Communication method and communication device

Abstract

The present application provides a communication method and apparatus for releasing a tunnel for transmitting data of a multicast service between an access network device and a core network device, thereby helping to reduce network resource overhead. The method includes, when a first terminal device is in a handover preparation phase in which the first terminal device is handed over from the first access network device to a second access network device, the first access network device knowing that the first terminal device is the last terminal device to receive data of the first multicast service via the first access network device. The first access network device transmits first information, where the first information is used to release the first tunnel, and the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device.

Description

[Technical field]

[0001] The present application relates to the field of communications, and more particularly to a communication method and device. [Background technology]

[0002] With the development of mobile Internet, mobile high definition video services are rapidly increasing. Users are gradually changing from watching trending programs on fixed televisions to watching trending programs on mobile terminals such as mobile phones. Therefore, the impact of video services on mobile Internet is becoming stronger and stronger. If the transmission of video services can be optimized through air interface multicast, the impact of video traffic on mobile networks will be greatly reduced.

[0003] It is very difficult to implement a multicast solution in previous generations of mobile communication technologies, such as the third generation (3G) and fourth generation (4G) mobile communication technologies. For example, in the multicast solution in previous generations of mobile communication technologies, dedicated network elements and interfaces supporting multicast need to be added based on the existing communication architecture, and a dedicated multicast channel is also required for support. This not only increases the operator's overhead, but also increases the complexity of the terminal.

[0004] To overcome the above difficulties, how to support multicast / broadcast service (5G Multicast Broadcast Service, 5MBS) based on the 5th generation (5G) mobile communication network architecture has become a major research topic. The key issue in the research of 5MBS research topic is multicast / broadcast service session management (MBS (multicast / broadcast service) session management). For this research issue, how to release the multicast session tunnel is an urgent problem to be solved. Summary of the Invention

[0005] The embodiments of the present application provide a communication method and apparatus for a multicast service, and open a tunnel for transmitting data of the multicast service between an access network device and a core network device, thereby helping to reduce network resource overhead.

[0006] According to a first aspect, there is provided a method of communication, the method including:

[0007] The first access network device knows that when the first terminal device is in a handover preparation phase in which the first terminal device is handed over from the first access network device to the second access network device, the first terminal device is the last terminal device to receive data of the first multicast service via the first access network device.

[0008] The first access network device transmits first information, where the first information is used to release a first tunnel, and the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device.

[0009] Therefore, in this embodiment of the present application, when the first terminal device is in a handover preparation phase in which the first terminal device is handed over from the first access network device to the second access network device, the first access network device can know that the first terminal device is the last terminal device to receive data of the first multicast service through the first access network device, and can send the first information to release the first tunnel used to transmit data of the first multicast service between the first access network device and the core network device, thereby helping to reduce network resource overhead.

[0010] For example, the first access network device may be a source access network device, and the second access network device is a target access network device.

[0011] The first multicast service may include, but is not limited to, one multicast service or multiple different multicast services.

[0012] In the present example, the first information may include an indication used to release the first tunnel and information about the first tunnel.

[0013] In another example of the present application, the first information may include an indication used to release the first tunnel and an identification of the first multicast service.

[0014] In another example of the present application, the first information may include an indication used to release the first tunnel, an identification of the first multicast service, and information about the first tunnel.

[0015] The information about the first tunnel may be used to uniquely determine the first tunnel, and may be, for example, a tunnel endpoint identifier (TEID) of the first tunnel or an ID of the first tunnel, but is not limited thereto herein. The identification information of the first multicast service may be used to uniquely determine the multicast service, and may be, for example, a multicast service ID, a multicast service name, a multicast address, or a multicast group ID, but is not limited thereto herein.

[0016] In this embodiment of the present application, the handover preparation phase may be a phase in which a source access network device, a target access network device, or a core network device (which may be, but is not limited to, AMF, SMF, UPF, or the like) prepares resources required by handover for the first terminal device. The resources required by handover may include a forwarding tunnel, radio bearer configuration information required by the first terminal device to receive service data via the target access network device, air interface resources configured by the target access network device for the first terminal device, or the like, which is not limited to in this embodiment of the present application.

[0017] In an example, in an Xn handover scenario, the handover preparation phase may be a process in which the source access network device receives a measurement report of a first terminal device and makes a handover decision to the first terminal device based on the measurement report, where the decision result is handover; the source access network device sends a handover request to the target access network device and receives a handover request acknowledgment response sent by the target access network device.

[0018] In an example, in an N2 handover, the handover preparation phase may be a process in which the source access network device receives a measurement report of the first terminal device, and based on the measurement report, sends a handover request (handover required) to the source access and mobility management function network element, and the source access and mobility management function network element receives a UE context creation response from the target access and mobility management network element.

[0019] The source access network device may know that at any point in the handover preparation phase, the first terminal device is the last terminal device that will receive data of the first multicast service via the first access network device.

[0020] In some optional embodiments, in the handover preparation phase, when a first terminal device that has subscribed to the first multicast service sends a measurement report to the source access network device, the source access network device makes a handover decision for the first terminal device based on the measurement report, where the decision result is handover; the source access network device may update the number of terminal devices that have subscribed to the first multicast service via the source access network device, for example, reduce the number of terminal devices by 1. When the number of terminal devices is 0, the source access network device may know that the first terminal device is the last terminal device that receives data of the first multicast service via the first access network device.

[0021] In some optional embodiments, the number of terminal devices subscribed to the multicast service via the source access network device may be included in a Multicast Context, Multicast Session Context, Multicast Group Context, or Multicast Service Context corresponding to the multicast service associated with the PDU session of the first terminal device.

