Data forwarding method in wireless communication system and nodes performing the method

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. According to an aspect of the present disclosure, a method performed by a first node in a wireless communication system is provided. The method comprises: transmitting a first message to a second node, wherein the first message comprises first identifier information and first information related to data forwarding, and the first information comprises information for requesting a direct forwarding path or a data forwarding proposal; and receiving a second message transmitted by the second node, wherein the second message comprises second information related to data forwarding of the second node, and the second information comprises direct forwarding path related information or data forwarding proposal related information.

Description

DATA FORWARDING METHOD IN WIRELESS COMMUNICATION SYSTEM AND NODES PERFORMING THE METHOD

[0001] The present disclosure relates to the wireless communication technology, and specifically to a data forwarding method in a UE mobility situation and nodes performing the data forwarding method.

[0002] 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in "Sub 6GHz" bands such as 3.5GHz, but also in "Above 6GHz" bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] The present disclosure relates to providing a data forwarding scheme that reduces traffic service interruption and latency during continuous mobility handover in wireless communication systems.

[0009] According to an aspect of the present disclosure, a method performed by a first node in a wireless communication system is provided. The method may comprise: transmitting a first message to a second node, wherein the first message comprises first identifier information and first information related to data forwarding, and the first information comprises information for requesting a direct forwarding path or a data forwarding proposal; and receiving a second message transmitted by the second node, wherein the second message comprises second information related to data forwarding of the second node, and the second information comprises direct forwarding path related information or data forwarding proposal related information.

[0010] According to an exemplary embodiment, the first identifier information may comprise identifier information of at least one candidate node for a UE handover, and the direct forwarding path related information may comprise the identifier information of the at least one candidate node and availability information of a direct forwarding path between the second node and the at least one candidate node.

[0011] According to an exemplary embodiment, the first message may be transmitted after a user equipment (UE) handover to a third node. The first identifier information may comprise identifier information of the third node, and the direct data forwarding path related information may comprise availability information of a direct forwarding path between the second node and the third node.

[0012] According to an exemplary embodiment, the first message may be transmitted after a UE handover to the second node. The first identifier information may comprise the identifier information of the at least one candidate node for the UE handover. The direct forwarding path related information may comprise the identifier information of the at least one candidate node and the availability information of the direct forwarding path between the second node and the at least one candidate node.

[0013] According to an exemplary embodiment, the method may further comprise: receiving a secondary node (SN) Change Required message from a source node. The SN Change Required message may comprise: the identifier information of the at least one candidate node for the UE handover and availability information of a direct forwarding path between the source node and the at least one candidate node. The second node may be a node in the at least one candidate node.

[0014] According to an exemplary embodiment, the first identifier information may comprise a packet data unit (PDU) session identifier and / or a quality of service (QoS) flow identifier, and the data forwarding proposal related information may be a data forwarding proposal. The data forwarding proposal related information may comprise a PDU session identifier and / or QoS identifier accepted by the second node, and a data forwarding proposal and data forwarding address related to the PDU session identifier and / or QoS identifier accepted by the second node.

[0015] According to an exemplary embodiment, the method may further comprise: transmitting a third message to the second node. The third message may comprise the data forwarding proposal related information associated with the at least one candidate node for the UE handover. The third message may be transmitted after an early data forwarding procedure.

[0016] According to an exemplary embodiment, the method may further comprise: transmitting a third message to a target node for a UE handover. The third message may comprise the data forwarding proposal related information associated with the at least one candidate node for the UE handover. The third message may be transmitted after a measurement report reported by the UE is received, or transmitted after a successful handover of the UE to the target node.

[0017] According to an exemplary embodiment, the first message may comprise an SN Addition Request message, an SN Modification Request message or a Handover Request message, and the second message may comprise an SN Addition Request Acknowledge message, an SN Modification Request Acknowledge message or a Handover Request Acknowledge message.

[0018] According to an exemplary embodiment, the third message may be transmitted through an XnAP message or Data Forwarding Information Transfer message.

[0019] According to another aspect of the present disclosure, a method performed by a second node in a wireless communication system is provided. The method may comprise: receiving a first message transmitted by a first node, wherein the first message may comprise first identifier information and first information related to data forwarding, and the first information comprises information for requesting a direct forwarding path or a data forwarding proposal; and transmitting a second message to the first node, wherein the second message may comprise second information related to data forwarding of the second node, and the second information may comprise direct forwarding path related information or data forwarding proposal related information.

[0020] According to an exemplary embodiment, the first identifier information may comprise identifier information of at least one candidate node for a UE handover. The direct forwarding path related information may comprise the identifier information of the at least one candidate node and availability information of a direct forwarding path between the second node and the at least one candidate node.

[0021] According to an exemplary embodiment, the first message may be transmitted after a UE handover to a third node. The first identifier information may comprise identifier information of the third node, and the direct forwarding path related information may comprise availability information of a direct forwarding path between the second node and the third node.

[0022] According to an exemplary embodiment, the first message may be transmitted after a UE handover to the second node. The direct forwarding path related information may comprise the identifier information of the at least one candidate node and the availability information of the direct forwarding path between the second node and the at least one candidate node.

[0023] According to an exemplary embodiment, the first identifier information may comprise a packet data unit (PDU) session identifier and / or a quality of service (QoS) flow identifier, and the data forwarding proposal related information may be a data forwarding proposal. The data forwarding proposal related information may comprise a PDU session identifier and / or QoS identifier accepted by the second node, and a data forwarding proposal and a data forwarding address related to the PDU session identifier and / or QoS identifier accepted by the second node.

[0024] According to an exemplary embodiment, the method may further comprise: receiving a third message transmitted by the first node. The third message may comprise the data forwarding proposal related information associated with the at least one candidate node for the UE handover.

[0025] According to an exemplary embodiment, the third message may be transmitted by the first node after an early data forwarding procedure, transmitted by the first node after a measurement report reported by a UE is received, or transmitted by the first node after a successful handover of the UE to the second node.

[0026] According to an exemplary embodiment, the first message may comprise an SN Addition Request message, an SN Modification Request message or a Handover Request message, and the second message may comprise an SN Addition Request Acknowledge message, an SN Modification Request Acknowledge message or a Handover Request Acknowledge message.

[0027] According to an exemplary embodiment, the third message may be transmitted through an XnAP message or Data Forwarding Information Transfer message.

[0028] According to another aspect of the present disclosure, a method performed by a user equipment (UE) in a wireless communication system is provided. The method may comprise: transmitting a layer 1 or layer 3 measurement report to a first node. Here, a first message may be transmitted by the first node to a second node, the first message comprises first identifier information and first information related to data forwarding, and the first information comprises information for requesting a direct forwarding path or a data forwarding proposal. Here, a second message from the second node may be received by the first node, the second message comprises second information related to data forwarding of the second node, and the second information comprises direct forwarding path related information or data forwarding proposal related information.

[0029] According to an exemplary embodiment, the first identifier information may comprise identifier information of at least one candidate node for a UE handover. The direct forwarding path related information may comprise the identifier information of the at least one candidate node and availability information of a direct forwarding path between the second node and the at least one candidate node.

[0030] According to an exemplary embodiment, the method may further comprise: performing a UE handover to a third node. The first message may be transmitted by the first node after the UE handover to the third node. The first identifier information may comprise identifier information of the third node, and the direct data forwarding path related information may comprise availability information of a direct forwarding path between the second node and the third node.

[0031] According to an exemplary embodiment, the method may further comprise: performing a UE handover to the second node. The first message may be transmitted by the first node after the UE handover to the second node. The first identifier information may comprise the identifier information of the at least one candidate node for the UE handover. The direct forwarding path related information may comprise the identifier information of the at least one candidate node and the availability information of the direct forwarding path between the second node and the at least one candidate node.

[0032] According to an exemplary embodiment, a secondary node (SN) Change Required message from a source node may be received by the first node. The SN Change Required message may comprise: the identifier information of the at least one candidate node for the UE handover and availability information of a direct forwarding path between the source node and the at least one candidate node. The second node may be a node in the at least one candidate node.

[0033] According to an exemplary embodiment, the first identifier information may comprise a packet data unit (PDU) session identifier and / or a quality of service (QoS) flow identifier, and the data forwarding proposal related information may be a data forwarding proposal. The data forwarding proposal related information may comprise a PDU session identifier and / or QoS identifier accepted by the second node, and a data forwarding proposal and data forwarding address related to the PDU session identifier and / or QoS identifier accepted by the second node.

[0034] According to an exemplary embodiment, the method may further comprise: transmitting, by the first node, a third message to the second node. The third message may comprise the data forwarding proposal related information associated with the at least one candidate node for the UE handover. The third message may be transmitted by the first node after an early data forwarding procedure.

[0035] According to an exemplary embodiment, the third message may be transmitted by the first node to a target node for a UE handover. The third message may comprise the data forwarding proposal related information associated with the at least one candidate node for the UE handover. The third message may be transmitted by the first node after the layer 1 or layer 3 measurement report is received by the first node, or transmitted by the first node after a successful handover of the UE to the target node.

[0036] According to an exemplary embodiment, the first message may comprise an SN Addition Request message, an SN Modification Request message or a Handover Request message, and the second message may comprise an SN Addition Request Acknowledge message, an SN Modification Request Acknowledge message or a Handover Request Acknowledge message.

[0037] According to an exemplary embodiment, the third message may be transmitted through an XnAP message or Data Forwarding Information Transfer message.

[0038] According to another aspect of the present disclosure, a first node, a second node and a user equipment (UE) that perform the above methods are further disclosed.

[0039] According to another aspect of the present disclosure, a computer readable storage medium is further disclosed. The computer readable storage medium stores a computer executable instruction. When the computer executable instruction is executed by a processor, the processor may perform the above methods performed by the first node, the second node or the UE.

[0040] According to the implementations of the present disclosure, it is possible to support more mobility scenarios, especially the implementation of a data forwarding mechanism in a continuous mobility scenario, thereby ensuring the service quality and lower data interrupt latency in the corresponding scenario.

[0041] FIG. 1 is an exemplary system architecture of a system architecture evolution according to the present disclosure;

[0042] FIG. 2 is an exemplary system architecture according to embodiments of the present disclosure;

[0043] FIG. 3 is a schematic flowchart of a data forwarding scheme according to an exemplary embodiment of the present disclosure;

[0044] FIG. 4a is a schematic flowchart of a data forwarding scheme in dual connectivity when an SN change or handover occurs without an MN change according to an exemplary embodiment of the present disclosure;

[0045] FIG. 4b is a schematic flowchart of a data forwarding scheme in dual connectivity when an SN change or handover occurs without an MN change according to an exemplary embodiment of the present disclosure;

[0046] FIG. 4c is a schematic flowchart of a data forwarding scheme in dual connectivity when an SN change or handover occurs without an MN change according to an exemplary embodiment of the present disclosure;

[0047] FIG. 5 is a schematic flowchart of a data forwarding scheme in a continuous inter-CU / gNB LTM or CHO scenario according to an exemplary embodiment of the present disclosure;

[0048] FIG. 6 is a flow block diagram of a method performed by a first node in a wireless communication system according to an exemplary embodiment of the present disclosure;

[0049] FIG. 7 is a flow block diagram of a method performed by a second node in a wireless communication system according to an exemplary embodiment of the present disclosure;

[0050] FIG. 8 is a flow block diagram of a method performed by a user equipment (UE) in a wireless communication system according to an exemplary embodiment of the present disclosure; and

[0051] FIG. 9 illustrates an exemplary structure of each node of the present disclosure.

[0052] Exemplary figures discussed below and various embodiments for describing the principles of the present disclosure in this patent document are only for illustration and should not be interpreted as limiting the scope of the disclosure in any way. Those skilled in the art will understand that the principles of the present disclosure can be implemented in any suitably arranged system or device.

[0053] Fig. 1 is an exemplary system architecture 1000 of system architecture evolution (SAE). User equipment (UE) 1001 is a terminal device for receiving data. An evolved universal terrestrial radio access network (E-UTRAN) 1002 is a radio access network, which includes a macro base station (eNodeB / NodeB) that provides UE with interfaces to access the radio network. A mobility management entity (MME) 1003 is responsible for managing mobility context, session context and security information of the UE. A serving gateway (SGW) 1004 mainly provides functions of user plane, and the MME 1003 and the SGW 1004 may be in the same physical entity. A packet data network gateway (PGW) 1005 is responsible for functions of charging, lawful interception, etc., and may be in the same physical entity as the SGW 1004. A policy and charging rules function entity (PCRF) 1006 provides quality of service (QoS) policies and charging criteria. A general packet radio service support node (SGSN) 1008 is a network node device that provides routing for data transmission in a universal mobile telecommunications system (UMTS). A home subscriber server (HSS)1009 is a home subsystem of the UE, and is responsible for protecting user information including a current location of the user equipment, an address of a serving node, user security information, and packet data context of the user equipment, etc.

