User device context fetch for small data transmission

Abstract

A network device (203) configured to operate as a first node in a communication network (200) for a user device (201) initiating a small data transmission communication session via a target node (202) in the communication network (200) is described, the network device (203) being configured to send a message to the target node (202) upon receiving a request from the target node (202), the message including an indication of small data transmission configuration information (401, 506) for the user device (201). A corresponding network device (202) configured to operate as a target node is also described. Based on the small data transmission configuration information for the user device sent to the target node, the target node can establish a user device context to successfully perform small data transmission related procedures.

Description

Technical Field

[0001] The present disclosure relates to data transmission in a communication network, and more particularly to small data transmission (SDT) procedures in such a network.

Background Art

[0002] A communication network generally includes a plurality of nodes. Each node is a connection point within the communication network and can function as an endpoint for data transmission or redistribution. Each node may be, for example, a gNodeB (gNB).

[0003] When a user equipment device (UE) such as a mobile phone within a communication network is configured with SDT, SDT-related context information for the UE is stored in an anchor node for the communication session.

[0004] However, the UE can initiate SDT procedures at a different node (i.e., a node different from the node where context information for the UE, referred to herein as UE context, including SDT-related context information, is available).

Summary of the Invention

Means for Solving the Problems

[0005] According to one aspect, there is provided a network device configured to operate as a first node within a communication network for a user device that initiates a small data transmission communication session via a target node within the communication network, the network device being configured to transmit a message to the target node upon receiving a request from the target node, the message including an indication of small data transmission configuration information for the user device.

[0006] In another embodiment, a network device is provided which is configured to act as a first node in a communication network for a user device transitioning from a first node in the communication network to a target node during a small data transmission communication session, wherein the network device is configured to send a message to the target node containing instructions for small data transmission configuration information for the user device upon receiving a request from the target node.

[0007] Based on the small data transmission configuration information for the user device sent to the target node, the target node can establish a user device context in order to successfully execute small data transmission-related procedures.

[0008] The following features may apply to any embodiment of the present invention, wherein the first node operates as a first node for a user device that initiates a small data transmission communication session via a target node, or as a first node for a user device that transitions from a first node in the communication network to a target node during a small data transmission communication session.

[0009] The first node may be a source node in the communication network. The first node may be the previous / last serving node to the target node, holding small data transmission configuration information for a user device in the communication network. The target node does not need to have prior knowledge of the small data transmission configuration information for the user device. The target node may act as a receiving node. Once the small data configuration information has been transferred to the target node, the target node may act as a new serving node for the user device in the SDT session. Thus, the SDT configuration information for the user device may be transferred from the last serving node when the SDT session is started at a non-anchor node or when the last serving node relocates the UE Context (containing the SDT configuration information for the UE) when the user device performs cell reselection and leaves the serving node during the SDT session, or when the last serving node decides to anchor the SDT session (i.e., not relocate the UE Context). This may assist in the initiation or transfer of the SDT session. Once received, the SDT configuration information for the user device may be stored in the target node.

[0010] Network devices can be configured to transmit messages as radio resource control (RRC) messages. For example, a network device may be configured to generate inter-node (from a first node to a target node) radio resource control messages that include an RRC context information element (IE) transmitted as part of a small data transmission procedure. Thus, the message may contain context information for the user device. This provides compatibility with existing architectures and can accommodate future expansions.

[0011] Wireless resource control messages may include Access Stratum Configuration (AS-Config) and Access Stratum Context (AS-Context) fields. Network devices may be configured to include instructions for small data transmission configuration information for user devices in the AS-Config field. Network devices may also be configured to include instructions for small data transmission configuration information for user devices in the AS-Context field. This provides compatibility with existing architectures and allows for future expansion.

[0012] The message may include previous RRC Release messages sent to the user device when configuring small data transmission with the first node. These previous RRC messages may contain unencrypted or unencrypted content. This can be an efficient way to transmit SDT configuration information.

[0013] Requests from the target node may be part of the XnAP Retrieve UE Context procedure. Instructions for small data transmission configuration information for the user device may be included in the UE Context Information field within the XnAP Retrieve UE Context response message.

