message to indicate the handover to the UE 1f-01, the target BS1f-03 may configure the RRC Reconfiguration message as follows: when a DAPS handover request is determined, the RRC Reconfiguration message includes an indicator indicating a DAPS handover method; or when a DAPS handover request is determined, the RRC Reconfiguration message includes an indicator indicating another handover method, and the RRC Reconfiguration message includes the bearer configuration information, bearer configuration information, security key information, cell group configuration information, or system information required for the UE 1f-01 to perform the DAPS handover method or another handover method. In addition, the target BS1f-03 may add the RRC Reconfiguration message to the DL-DCCH message in the handover command message, and may send the handover command message to the source BS1f-02. The target BS1f-03 may perform an indication of the DAPS handover method for each bearer (DRB or SRB).

[0184] -When the source BS1f-02 receives the handover command message, the source BS1f-02 may determine the indicator included in the handover command message, and thus may identify whether the DAPS handover method is determined. When the DAPS handover method is indicated, the source BS1f-02 may execute the DAPS handover method, may extract the RRC Reconfiguration message included in the handover command message, and may send the RRC Reconfiguration message to the UE 1f-01, thereby indicating the handover. When the source BS1f-02 determines the indicator included in the handover command message, when the DAPS handover method is not determined or another handover message is indicated, the source BS1f-02 may execute another handover method indicated by the target BS1f-03. In addition, the source BS1f-02 may extract the RRC Reconfiguration message included in the handover command message, and may send the RRC Reconfiguration message to the UE 1f-01, thereby indicating the handover. As another method, when a separate indicator is not included in the handover command message, the source BS 1f-02 may determine the type of the handover message indicated by the target BS 1f-03 by reading the RRC Reconfiguration message included in the handover command message, and may identify whether the DAPS handover method is determined. When another handover method is indicated, the source BS 1f-02 may execute the indicated another handover method. The source BS 1f-02 may identify the indicated DAPS handover method for each bearer, and may execute the DAPS handover method for each bearer (DRB or SRB).

[0185] A new implementation can be obtained by combining the methods of implementation 1, implementation 2, or implementation 3 for determining an efficient DAPS switching method.

[0186] According to an embodiment of the present disclosure, the BS may indicate the efficient switching method (DAPS switching method) proposed in the present disclosure to UE 1f-01 via an RRC Reconfiguration message; or in another method, the BS may configure the DAPS switching method for each bearer (DRB or SRB) of UE 1f-01. For example, a new indicator may be defined in the RRC Reconfiguration message to indicate the bearer configuration information, DPC PDCP configuration information, or RLC configuration information for each bearer identifier or each logical channel identifier, and the BS may indicate the efficient switching message for each bearer identifier or each logical channel identifier to UE 1f-01 by using the new identifier. When the BS configures the DAPS switching method for UE 1f-01, the BS also indicates other switching methods (for example, a conditional switching method (a configuration of multiple target cells and multiple conditions is configured for UE 1f-01, and when UE 1f-01 meets the conditions during the cell selection process or the cell reselection process, UE 1f-01 performs a switching process on a target cell) or a switching method without a random access process), thereby preventing data loss or transmission delay that may occur during switching.

[0187] When UE 1f-01 receives the RRC Reconfiguration message, UE 1f-01 interrupts or continues to send and receive data to and from the source gNB 1f-02 by using the configured handover method, and starts the T304 timer in operation 1f-25. When UE 1f-01 fails to successfully switch to the target gNB 1f-03 within a preset time (for example, when the T304 timer expires), in response to the expiration of the T304 timer, UE 1f-01 returns to its default configuration and transitions to the RRC idle state. In addition, UE 1f-01 may trigger the RRC connection reestablishment process, and when an efficient handover method is configured and the link to the source gNB 1f-02 is active, UE 1f-01 may fall back and report its handover failure to the source gNB 1f-02. In operation 1f-30 and operation 1f-35, the source gNB 1f-02 provides a sequence number (SN) status of UL / DL data for each bearer (e.g., for each RLC UM bearer or each RLC AM bearer), and when there is DL data or UL data, the source gNB 1f-02 sends the DL data or UL data to the target gNB 1f-03. In operation 1f-40, the UE 1f-01 attempts random access to the target cell indicated by the source gNB 1f-02. The UE 1f-01 performs random access to switch to the target cell via a switching notification and simultaneously match UL synchronization. For random access, the UE 1f-01 sends a preamble corresponding to the preamble ID provided by the source gNB 1f-02 or corresponding to a randomly selected preamble to the target cell. After sending the preamble and after a time period corresponding to a specific number of subframes, the 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 a RAR message is received during the RAR window in operation 1f-45, UE 1f-01 sends a handover complete message in an RRC Reconfiguration Complete message to the target gNB 1f-03 in operation 1f-55. When UE 1f-01 successfully receives the RAR message from the target gNB 1f-03, UE 1f-01 ends the T304 timer in operation 1f-50.

[0188] In order to switch the path of the bearer configured for the source gNB 1f-02, the target gNB 1f-03 requests the core network 1f-04 (e.g., MME / S-GW / AMF) to switch the path of the bearer in operations 1f-60 and 1f-65, and instructs the source gNB 1f-02 to discard the UE context of UE 1f-01 in operation 1f-70. The target gNB 1f-03 may send an RRC message (e.g., an RRC Reconfiguration message) to UE 1f-01 in operation 1f-71, and may instruct UE 1f-01 to release the link to the source gNB 1f-02 by using an indicator. As another method, the target gNB 1f-03 may send MAC control information, RLC control information, or PDCP control information to UE 1f-01, thereby instructing UE 1f-01 to release the link to the source gNB 1f-02. UE 1f-01 attempts to receive data from the target gNB 1f-03 at the starting point of the RAR window, and after receiving the RAR message, UE 1f-01 sends an RRC Reconfiguration Complete message and receives DL transmission resources or UL transmission resources, thereby starting to send and receive data to and from the target gNB 1f-03.

[0189] According to an embodiment of the present disclosure, when the BS configures or indicates the embodiment 2 (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 BS may apply the following method. In the present disclosure, when the BS configures the DAPS switching method to the UE 1f-01 or the UE 1f-01 receives a switching command message for configuring the DAPS switching method from the BS, one of the following methods or a combination of various methods in the following methods may be performed.

[0190] -Method 1-1: When the BS (source gNB 1f-02, target gNB 1f-03, LTE BS or NR BS) instructs or configures UE 1f-01, the BS may add Mobility Control Info or Reconfiguration With Sync configuration information to the RRC Reconfiguration message. The BS may define an indicator in the SRB-ToAddMod of the SRB-ToAddModList or the DRB-ToAddMod of the DRB-ToAddModList in the bearer configuration information (dedicated radio resource configuration or radio bearer configuration) of the RRC Reconfiguration message, and may indicate the DAPS switching method for each bearer (each SRB or DRB) by using the defined indicator. In addition, the BS may indicate the DAPS switching method for each bearer by defining an indicator in the pdcp-config in the SRB-ToAddMod or DRB-ToAddMod. In the case where the LTE BS indicates or configures switching to the UE 1f-01 by using the LTERRCRecofiguration message, since pdcp-config is not defined in SRB-ToAddMod but the default PDCP layer configuration is defined in LTE, the LTE BS can configure the DAPS switching method for each bearer by defining an indicator in the SRB-ToAddMod regarding the SRB, and can configure the DAPS switching method for each bearer by defining an indicator in the pdcp-config in the DRB-ToAddMod.

[0191] According to the configuration indicated in the received switching command message (RRC Reconfiguration message), for each bearer, UE 1f-01 may perform the DAPS switching method on the bearer configured with the DAPS switching method, and may perform the conventional switching method on the bearer not configured with the DAPS switching method. In addition, when an indicator indicating or configuring the switching method type (e.g., MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO) regarding UE 1f-01 is included in the Mobility Control Info or Reconfiguration With Sync configuration information of the switching command message and the DAPS switching method is configured for each bearer, when UE 1f-01 performs the switching process for each bearer, UE 1f-01 may preferentially apply the DAPS switching method compared to other switching method types. For example, according to the configuration, for each bearer, UE 1f-01 may perform a DAPS switching method on a bearer configured with a DAPS switching method, and may perform a switching method on a bearer not configured with a DAPS switching method, the switching method being configured based on an indicator in the MobilityControl Info or Reconfiguration With Sync configuration information of a switching command message indicating or configuring a switching method type (e.g., MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO) for UE 1f-01. In addition, in order to reduce the implementation complexity of UE 1f-01, when a DAPS switching method is configured for at least one bearer or a certain bearer, the Mobility Control Info or Reconfiguration With Sync configuration information of the switching command message may be configured not to indicate or configure different switching method types (e.g., MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO) for UE 1f-01.

[0192] In addition, when UE 1f-01 receives a switching command message (RRC Reconfiguration message), when the DAPS switching method is configured for at least one bearer or a certain bearer for each bearer in the switching command message (RRC Reconfiguration message), UE 1f-01 can apply the processing method of the RRC layer, SDAP layer, MAC layer, PHY layer or SRB to execute the DAPS switching method proposed in the present disclosure; and for each bearer configured with the DAPS switching method, UE1f-01 can apply the processing method of the PDCP layer or the RLC layer to execute the DAPS switching method proposed in the present disclosure.

[0193] -Method 1-2: When the BS (source gNB 1f-02, target gNB 1f-03, LTE BS or NR BS) instructs or configures UE 1f-01, the BS may add Mobility Control Info or Reconfiguration With Sync configuration information to the RRC Reconfiguration message. The BS may define an indicator in the DRB-ToAddMod of the DRB-ToAddModList in the bearer configuration information (dedicated radio resource configuration or radio bearer configuration) of the RRC Reconfiguration message, thereby indicating the DAPS switching method for each bearer (each DRB) by using the defined indicator; and a separate indicator may not be introduced for the configuration of the DAPS switching method for SRBs. For example, when the DAPS switching method is configured for at least one bearer (DRB) or a certain bearer (DRB) for each bearer in the received switching command message (RRCReconfiguration message), UE 1f-01 may apply the SRB processing method to perform the DAPS switching method proposed in the present disclosure. In addition, the BS may indicate the DAPS switching method for each bearer by defining an indicator in pdcp-config in DRB-ToAddMod.

[0194] According to the configuration indicated in the received switching command message (RRC Reconfiguration message), for each bearer, UE 1f-01 may perform the DAPS switching method on the bearer configured with the DAPS switching method, and may perform the conventional switching method on the bearer not configured with the DAPS switching method. In addition, when an indicator indicating or configuring the switching method type (e.g., MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO) regarding UE 1f-01 is included in the Mobility Control Info or Reconfiguration With Sync configuration information of the switching command message and the DAPS switching method is configured for each bearer, when UE 1f-01 performs the switching process for each bearer, UE 1f-01 may preferentially apply the DAPS switching method compared to other switching method types. For example, according to the configuration, for each bearer, UE 1f-01 may perform a DAPS switching method on a bearer configured with a DAPS switching method, and may perform a switching method on a bearer not configured with a DAPS switching method, the switching method being configured based on an indicator in the MobilityControl Info or Reconfiguration With Sync configuration information of a switching command message indicating or configuring a switching method type (e.g., MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO) for UE 1f-01. In addition, in order to reduce the implementation complexity of UE 1f-01, when a DAPS switching method is configured for at least one bearer or a certain bearer, the Mobility Control Info or Reconfiguration With Sync configuration information of the switching command message may be configured not to indicate or configure different switching method types (e.g., MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO) for UE 1f-01. In addition, when UE 1f-01 receives a switching command message (RRC Reconfiguration message), when the DAPS switching method is configured for at least one bearer or a certain bearer for each bearer in the switching command message (RRC Reconfiguration message), UE 1f-01 can apply the processing method of the RRC layer, SDAP layer, MAC layer, PHY layer or SRB to execute the DAPS switching method proposed in the present disclosure; and for each bearer configured with the DAPS switching method, UE 1f-01 can apply the processing method of the PDCP layer or the RLC layer to execute the DAPS switching method proposed in the present disclosure.

[0195] -Method 2-1: When the BS (source gNB 1f-02, target gNB 1f-03, LTE BS or NR BS) indicates or configures UE 1f-01, the BS may add Mobility Control Info or Reconfiguration With Sync configuration information to the RRC Reconfiguration message. The BS may indicate that the DAPS switching method is configured for at least one bearer or a certain bearer via an indicator by defining and including an indicator for indicating or configuring the DAPS switching method in Mobility Control Info or Reconfiguration WithSync. In addition, the BS may define an indicator in SRB-ToAddMod of SRB-ToAddModList or DRB-ToAddMod of DRB-ToAddModList in the bearer configuration information (dedicated radio resource configuration or radio bearer configuration) of the RRC Reconfiguration message, thereby indicating the DAPS switching method used for each bearer (each SRB or DRB). In addition, the BS can indicate the DAPS switching method for each bearer by defining an indicator in pdcp-config in SRB-ToAddMod or DRB-ToAddMod. In addition, in the case where the LTE BS indicates or configures the switching to the UE 1f-01 by using the LTERRCRecofiguration message, since pdcp-config is not defined in SRB-ToAddMod but the use of the default PDCP layer configuration is defined in LTE, the LTE BS can configure the DAPS switching method for each bearer by defining an indicator in SRB-ToAddMod about the SRB, and can configure the DAPS switching method for each bearer by defining an indicator in pdcp-config in DRB-ToAddMod.

[0196] According to the configuration indicated in the received switching command message (RRC Reconfiguration message), for each bearer, UE 1f-01 may perform the DAPS switching method on the bearer configured with the DAPS switching method, and may perform the conventional switching method on the bearer not configured with the DAPS switching method. In addition, when an indicator indicating or configuring the switching method type (e.g., MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO) regarding UE 1f-01 is included in the Mobility Control Info or Reconfiguration With Sync configuration information of the switching command message and the DAPS switching method is configured for each bearer, when UE 1f-01 performs the switching process for each bearer, UE 1f-01 may preferentially apply the DAPS switching method compared to other switching method types. For example, according to the configuration, for each bearer, UE 1f-01 may perform a DAPS switching method on a bearer configured with a DAPS switching method, and may perform a switching method on a bearer not configured with a DAPS switching method, the switching method being configured based on an indicator in the MobilityControl Info or Reconfiguration With Sync configuration information of a switching command message indicating or configuring a switching method type (e.g., MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO) for UE 1f-01. In addition, in order to reduce the implementation complexity of UE 1f-01, when a DAPS switching method is configured for at least one bearer or a certain bearer, the Mobility Control Info or Reconfiguration With Sync configuration information of the switching command message may be configured not to indicate or configure different switching method types (e.g., MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO) for UE 1f-01.

[0197] In addition, when UE 1f-01 receives a switching command message (RRC Reconfiguration message), when an indicator indicating or configuring the DAPS switching method is included (or configured) in the Mobility Control Info or Reconfiguration With Sync in the switching command message (RRC Reconfiguration message), UE 1f-01 can apply the processing method of the RRC layer, SDAP layer, MAC layer, PHY layer or SRB to perform the DAPS switching method proposed in the present disclosure; and for each bearer configured with the DAPS switching method, UE 1f-01 can apply the processing method of the PDCP layer or the RLC layer to perform the DAPS switching method proposed in the present disclosure.

[0198] -Method 2-2: When the BS (source gNB 1f-02, target gNB 1f-03, LTE BS or NR BS) indicates or configures to UE 1f-01, the BS may add Mobility Control Info or Reconfiguration With Sync configuration information to the RRC Reconfiguration message. The BS may indicate that the DAPS switching method is configured for at least one bearer or a certain bearer via an indicator by defining and including an indicator for indicating or configuring the DAPS switching method in Mobility Control Info or Reconfiguration WithSync. In addition, the BS may indicate the DAPS switching method for each bearer (each DRB) by defining an indicator in DRB-ToAddMod of DRB-ToAddModList in the bearer configuration information (dedicated radio resource configuration or radio bearer configuration) of the RRC Reconfiguration message, and may not introduce a separate indicator for the configuration of the DAPS switching method for SRBs. For example, when UE 1f-01 receives a switching command message (RRCReconfiguration message), in which the DAPS switching method is configured for at least one bearer (DRB) or a certain bearer (DRB) relative to each bearer in the received switching command message (RRCReconfiguration message), UE 1f-01 can apply the SRB processing method to perform the DAPS switching method proposed in the present disclosure. In addition, the BS can indicate the DAPS switching method for each bearer by defining an indicator in pdcp-config in DRB-ToAddMod.

[0199] According to the configuration indicated in the received handover command message (RRC Reconfiguration message), for each bearer, UE 1f-01 may perform the DAPS handover method on the bearer configured with the DAPS handover method, and may perform the conventional handover method on the bearer not configured with the DAPS handover method. When an indicator indicating or configuring the handover method type (e.g., MakeBeforeBreak handover, Rach-skip handover, RACH-less handover, or conditional handover CHO) about UE 1f-01 is included in the Mobility Control Info or Reconfiguration With Sync configuration information of the handover command message and the DAPS handover method is configured for each bearer, when UE 1f-01 performs the handover process for each bearer, UE 1f-01 may preferentially apply the DAPS handover method compared to other handover method types. For example, according to the configuration, for each bearer, UE 1f-01 may perform a DAPS switching method on a bearer configured with a DAPS switching method, and may perform a switching method on a bearer not configured with a DAPS switching method, the switching method being configured based on an indicator in the Mobility ControlInfo or Reconfiguration With Sync configuration information of a switching command message indicating or configuring a switching method type (e.g., MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO) for UE 1f-01. In addition, in order to reduce the complexity of the implementation scheme of UE 1f-01, when a DAPS switching method is configured for at least one bearer or a certain bearer, the Mobility Control Info or ReconfigurationWith Sync configuration information of the switching command message may be configured not to indicate or configure different switching method types (e.g., MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO) for UE 1f-01.In addition, when UE 1f-01 receives a switching command message (RRC Reconfiguration message), when an indicator indicating or configuring the DAPS switching method is included (or configured) in the Mobility ControlInfo or Reconfiguration With Sync in the switching command message (RRC Reconfiguration message), UE 1f-01 can apply the processing method of the RRC layer, SDAP layer, MAC layer, PHY layer or SRB to perform the DAPS switching method proposed in the present disclosure, and for each bearer configured with the DAPS switching method, UE 1f-01 can apply the processing method of the PDCP layer or the RLC layer to perform the DAPS switching method proposed in the present disclosure.

[0200] -Method 3-1: When the BS (source gNB 1f-02, target gNB 1f-03, LTE BS or NR BS) instructs or configures UE 1f-01, the BS may add Mobility Control Info or Reconfiguration With Sync configuration information to the RRC Reconfiguration message. The BS may indicate that the DAPS switching method is configured for at least one bearer or a certain bearer via an indicator by defining and including an indicator for indicating or configuring the DAPS switching method in Mobility Control Info or Reconfiguration With Sync. In addition, the BS may configure a list of bearers configured with the DAPS switching method and include the list in Mobility Control Info or Reconfiguration With Sync, and may include an identifier (SRB or DRB) of the bearer configured with the DAPS switching method in the bearer list, thereby indicating whether the DAPS switching method is configured for each bearer. In addition, the BS may configure a list of bearers that are not configured with the DAPS switching method and include the list in Mobility Control Info or Reconfiguration With Sync, and may include identifiers (SRBs or DRBs) of bearers that are not configured with the DAPS switching method in the bearer list, thereby indicating whether the DAPS switching method is configured for each bearer.

[0201] According to the configuration indicated in the received switching command message (RRC Reconfiguration message), for each bearer, UE 1f-01 may perform the DAPS switching method on 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 may perform a conventional switching method on 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, or a bearer whose identifier is included in the bearer list not configured with the DAPS switching method. In addition, when 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) is included in the Mobility Control Info or Reconfiguration With Sync configuration information of the switching command message and the DAPS switching method is configured for each bearer, when UE 1f-01 performs the switching process for each bearer, UE 1f-01 may preferentially apply the DAPS switching method compared to other switching method types. For example, according to the configuration, for each of the bearers, UE 1f-01 may perform the DAPS switching method on a bearer configured with the DAPS switching method, a bearer whose identifier is included in a bearer list configured with the DAPS switching method, or a bearer whose identifier is not included in a bearer list not configured with the DAPS switching method, and may perform a conventional switching method on a bearer not configured with the DAPS switching method, a bearer whose identifier is not included in a bearer list configured with the DAPS switching method, or a bearer whose identifier is included in a bearer list not configured with the DAPS switching method, wherein the switching method is configured based on an indication in the Mobility Control Info or Reconfiguration With Sync configuration information of the switching command message or an indicator configuring the switching method type of UE 1f-01 (e.g., MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO). In addition, in order to reduce the implementation complexity of UE 1f-01, when the DAPS switching method is configured for at least one bearer or a certain bearer, the Mobility Control Info or Reconfiguration With Sync configuration information of the switching command message can be configured not to indicate or configure different switching method types regarding UE 1f-01 (for example, MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO).In addition, when UE 1f-01 receives a switching command message (RRC Reconfiguration message), when an indicator indicating or configuring the DAPS switching method is included (or configured) in the Mobility ControlInfo or Reconfiguration With Sync of the switching command message (RRC Reconfiguration message), UE 1f-01 can apply the processing method of the RRC layer, SDAP layer, MAC layer, PHY layer or SRB to perform the DAPS switching method proposed in the present disclosure, and for each bearer, UE 1f-01 can apply the processing method of the PDCP layer or the RLC layer to perform the DAPS switching method proposed in the present disclosure on 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.

[0202] -Method 3-2: When the BS (source gNB 1f-02, target gNB 1f-03, LTE BS or NR BS) instructs or configures UE 1f-01, the BS may add Mobility Control Info or Reconfiguration With Sync configuration information to the RRC Reconfiguration message. The BS may indicate that the DAPS switching method is configured for at least one bearer or a certain bearer via an indicator by defining and including an indicator for indicating or configuring the DAPS switching method in Mobility Control Info or Reconfiguration With Sync. In addition, the BS may configure a list of bearers configured with the DAPS switching method and include the list in Mobility Control Info or Reconfiguration With Sync, and may include an identifier (SRB or DRB) of the bearer configured with the DAPS switching method in the bearer list, thereby indicating whether the DAPS switching method is configured for each bearer. In addition, the BS may configure a list of bearers that are not configured with the DAPS switching method, and include the list in Mobility Control Info or Reconfiguration With Sync, and may include identifiers (SRBs or DRBs) of bearers that are not configured with the DAPS switching method in the bearer list, thereby indicating whether the DAPS switching method is configured for each bearer. In addition, for SRBs, a separate indicator for configuring the DAPS switching method may not be introduced. For example, when UE 1f-01 receives a switching command message (RRC Reconfiguration message), when the DAPS switching method is configured for at least one bearer (DRB) or a certain bearer (DRB) for each bearer in the received switching command message (RRC Reconfiguration message), UE 1f-01 may apply the SRB processing method to perform the DAPS switching method proposed in the present disclosure.