[0022] For example, the core network device may be a multicast user plane function network element, such as, but not limited to, a MUF, an M-UPF, an MS-UPF, or an MB-UPF. In this case, the first tunnel may include a tunnel used to transmit the first multicast service between the source access network device and the multicast user plane function network element (such as a MUF, an M-UPF, an MS-UPF, or an MB-UPF).

[0023] For example, the core network device may be a user plane function network element, such as a UPF, in which case the first tunnel may include a tunnel used to transmit the first multicast service between the source access network device and the user plane function network element (e.g., a UPF).

[0024] It should be noted that when the core network device is a user plane function network element, the user plane function network element may include a user plane function that can be used to process a multicast service. That is, it may be considered that a user plane function (e.g., MUF, M-UPF, MS-UPF, or MB-UPF) that can be used to process a multicast service may be combined with a user plane function network element in a function network element. Correspondingly, in this case, the session management function network element may include a control plane function that can be used to process a multicast service. That is, a control plane function (e.g., MCF, M-SMF, MS-SMF, or MB-SMF) that can be used to process a multicast service may be combined with a session management function network element in a function network element.

[0025] Referring to the first aspect, in some implementations of the first aspect, for example, in an Xn handover scenario, the first access network device sending the first information includes:

[0026] The first access network device sends a handover request to the second access network device, where the handover request requests handover of the first terminal device from the first access network device to the second access network device, and the handover request includes first information.

[0027] For example, when receiving a measurement report of the first terminal device and determining based on the measurement report that the first terminal device needs to be handed over to the second access network device or determining to send a handover request to the second access network device, the first access network device may know that the first terminal device is the last terminal device that subscribed to the first multicast service through the first access network device. In this case, the handover request sent by the first access network device to the second access network device may carry the first information.

[0028] Correspondingly, after receiving the handover request from the first access network device, the second access network device may send a path switch request (e.g., N2 path switch request, N2 path switch request) to an access and mobility management function network element (e.g., AMF), where the path switch request includes the first information. Then, the access and mobility management function network element may send a PDU session context update request (e.g., Nsmf_PDUSession_UpdateSMContextRequest) to the session management function network element, where the PDU session context update request includes the first information.

[0029] Further, when the core network device is a multicast user plane function network element, after receiving the PDU session context update request, the session management function network element may send a first message to the multicast session management function network element, where the first message includes the first information. For example, the first message may be an N16 message. After receiving the first message, the multicast session management function network element may send a fifth message to the multicast user plane function network element, where the fifth message may include the first information. For example, the fifth message may be an N4 session update request. The multicast user plane function network element may obtain the first information based on the fifth message and release the first tunnel.

[0030] When the core network device is a user plane function network element, after receiving the PDU session context update request, the session management function network element may send an N4 session update request to the user plane function network element, where the N4 session update request may include first information. The user plane function network element may obtain the first information based on the N4 session update request to release the first tunnel.

[0031] Therefore, in this embodiment of the present application, in an Xn handover scenario, the handover request sent by the first access network device to the second access network device carries the first information, so that the first information is transmitted to the core network device, and the core network device can release the first tunnel based on the first information. Therefore, in this embodiment of the present application, the first tunnel for transmitting data of the first multicast service between the access network device and the core network device can be released in an Xn handover scenario, which helps reduce network resource overhead.

[0032] In addition, in an Xn handover scenario, the first access network device can include the first information in existing signaling (e.g., handover request), so that the first information is eventually sent to the multicast user plane function network element or the user plane function network element, which helps to further reduce network resource overhead.

[0033] Referring to the first aspect, in some implementations of the first aspect, for example, in an N2 handover scenario, the first access network device sending the first information includes:

[0034] The first access network device sends a handover request (eg, a handover request) to the first access and mobility management function network element, where the handover request includes the first information.

[0035] For example, when receiving a measurement report of the first terminal device or deciding to send a handover request to the first access and mobility management function network element, the first access network device may know that the first terminal device is the last terminal device that subscribed to the first multicast service through the first access network device. In this case, the handover request sent by the first access network device to the first access and mobility management function network element may include the first information. For example, the first access and mobility management function network element may be a source access and mobility management function network element.

[0036] Correspondingly, after receiving the handover request, the first access and mobility management function network element may send a UE context creation request (e.g., Namf_Communication_CreateUEContext Request) to the second access and mobility management function network element, where the UE context creation request includes the first information. Then, the second access and mobility management function network element sends a PDU session update context request to the session management function network element, where the PDU session update context request may include the first information. The second access and mobility management function network element may be referred to as a target access and mobility management function network element.

[0037] Further, when the core network device is a multicast user plane function network element, after receiving the PDU session context update request, the session management function network element may send a first message to the multicast session management function network element, where the first message includes the first information. For example, the first message may be an N16 message. After receiving the first message, the multicast session management function network element may send a fifth message to the multicast user plane function network element, where the fifth message may include the first information. For example, the fifth message may be an N4 session update request. Correspondingly, the multicast user plane function network element may obtain the first information based on the fifth message and release the first tunnel. Alternatively, the multicast user plane function network element may release the first tunnel based on the fifth message.

[0038] When the core network device is a user plane function network element, after receiving the PDU session context update request, the session management function network element may send a session update request (e.g., an N4 session update request) to the user plane function network element, where the session update request may include the first information. Correspondingly, the multicast user plane function network element may obtain the first information based on the session update request and release the first tunnel.

