Method and apparatus for SRB transmission using SDT

Abstract

A method and apparatus for signaling radio bearer (SRB) transmission using small data transmission (SDT) is disclosed, which includes the steps of: a base station receiving a small data packet from a UE in an RRC_INACTIVE or RRC_IDLE state, the small data packet including an SRB (signaling radio bearer), sending a RETRIEVE UE CONTEXT REQUEST to a last serving base station of the UE, and receiving from the last serving base station a UE context for anchor location or SRB data forwarding information and / or an SRB configuration for transmission of the small data packet.

Description

[Technical Field]

[0001] The subject matter disclosed herein relates generally to wireless communications, and more particularly, but not limited to, methods and apparatus for Signaling Radio Bearer (SRB) transmission using Small Data Transmission (SDT). [Background technology]

[0002] The following abbreviations and acronyms are defined herein, at least some of which may be referenced within this specification:

[0003] Third Generation Partnership Project (3GPP (registered trademark)), 5th Generation (5G), New Radio (NR), 5G Node B / generalized Node B (gNB), Long Term Evolution (LTE), LTE Advanced (LTE-A), E-UTRAN Node B / Evolved Node B (eNB), Universal Mobile Telecommunications System (UMTS), Worldwide Interoperability for Microwave Access (WiMax), Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), Wireless Local Area Networking (WLAN), Orthogonal Frequency Division Multiplexing (FDM), OFDM, Single-Carrier Frequency-Division Multiple Access (SC-FDMA), Downlink (DL), Uplink (UL), User Entity / Equipment (UE), Network Equipment (NE), Radio Access Technology (RAT), Receive or Receiver (RX), Transmit or Transmitter (TX), Acknowledgement (ACK), Random Access ChannelAccess Channel (RACH), Configured Grant (CG), Frequency Division Multiple Access (FDMA), Media Access Control (MAC), Non-Access Stratum (NAS), Packet Data Convergence Protocol (PDCP), Protocol Data Unit (PDU), Radio Access Network (RAN), Radio Link Control (RLC), Radio Network Temporary Identifier (RNTI), Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), Access and Mobility Management Function (AMF), Cell Radio Network Temporary Identifier (C-RNTI), Frequency Range 1 (FR1), Frequency Range 2 (Frequency Range 2: FR2), Internet Protocol (IP), NG Application Protocol (NGAP), 5G Core Network (5GC), Interface between gNB and 5GC (NG), Physical Cell Identity (PCI), Service Data Unit (SDU), Technical Specification (TS), User Plane Function (UPF)UPF), gNB-to-gNB interface (Xn), GPRS Tunneling Protocol User Plane (GTP-U), RAN-based Notification Area (RNA), Xn Application Protocol (XnAP), Signaling Radio Bearer (SRB), Data Radio Bearer (DRB), Small Data Transmission (SDT), Tunnel Endpoint Identifier (TEID), Inactive Radio Network Temporary Identifier (I-RNTI).

[0004] In wireless communications, such as Third Generation Partnership Project (3GPP) mobile networks, wireless mobile networks may provide seamless wireless communications services to wireless communications terminals, i.e., user equipment (UE), with mobility. A wireless mobile network may be formed of multiple base stations, and the base stations may be in wireless communication with the UE.

[0005] 5G New Radio (NR) is the latest in a series of 3GPP standards that supports significantly higher data rates with lower latency compared to its predecessor, LTE (4G) technology. Two frequency ranges (FR) are defined by 3GPP: frequencies in the sub-6 GHz range (450 to 6000 MHz) are called FR1, and frequencies in the mmWave range (24.25 GHz to 52.6 GHz) are called FR2. 5G NR supports both FR1 and FR2 frequency bands.

[0006] NR supports the RRC_INACTIVE state, in which UEs with infrequent data transmissions (periodic and / or aperiodic) are typically kept by the network. Until Release 16, the RRC_INACTIVE state does not support data transmission. Therefore, the UE must resume connection (i.e., move to RRC_CONNECTED state) for any DL and UL data. Connection setup and subsequent release to the INACTIVE state are required for each data transmission, no matter how small and infrequent the data packets. This results in unnecessary power consumption and signaling overhead. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Technical Specification TS38.300 Summary of the Invention [Problem to be solved by the invention]

[0008] A method and apparatus for SRB transmission using SDT is disclosed. [Means for solving the problem]

[0009] According to a first aspect, there is provided a method, performed by a current serving base station, comprising: receiving a small data packet from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state, the small data packet including an SRB (Signaling Radio Bearer); sending a RETRIEVE UE CONTEXT REQUEST to a last serving base station of the UE; and receiving, from the last serving base station, a UE context for anchoring or SRB data forwarding information and / or an SRB configuration for transmission of the small data packet.

[0010] According to a second aspect, there is provided a method performed by a last serving base station, the method comprising: receiving from the base station a RETRIEVE UE CONTEXT REQUEST initiated by reception of a small data packet with an SRB (Signaling Radio Bearer) from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state; transmitting the UE context to the base station in response to a determination that anchor location is required; and transmitting SRB data forwarding information and / or an SRB configuration to the base station in response to a determination that anchor location is not required.

[0011] According to a third aspect, there is provided a current serving base station including: a processor; and a transceiver coupled to the processor, wherein the processor is configured to receive a small data packet from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state, the small data packet including an SRB (Signaling Radio Bearer), send a RETRIEVE UE CONTEXT REQUEST to a last serving base station of the UE, and receive, from the last serving base station, a UE context for anchor location or SRB data forwarding information and / or an SRB configuration for transmission of the small data packet.

[0012] According to a fourth aspect, there is provided a last serving base station including: a processor; and a transceiver coupled to the processor, wherein the processor is configured to receive, from the base station, a RETRIEVE UE CONTEXT REQUEST initiated by reception of a small data packet with an SRB (Signaling Radio Bearer) from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state; in response to a determination that anchor location is required, transmit the UE context to the base station; and in response to a determination that anchor location is not required, further transmit SRB data forwarding information and / or an SRB configuration to the base station.

[0013] A more particular description of the embodiments will be given by reference to specific embodiments that are illustrated in the accompanying drawings. Given that these drawings depict only some embodiments and are therefore not to be considered limiting in scope, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating a wireless communication system according to some implementations of the present disclosure. [Figure 2] FIG. 1 is a schematic block diagram illustrating components of a user equipment (UE) according to some implementations of the present disclosure. [Figure 3] FIG. 1 is a schematic block diagram illustrating components of a network equipment (NE) according to some implementations of the present disclosure. [Figure 4A] FIG. 1 is a schematic diagram illustrating an example of a UE-triggered transition from RRC_INACTIVE to RRC_CONNECTED in accordance with some implementations of the present disclosure. [Figure 4B] FIG. 10 is a schematic diagram illustrating an example of a periodic RNA update procedure without UE context relocation according to some implementations of the present disclosure. [Figure 5A]FIG. 1 is a schematic diagram illustrating an example of a dedicated SRB data forwarding GTP-U tunnel without anchor location according to some implementations of the present disclosure. [Figure 5B] FIG. 1 is a schematic diagram illustrating an example of SRB PDCP PDU transmission over a control plane without anchor location in accordance with some implementations of the present disclosure. [Figure 5C] 1 is a schematic diagram illustrating an example of a common data forwarding GTP-U tunnel for MAC PDUs including SRBs without anchoring location according to some implementations of the present disclosure. [Figure 5D] FIG. 10 is a schematic diagram illustrating an example of a MAC PDU transmission including an SRB over a control plane without anchor location according to some implementations of the present disclosure. [Figure 5E] FIG. 10 is a schematic diagram illustrating an example of SRB transmission using SDT with anchor location according to some implementations of the present disclosure. [Figure 6] A flowchart illustrating steps for SRB transmission using SDT by a receiving gNB according to some implementation examples of the present disclosure. [Figure 7] A flowchart illustrating steps of SRB transmission using SDT by the last serving gNB according to some implementation examples of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] As will be appreciated by one skilled in the art, aspects of the embodiments may be embodied as a system, apparatus, method or program product. Accordingly, the embodiments may take the form of an all-hardware embodiment, an all-software embodiment (including firmware, resident software, microcode, etc.) or an embodiment combining software and hardware aspects.