[0203] According to the configuration indicated in the received switching command message (RRC Reconfiguration message), for each bearer, UE 1f-01 may perform the DAPS switching method on 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 may perform a conventional switching method on 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, or a bearer whose identifier is included in the bearer list not configured with the DAPS switching method. In addition, when 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) is included in the Mobility Control Info or Reconfiguration With Sync configuration information of the switching command message and the DAPS switching method is configured for each bearer, when UE 1f-01 performs the switching process for each bearer, UE 1f-01 may preferentially apply the DAPS switching method compared to other switching method types. For example, for each of the bearers, according to the configuration, UE 1f-01 can perform the DAPS switching method on 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 can perform a general switching method on 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, or a bearer whose identifier is included in the bearer list not configured with the DAPS switching method, wherein the switching method is configured based on an indication in the Mobility Control Info or Reconfiguration With Sync configuration information of the switching command message or an indicator configuring the switching method type of UE 1f-01 (for example, MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO). In addition, in order to reduce the implementation complexity of UE 1f-01, when the DAPS switching method is configured for at least one bearer or a certain bearer, the Mobility Control Info or Reconfiguration With Sync configuration information of the switching command message can be configured not to indicate or configure different switching method types regarding UE 1f-01 (for example, MakeBeforeBreak switching, Rach-skip switching, RACH-less switching, or conditional switching CHO).In addition, when an indicator indicating or configuring the DAPS switching method is included (or configured) in the Mobility Control Info or Reconfiguration With Sync in the received switching command message (RRCReconfiguration message), the UE 1f-01 can apply the processing method of the RRC layer, SDAP layer, MAC layer, PHY layer or SRB to perform the DAPS switching method proposed in the present disclosure, and for each bearer, the UE 1f-01 can apply the processing method of the PDCP layer or the RLC layer to perform the DAPS switching method proposed in the present disclosure on 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.

[0204] Hereinafter, the present disclosure proposes a hitless handover method capable of minimizing a data interruption time due to handover or making the data interruption time 0 ms in a next generation mobile communication system.

[0205] UE 1f-01 can be configured with multiple first bearers with the source BS1f-02. For each of the multiple first bearers, data sending and receiving (transmission and reception of UL or DL ​​data) can be performed by using the protocol layer (PHY layer, MAC layer, RLC layer, PDCP layer, etc.), and in the present disclosure, for the sake of ease of description, it is assumed in the drawings and description that UE 1f-01 has one bearer.

[0206] Figure 1G Specific operations of Embodiment 1 of an efficient handover method for minimizing data interruption time due to handover according to an embodiment of the present disclosure are shown.

[0207] refer to Figure 1G According to an embodiment of the present disclosure, in embodiment 1 of the efficient handover method, when UE 1g-20 transmits data to or receives data from source BS 1g-05 in the first operation 1g-01 and then receives a handover command message, UE 1g-20 may release the link to source BS 1g-05 based on the handover method indicated by the handover command message (e.g., RRC Reconfiguration message), may perform a random access procedure to target BS 1g-10, and may perform a handover procedure. As another method, in order to minimize the data interruption time occurring at the time of handover based on the indicated handover method, UE 1g-20 may continuously transmit and receive data to and from source BS 1g-05.

[0208] According to an embodiment of the present disclosure, in the second operation 1g-02, when UE 1g-20 performs a random access procedure on the target BS 1g-10 by using the handover method indicated by the handover command message received from the source BS 1g-05, sends a preamble to the target BS 1g-10, or initially sends data in UL transmission resources by using PUCCH or PUSCH transmission resources, UE1g-20 may suspend sending and receiving data to and from the source BS 1g-05 (UL data transmission and DL data reception).

[0209] According to an embodiment of the present disclosure, in the third operation 1g-03, UE 1g-20 can complete the random access process to the target BS1g-10, send a switching completion message to the target BS1g-10, and start sending and receiving data to and from the target BS1g-10 (UL data sending and DL data reception).

[0210] According to an embodiment of the present disclosure, in Embodiment 1 of the efficient handover method of the present disclosure, it may be described that the handover method of the present disclosure is performed when the DAPS handover method is not configured.

[0211] Figure 1H Specific operations of Embodiment 2 of an efficient handover method for minimizing data interruption time due to handover according to an embodiment of the present disclosure are shown.

[0212] refer to Figure 1H According to an embodiment of the present disclosure, in embodiment 2 of the efficient switching method, in the first operation 1h-01, when the UE 1h-20 sends or receives data with the source BS1h-05, the UE 1h-20 may receive a switching command message from the source BS1h-05. When the source BS1h-05 indicates a switching method (e.g., a DAPS switching method) or indicates switching for each bearer in the switching command message according to embodiment 2 of the efficient switching method proposed in the present disclosure, even when the UE 1h-20 has received the switching command message, the UE 1h-20 may continue to send and receive data to and from the source BS1h-05 by using the protocol layer 1h-22 for the first bearer, so as to minimize the data interruption time occurring during the switching.

[0213] In addition, when the RRC layer of the UE 1h-20 identifies an indication of a handover method (e.g., a DAPS handover method) in a handover command message according to implementation mode 2 of the efficient handover method proposed in the present disclosure, or identifies an identifier of a DAPS handover method for each bearer, the RRC layer may send an indicator to a PDCP layer corresponding to each bearer or a bearer indicating a DAPS handover method. When the PDCP layer receives the indicator, the PDCP layer may, from the first PDCP layer architecture 1i-11 or 1i-12 (see Fig. 1I ) Switch to the second PDCP layer architecture 1i-20 (see Fig. 1I ).

[0214] Figure 1H The first operation 1h-01 can be described as an operation in which UE 1h-20 receives a handover command message (RRCReconfiguration message) from a BS. When UE 1h-20 switches to the second PDCP layer architecture 1i-20 according to the configuration included in the received handover command message, UE 1h-20 can pre-configure or pre-establish a protocol layer (PHY layer, MAC layer, RLC layer or PDCP layer) 1h-21 for the second bearer of the target BS1h-10, can generate and update security keys for the target BS1h-10, and can configure a header (or data) compression context for the target BS1h-10. In addition, the UE 1h-20 may receive a handover command message from the source BS 1h-05, and in the handover command message, when the source BS 1h-05 indicates the DAPS handover method proposed in the present disclosure, when the source BS 1h-05 indicates the DAPS handover method for a specific bearer, or when the PDCP realignment timer value is newly configured, the UE 1h-20 may, for each bearer or a bearer indicating the DAPS handover method, Fig. 1I The first PDCP layer architecture or function 1i-11 or 1i-12 is switched to the one proposed in the present disclosure Fig. 1I The second PDCP layer architecture or function 1i-20. When the UE 1h-20 Fig. 1I The first PDCP layer architecture or function 1i-11 or 1i-12 is switched to the one proposed in the present disclosure Fig. 1I When the second PDCP layer architecture or function 1i-20 is implemented, the UE 1h-20 may update the variable used for realignment to a predicted PDCP SN or COUNT value to be received next time, may stop the realignment timer and may restart the realignment timer.

[0215] In addition, in the aforementioned situation, when UE 1h-20 receives a handover command message (e.g., an RRCReconfiguration message), the RRC layer (not shown) of UE 1h-20 may start a first timer (e.g., T304). When UE 1h-20 performs a random access procedure on the target BS1h-10 to perform handover and then 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. In the event of a handover failure and the expiration of the first timer, when the link to the source BS1h-05 is active, UE 1h-20 may fall back and report its handover failure to the source BS 1h-05, and may attempt link recovery; and when the link to the source BS1h-05 is inactive, UE 1h-20 may perform an RRC connection reestablishment procedure.

[0216] The handover command message received by the UE 1h-20 from the source BS 1h-05 may include information by which the second bearer is configured to have the same identifier as the first bearer and is established so that a data interruption time does not occur in each bearer. In embodiment 2 of the present disclosure, the PDCP layer for the first bearer and the PDCP layer for the second bearer may be logically operated as one PDCP layer, and reference will now be made to Fig. 1I Provide a detailed description of the operation.

[0217] In embodiment 2 of the present disclosure, when UE 1h-20 is configured to send UL data to the source BS 1h-05 and the target BS 1h-10, in order to avoid coverage reduction or prevent link selection due to insufficient transmission power of UE 1h-20, when UE 1h-20 sends UL data, UE 1h-20 must determine which BS UE 1h-20 must request transmission resources from and send UL data, and UE 1h-20 in embodiment 2 of the present disclosure may send UL data to only one of the source BS 1h-05 and the target BS 1h-10. More specifically, in embodiment 2 of the present disclosure, when UE 1h-20 does not have the ability to send UL data to different BSs at the same time at different frequencies or the same frequency (dual uplink transmission), UE 1h-20 may send UL data to only one BS of the source BS 1h-05 and the target BS 1h-10 within one time unit. Therefore, UE 1h-20 can perform a scheduling request only on one BS of the source BS1h-05 and the target BS1h-10, can send a report (e.g., a buffer status report) on the size of multiple data items to be sent by the PDCP layer to only one BS of the source BS1h-05 and the target BS 1h-10, can receive UL transmission resources, and thus can send UL data to only one BS. In addition, even when UE 1h-20 receives a switching command message from the source BS1h-05, UE1h-20 can continue to send and receive data by retransmission HARQ to prevent data loss without resetting the MAC layer for the first bearer. In addition, the RLC layer in AM mode can continuously perform RCL retransmission.

[0218] As another method, when the handover command message indicates implementation mode 2 (DAPS handover method) of the efficient handover method proposed in the present disclosure for each bearer, the UE 1h-20 may continue to send data to the source BS1h-05 or receive data from the source BS1h-05 only for the PDCP layer, RLC layer or MAC layer corresponding to the bearer or logical channel identifier indicated in the handover command message for implementation mode 2 (DAPS handover method), or only for the data corresponding to the bearer or logical channel identifier. In addition, when the first condition proposed in the present disclosure is met (for example, when UL data transmission is switched to the target BS1h-10), the UE 1h-20 may continue to send RLC control data (RLC status report), PDCP control data (ROHC feedback or PDCP status report) or HARQ retransmission to the source BS1h-05 or receive the above data from the source BS1h-05 only for the PDCP layer, RLC layer or MAC layer corresponding to the bearer or logical channel identifier indicated in the handover command message for implementation mode 2 (DAPS handover method). In addition, when the switching command message indicates implementation mode 2 (DAPS switching method) of the efficient switching method proposed in the present disclosure for each bearer, UE 1h-20 may stop sending data to or receiving data from the source BS1h-05 for the PDCP layer, RLC layer or MAC layer corresponding to the bearer or logical channel identifier indicating implementation mode 2 (DAPS switching method) in the switching command message.

[0219] Afterwards, the UE 1h-20 may receive a switching command message. According to an embodiment of the present disclosure, when the switching command message indicates the DAPS switching method proposed in the present disclosure, indicates the DAPS switching method for a specific bearer, configures the DAPS switching method for at least one bearer, configures the DAPS switching method for a certain bearer, or newly configures QoS flow and bearer mapping information, the UE 1h-20 may switch from the first SDAP layer architecture or functions 1j-10 and 1j-12 proposed in the present disclosure to the second SDAP layer architecture or function 1j-20 for each bearer or a bearer indicating the DAPS switching method.

[0220] In addition, the second SDAP layer architecture can be configured in the following manner: the existing first QoS flow and the existing bearer mapping information for the source BS are maintained to process the UL data to be sent to the source BS and the DL data to be received from the source BS. The second QoS flow and the bearer mapping information newly configured in the switching command message can be configured for the target BS and can be used to process the UL data to be sent to the target BS and the DL data to be received from the target BS. For example, in the second SDAP layer architecture proposed in the present disclosure, the first QoS flow and the bearer mapping information of the source BS or the second QoS flow and the bearer mapping information of the target BS are maintained, so that the data for the source BS and the data for the target BS can be processed separately.

[0221] According to an embodiment of the present disclosure, the SDAP layer in the second SDAP layer architecture can identify whether the data received from the lower layer is data received from the source BS or data received from the target BS by using a 1-bit indicator of the SDAP header, a 1-bit indicator of the PDCP header, or information indicated by the PDCP layer. When the BS indicates the DAPS switching method for each bearer to the UE by using a switching command message, the BS can always indicate the DAPS switching method for the default bearer (default DRB). In this way, when data that does not correspond to the QoS flow and bearer mapping information occurs in the new QoS flow when performing the DAPS switching process, the BS can instruct the UE to always send UL data via the default bearer.

[0222] When the DAPS switching method is not configured for the default bearer, UL data transmission for the new QoS flow occurring in the switching is unavailable, so that data interruption time may occur. As another method, when the UE receives a switching command message (e.g., an RRC Reconfiguration message) indicating implementation mode 2 (DAPS switching method) and the SDAP layer configuration information or the second QoS flow and bearer mapping information of the target BS is configured in the RRC message, when the first condition proposed by the present disclosure is met, the UE can apply the SDAP layer configuration information or the second QoS flow and bearer mapping information. In addition, in the above situation, when the switching command message indicates implementation mode 2 (DAPS switching method) for each bearer, when the UE maintains the first QoS flow and bearer mapping information of the source BS, the UE may only maintain and apply the first QoS flow and bearer mapping information corresponding to the bearer indicating implementation mode 2, and the UE may release or not apply the first QoS flow and bearer mapping information corresponding to the bearer not indicating implementation mode 2; and when the SDAP layer configuration information or the second QoS flow and bearer mapping information of the target BS is configured in the RRC message, when the first condition proposed in the present disclosure is met, the UE may apply the SDAP layer configuration information or the second QoS flow and bearer mapping information to send data to or receive data from the target BS.

[0223] According to an embodiment of the present disclosure, Figure 1H In implementation mode 2 of the efficient switching method, in the second operation 1h-02, the UE 1h-20 may perform a random access procedure on the target BS1h-10 by using the protocol layer of the second bearer, and the target BS1h-10 is indicated in the switching command message. When the random access procedure is performed by using the protocol layer of the second bearer, the UE 1h-20 may continue to send data to or receive data from the source BS1h-05 (UL data transmission or DL ​​data reception) by using the protocol layer of the first bearer. The second operation 1h-02 may be described as the following operation: the UE 1h-20 performs a cell selection procedure or a cell reselection procedure, and performs a random access procedure on the target cell indicated by the switching command message (RRCReconfiguration message) received from the source BS1h-05.

[0224] According to an embodiment of the present disclosure, Figure 1H In implementation mode 2 of the efficient switching method, when the first condition to be described below is satisfied in the third operation 1h-03, the UE 1h-20 may suspend sending UL data to the source BS1h-05 by using the protocol layer 1h-22 of the first bearer among the bearers configured with the DAPS switching method, and may send UL data to the target BS1h-10 by using the protocol layer 1h-21 of the second bearer. In this regard, the UE 1h-20 may continue to receive DL data from the source BS1h-05 and the target BS1h-10 by using the protocol layers of the first bearer and the second bearer. The third operation 1h-03 may be the following operation: the UE 1h-20 satisfies the first condition, thereby switching the UL transmission from the source BS1h-05 to the target BS1h-10. More specifically, in this operation, UE 1h-20 sends UL data to the source BS 1h-05 via the first bearer until UE 1h-20 satisfies the first condition. When UE 1h-20 satisfies the first condition, UE 1h-20 stops sending UL data 1h-10 to the source BS 1h-05 via the first bearer, and starts sending UL data 1h-10 to the target BS via the second bearer.

[0225] More specifically, in the second PDCP layer architecture proposed in the present disclosure for the bearer configured with the DAPS switching method, when the PDCP layer sends UL data via the first bearer and satisfies the first condition, thereby receiving an indicator from the lower layer (when the random access procedure of the MAC layer to the target BS1h-10 is successful) or from the upper layer (when the first timer in the RRC layer expires), the PDCP layer may suspend sending UL data via the first bearer, may perform switching, and may start sending UL data via the second bearer. In addition, as described in reference Fig. 1IIn the proposed PDCP layer structure, the receiving PDCP layer 1h-21 of the second bearer and the receiving PDCP layer 1h-22 of the first bearer can operate as one entity, and the receiving PDCP layer 1h-21 can continue to receive data from the source BS1h-05 or the target BS1h-10 without interruption by using the stored transceived data, SN 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 a UL data transmission switching time point at which the transmission resources can be maximized and effectively used and the data interruption time can be minimized.

[0226] -It can be determined that the first condition is satisfied when: UE 1h-20 successfully completes a random access procedure to the target BS1h-10 by using a layer of the second bearer (e.g., a MAC layer), the UE successfully completes a random access procedure to the target BS1h-10 by using a layer of the second bearer (e.g., a MAC layer) and receives an allocation of a first UL transmission resource from the target BS1h-10, or the UL transmission resource is indicated to UE 1h-20 for the first time.

[0227] ■ For example, in the case where the UE 1h-20 receives a handover command message from the source BS 1h-05 and receives an indication of random access to the target BS 1h-10, when the indicated random access is a contention-free random access (CFRA) (e.g., when a predefined preamble or a UE cell identifier (e.g., a cell radio network temporary identifier (C-RNTI)) is allocated),

[0228] ◆When UE 1h-20 sends a predefined preamble to the cell of the target BS and receives a RAR message, it can be determined that the random access procedure is successfully completed. Therefore, when UE 1h-20 receives (is allocated) the first UL transmission resource allocated (or included or indicated) in the RAR message, it can be determined that the first condition is satisfied. As another method, when UE 1h-20 receives a UL transmission resource for the first time after UE 1h-20 receives the RAR message, it can be determined that the first condition is satisfied.

[0229] ■ In the case where the UE 1h-20 receives a handover command message from the source BS 1h-05 and receives an indication of random access to the target BS 1h-10, when the indicated random access is a contention-based random access (CBRA) (e.g., when a predefined preamble or a UE cell identifier (e.g., C-RNTI) is not allocated),

[0230] ◆When UE 1h-20 sends a preamble (e.g., a random preamble) to the cell of the target BS and receives a RAR message, sends message 3 (e.g., a handover completion message) to the target BS 1h-10 by using the UL transmission resources allocated (or included or indicated) in the RAR message, and receives a Contention Resolution MAC CE indicating a contention resolution from the target BS 1h-10 via message 4, or receives UL transmission resources via a PDCCH corresponding to the C-RNTI of UE 1h-20, it can be determined that the random access procedure to the target BS 1h-10 is successfully completed. Therefore, when UE 1h-20 monitors the PDCCH and receives (or indicates for the first time) UL transmission resources via the PDCCH corresponding to the C-RNTI of UE 1h-20 for the first time, it can be determined that the first condition is satisfied. As another method, when the size of the UL transmission resource allocated in the RAR message is sufficient so that the UE 1h-20 can send message 3 and also send UL data, the UE 1h-20 can determine that the UE 1h-20 receives the UL transmission resource for the first time, and thus can determine that the first condition is satisfied. For example, when the UE 1h-20 receives the RAR message, the UE 1h-20 can determine that the UE 1h-20 receives the UL transmission resource for the first time, and thus can determine that the first condition is satisfied.

[0231] When the handover command message received by the UE 1h-20 also indicates a handover method that does not request a random access procedure (RACH-Less handover),

[0232] ■ When the handover command message includes UL transmission resources for the target BS 1h-10,

[0233] ◆UE 1h-20 sends message 3 (e.g., a handover complete message or an RRC ReconfigurationComplete message) by using the UL transmission resources for the target BS1h-10, and when UE 1h-20 receives UE Identity Confirmation MAC CE from the target BS1h-10 via message 4, or receives UL transmission resources via a PDCCH corresponding to the C-RNTI of UE 1h-20, it can be determined that the random access procedure is successfully completed and the first condition is satisfied. As another method, after the random access procedure is successfully completed, UE 1h-20 performs PDCCH monitoring and receives the first UL transmission resources via a PDCCH corresponding to the C-RNTI of UE 1h-20, and it can be determined that the first condition is satisfied.

[0234] ■ When the handover command message does not include UL transmission resources for the target BS 1h-10,

[0235] ◆UE 1h-20 performs PDCCH monitoring on the target BS1h-10 (or cell), and when UE 1h-20 receives UL transmission resources via the PDCCH corresponding to the C-RNTI of the UE, or sends message 3 (for example, a handover completion message or an RRC ReconfigurationComplete message) by using the UL transmission resources, and receives the UE IdentityConfirmation MAC CE from the target BS1h-10 or receives UL transmission resources via the PDCCH corresponding to the C-RNTI of the UE 1h-20, it can be determined that the random access procedure is successfully completed and the first condition is satisfied. As another method, after the random access procedure is successfully completed, when UE 1h-20 performs PDCCH monitoring and receives the first UL transmission resource via the PDCCH corresponding to the C-RNTI of the UE 1h-20, it can be determined that the first condition is satisfied.

[0236] Hereinafter, a method for efficiently switching UL data from a source BS 1h-05 to a target BS 1h-10 is provided, which is performed when the DAPS switching method proposed in the present disclosure is performed. The MAC layer or RRC layer of the second bearer corresponding to the target BS 1h-10 may determine or identify whether the first condition is met according to one or a combination of the following methods.

[0237] -First method: For example, when the RRC Reconfiguration message received by the UE 1h-20 indicates DAPS switching, the UE 1h-20 may configure a MAC layer for a second bearer corresponding to the target BS 1h-10, and the MAC layer for the target BS 1h-10 may perform a random access procedure and may identify whether the first condition is met. In the DAPS switching method proposed in the present disclosure, when the first condition is met, the MAC layer for the target BS 1h-10 may instruct an upper layer (e.g., PDCP layer) for the bearer configured with the DAPS switching method to switch UL data transmission from the source BS 1h-05 via the first bearer to the target BS 1h-10 via the second bearer by using an indicator.

