User equipment context fetching for small data transmission - Patents.com

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 communication networks, and in particular to small data transmission (SDT) procedures in such networks. [Background technology]

[0002] A communication network generally includes a number of nodes. Each node is a connection point in 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, in a communication network is configured with an SDT, SDT-related context information for the UE is stored in an anchor node for the communication session.

[0004] However, the UE may initiate an SDT procedure at a different node (i.e., a node different from the node at which context information for the UE is available, including SDT-related context information, referred to herein as the UE context). Summary of the Invention [Means for solving the problem]

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

[0006] According to another aspect, there is provided a network device configured to operate as a first node in a communications network for a user device transitioning from a first node in the communications network to a target node during a small data transmission communication session, the network device being configured to send a message to the target node including an indication of 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 to successfully perform small data transmission related procedures.

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

[0009] The first node may be a source node in the communication network. The first node may be a previous / last serving node to the target node that holds small data transmission configuration information for the user device in the communication network. The target node may not have prior knowledge of the small data transmission configuration information for the user device. The target node may act as a receiving node. Upon forwarding the small data configuration information 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 forwarded from the last serving node when the last serving node decides to relocate the UE Context (including the SDT configuration information for the UE) or to anchor the SDT session (i.e., not relocate the UE Context) when the SDT session is initiated at a non-anchor node or when the user device performs cell reselection during the SDT session to move away from the serving node. This may assist in the initiation or transfer of the SDT session. The SDT configuration information for the user device may be stored in the target node once it is received.

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

[0011] The radio resource control message may include an Access Stratum Configuration (AS-Config) field and an Access Stratum Context (AS-Context) field. The network device may be configured to include an indication of small data transmission configuration information for the user device in the AS-Config field. The network device may be configured to include an indication of small data transmission configuration information for the user device in the AS-Context field. This may provide compatibility with existing architectures and accommodate future extensions.

[0012] The message may include a previous RRCRelease message sent to the user device when configuring small data transmission with the first node. The previous RRC message may include content that is not encrypted or integrity protected. This may be an efficient way to transmit SDT configuration information.

[0013] The request from the target node may be part of an XnAP Retrieve UE Context procedure. An indication of the small data transmission configuration information for the user device may be included in a UE Context Information field in the XnAP Retrieve UE Context response message.

[0014] The network device may be a base station. The network device may be a gNodeB.

[0015] This may enable the network device to be used in a telecommunications network.

[0016] A user device can be in either 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 RRC_IDLE state. In RRC_INACTIVE state, a UE in a network such as a Next Generation Radio Access Network (NG-RAN) can move within an area configured by the NG-RAN (RAN-based Notification Area, RNA) without informing the NG-RAN. In RRC_INACTIVE state, the last serving node (the first node above) keeps the UE context information and the UE-related NG connection with the serving Access and Mobility Management Function and User Plane Function.

[0017] Once the message has been sent to the target node, the user device may remain in RRC INACTIVE Mode and be able to transmit or receive small data to or from the target node.

[0018] According to a further aspect, there is provided a method for implementation in a network device configured to operate as a first node in a communications network for a user device to initiate a small data transmission communications session via a target node in the communications network, the method including a step of sending 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.

[0019] According to another aspect, a method is provided for implementation in a network device configured to operate as a first node in a communications network for a user device transitioning from a first node in the communications network to a target node during a small data transmission communications session, the method including a step of sending 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.

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

[0021] According to another aspect, there is provided a network device configured to operate as a target node in a communications network for a user device initiating a small data transmission communications session via the target node, the network device being configured to: receive a request from the user device for the network device to operate as a target node for the small data transmission communications session; send a request to a first node in the communications network for context information for the user device; and receive a message from the first node including the context information for the user device, the context information including an indication of small data transmission configuration information for the user device.

[0022] According to a further aspect, there is provided a network device configured to operate as a target node in a communications network for a user device transitioning from a first node in the communications network to the target node during a small data transmission communication session, the network device being configured to: receive a request from the user device for the network device to operate as a target node for the small data transmission communication session; send a request to the first node for context information for the user device; and receive a message from the first node including the context information for the user device, the context information including an indication of small data transmission configuration information for the user device.

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

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

[0025] The network device may be configured to operate as a new serving node for the user device after relocating the context information for the user device from the first node to the network device. The first node may be a source node in the communication network. The first node may be a previous / last serving node to the target node, which holds the small data transmission configuration information for the user device in the communication network. The target node may not have prior knowledge of the small data transmission configuration information for the user device. The target node may operate as a receiving node. Upon forwarding the small data configuration information to the target node, the target node may operate 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 last serving node decides to relocate the UE context (including the SDT configuration information for the UE) or to anchor the SDT session (i.e., not relocate the UE Context) when the SDT session is initiated at a non-anchor node or when the user device performs cell reselection during the SDT session to move away from the serving node. 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.