[0016] Furthermore, one or more embodiments may take the form of a program product embodied in one or more computer-readable storage devices that store machine-readable code, computer-readable code, and / or program code, hereinafter referred to as "code." The storage devices may be tangible, non-transitory, and / or non-transmittable.

[0017] References throughout this specification to "one embodiment," "an embodiment," "one example," "some embodiments," "some examples," or similar words mean that a particular feature, structure, or characteristic being described is included in at least one embodiment or example. Thus, instances of the phrases "in one embodiment," "in one example," "in some embodiments," and similar words throughout this specification may, but do not necessarily, all refer to the same embodiment. It may or may not include all disclosed embodiments. A feature, structure, element, or characteristic described in connection with one or some embodiments is applicable to other embodiments, unless expressly stated otherwise. The terms "including," "comprising," "having," and variations thereof mean "including, but not limited to," unless expressly stated otherwise.

[0018] An enumerated list of items does not imply that any or all of the items are mutually exclusive unless expressly stated otherwise. The terms "a," "an," and "the" also refer to "one or more" unless expressly stated otherwise.

[0019] Throughout this disclosure, the terms "first," "second," "third," etc. are used solely as terminology to refer to all related devices, components, procedural steps, etc., without any spatial or chronological order implied, unless otherwise specified. For example, a "first device" and a "second device" may refer to two separately formed devices or two parts or components of the same device. In some cases, for example, a "first device" and a "second device" may be identical and arbitrarily named. Similarly, a "first step" of a method or process may be performed or occur after or simultaneously with a "second step."

[0020] As used herein, the term "and / or" should be understood to refer to and include any and all possible combinations of one or more of the associated listed items. For example, "A and / or B" may refer to any one of the following three combinations: the presence of A alone, the presence of B alone, and the coexistence of both A and B. The character " / " generally indicates an "or" relationship between the associated items. However, it may also include an "and" relationship between the associated items. For example, "A / B" means "A or B," but may also include the coexistence of both A and B unless the context indicates otherwise.

[0021] Furthermore, the described features, structures, or characteristics of the embodiments may be combined in any suitable manner. In the following description, numerous specific details are provided, such as examples of programming, software modules, user selections, network transactions, database queries, database structures, hardware modules, hardware circuits, hardware chips, etc., to provide a thorough understanding of the embodiments. Those skilled in the art will recognize, however, that the embodiments may be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the embodiments.

[0022] Aspects of various embodiments are described below with reference to schematic flowchart illustrations and / or schematic block diagrams of methods, apparatus, systems, and program products. It will be understood that each block of the schematic flowchart illustrations and / or schematic block diagrams, as well as combinations of blocks in the schematic flowchart illustrations and / or schematic block diagrams, may be implemented by code. This code may be provided to a processor of a general-purpose computer, special-purpose computer, or other programmable data processing apparatus to generate machine instructions that execute via the processor of the computer or other programmable data processing apparatus to create means for implementing the functions or acts identified in the schematic flowchart illustrations and / or schematic block diagrams.

[0023] The code may be stored in a storage device that can direct a computer, other programmable data processing apparatus, or other device to function in a particular manner, such that the instructions stored on the storage device create an article of manufacture that includes instructions that implement the functions or acts identified in the schematic flowchart diagrams and / or schematic block diagrams.

[0024] The schematic flowchart diagrams and / or schematic block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of various apparatus, systems, methods, and program products according to various embodiments. In this regard, each block in the schematic flowchart diagrams and / or schematic block diagrams may represent a module, segment, or portion of code, and contains one or more executable instructions of code for implementing the specified logical function(s). Those skilled in the art will recognize that the flowchart diagrams do not necessarily have to be performed in the order shown, and may be performed without one or more of the specified steps, or with other steps not shown.

[0025] It should also be noted that in some alternative implementations, the functions noted in the identified blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.

[0026] 1 is a schematic diagram illustrating a wireless communication system. It depicts one embodiment of the wireless communication system 100. In one embodiment, the wireless communication system 100 may include user equipment (UE) 102 and network equipment (NE) 104. Although FIG. 1 depicts a particular number of UEs 102 and NEs 104 (e.g., 104A, 104B, 104C), those skilled in the art will recognize that any number of UEs 102 and NEs 104 may be included in the wireless communication system 100.

[0027] The UE 102 may be referred to as a remote device, remote unit, subscriber unit, mobile, mobile station, user, terminal, mobile terminal, fixed terminal, subscriber station, user terminal, apparatus, device, or other terminology used in the art.

[0028] In one embodiment, the UE 102 may be an autonomous sensor device, an alarm device, an actuator device, a remote control device, etc. In some other embodiments, the UE 102 may include a computing device such as a desktop computer, a laptop computer, a personal digital assistant (PDA), a tablet computer, a smartphone, a smart television (e.g., a television connected to the Internet), a set-top box, a game console, a security system (including security cameras), an in-vehicle computer, a network device (e.g., a router, a switch, a modem), etc. In some embodiments, the UE 102 includes a wearable device such as a smart watch, a fitness band, an optical head-mounted display, etc. The UE 102 may communicate directly with one or more of the NEs 104.

[0029] The NE 104 may be referred to as a base station, access point, access terminal, base, Node B, eNB, gNB, Home Node B, relay node, apparatus, device, or any other terminology used in the art. Throughout this specification, references to a base station may refer to any one of the above-mentioned types of network equipment 104, such as eNBs and gNBs.

[0030] The NEs 104 may be distributed across a geographic region. The NEs 104 are part of a radio access network that typically includes one or more controllers communicatively coupled to one or more corresponding NEs 104. The radio access network is typically communicatively coupled to one or more core networks, which may be coupled to other networks, such as the Internet and the public switched telephone network. These and other elements of the radio access and core networks are not illustrated but are generally known by those skilled in the art.

[0031] In one implementation, the wireless communication system 100 complies with 3GPP 5G New Radio (NR). In some implementations, the wireless communication system 100 complies with 3GPP protocols, with the NE 104 transmitting on the DL using an OFDM modulation scheme and the UE 102 transmitting on the uplink (UL) using an SC-FDMA or OFDM scheme. However, more generally, the wireless communication system 100 may implement some other open or proprietary communication protocol, such as WiMax. This disclosure is not intended to be limited to any particular wireless communication system architecture or protocol implementation.