[0238] -Second method: As another method, for example, when the RRC Reconfiguration message received by the UE 1h-20 indicates DAPS switching, the UE 1h-20 may configure a MAC layer for a second bearer corresponding to the target BS 1h-10, and the MAC layer for the target BS1h-10 may perform a random access procedure and may identify whether the first condition is satisfied. When the first condition is satisfied, the MAC layer for the target BS1h-10 may indicate to the upper layer (e.g., RRC layer) that the first condition is satisfied. In addition, in the DAPS switching method proposed in the present disclosure, the upper layer (e.g., RRC layer) may indicate to the lower layer (e.g., PDCP layer) for the bearer configured with the DAPS switching method to switch UL data transmission from the source BS1h-05 via the first bearer to the target BS1h-10 via the second bearer by using an indicator. When the first condition proposed in the present disclosure is met or the random access process to the target BS1h-10 is successfully performed, the upper layer (e.g., the RRC layer) may stop the first timer, and when the first timer stops, the RRC layer may indicate the PDCP layer configured with the DAPS switching method to switch the bearer for UL data transmission by using an indicator.

[0239] -Third method: When the RRC Reconfiguration message received by the UE 1h-20 indicates DAPS switching, the UE 1h-20 may configure a MAC layer for a second bearer corresponding to the target BS 1h-10; and when the RRC layer of the UE 1h-20 instructs a lower layer (e.g., a MAC layer) to perform DAPS switching by using an indicator, the MAC layer for the target BS 1h-10 may perform a random access procedure and may determine whether the first condition is satisfied. In the DAPS switching method proposed in the present disclosure, when the first condition is satisfied, the MAC layer for the target BS 1h-10 may instruct an upper layer (e.g., a PDCP layer) for the bearer configured with the DAPS switching method to switch UL data transmission from the source BS 1h-05 via the first bearer to the target BS 1h-10 via the second bearer by using an indicator.

[0240] -Fourth method: As another method, when the RRC Reconfiguration message received by the UE 1h-20 indicates DAPS switching, the UE 1h-20 may configure a MAC layer for a second bearer corresponding to the target BS1h-10; and when the RRC layer of the UE 1h-20 instructs the lower layer (e.g., MAC layer) to perform DAPS switching by using an indicator, the MAC layer for the target BS1h-10 may perform a random access procedure and may determine whether the first condition is met. When the first condition is met, the MAC layer may indicate to the upper layer (e.g., RRC layer) that the first condition is met. In the case where the indicator is identified, when the first condition proposed in the present disclosure is met or the random access procedure to the target BS1h-10 is successfully performed, the upper layer (e.g., RRC layer) may stop the first timer. In addition, in the DAPS switching method proposed in the present disclosure, the upper layer (e.g., the RRC layer) can use an indicator to instruct the lower layer (e.g., the PDCP layer) of the bearer configured with the DAPS switching method to switch UL data transmission from the source BS1h-05 via the first bearer to the target BS1h-10 via the second bearer.

[0241] When the PDCP layer receives an indicator indicating that the first condition is satisfied or an indicator indicating that UL data transmission is switched from the source BS1h-05 to the target BS1h-10 from an upper layer (e.g., RRC layer) or a lower layer (e.g., MAC layer) according to the first method, the second method, the third method, or the fourth method (e.g., when the DAPS switching method is indicated), the PDCP layer may perform the following proposed protocol layer operations to efficiently perform switching of UL data transmission, and may perform one or more of the following operations to prevent data loss due to UL data transmission.

[0242] The following operations may be applied to the PDCP layer connected to an AM DRB or a UM DRB (an RLC layer operating in an AM mode or an RLC layer operating in an UM mode). Before a first condition is satisfied or before an indicator indicating that the first condition is satisfied is received, when the buffer stores data to be sent, the PDCP layer may indicate to the MAC layer of the first bearer corresponding to the source BS1h-05 that there is data to be sent by indicating the size or amount of data to be sent (e.g., the PDCP data amount), and UL data transmission to the source BS1h-05 may be performed. Thereafter, the MAC layer of the first bearer corresponding to the source BS1h-05 may perform a scheduling request or buffer status report procedure to receive an allocation of UL transmission resources from the source BS1h-05. When the first condition is satisfied or an indicator indicating that the first condition is satisfied is received, switching of UL data transmission to the target BS 1h-10 may be performed on the bearer configured with the DAPS switching method.

[0243] - The UE 1h-20 may not reset but use the UL or DL ​​ROHC context of the source BS 1h-05 unchanged, may reset the UL or DL ​​ROHC context of the target BS 1h-10, and may start in an initial state (eg, IR state in U mode).

[0244] -In order to switch UL data transmission from the first bearer used for the source BS1h-05 to the second bearer used for the target BS1h-10, the PDCP layer may indicate to the MAC layer of the first bearer corresponding to the source BS1h-05 that the size or amount of data to be sent is 0 (or none). For example, the PDCP layer may indicate to the MAC layer for the first bearer that the data amount of the PDCP layer (PDCP data amount) is 0, thereby indicating that there is no more data to be transmitted (even when the buffer actually stores multiple data items to be sent, in order to switch UL data transmission, the PDCP layer may also indicate to the MAC layer of the first bearer corresponding to the source BS1h-05 that there is no more data to be transmitted).

[0245] However, when the switching method (DAPS switching method) of embodiment 2 proposed in the present disclosure is indicated, the switching method (DAPS switching method) of embodiment 2 proposed in the present disclosure is indicated for carrying or the first condition is satisfied, when RLC control data (RLC status report) or PDCP control data (PDCP status report or ROHC feedback) for the source BS1h-05 is generated, the PDCP layer used for carrying may indicate the amount of data corresponding to the RLC control data or PDCP control data to the MAC layer used for the source BS1h-05, and may perform data sending to the source BS1h-05 or the RLC layer used for the source BS1h-05. However, in the case where the handover method (DAPS handover method) of embodiment 2 proposed in the present disclosure is indicated, the handover method (DAPS handover method) of embodiment 2 proposed in the present disclosure is indicated for bearer or the first condition is satisfied, when RLC control data (RLC status report) or PDCP control data (PDCP status report or ROHC feedback) for the target BS1h-10 is generated, the PDCP layer for bearer may indicate the amount of data corresponding to the RLC control data or PDCP control data to the MAC layer for the target BS1h-10, and may perform data transmission to the target BS1h-10 or the RLC layer for the target BS1h-10. 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 for the source BS1h-05, and may perform data transmission to the source BS1h-05 or the RLC layer for the source BS 1h-05. Therefore, in the second PDCP layer architecture proposed for a bearer configured with a DAPS switching method, when an indicator indicating that the first condition is satisfied is received so that the second PDCP layer indicates the amount of data to the MAC layer for the target BS1h-10, the second PDCP layer may indicate the amount of data to the MAC layer for the target BS1h-10, wherein the amount of data excludes PDCP control data or RLC control data, or data size, to be sent to the source BS1h-05 or the MAC layer for the source BS1h-05.

[0246] -The PDCP layer connected to the AM DRB (RLC layer operating in AM mode) (all pre-stored PDCP PDUs are discarded (for example, PDCP SDUs are not discarded to prevent loss of original data)) may perform a new header compression process on a plurality of data items (PDCP SDUs of the buffer) based on the header context of the target BS1h-10, in an ascending order of COUNT values ​​(or PDCP SNs) assigned before a first condition is satisfied or an indicator indicating that the first condition is satisfied is received, the ascending order starting from the first data (for example, PDCP SDU) for which a positive acknowledgement of successful transmission is obtained from a lower layer (for example, the RLC layer of the first bearer corresponding to the source BS1h-05). The PDCP layer may re-perform an integrity process (for example, an integrity protection or authentication process) or a ciphering process by applying a security key to the target BS1h-10, may configure a PDCP header, and may transfer the PDCP header to its lower layer (the RLC layer of the second bearer corresponding to the target BS1h-10), thereby performing retransmission or sending. For example, the PDCP layer may perform cumulative retransmission of data starting from the first data that did not receive a successful transmission positive acknowledgement. As another method, when the PDCP layer performs retransmission, the PDCP layer may perform retransmission only on multiple data items that did not receive a successful transmission positive acknowledgement from a lower layer (e.g., the RLC layer of the first bearer corresponding to the source BS1h-05). More specifically, the PDCP layer connected to the AM DRB (or the RLC layer operating in the AM mode) (which may discard all stored PDCP PDUs to be sent to the source BS1h-05 (e.g., PDCP SDUs may not be discarded to prevent loss of original data) by using the first protocol layer previously connected to the PDCP layer) may perform a new header or data compression process on multiple data items (e.g., PDCP SDUs) that have not received a positive acknowledgement of successful transmission from a lower layer (e.g., RLC layer) of the first protocol layer of the source BS1h-05, based on the COUNT value (or PDCP SN) assigned before the first condition is satisfied or an indicator indicating that the first condition is satisfied is received, by applying a header compression (or data compression) protocol context or security key corresponding to the target BS1h-10. The PDCP layer may re-execute an integrity process (e.g., integrity protection or authentication process) or a ciphering process, may configure a PDCP header, and may transmit the PDCP header to its lower layer as a second protocol layer to be sent to the target BS1h-10, thereby performing retransmission or sending. For example, in order to prevent waste of transmission resources, the PDCP layer may perform selective retransmission only for multiple data items that have not received a successful transmission confirmation. As another method, transmission or retransmission may be performed after a lower layer (e.g., a transmitting or receiving RLC layer or MAC layer) that is a first protocol layer for transmitting data to the source BS1h-05 is released.When the transmission or retransmission process is extended to the UM DRB, the PDCP layer connected to the RLC layer operating in the UM mode may regard data that has not been sent to the lower layer, data that has not expired the PDCP discard timer, or multiple data items that have been assigned a PDCP SN (or COUNT value) as multiple data items received or newly received from the upper layer, may not restart the PDCP discard timer for each data, and may perform header (or data) compression on the multiple data items by using the header (or data) compression context or security key of the target BS1h-10. Alternatively, the PDCP layer may perform a ciphering or integrity protection process, may generate a PDCP header and combine it with multiple data items, and then may perform transmission or retransmission; and may process the data in ascending order of the COUNT value assigned before the process is triggered, and then may perform transmission or retransmission. The window state variable of the PDCP layer connected to the UM DRB or AM DRB may not be reset, and may be maintained and used.

[0247] -When the buffer stores data to be transmitted, the PDCP layer may indicate to the MAC layer of the second bearer corresponding to the target BS 1h-10 that there is data to be transmitted by indicating the size or amount of the data to be transmitted (e.g., the PDCP data amount), and may perform switching of UL data transmission to the target BS 1h-10. Thereafter, the MAC layer of the second bearer corresponding to the target BS 1h-10 may perform a scheduling request or buffer status report procedure to receive allocation of UL transmission resources from the target BS 1h-10.

[0248] According to implementation mode 2 of the efficient switching method (e.g., DAPS switching method) proposed in the present disclosure, even after UE1h-20 receives a switching command message (e.g., RRC Reconfiguration message), UE 1h-20 can continue to receive DL data from the source BS1h-05 or the target BS1h-10 by using the protocol layer of the first bearer corresponding to the source BS1h-05 or the second bearer corresponding to the target BS1h-10. In an embodiment of the present disclosure, in order to allow UE 1h-20 to smoothly receive DL data from the source BS1h-05 (or target BS1h-10), or to allow the source BS1h-05 (or target BS1h-10) to smoothly send DL data to UE 1h-20, for an AM bearer, UE 1h-20 can be allowed to continue to perform RLC status reporting instead of UL transmission of data to the source BS1h-05 (or target BS1h-10) by using the protocol layer of the first bearer (or the second bearer). For example, even when the first condition is satisfied and the UE switches UL data transmission to the target BS1h-10, when the UE 1h-20 must send an RLC status report, HARQ ACK or NACK, or PDCP control data (PDCP ROHC feedback or PDCP status report) to the source BS1h-05, the UE 1h-20 may be allowed to perform data transmission via the first bearer of the source BS1h-05. In the case of an AM bearer, when data is transmitted to the transmitting end and then the transmission success is not indicated by using an RLC status report (i.e., when the RLC status report is not received), the data cannot be continuously transmitted thereafter. More specifically, when Figure 1H In the third operation 1h-03 in implementation mode 2 of the efficient switching method, the first condition is satisfied. When UE 1h-20 stops sending UL data to the source BS1h-05 by using the protocol layer 1h-22 of the first bearer, performs switching, and then starts sending UL data to the target BS1h-10 by using the protocol layer 1h-21 of the second bearer, UE 1h-20 can continuously send HARQ ACK or HARQ NACK information, RLC status report (ACK or NACK information), or PDCP control data (for example, PDCP status report or PDCP PROHC feedback information) by using the protocol layer of the first bearer (or the second bearer) to smoothly receive DL data from the source BS1h-05 (or target BS1h-10) or allow the source BS1h-05 (or target BS1h-10) to smoothly send DL data.

[0249] More specifically, in Figure 1HIn the third operation 1h-03 in implementation mode 2 of the efficient switching method, even when the first condition is satisfied so that the UE 1h-20 suspends data transmission to the source BS 1h-05 by using the protocol layer 1h-22 of the first bearer, performs switching, and then starts UL data transmission to the target BS 1h-10 by using the protocol layer 1h-21 of the second bearer, the UE 1h-20 can continue to perform data transmission caused by HARQ retransmission of the MAC layer or data transmission caused by retransmission of the RLC layer in the AM mode to prevent data loss to the source BS 1h-05. More specifically, in Figure 1H In the third operation 1h-03 in implementation mode 2 of the efficient switching method, when the first condition is satisfied so that the UE 1h-20 suspends data transmission to the source BS 1h-05 by using the protocol layer 1h-22 of the first bearer, performs switching, and then starts UL data transmission to the target BS1h-10 by using the protocol layer 1h-21 of the second bearer, the source BS1h-05 or the target BS1h-10 may divide time and may allocate transmission resources to the UE 1h-20 to prevent a conflict between the UL transmission resources to the target BS1h-10 and the UL transmission resources to the source BS1h-05. When the UL transmission resources to the target BS1h-10 conflict with and overlap with the UL transmission resources to the source BS1h-05, the UE 1h-20 may perform data transmission to the source BS 1h-05 by giving priority to the UL transmission resources to the source BS1h-05 to maintain the transmission of DL data or continue to receive DL data from the source BS1h-05 without causing any problems. As another method, when the UL transmission resources to the target BS1h-10 conflict with and overlap with the UL transmission resources to the source BS1h-05, UE 1h-20 may perform data transmission to the target BS1h-10 by giving priority to the UL transmission resources to the target BS1h-10 to maintain DL data transmission from the target BS1h-10.

[0250] More specifically, when UE 1h-20 receives a switching command message indicating or indicating a switching (DAPS switching method) corresponding to embodiment 2 of the present disclosure for each bearer, UE 1h-20 or the bearer indicating DAPS switching may perform a scheduling request via the first protocol layer, may receive UL transmission resources by sending a buffer status report to the source BS1h-05, and may send UL data until the first condition is met. Thereafter, UE 1h-20 may receive DL data from the source BS1h-05. However, when the first condition is met and UE 1h-20 no longer sends data to the source BS1h-05, a scheduling request may be performed by switching UL using the second protocol layer, UL transmission resources may be received by sending a buffer status report to the target BS1h-10, and UL data may be sent to the target BS1h-10. However, UE 1h-20 can continue to receive DL data from the source BS1h-05, and even after the UL transmission switching, UE 1h-20 can continue to send HARQ ACK or HARQ NACK, RLC status report, or PDCP control data corresponding to the DL data (e.g., PDCP status report or ROHC feedback information). In addition, even when the first condition is met, UE1h-20 can continue to receive DL data from the source BS1h-05 or the target BS1h-10.

[0251] exist Figure 1H In implementation mode 2 of the efficient switching method, when the second condition is met in the fourth operation 1h-04, the UE 1h-20 may terminate the DL data reception from the source BS1h-05 by using the protocol layer 1h-22 of the first bearer, or may release the link to the source BS1h-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 send data to the target BS1h-10 or receive data from the target BS1h-10 without interruption by using the data to be sent or the data to be received, the SN information, or the header compression and decompression context stored in the PDCP layer 1h-22 of the first bearer.

[0252] - When the UE 1h-20 performs a random access procedure on the target BS 1h-10 by using a layer 1h-21 of the second bearer and receives a RAR message, the UE 1h-20 may determine that the second condition is satisfied.

[0253] - When the UE 1h-20 performs a random access procedure on the target BS 1h-10 by using the layer 1h-21 of the second bearer, receives a RAR message, and configures and sends a handover complete message to the target BS 1h-10, the UE 1h-20 may determine that the second condition is satisfied.

[0254] -When the UE 1h-20 performs a random access procedure on the target BS 1h-10 by using a layer 1h-21 of the second bearer and sends data for the first time by using a PUCCH or a PUCCH UL transmission resource or receives a PUCCH or a PUCCH UL transmission resource for the first time, the UE 1h-20 may determine that the second condition is satisfied.

[0255] - When the BS configures a separate timer to the UE 1h-20 by using an RRC message and the separate timer expires, the UE 1h-20 may determine that the second condition is satisfied.

[0256] ■A separate timer may be started when UE 1h-20 receives a handover command message from the source BS1h-05, UE 1h-20 starts random access (sending a preamble) to the target BS1h-10, UE 1h-20 receives a RAR message from the target BS1h-10, UE 1h-20 sends a handover completion message to the target BS1h-10, or UE 1h-20 sends data for the first time by using PUCCH or PUCCH UL transmission resources.

[0257] -When UE 1h-20 performs a random access procedure to the target BS 1h-10 by using the protocol layer of the second bearer, receives a RAR message, configures and sends a switching completion message to the target BS 1h-10, and then receives a positive acknowledgement about the successful transmission of the switching completion message by using the MAC layer (HARQACK) or the RLC layer (RLC ACK), UE 1h-20 can determine that the second condition is met.

[0258] -When UE 1h-20 performs a random access procedure on the target BS1h-10 by using the protocol layer of the second bearer, receives a RAR message, or configures a switching completion message and sends it to the target BS1h-10, and then receives an allocation of UL transmission resources from the target BS1h-10 for the first time or receives an indication of UL transmission resources for the first time, UE 1h-20 can determine that the second condition is met.

[0259] -When the source BS1h-05 performs the efficient switching proposed in the present disclosure, the source BS1h-05 may determine when to stop sending DL data to the UE1h-20 or when to release the link to the UE 1h-20. For example, the source BS1h-05 may determine the above matters based on a certain method (for example, when a certain timer expires (the timer may be started after indicating the switching) or the source BS1h-05 receives an indication from the target BS1h-10 indicating that the UE 1h-20 has successfully performed the switching to the target BS1h-10). When the UE 1h-20 does not receive DL data from the source BS1h-05 within a certain period of time, the UE 1h-20 may determine that the second condition is met, and may determine to release the link to the source BS1h-05, so that the link may be released.

[0260] -When the UE 1h-20 receives an indication (eg, an RRC message (eg, an RRC Reconfiguration message)), a MAC CE, an RLC control PDU, or a PDCP control PDU indicating release of the link to the source BS from the target BS 1h-10, the UE 1h-20 may determine that the second condition is met.

[0261] -When UE 1h-20 receives an indication (e.g., an RRC message (e.g., an RRC Reconfiguration message)), a MAC CE, an RLC control PDU, or a PDCP control PDU from the source BS 1h-05 indicating the release of the link to the source BS 1h-05, UE 1h-20 may determine that the second condition is met.

[0262] -When the UE 1h-20 does not receive DL data from the source BS 1h-05 within a certain period of time, the UE 1h-20 may determine that the second condition is satisfied.

[0263] -When UE 1h-20 successfully completes the random access procedure to the target BS1h-10 by using the layer of the second bearer (e.g., the MAC layer), UE 1h-20 successfully completes the random access procedure to the target BS1h-10 by using the layer of the second bearer, and then receives the allocation of the first UL transmission resource from the target BS1h-10, or UE 1h-20 receives an indication of the UL transmission resource for the first time, UE 1h-20 can determine that the second condition is met.

[0264] ■ For example, more specifically, in the case where the UE 1h-20 receives a handover command message from the source BS 1h-05 and receives an indication of random access to the target BS 1h-10, when the indicated random access is CFRA (e.g., when a predefined preamble or a UE cell identifier (e.g., C-RNTI) is allocated),

[0265] ◆When UE 1h-20 sends a predefined preamble to the cell of the target BS 1h-10 and receives a RAR message, it can be determined that the random access procedure is successfully completed, so when UE 1h-20 receives the first UL transmission resource allocated, included or indicated in the RAR message, UE 1h-20 can determine that the second condition is satisfied. As another method, when UE 1h-20 receives a UL transmission resource for the first time after UE 1h-20 receives the RAR message, UE 1h-20 can determine that the second condition is satisfied.

[0266] ■ In the case where the UE 1h-20 receives a handover command message from the source BS 1h-05 and receives an indication of random access to the target BS 1h-10, when the indicated random access is CBRA (e.g., when a predefined preamble or UE cell identifier (e.g., CRNTI) is not allocated),

[0267] ◆When UE 1h-20 sends a preamble (e.g., a random preamble) to the cell of the target BS1h-10 and receives a RAR message UE, sends message 3 (e.g., a handover completion message) by using the UL transmission resources allocated (or included or indicated) in the RAR message, and receives a Contention Resolution MAC CE indicating a solution for a contention resolution from the target BS1h-10 via message 4, or receives UL transmission resources by using a PDCCH corresponding to the C-RNTI of UE 1h-20, UE 1h-20 can determine that the random access procedure to the target BS1h-10 is successfully completed. Therefore, when UE 1h-20 monitors the PDCCH and receives UL transmission resources for the first time or indicates UL transmission resources for the first time by using a PDCCH corresponding to the C-RNTI of UE 1h-20, UE 1h-20 can determine that the second condition is satisfied. As another method, when the size of the UL transmission resource allocated in the RAR message is sufficient so that the UE 1h-20 can send message 3 and also send UL data, the UE 1h-20 can determine that the UE 1h-20 receives the UL transmission resource for the first time, and thus can determine that the second condition is satisfied. For example, when the UE 1h-20 receives the RAR message, the UE 1h-20 can determine that the UE 1h-20 receives the UL transmission resource for the first time, and thus can determine that the second condition is satisfied.