[0026] The message (transmitted 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. An indication of small data transmission configuration information for a user device may be included in the AS-Config field. An indication of small data transmission configuration information for a user device may be included in the AS-Context field. This may provide compatibility with existing architectures.

[0028] The message may include a previous RRCRelease message sent to the user device when configuring a 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] An indication of the small data transmission configuration information for the user device may be included in a UE Context Information field in the XnAP Retrieve UE Context response message, which may allow compatibility with existing processes.

[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] Once the message has been sent to the target node, the user device may remain in RRC INACTIVE Mode and be able to transmit or receive small data to or from the target node.

[0032] According to a further aspect, there is provided a method for implementation in a network device configured to operate as a target node in a communications network for a user device initiating a small data transmission communications session via the target node, the method including the steps of receiving a request from the user device for the network device to operate as a target node for the small data transmission communications session, sending a request to a first node in the communications network for context information for the user device, and receiving a message from the first node including the context information for the user device, the context information including an indication of small data transmission configuration information for the user device.

[0033] According to a further aspect, there is provided a method for implementation in a network device configured to operate as a target node in a communications network for a user device transitioning from a first node in the communications network to a target node during a small data transmission communications session, the method including the steps of receiving a request from the user device for the network device to operate as a target node for the small data transmission communications session, sending a request to the first node for context information for the user device, and receiving a message from the first node including the context information for the user device, the context information including an indication of small data transmission configuration information for the user device.

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

[0035] According to a further aspect, there is provided a computer readable storage medium having stored thereon computer readable instructions that, when executed on a computer system, cause the computer system to perform the method described above. The computer system may include one or more processors. The computer readable storage medium may be a non-transitory computer readable storage medium.

[0036] The present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0037] [Figure 1(a)] 1 illustrates a schematic diagram of components in a Next Generation Radio Access Network (NG-RAN). [Figure 1(b)] 1 illustrates a schematic diagram of components in a Next Generation Radio Access Network (NG-RAN). [Diagram 2] 1 illustrates an exemplary communication flow between devices in a network. [Diagram 3] An example of a RETRIEVE UE CONTEXT RESPONSE message is shown below. [Figure 4] An example of detailed SDT configuration information in a RRCRelease message is shown below. [Diagram 5] 13 shows an example in which SDT configuration information for the UE is included within an RRC Container within an RRC Context IE within an XnAP:RETRIEVE UE CONTEXT RESPONSE message. [Figure 6] An example is shown in which SDT-related UE-specific information is included as part of the AS-Config field. [Figure 7] An example is shown in which SDT-related UE-specific information is included as part of the AS-Context field. [Figure 8] An example is shown in which SDT-related UE-specific information is included in the RRCRelease message in the AS-Config field in the RRC Context IE. [Figure 9] An example is shown where the SDT related UE specific information is directly included as part of the UE Context Information IE in the XnAP:RETRIEVE UE CONTEXT RESPONSE message. [Figure 10] 1 illustrates a flowchart of example method steps for implementation in a network device configured to operate as a target node in a communications network for a user device initiating a small data transmission communications session via the target node. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] As shown diagrammatically in FIG. 1(a), a Next Generation Radio Access Network (NG-RAN) 100 may include multiple nodes. In this example, the network 100 includes gNodeBs (gNBs) 101, 102. Each gNB 101, 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 that connects the CUs of the gNBs to the DUs of the gNBs.

[0039] The two gNBs 101, 102 may be interconnected with each other using an Xn network interface 106, which is a network interface between the NG-RAN nodes 101, 102 of the NG-RAN 100. In this example, the Xn interface 106 is an Xn-Control plane interface (Xn-C). The gNB is also connected to a 5G Core Network (5GC) 108 using a Next Generation (NG) network interface 107, more specifically to an Access and Mobility Management Function (AMF) using a control plane interface (NG-C) between the NG-RAN 100 and the 5GC 108, and to a User Plane Function (UPF) using a 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 non-transitory method code executable by the processor to implement the node in the manner described herein. The node may also comprise a transceiver for transmitting and receiving data. The communication network is preferably a wireless network.