[0054] Fig. 2 is an exemplary system architecture 2000 according to various embodiments of the present disclosure. Other embodiments of the system architecture 2000 can be used without departing from the scope of the present disclosure.User equipment (UE) 2001 is a terminal device for receiving data. A next generation radio access network (NG-RAN) 2002 is a radio access network, which includes a base station (a gNB or an eNB connected to 5G core network 5GC, and the eNB connected to the 5GC is also called ng-gNB) that provides UE with interfaces to access the radio network. An access control and mobility management function entity (AMF) 2003 is responsible for managing mobility context and security information of the UE. A user plane function entity (UPF) 2004 mainly provides functions of user plane. A session management function entity SMF 2005 is responsible for session management. A data network (DN) 2006 includes, for example, services of operators, access to the Internet and service of third parties.

[0055] For the convenience of description, the terms involved in the following description of the embodiments of the present disclosure and their explanations are provided as follows:

[0056] 1. LTM: L1 / L2 Triggered Mobility.

[0057] 2. SCPAC: subsequent CPAC, Subsequent Conditional PSCell Addition or Change, which is a continuous (or subsequent) conditional primary secondary cell addition or change. After a PSCell addition (or increase), a PSCell change (or alteration), a primary cell (PCell) change or a secondary cell group SCG release, a conditional PSCell addition procedure or a conditional PSCell change (or alteration) procedure is performed based on the pre-configured subsequent CPAC configuration of the candidate PSCell, without reconfiguring or restarting the Conditional PSCell Change (CPC) and / or the Conditional PSCell Addition (CPA).

[0058] 3. CHO: Conditional Handover, for example, a handover procedure which is performed only when an evaluation condition is satisfied. The network side preconfigures resources for a plurality of candidate cells (the plurality of candidate cells may be positioned in the same base station or may be positioned in different base stations) based on a measurement report of the UE, and transmits the resource and measurement configuration corresponding to each candidate cell to the UE in advance. The UE saves the corresponding resource of each candidate cell and performs a measurement to perform a condition evaluation. If the UE finds a candidate cell satisfying the condition, the UE leaves the source cell, accesses the candidate cell (e.g., a target cell) satisfying the condition, and applies the corresponding configuration after the successful access. Then, the UE releases all configurations of other candidate cells, and the base station (or node) to which the target cell belongs notifies the source base station (or node) of which candidate cell is selected. Then, the network side performs the operation of releasing all the configurations of the other candidate cells.

[0059] 4. AMF: Access and Mobility Management Function, which is a network element in a 5G core network and is responsible for the access and mobility management of a 5G base station. The 5G base station and the AMF are connected through an NG-C interface.

[0060] 5. NG-RAN node: New Generation Radio Access Network, for example, a 5G base station, including a gNB or an ng-eNB.

[0061] 6. gNB (next Generation Node B): next Generation Node B, for example, a 5G NR (New Radio) base station.

[0062] 7. gNB-DU: a gNB Distributed Unit, which has functions such as a Radio Link Control (RLC) protocol, a Medium Access Control (MAC) protocol and a Physical Layer (PHY) protocol.

[0063] 8. gNB-CU: a gNB Central Unit, which has functions such as a Radio Resource Control (RRC) protocol, a Service Data Adaptation Protocol (SDAP) and a Packet Data Convergence Protocol (PDCP).

[0064] 9. NR-DC: NR-NR Dual Connectivity, or a next generation radio access network dual connectivity.

[0065] 10. MN: Master Node.

[0066] 11. SN: Secondary Node.

[0067] 12. MCG: Master Cell Group, which is a group of serving cells associated with a master node in a radio access network dual connectivity (MR-DC). The MCG includes an SpCell (specifically, the primary cell (PCell) of the master cell group), and optionally includes one or more secondary cells (SCells).

[0068] 13. SCG: Secondary Cell Group, which is a group of serving cells associated with a secondary node in the radio access network dual connectivity (MR-DC). The SCG includes an SpCell (specifically, the primary cell (PSCell) of the secondary cell group), and optionally includes one or more secondary cells (SCells).

[0069] 14. SpCell: the primary cell of a master cell group or a secondary cell group.

[0070] 15. PSCell (SpCell of a secondary cell group): a primary secondary cell, or the primary cell of a secondary cell group.

[0071] 16. PCell (SpCell of a master cell group): a primary cell, or the primary cell of a master cell group.

[0072] 17. MR-DC (Multi-Radio Dual Connectivity): the dual connectivity between an E-UTRA node and an NR node, or between an NR node and an NR node.

[0073] It should be understood that the message names in the present disclosure are examples only and other names may be adopted. The information transmitted between interfaces may be implemented by separately defining a new message, or by adding a new information element (IE) into an existing message in an existing interface specification.

[0074] Exemplary embodiments of the present disclosure are further described below with reference to the accompanying drawings.

[0075] The text and drawings are provided as examples only to help understand the present disclosure. They should not be interpreted as limiting the scope of the present disclosure in any way. Although certain embodiments and examples have been provided, based on the disclosure herein, it will be apparent to those skilled in the art that changes may be made to the illustrated embodiments and examples without departing from the scope of the present disclosure.

[0076] In order to reduce the latency caused by traffic service interrupt during a UE mobility procedure and to ensure the reliability of the UE mobility, L1 / L2 triggered mobility (LTM) and a continuous (or subsequent) CPAC (Subsequent CPAC, S-CPAC or SCPAC) are proposed. The main process of LTM is that, based on the Layer 1 (L1) measurement report reported by the UE, the gNB-DU decides a target cell and transmits a mobility command to the UE. Compared with the previous handover procedure performed based on an L3 measurement report, since the L3 measurement report is obtained based on a re-processing such as linear averaging on the L1 measurement, the mobility command can be obtained more quickly in the handover based on the L1 measurement report, and the UE can receive this command more quickly through the L2 MAC CE of the gNB-DU. In addition, for the access procedure of the UE, a procedure without a traditional RACH (random access channel) access (i.e., a rach-less procedure) can be applied, thereby further reducing the latency caused by traffic service interrupt of the UE in the mobility procedure. For an SCPAC procedure, when the UE evaluates a candidate cell, the source SN at the network side may forward early data to other potential candidate / target SNs, so as to reduce the retransmission due to the interruption of partial data occurring when the UE leaves the source SN to access a candidate / target SN.

[0077] In some examples, for the SCPAC procedure or a continuous (subsequent) LTM procedure in a situation where an SN change (handover) occurs without an MN change (subsequent Inter-SN LTM procedure without MN change, which may be hereinafter referred to as a continuous Inter-SN LTM procedure without MN change), during the UE leaves (disconnects from) a secondary cell of the source SN and accesses a secondary cell of the candidate / target SN, since the UE disconnects from the source SN and is intended to access the candidate / target SN, an interrupt will occur for the data transmission from the source SN to the UE. The data reception and transmission can be recovered after the UE successfully accesses the candidate / target SN.

[0078] In some examples, when the UE performs an evaluation on candidate cells, the source SN may transmit data to the UE and forward early data to other candidate / target SNs at the same time. For the data successfully received by the UE from the source SN during this procedure, the source SN may notify the other candidate SNs of the state of the data, so that the candidate / target SNs may discard the data. When the UE determines that a certain candidate cell satisfies the execution conditions and is about to perform a handover, the UE disconnects from the source SN. Thus, the data transmission from the source SN to the UE is interrupted and the source SN will not receive feedback from the UE. However, since the interrupted data is also transmitted to the other candidate / target SNs, the interrupted data is of course transmitted to the candidate / target SN selected by the UE. After the UE successfully accesses the candidate / target SN, the candidate / target SN can transmit the data to the UE in time. This avoids that the interrupted data is retransmitted from the node responsible for the data plane function in a core network to the candidate / target SN and then transmitted to the UE by the candidate / target SN.

[0079] As can be seen from the above, the early data forwarding mechanism can effectively avoid the data retransmission and reduce the interrupt latency. Similarly, when the UE successfully accesses the candidate / target SN but does not complete a path switch procedure with the core network, the source SN will still receive the data transmitted from the node responsible for the data plane function in the core network. Accordingly, the source SN can also forward the late data to the target SN, which also reduces the data retransmission and the interrupt latency. Here, the data forwarding schemes involved in the early data forwarding and late data forwarding can be divided into direct data forwarding and indirect data forwarding. In the SCPAC procedure or continuous Inter-SN LTM procedure without MN change, if the MN knows that there is a direct user plane connection between the source SN and the candidate / target SN, the data forwarding address received from the candidate / target SN can be directly transmitted to the source SN. Then, the source SN can directly forward the data to the candidate / target SN, thereby realizing the direct data forwarding. If the MN knows that there is no direct user plane connection between the source SN and the candidate / target SN, the MN may allocate a data forwarding address and notify the source SN of the data forwarding address. The source SN then forwards the data to the MN, which then forwards the data to the candidate / target SN, thereby realizing the indirect data forwarding.

[0080] Here, the above-mentioned early data forwarding may refer to the forwarding of the data to be transmitted to the UE that is received by the source SN from the core network before the UE successfully switches from the source SN to the selected candidate / target SN. The above-mentioned late data forwarding may refer to the forwarding of the data to be transmitted to the UE that is received by the source SN from the core network after the UE successfully switches from the source SN to the selected candidate / target SN but before the UE completes the path switch with the core network.

[0081] In the SCPAC procedure or the continuous Inter-SN LTM procedure without MN change, a scenario where continuous handover may occur due to a continuous movement of the UE needs to be considered. In such scenario, the role of each candidate / target SN may change. In a possible scenario, after the UE successfully switches to a candidate / target SN, the candidate / target SN will change from the role of the candidate / target SN in a previous round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change to the role of the source SN in a next round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change. For each round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the direct data forwarding mechanism or the indirect data forwarding mechanism needs to work.

[0082] In the SCPAC procedure or the continuous Inter-SN LTM procedure without MN change, the direct data forwarding mechanism between the source SN and the candidate / target SN cannot support the proper operation in each round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change.

[0083] The present disclosure proposes a data forwarding scheme for the above mobility scenarios, and improves the existing data forwarding scheme, especially the direct data forwarding mechanism. Meanwhile, the data forwarding scheme proposed in the present disclosure can be applied to more mobility scenarios, including, but not limited to, the continuous Inter-SN LTM procedure without MN change initiated by the MN or SN.

[0084] FIG. 3 is a flowchart of a data forwarding scheme, especially a data forwarding scheme of a UE when an SN change or handover occurs in a dual connectivity scenario, according to an exemplary embodiment of the present disclosure. The procedures are as follows:

[0085] Procedure 3-1: In a preparation phase of an SCPAC procedure or a continuous Inter-SN LTM procedure without MN change, a master node MN performs an SN addition procedure with each candidate / target secondary node SN, and requests the candidate / target SN(s) to establish resource of a candidate primary secondary cell PSCell. The MN may further make a data forwarding request to each candidate / target SN, and request the candidate / target SN to provide availability information of a direct forwarding path (Direct Forwarding Path Availability) in the user plane connection between the candidate / target SN and the source SN. Here, the availability information of the direct forwarding path is used to indicate whether there is an available direct forwarding path between SNs (which may include the candidate / target SN and the source SN). Then, the candidate / target SN provides a data forwarding address, the direct forwarding path availability information, etc. to the MN.

[0086] Procedure 3-2-1: If the MN knows that there is an available direct forwarding path in the user plane connection between the source SN and the candidate / target SN, the MN directly forwards the data forwarding address provided by the candidate / target SN to the source SN. Next, in a data forwarding phase, the source SN directly forwards the data to the candidate / target SN according to the data forwarding address provided by the candidate / target SN and forwarded by the MN, thus implementing the data forwarding corresponding to the direct data forwarding mechanism.

[0087] Procedure 3-2-2: If the MN knows that there is no available direct forwarding path in the user plane connection between the source SN and the candidate / target SN, the MN allocates a data forwarding address and transmits the data forwarding address to the source SN. Next, in the data forwarding phase, the source SN forwards the data to the MN according to the data forwarding address allocated by the MN to the source SN, and then forwards the data to the candidate / target SN, thus implementing the data forwarding corresponding to the indirect data forwarding mechanism.