[0039] Therefore, in this embodiment of the present application, in the N2 handover scenario, the handover request sent by the first access network device to the first access and mobility management function network element carries the first information, so that the first information is transmitted to the core network device, and the core network device can release the first tunnel based on the first information. Therefore, in this embodiment of the present application, the first tunnel for transmitting data of the first multicast service between the access network device and the core network device can be released in the N2 handover scenario, which helps reduce network resource overhead.

[0040] In addition, in an N2 handover scenario, the first access network device can include the first information in existing signaling (e.g., a handover request), so that the first information is eventually sent to the multicast user plane function network element or the user plane function network element, which helps to further reduce network resource overhead.

[0041] Referring to the first aspect, in some implementations of the first aspect, the first access network device sending the first information includes:

[0042] The first access network device sends a third message to a third access and mobility management function network element, where the third message includes the first information, and the third access and mobility management function network element is an access and mobility management function network element selected by the first access network device for the first multicast service when the first terminal device joins the first multicast service.

[0043] For example, the first access network device may know that the first terminal device is the last terminal device that subscribed to the first multicast service through the first access network device at any time in the handover preparation phase. When or after knowing that the first terminal device is the last terminal device that subscribed to the first multicast service through the first access network device, the first access network device may send a third message to a third access and mobility management function network element. This is not limited in the present application.

[0044] Correspondingly, the third access and mobility management function network element may receive the third message. Then, the third access and mobility management function network element may send a fourth message to the multicast session management function network element, where the fourth message carries the first information. For example, the fourth message may be an N11 message. After receiving the fourth message, the multicast session management function network element may send a fifth message carrying the first information to the multicast user plane function network element. For example, the fifth message may be an N4 session update request. Correspondingly, the multicast user plane function network element may obtain the first information based on the fifth message and release the first tunnel.

[0045] In some optional embodiments, the third access and mobility management function network element may alternatively be another access and mobility management function network element associated or not associated with the first terminal device. For example, the access and mobility management function network element associated with the first terminal device may be an access and mobility management function network element capable of providing a non-access stratum (NAS) signaling service to the first terminal device, and the access and mobility management function network element not associated with the first terminal device may be an access and mobility management function network element not capable of providing a NAS signaling service to the first terminal device.

[0046] In some optional embodiments, the third access and mobility management function network element may be the same network element as the source access and mobility management function network element described above, or may be the same network element as the target access and mobility management function network element described above, which is not limited in this embodiment of the present application.

[0047] Therefore, in this embodiment of the present application, the third message sent by the first access network device to the third access and mobility management function network element carries the first information, so that the first information is transmitted to the core network device, and the core network device can release the first tunnel based on the first information. Therefore, in this embodiment of the present application, the first tunnel for transmitting data of the first multicast service between the access network device and the core network device can be released, which helps reduce network resource overhead.

[0048] According to a second aspect, there is provided a method of communication, the method comprising:

[0049] The second access network device receives a handover request from the first access network device, where the handover request requests handover of the first terminal device from the first access network device to the second access network device, the handover request includes first information, the first information is used to release a first tunnel, and the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device.

[0050] The second access network device sends a reroute request to the access and mobility management function network element, where the reroute request includes the first information.

[0051] According to a third aspect, there is provided a method of communication, the method including:

[0052] An access and mobility management function network element receives a path switching request from a second access network device, where the path switching request includes first information, the first information is used to release a first tunnel, and the first tunnel is used to transmit data of a first multicast service between the first access network device and a core network device.

[0053] The access and mobility management function network element sends a protocol data unit PDU session context update request to the session management function network element, where the PDU session context update request includes first information.

[0054] According to a fourth aspect, there is provided a method of communication, the method including:

[0055] A session management function network element receives a protocol data unit PDU session context update request from an access and mobility management function network element, where the PDU session context update request includes first information, the first information is used to release a first tunnel, and the first tunnel is used to transmit data of a first multicast service between a first access network device and a core network device.

[0056] The session management function network element sends a first message to a multicast session management function network element, where the first message includes first information.

[0057] Referring to the fourth aspect, in some possible implementations of the fourth aspect, the first message is an N16 message.

[0058] According to a fifth aspect, there is provided a method of communication, the method including:

[0059] A session management function network element receives a protocol data unit PDU session context update request from an access and mobility management function network element, where the PDU session context update request includes first information, the first information is used to release a first tunnel, and the first tunnel is used to transmit data of a first multicast service between a first access network device and a core network device.

[0060] The session management function network element sends a session update request to the user plane function network element, where the session update request includes the first information.

[0061] According to a sixth aspect, there is provided a method of communication, the method including:

[0062] A multicast session management function network element receives a first message from the session management function network element, where the first message includes first information, the first information is used to release a first tunnel, and the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device.

[0063] The multicast session management function network element sends a fifth message to the multicast user plane function network element, where the fifth message includes the first information.

[0064] Referring to the sixth aspect, in some possible implementations of the sixth aspect, the first message is an N16 message.

[0065] Referring to the sixth aspect, in some possible implementations of the sixth aspect, the fifth message is an N4 session update request.

[0066] According to a seventh aspect, there is provided a method of communication, the method including:

[0067] A first access and mobility management function network element receives a handover request from a first access network device, where the handover request includes first information, the first information is used to release a first tunnel, and the first tunnel is used to transmit data of a first multicast service between the first access network device and a core network device.

[0068] A first access and mobility management function network element sends a create user equipment (UE) context request to a second access and mobility management function network element, where the create UE context request includes first information.