[0268] - When the handover command message received by the UE 1h-20 also indicates a handover method that does not request a random access procedure (RACH-Less handover),

[0269] ■ When the handover command message includes UL transmission resources for the target BS 1h-10,

[0270] ◆UE 1h-20 sends message 3 (e.g., a handover completion message or an RRC ReconfigurationComplete message) by using the UL transmission resources for the target BS1h-10, and when UE 1h-20 receives UE Identity Confirmation MAC CE from the target BS1h-10 via message 4, or receives UL transmission resources by using a PDCCH corresponding to the C-RNTI of UE 1h-20, UE 1h-20 may determine that the random access procedure is successfully completed. Thereafter, UE 1h-20 may determine that the second condition is satisfied. As another method, after the random access procedure is successfully completed, when UE 1h-20 performs PDCCH monitoring and thereby receives a first UL transmission resource by using a PDCCH corresponding to the C-RNTI of UE 1h-20, UE 1h-20 may determine that the second condition is satisfied.

[0271] ■ When the handover command message does not include UL transmission resources for the target BS 1h-10,

[0272] UE 1h-20 performs PDCCH monitoring on the target BS1h-10 (or cell), and when UE 1h-20 receives UL transmission resources by using the PDCCH corresponding to the C-RNTI of UE1h-20, or sends message 3 (for example, a handover completion message or an RRC ReconfigurationComplete message) by using the UL transmission resources, and receives UEIdentity Confirmation MAC CE from the target BS1h-10 or receives UL transmission resources by using the PDCCH corresponding to the C-RNTI of UE 1h-20, UE 1h-20 can determine that the random access procedure is successfully completed and the second condition is satisfied. As another method, after the random access procedure is successfully completed, when UE 1h-20 performs PDCCH monitoring and thereby receives the first UL transmission resource by using the PDCCH corresponding to the C-RNTI of UE 1h-20, UE 1h-20 can determine that the second condition is satisfied.

[0273] In the case where UE 1h-20 performs implementation mode 2 of the efficient handover method (e.g., DAPS handover method) proposed in the present disclosure, when it is identified that the RRC layer, MAC layer, or RLC layer of UE 1h-20 for the first bearer corresponding to the source BS, and the RRC layer, MAC layer, or RLC layer of UE 1h-20 for the second bearer corresponding to the target BS1h-10 meet the second condition proposed in the present disclosure, an indicator that the second condition is met may be indicated to the PDCP layer of UE 1h-20 or the bearer performing the DAPS handover method. When the second condition is met or the PDCP layer of UE 1h-20 receives an indicator indicating that the second condition is met from a lower layer or an upper layer, the following one or more processes may be performed on the bearer configured with the DAPS handover method or UE 1h-20, so that implementation mode 2 of the efficient handover method proposed in the present disclosure can be successfully completed.

[0274] -UE 1h-20 may release the first bearer of the source BS1h-05, and may release the link to the source BS1h-05. Afterwards, before UE 1h-20 releases the first bearer of the source BS1h-05, UE 1h-20 may perform an RLC reconstruction process on the RLC layer of the first bearer corresponding to the source BS1h-05 (for example, when the realignment timer is running, UE 1h-20 may stop or reset the timer, and when the received data is stored in the buffer, UE 1h-20 may process the stored data and provide it to the upper layer. In addition, when the data to be sent exists in the buffer, UE 1h-20 may discard the data) or may reset the MAC layer.

[0275] -When UE 1h-20 releases the link to the source BS1h-05, in order to report the reception status of multiple DL data items received from the source BS1h-05 to the target BS1h-10, UE 1h-20 can trigger the PDCP status reporting process, configure the PDCP status report, and send the PDCP status report to the target BS1h-10.

[0276] -When the second condition is met, the UE 1h-20 may switch the second PDCP layer architecture or function 1i-20 proposed in the present disclosure to the first PDCP layer architecture or function 1i-11 or 1i-12 for each bearer or a bearer indicating a DAPS switching method, may reset a variable for realignment, may stop and reset a realignment timer, may perform a decryption process or header (or data) decompression by applying a security key or header decompression context for the source BS1h-05 to a plurality of data items for reordering stored in a buffer (e.g., a plurality of data items received from the source BS1h-05), and may discard the security key or header decompression context for the source BS1h-05. Thereafter, the UE 1h-20 may provide the processed plurality of data items to an upper layer in ascending order. For example, when the second condition is met, UE 1h-20 may perform a decryption process or header (or data) decompression by applying the security key or header decompression context for the source BS1h-05 to multiple data items for reordering stored in a buffer (e.g., multiple data items received from the source BS1h-05), and then discard the security key or header decompression context for the source BS1h-05. As another method, when the second condition is met, UE 1h-20 may switch the second PDCP layer architecture or function 1i-20 proposed in the present disclosure to the third PDCP layer architecture or function 1i-30 for each bearer or bearer indicating the DAPS switching method. Thereafter, UE 1h-20 may not stop or reset, but may continue to use the variables and realignment timer used for realignment. However, UE 1h-20 may perform a decryption process or header (or data) decompression by applying a security key or header decompression context for the source BS1h-05 to a plurality of data items for reordering stored in a buffer (e.g., a plurality of data items received from the source BS1h-05), and then may discard the security key or header decompression context for the source BS1h-05. In addition, UE 1h-20 may provide the processed plurality of data items to an upper layer in ascending order. For example, when the second condition is met, UE 1h-20 may perform a decryption process or header (or data) decompression by applying a security key or header decompression context for the source BS1h-05 to a plurality of data items for reordering stored in a buffer (e.g., a plurality of data items received from the source BS1h-05), and then may discard the security key or header decompression context for the source BS1h-05. UE 1h-20 may release QoS mapping information of the SDAP layer, security key information of the PDCP layer for the source BS1h-05, header (or data) compression context information for the source BS1h-05, or the RLC layer or MAC layer for the source BS1h-05.

[0277] -When the second condition proposed in the present disclosure is met when UE 1h-20 performs the DAPS switching method, UE 1h-20 may release the first bearer for the source BS1h-05 for the second SDAP layer architecture and function 1j-20 applied to each bearer or applied to the bearer indicating the DAPS switching method, and may switch the second SDAP layer architecture and function 1j-20 to the first SDAP layer architecture or functions 1j-10 and 1j-12 and apply the first SDAP layer architecture or functions 1j-10 and 1j-12. In addition, when the second condition is met, UE 1h-20 may switch the second SDAP layer architecture and function 1j-20 proposed in the present disclosure to the first SDAP layer architecture or functions 1j-10 and 1j-12 for each bearer or the bearer indicating the DAPS switching method. Here, UE1h-20 may maintain the second bearer or second QoS flow and bearer mapping information for the target BS1h-10. Before UE 1h-20 releases the first bearer or the first QoS flow and bearer mapping information of the source BS1h-05, UE 1h-20 may complete data processing by applying the first QoS flow and bearer mapping information to multiple data items received from the source BS1h-05 (e.g., all data received from the source BS1h-05), and then release the first QoS flow and bearer mapping information or the first bearer. Thereafter, UE 1h-20 may provide the processed multiple data items to the upper layer in ascending order. For example, when the second condition is met, UE 1h-20 may process the data (e.g., a process of reading SDAP header information and updating mapping information or configuring an SDAP header, or a process of routing based on the first QoS flow and bearer mapping information or providing the processed data to an appropriate upper layer or lower layer) by applying the first QoS flow and bearer mapping information for the source BS1h-05 to multiple data items stored in a buffer (e.g., multiple data items received from the source BS1h-05), and then discard the first QoS flow and bearer mapping information for the source BS1h-05. The SDAP layer may define and apply information indicated by a 1-bit indicator of a new SDAP header, a 1-bit indicator of a new PDCP header, SDAP control data (e.g., a DL end marker), or a PDCP layer. Thereafter, the SDAP layer may identify data most recently received from the source BS1h-05 based on the information. Therefore, the SDAP layer may perform data processing on the data, which was most recently received from the source BS1h-05, by applying the first QoS flow and bearer mapping information for the source BS 1h-05, and then may discard the first QoS flow and bearer mapping information for the source BS1h-05. In addition, the SDAP layer may continuously maintain the second QoS flow and bearer mapping information, and may process UL data or DL ​​data regarding the target BS1h-10 based on the second QoS flow and the bearer mapping information.

[0278] -When UE 1h-20 resets the MAC layer for the source BS1h-05 and switches the second PDCP layer architecture for the bearer configured with the DAPS switching method to the first PDCP layer architecture, UE 1h-20 may perform an RLC layer reconstruction process or an RLC layer release process on the RLC layer for the source BS1h-05 in the second PDCP layer architecture.

[0279] -The receiving PDCP layer can process data received or stored data due to the reconstruction process of the lower layer (e.g., RLC layer), and can perform a header decompression process for multiple stored data or all stored data (received from the source BS1h-05) for the UM DRB based on ROHC or Ethernet Header Compression (EHC) (for the source BS1h-05).

[0280] -The receiving PDCP layer can process data received or stored data due to the reconstruction process of the lower layer (e.g., the RLC layer), and can perform a header decompression process for multiple stored data or all stored data (received from the source BS1h-05) for the AM DRB based on the ROHC or EHC (for the source BS1h-05).

[0281] -As another method, the receiving PDCP layer may process data received or stored data due to a lower layer (e.g., RLC layer) reconstruction process, and when an indicator (drb-Continue ROHC or drb-Continue EHC) indicating maintaining the use of a header compression context is not configured for a UM DRB or an AM DRB, a header decompression process may be performed on a plurality of stored data (received from the source BS1h-05) or all stored data based on the ROHC or EHC.

[0282] -After performing the procedure, the transmitting PDCP layer or the receiving PDCP layer may discard or release the security key or header compression context for the source BS1h-05.

[0283] When referring to the present disclosure Figure 1FWhen the BS sends a handover command message to the UE in operation 1f-20, the BS may define an indicator related to an embodiment of the present disclosure in the handover command message (e.g., an RRC Reconfiguration message), and may indicate to the UE which handover process corresponding to which embodiment is to be triggered. Afterwards, the UE may perform the handover process according to the handover method indicated in the handover command message. For example, the UE may execute embodiment 2 (DAPS handover method) of the efficient handover method proposed in the present disclosure, thereby performing handover to the target BS 1h-10 while minimizing the data interruption time. As another method, the handover command message may define an indicator for each bearer in the handover command message, which indicator is related to an embodiment of the present disclosure, and may further clearly indicate which embodiment is to be applied to which bearer in the handover. For example, it may be indicated that embodiment 2 of the present disclosure will only apply to AM bearers in which the RLC layer operating in AM mode is active, or may be widely applicable to UM bearers in which the RLC layer operating in UM mode is active. It is assumed that an embodiment of the present disclosure is applicable to DRB. However, when necessary (for example, when the UE maintains the SRB for the source BS1h-05 and cannot switch to the target BS1h-10, so that the UE can report a switching failure message or a recoverable link via the SRB for the source BS1h-05), the embodiments of the present disclosure can be widely applicable to SRB.

[0284] In an embodiment of the present disclosure, when UE 1h-20 performs sending and receiving data to and from a source BS1h-05 by using a protocol layer of a first bearer, and performs sending and receiving data to and from a target BS1h-10 by using a protocol layer of a second bearer, the MAC layer for the first bearer and the MAC layer for the second bearer may each operate a non-continuous reception (DRX) period, thereby reducing battery consumption in UE 1h-20. For example, even after UE1h-20 receives a switching command message, UE 1h-20 may continue to apply the DRX period of the MAC layer applied when sending and receiving data by using the protocol layer of the first bearer. UE 1h-20 may terminate the DRX period according to the first condition or the second condition. In addition, UE 1h-20 may manage whether to apply the DRX period to the MAC layer of the second bearer alone in response to an instruction from the target BS1h-10.

[0285] In the present disclosure, UE 1h-20 suspends sending UL to the source BS1h-05 by using the protocol layer of the first bearer, and suspends receiving DL data from the source BS1h-05 may mean that UE 1h-20 rebuilds, resets or releases the protocol layer (PHY layer, MAC layer, RLC layer or PDCP layer) used for the first bearer.

[0286] In an embodiment of the present disclosure, for ease of description, UE 1h-20 is described as being configured with a first bearer for a source BS1h-05 or a second bearer for a target BS1h-10, and the embodiment of the present disclosure can be easily extended to and is also applicable to a case where UE 1h-20 is configured with multiple first bearers for a source BS1h-05 or multiple second bearers for a target BS1h-10. In addition, the embodiment of the present disclosure can be extended to and is also applicable to a case where multiple bearers for multiple target BS1h-10 are configured. For example, UE 1h-20 can configure a second bearer while performing a handover process on a first target BS1h-10, and when the handover fails, UE 1h-20 can configure a second bearer while performing a handover process on a second target BS1h-10, so that UE 1h-20 can automatically detect and determine a cell that satisfies a certain condition (for example, a signal with a strength equal to or greater than a certain value) from multiple cells, can determine a cell, and can then perform a handover process on the cell.

[0287] Fig. 1I The architecture of an efficient PDCP layer to be applied to a DAPS handover method of Embodiment 2 as an efficient handover method according to an embodiment of the present disclosure and a method of applying the architecture are shown.

[0288] refer to Fig. 1I The present disclosure proposes a specific architecture and function of an efficient layer to be applied to a DAPS switching method as implementation mode 2 of the efficient switching method proposed in the present disclosure, and the architecture of the PDCP layer to be proposed below is characterized in that, when performing a DAPS switching process, different PDCP layer architectures can be applied to corresponding bearers at different time points.

[0289] For example, before the UE receives a handover command message from the BS, in operation 1i-01, the UE may process and send or receive data by applying the first PDCP layer architecture and function 1i-11 or 1i-12 proposed in the present disclosure to each bearer.

[0290] However, when the UE receives a handover command message from the BS and the handover command message indicates the DAPS handover method proposed in the present disclosure or indicates the DAPS handover method for a specific bearer, in operation 1i-02, the UE may process and send or receive data by applying the second PDCP layer architecture and function 1i-20 proposed in the present disclosure to each bearer or a bearer indicating the DAPS handover method. For example, when the UE receives a handover command message from the BS and the handover command message indicates the DAPS handover method proposed in the present disclosure or indicates the DAPS handover method for a specific bearer, the UE may switch the first PDCP layer architecture or function 1i-11 or 1i-12 for each bearer proposed in the present disclosure to the second PDCP layer architecture or function 1i-20 for each bearer or a bearer indicating the DAPS handover method.

[0291] As another method, when the first condition proposed in the present disclosure is met, in operation 1i-02, the UE may switch the first PDCP layer architecture or function 1i-11 or 1i-12 proposed in the present disclosure for each bearer or a bearer indicating a DAPS switching method to a second PDCP layer architecture or function 1i-20. In addition, when the UE receives a switching command message from the BS and the switching command message indicates the DAPS switching method proposed in the present disclosure or indicates the DAPS switching method for a specific bearer or a PDCP realignment timer value is newly set, when the UE switches the first PDCP layer architecture or function 1i-11 or 1i-12 proposed in the present disclosure to the second PDCP layer architecture or function 1i-20 for each bearer or a bearer indicating a DAPS switching method, the UE may update the variable used for realignment to the predicted PDCP SN or COUNT value to be received next, and may stop and restart the realignment timer.

[0292] When the second condition proposed in the present disclosure is met when the UE performs the DAPS switching method proposed in the present disclosure, the UE may release the second PDCP layer architecture and function 1i-20 applied to each bearer or the bearer indicating the DAPS switching method from the first bearer for the source BS, and may switch back to the first PDCP layer architecture and function 1i-11 or 1i-12 and may apply the first PDCP layer architecture and function 1i-11 or 1i-12. When the second condition is met, and the UE switches the second PDCP layer architecture or function 1i-20 proposed in the present disclosure to the first PDCP layer architecture or function 1i-11 or 1i-12 for each bearer or the bearer indicating the DAPS switching method, the UE may reset the variable for realignment, and may stop and reset the realignment timer. Thereafter, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context for the source BS to a plurality of data items (e.g., a plurality of data items received from the source BS) stored in a buffer for reordering, and may discard the security key or header decompression context for the source BS. In addition, the UE may provide the processed multiple data items to the upper layer in ascending order. For example, when the second condition is met, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context for the source BS to the multiple data items stored in the buffer for reordering (e.g., multiple data items received from the source BS), and then may discard the security key or header decompression context for the source BS.

[0293] As another method, when the second condition proposed in the present disclosure is met when the UE performs the DAPS switching method proposed in the present disclosure, the UE may release the second PDCP layer architecture and function 1i-20 applied to each bearer or the bearer indicating the DAPS switching method from the bearer used for the source BS, and may switch to the third PDCP layer architecture or function 1i-30 and may apply the third PDCP layer architecture or function 1i-30. When the second condition is met so that the UE switches the second PDCP layer architecture or function 1i-20 proposed in the present disclosure to the third PDCP layer architecture or function 1i-30 for each bearer or the bearer indicating the DAPS switching method, the UE may not stop or reset but may continue to use the variables and the realignment timer for realignment. However, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context for the source BS to a plurality of data items (e.g., a plurality of data items received from the source BS) stored in a buffer for reordering, and then may discard the security key or header decompression context for the source BS. Thereafter, the UE may provide the processed plurality of data items to the upper layer in ascending order. For example, when the second condition is met, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context for the source BS to multiple data items stored in a buffer for reordering (e.g., multiple data items received from the source BS), and may then discard the security key or header decompression context for the source BS.

[0294] Reference Figures disclosed herein Fig. 1I When the UE performs switching by applying different first PDCP layer architectures or functions 1i-11 or 1i-12, second PDCP layer architectures or functions 1i-20, or third PDCP layer architectures or functions 1i-30 to corresponding bearers at different time points, the UE can prevent data loss and minimize data interruption time.

[0295] Fig. 1I The first PDCP layer architecture 1i-11 or 1i-12 proposed in the disclosure may have the 1-1PDCP layer architecture, 1-2PDCP layer architecture, 1-3PDCP layer architecture or 1-4PDCP layer architecture proposed in the present disclosure, and the embodiments of the present disclosure may have the features to be described below.

[0296] -1> (when it is a 1-1PDCP layer architecture), for example, when the UE applies the first PDCP layer architecture and function 1i-11 to the PDCP layer (e.g., E-UTRA PDCP layer or LTE PDCP layer) connected to the AM RLC layer (e.g., E-UTRA AM RLC layer), the PDCP layer may have the following characteristics.

[0297] ■2> The receiving PDCP layer may first perform out-of-window data or duplicate data detection on the received multiple data items. (Retransmission may occur in RLC AM, and the size of LTE RLC SN and PDCP SN may be different so that duplicate data or out-of-window data may be received. In the above, window refers to the range of PDCP SN or COUNT values ​​where valid data is received).

[0298] ◆3> Before the UE discards out-of-window data or duplicate data, the UE performs a decryption process and a header decompression process, and then performs a discard operation. (Since the data may include useful information for the header decompression process (e.g., initialization and refresh (IR)) packets or header compression information), the UE may determine and then discard the data).

[0299] ■2> The UE can immediately decrypt a plurality of data items without sorting, the data is received without being discarded, and a header decompression process can be performed. This is because the E-UTRA AM RLC layer performs sorting on a plurality of data items and provides the plurality of data items to the PDCP layer.

[0300] ■2>After that, the multiple data items are provided to the upper layer in ascending order of COUNT values.

[0301] -1> (when it is a 1-2PDCP layer architecture), for example, when the UE applies the first PDCP layer architecture and function 1i-11 to the PDCP layer (e.g., E-UTRA PDCP layer or LTE PDCP layer) connected to the UM RLC layer (e.g., E-UTRA UM RLC layer), the embodiments of the present disclosure may have the following features.

[0302] ■2> The PDCP layer can be configured not to perform the process of detecting out-of-window data or duplicate data. This is because the UM E-UTRA RLC layer does not perform the retransmission process.

[0303] ■2>Afterwards, the PDCP layer may be configured to immediately perform a decryption process on the received multiple data items and then perform a header decompression process.

[0304] ■2> Thereafter, the PDCP layer may perform a reordering procedure and then provide the plurality of data items (eg, in ascending order) to its immediate upper layer.

[0305] -1> (when it is a 1-3PDCP layer architecture), for example, when the UE applies the first PDCP layer architecture 1i-11 to a PDCP layer (for example, an E-UTRA PDCP layer or an LTE PDCP layer) configured for a scattered bearer, a packet repetition bearer, or a LTE WLAN aggregation (LWA) bearer, the embodiments of the present disclosure may always apply the reordering process and the realignment timer, and the PDCP layer may have the following characteristics.

[0306] ■2> The PDCP layer can be configured to first perform out-of-window data or duplicate data detection on multiple received data items. (Retransmission can occur in RLC AM, data can be received from different RLC layers at different time points, and the sizes of LTE RLC SN and PDCP SN can be different, so that out-of-window data or duplicate data can be received).

[0307] ◆3> The PDCP layer performs the decryption process. However, the PDCP layer is configured not to perform the header decompression process. (This is because the E-UTRA PDCP layer cannot configure the header compression protocol for distributed bearers or LWA bearers).

[0308] ◆3> When the integrity protection or verification process has been performed, the PDCP layer may perform the integrity protection verification process and then discard the data. When the integrity verification process fails, the PDCP layer may discard the data and report the failure to its upper layer.

[0309] ◆3> The PDCP layer discards out-of-window data or duplicate data.

[0310] ■2> When data is not discarded, the PDCP layer may be configured to immediately perform a decryption process without reordering the received multiple data items. Thereafter, when an integrity protection or verification process is configured, the PDCP layer may perform integrity verification. When an integrity protection or verification process is performed, the PDCP layer may discard the data after the integrity protection or verification process. When the integrity verification process fails, the PDCP layer may discard the data and report the failure to the upper layer.

[0311] ■2>Afterwards, the PDCP layer may reorder the received multiple data items, and when the PDCP SN or COUNT values ​​are aligned in ascending order without gaps therebetween, the PDCP layer may perform a header compression process (when the header compression process or the header decompression process is configured), and may provide the data to the upper layer in ascending order.