[0088] In combination with the analysis for the process shown in FIG. 3, for example, in an SCPAC scenario (or procedure) or in a continuous Inter-SN LTM without MN change scenario (or procedure), the UE may continuously move, and may accordingly generate handovers between different SNs, and thus the role of each SN may change. For example, an SN, after being selected by the UE, is changed from the candidate / target SN in a previous round of SCPAC or continuous Inter-SN LTM procedure without MN change to the source SN in a next round of SCPAC or continuous Inter-SN LTM procedure without MN change. In each round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, in order to enable the direct data forwarding, the MN needs to know whether there is an available direct forwarding path in the user plane connection between the current source SN and the candidate / target SN, and then performs a proper action, for example, whether the MN forwards the data forwarding address provided by the candidate / target SN to the source SN, or the MN allocates the data forwarding address and notifies the source SN of the data forwarding address.

[0089] The data forwarding scheme when an SN change or handover occurs without an MN change in dual connectivity according to an exemplary embodiment of the present disclosure is described below in combination with FIGS. 4a-4c.

[0090] In an embodiment shown in FIG. 4a, in the resource preparation phase of the SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the MN performs an SN addition preparation procedure (S-NG-RAN node Addition Preparation procedure) with each candidate / target SN, requesting each candidate / target SN to allocate dual connectivity resources, which may include resources of a PSCell, for the UE. In this resource preparation phase, the MN may respectively request, from each candidate / target SN, the availability information of a direct forwarding path between this candidate / target SN and each candidate / target SN in the remaining candidate / target SNs except this candidate / target SN. The request may specifically include, but not limited to the following procedures:

[0091] Procedure 4a-1: The MN may request relevant information by transmitting an SN addition request (S-Node Addition Request) message to each candidate / target SN (e.g., a candidate / target SN1, a candidate / target SN2, and other candidate / target SNs as shown in the figure). Here, the S-Node Addition Request message may carry one or more of the following information:

[0092] - Multiple Candidate / Target S-NG-RAN Node List

[0093] ▷Here, in an embodiment, the list information contains ID information of all other candidate / target SNs except the candidate / target SN receiving the S-Node Addition Request message, wherein all the other candidate / target SNs also include the source SN (corresponding to the candidate / target SN0 in the figure) configured as a candidate / target SN. For example, the ID information of all the other candidate / target SNs includes the ID information of the source SN and the ID information of all other candidate / target SNs except the source SN and the candidate / target SN receiving the S-Node Addition Request message. Here, the ID information of each candidate / target SN may be a Global NG-RAN Node ID, and the Global NG-RAN Node ID may include a Global gNB ID or Global ng-eNB ID.

[0094] ▷In a specific example, 8 candidate / target SNs in total are configured. If the source SN is also configured as a candidate / target SN, the 8 candidate / target SNs include the source SN. In a situation where the MN transmits the S-Node Addition Request message to the candidate / target SN1, the Multiple Candidate / Target S-NG-RAN Node List in the S-Node Addition Request message includes the ID information of all other candidate / target SNs except the candidate / target SN1, wherein the ID information of all the other candidate / target SNs includes the ID information of the source SN.

[0095] - Direct Forwarding Path Request Indication, which may be used to make a request based on the IDs of all the candidate / target SNs contained in the Multiple Candidate / Target S-NG-RAN Node List, or may be used to indicate a request respectively based on the ID of each candidate / target SN in a one-to-one corresponding manner so as to avoid an information overlap. Here, the Direct Forwarding Path Request Indication is used to request, from the candidate / target SN, the availability information of the direct forwarding path between the candidate / target SN receiving the S-Node Addition Request message and other candidate / target SNs (candidate / target SNs contained in the Multiple Candidate / Target S-NG-RAN Node List) except the candidate / target SN receiving the S-Node Addition Request message.

[0096] Procedure 4a-2: After receiving the S-Node Addition Request message, each candidate / target SN performs a corresponding resource allocation and determines whether there is an available direct forwarding path between the candidate / target SN itself and each of the other candidate / target SNs, and then replies an SN addition request acknowledge (S-Node Addition Request Acknowledge) message to the MN. Here, the S-Node Addition Request Acknowledge message may carry one or more of the following information:

[0097] - Direct Forwarding Path Information List, containing the availability information of a direct forwarding path between the candidate / target SN receiving the S-Node Addition Request message and each candidate / target SN in all other candidate / target SNs except the candidate / target SN receiving the S-Node Addition Request message, and the ID information of the candidate / target SN corresponding to the availability information of each direct forwarding path.

[0098] ▷Here, the Direct Forwarding Path Information List contains the ID information of all or some of the other candidate / target SNs except the candidate / target SN receiving the S-Node Addition Request message (may contain the ID information of the source SN and the ID information of the other remaining candidate / target SNs). Here, the ID information of each candidate / target SN (Candidate / Target S-NG-RAN Node ID) may be represented by a Global NG-RAN Node ID, and the Global NG-RAN Node ID may contain a Global gNB ID or Global ng-eNB ID.

[0099] ▷Here, in this embodiment, the direct forwarding path availability information is used to indicate the availability information of the direct forwarding path between the candidate / target SN receiving the S-Node Addition Request message and the candidate / target SN indicated by the ID information of each candidate / target SN. For example, the direct forwarding path availability information is used to indicate whether the direct forwarding path between a current candidate / target SN (e.g., the candidate / target SN receiving the S-Node Addition Request message) and the candidate / target SN indicated by the ID information of each candidate / target SN is available. Here, in an embodiment, the direct forwarding path availability information may directly and explicitly indicate that the direct forwarding path is available or unavailable. Alternatively, in another embodiment, the direct forwarding path availability information may only indicate that the direct forwarding path is available, and accordingly, when the IE corresponding to the direct forwarding path availability information does not exist, it may be implicitly indicated that the direct forwarding path is unavailable. Alternatively, in another embodiment, the direct forwarding path availability information may only indicate that the direct forwarding path is unavailable, and accordingly, when the IE corresponding to the direct forwarding path availability information does not exist, it may be implicitly indicated that the direct forwarding path is available.

[0100] In some embodiments, after the MN completes the above SN addition preparation procedure with all the candidate / target SNs, the information on whether there is an available direct forwarding path between any two candidate / target SNs (including the current source SN, e.g., the candidate SN0 shown in the figure) is acquired by the MN. Then, the MN stores the information and performs a proper action based on the information.

[0101] Procedure 4a-4: The MN may forward the data forwarding address allocated by a candidate / target SN (or the data forwarding address provided by the candidate / target SN to the MN) to the source SN through an Xn-U Address Indication message, in the case that the direct forwarding path between the source SN and the corresponding candidate / target SN is available. Alternatively, the MN may transmit the data forwarding address allocated by the MN to the source SN through the Xn-U Address Indication message, in the case that there is no direct forwarding path available between the source SN and the corresponding candidate / target SN.

[0102] Procedure 4a-5: If the UE selects and accesses the candidate / target SN1 to perform a round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the UE switches from the source SN to the candidate / target SN1. Then, in the next round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the role of the source SN will become the candidate SN0, and the role of the candidate / target SN1 will become the source SN. Since the MN have stored the information on whether there is an available direct forwarding path between any two candidate / target SNs in the initial resource preparation phase, it knows whether there is an available direct forwarding path between any two candidate / target SNs, and thus can perform a corresponding action.

[0103] Procedure 4a-6: The MN forwards, to the current source SN (e.g., the candidate / target SN1) through the Xn-U Address Indication message, the data forwarding address allocated by other candidate / target SNs (any candidate / target SNs except the candidate / target SN1) (alternatively, the data forwarding address provided by other candidate / target SNs to the MN), in the case that the direct forwarding path between the source SN and the corresponding candidate / target SN is available. Alternatively, the MN may transmit the data forwarding address allocated by the MN to the source SN through the Xn-U Address Indication message, in the case that there is no direct forwarding path available between the source SN and the corresponding candidate / target SN. In this way, the proper operation of the direct data forwarding mechanism is ensured.

[0104] In another embodiment of the present disclosure, if the S-CPAC Request Information IE in the Conditional PSCell Addition Information Request IE contained in the S-Node Addition Request message includes a Direct Forwarding Path Information Request IE set to "true" the S-NG-RAN node should (if supported) set the Direct Forwarding Path Availability IE as "Direct Path Available" in the Direct Forwarding Path Information List IE in the S-Node Addition Request Acknowledge message, if a direct forwarding path between the S-NG-RAN node and another candidate SN node indicated by a Target S-NG-RAN node ID IE (Target S-NG-RAN Node ID) is available. The M-NG-RAN node should (if supported) consider or store the information that there is a direct forwarding path between the S-NG-RAN node and the other candidate / target S-NG-RAN node.

[0105] In another embodiment of the present disclosure, if the S-CPAC Request Information IE in the Conditional PSCell Addition Information Request IE contained in the S-Node Addition Request message includes an S-CPAC Multiple Target S-NG-RAN Node List IE, the S-NG-RAN node should (if supported by the S-NG-RAN node) set the Direct Forwarding Path Availability IE to "Direct Path Available" in the Direct Forwarding Path Information List IE in the S-Node Addition Request Acknowledge message, in the case that a direct forwarding path between the S-NG-RAN node and another candidate SN node indicated by a Target S-NG-RAN node ID IE (Target S-NG-RAN Node ID) is available. The M-NG-RAN node should (if supported) consider or store the information that there is a direct forwarding path between the S-NG-RAN node and the other candidate / target S-NG-RAN node.

[0106] In another embodiment shown in FIG. 4b, in the resource preparation phase of the SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the MN can obtain, by performing the SN addition preparation procedure (S-NG-RAN node Addition Preparation Procedure) with each candidate / target SN, the information on whether there is an available direct forwarding path between each candidate / target SN and the source SN. Then, the MN can perform a proper action based on the information. Specifically, the MN may forward the data forwarding address allocated by another candidate / target SN to the source SN through the Xn-U Address Indication message, in the case that the direct forwarding path between the source SN and the corresponding candidate / target SN is available. Alternatively, the MN may transmit the data forwarding address allocated by the MN to the source SN through the Xn-U Address Indication message, in the case that there is no direct forwarding path available between the source SN and the corresponding candidate / target SN. In this way, the proper operation of the direct data forwarding mechanism in the initial first round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change is ensured.

[0107] However, if the UE selects and accesses the candidate / target SN1 (i.e., the UE switches from the source SN to the candidate / target SN1) after completing the first round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, in the next round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the role of the source SN will become the candidate / target SN0, and the role of the candidate / target SN1 will become the source SN. At this time, for the information on whether there is an available direct forwarding path between the current source SN (e.g., the candidate / target SN1) and another candidate / target SN (including the candidate / target SN0) that the MN needs to know, since the MN has performed the SN addition preparation procedure with each candidate / target SN in the first round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the MN knows the information on whether there is an available direct forwarding path between any two candidate / target SNs (including the current source SN (e.g., the candidate / target SN1) and the other candidate / target SN (e.g., including the candidate / target SN0)). Further, an SN modification procedure performed between the MN and the corresponding candidate / target SN may be considered, which is used to query whether the direct forwarding path between the corresponding candidate / target SN and the current source SN is available. This procedure may include, but not limited to, the following procedures:

[0108] Procedure 4b-1: The MN may transmit an SN modification request (S-Node Modification Request) message to the corresponding candidate / target SNs (as shown in the figure). In this procedure, the MN may not transmit this SN request message to the previous source SN (e.g., the candidate / target SN0) to query the relevant information on whether the direct forwarding path between the previous source SN and the current source SN (e.g., the candidate / target SN1) is available, because the MN has learned the relevant information between the current source SN (e.g., the candidate / target SN1) and the previous source SN (e.g., the candidate / target SN0) in the previous SN addition preparation procedure. Here, the SN Modification Request message may carry one or more of the following information:

[0109] - ID Information of the Source SN, which may be specifically represented by a Global NG-RAN Node ID, which may include a Global gNB ID or Global ng-eNB ID. Here, the ID information of the source SN is used to indicate the ID of the SN to which the UE currently connects or accesses for the current round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change.

[0110] - Direct Forwarding Path Request Indication, which is based on the ID Information of the source SN. Here, the Direct Forwarding Path Request Indication is used to request, from the candidate / target SN, the availability information of the direct forwarding path between the candidate / target SN and the source SN indicated by the ID information of the Source SN.