[0041] SDT aims to create a solution that allows a UE to transmit or receive small data to or from a network node 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 an embodiment of the present invention, SDT configuration information may be transferred between a first node (e.g., a source node, an anchor node, or a last serving node) and a target node (which may 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 a communication network, or when a user device transitions from a first node in a communication network to a target node during a small data transmission communication session.

[0044] The source and target nodes are typically used in handover procedures or cell reselection procedures while continuing an SDT session across nodes of 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 the node in the network other than the last serving node where the UE initiates an SDT session. The receiving node becomes the new serving node for the UE after the UE context information is relocated from the last serving node to the receiving node.

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

[0047] This information may be forwarded from the last serving gNB to the receiving gNB on the Xn interface. This information may then be forwarded on the control plane of the F1 interface (F1-C (F1-U) and E1 (transmission) interfaces, as shown at 105a, 105b, and 109, respectively, in FIG. 1(b).

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

[0049] In a first example, a UE device in a communication network (which may be an NG-RAN as shown in FIG. 1) initiates a new SDT session at a different node than the node at which the UE context containing SDT related context / configuration information is available. This node at which 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 techniques can be used when the 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 from the last serving node to the new serving node (which may also be called the receiving node or the target node) during relocation. Without the transfer of SDT-related configuration, the new serving node cannot continue the SDT procedure. Based on the received SDT-related information for the UE, the receiving node can establish the UE context and can continue the SDT procedure.

[0051] For random access channel (RACH) based SDT, a UE in RRC_INACTIVE mode may initiate RACH and request RRC resumption along with uplink SDT data / signaling.

[0052] An example will now be described with reference to FIG. 2, which shows the overall procedure of a RACH-based SDT procedure with UE context relocation.

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

[0054] To illustrate this aspect, Figure 2 shows an example communication flow between devices in a network 200. The devices in the network include a UE 201, gNBs 202 and 203, an AMF 204, and a UPF 205. The gNBs 202, 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 may be a source node or an anchor node of the communication network.

[0056] At the start of the communication flow, the UE 201 is in RRC_INACTIVE mode. Then, an SDT procedure is initiated, for example because the UE 201 wants to transmit data to the gNB 202.

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

[0058] In step 1, the UE 201 sends a RRCResumeRequest, as well as UL SDT data and / or UL SDT signaling to the receiving gNB 202.

[0059] In step 2, the receiving gNB202 identifies the last serving gNB203, for example, using an 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 assistance information (i.e., single packet, multiple packets).

[0060] In step 3, the last serving gNB 203 decides to relocate the UE context for SDT to gNB 202 and responds with a RETRIEVE UE CONTEXT RESPONSE message as shown in 300 of Figure 3. The UE context may be transferred between gNB 203 and gNB 202 in a UE Context Information Element (IE) 301 of the RETRIEVE UE CONTEXT RESPONSE message 300. The UL SDT data, if any, is delivered to the UPF 205.

[0061] In steps 4-6, the receiving gNB 202 decides to keep the UE 201 in RRC_INACTIVE state for SDT. The receiving gNB 202 can provide a forwarding address if loss of downlink (DL) user data buffered in the last serving gNB 203 should be prevented. The receiving gNB 202 can also initiate an NG-AP Path Switch procedure to establish an NG UE-associated signaling connection to the serving AMF 204. After the path switch, the UL NAS PDU is delivered to the AMF 204.

[0062] In step 7, after the SDT transmission is completed, the receiving gNB 202 generates and sends an RRCRelease message. The RRCRelease message is a message used by the network to initiate an RRC connection release procedure to transition a UE in RRC_CONNECTED state to RRC_IDLE or to transition an RRC_CONNECTED UE to RRC_INACTIVE state. In this example, in step 7, the receiving gNB 202 generates and sends an RRCRelease message including a pause instruction to the UE 201, returning the UE to RRC_INACTIVE.

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

[0064] In step 8, the receiving gNB 202 may indicate to the last serving gNB 203 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, the gNB 202 sends an RRCRelease message to the UE 201. The SDT procedure ends and the UE 201 goes into RRC_INACTIVE mode.

[0066] In an embodiment of the present invention, there are multiple ways in which the SDT configuration information can be transferred from the last serving gNB to the receiving / new serving gNB (target node). Next, several possible ways in which the SDT configuration information can be transferred from the last serving gNB to the receiving / new serving gNB (target node) are described. The signaling can be performed on the Xn interface according to the procedure outlined with reference to FIG. 2.

[0067] The SDT related configuration information may be configured for the UE using a RRCRelease message, as shown generally in Figure 4. The SDT related configuration information is shown at 401.