[0069] According to an eighth aspect, there is provided a method of communication, the method including:

[0070] A second access and mobility management function network element receives a user equipment (UE) context creation request from a first access and mobility management function network element, where the UE context creation request includes first information, the first information is used to release a first tunnel, and the first tunnel is used to transmit data of a first multicast service between the first access network device and a core network device.

[0071] The second access and mobility management function network element sends a protocol data unit PDU session context update request to the session management function network element, where the PDU session context update request includes the first information.

[0072] According to a ninth aspect, there is provided a communication method, including:

[0073] The third access and mobility management function network element receives a third message from the first access network device, where the third message includes first information, the first information is used to release a first tunnel, the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device, and when the first terminal device subscribes to the first multicast service, the third access and mobility management function network element is an access and mobility management function network element selected by the first access network device for the first multicast service.

[0074] The third access and mobility management function network element sends a fourth message to the multicast session management function network element, where the fourth message includes the first information.

[0075] Referring to the ninth aspect, in some possible implementations of the ninth aspect, the third message is an N2 message.

[0076] According to a tenth aspect, there is provided a communication method, including:

[0077] The multicast session management function network element receives a fourth message from a third access and mobility management function network element, where the fourth message includes first information, the first information is used to release a first tunnel, the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device, and when the first terminal device subscribes to the first multicast service, the third access and mobility management function network element is an access and mobility management function network element selected by the first access network device for the first multicast service.

[0078] The multicast session management function network element sends a fifth message to the multicast user plane function network element, where the fifth message includes the first information.

[0079] Referring to the tenth aspect, in some possible implementations of the tenth aspect, the fifth message is an N4 session update request.

[0080] Referring to the ninth or tenth aspect, in some possible implementations of the ninth or tenth aspect, the fourth message is an N11 message.

[0081] According to an eleventh aspect, there is provided a method of communication, the method including:

[0082] The multicast user plane function network element receives a fifth message from the multicast session management function network element, where the fifth message includes first information, the first information is used to release a first tunnel, and the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device.

[0083] The multicast user plane function network element releases the first tunnel based on the first information.

[0084] According to a twelfth aspect, there is provided a method of communication, the method comprising:

[0085] A user plane function network element receives a session update request from a session management network element, where the session update request includes first information, the first information is used to release a first tunnel, and the first tunnel is used to transmit data of a first multicast service between a first access network device and a core network device.

[0086] The user plane function network element releases the first tunnel based on the first information.

[0087] Referring to the eleventh or twelfth aspect, in some possible implementations of the eleventh or twelfth aspect, the first tunnel may be released by removing an associated resource of the first tunnel, such as a tunnel endpoint identifier.

[0088] Referring to the eleventh or twelfth aspect, in some possible implementations of the eleventh or twelfth aspect, the first information includes an instruction used to release the first tunnel and information about the first tunnel.

[0089] Releasing the first tunnel includes releasing the first tunnel based on the indication used to release the first tunnel and information about the first tunnel.

[0090] In this manner, the multicast user plane function network element or the user plane function network element may release a first tunnel (e.g., which may be, but is not limited to, one or more first tunnels) corresponding to the information about the first tunnel included in the first information.

[0091] Referring to the 11th or 12th aspect, in some possible implementations of the 11th or 12th aspect, the first information includes an instruction used to release the first tunnel and identification information of the first multicast service.

[0092] Releasing the first tunnel includes determining a first multicast service based on identification information of the first multicast service; determining a first tunnel for transmitting data of the first multicast service between the first access network device and the core network device; and releasing the first tunnel based on an instruction used to release the first tunnel.

[0093] In this way, the multicast session function network element, or the session function network element, may release all multicast session tunnels corresponding to the first multicast service indicated in the first information, i.e., the first tunnels (e.g., all the first tunnels) used to transmit data of the first multicast service between the source access network device and the core network device.

[0094] Referring to the 11th or 12th aspect, in some possible implementations of the 11th or 12th aspect, the first information includes an instruction used to release the first tunnel, an identification information of the first multicast service, and information about the first tunnel.

[0095] Releasing the first tunnel includes determining the first multicast service based on identification information of the first multicast service; determining the first tunnel from tunnels for transmitting data of the first multicast service between the first access network device and the core network device based on information about the first tunnel; and releasing the first tunnel based on an instruction used to release the first tunnel.

[0096] In this way, the multicast user plane function network element or the user plane function network element can release the first tunnel corresponding to the information about the first tunnel included in the first information. In addition, when the first tunnel is determined based on both the identification information of the first multicast service and the information about the first tunnel, the first tunnel needs to be determined only from one or more multicast session tunnels corresponding to the first multicast service. This helps to determine the first tunnel more accurately and quickly and improve the efficiency of releasing the first tunnel.

[0097] It should be understood that the beneficial effects realized in the second to twelfth aspects of the present application and the corresponding implementations refer to the beneficial effects realized in the first aspect of the present application and the corresponding implementations, and details will not be described again.

[0098] According to a thirteenth aspect there is provided a communication device, comprising a module or unit configured to perform a communication method according to any one of the first to twelfth aspects or a possible implementation of any one of the first to twelfth aspects.

[0099] According to a fourteenth aspect there is provided a communication device comprising a processor configured to call a computer program from a memory and to execute the computer program to perform a communication method according to any one of the first to twelfth aspects or a possible implementation of any one of the first to twelfth aspects.

[0100] Optionally, the communication device may further comprise a memory, the memory configured to store the program executed by the processor.

[0101] The communication device may be, for example, an access network device, an access and mobility management function network element, a session management function network element, a multicast session management function network element, or a multicast user plane function network element.