[0014] A network device could be a base station. A network device could be a gNodeB.

[0015] This could enable network devices to be used in telecommunications networks.

[0016] A user device can be in either the RRC_CONNECTED or RRC_INACTIVE state when an RRC connection is established. Otherwise, i.e., when an RRC connection is not established, the UE is in the RRC_IDLE state. In the RRC_INACTIVE state, a UE in a network such as the Next Generation Radio Access Network (NG-RAN) can move within the area configured by the NG-RAN (RAN-based notification area, RNA) without notifying the NG-RAN. In the RRC_INACTIVE state, the last serving node (the first node mentioned above) maintains the UE context information and the UE-related NG connections with the Serving Access and Mobility Management Function and the User Plane Function.

[0017] Once a message is sent to the target node, the user device can transmit or receive small data to or from the target node while remaining in RRC INACTIVE Mode.

[0018] In a further embodiment, a method is provided for implementation on a network device configured to act as a first node in a communication network for a user device to initiate a small data transmission communication session via a target node in the communication network, the method comprising the step of sending a message to the target node upon receiving a request from the target node, the message comprising instructions for small data transmission configuration information for the user device.

[0019] In another embodiment, a method is provided for implementation on a network device configured to act as a first node in a communication network for a user device transitioning from a first node in the communication network to a target node during a small data transmission communication session, the method comprising the step of sending a message to the target node upon receiving a request from the target node, the message comprising instructions for small data transmission configuration information for the user device.

[0020] Based on small data transmission configuration information for a user device sent to the target node, this method may enable the target node to establish a user device context in order to successfully perform small data transmission-related procedures.

[0021] In another embodiment, a network device is provided which is configured to act as a target node in a communication network for a user device to initiate a small data transmission communication session via a target node, wherein the network device receives a request from the user device to act as a target node for a small data transmission communication session, sends a request to a first node in the communication network for context information for the user device, receives a message from the first node containing context information for the user device, and the context information contains instructions for small data transmission configuration information for the user device.

[0022] In a further embodiment, a network device is provided which is configured to act as a target node in a communication network for a user device that transitions from a first node in the communication network to a target node during a small data transmission communication session, wherein the network device receives a request from the user device to act as a target node for a small data transmission communication session, sends a request to the first node for context information for the user device, receives a message from the first node containing context information for the user device, and the context information contains instructions for small data transmission configuration information for the user device.

[0023] Based on the small data transmission configuration information for the received user device, the target node can establish a user device context to successfully execute small data transmission-related procedures.

[0024] The following features may correspond to any embodiment of the present invention, wherein the target node operates as a target node for a user device that initiates a small data transmission communication session via the target node, or as a target node for a user device that transitions from a first node in the communication network to the target node during a small data transmission communication session.

[0025] A network device may be configured to act as a new serving node for a user device after relocating context information for the user device from a first node to the network device. The first node may be a source node in a communication network. The first node may be the previous / last serving node to the target node, holding small data transmission configuration information for the user device in the communication network. The target node does not need to have prior knowledge of the small data transmission configuration information for the user device. The target node may act as a receiving node. Once the small data configuration information has been transferred to the target node, the target node may act as a new serving node for the user device in the SDT session. Thus, the SDT configuration information for the user device may be transferred from the last serving node when the SDT session is started at a non-anchor node or when the last serving node relocates the UE context (including the SDT configuration information for the UE) when the user device performs cell reselection during the SDT session and leaves the serving node, or when the last serving node decides to anchor the SDT session (i.e., not relocate the UE context). This may assist in starting or transferring an SDT session. SDT configuration information for user devices can be stored on the target node once received.

[0026] The message (sent between the first node and the target node) may be a Radio Resource Control (RRC) message. For example, the message may include an RRC Context information element (IE) transmitted as part of a small data transmission procedure. This may provide compatibility with existing architectures.

[0027] The radio resource control message may include an AS-Config field and an AS-Context field. The indication of the small data transmission configuration information for the user device may be included in the AS-Config field. The indication of the small data transmission configuration information for the user device may be included in the AS-Context field. This may provide compatibility with the existing architecture.