[0111] Procedure 4b-2: Each candidate / target SN determines whether there is an available direct forwarding path between the candidate / target SN itself and the source SN indicated by the ID information of the Source SN upon receiving the S-Node Modification Request message, and then replies an SN modification request acknowledge (S-Node Modification Request Acknowledge) message to the MN. Here, the S-Node Modification Request Acknowledge message may carry one or more of the following information:

[0112] - Direct Forwarding Path Availability Information, which in this embodiment may be used to indicate the availability information of the direct forwarding path between this candidate / target SN (e.g., the candidate / target SN receiving the above SN Modification Request message) and the source SN indicated by the ID information of the source SN. For example, the direct forwarding path availability information is used to indicate whether the direct forwarding path between this candidate / target SN and the current source SN is available. In an embodiment, the direct forwarding path availability information may directly and explicitly indicate that the direct forwarding path is available or unavailable. Alternatively, in another embodiment, the direct forwarding path availability information may only indicate that the direct forwarding path is available, and accordingly, when the IE corresponding to the direct forwarding path availability information does not exist, it may be implicitly indicated that the direct forwarding path is unavailable. Alternatively, in another embodiment, the direct forwarding path availability information may only indicate that the direct forwarding path is unavailable, and accordingly, when the IE corresponding to the direct forwarding path availability information does not exist, it may be implicitly indicated that the direct forwarding path is available.

[0113] In some embodiments, after the MN and the corresponding candidate / target SN complete the above SN modification procedure, the information on whether there is an available direct forwarding path between the corresponding candidate / target SN (which may not include the candidate SN0) and the current source SN is acquired by the MN. Then, the MN stores the information and performs a corresponding proper action based on the information.

[0114] Procedure 4b-4: The MN may forward the data forwarding address allocated by another candidate / target SN (or the data forwarding address provided by the candidate / target SN to the MN) to the source SN through an Xn-U Address Indication message, in the case that the direct forwarding path between the source SN and the corresponding candidate / target SN is available. Alternatively, the MN may transmit the data forwarding address allocated by the MN to the source SN through the Xn-U Address Indication message, in the case that there is no direct forwarding path available between the source SN and the corresponding candidate / target SN.

[0115] When the UE selects and accesses another candidate / target SN (e.g., the UE switches to the candidate SN2), for the next round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the role of the candidate SN2 will become the source SN, and the roles of the other SNs will become the candidate SNs. At this time, the MN needs to know the information on whether there is an available direct forwarding path between the current source SN (e.g., the candidate / target SN2) and the other candidate / target SN. Similarly, the MN may use the above scheme (e.g., referring to the description of procedures 4b-1 and 4b-2) to respectively trigger an SN modification procedure with a corresponding candidate / target SN (similarly, SN0 and SN1 may be excluded because the MN already knows the availability information of the direct forwarding paths from SN0 and SN1 to SN2), to query the information on whether there is an available direct forwarding path between each candidate / target SN and the current source SN (e.g., the candidate / target SN2). After the MN and the corresponding candidate / target SN (e.g., SN0 and SN1 may be excluded because the MN already knows the availability information of the direct forwarding paths from SN0 and SN1 to SN2) complete the above SN modification procedure, the information on whether there is an available direct forwarding path between the corresponding candidate / target SN and the current source SN (e.g., the candidate / target SN2) is acquired by the MN. Then, the MN stores the information and performs a corresponding proper action based on the information. For example, the MN may forward the data forwarding address allocated by another candidate / target SN (or the data forwarding address provided by the other candidate / target SN to the MN) to the source SN (e.g., the candidate / target SN2) through the Xn-U Address Indication message, in the case that the direct forwarding path between the current source SN (e.g., the candidate / target SN2) and the corresponding candidate / target SN is available. Alternatively, the MN may transmit the data forwarding address allocated by the MN to the current source SN (e.g., the candidate / target SN2) through the Xn-U Address Indication message, in the case that there is no direct forwarding path available between the current source SN (e.g., the candidate / target SN2) and the corresponding candidate / target SN. In this way, the proper operation of the direct data forwarding mechanism in each round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change is ensured.

[0116] In another embodiment of the present disclosure, if the Source S-NG-RAN Node ID IE (or Source S-Node ID) is contained in the S-Node Modification Request message, the S-NG-RAN node should (if supported) use the Source S-NG-RAN Node ID IE to determine the availability of a direct data path with a specified target S-NG-RAN node, and, if the direct data forwarding path is available, include the Direct Forwarding Path Availability IE set as "Direct Path Available" in the S-Node Addition Moditication Acknowledge message. The M-NG-RAN node should (if supported) considere or store the information that there is a direct forwarding path between the S-NG-RAN node and the source S-NG-RAN node.

[0117] In another embodiment of the present disclosure, the high signaling overhead that may exist in the embodiment corresponding to FIG. 4b can be further reduced. In the embodiment corresponding to FIG. 4b, the MN needs to transmit an S-Node Modification Request to each corresponding candidate / target SN to query the information on whether there is a direct forwarding path with the current source SN. Therefore, the signaling overhead of the interaction between the MN and the SN may be large. In order to reduce the signaling overhead, the MN may only transmit the S-Node Modification Request to the current source SN to query the information on whether there is a direct forwarding path between the current source SN and other corresponding candidate / target SNs.

[0118] As shown in FIG. 4c, the interaction among the MN, the candidate / target SN0 and the candidate / target SN1 is taken as an example. If the UE selects and accesses the candidate / target SN1 (i.e., the UE switches from the source SN to the candidate / target SN1) to complete the first round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, in the next round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the role of the source SN will become the candidate / target SN0, and the role of the candidate / target SN1 will become the source SN. At this time, the MN needs to know the information on whether there is an available direct forwarding path between the current source SN (e.g., the candidate / target SN1) and the corresponding candidate / target SN. The SN modification procedure between the MN and the current source SN may be used to query the relevant information on whether the direct forwarding path between the current source SN and each candidate / target SN is available. The procedure may include, but not limited to, the following procedures:

[0119] Procedure 4c-1: The MN may transmit an SN Modification Request message to the current source SN (e.g., the candidate / target SN1). Here, the SN Modification Request message may carry one or more of the following information:

[0120] - Multiple Candidate / Target S-NG-RAN Node List

[0121] ▷Here, in an embodiment, the list contains the ID information of all corresponding candidate / target SNs except the source SN receiving the SN Modification Request message. The ID information of each candidate / target SN may be represented by a Global NG-RAN Node ID, and the Global NG-RAN Node ID may contain a Global gNB ID or Global ng-eNB ID.

[0122] - Direct Forwarding Path Request Indication, which may be used to make a request based on the IDs of all the candidate / target SNs contained in the Multiple Candidate / Target S-NG-RAN Node List, or may be used to indicate a request respectively based on the ID of each candidate / target SN in a one-to-one corresponding manner so as to avoid an information overlap. Here, the Direct Forwarding Path Request Indication is used to request, from the source SN receiving the SN Modification Request message, the availability information of the direct forwarding path between the source SN and each of the other candidate / target SNs (candidate / target S-Nodes contained in the Multiple Candidate / Target S-NG-RAN Node List).

[0123] Procedure 4c-2: After receiving the S-Node Modification Request message, the current source SN determines whether there is an available direct forwarding path between the current source SN and each of the other candidate / target SNs, and then replies an S-Node Modification Request Acknowledge message to the MN. Here, the S-Node Modification Request Acknowledge message may carry one or more of the following information:

[0124] - Direct Forwarding Path Information List, containing the direct forwarding path availability information between the source SN receiving the S-Node Modification Request message and each candidate / target SN, and the ID information of the candidate / target SN corresponding to each direct forwarding path availability information. For example, the Direct Forwarding Path Information List contains the ID information of all or some of the other candidate / target SNs except the current source SN.

[0125] ▷Here, the ID information of each candidate / target SN may be represented by a Global NG-RAN Node ID, and the Global NG-RAN Node ID may contain a Global gNB ID or Global ng-eNB ID.

[0126] ▷Here, in this embodiment, the direct forwarding path availability information is used to indicate the availability information of the direct forwarding path between the current source SN and the candidate / target SN indicated by the ID information of each candidate / target SN. For example, the direct forwarding path availability information is used to indicate whether the direct forwarding path between the current source SN and the candidate / target SN indicated by the ID information of each candidate / target SN is available. In an embodiment, the direct forwarding path availability information may directly and explicitly indicate that the direct forwarding path is available or unavailable. Alternatively, in another embodiment, the direct forwarding path availability information may only indicate that the direct forwarding path is available, and accordingly, when the IE corresponding to the direct forwarding path availability information does not exist, it may be implicitly indicated that the direct forwarding path is unavailable. Alternatively, in another embodiment, the direct forwarding path availability information may only indicate that the direct forwarding path is unavailable, and accordingly, when the IE corresponding to the direct forwarding path availability information does not exist, it may be implicitly indicated that the direct forwarding path is available.

[0127] In some embodiments, after the MN and the current source SN complete the above SN modification procedure, the information on whether there is an available direct forwarding path between the current source SN and each of the other candidate / target SNs is acquired by the MN. Then, the MN stores the information and performs a corresponding proper action based on the information.

[0128] Procedure 4c-4: In the case that the direct forwarding path between the source SN and the corresponding candidate / target SN is available, the MN may forward the data forwarding address allocated by the candidate / target SN (or the data forwarding address provided by the candidate / target SN to the MN) to the source SN through an Xn-U Address Indication message. Alternatively, the MN may transmit the data forwarding address allocated by the MN to the source SN through the Xn-U Address Indication message, when there is no direct forwarding path available between the source SN and the corresponding candidate / target SN.

[0129] When the UE selects and accesses another candidate / target SN (e.g., the UE switches to the candidate SN2), for the next round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the role of the candidate SN2 will become the source SN, and the roles of the others become the candidate SN. At this time, the MN needs to know the information on whether there is an available direct forwarding path between the current source SN (e.g., the candidate / target SN2) and the other candidate / target SN. Similarly, the MN may use the above scheme (referring to the description of procedures 4c-1 and 4c-2) to trigger only an SN modification procedure to the current source SN (e.g., the candidate / target SN2), to query the information on whether there is an available direct forwarding path between the current source SN (e.g., the candidate / target SN2) and each of the other candidate / target SNs. After the MN and the current source SN complete the SN modification procedure, the information on whether there is an available direct forwarding path between the current source SN (e.g., the candidate / target SN2) and each of the other candidate / target SNs is acquired by the MN. Then the MN stores the information and performs a corresponding proper action based on the information. For example, when the direct forwarding path between the current source SN (e.g., the candidate / target SN2) and the corresponding candidate / target SN is available, the MN may forward the data forwarding address allocated by the candidate / target SN (or the data forwarding address provided by the candidate / target SN to the MN) to the current source SN (e.g., the candidate / target SN2) through the Xn-U Address Indication message. Alternatively, the MN may transmit the data forwarding address allocated by the MN to the source SN through the Xn-U Address Indication message, when there is no direct forwarding path available between the current source SN (e.g., the candidate / target SN2) and the corresponding candidate / target SN. In this way, the proper operation of the direct data forwarding mechanism in each round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change is ensured.

[0130] For the data forwarding scheme in the above embodiment corresponding to FIG. 4c, after the UE accesses a candidate SN to complete the execution of one round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the MN queries the current source SN for the information on whether there is an available direct forwarding path between the current source SN and each candidate / target SN by using the SN Modification Request message. During the resource preparation phase of the SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the MN can respectively obtain, via the SN addition preparation procedure (referring to the description of the procedures 4a-1 and 4a-2) with each candidate / target SN, the information on whether there is an available direct forwarding path between each candidate / target SN and the source SN. Then, the MN can perform a proper action based on the information. Accordingly, in the resource preparation phase of the initial SCPAC procedure or continuous Inter-SN LTM procedure without MN change, the data forwarding scheme in the above embodiment corresponding to FIG. 4c may also be used (e.g., the SN modification procedure performed between the MN and the source SN may be used), to query the relevant information on whether the direct forwarding path between the source SN and the corresponding candidate / target SN is available, which may specifically include, but not limited to, the following procedures:

[0131] (1) The MN transmits an SN Modification Request message to the current source SN. Here, the SN Modification Request message may carry one or more of the following information:

[0132] - Multiple Candidate / Target SNs List Information

[0133] ▷Here, in an embodiment, the list information contains the ID information of all other candidate / target SNs except the source SN receiving the SN Modification Request message. The ID information of each candidate / target SN may be represented by a global NG-RAN node ID, and the global NG-RAN node ID may contain a global gNB ID or global ng-eNB ID.