[0032] The NE 104 may serve several UEs 102 within a serving area, e.g., a cell (or cell sector) or multiple cells, via wireless communication links. The NE 104 transmits DL communication signals to serve the UEs 102 in the time, frequency, and / or spatial domains.

[0033] In the example illustrated in FIG. 1, the NE 104 may include gNBs 104A, 104B and a 5G core network (5GC) 104C. The gNB 104A may be the receiving gNB for the UE 102, and the gNB 104B may be the last serving gNB for the UE 102.

[0034] A communication link is provided between the gNB 104A and the UE 102, and may be an UL or DL ​​communication link. Some UEs 102 may communicate simultaneously over different radio access technologies (RATs), such as NR and LTE. A direct or indirect communication link Xn between two or more gNBs 104A, 104B may be provided.

[0035] The 5G Core Network (5GC) 104C may include an Access and Mobility Management Function (AMF) and a User Plane Function (UPF). A communication link NG between the gNBs 104A, 104B and the 5G Core Network (5GC) may also be provided.

[0036] 2 is a schematic block diagram illustrating components of a user equipment (UE) according to one embodiment. The UE 200 may include a processor 202, a memory 204, an input device 206, a display 208, and a transceiver 210. In some embodiments, the input device 206 and the display 208 are combined into a single device, such as a touchscreen. In some embodiments, the UE 200 may not include any input device 206 and / or display 208. In various embodiments, the UE 200 may include one or more processors 202 and may not include any input device 206 and / or display 208.

[0037] The processor 202, in one embodiment, may include any known controller capable of executing computer-readable instructions and / or performing logical operations. For example, the processor 202 may be a microcontroller, microprocessor, central processing unit (CPU), graphics processing unit (GPU), auxiliary processing unit, field programmable gate array (FPGA), or similar programmable controller. In some embodiments, the processor 202 executes instructions stored in the memory 204 to perform the methods and routines described herein. The processor 202 is communicatively coupled to the memory 204 and the transceiver 210.

[0038] In one embodiment, memory 204 is a computer-readable storage medium. In some embodiments, memory 204 includes a volatile computer storage medium. For example, memory 204 may include RAM, including dynamic RAM (DRAM), synchronous dynamic RAM (SDRAM), and / or static RAM (SRAM). In some embodiments, memory 204 includes a non-volatile computer storage medium. For example, memory 204 may include a hard disk drive, flash memory, or any other suitable non-volatile computer storage device. In some embodiments, memory 204 includes both volatile and non-volatile computer storage media. In some embodiments, memory 204 stores data regarding trigger conditions for transmitting measurement reports to network devices. In some embodiments, memory 204 also stores program code and associated data.

[0039] The input device 206, in one embodiment, may include any known computer input device, including a touch panel, buttons, a keyboard, a stylus, a microphone, etc. In some embodiments, the input device 206 may be integrated with the display 208, for example, as a touch screen or similar touch-sensitive display.

[0040] Display 208, in one embodiment, may include any known electronically controllable display or display device. Display 208 may be designed to output visual, audio, and / or tactile signals.

[0041] The transceiver 210, in one embodiment, is configured to communicate wirelessly with network equipment. In some embodiments, the transceiver 210 comprises a transmitter 212 and a receiver 214. The transmitter 212 is used to transmit UL communication signals to the network equipment, and the receiver 214 is used to receive DL communication signals from the network equipment.

[0042] The transmitter 212 and the receiver 214 may be any suitable type of transmitter and receiver. Although only one transmitter 212 and one receiver 214 are illustrated, the transceiver 210 may have any suitable number of transmitters 212 and receivers 214. For example, in some embodiments, the UE 200 includes multiple transmitter 212 and receiver 214 pairs for communicating over multiple wireless networks and / or radio frequency bands, each of the transmitter 212 and receiver 214 pairs configured to communicate over a different wireless network and / or radio frequency band.

[0043] 3 is a schematic block diagram illustrating components of a network equipment (NE) 300 according to one embodiment. The NE 300 (or gNB 300) may include a processor 302, a memory 304, an input device 306, a display 308, and a transceiver 310. As will be appreciated, the processor 302, the memory 304, the input device 306, the display 308, and the transceiver 310 may be similar to the processor 202, the memory 204, the input device 206, the display 208, and the transceiver 210 of the UE 200, respectively.

[0044] In some embodiments, the processor 302 controls the transceiver 310 to transmit DL signals or data to the UE 200. The processor 302 may also control the transceiver 310 to receive UL signals or data from the UE 200. In another example, the processor 302 may control the transceiver 310 to transmit DL signals to the UE 200 that include various configuration data.

[0045] In some embodiments, the transceiver 310 comprises a transmitter 312 and a receiver 314. The transmitter 312 is used to transmit DL communication signals to the UE 200, and the receiver 314 is used to receive UL communication signals from the UE 200.

[0046] The transceiver 310 may communicate with multiple UEs 200 simultaneously. For example, the transmitter 312 may transmit DL communication signals to the UEs 200. As another example, the receiver 314 may simultaneously receive UL communication signals from the UEs 200. The transmitter 312 and receiver 314 may be any suitable type of transmitter and receiver. Although only one transmitter 312 and one receiver 314 are illustrated, the transceiver 310 may have any suitable number of transmitters 312 and receivers 314. For example, the NE 300 may serve multiple cells and / or cell sectors, and the transceiver 310 includes a transmitter 312 and a receiver 314 for each cell or cell sector.

[0047] NR supports the RRC_INACTIVE state, and UEs with infrequent data transmissions (periodic and / or aperiodic) are typically maintained in the RRC_INACTIVE state by the network. The UE must transition to the RRC_CONNECTED state for any DL and UL data. Figure 4A is a schematic diagram illustrating an example of a UE-triggered transition from RRC_INACTIVE to RRC_CONNECTED according to some implementation examples of the present disclosure, and Figure 4B is a schematic diagram illustrating an example of a periodic RNA (RAN-based notification area) update procedure without UE context relocation according to some implementation examples of the present disclosure. In Figures 4A and 4B, messages are transmitted between the UE 200, the receiving gNB 300 with which the UE 200 is currently communicating, the UE's last serving gNB 400, and / or the AMF 500.

[0048] As illustrated in FIG. 4A, the state transition from the RRC_INACTIVE state to the RRC_CONNECTED state is described in the technical specification TS38.300 as follows.

[0049] [Table 1]

[0050] In Figure 4A, UE 200 is initially in RRC_INACTIVE state 410. It sends an RRC_ResumeRequest message to gNB 300 (or the receiving gNB 300). Upon receiving the RRC message, gNB 300 forwards a RETRIEVE UE CONTEXT REQUEST message to UE 200's last serving gNB 400, which then returns a UE Context Search Response message. gNB 300 then sends an RRC_Resume message to the UE, and the UE switches to RRC-CONNECTED state 420. The UE then sends an RRC_ResumeComplete message to the receiving gNB 300, which triggers steps 6-9 to complete the path switch.