[0028] The message may include a previous RRCRelease message sent to the user device when configuring small data transmission with the first node. The previous RRCRelease message may include content that is not encrypted or integrity protected. This may be an efficient way to transmit SDT configuration information.

[0029] The indication of the small data transmission configuration information for the user device may be included within the UE Context Information field in the XnAP Retrieve UE Context response message. This may enable compatibility with the existing process.

[0030] The network device may be a base station. The network device may be a gNodeB. This may enable the network device to be used in a telecommunications network.

[0031] After sending the message to the target node, the user device may be able to transmit or receive small data with the target node while remaining in the RRC INACTIVE Mode.

[0032] In a further embodiment, a method is provided for implementation on a network device configured to act as a target node in a communication network for a user device to initiate a small data transmission communication session via a target node, the method comprising: receiving a request from a user device asking the network device to act as a target node for a small data transmission communication session; sending a request to a first node in the communication network asking for context information for the user device; and receiving a message from the first node containing context information for the user device, wherein the context information includes instructions for small data transmission configuration information for the user device.

[0033] A further embodiment provides a method for implementation on a network device configured to act as a target node in a communication network for a user device transitioning from a first node in the communication network to a target node during a small data transmission communication session, the method comprising: receiving a request from the user device for the network device to act as a target node for a small data transmission communication session; sending a request to the first node for context information for the user device; and receiving a message from the first node containing context information for the user device, wherein the context information includes instructions for small data transmission configuration information for the user device.

[0034] Based on the small data transmission configuration information for the received user device, the above method may enable the target node to establish a user device context in order to successfully perform small data transmission-related procedures.

[0035] In a further embodiment, a computer-readable storage medium is provided that stores computer-readable instructions causing a computer system to perform the method described above when executed on the computer system. The computer system may comprise one or more processors. The computer-readable storage medium may be a non-temporary computer-readable storage medium.

[0036] Next, this disclosure will be described by reference to the attached drawings. [Brief explanation of the drawing]

[0037] [Figure 1(a)] This outlines the components of the Next Generation Radio Access Network (NG-RAN). [Figure 1(b)] This outlines the components of the Next Generation Radio Access Network (NG-RAN). [Figure 2] This shows an example of communication flow between devices in a network. [Figure 3] Here is an example of the RETRIEVE UE CONTEXT RESPONSE message. [Figure 4] An example of detailed SDT configuration information within an RRCRelease message is shown. [Figure 5] This example shows that SDT configuration information for the UE is included within the RRC Container in the RRC Context IE within the XnAP:RETRIEVE UE CONTEXT RESPONSE message. [Figure 6] This example shows how SDT-related UE-specific information is included as part of the AS-Config field. [Figure 7] This example shows how SDT-related UE-specific information is included as part of the AS-Context field. [Figure 8] This example shows how SDT-related UE-specific information is included in the RRCRelease message within the AS-Config field of the RRC Context IE. [Figure 9] This example shows how SDT-related UE-specific information is directly included as part of the UE Context Information IE within the XnAP:RETRIEVE UE CONTEXT RESPONSE message. [Figure 10] A flowchart of example steps for implementation on a network device configured to act as a target node in a communication network for a user device to initiate a small data transmission communication session via a target node is shown. [Modes for carrying out the invention]

[0038] As schematically shown in Figure 1(a), the Next Generation Radio Access Network (NG-RAN) 100 may include multiple nodes. In this example, the network 100 includes gNodeBs (gNBs) 101 and 102. Each gNB 101 and 102 may comprise multiple computing entities, such as a Centralised Unit (CU) 103 and multiple Distributed Units (DUs) 104. The CUs may communicate with the DUs via an F1 interface 105, which is an interface connecting the CUs of the gNBs to the DUs of the gNBs.

[0039] The two gNBs 101 and 102 can be interconnected using the Xn network interface 106, which is the network interface between the NG-RAN nodes 101 and 102 of the NG-RAN 100. In this example, the Xn interface 106 is the Xn-Control plane interface (Xn-C). The gNBs are also connected to the 5G Core Network (5GC) 108 using the Next Generation (NG) network interface 107, more specifically to the Access and Mobility Management Function (AMF) using the control plane interface (NG-C) between the NG-RAN 100 and the 5GC 108, and to the User Plane Function (UPF) using the user plane interface (NG-U) between the NG-RAN 100 and the 5GC 108.