[0134] - Direct Forwarding Path Request Indication, which may be used to make a request based on the IDs of all the candidate / target SNs contained in the Multiple Candidate / Target S-NG-RAN Node List, or may be used to indicate a request respectively based on the ID of each candidate / target SN in a one-to-one corresponding manner so as to avoid an information overlap. Here, the Direct Forwarding Path Request Indication is used to request, from the source SN receiving the SN Modification Request message, the availability information of the direct forwarding path between the source SN and each of the other candidate / target SNs (candidate / target SNs contained in the Multiple Candidate / Target S-NG-RAN Node List).

[0135] (2) Then, after receiving the SN Modification Request message, the source SN determines whether there is an available direct forwarding path between the source SN and each of the other candidate / target SNs, and then replies an S-Node Modification Request Acknowledge message to the MN. Here, the S-Node Modification Request Acknowledge message may carry one or more of the following information:

[0136] - Direct Forwarding Path Information List, containing the availability information of a direct forwarding path between the source SN receiving the S-Node Modification Request message and each candidate / target SN, and the ID information of the candidate / target SN corresponding to the availability information of each direct forwarding path. For example, the Direct Forwarding Path Information List contains the ID information of all or some of the other candidate / target SNs except the current source SN.

[0137] ▷Here, the ID information of each candidate / target SN may be represented by a Global NG-RAN Node ID, and the Global NG-RAN Node ID may contain a Global gNB ID or Global ng-eNB ID.

[0138] ▷Here, in this embodiment, direct forwarding path availability information is used to indicate the availability information of the direct forwarding path between the current source SN and the candidate / target SN indicated by the ID information of each candidate / target SN. For example, the direct forwarding path availability information is used to indicate whether the direct forwarding path between the current source SN and each candidate / target SN is available. Here, in an embodiment, the direct forwarding path availability information may directly and explicitly indicate that the direct forwarding path is available or unavailable. Alternatively, in another embodiment, the direct forwarding path availability information may only indicate that the direct forwarding path is available, and accordingly, when the IE corresponding to the direct forwarding path availability information does not exist, it may be implicitly indicated that the direct forwarding path is unavailable. Alternatively, in another embodiment, the direct forwarding path availability information may only indicate that the direct forwarding path is unavailable, and accordingly, when the IE corresponding to the direct forwarding path availability information does not exist, it may be implicitly indicated that the direct forwarding path is available.

[0139] (3) After the MN and the current source SN complete the above SN modification procedure, the information on whether there is an available direct forwarding path between the current source SN and each of the other candidate / target SNs is acquired by the MN. Then, the MN stores the information and performs a corresponding proper action based on the information. For example, when the direct forwarding path between the current source SN and the corresponding candidate / target SN is available, the MN may forward the data forwarding address allocated by the candidate / target SN (or the data forwarding address provided by the candidate / target SN to the MN) to the source SN through an Xn-U Address Indication message. Alternatively, the MN may transmit the data forwarding address allocated by the MN to the current source SN through the Xn-U Address Indication message, when there is no direct forwarding path available between the current source SN and the corresponding candidate / target SN.

[0140] In another embodiment of the present disclosure, if the S-Node Modification Request message contains a Multiple Target S-NG-RAN Node List IE, and possibly contains a Direct Forwarding Path Information Request Indication IE (Direct Forwarding Path Information Request) set as "true" the S-NG-RAN node should (if supported by the S-NG-RAN node) determine the availability of a direct data path with a specified target S-NG-RAN node, and set the Direct Forwarding Path Availability IE as "Direct Path Available" in the Direct Forwarding Path Information List IE in the S-Node Moditication Request Acknowledge message if a direct forwarding path between the S-NG-RAN node and another candidate SN node indicated by a Target S-NG-RAN Node ID IE (Target S-NG-RAN node ID) is available. The M-NG-RAN node should (if supported) consider or store the information that there is a direct forwarding path between the S-NG-RAN node and another candidate / target S-NG-RAN node.

[0141] In another embodiment of the present disclosure, the data forwarding scheme involved in the SCPAC procedure or continuous Inter-SN LTM procedure without MN change triggered by a candidate / target SN may specifically include, but not limited to, the following procedures:

[0142] Procedure 1: The source SN first triggers an SN (S-Node) Change Required message to the MN, and then the MN triggers an SN addition preparation procedure to each candidate / target SN to request each candidate SN to allocate dual connectivity resources to the UE. In a situation where the MN does not query the availability information of the direct forwarding path between the source SN and each candidate / target SN, the source SN first determines whether there is an available direct forwarding path between the source SN and each candidate / target SN. Then, the information related to the direct forwarding path is carried in the triggered SN Change Required message, and the source SN directly notifies the MN of the information. The SN Change Required message may carry one or more of the following information:

[0143] - Direct Forwarding Path Information List, containing the availability information of a direct forwarding path between the source SN and each candidate / target SN, and the ID information of the candidate / target SN corresponding to the availability information of each direct forwarding path. For example, the Direct Forwarding Path Information List contains the ID information of all or some of the other candidate / target SNs except the current source SN.

[0144] ▷Here, the ID information of each candidate / target SN may be represented by a Global NG-RAN Node ID, and the Global NG-RAN Node ID may contain a Global gNB ID or Global ng-eNB ID.

[0145] ▷Here, in this embodiment, direct forwarding path availability information is used to indicate the availability information of the direct forwarding path between the current source SN and the candidate / target SN indicated by the ID information of each candidate / target SN. For example, the direct forwarding path availability information is used to indicate whether the direct forwarding path between the current source SN and each candidate / target SN is available. Here, in an embodiment, the direct forwarding path availability information may directly and explicitly indicate that the direct forwarding path is available or unavailable. Alternatively, in another embodiment, the direct forwarding path availability information may only indicate that the direct forwarding path is available, and accordingly, when the IE corresponding to the direct forwarding path availability information does not exist, it may be implicitly indicated that the direct forwarding path is unavailable. Alternatively, in another embodiment, the direct forwarding path availability information may only indicate that the direct forwarding path is unavailable, and accordingly, when the IE corresponding to the direct forwarding path availability information does not exist, it may be implicitly indicated that the direct forwarding path is available.

[0146] Procedure 2: After receiving the related information carried in the S-Node Change Required message, the MN first stores the information, and then performs a corresponding proper action when it is required to transmit the data forwarding address to the source SN. For example, when the direct forwarding path between the source SN and the corresponding candidate / target SN is available, the MN may forward the data forwarding address allocated by the candidate SN (or the data forwarding address provided by the candidate / target SN to the MN) to the source SN through an Xn-U Address Indication message. Alternatively, the MN may transmit the data forwarding address allocated by the MN to the source SN through the Xn-U Address Indication message, when there is no direct forwarding path available between the source SN and the corresponding candidate / target SN.

[0147] The data forwarding schemes in the above embodiments of the present disclosure may be used separately, used repeatedly or used by combining any two or more of the schemes or embodiments in each round of SCPAC procedure or continuous Inter-SN LTM procedure without MN change, all of which are within the scope of the present disclosure. In addition, the messages used in the present disclosure, for example, in the procedure that a first node 1 (a master node MN) requests a second node 2 (a secondary node SN) to provide the information on whether there is a direct data forwarding path between the second node and another candidate / target SN node except the second node, and in a procedure that the second node replies the information on the availability of the direct forwarding path, such as the S-Node Addition Request message, the S-Node Addition Request Acknowledge message, the SN Modification Request message, the SN Modification Request Acknowledge message and the SN Change Required message are only example messages in corresponding scenarios. The related information may also be carried on a new message or a new IE in a future communication system or technology. All messages or IEs consistent with or similar to the idea in the present disclosure are within the scope of the present disclosure.

[0148] In the foregoing corresponding embodiment (e.g., the embodiment corresponding to FIG. 4a), if a Direct Forwarding Path Information Request IE (which may specifically refer to the foregoing Direct Forwarding Path Request Indication) set as "request" is contained in an SCPAC Request Information IE (which may be contained in the Conditional PSCell Addition Information Request IE in the S-Node Addition Request message), then when the above setting is supported, if there is an available direct forwarding path between the source SN and the candidate / target SN indicated by the corresponding Candidate / Target SN ID IE, the corresponding candidate / target SN may contain the Direct Forwarding Path Information List IE in the S-Node Addition Request Acknowledge message.

[0149] In the foregoing corresponding embodiment (e.g., the embodiment corresponding to FIG. 4c), if a Direct Forwarding Path Information Request IE (which may specifically refer to the foregoing Direct Forwarding Path Request Indication) set as "request" is contained in an SCPAC Request Information IE (which may be contained in the Conditional PSCell Addition Information Modification Request IE in the SN Modification Request message), then when the above setting is supported, if there is an available direct forwarding path between the source SN and the candidate / target SN indicated by the corresponding Candidate / Target SN ID IE, the source SN may contain the Direct Forwarding Path Information List IE in the SN Modification Request Acknowledge message.

[0150] In the foregoing corresponding embodiment (e.g., the embodiment corresponding to FIG. 4a), if the Multiple Candidate / Target SN List IE is contained in an SCPAC Request Information IE (which may be contained in the Conditional PSCell Addition Information Request IE in the S-Node Addition Request message), then when the above setting is supported, if there is an available direct forwarding path between the candidate SN node and the candidate / target SN indicated by the corresponding other Candidate / Target SN ID IE, the Direct Forwarding Path Information List IE may be contained in the S-Node Addition Request Acknowledge message.

[0151] In the foregoing corresponding embodiment (e.g., the embodiment corresponding to FIG. 4c), if the Multiple Candidate / Target SN List IE is contained in an SCPAC Request Information IE (which may be contained in the Conditional PSCell Addition Information Modification Request IE in the SN Modification Request message), then when the above setting is supported, if there is an available direct forwarding path between the source SN and the candidate / target SN indicated by the corresponding Candidate / Target SN ID IE, the Direct Forwarding Path Information List IE may be contained in the SN Modification Request Acknowledge message.

[0152] As shown in FIG. 5, in a continuous (or subsequent) CHO procedure or inter-CU / gNB LTM procedure (e.g., the UE performs LTM or CHO between different CU / gNBs with an MN change), in order to support the UE for a continuous mobility handover, the network side may perform an RRC configuration for the UE after preparing resources for the continuous mobility handover, such that the UE may perform the continuous mobility handover among the candidate / target nodes. Here, this candidate / target node may be a base station (e.g., an NG-RAN node or a gNB), or a base station node in a future communication system. In this embodiment, after each candidate / target node is accessed by the UE, the role of this candidate / target node will become a source node in a next round of CHO procedure or inter-CU / gNB LTM procedure. Since early data forwarding and late data forwarding are possible in each round of CHO procedure or inter-CU / gNB LTM procedure, each candidate / target node may propose a data forwarding proposal after being accessed by the UE, thereby performing the early data forwarding or late data forwarding to another candidate / target node. Therefore, in the resource preparation phase of each CHO procedure or inter-CU / gNB LTM procedure, each candidate / target node may propose a data forwarding proposal in advance, and obtain data forwarding address information provided by another node in advance. Thus, after the UE accesses the corresponding candidate / target node, this node can directly utilize the information related to data forwarding (e.g., including data forwarding address information of another node) to perform data forwarding in time, thus avoiding the latency of data forwarding. In an embodiment, the candidate / target node (e.g., the source node) to which the UE currently accesses needs to provide a data forwarding address to the node proposing the data forwarding proposal according to the information related to the data forwarding, such that the UE may perform a CHO or LTM, and perform data forwarding in time after accessing a new source node. The corresponding procedures shown in FIG. 5 are described below.

[0153] Procedure 501: The UE may directly transmit an L3 measurement report to a source SN / gNB.

[0154] Procedurec 502: The source gNB (e.g., the source node) receives the L3 measurement report reported by the UE, and then triggers a continuous CHO procedure or inter-CU / gNB LTM procedure configuration decision.

[0155] Procedure 503: The source gNB transmits a Handover Request message to each candidate / target gNB to trigger a continuous CHO procedure or inter-CU / gNB LTM procedure. The Handover Request message may carry one or more of the following information:

[0156] - Packet Data Unit Sesseion Identifier, PDU Session ID.

[0157] - Data Forwarding Proposal, which may be represented by a data forwarding and offloading information IE from the source gNB (Data Forwarding and Offloading Info IE from source NG-RAN node). Based on the data forwarding proposal, a corresponding candidate gNB establishes a PDU session corresponding to the PDU session ID (the PDU session may be represented by the PDU session ID) and a Quality of Service (QoS) Flow (which may be represented by a QoS flow ID).