[0312] ■2> While the realignment timer is running,

[0313] ◆3> When data is provided to the upper layer, data corresponding to the COUNT value (which is the same as the value obtained by subtracting 1 from the variable value used for alignment) is maintained; or when multiple data items are all provided to the upper layer without gaps between PDCP SNs (COUNT values),

[0314] ●4>The PDCP layer stops and resets the realignment timer.

[0315] ■2> When the realignment timer is not running,

[0316] ◆3> When the buffer stores data that is not provided to the upper layer, or when there is a gap between PDCP SNs (COUNT values),

[0317] ●4>The PDCP layer starts the realignment timer.

[0318] ●4> After that, the PDCP layer updates the variable used for realignment to the predicted PDCP SN or COUNT value to be received next time.

[0319] ■2> When the realignment timer expires,

[0320] ◆3> When the header decompression process is configured to the value of the plurality of data items stored in ascending order of the PDCP SN or COUNT value, which value is less than the variable used for realignment, the PDCP layer performs the header decompression process and provides the data to the upper layer.

[0321] ◆3> When the header decompression process is configured as the value of the stored multiple data items in ascending order of the PDCP SN or COUNT value, which is equal to or greater than the variable used for realignment, the PDCP layer performs the header decompression process and provides the data to the upper layer.

[0322] ◆3> Thereafter, the PDCP layer updates the variable value of the data most recently provided to the upper layer to the PDCP SN or COUNT value of the data most recently provided to the upper layer.

[0323] ◆3> When the buffer stores data that is not provided to the upper layer, or when there is a gap between PDCP SNs (COUNT values),

[0324] ●4>The PDCP layer starts the realignment timer.

[0325] ●4> After that, the PDCP layer updates the variable used for realignment to the predicted PDCP SN or COUNT value to be received next time.

[0326] -1>(When it is a 1-4PDCP layer architecture) For example, when the UE applies the first PDCP layer architecture and function 1i-12 to the NR PDCP layer, the reordering process and realignment timer can always be applied, and the NR PDCP layer can have the following characteristics.

[0327] ■2>The NR PDCP layer may first perform a decryption process on the received multiple data items.

[0328] ■2> When integrity protection or verification process is configured, the NR PDCP layer may perform integrity protection or verification process on the received data, and when the integrity verification process fails, the NR PDCP layer may discard the data and may report the failure to its upper layer.

[0329] ■2> The NR PDCP layer performs out-of-window data or duplicate data detection on the received data. (The present disclosure may be characterized in that a decryption process is performed first and then out-of-window data or duplicate data detection is performed. As another method, when an integrity protection or verification process is configured, only a decryption process is performed, and then out-of-window data or duplicate data detection is performed but the integrity protection or verification process is not configured, the decryption process may be performed only on a plurality of data items that are not discarded after out-of-window data or duplicate data detection is performed.)

[0330] ◆3>NR PDCP layer discards out-of-window data or duplicate data.

[0331] ■2> When data is not discarded, the NR PDCP layer can reorder the received multiple data items, and when the PDCP SN or COUNT values ​​are aligned in ascending order without gaps, the NR PDCP layer can perform a header compression process (when the header compression process or the header decompression process is configured) and provide the data to the upper layer in ascending order.

[0332] ■2>After that, the NR PDCP layer provides the data to the upper layer in the ascending order of COUNT value.

[0333] ■2> While the realignment timer is running,

[0334] ◆3> When data is provided to an upper layer and data corresponding to a COUNT value (the value is the same as the value obtained by subtracting 1 from the variable value for alignment) is maintained; when multiple data items are all provided to an upper layer without gaps between PDCP SNs (COUNT values); or when the variable value storing the PDCP SN or COUNT value of data to be provided to an upper layer is equal to or greater than the variable value for realignment,

[0335] ●4>NR PDCP layer stops and resets the realignment timer.

[0336] ■2> In the case where the realignment timer is not running,

[0337] ◆3> When the buffer stores data that is not provided to the upper layer, when there is a gap between PDCP SNs (COUNT values), or when the variable value storing the COUNT value of the first data that is not provided to the upper layer is less than the variable value for realignment,

[0338] ●4> The NR PDCP layer updates the variables used for realignment to the predicted PDCP SN or COUNT value to be received next time.

[0339] ●4>NR PDCP layer starts the realignment timer.

[0340] ■2> When the realignment timer expires,

[0341] ◆3> When the header decompression process is configured with the value of the plurality of data items stored in ascending order of the PDCP SN or COUNT value, which value is less than the variable for realignment, the NR PDCP layer performs the header decompression process and provides the data to the upper layer.

[0342] ◆3> When the header decompression process is configured with the value of the plurality of data items stored in ascending order of the PDCP SN or COUNT value, which is equal to or greater than the variable for realignment, the NR PDCP layer performs the header decompression process and provides the data to the upper layer.

[0343] ◆3>Afterwards, the NR PDCP layer updates the variable value of the first data not provided to the upper layer to the PDCP SN or COUNT value of the first data not provided to the upper layer.

[0344] ◆3> When the buffer stores data that is not provided to the upper layer, or when there is a gap between PDCP SNs (COUNT values), or when the variable value storing the COUNT value of the first data that is not provided to the upper layer is less than the variable value for realignment,

[0345] ●4> The NR PDCP layer updates the variables used for realignment to the predicted PDCP SN or COUNT value to be received next time.

[0346] ●4>NR PDCP layer starts the realignment timer.

[0347] Fig. 1I The second PDCP layer architecture or function 1i-20 proposed in the disclosure may have the 2-1PDCP layer architecture or 2-2PDCP layer architecture proposed in the present disclosure, and may have the features to be described below.

[0348] The present disclosure proposes a second PDCP layer architecture 1i-20 for efficient switching. The second PDCP layer architecture can be applied to implementation example 2 of the efficient switching method for minimizing data interruption time proposed in the present disclosure.

[0349] In the second PDCP layer architecture, the UE may send or receive data to or from the source BS1i-21 by using a protocol layer (eg, SDAP layer, PDCP layer, RLC layer, or MAC layer) for the first bearer.

[0350] In an embodiment of the present disclosure, the PDCP layer function of the source BS may include a transmitting PDCP layer function for the source BS or a receiving PDCP layer function for the source BS.

[0351] In an embodiment of the present disclosure, the PDCP layer function 1i-21 may indicate a lower function of a transmission PDCP layer function for a source BS.

[0352] In an embodiment of the present disclosure, the PDCP layer function 1i-21 may indicate a lower function of a reception PDCP layer function for a source BS.

[0353] According to an embodiment of the present disclosure, reference numeral 1j-21 or 1v-21 may indicate the same object as 1i-21. The UE may send data to or receive data from the target BS 1i-22 by using a protocol layer (e.g., SDAP layer, PDCP layer, RLC layer, or MAC layer) for the second bearer.

[0354] In an embodiment of the present disclosure, the PDCP layer function of the target BS may include a transmitting PDCP layer function for the target BS or a receiving PDCP layer function for the target BS.

[0355] In an embodiment of the present disclosure, the PDCP layer function 1i-22 may indicate a lower function of a transmission PDCP layer function for a target BS.

[0356] In an embodiment of the present disclosure, the PDCP layer function 1i-22 may indicate a lower function of a reception PDCP layer function for the target BS.

[0357] According to an embodiment of the present disclosure, reference numerals 1j-22 or 1v-22 may indicate the same objects as 1i-22.

[0358] The PDCP layer for the first bearer and the PDCP layer for the second bearer may be configured in the UE separately, but may be logically operated as one PDCP layer, as shown in 1i-20. More specifically, by distinguishing the functions of the PDCP layer, one PDCP layer may be implemented as the functions of the upper PDCP layer (e.g., SN allocation function, realignment function, in-sequence delivery function, or duplicate detection function), and the functions of two lower PDCP layers for the source BS and the target BS, respectively (e.g., decryption or encryption function, header (or data) compression or decompression function, integrity protection or verification function, or duplicate detection function). In addition, as mentioned above, when the DAPS switching method is performed, the UE may send UL data to the source BS, and when the first condition is met, the UE may switch to the target BS, and may continue to receive DL data from the source BS and the target BS. Therefore, only one header (or data) compression protocol context for the source BS or the target BS may be maintained and applied to the UL, and two contexts for the source BS or the target BS may be maintained and applied to the DL.

[0359] The 2-1 PDCP layer architecture based on the second PDCP layer architecture proposed in the present disclosure (eg, the E-UTRA PDCP layer for the DAPS handover method) may have the following features.

[0360] The upper function of the transmitting PDCP layer function may be used to assign a PDCP SN to a plurality of data items received from an upper layer. The two lower functions of the transmitting PDCP layer functions 1i-21 and 1i-22 for the source BS and the target BS, respectively, may be used to apply a header (or data) compression context or a security key configured with the source BS to the data to be transmitted to the source BS, and to apply a header (or data) compression context or a security key configured with the target BS to the data to be transmitted to the target BS, by using a separate security key configured with each of the source BS and the target BS, and to apply a header (or data) compression context or a security key configured with the target BS to the data to be transmitted to the target BS, and to apply a header (or data) compression process when the header (or data) compression process is configured. When integrity protection is configured, the lower functions of the transmitting PDCP layer functions 1i-21 and 1i-22 may be used to apply a ciphering process by applying an integrity protection process to the PDCP header and data (PDCP SDU), and the data to be transmitted to the source BS may be provided to the transmitting RLC layer for the first bearer, and the data to be transmitted to the target BS may be provided to the transmitting RLC layer for the second bearer, thereby performing transmission. In order to speed up data processing, the two lower functions of the transmit PDCP layer functions 1i-21 and 1i-22 can be used to perform parallel processing of header compression, integrity protection or encryption processes. In addition, the two lower functions of the transmit PDCP layer functions 1i-21 and 1i-22 can be used to perform integrity protection or encryption processes by using different security keys. In addition, compression, integrity protection or encryption processes for multiple different data items can be performed by applying different compression contexts, different security keys or different security algorithms in a logically one transmit PDCP layer.

[0361] In the aforementioned situation, the receiving PDCP layer functions, which are lower functions of the receiving PDCP layer functions 1i-21 and 1i-22 for the source BS or the target BS, may each independently perform an out-of-window data detection or a repeat detection process for each of the multiple data items received from the RLC layer based on the PDCP SN or COUNT value for each of the multiple data items received from the lower layer (specifically, for the multiple data items received from the two RLC layers for each of the source BS and the target BS). As another method, for ease of implementation, the out-of-window data detection or the repeat detection process may be performed on all the received data based on the PDCP SN or COUNT value without distinguishing the RLC layer. As another method, for more accurate repeat detection, the out-of-window data detection may be performed on all the received data based on the PDCP SN or COUNT value without distinguishing the RLC layer; and the repeat detection process may be performed separately for each of the multiple data items received from the RLC layer. As another method, when a plurality of data items received from different BSs overlap each other, in order to prevent data loss for the header compression protocol, out-of-window data detection may be performed on all received data based on the PDCP SN or COUNT value without distinguishing the RLC layer. In addition, a duplicate detection process may be performed on all data after a decryption process, an integrity protection process, or a header (or data) decompression process for each of the plurality of data items received from the RLC layer.

[0362] The sub-function of the receiving PDCP layer may be used to apply a decryption process to multiple data items received at once by using separate header (or data) compression contexts or security keys configured separately with the source BS and the target BS. When integrity protection is configured, the sub-function of the receiving PDCP layer may be used to apply an integrity verification process to the PDCP header and data (PDCP SDU).

[0363] In the 2-1 PDCP layer architecture, a header (or data) decompression process may be immediately performed on a plurality of data items received from the RLC layer of a first bearer corresponding to a source BS without reordering, and a header (or data) decompression process may be immediately performed on a plurality of data items received from the RLC layer of a second bearer corresponding to a target BS without reordering. In addition, in order to distinguish between data received from the RLC layer of a first bearer corresponding to a source BS and data received from the RLC layer of a second bearer corresponding to a target BS, an indicator is defined for each data so that the PDCP layer can identify whether the data is received from the source BS or the target BS. As another method, a 1-bit indicator is defined in a PDCP header, an SDAP header, or an RLC header so that the PDCP layer can identify whether the data is received from the source BS or the target BS. In addition, based on the PDCP SN or COUNT value, a duplicate detection process (a process in which only one data (including pre-received data or data provided to the upper layer) is allocated to each PDCP SN or each COUNT value and all other data are discarded) may be performed on all the multiple data items received from the RLC layer of the first bearer corresponding to the source BS and the multiple data items received from the RLC layer of the second bearer corresponding to the target BS, wherein the header (or data) compression process for the multiple data items has been completed. Thereafter, based on the PDCP SN or COUNT value, a realignment process may be performed on all the multiple data items received from the RLC layer of the first bearer corresponding to the source BS and the multiple data items received from the RLC layer of the second bearer corresponding to the target BS in ascending order, and the multiple data items may be sequentially provided to the upper layer. Since the PDCP layer may receive data from different BSs (i.e., from the first bearer or from the second bearer) out of order, the PDCP layer must always perform the realignment process.

[0364] In order to speed up data processing, the two lower functions of the receiving PDCP layer function can be used to perform parallel processing of header compression, integrity protection or encryption process based on each PDCPSN or each COUNT value. Integrity protection, encryption process or header decompression process can be performed by using different header (or data) compression contexts or different security keys. Integrity protection, encryption process or decompression process can be performed on multiple different data items by applying different header (or data) compression contexts, different security keys or different security algorithms in a logically transmitting PDCP layer. In addition, the lower function of the receiving PDCP layer function can be used to perform an unordered decryption or integrity verification process on each of the multiple received data items, regardless of the order of the PDCP SN or COUNT values.

[0365] When the PDCP layer distinguishes between a layer for a first bearer and a layer for a second bearer, considering that the layer for the first bearer and the layer for the second bearer are connected to different MAC layers, have different logical channel identifiers, are different RLC layers connected to different MAC layers, or use different encryption keys, the PDCP layer can distinguish between the layer for the first bearer (or the first RLC layer) and the layer for the second bearer (or the second RLC layer), and in this way, an encryption process or a decryption process can be performed on the UL data and the DL data by using different security keys, and the UL data and the DL data can be compressed or decompressed by using different compression protocol contexts.

[0366] The 2-2 PDCP layer architecture based on the second PDCP layer architecture proposed in the present disclosure (e.g., the NR PDCP layer for the DAPS switching method) may have the following features.

[0367] The upper function of the transmitting PDCP layer function can be used to assign a PDCP SN to a plurality of data items received from its upper layer. The two lower functions of the transmitting PDCP layer functions 1i-21 and 1i-22 for the source BS and the target BS, respectively, can be used to apply a header (or data) compression context or a security key configured with the source BS to the data to be sent to the source BS by using a separate security key configured with each of the source BS and the target BS, and to apply a header (or data) compression context or a security key configured with the target BS to the data to be sent to the target BS, and the header (or data) compression process can be applied when the header (or data) compression process is configured; and when integrity protection is configured, the lower functions of the transmitting PDCP layer functions 1i-21 and 1i-22 can be used to apply a ciphering process by applying an integrity protection process to the PDCP header and data (PDCP SDU), the data to be sent to the source BS can be provided to the transmitting RLC layer for the first bearer, and the data to be sent to the target BS can be provided to the transmitting RLC layer for the second bearer, thereby performing transmission. In order to speed up data processing, the two lower functions of the transmit PDCP layer functions 1i-21 and 1i-22 can be used to perform parallel processing of header compression, integrity protection or encryption processes. In addition, the two lower functions of the transmit PDCP layer functions 1i-21 and 1i-22 can be used to perform integrity protection or encryption processes by using different security keys. In addition, compression, integrity protection or encryption processes can be performed on multiple different data items by applying different compression contexts, different security keys or different security algorithms in a logically one transmit PDCP layer.

[0368] In the aforementioned situation, the receiving PDCP layer function, which is a lower function of the receiving PDCP layer functions 1i-21 and 1i-22 for the source BS or the target BS, can each independently perform an out-of-window data detection or a duplicate detection process for each of the multiple data items received from the RLC layer based on the PDCP SN or COUNT value for each of the multiple data items received from the lower layer (specifically, for the multiple data items received from the two RLC layers for each of the source BS and the target BS). As another method, for ease of implementation, the out-of-window data detection or duplicate detection process can be performed on all received data based on the PDCP SN or COUNT value without distinguishing the RLC layer. As another method, for more accurate duplicate detection, the receiving PDCP layer can be used to perform out-of-window data detection on all received data based on the PDCP SN or COUNT value without distinguishing the RLC layer; and perform a duplicate detection process separately for each of the multiple data items received from the RLC layer. As another method, when multiple data items received from different BSs overlap with each other, in order to prevent data loss for the header compression protocol, the receiving PDCP layer can be used to perform out-of-window data detection on all received data based on the PDCP SN or COUNT value without distinguishing the RLC layer; and after receiving the decryption process, integrity protection process or header (or data) decompression process for each of the multiple data items received from the RLC layer, a repeated detection process can be performed on all the data.

[0369] The sub-function of the receiving PDCP layer can be used to immediately apply a decryption process to multiple received data items by using separate header (or data) compression contexts or security keys configured separately with the source BS and the target BS; and when integrity protection is configured, the sub-function of the receiving PDCP layer can be used to apply an integrity verification process to the PDCP header and data (PDCP SDU).

[0370] In the 2-2PDCP layer architecture, a plurality of data items received from the RLC layer of the first bearer corresponding to the source BS and a plurality of data items received from the RLC layer of the second bearer corresponding to the target BS may be reordered, and a header (or data) decompression process may be performed on the plurality of data items received from each BS (source BS or target BS) by applying a header (or data) compression context of each BS (source BS or target BS) in ascending order of PDCP SN or COUNT value. In addition, in order to distinguish between data received from the RLC layer of the first bearer corresponding to the source BS and data received from the RLC layer of the second bearer corresponding to the target BS, an indicator is defined for each data so that the PDCP layer can identify whether the data is received from the source BS or the target BS.

[0371] As another method, a 1-bit indicator is defined in a PDCP header, an SDAP header, or an RLC header so that the PDCP layer can identify whether the data is received from a source BS or a target BS. In addition, based on the PDCP SN or COUNT value, a duplicate detection process (a process in which only one data (including pre-received data or data provided to an upper layer) is allocated to each PDCP SN or each COUNT value and all other data are discarded) is performed on all multiple data items received from the RLC layer of the first bearer corresponding to the source BS and the multiple data items received from the RLC layer of the second bearer corresponding to the target BS, wherein the header (or data) compression process for the multiple data items has been completed. Thereafter, based on the PDCP SN or COUNT value, the multiple data items received from the RLC layer of the first bearer corresponding to the source BS and the multiple data items received from the RLC layer of the second bearer corresponding to the target BS can all be sequentially provided to the upper layer in ascending order. Since the PDCP layer may receive data from different BSs (ie, from the first bearer or from the second bearer) out of order, the PDCP layer must always perform a realignment procedure.

[0372] In order to speed up data processing, the two lower functions of the receiving PDCP layer function can be used to perform parallel processing of header compression, integrity protection or encryption process based on each PDCPSN or each COUNT value. In addition, the lower function of the receiving PDCP layer function can be used to perform integrity protection, encryption process or header decompression process by using different header (or data) compression contexts or different security keys. Integrity protection, encryption process or decompression process can be performed on multiple different data items by applying different header (or data) compression contexts, different security keys or different security algorithms in a logically transmitting PDCP layer. In addition, the lower function of the receiving PDCP layer function can be used to perform an unordered decryption or integrity verification process on each of the multiple received data items, regardless of the order of the PDCP SN or COUNT value.

[0373] When the PDCP layer distinguishes between a layer for a first bearer and a layer for a second bearer, considering that the layer for the first bearer and the layer for the second bearer are connected to different MAC layers, have different logical channel identifiers, are different RLC layers connected to different MAC layers, or use different encryption keys, the PDCP layer can distinguish between the layer for the first bearer (or the first RLC layer) and the layer for the second bearer (or the second RLC layer), and in this way, an encryption process or a decryption process can be performed on the UL data and the DL data by using different security keys, and the UL data and the DL data can be compressed or decompressed by using different compression protocol contexts.

[0374] In the present disclosure, a third PDCP layer architecture 1i-30 for efficient switching is provided. The third PDCP layer architecture may be applicable to implementation 2 of the efficient switching method for minimizing data interruption time proposed in the present disclosure. The PDCP layer function in the third PDCP layer architecture proposed in the present disclosure may be equivalent to the second PDCP layer architecture proposed in the present disclosure. However, the third PDCP layer architecture may correspond to an architecture for releasing the first bearer for the source BS from the second PDCP layer architecture. More specifically, the third PDCP layer architecture proposed in the present disclosure may have the same function as the second PDCP layer architecture, but may have an architecture for releasing the first bearer (e.g., SDAP layer, PDCP layer, RLC layer, or MAC layer) for the source BS. Therefore, the third PDCP layer architecture may release QoS mapping information for the SDAP layer of the source BS, security key information for the PDCP layer of the source BS, header (or data) compression context information for the source BS, or RLC layer or MAC layer for the source BS.

[0375] Figure 1J The architecture of an efficient SDAP layer to be applied to a DAPS handover method of Embodiment 2 as an efficient handover method according to an embodiment of the present disclosure and a method of applying the architecture are shown.

[0376] refer to Figure 1J The present disclosure proposes a specific architecture and function of an efficient SDAP layer to be applied to a DAPS switching method as implementation mode 2 of the efficient switching method proposed in the present disclosure, and the architecture of the SDAP layer to be proposed below is characterized in that, when a DAPS switching process is performed, different SDAP layer architectures can be applied to each bearer at different time points.

[0377] For example, before the UE receives a switching command message from the BS, the UE may process and send or receive data by applying the first SDAP layer architecture and functions 1j-10 and 1j-12 proposed in the present disclosure to each bearer in operation 1j-01. In the first SDAP layer architecture, the SDAP layer may perform data processing (e.g., based on the first QoS flow and bearer mapping information, read the SDAP header information and update the mapping information or configure the SDAP header, or route or provide the processed data to the appropriate upper or lower layer) on multiple UL data items to be sent or multiple DL data items received (e.g., multiple data items received from the source BS) by maintaining and applying the first QoS flow and bearer mapping information of the source BS.