[0040] Each node may comprise at least one processor and at least one memory. The memory stores code in a non-transient manner that can be executed by the processor to implement the node in the manner described herein. The node may also comprise transceivers for transmitting and receiving data. The communication network is preferably a wireless network.

[0041] SDT aims to create a solution that allows UEs to transmit or receive small data to and from network nodes while remaining in RRC inactive mode.

[0042] The solutions described herein detail the information that may be transferred as part of the SDT-related UE context, and how this information may be transferred between nodes.

[0043] In embodiments of the present invention, SDT configuration information may be transferred between a first node (e.g., a source node, anchor node, or last serving node) and a target node (which can function as a receiving node or a new serving node) when a user device initiates a new small data transmission communication session via a target node in the communication network, or when a user device transitions from a first node to a target node in the communication network during a small data transmission communication session.

[0044] Source and target nodes are typically used in handover procedures or cell reselection procedures while continuing the SDT session across nodes in the network.

[0045] The last serving node is the node in the network where the UE context information (including SDT configuration information) resides, and where the UE had its last SDT session. The receiving node is any node in the network other than the last serving node where the UE initiates its SDT session. The receiving node becomes the new serving node for the UE after the UE context information has been relocated from the last serving node to the receiving node.

[0046] The UE context can generally include information such as the Security Key, UE Radio Capability, UE Security Capability, and configuration parameters for configuring the radio interface protocol layer.

[0047] This information can be transferred from the last serving gNB to the receiving gNB via the Xn interface. This information can then be transferred via the control plane of the F1 interface (F1-C (F1-U)) and the E1 (transmission) interface, as shown in 105a, 105b, and 109 of Figure 1(b), respectively.

[0048] When a UE is configured with an SDT, the UE's SDT-related UE context / configuration is stored in the last serving gNB, which can be the anchor gNB.

[0049] In the first example, a UE device in a communication network (which may be an NG-RAN as shown in Figure 1) initiates a new SDT session on a node different from the node where the UE context containing SDT-related context / configuration information is available. This node where the UE context is available is referred to herein as the last (or previous) serving node. The last serving node may have previously acted as an anchor node. The last serving node may be a source node in the communication network. However, as will be described in more detail later, the same technique can be used when a device transitions between the last serving node and a receiving node during an ongoing (i.e., active) communication session.

[0050] SDT-related UE context transfer should be performed during relocation from the last serving node to the new serving node (which may also be called the receiving node or target node). Without the transfer of SDT-related configuration, the new serving node cannot proceed with the SDT procedure. Based on the SDT-related information for the received UE, the receiving node can establish the UE context and proceed with the SDT procedure.

[0051] In the case of Random Access Channel (RACH) based SDT, a UE in RRC_INACTIVE mode can initiate RACH and request RRC restart along with uplink SDT data / signaling.

[0052] Next, an example is illustrated with reference to Figure 2, which shows the overall procedure for a RACH-based SDT procedure involving UE context relocation.

[0053] This procedure is also applicable to the Mobile Terminated SDT procedure.

[0054] To illustrate this embodiment, Figure 2 shows an exemplary communication flow between devices in network 200. The devices in the network include UE201, gNB202 and 203, AMF204, and UPF205. gNB202 and 203 may be base stations or other network devices.

[0055] gNB202 is the new serving / receiving / target node, and gNB203 is the last serving node, which can be the source node or anchor node of the communication network.

[0056] At the start of the communication flow, UE201 is in RRC_INACTIVE mode. Next, the SDT procedure is initiated, for example, because UE201 wants to transmit data to gNB202.

[0057] If UE201 accesses a gNB202 other than the last serving gNB203, the uplink (UL)SDT data / signaling is buffered in the receiving gNB202, which can then trigger the XnAP Retrieve UE Context procedure.

[0058] In step 1, UE201 sends an RRCResumeRequest, along with UL SDT data and / or UL SDT signaling, to the receiving gNB202.