[0051] The periodic RNA (RAN-based Notification Area) update procedure without UE context relocation illustrated in Figure 4B is described in Technical Specification TS38.300 as follows:

[0052] [Table 2]

[0053] 4B, UE 200 is initially in RRC_INACTIVE state 410. It sends an RRCResumeRequest message to gNB 300 with a RAN (Radio Access Network) notification area update. The receiving gNB 300 forwards a RETRIEVE UE CONTEXT REQUEST message to UE 200's last serving gNB 400 with the received RAN notification area update. The last serving gNB 400 responds to the receiving gNB 300 with a RETRIEVE UE CONTEXT FAILURE message, and gNB 300 then forwards an RRCRelease message to UE 200. UE 200 remains in RRC_INACTIVE state 410.

[0054] In Release 17, small data transmission in RRC_INACTIVE state is enabled without the UE switching to RRC_CONNECTED state. Currently, only DRB SDT is considered during context fetch and data transfer with and without anchor location. How to support SRB SDT during context fetch and data transfer procedures with and without anchor location has not been addressed. In this disclosure, a method of SRB transmission using SDT to support context fetch and data transfer is proposed and described with the following exemplary embodiments.

[0055] Dedicated Data Forwarding GTP-U Tunnel for SRB PDCP PDUs without Anchoring In some embodiments, SRB SDT without anchorage is performed. To transmit NAS PDUs encapsulated in SRBs to the AMF, the receiving gNB 300 must forward the SRBs to the final serving gNB 400 via a dedicated GTP-U tunnel. In one embodiment, the PDCP PDUs of the SRBs are forwarded from the receiving gNB 300 to the final serving gNB 400. A "signaling radio bearer" (SRB) is defined as a radio bearer (RB) used exclusively for the transmission of RRC and NAS messages.

[0056] FIG. 5A is a schematic diagram illustrating an example of a dedicated SRB data forwarding GTP-U tunnel without anchoring location according to some implementations of the present disclosure.

[0057] As shown in FIG. 5A, the UE 200 sends an RRC Resume Request message to the receiving gNB 300 along with UL small data including an SRB (e.g., SRB2) (step 501 in FIG. 5A). The UL small data may be transmitted in a RACH (Random Access Channel)-based or CG (Configured Grant)-based SDT. Optionally, an SRB SDT indication may be provided to indicate that the small data includes an SRB, and the corresponding SRB type may also be indicated. The indication may be in the RRC Resume Request message or in the MAC subheader of the MAC PDU.

[0058] Upon receiving the UL small data containing an SRB, if the receiving gNB 300 can resolve the gNB identity contained in the I-RNTI (Inactive Radio Network Temporary Identifier), it requests the last serving gNB 400 to provide the UE context data by sending a RETRIEVE UE CONTEXT REQUEST message (step 502). Optionally, the message may include an SRB SDT indication, so that upon receiving the message, the last serving gNB 400 knows that the small data contains an SRB, and the corresponding SRB type (i.e., SRB1 or SRB2) may also be indicated. The SRB SDT indication may be included in the assistance information and used by the last serving gNB 400 to determine whether anchorage is required.

[0059] In some embodiments, the last serving gNB 400 determines that anchoring is not required. According to the SRB SDT indication, the last serving gNB 400 determines that data forwarding for an SRB is required and allocates SRB data forwarding information. The SRB data forwarding information may include the IP address of the GTP-U tunnel and the GTP-U TEID. The SRB data forwarding information may be per SRB type (i.e., SRB1 or SRB2). Alternatively, the SRB data forwarding information may apply to both SRB1 and SRB2. The last serving gNB 400 sends a RETRIEVE UE CONTEXT FAILURE message and the SRB data forwarding information to the receiving gNB 300 (step 503). The last serving gNB 400 may also send an SRB configuration to the receiving gNB 300. The SRB configuration may include the RLC configuration for the SRB. Alternatively, the last serving gNB400 may always allocate SRB data forwarding information regardless of whether an SRB SDT indication is received.

[0060] According to the received SRB configuration, the receiving gNB 300 extracts the PDCP PDU of the SRB and identifies the SRB type. The receiving gNB 300 then forwards the PDCP PDU of the SRB through a corresponding GTP-U tunnel (e.g., a dedicated GTP-U tunnel for the SRB) with an IP address and a GTP-U TEID (step 504).

[0061] Upon receiving the PDCP PDU of the SRB, the final serving gNB 400 processes PDCP-related handling for the PDCP PDU of the SRB according to the mapping between the SRB data forwarding information and the SRB type. The final receiving gNB 400 then extracts the NAS PDU from the RRC message (step 505) and forwards the NAS PDU to the AMF 500 (step 506).

[0062] According to some embodiments, the receiving gNB 300 receives a small data packet containing an SRB from the UE 200 in the RRC_INACTIVE state, sends a RETRIEVE UE CONTEXT REQUEST to the last serving gNB 400 of the UE 200, and receives SRB data forwarding information and an SRB configuration from the last serving gNB 400. The receiving gNB 300 extracts the PDCP PDU of the SRB and sends the PDCP PDU to the last serving gNB 400 via a dedicated GTP-U tunnel.

[0063] The final serving gNB 400 receives from the receiving gNB 300 a RETRIEVE UE CONTEXT REQUEST initiated by the reception of a small data packet with an SRB from the UE 200 in the RRC_INACTIVE state, and in response to determining that anchoring is not required, transmits SRB data forwarding information and an SRB configuration to the receiving gNB 300. The final serving gNB 400 further receives a PDCP PDU for the SRB from the receiving gNB 300 via a dedicated GTP-U tunnel.

[0064] In another example, the SRB SDT (e.g., a small data packet containing an SRB) may come after the UE context fetch procedure. For example, it may be sent after receiving a RETRIEVE UE CONTEXT FAILURE message. In this case, the receiving gNB 300 may also send an SRB SDT indication to the last serving gNB 400 in a new XnAP message. Correspondingly, the last serving gNB 400 sends SRB data forwarding information to the receiving gNB 300 for data forwarding of the SRB PDCP PDU.

[0065] SRB PDCP PDU transmission through the control plane without anchorage In some embodiments, SRB SDT without anchorage is performed. To transmit the NAS PDU encapsulated in the SRB to the AMF, the receiving gNB 300 may forward the SRB PDCP PDU to the last serving gNB 400 via control plane Xn signaling.

[0066] FIG. 5B is a schematic diagram illustrating an example of SRB PDCP PDU transmission over a control plane without anchor location according to some implementations of the present disclosure.

[0067] The UE 200 sends an RRC Resume Request message to the receiving gNB 300 along with UL small data including an SRB (e.g., SRB2) (step 501). The UL small data may be transmitted in a RACH (Random Access Channel)-based or CG (Configured Grant)-based SDT. Optionally, an SRB SDT indication may be provided to indicate that the small data includes an SRB, and the corresponding SRB type may also be indicated. The indication may be in the RRC Resume Request message or in the MAC subheader of the MAC PDU.

[0068] Upon receiving the UL small data containing SRBs, if the receiving gNB 300 can resolve the gNB identity contained in the I-RNTI (Inactive Radio Network Temporary Identifier), it requests the last serving gNB 400 to provide the UE context data by sending an XnAP message, for example, a RETRIEVE UE CONTEXT REQUEST message (step 502). Optionally, an SRB SDT indication may be included in the message, so that the last serving gNB 400, upon receiving the message, knows that the small data contains SRBs, and the corresponding SRB type may also be indicated. The SRB SDT indication may be included in the assistance information and used by the last serving gNB 400 to determine whether anchorage is required.