[0158] Procedure 504: In the resource preparation phase of each CHO procedure or inter-CU / gNB LTM procedure, each candidate / target gNB replies a Handover Request Acknowledge message to the source gNB. Here, the Handover Request Acknowledge message may carry one or more of the following information:

[0159] - Data Forwarding Proposal, which may be represented by a Data Forwarding and Offloading Information IE from the source gNB (Data Forwarding and Offloading Info IE from source NG-RAN node).

[0160] - PDU Session ID.

[0161] - QoS Flow ID (Quality of Service Flow Identifier) of one or more QoSs established on the PDU session indicated by the above PDU session ID.

[0162] - Data Forwarding Address, which may be represented by data forwarding information (Data Forwarding Info from target NG-RAN node) IE from candidate / target gNB.

[0163] In an embodiment, the data forwarding proposal mentioned in the above procedure may be contained in a PDU Session Resources Admitted List IE in the Handover Request Acknowledge message as follows:

[0164] - PDU Session Resources Admitted List

[0165] > PDU Session ID

[0166] >>QoS Flows Admitted List

[0167] >Data Forwarding and Offloading Info from source NG-RAN node (containing the above data forwarding proposal, and used after a candidate / target gNB is selected and accessed by the UE)

[0168] As can be seen from the above procedures 503 and 504, in an embodiment, the source gNB may propose a data forwarding proposal for each to-be-established PDU session and QoS flow by using the Handover Request message. Then, each candidate gNB replies or responds to the source gNB by using the Handover Request Acknowledge message. The Handover Request Acknowledge message will carry the data forwarding address allocated by the candidate gNB based on an accepted PDU session or QoS flow. In this way, after the above procedures 503 and 504 are performed between the source node (which may refer to the above source gNB) and each candidate node (which may refer to the above candidate gNB) to complete the resource preparation phase of the CHO procedure or inter-CU / gNB LTM procedure, the source node acquires the relevant information such as the data forwarding address and the data forwarding proposal provided by each candidate node, and then stores the information. For example, the source gNB stores the data forwarding address and data forwarding proposal provided by each candidate gNB. Accordingly, the source gNB may acquire the above data forwarding related information of all candidate / target gNBs (e.g., including the data forwarding address and data forwarding proposal provided by each candidate gNB) through the above procedures 503 and 504. Next, an early data forwarding procedure 506 may occur, in which the source gNB transmits data to the UE, and at the same time, forwards the data to each of the other candidate gNBs. Alternatively, the early data forwarding procedure 506 may occur after the source gNB completes an RRC reconfiguration for the UE and receives an RRC Reconfiguration Complete (procedure 5010) message and before the source gNB triggers a Cell Switch Command (procedure 5012). Specifically, for the collected data forwarding related information such as the data forwarding proposal and the data forwarding address provided by each candidate node, the source gNB needs to provide a corresponding data forwarding address to the candidate / target gNB (e.g., a candidate / target gNB1) proposing the data forwarding proposal. After the UE selects and accesses the candidate gNB proposing the data forwarding proposal, the role of this candidate gNB will become the source gNB, and the role of the previous source gNB will become a candidate / target gNB (e.g., a candidate / target gNB0). Accordingly, the previous source gNB (e.g., the candidate / target gNB0) may directly forward, using the above corresponding data forwarding address, the data to the corresponding candidate / target gNB (e.g., the candidate / target gNB1) proposing the data forwarding proposal during the early data forwarding, and may perform the late data forwarding when the UE switches from this candidate / target node (e.g., the candidate / target gNB1) to access a next candidate / target node (e.g., a candidate / target gNB2). Then, regarding how the source node provides the collected data forwarding proposal and / or data forwarding address (provided by each candidate / target node) to each candidate / target node requiring such information, the embodiments of the present disclosure provide the following several alternative schemes, but the present disclosure is not limited thereto:

[0169] Alternative Scheme 1: The source node provides the collected PDU session-based or Qos flow-based data forwarding proposal and / or data forwarding address (which may include the data forwarding proposal and data forwarding address of the source node) provided by each candidate / target node to each of the other candidate / target nodes requiring such information except the source node (e.g., the source node is also configured as a candidate / target node) in advance. In an embodiment, the data forwarding proposal and / or the data forwarding address, etc., may be provided in advance to the corresponding candidate / target node by means of a new message or a new IE. Specifically, the source node may provide, through a Data Forwarding Information (Info) Transfer or LTM / Handover Modification Request message (e.g., procedure 507 in FIG. 5), corresponding information to another candidate / target node proposing the data forwarding proposal (alternatively, the source node may provide the data forwarding address information to all other candidate / target nodes regardless of whether the candidate / target node proposes the data forwarding proposal). Here, the Data Forwarding Information Transfer or LTM / Handover Modification Request message may contain one or more of the following information:

[0170] - Data Forwarding Information List, used to provide data forwarding addresses and / or data forwarding proposal allocated by multiple candidate / target gNBs (including the source gNB) based on a PDU session ID and / or QoS flow ID, and including one or more of the following information:

[0171] (1) Candidate / Target gNB ID Information, which may be represented by a Global NG-RAN Node ID, which may contain a Global gNB ID or a Global ng-eNB ID. Here, the candidate / target gNB ID information may also include the ID information of the source gNB if the source gNB is configured as a candidate / target gNB.

[0172] (2) Candidate / Target Cell ID Information, used to represent the ID (which may be represented by an NR CGI) of a candidate / target cell contained on a candidate gNB.

[0173] (3) PDU Session ID, used to represent or indicate a PDU session established on the candidate gNB indicated by the candidate / target gNB ID information or the candidate / target cell indicated by the candidate / target cell ID information. Here, a plurality of cells may be configured in one gNB, and a plurality of different PDU sessions may be configured in one cell.

[0174] (4) QoS Flow ID, used to represent or indicate one or more QoS flows in the above established PDU session.

[0175] (5) Data Forwarding Proposal, which may be represented by a Data Forwarding and Offloading Information IE from the source node (Data Forwarding and Offloading Info from source NG-RAN node IE). The data forwarding proposal may be set or proposed based on the ID of a PDU session / QoS flow established in a certain candidate / target gNB or in a certain candidate / target cell.

[0176] (6) Data Forwarding Address, which may be represented by a Data Forwarding Information IE from the candidate / target node (Data Forwarding Info from candidate / target NG-RAN node IE). The data forwarding address may be set or configured based on the ID of a PDU session / QoS flow established in a certain candidate / target gNB or in a certain candidate / target cell.

[0177] After receiving the data forwarding address and / or data forwarding proposal provided by each of the other candidate / target gNBs (optionally, including the source gNB), each candidate / target gNB stores such information. For example, each candidate gNB stores the data forwarding address and data forwarding proposal provided by each of the other candidate gNBs. The information may be used during the early data forwarding when the UE selects and accesses one of the candidate / target gNBs, and the information (referring to the foregoing corresponding description) may be used during the late data forwarding when the UE switches from this candidate / target gNB to access a next candidate / target gNB. Therefore, it is ensured that the UE obtains the data forwarding address information provided by another node in advance during the continuous mobility handover procedure and performs data forwarding in time to avoid the latency of data forwarding. Accordingly, the proper operation of the data forwarding mechanism is ensured.

[0178] Alternative Scheme 2: For the continuous or subsequent inter-CU / gNB LTM procedure, the UE performs the handover only after the source node (e.g. the source gNB) transmits an LTM Cell Switch Command (referring to procedure 5012 as shown in the drawing). Then, the source node notifies the candidate / target gNB through an XnAP message (e.g., an LTM Cell Switch Notification message). Next, the late data forwarding in the procedure 5016 may occur. Therefore, the data forwarding related information may be carried in the XnAP message in the procedure 5013 (e.g., a Random Access procedure or a Cell Switch Notification procedure) as shown in FIG. 5, or the procedure 507 (using the Data Forwarding Information (Info) Transfer or LTM / Handover Modification Request message) in the foregoing scheme 1 may be transmitted at this time. Thus, it is implemented that the source node gNB notifies the candidate / target gNB (the target node to which the UE accesses) of the data forwarding related information. The above message may specifically contain one or more of the following information:

[0179] - Data Forwarding Information List, used to provide data forwarding addresses and / or data forwarding proposal allocated by multiple candidate / target gNBs (including the source gNB) based on a PDU session ID and / or QoS flow ID, and including one or more of the following information:

[0180] (1) Candidate / Target gNB ID Information, which may be represented by a Global NG-RAN Node ID, which may contain a Global gNB ID or a Global ng-eNB ID. Here, the candidate / target gNB ID information may also include the ID information of the source gNB if the source gNB is configured as a candidate / target gNB.

[0181] (2) Candidate / Target Cell ID Information, used to represent the ID (which may be represented by an NR CGI) of a candidate / target cell contained on a candidate gNB.

[0182] (3) PDU Session ID, used to represent or indicate a PDU session established on the candidate gNB indicated by the candidate / target gNB ID information or the candidate / target cell indicated by the candidate / target cell ID information. Here, a plurality of cells may be configured in one gNB, and a plurality of different PDU sessions may be configured in one cell.

[0183] (4) QoS Flow ID, used to represent or indicate one or more QoS flows in the above established PDU session.

[0184] (5) Data Forwarding Proposal, which may be represented by a Data Forwarding and Offloading Information IE from the source node (Data Forwarding and Offloading Info from source NG-RAN node IE). The data forwarding proposal may be set or proposed based on the ID of a PDU session / QoS flow established in a certain candidate / target gNB or in a certain candidate / target cell.

[0185] (6) Data Forwarding Address, which may be represented by a Data Forwarding Information IE from the candidate / target node (Data Forwarding Info from candidate / target NG-RAN node IE). The data forwarding address may be set or configured based on the ID of a PDU session / QoS flow established in a certain candidate / target gNB or in a certain candidate / target cell.

[0186] After receiving the data forwarding address and / or data forwarding proposal provided by each of the other candidate / target gNBs and transmitted by the source gNB, the candidate / target gNB stores such information. The information may be used during the early data forwarding after the candidate / target gNB and a core network complete a path switch procedure, and the information may be used during the late data forwarding when the UE switches from this candidate / target gNB to access a next candidate / target gNB. A next round of inter-CU / gNB LTM may be performed in a similar way. The current source gNB continues to notify a new candidate / target gNB of the information through an XnAP message (e.g., an LTM Cell Switch Notification message or LTM / Handover Modification Request message), thereby ensuring that the UE obtains the data forwarding address information provided by another node in time during the continuous mobility handover procedure and performs data forwarding in time to avoid the latency of data forwarding. Accordingly, the proper operation of the data forwarding mechanism is ensured.

[0187] The alternative scheme 2 is only suitable for the Inter-CU / gNB LTM procedure. In the CHO procedure, the UE evaluates an execution condition. If the execution condition is satisfied, the UE decides to perform a handover, and the source gNB does not know when the UE performs the handover. Therefore, there is no similar Xnap message (e.g., LTM Cell Switch Notification message) for the source gNB to notify the candidate / target gNB. Only when the UE successfully accesses the candidate / target gNB, the source gNB will receive a Handover Success message transmitted by the candidate / target gNB.

[0188] Alternative Scheme 3: For either the continuous or subsequent CHO procedure or the continuous or subsequent inter-CU / gNB LTM procedure, after the UE successfully performs the handover to access the candidate / target gNB, the source gNB will be notified through the Handover Success message in procedure 5015. Next, the late data forwarding in procedure 5016 may occur. Therefore, after receiving the Handover Success message, the source gNB notifies the corresponding candidate / target gNB of the data forwarding address information provided by another node. Therefore, the source gNB may transmit a Data Forwarding Information Transfer (or Data Forwarding Information Transfer message) or LTM / Handover Modification Request message to the corresponding candidate / target gNB (the target node to which the UE accesses) by means of a new message or a new IE in procedure 5017. This procedure contains one or more of the following information:

[0189] - Data Forwarding Information List, used to provide data forwarding addresses and / or data forwarding proposal allocated by multiple candidate / target gNBs (including the source gNB) based on a PDU session ID and / or QoS flow ID, and including one or more of the following information:

[0190] (1) Candidate / Target gNB ID Information, which may be represented by a Global NG-RAN Node ID, which may contain a Global gNB ID or a Global ng-eNB ID. Here, the candidate / target gNB ID information may also include the ID information of the source gNB if the source gNB is configured as a candidate / target gNB.