[0059] In step 2, the receiving gNB202 identifies the last serving gNB203, for example, using the Inactive Radio Network Temporary Identifier (I-RNTI). The gNB202 retrieves UE context information from the gNB203 using the Xn-AP Retrieve UE Context procedure. The receiving gNB202 sends a RETRIEVE UE CONTEXT REQUEST message to the last serving gNB203. The receiving gNB202 indicates that the UE request is for an SDT transaction and may also provide SDT support information (i.e., single packet, multiple packets).

[0060] In step 3, the last serving gNB203 decides to relocate the UE context for SDT to gNB202 and responds with a RETRIEVE UE CONTEXT RESPONSE message as shown in 300 in Figure 3. The UE context can be transferred between gNB203 and gNB202 within the UE Context Information Element (IE) 301 of the RETRIEVE UE CONTEXT RESPONSE message 300. If any, the UL SDT data is delivered to UPF205.

[0061] In steps 4-6, the receiving gNB202 decides to keep UE201 in the RRC_INACTIVE state for SDT. If loss of buffered downlink (DL) user data to the last serving gNB203 should be prevented, the receiving gNB202 can provide a forwarding address. The receiving gNB202 can also initiate the NG-AP Path Switch procedure to establish the NG UE-related signaling connection to the serving AMF204. After the path switch, the UL NAS PDU is delivered to the AMF204.

[0062] In step 7, after the SDT transmission is complete, the receiving gNB202 generates and sends an RRCRelease message. The RRCRelease message is used by the network to initiate an RRC connection release procedure to transition a UE in the RRC_CONNECTED state to RRC_IDLE, or to transition a UE in RRC_CONNECTED to the RRC_INACTIVE state. In this example, in step 7, the receiving gNB202 generates an RRCRelease message containing a pause instruction and sends it to UE201, returning the UE to RRC_INACTIVE.

[0063] When DL non-SDT data or DL ​​non-SDT signaling arrives, the receiving gNB202 may decide to put UE201 directly into the RRC_CONNECTED state by sending an RRCResume message.

[0064] In step 8, the receiving gNB202 may instruct the last serving gNB203 to delete the UE context by sending an XnAP UE CONTEXT RELEASE message. The XnAP UE CONTEXT RELEASE message may be sent after step 6.

[0065] At the end of the session, gNB202 sends an RRCRelease message to UE201. The SDT procedure is complete, and UE201 enters RRC_INACTIVE mode.

[0066] In embodiments of the present invention, there are multiple ways in which SDT configuration information can be transferred from the last serving gNB to the receiving / new serving gNB (target node). Several possible ways in which SDT configuration information can be transferred from the last serving gNB to the receiving / new serving gNB (target node) are described below. Signaling can be performed on the Xn interface following the procedure outlined with reference to Figure 2.

[0067] SDT-related configuration information can be configured for the UE using the RRCRelease message, as schematically shown in Figure 4. SDT-related configuration information is shown in 401.

[0068] Similar SDT configuration information can also be stored in the UE context within the last serving node and transferred to the new serving node when a relocation is performed.

[0069] In some possible embodiments, as schematically shown in Figure 5, SDT configuration information for the user device can be contained within the Xn Application Protocol (XnAP) RETRIEVE UE CONTEXT RESPONSE message 500. As mentioned above, this is a message sent between nodes via the Xn interface to transfer UE context information from a first node to a target node (for example, from node 203 to node 202 in step 3 of Figure 2).

[0070] In this example, the RETRIEVE UE CONTEXT RESPONSE message includes a UE Context Information Element (IE) 501 containing an RRC Context IE502. SDT configuration information can be contained within an RRC Container in the RRC Context IE502. In this example, the RRC Context IE502 contains a "HandoverPreparationInformation" IE503, which in one embodiment contains fields for Access Stratum Configuration (AS-Config) (including RRCReconfiguration), Radio Resource Monitoring (RRM)config, and Access Stratum Context (AS-Context).

[0071] The HandoverPreparationInformation IE can be used to transfer New Radio (NR) Radio Resource Control (RRC) information used by the target node for handover preparation or UE context acquisition, for example, in the case of restart or re-establishment, which includes UE capability information.