[0102] According to a fifteenth aspect, there is provided a chip. The chip comprises a processor and a communication interface. The communication interface is configured to communicate with an external device or an internal device. The processor is configured to implement a method according to any one of the first to twelfth aspects or a possible implementation of any one of the first to twelfth aspects.

[0103] Optionally, the chip may further include a memory. The memory stores instructions. The processor is configured to execute the instructions stored in the memory or other instructions. When the instructions are executed, the processor is configured to implement a method according to any one of the first to twelfth aspects or possible implementations of the first to twelfth aspects.

[0104] Optionally, the chip may be integrated into an access network device, an access and mobility management function network element, a session management function network element, a multicast session management function network element, or a multicast user plane function network element.

[0105] According to a sixteenth aspect there is provided a computer readable storage medium storing program code for execution by a synchronization device, the program code comprising instructions used to implement a method according to any one of the first to twelfth aspects or a possible implementation of any one of the first to twelfth aspects.

[0106] According to a seventeenth aspect there is provided a computer program product comprising instructions which, when executed on a computer, are capable of causing the computer to carry out a method according to any one of the first to twelfth aspects or a possible implementation of any one of the first to twelfth aspects.

[0107] According to an 18th aspect, there is provided a communication system comprising an apparatus configured to perform a method according to the first aspect or any one of the possible implementations of the first aspect, an apparatus configured to perform a method according to the second aspect, the third aspect and the fourth aspect, and an apparatus configured to perform a method according to the 11th aspect or any one of the possible implementations of the 11th aspect.

[0108] According to a 19th aspect, there is provided a communication system comprising an apparatus configured to perform a method according to the first aspect or any one of the possible implementations of the first aspect, an apparatus configured to perform a method according to the second aspect, the third aspect, the fifth aspect and the sixth aspect, and an apparatus configured to perform a method according to the 12th aspect or any one of the possible implementations of the 12th aspect.

[0109] According to a twentieth aspect, there is provided a communication system comprising an apparatus configured to perform a method according to the first aspect or any one of the possible implementations of the first aspect, an apparatus configured to perform a method according to the seventh aspect, the eighth aspect and the fourth aspect, and an apparatus configured to perform a method according to the eleventh aspect or any one of the possible implementations of the eleventh aspect.

[0110] According to a 21st aspect, there is provided a communication system comprising an apparatus configured to perform a method according to the first aspect or any one of the possible implementations of the first aspect, an apparatus configured to perform a method according to the seventh aspect, the eighth aspect, the fifth aspect and the sixth aspect, and an apparatus configured to perform a method according to the 12th aspect or any one of the possible implementations of the 12th aspect.

[0111] According to a 22nd aspect, there is provided a communication system comprising an apparatus configured to perform a method according to the first aspect or any one of the possible implementations of the first aspect, an apparatus configured to perform the methods according to the 9th and 10th aspects, and an apparatus configured to perform a method according to the 11th aspect or any one of the possible implementations of the 11th aspect. [Brief description of the drawings]

[0112] [Figure 1] FIG. 1 is a schematic diagram of a system architecture according to an embodiment of the present application.

[0113] [Diagram 2] FIG. 2 is a schematic diagram of another system architecture according to an embodiment of the present application.

[0114] [Figure 3A] FIG. 2 is a schematic diagram of transmission service data according to an embodiment of the present application;

[0115] [Figure 3B] FIG. 2 is a schematic diagram of another service data transmission according to an embodiment of the present application;

[0116] [Figure 4A] 1 is a schematic flowchart of a terminal device subscribing to a multicast service; [Figure 4B] 1 is a schematic flowchart of a terminal device subscribing to a multicast service; [Figure 4C] 1 is a schematic flowchart of a terminal device subscribing to a multicast service;

[0117] [Figure 5A] FIG. 2 is a schematic diagram of an application scenario in which the solution according to an embodiment of the present application is applicable;

[0118] [Figure 5B] FIG. 2 is a schematic diagram of an application scenario in which the solution according to an embodiment of the present application is applicable;

[0119] [Figure 5C] FIG. 2 is a schematic diagram of an application scenario in which the solution according to an embodiment of the present application is applicable;

[0120] [Figure 6] 1 is a schematic flowchart of a communication method according to an embodiment of the present application;

[0121] [Figure 7A] 1 is a specific example of a communication method according to an embodiment of the present application. [Figure 7B] 1 is a specific example of a communication method according to an embodiment of the present application.

[0122] [Figure 8] 4 is a schematic flowchart of another communication method according to an embodiment of the present application;

[0123] [Figure 9A] 4 is a specific example of another communication method according to an embodiment of the present application. [Figure 9B] 4 is a specific example of another communication method according to an embodiment of the present application.

[0124] [Figure 10A] 4 is a specific example of another communication method according to an embodiment of the present application. [Figure 10B] 4 is a specific example of another communication method according to an embodiment of the present application. [Figure 10C] 4 is a specific example of another communication method according to an embodiment of the present application.

[0125] [Figure 11] 1 is a schematic diagram of the structure of a wireless communication device according to an embodiment of the present application;

[0126] [Figure 12] FIG. 2 is a schematic diagram of the structure of a network device according to an embodiment of the present application; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0127] The technical solutions of the present application are described below with reference to the accompanying drawings.