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

[0069] In some possible implementations, as shown generally in Figure 5, the SDT configuration information for the user device may be included in an Xn Application Protocol (XnAP) RETRIEVE UE CONTEXT RESPONSE message 500. As mentioned above, this is a message sent between nodes over the Xn interface to transfer UE context information from a first node to a target node (e.g., 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 that includes an RRC Context IE 502. The SDT configuration information can be included in an RRC Container within the RRC Context IE 502. In this example, the RRC Context IE 502 includes a "Handover Preparation Information" IE 503, which in one embodiment includes fields for Access Stratum Configuration (AS-Config) (including RRC Reconfiguration), 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 during handover preparation or for UE Context acquisition, e.g. in case of resumption or re-establishment including UE capability information.

[0072] As shown generally in Figures 6 and 7, the SDT related UE specific configuration information 506 may be included as part of the AS-Config field 504 or AS-Context field 505 of the Handover Preparation Information IE 503.

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

[0074] Alternatively, as shown diagrammatically in FIG. 8, the SDT related UE specific information can be included in an unencrypted and unintegrity protected RRCRelease message 507 in the AS-Config field 504 in the Handover Preparation Information IE 503 of the RRC Context IE 502 (e.g. a Transparent Container IE used to pass information between nodes).

[0075] The entire RRCRelease message (including the SDT configuration information) sent to the UE when configuring the SDT for the last serving node can be included in the RRCRelease message 507 or in the new message in the AS-Config field 504. Thus, the 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 to and from the last serving node.

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

[0077] Thus, the request (for the UE context) from the receiving / new serving node may be part of an XnAP Retrieve UE Context procedure, and an indication of the SDT configuration information for the UE may be included in the UE Context Information field in the XnAP Retrieve UE Context response message.

[0078] The 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 the SDT related UE context IE is received by the new serving node, the new serving node may be configured to store the information which may be used as follows.

[0080] sdt-DRB-List-r17 - Based on this information the new gNB-CU-CP can establish a UE context in the new gNB-CU-UP by 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 and establish the F1-U tunnel for SDT bearers only, 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 the SDT DRB shown above. Furthermore, based on this, the gNB can decide to forward any DL Non-Access Stratum (NAS) signaling using SDT, or it needs to forward it to put the UE in connected state when a DL NAS message arrives.

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

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

[0084] The new serving gNB may decide to keep the same configuration received from the last serving gNB and use delta signaling for these IEs, or it may change the configuration in the next RRCRelease message (i.e., the new serving gNB may perform delta signaling even after an 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 to also include the CG configuration during context transfer.

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

[0087] In summary, in an embodiment of the present invention, a network device configured to operate as a first node (such as a source node, anchor node, or previous / last serving node) in a communication network for a user device initiating a small data transmission communication session via a target node (which can function as a receiving node or a new serving node) in the communication network can perform a method including the steps of: upon receiving a request from the target node, sending a message to the target node, the message including an indication of small data transmission configuration information for the user device.

[0088] A similar method may be performed in a network device configured to operate as a first node in a communications network for a user device transitioning from a first node to a target node during a small data transmission communications session, where the method includes transmitting 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.

[0089] 10 shows a flow chart summarizing an example of a method for implementation in a network device configured to operate as a target node in a communication network for a user device initiating a small data transmission communication session via the target node according to an embodiment of the present invention. In step 1001, the method includes receiving a request from the user device for the network device to operate as a target node for the small data transmission communication session. In step 1002, the method includes sending a request for context information for the user device to a first node in the communication network. In step 1003, the method includes receiving a message from the first node including context information for the user device, the context information including an indication of small data transmission configuration information for the user device.

[0090] A similar method may be used for a user device transitioning from a first node to a target node during a small data transmission communication session, where the method includes receiving a request from the user device for a network device to act as a target node for the 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 including the context information for the user device, the context information including an indication of small data transmission configuration information for the user device.

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

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

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

[0094] The applicant hereby discloses each individual feature described herein and any combination of two or more such features solely to the extent that such feature or combination can be realized based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, regardless of whether such feature or combination solves the problem disclosed herein, and without being limited to the scope of the claims. The applicant indicates that an aspect of the present invention can consist of any such individual feature or combination of features. In view of the foregoing description, it will be apparent to a person skilled in the art that various modifications can be made within the scope of the present invention. [Explanation of symbols]

[0095] 100 Next Generation Radio Access Network (NG-RAN) 101 gNodeB (gNB) 102 gNodeB (gNB) 103 Centralised 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 Network 201UE 202 Received gNB 203 Last Serving gNB 204 AMF 205 UPF 300 RETRIEVE UE CONTEXT RESPONSE 301 UE Context Information Element (IE) 400RRCRelease 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 device (203) configured to operate as a first node in a communications network (200) for a user device (201) initiating a small data transmission communications session via a target node (202) in the communications network (200), 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).