[0072] As schematically shown in Figures 6 and 7, SDT-related UE-specific configuration information 506 can be included as part of the AS-Config field 504 or AS-Context field 505 of the HandoverPreparationInformation IE503.

[0073] Therefore, the last serving node may be configured to include instructions for SDT configuration information for the UE in the AS-Config field 504 or AS-Context field 505. This may provide compatibility with existing architectures.

[0074] Alternatively, as schematically shown in Figure 8, SDT-related UE-specific information can be contained in an unencrypted and unintegrated RRCRelease message 507 within the AS-Config field 504 of the HandoverPreparationInformation IE503 of the RRC Context IE502 (e.g., a Transparent Container IE used to pass information between nodes), which is neither encrypted nor integrity-protected.

[0075] The entire RRCRelease message (including SDT configuration information) sent to the UE when configuring SDT for the last serving node can be included in RRCRelease message 507 or in a new message within the AS-Config field 504. Therefore, a message sent from the first node to the target node containing SDT-related configuration information for the UE may include the previous RRCRelease message sent to the user device when configuring small data transmission between the last serving node and the target node.

[0076] In other embodiments, the SDT-related UE-specific information 506 may be directly included as part of the UE Context IE 501 within the XnAP:RETRIEVE UE CONTEXT RESPONSE message 500, as schematically shown in Figure 9.

[0077] Therefore, a request from an incoming / new serving node (for the UE context) can be part of the XnAP Retrieve UE Context procedure, and instructions for SDT configuration information for the UE can be included in the UE Context Information field within the XnAP Retrieve UE Context response message.

[0078] SDT-related configuration information may include one or more of the following fields or IEs: sdt-DRB-List-r17, sdt-SRB2-Indication-R17, and sdt-DRB-Continue-ROHC-R17, sdt-MAC-PHY-CG-Config-R17. Definitions of these exemplary information fields are given below.

[0079] Once an SDT-related UE context IE is received by a new serving node, the new serving node may be configured to store information that can be used as follows:

[0080] sdt-DRB-List-r17 - Based on this information, the new gNB-CU-CP can establish a UE context with the new gNB-CU-UP via the Bearer Context Setup procedure and indicate to the gNB-CU-UP which bearers are SDT bearers. Thus, the gNB-CU-UP can keep non-SDT bearers suspended and resume SDT bearers after the UE context is set up. Furthermore, the gNB CU can identify the SDT RLC configuration and forward it to its DU in the UE CONTEXT SETUP REQUEST message, establishing an F1-U tunnel only for SDT bearers, i.e., the gNB DU does not need to establish all RLC entities.

[0081] sdt-SRB2-Indication-R17 - The new gNB CU must know if the UE is configured with SRB2 for SDT, for similar reasons as indicated above for SDT DRB. Furthermore, based on this, the gNB can decide to forward any DL Non-Access Stratum (NAS) signaling using SDT, or it may need to forward it to put the UE into a connected state when a DL NAS message arrives.

[0082] sdt-DRB-Continue-ROHC-R17 - This can also be used by gNB CU to determine whether Robust Header Compression (ROHC) should be continued within RNA or only in the cell where the SDT procedure is initiated.

[0083] sdt-MAC-PHY-CG-Config-R17 - Since a new serving gNB can use its own configuration, it is not mandatory for this information to be forwarded to the new serving gNB. However, if the UE is configured with a Configured Grant (CG)SDT Configuration and this configuration is provided to the new gNB, it can reuse this and provide the delta configuration (i.e., not the complete configuration) to the UE in the next RRCRelease message. Thus, this can be an optional IE to be forwarded between nodes.

[0084] A new serving gNB can retain the same configuration received from the previous serving gNB and decide to use delta signaling for these IEs, or it can change the configuration in the next RRCRelease message (i.e., the new serving gNB can perform delta signaling even after inter-node UE context transfer).

[0085] The main advantage of using delta signaling is that the CG configuration can be updated using delta signaling, and therefore it is desirable that the CG configuration also be included during context transfer.