[0378] However, when the UE receives a switching command message from the BS and the switching command message indicates the DAPS switching method proposed in the present disclosure or indicates the DAPS switching method for a specific bearer, the UE may process and send or receive data in operation 1j-02 by applying the second PDCP layer architecture and function 1j-20 proposed in the present disclosure to each bearer or a bearer indicating the DAPS switching method. For example, when the UE receives a switching command message from the BS and the switching command message indicates the DAPS switching method proposed in the present disclosure, indicates the DAPS switching method for a specific bearer, configures the DAPS switching method for at least one bearer, or configures the DAPS switching method for a certain bearer, the UE may switch the first SDAP layer architecture or functions 1j-10 and 1j-12 for each bearer proposed in the present disclosure to the second SDAP layer architecture or function 1j-20 for each bearer or a bearer indicating the DAPS switching method.

[0379] As another method, when the first condition proposed in the present disclosure is met (for example, when the random access process to the target BS is completed or the first timer stops), the UE may switch the first SDAP layer architecture or functions 1j-10 and 1j-12 for each bearer proposed in the present disclosure to the second SDAP layer architecture or function 1j-20 for each bearer or a bearer indicating the DAPS switching method in operation 1j-02. In addition, when the UE receives a switching command message from the BS and the switching command message indicates the DAPS switching method proposed in the present disclosure, indicates the DAPS switching method for a specific bearer, or newly configures QoS flow and bearer mapping information, the UE may switch the first SDAP layer architecture or functions 1j-10 and 1j-12 to the second SDAP layer architecture or function 1j-20 for each bearer or a bearer indicating the DAPS switching method.

[0380] In addition, the second SDAP layer architecture can be configured in the following manner: the existing first QoS flow and the existing bearer mapping information of the source BS are maintained to process the UL data to be sent to the source BS and the DL data to be received from the source BS. The newly configured second QoS flow and bearer mapping information in the switching command message can be configured for the target BS, and the UE can use the configured information to process the UL data to be sent to the target BS and the DL data to be received from the target BS. For example, in the second SDAP layer architecture proposed in the present disclosure, the first QoS flow and bearer mapping information of the source BS or the second QoS flow and bearer mapping information of the target BS is maintained, so that the data for the source BS and the data for the target BS can be processed separately.

[0381] In addition, when the first condition proposed by the present disclosure is met, the UL data transmission for the bearer configured with the DAPS switching method must be switched to the target BS, so that the process of changing, switching or reconfiguring the first QoS flow and bearer mapping information about the source BS to the second QoS flow and bearer mapping information about the target BS can be performed on the UL. Since the mapping information is changed from the first QoS flow and bearer mapping information to the second QoS flow and bearer mapping information as described above, the UE can send the generated SDAP control data for each changed QoS flow to the target BS (for example, an end marker indicating the last data for the changed QoS flow), so that when the target BS receives UL data from the UE, the target BS can perform data processing by reflecting the changes in the QoS flow and bearer mapping information by the UE. In the second SDAP layer architecture, the SDAP layer can identify whether the data received from the lower layer is data received from the source BS or data received from the target BS by using a 1-bit indicator of the SDAP header, a 1-bit indicator of the PDCP header, or information indicated by the PDCP layer. When the BS indicates the DAPS switching method for each bearer to the UE by using the handover command message, the BS may always indicate the DAPS switching method for the default DRB, so that when data that does not correspond to the QoS flow and bearer mapping information occurs in the new QoS flow when the DAPS handover process is performed, the BS may instruct the UE to always send UL data via the default bearer. When the DAPS handover method is not configured for the default bearer, UL data transmission for the new QoS flow occurring in the handover is unavailable, so that data interruption time may occur.

[0382] When the second condition proposed in the present disclosure is met when UE 1h-20 performs the DAPS switching method, UE 1h-20 may release the first bearer for the source BS1h-05 for the second SDAP layer architecture and function 1j-20 applied to each bearer or bearer indicating the DAPS switching method, and may switch the second SDAP layer architecture and function 1j-20 to the first SDAP layer architecture or functions 1j-10 and 1j-12, and apply the first SDAP layer architecture or functions 1j-10 and 1j-12. In addition, when the second condition is met, the UE may switch the second SDAP layer architecture and function 1j-20 proposed in the present disclosure to the first SDAP layer architecture or functions 1j-10 and 1j-12 for each bearer or bearer indicating the DAPS switching method. Here, the UE may maintain the second bearer or second QoS flow and bearer mapping information for the target BS. Before the UE releases the first bearer or the first QoS flow and bearer mapping information for the source BS1h-05, the UE may complete data processing by applying the first QoS flow and bearer mapping information to multiple data items received from the source BS (e.g., all data received from the source BS), and then may release the first QoS flow and bearer mapping information or the first bearer. Thereafter, the UE may provide the processed multiple data items to the upper layer in ascending order. For example, when the second condition is met, the UE may process the data (e.g., based on the first QoS flow and bearer mapping information, read the SDAP header information and update the mapping information or configure the SDAP header, or route or provide the processed data to the appropriate upper or lower layer) by applying the first QoS flow and bearer mapping information for the source BS to multiple data items stored in the buffer (e.g., multiple data items received from the source BS), and then may discard the first QoS flow and bearer mapping information for the source BS.

[0383] The SDAP layer may define and apply information indicated by a 1-bit indicator of a new SDAP header, a 1-bit indicator of a new PDCP header, SDAP control data (e.g., a DL end marker), or a PDCP layer. Thereafter, the SDAP layer may identify data recently received from the source BS based on the information. Therefore, the SDAP layer may perform data processing on the data, which was recently received from the source BS, by applying the first QoS flow and bearer mapping information for the source BS, and then may discard the first QoS flow and bearer mapping information for the source BS. In addition, the SDAP layer may continuously maintain the second QoS flow and bearer mapping information, and may process UL data or DL ​​data regarding the target BS based on the second QoS flow and the bearer mapping information in operation 1j-03.

[0384] In the following, according to an embodiment of the present disclosure, a method is provided in which a UE receives a handover command message and refers to Figure 1FWhen applying the bearer configuration information included in the handover command message, a method of applying the bearer configuration information using different schemes according to the handover type indicated in the handover command message.

[0385] - In the case where the UE receives the handover command message, when the ReconfigWithSync information or the MobilityControl Info indicates the first handover method (for example, embodiment 1 of the present disclosure or the conventional handover method), the embodiment 2 (DAPS handover method) proposed in the present disclosure is not configured, or no bearer is configured in the bearer configuration information in embodiment 2 (DAPS handover method) proposed in the present disclosure,

[0386] ■ When a default bearer is configured in the SDAP layer configuration information configured in the handover command message, the UE may configure the default bearer for the source BS as the default bearer of the target BS indicated in the configuration information.

[0387] ■When the second QoS flow and bearer mapping information is configured in the SDAP layer configuration information configured in the handover command message, the UE may release the first QoS flow and bearer mapping information applied to the source BS, and may apply the second QoS flow and bearer mapping information. As another method, the UE may replace the first QoS flow and bearer mapping information for the source BS with the second QoS flow and bearer mapping information.

[0388] ■When a data discard timer value is configured in the PDCP layer configuration information configured in the handover command message, the UE may apply the discard timer value to the PDCP layer corresponding to the bearer identifier of the configuration information.

[0389] ■When the drb-ContinueROHC indicator in the PDCP layer configuration information configured in the handover command message is configured as false, the UE may reset the context of the header compression or decompression protocol in the PDCP layer corresponding to the bearer identifier of the configuration information. When the drb-ContinueROHC indicator is configured as true, the UE does not reset the context of the header compression or decompression protocol in the PDCP layer corresponding to the bearer identifier of the configuration information.

[0390] ■When the realignment timer value is configured in the PDCP layer configuration information configured in the handover command message, the UE may apply the realignment timer value to the PDCP layer corresponding to the bearer identifier of the configuration information.

[0391] ■When the UE receives the handover command message, the UE may reconstruct the PDCP layer. For example, the UE may reset the window state variable for the SRB, and may discard the stored multiple data items (PDCP SDU or PDCP PDU, may reset the window state variable for the UM DRB, may perform compression, encryption, or integrity protection on multiple data items that have not been sent to the lower layer or whose PDCP discard timer has not expired based on the header (or data) compression context or security key of the target BS in ascending order of COUNT value, and then may send or retransmit the data, and when the realignment timer is running, the UE may stop and reset the realignment timer, may process the received multiple data items (PDCP SDU or PDCP PDU) in sequence, and may provide the data to the upper layer, and the UE does not reset the window state variable for the AM DRB, may perform compression, encryption, or integrity protection on the data starting from the first data (PDCP SDU or PDCP PDU) that has not received a positive acknowledgement of successful transmission from the lower layer in ascending order of PDCP SN or COUNT value based on the header (or data) compression context or security key of the target BS.

[0392] ■When security key configuration information or security algorithm is configured in the security configuration information configured in the switching command message, the UE can derive a new security key or new security configuration information by using the configuration information, release an existing security key or existing security configuration information, or replace the existing security key or existing security configuration information with a new security key or new security configuration information.

[0393] ■When 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 may replace the existing logical channel identifier with the new logical channel identifier.

[0394] ■When 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 on the RLC layer corresponding to the bearer identifier indicated in the RLC layer configuration information. For example, the UE may perform the RLC reestablishment process so that the sending RLC layer may perform a process of discarding all stored data. In addition, when the realignment timer is running, the receiving RLC layer of the UE may stop and reset the realignment timer, process all stored data, and then provide the data to its upper layer. In addition, the UE may reset the MAC layer. In addition, the UE may reset the MAC layer for the source BS, and may use the MAC layer for the target BS.

[0395] ■When the RLC layer configuration information configured in the handover command message is newly configured, the UE may perform an RLC re-establishment procedure on the RLC layer corresponding to the bearer identifier indicated in the RLC layer configuration information.

[0396] ■When a second priority is newly configured for a logical channel in the MAC layer configuration information configured in the switching command message, the UE may release the first priority corresponding to the identifier of the logical channel indicated in the configuration information, or may replace the first priority corresponding to the logical channel identifier with the newly configured second priority.

[0397] ■When a second prioritisedBitRate (PBR) is newly configured for a logical channel in the MAC layer configuration information configured in the handover command message, the UE may release the first prioritisedBitRate (PBR) corresponding to the identifier of the logical channel indicated in the configuration information, or may replace the first prioritisedBitRate (PBR) corresponding to the identifier of the logical channel with the newly configured second prioritisedBitRate (PBR). PrioritisedBitRate refers to a value that increases for each logical channel at a preset time interval (e.g., at each TTI). When the UE receives UL transmission resources, the UE may perform a logical channel optimization (LCP) procedure and may send data for the logical channel based on the priority and the prioritisedBitRate. In this regard, the higher the priority or the larger the value of the prioritisedBitRate, the more data that can be sent.

[0398] ■When a second bucketSizeDuration is newly configured for a logical channel in the MAC layer configuration information configured in the handover command message, the UE may release the first bucketSizeDuration corresponding to the identifier of the logical channel indicated in the configuration information, or may perform configuration by replacing the first bucketSizeDuration corresponding to the identifier of the logical channel with the newly configured second bucketSizeDuration. As described above, the storage block size indicates the maximum value that the value of the prioritisedBitRate may have when the prioritisedBitRate is accumulated.

[0399] ■When the second available SCell information, available subcarrier gap information, maximum PUSCH duration 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 preconfigured first available SCell information, the preconfigured available subcarrier gap information, the preconfigured maximum PUSCH duration or the preconfigured logical channel group configuration information, or may perform the configuration by replacing the preconfigured first available SCell information, the preconfigured available subcarrier gap information, the preconfigured maximum PUSCH duration or the preconfigured logical channel group configuration information with the newly configured second available SCell information, the newly configured available subcarrier gap information, the newly configured maximum PUSCH duration or the newly configured logical channel group configuration information.

[0400] -When the UE receives a handover command message, when the handover command message or the ReconfigWithSync information or the Mobility Control Info information indicates or configures a second handover method (for example, implementation mode 2 or the DAPS handover method of the present disclosure), when the DAPS handover method is indicated or configured for each bearer identifier, when implementation mode 2 (DAPS handover method) proposed in the present disclosure is configured for a certain bearer in the bearer configuration information, or when implementation mode 2 (DAPS handover method) proposed in the present disclosure is configured for at least one bearer in the bearer configuration information,

[0401] ■When a 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 in the present disclosure, and may maintain the existing default bearer for the source BS by applying the second SDAP layer architecture 1j-20, and may configure the default bearer information indicated in the configuration information as the default bearer for the target BS. As another method, when the first condition proposed in the present disclosure is met, the UE may switch the existing default bearer for the source BS to the default bearer for the target BS indicated in the configuration information.

[0402] ■When the second QoS flow and bearer mapping information is configured in the SDAP layer configuration information configured in the handover command message, the UE may perform the DAPS handover method proposed in the present disclosure, and may maintain the first QoS flow and bearer mapping information for the source BS by applying the second SDAP layer architecture 1j-20, and may apply the second QoS flow and bearer mapping information to the data of the target BS. In addition, when the first condition proposed in the present disclosure is met, the UE may apply the second QoS flow and bearer mapping information for the target BS.

[0403] ■When a data discard timer value is configured in the PDCP layer configuration information configured in the handover command message, the UE can execute the DAPS handover method proposed in the present disclosure, and can apply the discard timer value to the PDCP layer corresponding to the bearer identifier of the configuration information by applying the second PDCP layer architecture.

[0404] ■When the handover command message indicates or configures the DAPS handover method, the PDCP layer may not be rebuilt and the following process may be performed. For example, the UE may reset the window state variable for the SRB (when the DAPS handover fails, the variable reset may be skipped to perform fallback), or may discard the stored multiple data items (PDCP SDU or PDCP PDU); the window state variable for the UM DRB may not be reset, and the sending of data to the source BS or the receiving of data from the source BS may be continued for the multiple data items that have not been sent to the lower layer or the PDCP discard timer has not expired; and the window state variable for the AM DRB may not be reset, and the sending of data to the source BS or the receiving of data from the source BS may be continued.

[0405] ■When the handover command message does not indicate or configure the DAPS handover method, the UE may re-establish the PDCP layer. For example, the UE may reset the window state variable for the SRB, and may discard the stored multiple data items (PDCP SDU or PDCP PDU); may reset the window state variable for the UM DRB, and may perform compression, encryption, or integrity protection on multiple data items that have not been sent to the lower layer or the PDCP discard timer has not expired in ascending order of COUNT value based on the header (or data) compression context or security key of the target BS, and then may send or retransmit the data; and when the realignment timer is running, the UE may stop and reset the realignment timer, may process the received multiple data items (PDCP SDU or PDCP PDU) in sequence, and may provide the data to the upper layer; and the UE does not reset the window state variable for the AM DRB, and may perform compression, encryption, or integrity protection on the data starting from the first data (PDCP SDU or PDCP PDU) that has not received a successful transmission positive acknowledgement from the lower layer in ascending order of PDCP SN or COUNT value based on the header (or data) compression context or security key of the target BS. In addition, the UE may perform a reestablishment procedure on the RLC layer.

[0406] ■When the drb-ContinueROHC indicator in the configuration information of the PDCP layer indicated by the handover command message or configured with the DAPS handover method is configured as false, the UE may perform the DAPS handover method proposed in the present disclosure, and may use the header compression or decompression protocol context for the source BS unchanged in the PDCP layer corresponding to the bearer identifier of the configuration information by applying the second PDCP layer architecture, reset the header compression or decompression protocol context for the target BS, and start in an initial state (e.g., IR state). When the drb-ContinueROHC indicator is configured as true, the UE may perform the DAPS handover method proposed in the present disclosure, and may use the header compression or decompression protocol context for the source BS unchanged in the PDCP layer corresponding to the bearer identifier of the configuration information by applying the second PDCP layer architecture, and may apply the header compression or decompression protocol context of the target BS likewise, such as the header compression or decompression protocol context of the source BS. For example, the UE may copy the header compression or decompression protocol context of the source BS and apply it unchanged to the header compression or decompression protocol context of the target BS. As another method, the UE may apply the same header compression or decompression protocol context to the target BS or the source BS.

[0407] ■When the handover command message indicates or the realignment timer value in the configuration information of the PDCP layer configuring the DAPS handover method is configured as false, the UE can execute the DAPS handover method proposed in the present disclosure, and can apply the realignment timer value to the PDCP layer corresponding to the bearer identifier of the configuration information by applying the second PDCP layer architecture.

[0408] ■When security key configuration information or a security algorithm is configured in the security configuration information indicating or configuring the DAPS switching method in a switching command message, or when an indicator indicating a new process is included in the PDCP layer configuration information, the UE can derive new security keys or new security configuration information by using the configuration information, and can perform the DAPS switching method proposed in the present disclosure: the existing security keys or existing security configuration information for the source BS can be maintained by applying the second PDCP layer architecture, and the security keys or security configuration information for the target BS can be configured as new security keys or new security configuration information.

[0409] ■In the configuration information of the RLC layer of the bearer indicated by the switching command message or configured with the DAPS switching method, the UE may not perform the RLC reconstruction process on the RLC layer used for the source BS. More specifically, the RLC reconstruction process may not be performed, the sending RLC layer may continue to send the stored multiple data, and the receiving RLC layer may continue to process the stored multiple data and the received multiple data, so that data interruption time does not occur. However, when the first condition proposed by the present disclosure is met, the PDCP layer configured with the DAPS switching method may send a data discard indicator for PDCP user data (PDCP data PDU) to instruct the RLC layer used for the source BS to discard the data (PDCP data PDU) for the AM bearer or the UM bearer. Therefore, the RLC layer used for the source BS may discard the PDCP data PDU, but may not discard and send the PDCP control PDU.

[0410] ■ An RLC reestablishment procedure may be performed at the RLC layer for a bearer for which the handover command message does not indicate or configure the DAPS handover method; or when the RLC reestablishment procedure is configured, an RLC reestablishment procedure may be performed. For example, in particular, the transmitting RLC layer may perform an RLC reestablishment procedure, thereby performing a procedure of discarding all stored data (PDCP data PDU or PDCP control PDU). In addition, when the realignment timer is running, the receiving RLC layer may stop and reset the realignment timer, may process all stored data, and may send the processed data to its upper layer.

[0411] ■When a new logical channel identifier is configured in the configuration information of the RLC layer of the bearer indicated in the switching command message or configured with the DAPS switching method, the UE can execute the DAPS switching method proposed in the present disclosure, and can maintain the existing logical channel identifier of the RLC layer or MAC layer of the first bearer of the source BS corresponding to the bearer identifier indicated in the RLC layer configuration information by applying the second PDCP layer architecture, and can configure the RLC layer or MAC layer of the second bearer configured with the target BS, the new logical channel identifier indicated in the configuration.

[0412] ■When the switching command message indicates or configures the DAPS switching method, the configuration information of the RLC layer of the bearer is newly configured, the UE can execute the DAPS switching method proposed in the present disclosure, and can maintain the existing RLC configuration information of the RLC layer of the first bearer of the source BS (corresponding to the bearer identifier indicated in the RLC layer configuration information) by applying the second PDCP layer architecture, and can configure the new configuration information of the RLC layer indicated in the configuration for the RLC layer of the second bearer corresponding to the target BS.

[0413] The present disclosure may be executed Figure 1KThe proposed method 1, method 2 or method 3 for configuring the MAC layer.

[0414] The present disclosure may be executed Figure 1K The proposed method 1, method 2 or method 3 for processing the SRB layer.

[0415] ■When a second priority is newly configured for a logical channel in the MAC layer configuration information configured in the handover command message, the UE may perform the DAPS handover method proposed in the present disclosure and may apply the second PDCP layer architecture. In this regard, the UE may maintain the existing configuration information for the MAC layer of the first bearer of the source BS corresponding to the bearer identifier indicated above, and may configure the new logical channel identifier indicated in the configuration information for the MAC layer of the second bearer corresponding to the target BS. The UE may configure the newly configured second priority corresponding to the logical channel identifier indicated in the configuration information. As another method, when the first condition proposed in the present disclosure is met, the UE may apply the priority order to the MAC layer of the second bearer corresponding to the target BS according to each logical channel identifier.

[0416] ■When a second prioritizedBitRate (PBR) is newly configured for a logical channel in the MAC layer configuration information configured in the handover command message, the UE may perform the DAPS handover method proposed in the present disclosure. In this regard, the UE applies a second PDCP layer architecture, and may maintain the existing configuration information for the MAC layer of the first bearer of the source BS corresponding to the bearer identifier indicated above, and may configure the new logical channel identifier indicated in the configuration information for the MAC layer of the second bearer corresponding to the target BS. The UE may configure the newly configured second prioritizedBitRate (PBR) corresponding to the logical channel identifier indicated in the configuration information. As another method, after the first condition proposed in the present disclosure is met, the UE may start applying the second prioritizedBitRate to the new logical channel identifier in the MAC layer of the second bearer corresponding to the target BS (so that when different handover methods are indicated for each bearer, UL transmission resources can be allocated fairly). PrioritisedBitRate refers to a value that is increased for each logical channel at a preset time interval (e.g., at each TTI) when the prioritizedBitRate is applied to each logical channel identifier. When the UE receives the UL transmission resource, the UE may perform the LCP process and may send data for the logical channel based on the priority and the prioritisedBitRate. In this regard, the higher the priority or the larger the value of the prioritisedBitRate, the more data that can be sent.

[0417] ■In the case where the DAPS switching method is applied in the above description, when the UE must send UL data via the first bearer for the source BS because the first condition proposed in the present disclosure has not been met, the UE may select the MAC layer for the first bearer as the target of the LCP process only for the bearer or logical channel identifier indicating the DAPS switching method (or the switching method that can continue to send data to the source BS even after receiving the switching command message), and may perform the LCP process. This is because when the UE receives a switching command message for a bearer or logical channel identifier to which the DAPS switching method is not applied, the UE cannot send UL data to the source BS, and the UE should not select the bearer or logical channel identifier as the target of the LCP process.