[0128] The technical solutions of the embodiments of the present application may be applied to various communication systems, such as global system for mobile communications (GSM), code division multiple access (CDMA) systems, wideband code division multiple access (WCDMA) systems, general packet radio service (GPRS), long term evolution (LTE) systems, system architecture evolution (SAE) systems, LTE frequency division duplex (FDD) systems, LTE time division duplex (TDD), universal mobile telecommunications system (UMTS), worldwide interoperability for microwave access (WiMAX) communication systems, 5th generation (5G) systems, or new radio (NR), and subsequent evolution communication systems.

[0129] Figure 1 is a schematic diagram of a communication system according to an embodiment of the present application. Figure 1 includes an access network device, a core network device and a terminal device. The terminal device is connected to the access network device, and the access network device is connected to the core network device, so that the terminal device can communicate with the core network device by using the access network device.

[0130] The terminal device in the embodiments of the present application may also be referred to as user equipment (UE), a mobile station (MS), a mobile terminal (MT), an access terminal, a subscriber unit, a subscriber station, a mobile station, a remote station, a remote terminal, a mobile device, a user terminal, a terminal, a wireless communication device, a user agent, a user equipment, or the like.

[0131] A terminal device may be a device that provides voice / data connectivity to a user, for example a handheld device with wireless connectivity or an on-board device. Currently, some terminals are, for example, a mobile phone, a tablet computer, a laptop computer, a palmtop, a mobile internet device (MID), a wearable device, a virtual reality (VR) device, an augmented reality (AR) device, a wireless terminal in industrial control, a wireless terminal in self-driving, a wireless terminal in remote medical surgery, a wireless terminal in a smart grid, a wireless terminal in transportation safety, a wireless terminal in a smart city, a wireless terminal in a smart home, a mobile phone, a cordless phone, a session initiation protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device with wireless communication capabilities, a computing device or another processing device connected to a wireless modem, an on-board device, a wearable device, a terminal device in a 5G network, or an evolved public land mobile network. The UE may be a terminal device in a Presence Mobile Network (PLMN), which is not limited in the embodiments of the present application.

[0132] By way of example and not of limitation, in the embodiment of the present application, the wearable device may also be referred to as a wearable intelligent device, which is a collective term for wearable devices, such as glasses, gloves, watches, clothes, shoes, etc., developed by applying wearable technology to the intelligent design of daily clothing. A wearable device is a portable device that can be worn directly on the body or integrated into a user's clothing or accessories. A wearable device is not only a hardware device, but also implements powerful functions through software support, data exchange, and cloud interaction. Common wearable intelligent devices include fully-equipped and large-sized devices, such as smart watches or smart glasses, which can implement full or partial functions without relying on smartphones, and devices that only focus on one type of application function and need to cooperate with other devices, such as smartphones, such as various smart bands or smart jewelry for monitoring physical signs.

[0133] In addition, in the embodiments of the present application, the terminal device may alternatively be a terminal device in an Internet of Things (IoT) system. IoT is an important part in the future development of information technology. The main technical feature of IoT is to connect things to a network by using communication technology to implement an intelligent network for the interconnection between humans and machines and between things.

[0134] When the various terminal devices described above are located in a vehicle (e.g., located in or installed in a vehicle), the terminal devices may all be considered as on-board terminal devices, e.g., the on-board terminal devices may also be referred to as on-board units (OBUs).

[0135] In the embodiment of the present application, the terminal device may further include a relay. Alternatively, it is understood that any device capable of performing data communication with a base station may be considered as a terminal device.

[0136] The access network device in the embodiment of the present application may be a device configured to communicate with a terminal device. The access network device may alternatively be referred to as an access device or a radio access network device, and may be an evolved NodeB (eNB or eNodeB) in an LTE system, or a radio controller in a cloud radio access network (CRAN) scenario. Alternatively, the access device may be a relay station, an access point, an on-board device, a wearable device, an access device in a 5G network, a network device in a future evolved PLMN network, or the like. The access device may be an access point (AP) in a WLAN, or a gNB in ​​a new radio (NR) system. This is not limited in the embodiment of the present application.

[0137] In addition, in an embodiment of the present application, the access network device is a device in the RAN, in other words, a RAN node that connects a terminal device to a wireless network. For example, and not by way of limitation, the access network device may be, for example, a gNB, a transmission reception point (TRP), an evolved NodeB (eNB), a radio network controller (RNC), a NodeB (NB), a base station controller (BSC), a base transceiver station (BTS), a home base station (e.g., a home evolved NodeB, or a home NodeB, HNB), a baseband unit (BBU), or a wireless fidelity (Wi-Fi) access point (AP). In the network structure, the network devices may include a centralized unit (CU) node, a distributed unit (DU) node, a RAN device including a CU node and a DU node, or a RAN device including a control plane CU node (CU-CP node), a user plane CU node (CU-UP node) and a DU node.

[0138] An access network device provides services to a cell. A terminal device communicates with the access network device by using a transmission resource (e.g., a frequency domain resource, or in other words, a spectrum resource) used for the cell. The cell may be a cell corresponding to an access network device (e.g., a base station), and the cell may belong to a macro base station, or may belong to a base station corresponding to a small cell. Here, the small cell may include a metro cell, a micro cell, a pico cell, a femto cell, etc. These small cells have the characteristics of small coverage and low transmission power, and are suitable for providing high-speed data transmission services.

[0139] In order to facilitate understanding of the embodiments of the present application, a communication system applicable to the embodiments of the present application will be described in detail first with reference to Fig. 1. As shown in Fig. 1, a system architecture 100 includes a terminal device 110, an access network device 120, an access and mobility management function network element 130 and a session management function network element 140.