[0069] Upon receiving the RETRIEVE UE CONTEXT REQUEST with or without the SRB SDT indication, the last serving gNB 400 determines that anchoring is not required. The last serving gNB 400 sends an XnAP message, such as a RETRIEVE UE CONTEXT FAILURE message and an SRB configuration to the receiving gNB 300 (step 503B). The SRB configuration may include an RLC configuration for the SRB. In some embodiments, as shown in FIG. 5B, the last serving gNB 400 may send only the SRB configuration to the receiving gNB 300 without SRB data forwarding information.

[0070] According to the SRB configuration, the receiving gNB 300 extracts the PDCP PDU of the SRB and identifies the SRB type. The receiving gNB 300 forwards the PDCP PDU of the SRB to the final serving gNB 400 via XnAP signaling, e.g., an RRC TRANSFER message (step 504B). The SRB type (i.e., SRB1 or SRB2) may be indicated in the XnAP message, e.g., the RRC TRANSFER message.

[0071] Upon receiving the PDCP PDU for the SRB, the final serving gNB 400 processes PDCP-related handling for the PDCP PDU for the SRB, and the final receiving gNB 400 extracts the NAS PDU from the RRC message (step 505) and forwards the NAS PDU to the AMF 500 (step 506).

[0072] Since the SRB SDT may come after the UE context fetch procedure, the receiving gNB 300 may send the RRC TRANSFER message at any time before the UE release.

[0073] According to some embodiments, the receiving gNB300 receives the SRB configuration from the last serving gNB400 and sends the extracted PDCP PDU to the last serving gNB400 via XnAP control plane signaling.

[0074] In response to determining that anchoring is not required, the last serving gNB400 sends an SRB configuration to the receiving gNB300 and receives a PDCP PDU for the SRB from the receiving gNB300 via XnAP control plane signaling.

[0075] Data forwarding GTP-U tunnel for MAC PDUs containing SRBs without anchorage In some embodiments, a data forwarding tunnel for MAC PDUs may be used for data forwarding in the case of SRB SDT without anchorage. The MAC PDU may contain an SRB. Both SRBs and DRBs may be multiplexed into the MAC PDU. In some embodiments, it is not required to send an SRB configuration from the last serving gNB 400 to the receiving gNB 300.

[0076] FIG. 5C is a schematic diagram illustrating an example of a common data forwarding GTP-U tunnel for a MAC PDU including an SRB without anchorage according to some implementations of the present disclosure.

[0077] The UE 200 sends an RRC Resume Request message to the receiving gNB 300 along with UL small data including an SRB (e.g., SRB2) (step 501). The UL small data may be transmitted in a RACH (Random Access Channel)-based or CG (Configured Grant)-based SDT. Optionally, an SRB SDT indication may be provided to indicate that the small data includes an SRB, and the corresponding SRB type may also be indicated. The indication may be in the RRC Resume Request message or in the MAC subheader of the MAC PDU.

[0078] Upon receiving the UL small data containing SRBs, if the receiving gNB 300 can resolve the gNB identity contained in the I-RNTI (Inactive Radio Network Temporary Identifier), it requests the last serving gNB 400 to provide the UE context data by sending an XnAP message, for example, a RETRIEVE UE CONTEXT REQUEST message (step 502). Optionally, an SRB SDT indication may be included in the message, so that the last serving gNB 400, upon receiving the message, knows that the small data contains SRBs, and the corresponding SRB type may also be indicated. The SRB SDT indication may be included in the assistance information and used by the last serving gNB 400 to determine whether anchorage is required.

[0079] Upon receiving the RETRIEVE UE CONTEXT REQUEST message with or without the SRB SDT indication, the last serving gNB 400 determines that anchoring is not required. In this embodiment, the SRB data forwarding information may comprise MAC PDU data forwarding information. The last serving gNB 400 sends an XnAP message, such as a RETRIEVE UE CONTEXT FAILURE message, and MAC PDU data forwarding information, which may also be referred to as SRB data forwarding information, to the receiving gNB 300 (step 503C). The MAC PDU data forwarding information includes the IP address of the GTP-U tunnel and the GTP-U TEID.

[0080] The receiving gNB 300 forwards the MAC PDU containing the SRB to the final serving gNB 400 via the GTP-U tunnel (step 504C). In some embodiments, the MAC PDU may be transmitted to the final serving gNB via a common GTP-U tunnel.

[0081] According to the DRB and SRB configuration, the last serving gNB 400 processes the MAC PDU, extracts the NAS PDU from the RRC message (step 505), and forwards the NAS PDU to the AMF (step 506). The last serving gNB 400 may further extract the SDAP SDU (if any) and forward the user data to the UPF 600 (steps 507, 508).

[0082] MAC PDU transmission including SRB through the control plane without anchoring In some further embodiments, the MAC PDU containing the SRB may be transferred via XnAP signaling.

[0083] FIG. 5D is a schematic diagram illustrating an example of a MAC PDU transmission including an SRB over a control plane without anchor location according to some implementations of the present disclosure.

[0084] The UE 200 sends an RRC Resume Request message to the receiving gNB 300 along with UL small data including an SRB (e.g., SRB2) (step 501). The UL small data may be transmitted in a RACH (Random Access Channel)-based or CG (Configured Grant)-based SDT. Optionally, an SRB SDT indication may be provided to indicate that the small data includes an SRB, and the corresponding SRB type may also be indicated. The indication may be in the RRC Resume Request message or in the MAC subheader of the MAC PDU.

[0085] Upon receiving the UL small data containing SRBs, if the receiving gNB 300 can resolve the gNB identity contained in the I-RNTI (Inactive Radio Network Temporary Identifier), it requests the last serving gNB 400 to provide the UE context data by sending an XnAP message, for example, a RETRIEVE UE CONTEXT REQUEST message (step 502). Optionally, an SRB SDT indication may be included in the message, so that the last serving gNB 400, upon receiving the message, knows that the small data contains SRBs, and the corresponding SRB type may also be indicated. The SRB SDT indication may be included in the assistance information and used by the last serving gNB 400 to determine whether anchorage is required.

[0086] Upon receiving a RETRIEVE UE CONTEXT REQUEST message with or without an SRB SDT indication, the last serving gNB 400 determines that anchoring is not required and sends an XnAP message, for example, a RETRIEVE UE CONTEXT FAILURE message.

[0087] Upon receiving the RETRIEVE UE CONTEXT FAILURE message, the receiving gNB300 forwards the MAC PDU to the last serving gNB400 via XnAP signaling, for example, an RRC TRANSFER message (step 504D).

[0088] According to the DRB and SRB configuration, the last serving gNB 400 processes the MAC PDU, extracts the NAS PDU from the RRC message (step 505), and forwards the NAS PDU to the AMF (step 506). The last serving gNB 400 may further extract the SDAP SDU (if any) and forward the user data to the UPF 600 (steps 507, 508).