[0086] Based on the transferred SDT configuration information for the UE, the new gNB can perform SDT-related procedures on the F1 and E1 interfaces.

[0087] In summary, in embodiments of the present invention, a network device configured to act as a first node in a communication network (such as a source node, anchor node, or previous / last serving node) for a user device to initiate a small data transmission communication session via a target node in the communication network (which may function as a receiving node or a new serving node) can, upon receiving a request from the target node, perform a method comprising the step of sending a message to the target node, the message including instructions for small data transmission configuration information for the user device.

[0088] A similar method may also be performed with a network device configured to act as the first node in the communication network for a user device transitioning from the first node to the target node during a small data transmission communication session. In this case, the method includes the step of receiving a request from the target node and sending a message to the target node containing instructions for small data transmission configuration information for the user device.

[0089] Figure 10 shows a flowchart summarizing an example of a method for implementation in a network device configured to act as a target node in a communication network for a user device to initiate a small data transmission communication session via a target node, according to an embodiment of the present invention. Step 1001 includes receiving a request from the user device asking the network device to act as a target node for a small data transmission communication session. Step 1002 includes sending a request to a first node in the communication network for context information for the user device. Step 1003 includes receiving a message from the first node containing context information for the user device, wherein the context information includes instructions for small data transmission configuration information for the user device.

[0090] A similar method may also be used for a user device that transitions from a first node to a target node during a small data transmission communication session. In this case, the method includes the steps of: receiving a request from the user device to a network device to act as a target node for a small data transmission communication session; sending a request to the first node for context information for the user device; and receiving a message from the first node containing context information for the user device, wherein the context information includes instructions for small data transmission configuration information for the user device.

[0091] As mentioned above, the first node can be a source node in the communication network. The first node can be the previous (i.e., last) serving node to the target node, holding small data transmission configuration information for user devices in the communication network. The target node can be a receiving / new serving node in the communication network.

[0092] Therefore, SDT configuration information for the UE can be transferred from the last serving gNB when the SDT session is started at a non-anchored gNB or when the UE performs cell reselection during the SDT session and moves away from the serving gNB, and the last serving gNB decides to relocate or anchor the SDT session.

[0093] Based on the SDT-related information received for the UE, the target node can establish a UE context to successfully start or continue the SDT procedure.

[0094] Regardless of whether each individual feature described herein and any combination of two or more such features solves a problem disclosed herein, and without being limited to the claims, the applicant discloses such features or combinations of features in isolation to the extent that such features or combinations can be realized as a whole under this specification in light of the common general knowledge of those skilled in the art. The applicant shows that aspects of the invention may consist of any individual features or combinations of features. In consideration of the foregoing, it will be apparent to those skilled in the art that various modifications can be made within the scope of the invention. [Explanation of Symbols]

[0095] 100 Next Generation Radio Access Network (NG-RAN) 101 gNodeB(gNB) 102 gNodeB(gNB) 103 Centralized Unit (CU) 104 Distributed Units (DU) 105 F1 Interface 105a F1-C 105b F1-U 106 Xn Interface 107 Next Generation (NG) Network Interface 108 5G Core Network (5GC) 109 E1 Interface 200 Communication Networks 201 UE 202 Received gNB 203 Last serving gNB 204 AMF 205 UPF 300 RETRIEVE UE CONTEXT RESPONSE 301 UE Context Information Element (IE) 400 RRCRelease 401 SDT-related configuration information 500 XnAP: RETRIEVE UE CONTEXT RESPONSE message 501 UE Context Information Element (IE) 502 RRC Context IE 503 HandoverPreparationInformation IE 504 AS-Config field 505 AS-Context field 506 SDT-related UE-specific information 507 RRCRelease message

Claims

1. A network node (203) configured to act as a first node in the communication network (200) for a user device (201) to initiate a small data transmission communication session via a receiving node (202) in the communication network (200), wherein the network node (203) is Upon receiving a request from the receiving node (202), A message is sent to the receiving node (202), the message includes user equipment (UE) context information, the UE context information includes an access layer configuration (AS-Config) field (504) and an access layer context (AS-Context) field (505), the AS-Config field (504) includes small data transmission configuration information (506) for the user device (201), Network node (203) configured as follows.