[0418] ■When a second bucketSizeDuration is newly configured for a logical channel in the MAC layer configuration information configured in the handover command message, the UE may perform the DAPS handover method proposed in the present disclosure. In this regard, the UE may apply a second PDCP layer architecture, and maintain the existing configuration information for the MAC layer of the first bearer of the source BS corresponding to the bearer identifier indicated above, and may configure a new logical channel identifier for the MAC layer for the second bearer corresponding to the target BS, the new logical channel identifier being indicated in the configuration information, and may configure a newly configured second bucketSizeDuration corresponding to the new logical channel identifier indicated in the configuration information. As another method, after the first condition proposed in the present disclosure is met, the UE may start applying the second bucketSizeDuration to the new logical channel identifier in the MAC layer of the second bearer corresponding to the target BS (by doing so, UL transmission resources may be fairly distributed when different handover methods are indicated for the corresponding bearers). In the above description, the bucket size indicates the maximum value that the value of the prioritisedBitRate may have when the prioritisedBitRate is accumulated.

[0419] ■When the second available SCell information, available subcarrier gap information, and maximum PUSCH duration logical channel group configuration information are configured in the MAC layer configuration information configured in the switching command message, the UE can execute the DAPS switching method proposed in the present disclosure, and can apply the second PDCP layer architecture, and maintain the existing configuration information for the MAC layer of the first bearer of the source BS corresponding to the bearer identifier indicated above, and can configure the second available SCell information, available subcarrier gap information, maximum PUSCH duration or logical channel group configuration information for the MAC layer of the second bearer corresponding to the target BS.

[0420] Figure 1Kis a diagram illustrating a method of applying configuration information to each bearer when performing a DAPS switching method according to an embodiment of the present disclosure.

[0421] refer to Figure 1K In the case where the UE receives a handover command message in operation 1k-01 as proposed in the present disclosure, when the reconfigWithSync information indicates a second handover method (e.g., implementation 2 or the DAPS handover method of the present disclosure), when a DAPS handover method for each bearer identifier or each logical channel identifier is indicated, when a DAPS handover method is configured for at least one bearer, or when a DAPS handover method is configured for a certain bearer, the UE may generate or establish a MAC layer for the target BS (or target cell) at the time point when the UE receives the handover command message. After the UE receives the handover command message and then until the first condition proposed in the present disclosure is met, the UE may continue to send data to or receive data from the source BS only for the bearer (AM bearer or UM bearer) for which the DAPS handover method is indicated via the MAC layer for the source BS (or source cell). When the first condition is met, the UE may handover UL data to the target BS, and may receive DL data from the source BS until the link to the source BS is released. However, for the bearer that does not indicate the DAPS switching method, after the UE receives the switching command message and then until the first condition proposed in the present disclosure is met, the UE cannot perform data transmission to the source BS or data reception from the source BS in a continuous manner. Therefore, in order to allow the UE to perform the operation proposed in the present disclosure, one or more methods to be described below may be applied, and reference may be made to Figure 1K -21 or Figure 1K -22 to model. When the second condition proposed in the present disclosure is met and the source BS is released, one or more methods may refer to Figure 1K -31 or Figure 1K -32 for modeling.

[0422] -Method 1: As described in the present disclosure, in the case where the UE receives a handover command message, when the ReconfigWithSync information indicates a second handover method (e.g., embodiment 2 or the DAPS handover method of the present disclosure), indicates a DAPS handover method for each bearer identifier or each logical channel identifier, indicates a DAPS handover method for at least one bearer, or indicates a DAPS handover method for a certain bearer, the UE may suspend configuring the SRB for the MAC layer. For example, when the MAC layer for the source BS performs an LCP procedure to send data when receiving a handover command message from the UE, the MAC layer for the source BS may select only the logical channel identifier corresponding to the bearer indicating the DAPS handover method as a candidate group, and may perform the LCP procedure. In addition, the MAC layer of the UE for the source BS may maintain only the logical channel identifier indicating the DAPS handover method or the prioritizedBitRate or the storage block size duration corresponding to such a logical channel identifier, and may release, may not use, or may not apply the logical channel identifier corresponding to the bearer not indicating the DAPS handover method or the prioritizedBitRate or the storage block size duration corresponding to such a logical channel identifier. In addition, the UE may perform a PDCP re-establishment procedure or an RLC re-establishment procedure for a bearer for which the DAPS switching method is not indicated, may suspend a bearer to which the PDCP configuration information or the RLC configuration information indicated in the switching message is applied, may suspend a bearer from the MAC layer for the source BS, or may configure a bearer for the MAC layer of the target BS (when the first condition is met, the bearer for the MAC layer of the target BS may be configured), may apply the bearer configuration information configured for the target BS (such as a logical channel identifier, a prioritisedBitRate, or a storage block size duration) to the MAC layer of the target BS for the bearer for which the DAPS switching method is not indicated in the switching message, and a link to the PDCP layer or the RLC layer corresponding to the bearer for which the DAPS switching method is not indicated may be switched from the MAC layer for the source BS to the MAC layer for the target BS. For example, the UE may release the configuration information of the PDCP layer, the RLC layer, or the MAC layer for the bearer for which the DAPS switching method is not indicated from the MAC layer for the source BS, and may perform a link to the MAC layer for the target BS applied to or connected to according to the bearer configuration for the target BS.In addition, the UE may perform data transmission to or reception from the source BS until the first condition proposed by the present disclosure is satisfied; the prioritisedBitRate may be reset for the logical channel identifier corresponding to the bearer not indicating the DAPS switching method in the MAC layer for the source BS; the bearer may be released or suspended without applying the prioritisedBitRate accumulation calculation process; and for the logical channel identifier corresponding to the bearer indicating the DAPS switching method, the prioritisedBitRate may be continuously maintained in the MAC layer for the source BS, and the accumulation calculation process may be performed. - When the first condition is satisfied, the UE may perform switching of data transmission to the target BS, and the prioritisedBitRate may be reset for the newly configured logical channel identifier in the MAC layer for the target BS or the accumulation calculation may be started (as another method, when the UE receives a switching command message for the MAC layer for the target BS, the UE may reset the prioritisedBitRate and may start the accumulation calculation). In addition, when a bearer that does not indicate a DAPS switching method is configured or suspended, the UE may resume the bearer, may start sending data to or receiving data from the target BS, and may reset the prioritisedBitRate or start cumulative calculation. When the first condition is met, the UE may reset the prioritisedBitRate for the logical channel identifier configured in the MAC layer for the source BS, and may stop cumulative calculation. In addition, the UE may perform data reception from the source BS or the target BS until the second condition proposed in the present disclosure is met. When the second condition is met in operation 1k-03, the UE may reset the MAC layer for the source BS, and may release the RLC layer, PDCP layer, or bearer configuration information corresponding to the bearer that is connected to the MAC layer for the source BS and does not indicate a DAPS switching method from the MAC layer for the source BS. The UE may release the RLC layer or bearer configuration information corresponding to the bearer that indicates the DAPS switching method from the second PDCP layer architecture or the MAC layer for the source BS in operation 1k-31 or 1k-32. As will be proposed below in the present disclosure, when the UE handover process fails and the link to the source BS is in an active state, the UE may perform a fallback process on the source BS in operation 1k-02, may restore the SRB configured for the MAC layer of the source BS and may report the handover failure, may reapply the previous bearer configuration information of the source BS before receiving the handover command message, may apply the original configuration information of the MAC layer, and may restore data transmission to the source BS or data reception from the source BS for each bearer in operation 1k-10. As another method, in the aforementioned situation, the upper layer (e.g., RRC layer) of the UE may indicate an RLC re-establishment process for a bearer configured with a DAPS handover method or a bearer not configured with a DAPS handover method.

[0423] -Method 2: As described in the present disclosure, in the case where the UE receives a handover command message, when the ReconfigWithSync information indicates the second handover method (e.g., embodiment 2 or the DAPS handover method of the present disclosure), indicates the DAPS handover method for each bearer identifier or each logical channel identifier, indicates the DAPS handover method for at least one bearer, or indicates the DAPS handover method for a certain bearer, the UE may suspend configuration of the SRB for the MAC layer, and the upper layer (e.g., RRC layer) of the UE may instruct the MAC layer for the source BS to perform MAC reconfiguration by using configuration information of the current MAC layer, which excludes configuration information related to the bearer for which the DAPS handover method is not indicated. As another method, the upper layer (e.g., RRC layer) of the UE may instruct the MAC layer for the source BS to perform MAC reconfiguration by using configuration information of the current MAC layer, which includes only configuration information related to the bearer for which the DAPS handover method is indicated. When the UE reconfigures the MAC layer for the source BS, the MAC layer of the UE for the source BS may maintain only the logical channel identifier indicating the DAPS switching method or the prioritisedBitRate or the storage block size duration corresponding to such a logical channel identifier, and may release, may not use, or may not apply the logical channel identifier corresponding to the bearer for which the DAPS switching method is not indicated or the prioritisedBitRate or the storage block size duration corresponding to such a logical channel identifier. In addition, the upper layer (e.g., the RRC layer) of the UE may perform a PDCP reestablishment procedure or an RLC reestablishment procedure for the bearer for which the DAPS switching method is not indicated, and may suspend the bearer to which the PDCP configuration information or the RLC configuration information indicated in the switching message is applied. Alternatively, the upper layer of the UE may suspend the bearer from the MAC layer for the source BS, or may configure the bearer for the MAC layer for the target BS (when the first condition is met, the bearer for the MAC layer of the target BS may be configured), and may instruct the MAC layer for the target BS to configure or apply the bearer configuration information (such as a logical channel identifier, a prioritizedBitRate, or a storage block size duration) for the MAC layer for the target BS for the bearer for which the DAPS switching method is not indicated in the switching message. Alternatively, the upper layer of the UE may switch the link to the PDCP layer or the RLC layer corresponding to the bearer for which the DAPS switching method is not indicated from the MAC layer for the source BS to the MAC layer for the target BS. In this case, when the MAC layer for the source BS performs the LCP process to start sending data when receiving the switching command message from the UE, the MAC layer for the source BS may select only the logical channel identifier corresponding to the bearer for which the DAPS switching method is indicated as a candidate group, and may perform the LCP process.In the aforementioned situation, the process of reconfiguring the MAC layer for the source BS (the process is performed by the upper layer (e.g., the RRC layer)) may include a process in which the MAC layer for the source BS is partially MAC reset to perform the same process. For example, the configuration information of the MAC layer for the bearer that does not indicate the DAPS switching method may be reset, suspended, or not applied. In addition, data transmission to the source BS or data reception from the source BS may be performed until the first condition proposed in the present disclosure is met. The UE may reset the prioritisedBitRate for the logical channel identifier corresponding to the bearer that does not indicate the DAPS switching method in the MAC layer for the source BS, and may release or suspend the bearer without applying the prioritisedBitRate accumulation calculation process. In addition, the UE may continue to maintain the prioritisedBitRate in the MAC layer for the source BS for the logical channel identifier corresponding to the bearer that indicates the DAPS switching method, and may perform the accumulation calculation process. When the first condition is met, the UE may reset the prioritisedBitRate for the newly configured logical channel identifier in the MAC layer for the target BS (the logical channel identifier corresponds to a bearer configured with the DAPS switching mode or a bearer not configured with the DAPS switching mode), or may start cumulative calculation (as another method, when the UE receives a switching command message for the MAC layer for the target BS, the UE may initialize the prioritisedBitRate and may start cumulative calculation). In addition, when a bearer that does not indicate the DAPS switching method is configured or suspended, the UE may configure or resume the bearer, may start sending data to or receiving data from the target BS, and may reset the prioritisedBitRate or start cumulative calculation. In addition, the UE may perform data reception from the source BS or the target BS until the second condition proposed in the present disclosure is met. When the second condition is met in operation 1k-03, the UE may reset the MAC layer for the source BS, and may release the RLC layer, PDCP layer or bearer configuration information corresponding to the bearer that is connected to the MAC layer for the source BS and does not indicate the DAPS switching method from the MAC layer for the source BS, and may release the RLC layer or bearer configuration information corresponding to the bearer that indicates the DAPS switching method from the second PDCP layer architecture or MAC layer for the source BS in operation 1k-31 or 1k-32.As will be proposed below in the present disclosure, when the UE handover process fails and the link to the source BS is active, the UE may perform a fallback process on the source BS in operation 1k-02, may restore the SRB configured for the MAC layer of the source BS and may report the handover failure, may reapply the previous bearer configuration information of the source BS before receiving the handover command message, may apply the original configuration information of the MAC layer (for example, the RRC layer may reconfigure the configuration of the MAC layer to the MAC layer configuration information used before receiving the handover command message), and may resume data transmission to the source BS or data reception from the source BS for each bearer in operation 1k-10. As another method, in the aforementioned situation, the upper layer of the UE (for example, the RRC layer) may indicate the RLC reestablishment process for a bearer configured with the DAPS handover method or a bearer not configured with the DAPS handover method. As another method, the configuration information of the MAC layer for the source BS to be applied when the source BS performs the DAPS handover method may be configured through an RRC message.

[0424] -Method 3: As described in the present disclosure, in the case where the UE receives a handover command message, when the ReconfigWithSync information indicates a second handover method (e.g., implementation 2 or the DAPS handover method of the present disclosure), indicates a DAPS handover method for each bearer identifier or each logical channel identifier, indicates a DAPS handover method for at least one bearer, or indicates a DAPS handover method for a certain bearer, the UE may suspend configuring the SRB for the MAC layer. For example, when the MAC layer of the UE for the source BS performs an LCP process to send data when the UE receives a handover command message, the UE may indicate to the MAC layer of the source BS that the PDCP layer corresponding to the bearer for which the DAPS handover method is not indicated has no data to be sent in the buffer or the PDCP data amount is 0, so that the LCP process may be performed only for the logical channel identifier corresponding to the bearer for which the DAPS handover method is indicated. Therefore, the MAC layer for the source BS may determine that there is no data to be sent for the bearer for which the DAPS handover method is not indicated, and may not perform the LCP process for the logical channel identifier corresponding to the bearer for which the DAPS handover method is not indicated. In addition, the UE may perform a PDCP re-establishment procedure or an RLC re-establishment procedure for a bearer for which the DAPS switching method is not indicated, may suspend a bearer to which the PDCP configuration information or the RLC configuration information indicated in the switching message is applied, may suspend a bearer from the MAC layer for the source BS, or may configure a bearer for the MAC layer of the target BS (when the first condition is met, the bearer for the MAC layer of the target BS may be configured), may apply the bearer configuration information configured for the target BS (such as a logical channel identifier, a prioritisedBitRate, or a storage block size duration) to the MAC layer of the target BS for the bearer for which the DAPS switching method is not indicated in the switching message, and a link to the PDCP layer or the RLC layer corresponding to the bearer for which the DAPS switching method is not indicated may be switched from the MAC layer for the source BS to the MAC layer for the target BS. For example, the UE may release the configuration information of the PDCP layer, the RLC layer, or the MAC layer for the bearer for which the DAPS switching method is not indicated from the MAC layer for the source BS, and may perform a link to the MAC layer for the target BS applied to or connected to according to the bearer configuration for the target BS.In addition, the UE may perform data transmission to or reception from the source BS until the first condition proposed in the present disclosure is satisfied; the prioritisedBitRate may be reset for the logical channel identifier corresponding to the bearer for which the DAPS switching method is not indicated in the MAC layer for the source BS; the bearer may be released or suspended without applying the prioritisedBitRate accumulation calculation process; and for the logical channel identifier corresponding to the bearer for which the DAPS switching method is indicated, the prioritisedBitRate may be continuously maintained in the MAC layer for the source BS, and the accumulation calculation process may be performed. When the first condition is satisfied, the UE may perform switching of data transmission to the target BS, and the prioritisedBitRate may be reset for the newly configured logical channel identifier in the MAC layer for the target BS or the accumulation calculation may be started (as another method, when the UE receives a switching command message for the MAC layer for the target BS, the UE may reset the prioritisedBitRate and may start the accumulation calculation). In addition, when the bearer for which the DAPS switching method is not indicated is suspended, the UE may resume the bearer, may start sending data to the target BS or receiving data from the target BS, and may reset the prioritisedBitRate or start cumulative calculation. When the first condition is met, the UE may reset the prioritisedBitRate for the logical channel identifier configured in the MAC layer for the source BS, and may stop cumulative calculation. In addition, the UE may perform data reception from the source BS or the target BS until the second condition proposed in the present disclosure is met, may reset the MAC layer for the source BS, and may release the RLC layer, PDCP layer or bearer configuration information connected to the MAC layer for the source BS and corresponding to the bearer for which the DAPS switching method is not indicated from the MAC layer for the source BS, and may release the RLC layer or bearer configuration information corresponding to the bearer for which the DAPS switching method is indicated from the second PDCP layer architecture or the MAC layer for the source BS in operation 1k-31 or 1k-32. As will be proposed below in the present disclosure, when the UE handover process fails and the link to the source BS is in an active state, the UE may perform a fallback process on the source BS in operation 1k-02, may restore the SRB configured for the MAC layer of the source BS and may report the handover failure, may reapply the previous bearer configuration information of the source BS before receiving the handover command message, may apply the original configuration information of the MAC layer, and may restore data transmission to the source BS or data reception from the source BS for each bearer in operation 1k-10. As another method, in the aforementioned situation, the upper layer (e.g., RRC layer) of the UE may indicate an RLC re-establishment process for a bearer configured with a DAPS handover method or a bearer not configured with a DAPS handover method.

[0425] In the method proposed in the present disclosure, when the UE receives a switching command message, when the reconfigWithSync information indicates the second switching method (implementation method 2 or the DAPS switching method of the present disclosure), when the DAPS switching method is indicated for each bearer identifier or each 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 certain bearer, the SRB configured for the MAC layer of the source BS can be applied based on various applications of one or more of the following methods.

[0426] - In the case where the UE receives the handover command message, when the reconfigWithSync information indicates the second handover method (for example, implementation mode 2 or the DAPS handover method of the present disclosure), when the DAPS handover method is indicated for each bearer identifier or each 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 certain bearer,

[0427] ■Method 1: The SRB may be suspended from the MAC layer for the source BS. Alternatively, the window state variable may be reset by performing an RLC layer reestablishment procedure or a PDCP layer reestablishment procedure for the SRB, and the stored multiple data items (PDCP SDU, PDCP PDU, RLC SDU, or RLC PDU) may be discarded. Alternatively, the SRB may be configured for the MAC layer of the target BS according to the configuration in the received handover command message. As another method, the SRB may be configured for the MAC layer of the source BS according to the configuration in the received handover command message, and may be switched to be connected to the MAC layer for the target BS. When the UE cannot perform the handover procedure and thus performs the fallback procedure, the UE may resume the SRB suspended from the MAC layer for the source BS, or the SRB configured for the target BS may be reconfigured to the previous configuration for the source BS, and the SRB may be switched and connected to the MAC layer for the source BS, thereby resuming the SRB.

[0428] ■Method 2: The SRB may be suspended from the MAC layer for the source BS. Alternatively, the RLC layer re-establishment process or the PDCP layer re-establishment process for the SRB may not be performed and may be stopped. Alternatively, the SRB may be configured for the MAC layer of the target BS according to the configuration in the received handover command message. As another method, the SRB may be configured for the MAC layer of the source BS according to the configuration in the received handover command message, and may be switched to be connected to the MAC layer for the target BS. When the UE cannot perform the handover process and thus performs the fallback process, the UE may resume the SRB suspended from the MAC layer for the source BS, or the SRB configured for the target BS may be reconfigured to the previous configuration for the source BS, and the SRB may be switched and connected to the MAC layer for the source BS, thereby resuming the SRB.

[0429] ■Method 3: The SRB may be suspended from the MAC layer for the source BS. Alternatively, the RLC layer reestablishment process or the PDCP layer reestablishment process for the SRB may not be performed; and the window state variable may not be reset, but the stored plurality of data items (PDCPSDU, PDCP PDU, RLC SDU, or RLC PDU) may be discarded (this is to prevent an unsent RRC message from being unnecessarily sent later). Alternatively, the SRB may be configured for the MAC layer of the target BS according to the configuration in the received handover command message. As another method, the UE may configure the SRB for the MAC layer of the source BS according to the configuration in the received handover command message, and may switch the SRB to connect the SRB with the MAC layer for the target BS. When the UE cannot perform the handover process and thus performs the fallback process, the UE may resume the SRB suspended from the MAC layer for the source BS, or the SRB configured for the target BS may be reconfigured to the previous configuration for the source BS, and the SRB may be switched and connected to the MAC layer for the source BS, thereby resuming the SRB.

[0430] According to the present disclosure, a method is proposed below, when the UE performs implementation mode 2 (DAPS handover method) of the efficient handover method proposed in the present disclosure and cannot perform handover, the UE quickly falls back to the source BS to reconfigure the link by using the features of the DAPS handover method proposed above. The features of the DAPS handover method proposed in the present disclosure can particularly represent that even when the UE performs the handover process, the UE maintains the link to the source BS to perform data transmission or reception. It is proposed below in the present disclosure that when the UE cannot perform handover, the UE falls back to the source BS by using the radio link established with the source BS.

[0431] See the disclosure of Figure 1HAccording to implementation 2 (DAPS handover method) of the efficient handover method proposed in the present disclosure, as described in 1h-02, even when the UE receives a handover command message from the source BS, the UE can perform a handover procedure on the target BS while the UE maintains data transmission to the source BS or data reception from the source BS. In addition, the present disclosure proposes a process in which the UE falls back to the source BS when the UE cannot perform a handover procedure on the target BS.

[0432] As mentioned above, when the UE cannot perform a handover procedure on the target BS and thus attempts to fall back to the source BS, a method is required in which the UE can identify whether the radio link to the source BS is in an active state. When the UE cannot perform a handover on the source BS and performs a fallback procedure, even when the radio link to the source BS is not in an active state, the UE cannot perform the fallback procedure on the source BS, which makes the data interruption time too long, and thus serious data interruption occurs. In addition, when the radio link to the source BS is in an active state, the SRB configured between the UE and the source BS must be maintained.

[0433] First, the present disclosure proposes a new timer applicable to a handover method, and proposes a detailed operation of each of the timers. In addition, according to the present disclosure, the detailed operation of each timer may include different operations according to the type of handover method indicated in a handover command message from a BS. In addition, a method for releasing or maintaining a link or SRB configuration to a source BS according to a handover method is provided.