[0089] Transmission of SRB SDT with anchorage In some embodiments, the anchor may be relocated, i.e., the UE context is fetched from the last serving gNB to the receiving gNB.

[0090] FIG. 5E is a schematic diagram illustrating an example of SRB transmission using SDT with anchor location according to some implementations of the present disclosure.

[0091] The UE 200 sends an RRC Resume Request message to the receiving gNB 300 along with UL small data including an SRB (e.g., SRB2) (step 501). The UL small data may be transmitted in a RACH (Random Access Channel)-based or CG (Configured Grant)-based SDT. Optionally, an SRB SDT indication may be provided to indicate that the small data includes an SRB, and the corresponding SRB type may also be indicated. The indication may be in the RRC Resume Request message or in the MAC subheader.

[0092] Upon receiving the UL small data containing SRBs, if the receiving gNB 300 can resolve the gNB identity contained in the I-RNTI (Inactive Radio Network Temporary Identifier), it requests the last serving gNB 400 to provide the UE context data by sending an XnAP message, a RETRIEVE UE CONTEXT REQUEST message (step 502). Optionally, an SRB SDT indication may be included in the message, so that the last serving gNB 400, upon receiving the message, knows that the small data contains SRBs, and the corresponding SRB type may also be indicated. The SRB SDT indication may be included in the assistance information and used by the last serving gNB 400 to determine whether anchorage is required.

[0093] After receiving the RETRIEVE UE CONTEXT REQUEST message with or without the SRB SDT indication, the last serving gNB 400 may determine that anchor location is required, and it sends an XnAP message, e.g., a search response message for UE context and UE context for anchor location, to the receiving gNB 300 (step 503E).

[0094] According to the UE context including the SRB-related configuration, the receiving gNB 300 processes the small data, extracts the NAS PDU from the small data (step 504E), and forwards the NAS PDU to the AMF 500 together with an NGAP message, for example, a PATH SWITCH REQUEST (step 505E). The AMF 500 may return an NGAP message, for example, a PATH SWITCH REQUEST ACK (step 506E). The NAS PDU may be included in the PATH SWITCH REQUEST message. In some embodiments, the receiving gNB 300 may also extract the SDAP SDU (if present) and forward the user data to the UPF 600 (steps 507E, 508E).

[0095] FIG. 6 is a flowchart illustrating steps for SRB transmission using SDT by a receiving gNB 300 according to some implementation examples of the present disclosure.

[0096] In step 602, the receiver 314 of the receiving gNB 300 receives a small data packet from a UE 200 in an RRC_INACTIVE or RRC_IDLE state, and the small data packet includes an SRB (signaling radio bearer).

[0097] In step 604, the transmitter 312 of the receiving gNB 300 sends a RETRIEVE UE CONTEXT REQUEST to the last serving gNB 400 (i.e., the last serving base station) of the UE 200.

[0098] In step 606, the receiver 314 of the receiving gNB 300 further receives from the last serving gNB 400 a UE context for anchorage or SRB data forwarding information and / or an SRB configuration for transmission of small data packets.

[0099] Figure 7 is a flowchart illustrating steps for SRB transmission using SDT by the last serving gNB400 according to some implementation examples of the present disclosure.

[0100] In step 702, the receiver 314 of the last serving gNB 400 receives a RETRIEVE UE CONTEXT REQUEST from the receiving gNB 300 (i.e., the base station) initiated by the reception of a small data packet with an SRB (signaling radio bearer) from a UE in RRC_INACTIVE or RRC_IDLE state.

[0101] In step 704, the transmitter 312 of the last serving gNB 400 transmits the UE context to the receiving gNB 300 in response to determining that anchorage is required.

[0102] In step 706, the transmitter 312 of the last serving gNB 400 transmits SRB data forwarding information and / or an SRB configuration to the receiving gNB 300 in response to determining that anchorage is not required.

[0103] In one aspect, some example items of the present disclosure relating to a method of a NE or a base station may be summarized as follows:

[0104] 1. A method performed by a current serving base station, comprising:

[0105] receiving a small data packet from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state, the small data packet including an SRB (Signaling Radio Bearer);

[0106] sending a RETRIEVE UE CONTEXT REQUEST to a last serving base station of the UE;

[0107] and receiving, from a last serving base station, a UE context for anchor location or SRB data forwarding information and / or an SRB configuration for transmission of small data packets.

[0108] 2. The method of item 1, further comprising the step of transmitting SRB data to the last serving base station upon receiving an SRB configuration from the last serving base station.

[0109] 3. The method of item 1, further comprising the step of transmitting SRB data to the last serving base station upon receiving SRB data forwarding information from the last serving base station.

[0110] 4. The method of item 3, wherein the SRB data forwarding information comprises the IP address of a dedicated or common GTP-U (GPRS Tunneling Protocol User Plane) tunnel and a GTP-U TEID (Tunnel Endpoint Identifier).

[0111] 5. The method of item 2 or 3, further comprising the steps of extracting a PDCP (Packet Data Convergence Protocol) PDU (Protocol Data Unit) of the SRB and transmitting the PDCP PDU to the last serving base station via a dedicated GTP-U tunnel using the SRB data forwarding information.

[0112] 6. The method of item 2 or 3, wherein the SRB is included in a MAC (Media Access Control) PDU, and the method further includes the step of transmitting the MAC PDU to the last serving base station via the common GTP-U tunnel using the SRB data forwarding information.

[0113] 7. The method of item 2, further comprising: extracting the PDCP PDU of the SRB and sending the PDCP PDU to the final serving base station via XnAP control plane signaling.

[0114] 8. The method of item 1, wherein the SRB is included in a MAC PDU, and the method further includes the step of transmitting the MAC PDU to the final serving base station via XnAP control plane signaling.

[0115] 9. The method of item 2, wherein the SRB configuration includes an RLC (Radio Link Control) configuration for the SRB.

[0116] 10. The method of item 1, further comprising receiving an SRB SDT (small data transmission) indication from the UE indicating that the SRB is included in a small data packet.

[0117] 11. The method of item 1, wherein the RETRIEVE UE CONTEXT REQUEST comprises an SRB SDT indication indicating that an SRB is included in the small data packet.

[0118] 12. The method of item 11, wherein the SRB SDT indication further indicates the type of SRB contained in the small data packet.

[0119] 13. The method of item 11, wherein the RETRIEVE UE CONTEXT REQUEST further comprises assistance information for the last serving base station to determine whether anchor location is required.

[0120] 14. The method of item 1, further comprising: extracting a NAS (Non-Access Stratum) PDU from the small data packet; and sending the NAS PDU to an AMF (Access and Mobility Management Function) upon receiving a UE context for anchor location from a last serving base station.

[0121] 15. The method of item 14, further comprising extracting an SDAP (Service Data Adaptation Protocol) SDU from the small data packet and sending the SDAP SDU to a UPF (User Plane Function).

[0122] In another aspect, some example items of the present disclosure relating to a method of a NE or a base station may be summarized as follows:

[0123] 16. A method performed by a last serving base station, comprising:

[0124] receiving, from a base station, a RETRIEVE UE CONTEXT REQUEST initiated by reception of a small data packet with an SRB (Signaling Radio Bearer) from a user equipment (UE) in RRC_INACTIVE or RRC_IDLE state;

[0125] transmitting, to the base station, a UE context in response to determining that anchorage is required;

[0126] and in response to determining that anchor location is not required, transmitting SRB data transfer information and / or an SRB configuration to the base station.