[0191] (2) Candidate / Target Cell ID Information, used to represent the ID (which may be represented by an NR CGI) of a candidate / target cell contained on a candidate gNB.

[0192] (3) PDU Session ID, used to represent or indicate a PDU session established on the candidate gNB indicated by the candidate / target gNB ID information or the candidate / target cell indicated by the candidate / target cell ID information. Here, a plurality of cells may be configured in one gNB, and a plurality of different PDU sessions may be configured in one cell.

[0193] (4) QoS Flow ID, used to represent or indicate one or more QoS flows in the above established PDU session.

[0194] (5) Data Forwarding Proposal, which may be represented by a Data Forwarding and Offloading Information IE from the source node (Data Forwarding and Offloading Info from source NG-RAN node IE). The data forwarding proposal may be set or proposed based on the ID of a PDU session / QoS flow established in a certain candidate / target gNB or in a certain candidate / target cell.

[0195] (6) Data Forwarding Address, which may be represented by a Data Forwarding Information IE from the candidate / target node (Data Forwarding Info from candidate / target NG-RAN node IE). The data forwarding address may be set or configured based on the ID of a PDU session / QoS flow established in a certain candidate / target gNB or in a certain candidate / target cell.

[0196] After receiving the data forwarding address and / or data forwarding proposal provided by each of the other candidate / target gNBs and transmitted by the source gNB, the candidate / target gNB stores such information. The information may be used during the early data forwarding after the candidate / target gNB and the core network complete the path switch procedure, and the information may be used during the late data forwarding when the UE switches from this candidate / target gNB to access a next candidate / target gNB. Meanwhile, a next round of CHO procedure or inter-CU / gNB LTM procedure may be performed in a similar way. After the UE successfully performs a handover to access the candidate / target gNB and the source gNB receives a Handover Success message, the source gNB notifies the corresponding candidate / target gNB of the above data forwarding address and / or data forwarding proposal, and the current source gNB continues to notify a new candidate / target gNB of the information by means of a new message or new IE, thereby ensuring the proper operation of the data forwarding mechanism during the continuous mobility handover procedure of the UE.

[0197] As shown in FIG. 5, in addition to the above procedures, one or more of the following procedures may be included:

[0198] Procedure 509: The source gNB transmits an RRC Reconfiguration message to the UE.

[0199] Procedure 5010: The UE transmits an RRC Recongiguration Complete message to the source gNB.

[0200] Procedure 5011: The UE reports a low-layer measurement report (e.g., a layer 1 (L1) Measurement Report) to the source gNB, such that the source gNB transmits a Cell Switch Command to the UE in step 5012 according to the measurement report of the UE.

[0201] Procedure 5014: After successfully switching from the source gNB (e.g., the candidate gNB0) to the candidate gNB1 and completing the random access procedure in the procedure 5013, the UE transmits an RRC Reconfiguration Complete message to the new source gNB (e.g., the candidate gNB1).

[0202] In an embodiment, if a continuous Inter-NG-RAN node CHO or LTM procedure is supported, a candidate NG-RAN node decides one or more QoS flows on one or more admitted PDU sessions, and the candidate NG-RAN node may propose a downlink and / or uplink data forwarding proposal based on the QoS flows in a Handover Request Acknowledge message, and contain a Data Forwarding and Offloading Information from source node (Data Forwarding and Offloading Info from source NG-RAN node) IE in a PDU Session Resource Admitted Information (Info) IE contained in a PDU Session Resources Admitted List IE.

[0203] In an embodiment, in the continuous Inter-NG-RAN node CHO or LTM procedure, the source NG-RAN node (if supported) may provide the collected PDU session-based (or Qos flow-based) data forwarding address and other infomration provided by another candidate NG-RAN node, may contain one Multiple Candidate NG-RAN node list in a Handover / LTM Modification Request message (or another new Xnap message such as an LTM Cell Switch Notification message or a Data Forwarding Information Transfer message). In the list, for PDU session IDs / QoS flow IDs / DRB IDs accepted by different candidate NG-RAN nodes, different downlink and / or uplink data forwarding address information (represented by a Data Forwarding Information IE from a target node (Data Forwarding Info from target NG-RAN node IE)) are provided.

[0204] The above schemes or embodiments of the present disclosure may be used separately, used repeatedly or used by combining any two or more of the schemes or embodiments in each round of continuous or subsequent Inter-CU / gNB LTM / CHO procedure, all of which are within the scope of the present disclosure. In addition, the messages used in the present disclosure are only example messages in corresponding scenarios. A new message or a new IE in a future communication system or technology may also be used. Messages consistent with or similar to the idea in the present disclosure all should be within the scope of the present disclosure.

[0205] The above method embodied with respect to the data forwarding mechanism in the present disclosure should not be limited to only a data forwarding scheme applicable to the above continuous mobility handover procedure, but also to a similar data forwarding procedure involved in a mobility procedure or other functions in another communication system (a 4G, 5G, 6G or next-generation mobile communication system).

[0206] FIG. 6 illustrates a method performed by a first node in a wireless communication system according to an exemplary embodiment of the present disclosure. The method may be performed by the MN (e.g., FIGS. 4a-4c) or the source gNB (e.g., FIG. 5) described with reference to the embodiments corresponding to FIGS. 3-5. According to an exemplary embodiment, the method performed by the first node in the wireless communication system may include the following steps:

[0207] Step 610, transmitting a first message to a second node. The first message may comprise first identifier information and first information related to data forwarding, and the first information may comprise information for requesting a direct forwarding path or a data forwarding proposal.

[0208] Step 620, receiving a second message transmitted by the second node. The second message may comprise second information related to data forwarding of the second node, and the second information may comprise direct forwarding path related information or data forwarding proposal related information.

[0209] According to an exemplary embodiment, the first identifier information may comprise identifier information of at least one candidate node for a UE handover, and the direct forwarding path related information may comprise the identifier information of the at least one candidate node and availability information of a direct forwarding path between the second node and the at least one candidate node.

[0210] According to an exemplary embodiment, the first message may be transmitted after a user equipment (UE) handover to a third node. The first identifier information may comprise identifier information of the third node, and the direct data forwarding path related information may comprise availability information of a direct forwarding path between the second node and the third node.

[0211] According to an exemplary embodiment, the first message may be transmitted after a UE handover to the second node. The first identifier information may comprise the identifier information of the at least one candidate node for the UE handover. The direct forwarding path related information may comprise the identifier information of the at least one candidate node and the availability information of the direct forwarding path between the second node and the at least one candidate node.

[0212] According to an exemplary embodiment, the method may further comprise: receiving a secondary node (SN) Change Required message from a source node. The SN Change Required message may comprise: the identifier information of the at least one candidate node for the UE handover and availability information of a direct forwarding path between the source node and the at least one candidate node. The second node may be a node in the at least one candidate node.

[0213] According to an exemplary embodiment, the first identifier information may comprise a packet data unit (PDU) session identifier and / or a quality of service (QoS) flow identifier, and the data forwarding proposal related information may be a data forwarding proposal. The data forwarding proposal related information may comprise a PDU session identifier and / or QoS identifier accepted by the second node, and a data forwarding proposal and data forwarding address related to the PDU session identifier and / or QoS identifier accepted by the second node.

[0214] According to an exemplary embodiment, the method may further comprise: transmitting a third message to the second node. The third message may comprise the data forwarding proposal related information associated with the at least one candidate node for the UE handover. The third message may be transmitted after an early data forwarding procedure.

[0215] According to an exemplary embodiment, the method may further comprise: transmitting a third message to a target node for a UE handover. The third message may comprise the data forwarding proposal related information associated with the at least one candidate node for the UE handover. The third message may be transmitted after a measurement report reported by the UE is received, or transmitted after a successful handover of the UE to the target node.

[0216] According to an exemplary embodiment, the first message may comprise an SN Addition Request message, an SN Modification Request message or a Handover Request message, and the second message comprises an SN Addition Request Acknowledge message, an SN Modification Request Acknowledge message or a Handover Request Acknowledge message.

[0217] According to an exemplary embodiment, when the first node is an MN and the second node is a candidate SN. The first message may comprise the SN Addition Request message or the SN Modification Request message, and the second message may comprise the SN Addition Request Acknowledge message or the SN Modification Request Acknowledge message.

[0218] According to an exemplary embodiment, when the first node is a source gNB and the second node is a candidate gNB, the first message may comprise the Handover Request message, and the second message may comprise the Handover Request Acknowledge message.

[0219] According to an exemplary embodiment, the third message may be transmitted through an XnAP message or Data Forwarding Information Transfer message.

[0220] It should be noted that the first message, the second message and the third message in the exemplary embodiments of the present disclosure may include, but not limited to, the above messages, and may alternatively include other messages except these messages.

[0221] FIG. 7 illustrates a method performed by a second node in a wireless communication system according to an exemplary embodiment of the present disclosure. The method may be performed by each candidate SN (e.g., FIGS. 4a-4c) or each candidate gNB (e.g., FIG. 5) described with reference to the embodiments corresponding to FIGS. 3-5. According to an exemplary embodiment, the method performed by the second node in the wireless communication system may include the following steps:

[0222] Step 710, receiving a first message transmitted by a first node. The first message may comprise first identifier information and first information related to data forwarding, and the first information may comprise information for requesting a direct forwarding path or a data forwarding proposal.

[0223] Step 720, transmitting a second message to the first node. The second message may comprise second information related to data forwarding of the second node, and the second information may comprise direct forwarding path related information or data forwarding proposal related information.

[0224] According to an exemplary embodiment, the first identifier information may comprise identifier information of at least one candidate node for a UE handover.The direct forwarding path related information may comprise the identifier information of the at least one candidate node and availability information of a direct forwarding path between the second node and the at least one candidate node.

[0225] According to an exemplary embodiment, the first message may be transmitted after a UE handover to a third node. The first identifier information may comprise identifier information of the third node, and the direct forwarding path related information may comprise availability information of a direct forwarding path between the second node and the third node.

[0226] According to an exemplary embodiment, the first message may be transmitted after a UE handover to the second node. The direct forwarding path related information may comprise the identifier information of the at least one candidate node and the availability information of the direct forwarding path between the second node and the at least one candidate node.

[0227] According to an exemplary embodiment, the first identifier information may comprise a packet data unit (PDU) session identifier and / or a quality of service (QoS) flow identifier, and the data forwarding proposal related information may be a data forwarding proposal. The data forwarding proposal related information may comprise a PDU session identifier and / or QoS identifier accepted by the second node, and a data forwarding proposal and data forwarding address related to the PDU session identifier and / or QoS identifier accepted by the second node.

[0228] According to an exemplary embodiment, the method may further comprise: receiving a third message transmitted by the first node. The third message may comprise the data forwarding proposal related information associated with the at least one candidate node for the UE handover.

[0229] According to an exemplary embodiment, the third message may be transmitted by the first node after an early data forwarding procedure, transmitted by the first node after a measurement report reported by a UE is received, or transmitted by the first node after a successful handover of the UE to the second node.

[0230] According to an exemplary embodiment, the first message may comprise an SN Addition Request message, an SN Modification Request message or a Handover Request message, and the second message comprises an SN Addition Request Acknowledge message, an SN Modification Request Acknowledge message or a Handover Request Acknowledge message.

[0231] According to an exemplary embodiment, when the second node is a candidate SN and the first node is an MN, the first message may comprise the SN Addition Request message or the SN Modification Request message, and the second message may comprise the SN Addition Request Acknowledge message or the SN Modification Request Acknowledge message.

[0232] According to an exemplary embodiment, when the second node is a candidate gNB and the first node is a source gNB, the first message may comprise the Handover Request message, and the second message may comprise the Handover Request Acknowledge message.

[0233] According to an exemplary embodiment, the third message may be transmitted through an XnAP message or Data Forwarding Information Transfer message.

[0234] The first message, the second message and the third message in the exemplary embodiments of the present disclosure may include, but not limited to, the above messages, and may alternatively include other messages except these messages.

[0235] FIG. 8 illustrates a method performed by a user equipment (UE) in a wireless communication system according to an exemplary embodiment of the present disclosure. The method may be performed by the UE (e.g., FIG. 5) described with reference to the embodiments corresponding to FIGS. 3-5. According to an exemplary embodiment, the method performed by the UE in the wireless communication system may include the following steps:

[0236] Step 810, transmitting a layer 1 or layer 3 measurement report to a first node. Here, a first message may be transmitted by the first node to a second node, wherein the first message may comprise first identifier information and first information related to data forwarding, and the first information may comprise information for requesting a direct forwarding path or a data forwarding proposal. Here, a second message from the second node may be received by the first node, wherein the second message may comprise second information related to data forwarding of the second node, and the second information may comprise direct forwarding path related information or data forwarding proposal related information.