[0140] The access and mobility management function network element 130 and the session management function network element 140 are core network devices. For example, the terminal device 110 may access the core network by using the access network device 120 to implement data transmission. The access and mobility management function network element 130 may receive a request for subscribing the terminal device 110 to a multicast service from the access network device, and may request the session management function network element 140 to subscribing the terminal device 110 to the multicast service. The session management function network element 140 may create a corresponding multicast session tunnel for the terminal device 110, subscribe the terminal device 110 to the multicast service, and transmit the data stream of the multicast service to the terminal device 110.

[0141] The system architecture 100 may be configured to perform the multicast service transmission method in the embodiment of the present application.

[0142] Since the multicast service transmission method in this application is mainly based on 5G mobile communication technology and other future mobile communication technologies, another system architecture, i.e., the 5G system architecture in the embodiment of this application, is described below with reference to FIG. 2.

[0143] It should be noted that the multicast service solution in this application can also be applied to broadcast services.

[0144] 2 shows another system architecture 200 according to an embodiment of the present application. As shown in FIG. 2, the system architecture 200 may specifically include the following network elements:

[0145] 1. User Equipment (UE)

[0146] 2. (radio) access network ((R)AN): Used to provide network access functions to authorized users in a specific area, and can use transmission tunnels of different quality based on user level, service requirements, and the like. (R)AN network elements can manage radio resources, provide access services to terminal devices, and realize the transfer of control signals and user data between terminal devices and the core network. (R)AN can also be understood as a base station in a conventional network.

[0147] 3. Access and mobility management function (AMF): Mainly used for mobility management, access management, and the like. Specifically, the AMF can be configured to implement functions other than session management in the functions of a mobility management entity (MME), such as lawful interception or access authorization (or authentication).

[0148] 4. Session Management Function (SMF): Mainly used for session management, Internet Protocol (IP) address allocation and management of terminal devices, manageable user plane function selection, policy control or charging function interface termination point, downlink data notification, and the like.

[0149] It should be understood that in the system architecture 100, the terminal device 110 may be a UE in Fig. 2, the access network device 120 may be a RAN in Fig. 2, the access and mobility management function network element 130 may be an AMF in Fig. 2, and the session management function network element 140 may be an SMF in Fig. 2. This is not limited thereto.

[0150] Optionally, the system architecture 200 may further comprise:

[0151] 5. User Plane Function (UPF): Also referred to as a user plane function network element, it is used for packet routing and forwarding, quality of service (QoS) handling of user plane data, and the like. UPF is specifically classified into intermediate-UPF (I-UPF) and anchor UPF (PDU session anchor, PSA).

[0152] 6. Data network (DN): Used to provide a network for transmitting data, such as the Internet network. In the architecture of this embodiment of the present application, the PSA can access the remote DN, and the L-PSA can access the local DN.

[0153] 7. Authentication server function (AUSF): Mainly used for user authentication and the like.

[0154] 8. Policy control function (PCF): A unified policy framework used to guide network behavior and provides policy rule information and the like to control plane function network elements (e.g., AMF or SMF network elements).

[0155] 9. Unified data management (UDM): Used for user identity handling, access authentication, registration, mobility management, and the like.

[0156] 10. Application function (AF): Mainly supports interaction with 3rd generation partnership project (3GPP) core network to provide services, such as influencing data routing decisions or policy control functions, or providing some third-party services to the network side. The AF can be understood as a third-party server, such as an application server in the Internet, providing related service information (including providing quality of service requirement information corresponding to the service to the PCF), and sending user plane data information of the service to the PSA-UPF. The AF can be a content provider (CP).

[0157] 11. Network slice selection function (NSSF): Used for network slice selection.

[0158] In the system architecture 200, the N1 interface is a reference point between the terminal device and the AMF, and the N2 interface is a reference point between the (R)AN and the AMF, and is a non-access stratum (NAS). the N3 interface is a reference point between the (R)AN and the I-UPF and is configured to transmit user plane data and the like; the N4 interface is a reference point between the SMF and the I-UPF and is configured to transmit information such as tunnel identifier information, data buffer indication information, and downlink data notification messages of the N3 connection; the N5 interface is a reference point between the PCF and the AF; the N6 interface is a reference point between the UPF and the DN and is used to transmit user plane data and the like; the N7 interface is a reference point between the SMF and the PCF; the N8 interface is a reference point between the AMF and the UDM; the N9 interface is a reference point between the UPF; the N10 interface is a reference point between the SMF and the UDM; the N11 interface is a reference point between the AMF and the SMF; the N12 interface is a reference point between the AMF and the AUSF; and the N22 interface is a reference point between the AMF and the NSSF.

[0159] Optionally, the system architecture 200 may further comprise:

[0160] 12. Multicast control plane function (MCF): Also referred to as multicast session management function (M-SMF), multicast service session management function (MS-SMF) or multicast / broadcast session management function (MB-SMF), it is a control plane function that can be used to interconnect MCF, M-SMF or MB-SMF with PCF to create resources for multicast services to process multicast services. In this specification, it is noted that in a 5G network, MCF, M-SMF, MS-SMF or MB-SMF network elements may have alternative or different names and implement control plane functions for multicast services. In this specification, it is noted that, as described above, "multicast" in this application is a broad concept and may include multicast or broadcast. That is, the embodiments of this application may be applied to both multicast service transmission and broadcast service transmission. "Multicast" referred to in this application may be replaced with "multicast or broadcast". Therefore, the terms Multicast Control Plane Function (MCF), Multicast Session Management Function (M-SMF), Multicast Service Session Management Function (MS-SMF) and Multicast / Broadcast Session Management Function (MB-SMF) have the same meaning and may be interchanged, but this is not limited here.