[0127] 17. The method of item 16, further comprising receiving SRB data from the base station after transmitting the SRB configuration.

[0128] 18. The method of item 16, further comprising receiving SRB data from the base station after transmitting the SRB data transfer information.

[0129] 19. The method of item 18, wherein the SRB data forwarding information comprises a dedicated or common GTP-U (GPRS Tunneling Protocol-User Plane) tunnel IP address and a GTP-U TEID (Tunnel Endpoint Identifier).

[0130] 20. The method of item 17 or 18, further comprising receiving, from the base station, a PDCP (Packet Data Convergence Protocol) PDU (Protocol Data Unit) of the SRB extracted by the base station via a dedicated GTP-U (GPRS Tunneling Protocol User Plane) tunnel using the SRB data forwarding information.

[0131] 21. The method of item 17 or 18, wherein the SRB is included in a MAC (Media Access Control) PDU, and the method further includes receiving a MAC PDU from the base station via the common GTP-U tunnel using the SRB data forwarding information.

[0132] 22. The method of item 17, further comprising receiving, from the base station via XnAP control plane signaling, a PDCP PDU for the SRB extracted by the base station.

[0133] 23. The method of item 16, wherein the SRB is included in a MAC PDU, and the method further includes receiving the MAC PDU from the base station via XnAP control plane signaling.

[0134] 24. The method of item 17, wherein the SRB configuration includes an RLC (Radio Link Control) configuration for the SRB.

[0135] 25. The method of claim 16, further comprising the step of receiving an SRB SDT (small data transmission) indication from the base station indicating that an SRB is included in the small data packet.

[0136] 26. The method of item 16, wherein the RETRIEVE UE CONTEXT REQUEST comprises an SRB SDT indication indicating that an SRB is included in the small data packet.

[0137] 27. The method of item 26, wherein the SRB SDT indication further indicates the type of SRB contained in the small data packet.

[0138] 28. The method of item 26, wherein the RETRIEVE UE CONTEXT REQUEST further comprises assistance information for determining whether anchor location is required.

[0139] 29. The method of item 17, further comprising the steps of extracting a NAS (Non-Access Stratum) PDU and sending the NAS PDU to an AMF (Access and Mobility Management Function).

[0140] 30. The method of item 29, further comprising the step of transmitting user data to a UPF (User Plane Function).

[0141] In a further aspect, some example items of the present disclosure related to a UE or remote device may be summarized as follows:

[0142] 31. An apparatus comprising:

[0143] a receiver for receiving a small data packet from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state, the small data packet including an SRB (Signaling Radio Bearer);

[0144] a transmitter for sending a RETRIEVE UE CONTEXT REQUEST to a last serving base station of the UE;

[0145] The apparatus, wherein the receiver further receives, from a last serving base station, a UE context for anchor location or SRB data forwarding information and / or an SRB configuration for transmission of small data packets.

[0146] 32. The apparatus of item 31, wherein the transmitter further transmits SRB data to the last serving base station upon receiving an SRB configuration from the last serving base station.

[0147] 33. The device of item 31, wherein the transmitter further transmits SRB data to the last serving base station when the transmitter receives SRB data forwarding information from the last serving base station.

[0148] 34. The apparatus of item 33, wherein the SRB data forwarding information comprises an IP address and a GTP-U TEID (Tunnel Endpoint Identifier) ​​of a dedicated or common GTP-U (GPRS Tunneling Protocol User Plane) tunnel.

[0149] 35. The device of item 32 or 33, further comprising a processor that extracts a PDCP (Packet Data Convergence Protocol) PDU (Protocol Data Unit) from the SRB, and the transmitter further transmits the PDCP PDU to the last serving base station via a dedicated GTP-U tunnel using the SRB data forwarding information.

[0150] 36. The apparatus of item 32 or 33, wherein the SRB is included in a MAC (Media Access Control) PDU, and the transmitter further transmits the MAC PDU to the last serving base station via a common GTP-U tunnel using the SRB data forwarding information.

[0151] 37. The apparatus of item 32, further comprising a processor that extracts the PDCP PDU of the SRB, and the transmitter further transmits the PDCP PDU to the final serving base station via XnAP control plane signaling.

[0152] 38. The apparatus of item 31, wherein the SRB is included in a MAC PDU, and the transmitter further transmits the MAC PDU to the final serving base station via XnAP control plane signaling.

[0153] 39. The apparatus of item 32, wherein the SRB configuration includes an RLC (Radio Link Control) configuration for the SRB.

[0154] 40. The apparatus of item 31, wherein the receiver further receives an SRB SDT (small data transmission) indication from the UE indicating that an SRB is included in the small data packet.

[0155] 41. The apparatus of item 31, wherein the RETRIEVE UE CONTEXT REQUEST comprises an SRB SDT indication indicating that an SRB is included in the small data packet.

[0156] 42. The apparatus of item 41, wherein the SRB SDT indication further indicates the type of SRB contained in the small data packet.

[0157] 43. The apparatus of item 41, wherein the RETRIEVE UE CONTEXT REQUEST further comprises assistance information for a last serving base station to determine whether anchor location is required.

[0158] 44. The device of item 31, further comprising a processor that extracts a NAS (non-access stratum) PDU from the small data packet, and further transmitting the NAS PDU to an AMF (access and mobility management function) when the transmitter receives a UE context for anchor location from the last serving base station.

[0159] 45. The device of item 44, further comprising a processor that extracts SDAP (Service Data Adaptation Protocol) SDUs from the small data packets, and the transmitter further transmits the SDAP SDUs to a UPF (User Plane Function).

[0160] In a further aspect, some example items of the present disclosure related to a NE or a base station may be summarized as follows:

[0161] 46. ​​An apparatus comprising:

[0162] a receiver for receiving, from a base station, a RETRIEVE UE CONTEXT REQUEST initiated by receiving a small data packet with an SRB (Signaling Radio Bearer) from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state;

[0163] a transmitter that transmits the UE context to the base station in response to determining that anchorage is required;

[0164] The apparatus, wherein the transmitter, in response to determining that anchor location is not required, further transmits SRB data transfer information and / or an SRB configuration to the base station.

[0165] 47. The apparatus of item 46, wherein the receiver further receives SRB data from the base station after transmitting the SRB configuration.

[0166] 48. The device of item 46, wherein the receiver further receives SRB data from the base station after transmitting the SRB data transfer information.

[0167] 49. The apparatus of item 48, wherein the SRB data forwarding information comprises a dedicated or common GTP-U (GPRS Tunneling Protocol-User Plane) tunnel IP address and a GTP-U TEID (Tunnel Endpoint Identifier).

[0168] 50. The device of item 47 or 48, wherein the receiver further receives, from the base station, a PDCP (Packet Data Convergence Protocol) PDU (Protocol Data Unit) of the SRB extracted by the base station via a dedicated GTP-U (GPRS Tunneling Protocol User Plane) tunnel using the SRB data forwarding information.

[0169] 51. The apparatus of item 47 or 48, wherein the SRB is included in a MAC (Media Access Control) PDU, and the receiver further receives the MAC PDU from the base station via the common GTP-U tunnel using the SRB data transfer information.