[0434] In order to efficiently perform the switching process, the present disclosure may introduce 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), and these timers may be run and applied to the switching process. 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 may perform the following different operations according to the type of the switching method. For example, the first timer (e.g., T304) is a timer configured to determine whether the switching has been successfully performed. In addition, the second timer (e.g., T310) is a timer configured to determine whether the radio link is in an active state. In addition, the third timer (e.g., T312) is an auxiliary timer configured to determine whether the radio link is in an active state, trigger a frequency measurement process, and report a frequency measurement report. When the UE performs implementation 2 (DAPS handover method) of the efficient handover method proposed in the present disclosure and then fails to perform handover, the UE performs a fallback procedure on the source BS, thereby sending a message indicating handover failure to the source BS. In this regard, the fourth timer (e.g., a timer for fallback) is a timer configured to determine whether the fallback procedure has been successfully performed or has failed.

[0435] Depending on the type of switching method indicated, the detailed 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 efficient switching method is presented below.

[0436] -1> When the UE receives an indicator (asynchronous indication) indicating that the radio link signal is out of synchronization from the lower layer (e.g., the MAC layer or the PHY layer) for a preset number of times (e.g., the preset number of times can be set by the BS), thereby detecting a problem with the PHY layer, the UE can start a second timer (e.g., T310) when the first timer (e.g., T304) is not running. Afterwards, the UE receives an indicator (synchronous indication) indicating that the radio link signal is synchronized from the lower layer for a preset number of times (e.g., the preset number of times can be set by the BS), triggering (starting) a handover process or starting an RRC connection reestablishment process, and the UE stops the second timer. When the second timer expires, the UE triggers or starts the RRC connection reestablishment process. Alternatively, the UE switches to the RRC inactive mode and triggers or starts the RRC connection reestablishment process.

[0437] -1> When the frequency measurement process is triggered for the frequency measurement identifier configured for the third timer while the second timer is running, the UE starts the third timer. Afterwards, when the UE receives an indicator (synchronization indication) indicating radio link signal synchronization from the lower layer for a preset number of times (for example, the preset number of times can be set by the BS), a handover process is triggered (started) or an RRC connection reestablishment process is started, and the UE stops the third timer. When the third timer expires, the UE triggers or starts the RRC connection reestablishment process. Alternatively, the UE switches to the RRC inactive mode and triggers or starts the RRC connection reestablishment process.

[0438] -1> When the UE receives a handover command message (an RRC Reconfiguration message or a handover indication including a mobility indication (MobilityControl information or Reconfiguration With Sync)) from the BS and the handover command message indicates a first handover method (e.g., implementation mode 1 or a conventional handover method), when implementation mode 2 (DAPS handover method) proposed in the present disclosure is not configured, or when implementation mode 2 (DAPS handover method) proposed in the present disclosure is not configured for any bearer in the bearer information,

[0439] ■2> According to the present disclosure, when the UE receives a handover command message (including a RRC Reconfiguration message or a handover indication including a mobility indication (MobilityControl information or Reconfiguration With Sync)), the UE may trigger the handover process and may start a first timer.

[0440] ■2> When the UE triggers the handover process, the UE releases the SRB configured for the source BS (e.g., SRB1) and configures the SRB for the target BS (e.g., SRB1) based on the configuration information configured in the handover command message.

[0441] ■2> When the UE triggers the handover process, if the second timer is running, the UE may stop the second timer. When the first timer is running, even if the condition for starting the second timer is met (the indicator indicating that the radio link signal is out of synchronization is received from the lower layer for a preset number of times), the second timer may not be started. For example, when the first timer is running, the second timer may not be used.

[0442] ■2> When the UE triggers the handover process, if the third timer is running, the UE may stop the third timer. Thereafter, only when the second timer is running, when the condition for starting the third timer is met (when the frequency measurement process is triggered for the frequency measurement identifier configured for the third timer), the UE may start the third timer. For example, since the second timer is not used when the first timer is running, the third timer may not be used.

[0443] ■2> When the UE successfully performs a handover procedure on the target BS or successfully completes a random access procedure for the target BS, the UE stops the first timer.

[0444] ■2> When the first timer expires (for example, the handover process to the target BS fails), the UE performs the RRC connection reestablishment process (the UE may release the link to the BS and may perform the RRC connection process from the beginning, that is, may perform a cell selection or reselection process, perform a random access process and send an RRC connection reestablishment request message).

[0445] -1> When the UE receives a handover command message (a RRC Reconfiguration message or a handover indication including a mobility indication (Mobility Control information or Reconfiguration With Sync)) from the BS and the handover command message indicates a second handover method (e.g., implementation mode 2 or a DAPS handover method) (or can be widely applied to a case where a conditional handover method is also indicated), when the UE receives a handover command message and the handover command message or the ReconfigWithSync information or the Mobility Control Info indicates implementation mode 2 (DAPS handover method) proposed in the present disclosure, when a certain bearer in the bearer information is configured with implementation mode 2 (DAPS handover method) proposed in the present disclosure, or when at least one bearer in the bearer information is configured with implementation mode 2 (DAPS handover method) proposed in the present disclosure,

[0446] ■2> According to the present disclosure, when the UE receives a handover command message (an RRC Reconfiguration message or a handover indication including a mobility indication (MobilityControl information or Reconfiguration With Sync)), the UE may trigger a handover process and may start a first timer. When a conditional handover method is also indicated, when the UE selects a cell from a plurality of target cells and starts a handover process or performs a random access process, the UE may start a first timer.

[0447] ■2> In the case where the UE triggers the handover process, when the UE starts the DAPS handover method, based on the configuration information configured in the handover command message, the UE maintains or suspends the SRB (e.g., SRB1) configured for the source BS, and configures the SRB (e.g., SRB1) for the target BS. As another method, in the case where the UE triggers the handover process, when the UE starts the DAPS handover method, the UE may maintain or suspend the SRB (e.g., SRB1) configured for the source BS, may reset the window state variable by reestablishing the PDCP layer or the RLC layer for the SRB corresponding to the source BS, may stop the timer, may indicate a plurality of stored data items (PDCPSDU or PDCP PDU) to be discarded (this may be performed when the fallback process proposed in the present disclosure is triggered), and may configure the SRB (e.g., SRB1) for the target BS based on the configuration information configured in the handover command message. As another method, the UE may apply the second PDCP layer architecture proposed in the present disclosure to the SRB, thereby configuring the first bearer for the source BS and configuring the second bearer for the target BS. As another method, when the UE applies the second PDCP layer architecture to the SRB, the UE may reset the window state variable by reestablishing the PDCP layer or RLC layer for the first bearer, may stop the timer, and may indicate a plurality of stored data items (PDCP SDU or PDCP PDU) to be discarded (this may be performed when the fallback process proposed in the present disclosure is triggered).

[0448] ■2> In the case where the UE triggers the handover process, when the UE starts the DAPS handover method, the UE may not stop the second timer for the source BS even when the second timer is running. When the first timer is running (or even when the first timer is not running), the second timer may be started when the condition for starting the second timer is met (an indicator indicating that the radio link signal is out of synchronization is received from the lower layer for a preset number of times). The second timer may be operated for the radio link between the UE and the source BS. As another method, two second timers may be operated so that one second timer may be operated for the radio link between the UE and the source BS, and another second timer may be operated for the radio link between the UE and the target BS. For example, even when the first timer is running, the second timer may be used for the radio link to the source BS or the target BS. However, even when the second timer expires, if the first timer has not expired but is running, the UE may not trigger the RRC connection reestablishment process. For example, even when the second timer for the source BS expires or RLF occurs, if the first timer has not expired but is running, a random access procedure is being performed on the target BS, or a handover procedure is being performed on the target BS, the UE may not trigger the RRC connection reestablishment procedure and may release the radio link to the source BS.

[0449] In addition, the UE may not release the RRC configuration information (e.g., bearer configuration information, etc.) configured by the source BS, and may reuse the configuration information when the RRC connection reestablishment process is triggered later. In addition, when the first timer has not expired but is running, the UE may not trigger the RRC connection reestablishment process even when the second timer expires, and the source BS may report the source link failure to the target BS, or the UE may release the link to the source BS (e.g., the UE may release the first bearer for the source BS) or may suspend the first bearer for the source BS. However, when the second timer expires, if the first timer expires, stops, or is not running because the first timer is not started, the UE may trigger the RRC connection reestablishment process. The reason for operating the second timer even when performing the handover process is that when a handover failure occurs while the UE monitors the radio link to the source BS or the target BS, the UE is allowed to perform a fallback process when the radio link to the source BS or the target BS is active. When the second timer for the target BS expires or the radio link to the target BS fails, the RRC connection reestablishment process may be triggered if the first timer expires, stops, or is not running because the first timer is not started, or the random access process to the target BS has been successfully performed.

[0450] ■2> In the case where the UE triggers the handover process, when the UE triggers the DAPS handover method, the UE may not stop the third timer for the source BS even if the third timer is running. Thereafter, only when the second timer is running, when the condition for starting the third timer is met (when the frequency measurement process is triggered for the frequency measurement identifier configured for the third timer), the UE may start the third timer. For example, since the UE uses the second timer even when the first timer is running, the UE may also use the third timer. The third timer may be operated for the radio link between the UE and the source BS. As another method, two third timers may be operated so that one third timer may be operated for the radio link between the UE and the source BS, and another third timer may be operated for the radio link between the UE and the target BS. For example, even when the first timer is running, the third timer may be used for the radio link to the source BS or the target BS. However, even when the third timer expires, if the first timer has not expired but is running, the UE may not trigger the RRC connection reestablishment process. In addition, when the first timer has not expired but is running, even when the third timer expires, the UE may not trigger the RRC connection reestablishment process and the source BS may report the source link failure to the target BS, or the UE may release the link to the source BS (for example, the UE may release the first bearer for the source BS) or may suspend the first bearer for the source BS. However, when the third timer expires, if the first timer expires, stops, or is not running because the first timer is not started, the UE may trigger the RRC connection reestablishment process. The reason for operating the third timer even when performing the handover process is that when a handover failure occurs while the UE monitors the radio link to the source BS, the UE is allowed to perform a fallback process while the radio link to the source BS is active and report the frequency measurement results obtained in the fallback process.

[0451] ■2> When the UE successfully performs the handover procedure to the target BS, the UE stops the first timer.

[0452] ■2> When the first timer expires (for example, when the handover procedure to the target BS fails); when the maximum number of retransmissions of the RLC layer for the target BS is exceeded; when the UE receives a handover command message but the configuration information of the handover command message exceeds the capability of the UE; when an error occurs in the application of the configuration information resulting in a handover failure; when a problem occurs in random access to the target BS and the UE keeps attempting a random access procedure but the first timer expires so that the UE cannot perform the handover procedure; when the UE runs a second timer or a third timer for the target BS but the second timer or the third timer expires before the handover procedure is completed; or when the T304 timer stops or expires and the UE determines that the handover procedure has failed,

[0453] ■3> When the second timer or the third timer for the radio link between the UE and the source BS has not expired (or when the second timer or the third timer for the radio link between the UE and the source BS is not started or is running), or when the radio link between the UE and the source BS is active,

[0454] ●4> The UE may determine that the radio link between the UE and the source BS is in an active state, and may perform the backoff process proposed in the present disclosure.

[0455] ●4> When the UE starts the fallback process, if the SRB configured for the source BS (e.g., SRB1 or the MAC layer, RLC layer, or PDCP layer for SRB1) has been released, the UE may reconfigure or newly configure the SRB, and may perform the fallback process on the SRB (e.g., SRB1). As another method, when the second PDCP layer architecture proposed in the present disclosure is applied to the SRB, the UE may perform the fallback process through the first bearer for the source BS, and may release the second bearer for the target BS. For example, the UE may switch UL data transmission to the first bearer for the source BS, may indicate to the RLC layer or MAC layer for the first bearer that there is data to be sent, and may send a switching failure report message for the fallback process via the first bearer.

[0456] ●4> In the above scenario, the fallback process refers to a process in which the UE configures a message reporting a handover failure and reports the handover failure to the source BS via an SRB (e.g., SRB1) configured for the source BS. When the UE sends a message reporting a handover failure to the source BS, the UE may also report the result of the frequency measured by the UE, thereby supporting a quick recovery of the link to the source BS. As another method, the UE may define and send MAC control information (e.g., the UE may indicate that there is data to be sent, or may define and indicate new MAC control information or a specific value in a buffer status report, thereby indicating a handover failure), RLC control information, or PDCP control information, thereby indicating a handover failure to the source BS. As another method, the UE may send an RRC connection reestablishment request message to an SRB (e.g., SRB0 or ​​SRB1) for the source BS. As another method, in the above scenario, the fallback process may refer to that when the handover fails, the UE releases the second bearer for the target BS in the second PDCP layer architecture of each bearer or the bearer configured with the DAPS handover method, or switches to the first PDCP layer architecture, and then resumes sending or receiving data via the first bearer for the source BS, and the UE may indicate to the MAC layer for the first bearer that there is data to be sent, may request scheduling or report data to be sent (e.g., buffer status report) from the source BS, or may send a new MAC CE, RLC control data, or PDCP control data to the source BS, thereby indicating to the source BS that the UE is to fall back to the source BS and resume data transmission. Afterwards, the UE may newly configure or resume the SRB for the source BS. In the fallback process, since each bearer or a bearer not configured with the DAPS switching method does not have a second PDCP layer architecture, when the switching fails, the UE may release the previously configured bearer configuration information or logical channel identifier information from the MAC layer, PDCP layer, and RLC layer for the target BS, and then reconfigure in the configuration information of the switching command message, or may switch to and configure the MAC layer for the source BS, and may resume sending data to the source BS or receiving data from the source BS via each bearer. When the UE receives the switching command message, the UE may apply the bearer configuration information configured in the switching command message to the MAC layer of the bearer corresponding to the target BS, which bearer is not configured with the DAPS switching method, and may switch the link of the PDCP layer or RLC layer for the bearer not configured with the DAPS switching method from the MAC layer for the source BS to the MAC layer for the target BS.For example, when the UE receives the handover command message, the upper layer (e.g., RRC layer) of the UE may instruct the MAC layer for the source BS to perform MAC reconfiguration by using the configuration information of the current MAC layer, the configuration information excluding the configuration information related to the bearer for which the DAPS handover method is not indicated, or the upper layer (e.g., RRC layer) of the UE may instruct the MAC layer for the source BS to perform MAC reconfiguration by using the configuration information of the current MAC layer, the configuration information including only the configuration information related to the bearer for which the DAPS handover method is indicated. For example, since when the UE receives the handover command message, the UE may release the configuration information of the PDCP layer, the RLC layer, or the MAC layer for the bearer for which the DAPS handover method is not configured from the MAC layer for the source BS, and may apply the configuration information to the MAC layer for the target BS or perform connection according to the bearer configuration of the target BS, if the UE performs the fallback procedure, the UE must reconfigure the bearer for which the DAPS handover method is not configured to the MAC layer for the source BS. For example, when the UE performs a fallback procedure, the upper layer of the UE (e.g., the RRC layer) may instruct the MAC layer for the source BS to perform MAC reconfiguration by using the configuration information of the current MAC layer, wherein the configuration information includes configuration information related to the bearer for which the DAPS switching method is not indicated, and configuration information related to the bearer for which the DAPS switching method is indicated; or 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 switching command message, and may apply it to the bearer of the source BS (PDCP layer configuration information, RLC layer configuration information, MAC layer configuration information, or PHY layer configuration information for SRB, AM DRB, or UM DRB).

[0457] ●4> During the fallback process, when the UE sends a handover failure report message (e.g., the RRC message, MAC CE, RLC control data, or PDCP control data proposed above) to the source BS, the UE may start a fourth timer. When the UE receives an indication or message from the source BS, in response to the UE sending a handover failure report message, the UE may stop the fourth timer. However, when the fourth timer expires or no response message is received until the fourth timer expires, the UE performs an RRC connection reestablishment process (the UE may release the link to the BS and may perform the RRC connection process from the beginning, i.e., perform a cell selection or reselection process, perform a random access process, and send an RRC connection reestablishment request message). When the UE triggers the RRC connection reestablishment process due to the expiration of the fourth timer, if the second timer or the third timer is running, the UE may stop the second timer or the third timer.

[0458] ◆3> When the second timer or the third timer for the radio link between the UE and the source BS or the target BS expires, or the radio link between the UE and the source BS or the target BS is not active,

[0459] ●4>UE performs the RRC connection reestablishment process (UE can release the link to the BS and can perform the RRC connection process from the beginning, that is, perform the cell selection or reselection process, perform the random access process and send an RRC connection reestablishment request message).

[0460] ■2> When the UE performs a DAPS handover procedure, if the second condition proposed in the present disclosure is met, the UE may release the link to the source BS, or may release the SRB for the source BS, and if the second timer or the third timer is running, the second timer or the third timer for the source BS may be stopped and reset. Only when the UE stops the second timer or the third timer can the UE prevent an unnecessary RRC connection reestablishment procedure due to the expiration of the second timer or the third timer. Since the satisfaction of the second condition may mean that the handover procedure is successfully performed, the expiration of the second timer or the third timer due to the stopping of the first timer may trigger an unnecessary RRC connection reestablishment procedure. As another method, when the first condition proposed in the present disclosure is met or the handover procedure is successfully performed, the UE may release the SRB for the source BS, or may stop and reset the second timer or the third timer for the source BS when the second timer or the third timer is running. Only when the UE stops the second timer or the third timer can the UE prevent an unnecessary RRC connection reestablishment procedure due to the expiration of the second timer or the third timer. Since satisfying the first condition may mean that the handover procedure is successfully performed, the expiration of the second timer or the third timer due to the stopping of the first timer may trigger an unnecessary RRC connection reestablishment procedure.

[0461] When the UE determines that a handover failure has occurred according to the method proposed in the present disclosure and performs a fallback process when the conditions proposed in the present disclosure are met, the UE adds information indicating that a handover failure has occurred to an RRC message (e.g., a ULInformationTransferMRDC message or a FailureInformation message), and sends the RRC message to SRB1 or SRB1 to which the second PDCP layer architecture is applied, thereby allowing the source BS to identify the UE handover failure. When the source BS detects that the UE fails to switch, the source BS may configure an RRC message (for example, an RRC Reconfiguration message or an RRCRelease message) in response to the switching failure and send it to the UE, and when the UE receives the RRCReconfiguration message as an RRC message in response to the switching failure report (an RRC message received via SRB1 or SRB1 to which the second PDCP layer architecture is applied), the UE may apply and complete its configuration information; and may send an RRC ReconfigurationComplete message to the source BS via SRB1 or SRB1 to which the second PDCP layer architecture is applied in response to the message from the source BS; and if the RRC Reconfiguration message indicates switching or access to another cell, the UE may complete the random access procedure for the cell and may send an RRC ReconfigurationComplete message via SRB1. However, when the UE receives an RRCRelease message as an RRC message in response to a handover failure report, the UE may switch to an RRC idle mode or may switch to an RRC inactive mode according to the configuration information indicated by the RRCRelease, and may not send an additional RRC message to the BS in response to the RRC message.

[0462] Figure 1L is a diagram illustrating applicable UE operations according to an embodiment in the present disclosure.

[0463] refer to Figure 1L, UE 1l-01 can perform sending or receiving data to or from the source BS via each bearer by using the first PDCP layer architecture. When the handover command message received by UE 1l-01 in operation 1l-05 indicates the DAPS handover method of embodiment 2 proposed in the present disclosure or indicates the DAPS handover method for each bearer, UE 1l-01 can switch to the second PDCP layer architecture for each bearer or the bearer indicating the DAPS handover method for the target BS indicated in the handover command message, and can configure and establish the protocol layer for the second bearer. When UE 1l-01 performs a random access procedure on the target BS in operations 1l-10 and 1l-15, UE 1l-01 can continue to perform sending or receiving data to or from the source BS (UL data transmission and DL data reception) by using the protocol layer for the first bearer in operation 1l-20.

[0464] When the first condition of the present disclosure is met in operation 1l-25, UE 1l-01 may suspend sending UL data to the source BS by using the protocol layer for the first bearer, and may switch UL data transmission so that UL data can be sent to the target BS by using the protocol layer for the ...

Claims

1. A method performed by a terminal in a wireless communication system, the method comprising: receiving a control message for handover from a source base station, the control message comprising information indicating that a data radio bearer (DRB) is configured for dual active protocol stack (DAPS) handover; as well as In the case where no uplink data switching is requested from an upper layer, a Packet Data Convergence Protocol (PDCP) entity of the DRB indicates a PDCP data volume to a Media Access Control (MAC) entity of the source base station, In case uplink data switching is requested from an upper layer, the PDCP entity of the DRB indicates the amount of PDCP data other than the PDCP control protocol data unit PDU associated with the source base station to the MAC entity of the target base station.

2. The method according to claim 1, wherein: PDCP duplication is not activated for the DRB.

3. The method of claim 1, further comprising: A buffer status report (BSR) is triggered by a MAC entity of the target base station based on an amount of PDCP data other than a PDCP control PDU associated with the source base station.

4. The method of claim 1, further comprising: A buffer status report BSR is triggered by a MAC entity of the source base station based on a PDCP data volume of a PDCP control PDU associated with the source base station.

5. The method according to claim 1, wherein: When a random access procedure is successfully performed on the target base station, the uplink data switching is requested from the upper layer.

6. A terminal in a wireless communication system, the terminal comprising: Transceiver; and At least one processor configured to: receiving, via the transceiver, a control message for handover from a source base station, the control message comprising information indicating that a data radio bearer (DRB) is configured for dual active protocol stack (DAPS) handover; as well as In the case where no uplink data switching is requested from an upper layer, a Packet Data Convergence Protocol (PDCP) entity of the DRB indicates a PDCP data volume to a Media Access Control (MAC) entity of the source base station, In case uplink data switching is requested from an upper layer, the PDCP entity of the DRB indicates the amount of PDCP data other than the PDCP control protocol data unit PDU associated with the source base station to the MAC entity of the target base station.

7. The terminal according to claim 6, wherein: PDCP duplication is not activated for the DRB.

8. The terminal according to claim 6, wherein: The processor is further configured to: A buffer status report (BSR) is triggered by a MAC entity of the target base station based on an amount of PDCP data other than a PDCP control PDU associated with the source base station.

9. The terminal of claim 6, wherein the processor is further configured to: A buffer status report BSR is triggered by a MAC entity of the source base station based on a PDCP data volume of a PDCP control PDU associated with the source base station.

10. The terminal according to claim 6, wherein: When a random access procedure is successfully performed on the target base station, the uplink data switching is requested from the upper layer.

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