2. The network device (203) of claim 1, wherein the first node (203) is a source node in the communication network (200).

3. The network device (203) of claim 1, wherein the first node (203) is a previous serving node for the target node (202) that holds small data transmission configuration information for the user device (201) in the communication network (200).

4. The network device (203) of any one of claims 1 to 3, wherein the network device (203) is configured to transmit the message as a radio resource control message.

5. The network device (203) of claim 4, wherein the message includes an RRC Context information element transmitted as part of a small data transmission procedure.

6. The network device (203) of claim 4 or 5, wherein the radio resource control message includes an AS-Config field (504) and an AS-Context field (505).

7. The network device (203) of claim 6, wherein the network device (203) is configured to include the indication of the small data transmission configuration information (506) for the user device (201) in the AS-Config field (504).

8. The network device (203) of claim 6, configured to include the indication of the small data transmission configuration information (506) for the user device (201) in the AS-Context field (505).

9. The network device (203) of claim 4, wherein the message includes a previous RRCRelease message sent to the user device (201) when configuring a small data transmission with the first node (203).

10. The network device (203) of any one of claims 1 to 9, wherein the request from the target node (202) is part of an XnAP Retrieve UE Context procedure.

11. The network device (203) of claim 10, dependent on any one of claims 1 to 4, wherein the indication of the small data transmission configuration information (506) for the user device (201) is included in a UE Context Information field (501) in an XnAP Retrieve UE Context response message (500).

12. The network device (203) according to any one of claims 1 to 11, wherein the network device (203) is a gNodeB (102).

13. A method for implementation in a network device (203) configured to operate as a first node in a communications network (200) for a user device (201) to initiate a small data transmission communications session via a target node (202) in the communications network, the method comprising the step of sending 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).

14. A network device (202) configured to operate as a target node in a communication network (200) for a user device (201) initiating a small data transmission communication session via the target node, the network device (202) comprising: receiving (1001) a request from the user device (201) for the network device (202) to act as the target node for the small data transmission communication session; sending (1002) a request for context information for the user device (201) to a first node (203) in the communication network; receiving (1003) a message from the first node (203) including the context information for the user device (201), the context information including an indication of small data transmission configuration information (401, 506) for the user device (201); The network device (202) is configured to:

15. The network device (202) of claim 14, wherein the network device (202) is configured to operate as a new serving node for the user device (201) after relocating the context information for the user device from the first node (203) to the network device (202).

16. The network device (202) of claim 14 or 15, wherein the message is a radio resource control message.

17. The network device (202) of claim 16, wherein the message includes an RRC Context information element transmitted as part of a small data transmission procedure.

18. The network device (202) of claim 16 or 17, wherein the radio resource control message includes an AS-Config field (504) and an AS-Context field (505).

19. 20. The network device (202) of claim 18, wherein the indication of the small data transmission configuration information (506) for the user device (201) is included in the AS-Config field (504).

20. The network device (202) of claim 18, wherein the indication of the small data transmission configuration information (506) for the user device (201) is included in the AS-Context field (505).

21. The network device (202) of claim 16, wherein the message includes a previous RRCRelease message sent to the user device (201) when configuring a small data transmission with the first node (203).

22. 17. The network device (202) of claim 14, wherein the indication of the small data transmission configuration information (506) for the user device (201) is included in a UE Context Information field (501) in an XnAP Retrieve UE Context response message (500).

23. The network device (202) of any one of claims 14 to 22, wherein the network device (202) is a gNodeB.

24. A method (1000) for implementation in a network device (202) configured to operate as a target node in a communications network (200) for a user device (201) initiating a small data transmission communications session via the target node (202), the method comprising: receiving (1001) a request from the user device (201) for the network device (202) to act as the target node for the small data transmission communication session; sending (1002) a request for context information for said user device (201) to a first node (203) in said communication network (200); receiving (1003) a message from the first node (203) including the context information for the user device (201), the context information including an indication of small data transmission configuration information (401, 506) for the user device (201); A method (1000) comprising:

25. A computer readable storage medium having stored thereon computer readable instructions which, when executed on a computer system, cause the computer system to perform the method of claim 13 or 24.

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