2. The network node (203) according to claim 1, wherein the message is a RETRIEVE UE CONTEXT RESPONSE message.

3. The network node (203) according to claim 1, wherein the first node (203) is a source node in the communication network (200).

4. The network node (203) according to claim 1, wherein the first node (203) is the last serving node that holds small data transmission configuration information for the user device (201) in the communication network (200).

5. The request from the receiving node (202) is part of the XnAP Retrieve UE Context procedure, as described in claim 1, for the network node (203).

6. The network node (203) is a gNodeB (102), as described in claim 1.

7. A method for implementation on a network node (203) configured to act as a first node in a communication network (200) for a user device (201) to initiate a small data transmission communication session via a receiving node (202) in the communication network, wherein the method is The steps include receiving a request from the receiving node (202), A step of sending a message to the receiving node (202), wherein the message includes user equipment (UE) context information, the UE context information includes an access layer configuration (AS-Config) field (504) and an access layer context (AS-Context) field (505), the AS-Config field (504) includes small data transmission configuration information (506) for the user device (201), and Methods that include...

8. The method according to claim 7, wherein the message is a RETRIEVE UE CONTEXT RESPONSE message.

9. The method according to claim 7, wherein the first node (203) is a source node in the communication network (200).

10. The method according to claim 7, wherein the first node (203) is the last serving node holding small data transmission configuration information for the user device (201) in the communication network (200).

11. The method according to claim 7, wherein the request from the receiving node (202) is part of the XnAP Retrieve UE Context procedure.

12. The method according to claim 7, wherein the network node (203) is a gNodeB (102).

13. A network node (202) configured to act as the receiving node in a communication network (200) for a user device (201) that initiates a small data transmission communication session via a receiving node, wherein the network node (202) The user device (1001) receives a request from the network node (202) to act as the receiving node for the small data transmission communication session. A request for context information for the user device (201) is sent to the first node (203) in the communication network (1002), A message containing the context information for the user device (201) is received from the first node (203) (1003), wherein the context information includes user equipment (UE) context information, the UE context information includes an access layer configuration (AS-Config) field (504) and an access layer context (AS-Context) field (505), and the AS-Config field (504) includes small data transmission configuration information (506) for the user device (201). Network nodes (202) are configured as follows.

14. The network node (202) according to claim 13, wherein the message is a RETRIEVE UE CONTEXT RESPONSE message.

15. The network node (202) according to claim 13, wherein the network node (202) is configured to act as a receiving node for the user device (201) after relocating the context information for the user device from the first node (203) to the network node (202).

16. The network node (202) according to claim 13, wherein the network node (202) is a gNodeB.

17. A method (1000) for implementation on a network node (202) configured to act as the receiving node in a communication network (200) for a user device (201) to initiate a small data transmission communication session via the receiving node (202), wherein the method is Step (1001) receiving a request from the user device (201) to the network node (202) to act as the receiving node for the small data transmission communication session, Step (1002) of sending a request to a first node (203) in the communication network (200) for context information for the user device (201), Step (1003) receiving a message from the first node (203) containing the context information for the user device (201), wherein the context information includes user equipment (UE) context information, the UE context information includes an access layer configuration (AS-Config) field (504) and an access layer context (AS-Context) field (505), and the AS-Config field (504) includes small data transmission configuration information (506) for the user device (201), and Method (1000), including the method (1000).

18. The method according to claim 17 (1000), wherein the message is a RETRIEVE UE CONTEXT RESPONSE message.

19. The method according to claim 17 (1000), wherein the network node (202) is configured to act as a receiving node for the user device (201) after relocating the context information for the user device from the first node (203) to the network node (202).

20. The method according to claim 17 (1000), wherein the network node (202) is a gNodeB.

21. A computer-readable storage medium storing computer-readable instructions that, when executed on a computer system, cause the computer system to perform the method according to claims 7 to 12 or 17 to 20.

22. A system comprising a network node (203) and a network node (202), wherein the network node (203) is configured to perform the method described in any one of claims 7 to 12, and the network node (202) is configured to perform the method described in any one of claims 17 to 20.

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