[0170] 52. The apparatus of item 47, wherein the receiver further receives, from the base station via XnAP control plane signaling, a PDCP PDU of the SRB extracted by the base station.

[0171] 53. The apparatus of item 46, wherein the SRB is included in a MAC PDU, and the receiver further receives the MAC PDU from the base station via XnAP control plane signaling.

[0172] 54. The apparatus of item 47, wherein the SRB configuration includes an RLC (Radio Link Control) configuration for the SRB.

[0173] 55. The apparatus of item 46, wherein the receiver further receives an SRB SDT (small data transmission) indication from the base station indicating that an SRB is included in the small data packet.

[0174] 56. The apparatus of item 46, wherein the RETRIEVE UE CONTEXT REQUEST comprises an SRB SDT indication indicating that an SRB is included in the small data packet.

[0175] 57. The apparatus of item 56, wherein the SRB SDT indication further indicates the type of SRB contained in the small data packet.

[0176] 58. The apparatus of item 56, wherein the RETRIEVE UE CONTEXT REQUEST further comprises assistance information for determining whether anchor location is required.

[0177] 59. The device of item 46, further comprising a processor that extracts a NAS (Non-Access Stratum) PDU, and wherein the transmitter further transmits the NAS PDU to an AMF (Access and Mobility Management Function).

[0178] 60. The device of item 59, wherein the transmitter further transmits user data to a UPF (User Plane Function).

[0179] In some further aspects, the present disclosure relates to a current serving base station including: a processor; and a transceiver coupled to the processor, wherein the processor is configured to receive a small data packet from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state, the small data packet including an SRB (signaling radio bearer), send a RETRIEVE UE CONTEXT REQUEST to a last serving base station of the UE, and receive, from the last serving base station, a UE context for anchor location or SRB data forwarding information and / or an SRB configuration for transmission of the small data packet.

[0180] In some further aspects, the present disclosure relates to a last serving base station including a processor and a transceiver coupled to the processor, wherein the processor is configured to receive, from the base station, a RETRIEVE UE CONTEXT REQUEST initiated by reception of a small data packet with an SRB (signaling radio bearer) from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state, transmit the UE context to the base station in response to a determination that anchor location is required, and further transmit SRB data forwarding information and / or an SRB configuration to the base station in response to a determination that anchor location is not required.

[0181] Various embodiments and / or examples are disclosed to provide illustrative and explanatory information to enable those skilled in the art to practice the present disclosure, and features or components disclosed with reference to one embodiment or example are applicable to all embodiments or examples unless otherwise specified.

[0182] The embodiments may be embodied in other specific forms. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope. [Explanation of symbols]

[0183] 100 Wireless Communication System 102 User Equipment (UE) 104 Network Equipment (NE) 104A gNB 104B gNB 104C 5G Core Network (5GC) 200 User Equipment (UE) 202 processors 204 memory 206 Input Devices 208 Display 210 Transmitter / Receiver 212 Transmitter 214 Receiver 300 Network Equipment (NE), gNB 302 processor 304 memory 306 Input Devices 308 Display 310 Transmitter / Receiver 312 Transmitter 314 Receiver 400 last serving gNB 500 AMF 600 UPF

Claims

1. A method performed by a current serving base station, comprising: receiving a small data packet from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state, the small data packet including an SRB (Signaling Radio Bearer); sending a RETRIEVE UE CONTEXT REQUEST to a last serving base station of the UE; receiving, from the last serving base station, a UE context for anchoring or SRB data forwarding information and / or an SRB configuration for transmission of the small data packet; upon receiving the SRB configuration from the last serving base station, transmitting SRB data to the last serving base station.

2. A method performed by a current serving base station, comprising: receiving a small data packet from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state, the small data packet including an SRB (Signaling Radio Bearer); sending a RETRIEVE UE CONTEXT REQUEST to a last serving base station of the UE; receiving, from the last serving base station, a UE context for anchoring or SRB data forwarding information and / or an SRB configuration for transmission of the small data packet; upon receiving the SRB data forwarding information from the last serving base station, transmitting SRB data to the last serving base station.

3. 3. The method of claim 2, wherein the SRB data forwarding information comprises an IP address of a dedicated or common GTP-U (GPRS Tunneling Protocol User Plane) tunnel and a GTP-U TEID (Tunnel Endpoint Identifier).

4. 3. The method of claim 1, further comprising: extracting a PDCP (Packet Data Convergence Protocol) PDU (Protocol Data Unit) of the SRB; and transmitting the PDCP PDU to the last serving base station through a dedicated GTP-U tunnel using the SRB data forwarding information.

5. 3. The method according to claim 1, wherein the SRB is included in a MAC (Media Access Control) PDU, and the method further comprises transmitting the MAC PDU to the last serving base station through a common GTP-U tunnel using the SRB data forwarding information.

6. The method of claim 1 , further comprising: extracting a PDCP PDU from the SRB and sending the PDCP PDU to the last serving base station via XnAP control plane signaling.

7. The method of claim 1 , wherein the SRB is included in a MAC PDU, and the method further comprises transmitting the MAC PDU to the last serving base station via XnAP control plane signaling.

8. The method of claim 1 , wherein the SRB configuration includes an RLC (Radio Link Control) configuration for the SRB.

9. 2. The method of claim 1, further comprising receiving an SRB SDT (small data transmission) indication from the UE indicating that the SRB is included in the small data packet.

10. 2. The method of claim 1, wherein the RETRIEVE UE CONTEXT REQUEST comprises an SRB SDT indication indicating that the SRB is included in the small data packet.

11. The method of claim 10 , wherein the SRB SDT indication further indicates a type of the SRB included in the small data packet.

12. 11. The method of claim 10, wherein the RETRIEVE UE CONTEXT REQUEST further comprises assistance information for the last serving base station to determine whether anchor location is required.

13. 2. The method of claim 1, further comprising: extracting a NAS (Non-Access Stratum) PDU from the small data packet; and sending the NAS PDU to an AMF (Access and Mobility Management Function) upon receiving the UE context for anchor location from the last serving base station.

14. a current serving base station, a processor; a transceiver coupled to the processor; the processor: receiving a small data packet from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state, the small data packet including an SRB (Signaling Radio Bearer); sending a RETRIEVE UE CONTEXT REQUEST to a last serving base station of the UE; and receiving, from the last serving base station, a UE context for anchoring or SRB data forwarding information and / or an SRB configuration for transmission of the small data packet; a current serving base station configured to transmit SRB data to the last serving base station upon receiving the SRB configuration from the last serving base station; 15. A current serving base station, comprising: a processor; a transceiver coupled to the processor; the processor: receiving a small data packet from a user equipment (UE) in an RRC_INACTIVE or RRC_IDLE state, the small data packet including an SRB (Signaling Radio Bearer); sending a RETRIEVE UE CONTEXT REQUEST to a last serving base station of the UE; and receiving, from the last serving base station, a UE context for anchoring or SRB data forwarding information and / or an SRB configuration for transmission of the small data packet; a current serving base station configured to transmit SRB data to the last serving base station upon receiving the SRB data forwarding information from the last serving base station;

Images