[0237] According to an exemplary embodiment, the first identifier information may comprise identifier information of at least one candidate node for a UE handover. The direct forwarding path related information may comprise the identifier information of the at least one candidate node and availability information of a direct forwarding path between the second node and the at least one candidate node.

[0238] According to an exemplary embodiment, the method may further comprise: performing a UE handover to a third node. The first message may be transmitted by the first node after the UE handover to the third node. The first identifier information may comprise identifier information of the third node, and the direct data forwarding path related information may comprise availability information of a direct forwarding path between the second node and the third node.

[0239] According to an exemplary embodiment, the method may further comprise: performing a UE handover to the second node. The first message may be transmitted by the first node after the UE handover to the second node. The first identifier information may comprise the identifier information of the at least one candidate node for the UE handover. The direct forwarding path related information may comprise the identifier information of the at least one candidate node and the availability information of the direct forwarding path between the second node and the at least one candidate node.

[0240] According to an exemplary embodiment, a secondary node (SN) Change Required message from a source node may be received by the first node. The SN Change Required message may comprise: the identifier information of the at least one candidate node for the UE handover and availability information of a direct forwarding path between the source node and the at least one candidate node. The second node may be a node in the at least one candidate node.

[0241] According to an exemplary embodiment, the first identifier information may comprise a packet data unit (PDU) session identifier and / or a quality of service (QoS) flow identifier, and the data forwarding proposal related information may be a data forwarding proposal. The data forwarding proposal related information may comprise a PDU session identifier and / or QoS identifier accepted by the second node, and a data forwarding proposal and data forwarding address related to the PDU session identifier and / or QoS identifier accepted by the second node.

[0242] According to an exemplary embodiment, the method may further comprise: transmitting , by the first node, a third message to the second node. The third message may comprise the data forwarding proposal related information associated with the at least one candidate node for the UE handover. The third message may be transmitted by the first node after an early data forwarding procedure.

[0243] According to an exemplary embodiment, the third message may be transmitted by the first node to a target node for a UE handover. The third message may comprise the data forwarding proposal related information associated with the at least one candidate node for the UE handover. The third message may be transmitted by the first node after the layer 1 or layer 3 measurement report is received by the first node, or transmitted by the first node after a successful handover of the UE to the target node.

[0244] According to an exemplary embodiment, the first message may comprise an SN Addition Request message, an SN Modification Request message or a Handover Request message, and the second message may comprise an SN Addition Request Acknowledge message, an SN Modification Request Acknowledge message or a Handover Request Acknowledge message.

[0245] According to an exemplary embodiment, when the first node is an MN and the second node is a candidate SN, the first message may comprise the SN Addition Request message or the SN Modification Request message, and the second message may comprise the SN Addition Request Acknowledge message or the SN Modification Request Acknowledge message.

[0246] According to an exemplary embodiment, when the first node is a source gNB and the second node is a candidate gNB, the first message may comprise the Handover Request message, and the second message may comprise the Handover Request Acknowledge message.

[0247] According to an exemplary embodiment, the third message may be transmitted through an XnAP message or Data Forwarding Information Transfer message.

[0248] The first message, the second message and the third message in the exemplary embodiments of the present disclosure may include, but not limited to, the above messages, and may alternatively include other messages except these messages.

[0249] The above is an exemplary description of the methods performed by the first node, the second node and the user equipment (UE) according to the embodiments of the present disclosure. It should be understood that the corresponding steps shown in FIGS. 6, 7 and 8 and the information contained in the steps are also within the scope of the present disclosure. In addition, the nodes performing the corresponding methods are also within the scope of the present disclosure.

[0250] FIG. 9 illustrates an exemplary structure of each node applicable to the present disclosure. The exemplary node shown in FIG. 9 includes a transceiver 910 and a processor 920 coupled to the transceiver 910. The transceiver 910 is configured to transmit and receive a signal. The processor 920 is configured to perform the method described in the present disclosure. The present disclosure may alternatively be implemented as a computer storage medium. The computer storage medium stores computer executable instructions. When the stored computer executable instructions are executed by the processor, the processor performs the method described in the present disclosure.

[0251] The various illustrative logical blocks, modules, and circuits described in the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or　other programmable logic devices, a discrete gate or transistor logic, a discrete hardware component, or any combination thereof designed to perform the functions described herein. The general purpose processor may be a microprocessor, but in an alternative scheme, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may alternatively be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in collaboration with a DSP core, or any other such configuration.

[0252] The steps of the method or algorithm described in the present disclosure may be embodied directly in hardware, in a software module executed by the processor, or in a combination of the two. The software module may reside in a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a removable disk, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor, to enable the processor to read information from / write information to the storage medium. In an alternative scheme, the storage medium may be integrated to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In an alternative scheme, the processor and the storage medium may reside as discrete components in a user terminal.

[0253] In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in the software, the functions may be stored on or transmitted over a computer readable medium as one or more instructions or codes. The computer readable medium includes both a computer storage medium and a communication medium, the communication medium including any medium that facilitates the transfer of a computer program from one place to another. The storage medium may be any available medium that can be accessed by a general purpose or special purpose computer.

[0254] Example methods and apparatuses are described in combination with the accompanying drawings in the description set forth herein, and do not represent all the examples that may be implemented or that are within the scope of the claims. The term "example" used herein means "serving as an example, instance, or illustration," rather than "preferred" or "advantageous over other examples." The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some cases, well-known structures and devices are shown in the form of a block diagram in order to avoid obscuring the concepts of the described examples.

[0255] This specification contains many specific implementation details, but the implementation details should not be construed as a limitation to the scope of any disclosure or the scope claimed, but rather as a description for specific features in a specific embodiment of the specific disclosure. Certain features described in the context of separate embodiments in this specification may alternatively be implemented in combination in a single embodiment. Rather, the various features described in the context of a single embodiment may be implemented separately in a plurality of embodiments or implemented in any suitable sub-combination. Furthermore, the features may be described as functioning in certain combinations in the context, and even initially so claimed, but in some cases one or more features in a claimed combination may be deleted from the combination, and the claimed combination may be directed to a sub-combination or the variation of the sub-combination.

[0256] It should be understood that the specific order or hierarchy of steps in the method in the present disclosure is an illustration for an exemplary process. Based on design preferences, it may be understood that the specific order or hierarchy of the steps in the method may be rearranged to achieve the functions and effects disclosed in the present disclosure. The accompanying method claims present the elements of various steps in example order, but are not intended to be limited to the specific order or hierarchy presented, unless specifically stated otherwise. Furthermore, although an element may be described or claimed in a singular form, the plural can also be expected unless the limitation to the singular is explicitly stated. Thus, the present disclosure is not limited to the examples shown, and any apparatus for performing the functions described herein is included in the aspects of the present disclosure.

[0257] It can be understood that "at least one" described in the present disclosure includes any and / or all possible combinations of the listed items, the various embodiments described in the present disclosure and the various examples in the embodiments may be varied and combined in any suitable form, and " / " described in the present disclosure represents "and / or."

[0258] The text and drawings are provided as examples only to help readers understand the present disclosure. The text and drawings are not intended to limit and should not be interpreted as limiting the scope of the present disclosure in any way. Although certain embodiments and examples have been provided, based on the content disclosed herein, it is obvious to those skilled in the art that modifications to the illustrated embodiments and examples can be made without departing from the scope of the present disclosure.

Claims

1.A method performed by a first node in a wireless communication system, the method comprising:transmitting a first message to a second node, wherein the first message comprises first identifier information and first information related to data forwarding, and the first information comprises information for requesting a direct forwarding path or a data forwarding proposal; andreceiving a second message transmitted from the second node, wherein the second message comprises second information related to data forwarding of the second node, and the second information comprises direct forwarding path related information or data forwarding proposal related information.2.The method of claim 1, wherein the first identifier information comprises identifier information of at least one candidate node for a user equipment (UE) handover, andwherein the direct forwarding path related information comprises the identifier information of the at least one candidate node and availability information of a direct forwarding path between the second node and the at least one candidate node.3.The method of claim 1, wherein the first message is transmitted after a UE handover to a third node,wherein the first identifier information comprises identifier information of the third node, and the direct forwarding path related information comprises availability information of a direct forwarding path between the second node and the third node.4.The method of claim 1, wherein the first message is transmitted after a UE handover to the second node,wherein the first identifier information comprises identifier information of at least one candidate node for the UE handover,wherein the direct forwarding path related information comprises the identifier information of the at least one candidate node and availability information of a direct forwarding path between the second node and the at least one candidate node.5.The method of claim 1, further comprising:receiving a secondary node (SN) Change Required message from a source node,wherein the SN Change Required message comprises: identifier information of at least one candidate node for a UE handover and availability information of a direct forwarding path between the source node and the at least one candidate node,wherein the second node is a node among the at least one candidate node.6.The method of claim 1, wherein the first identifier information comprises a packet data unit (PDU) session identifier and / or a quality of service (QoS) flow identifier, and the data forwarding proposal related information is a data forwarding proposal,wherein the data forwarding proposal related information comprises a PDU session identifier and / or QoS identifier accepted by the second node, and the data forwarding proposal and a data forwarding address related to the PDU session identifier and / or QoS identifier accepted by the second node.7.The method of claim 6, further comprising:transmitting a third message to the second node, wherein the third message comprises the data forwarding proposal related information associated with at least one candidate node for a UE handover,wherein the third message is transmitted after an early data forwarding procedure.8.The method of claim 6, further comprising:transmitting a third message to a target node for a UE handover, wherein the third message comprises the data forwarding proposal related information associated with at least one candidate node for the UE handover,wherein the third message is transmitted after a measurement report reported by a UE is received, or transmitted after a successful handover of the UE to the target node.9.A method performed by a second node in a wireless communication system, the method comprising:receiving a first message transmitted by a first node, wherein the first message comprises first identifier information and first information related to data forwarding, and the first information comprises information for requesting a direct forwarding path or a data forwarding proposal; andtransmitting a second message to the first node, wherein the second message comprises second information related to data forwarding of the second node, and the second information comprises direct forwarding path related information or data forwarding proposal related information.10.The method of claim 9, wherein the first identifier information comprises a packet data unit (PDU) session identifier and / or a quality of service (QoS) flow identifier, and the data forwarding proposal related information is a data forwarding proposal,wherein the data forwarding proposal related information comprises a PDU session identifier and / or QoS identifier accepted by the second node, and a data forwarding proposal and a data forwarding address related to the PDU session identifier and / or QoS identifier accepted by the second node.11.The method of claim 10, further comprising:receiving a third message transmitted by the first node, wherein the third message comprises the data forwarding proposal related information associated with at least one candidate node for a UE handover.12.The method according to claim 11, wherein the third message is transmitted by the first node after an early data forwarding procedure, transmitted by the first node after a measurement report reported by a UE is received, or transmitted by the first node after a successful handover of the UE to the second node.13.A first node in a wireless communication system, the first node comprising:a transceiver, configured to transmit and receive a signal; anda processor, coupled to the transceiver,wherein the processor is configured to:transmit a first message to a second node, via the transceiver, wherein the first message comprises first identifier information and first information related to data forwarding, and the first information comprises information for requesting a direct forwarding path or a data forwarding proposal; andreceive a second message transmitted from the second node, via the transceiver, wherein the second message comprises second information related to data forwarding of the second node, and the second information comprises direct forwarding path related information or data forwarding proposal related information.14.The first node of claim 13, wherein the first identifier information comprises identifier information of at least one candidate node for a user equipment (UE) handover, andwherein the direct forwarding path related information comprises the identifier information of the at least one candidate node and availability information of a direct forwarding path between the second node and the at least one candidate node.15.A second node in a wireless communication system, the second node comprising:a transceiver, configured to transmit and receive a signal; anda processor, coupled to the transceiver,wherein the processor is configured to:receive a first message transmitted by a first node, via the transceiver, wherein the first message comprises first identifier information and first information related to data forwarding, and the first information comprises information for requesting a direct forwarding path or a data forwarding proposal; andtransmit a second message to the first node, via the transceiver, wherein the second message comprises second information related to data forwarding of the second node, and the second information comprises direct forwarding path related information or data forwarding proposal related information.

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