[0161] 13. Multicast user plane function (MUF): Also referred to as multicast user plane function (M-UPF), multicast service user plane function (MS-UPF), or multicast / broadcast user plane function (MB-UPF), it is a user plane function that processes multicast services, for example, can be used to forward multicast service data. In this specification, it is noted that in a 5G network, the MUF, M-UPF, MS-UPF, or MB-UPF network element may alternatively have another name and implement a user plane function for a multicast service. In this specification, it is noted that, as described above, "multicast" in this application is a broad concept and may include multicast or broadcast. That is, the embodiments of this application may be applied to both multicast service transmission and broadcast service transmission. "Multicast" referred to in this application may be replaced with "multicast or broadcast". Therefore, the terms Multicast User Plane Function (MUF), Multicast User Plane Function (M-UPF), Multicast Service Session Management (MS-UPF) and Multicast / Broadcast Session Management (MB-UPF) have the same meaning and may be interchanged, without any limitation thereto herein.

[0162] In the system architecture 200, the MCF, M-SMF, MS-SMF, or MB-SMF may be integrated into the PCF (or SMF or NEF), and the MUF, M-UPF, MS-UPF, or MB-UPF may be integrated into the UPF, which is not limited in this embodiment of the present application.

[0163] It should be understood that the above-mentioned system architecture 200 applied to this embodiment of the present application is merely an example of a network architecture described in terms of a reference point architecture, and the network architecture applicable to this embodiment of the present application is not limited thereto. Any network architecture capable of implementing the functions of the above-mentioned network elements is applicable to this embodiment of the present application.

[0164] It should be noted that the names of the interfaces between the above network elements in Figure 2 are merely examples, and the interfaces may have other names in a specific implementation, which is not specifically limited in this embodiment of the present application.

[0165] It should be noted that the names of the network elements (such as SMF, AF, and UPF) included in FIG. 2 are also only examples and do not constitute any limitation on the functions of the network elements. In 5G networks and other future networks, the aforementioned network elements may alternatively have other names. This is not specifically limited in this embodiment of the present application. For example, in the 6th generation (6G) network, some or all of the aforementioned network elements may still use the terminology in 5G or may have other names. A general expression is provided here. Details will not be described again below. In addition, it should be understood that the names of messages (or signaling) transmitted between the aforementioned network elements are only examples and do not constitute any limitation on the functions of the messages.

[0166] In order to facilitate understanding of the embodiments of the present application, the following first provides a brief explanation of terms used in the present application.

[0167] 1. Multicast and unicast

[0168] Unicast can be understood as "point to point" communication. Unicast has several meanings. Specifically, it is as follows:

[0169] At the service layer, a unicast service means that the data of the service is sent to a specific terminal device.

[0170] Unicast between network elements means that there is a unicast tunnel between the source network element and the target network element (ie, the IP address of the target network element is a unicast IP address).

[0171] For the air interface, the air interface unicast mode means that the radio access network transmits service data to a single terminal device.

[0172] In the core network service layer, unicast means that service data is transmitted to a terminal device by using a protocol data unit (PDU) session.

[0173] In this application document, the unicast method in the transmission method determined by the SMF means transmitting data of a multicast service to a terminal device by using a PDU session.

[0174] Multicast may be called "groupcast" and may be understood as "point to multipoint (PTM)" communication. Multicast has multiple meanings, specifically as follows:

[0175] At the service layer, a multicast service means that the data of the service is transmitted to multiple terminal devices.

[0176] Multicast between network elements means that there is a multicast tunnel between the source network element and the target network element (ie, the IP address of the target network element is a multicast IP address).

[0177] For the air interface, the air interface multicast mode means that multiple terminal devices can receive one service data transmitted by the radio access network at the same time or at the same frequency.

[0178] In the core network service layer, multicast means transmitting data of a multicast service to a terminal device by using a multicast session, which includes a unicast tunnel or a multicast tunnel between a network element and an air interface radio bearer in unicast mode or an air interface radio bearer in multicast mode.

[0179] In the embodiment of the present application, the multicast mode in the transmission mode determined by the SMF means transmitting data of a multicast service to a terminal device by using a multicast session.

[0180] In the multicast scheme, the service data can be transmitted to all target nodes at once, or the service data can be transmitted only to specific targets. Therefore, in the multicast scheme, point-to-multipoint transmission can be implemented between one sending node and multiple receiving nodes, which solves the problem of low efficiency of the unicast scheme.

[0181] It should be noted that a broadcast service may be transmitted to a terminal device by using a multicast session. This is not limited in the embodiments of the present application. "Multicast" in the present application is a broad concept and may include multicast or broadcast. That is, the embodiments of the present application may be applied to both multicast service transmission and broadcast service transmission. "Multicast" referred to in the present application may be replaced with "multicast or broadcast".

[0182] FIG. 3A is a schematic diagram of transmission service data according to an embodiment of the present application. The schematic diagram shown in FIG. 3A can be used to transmit multicast service data (in a unicast manner) and can also be used to transmit unicast service data. In FIG. 3A, each of the three UEs corresponds to a different PDU session, respectively. The three different service data sent by the CP can be transmitted to the UE by using their corresponding PDU sessions. Specifically, the service transmission path between the CP and the AN may include a transmission path between the CP and the UPF and a transmission path between the UPF and the AN. The transmission path between the UPF and the AN may be referred to as a PDU session tunnel, and different PDU sessions have different PDU session tunnels. The three PDU session tunnels in this schematic diagram correspond to the three UEs, respectively. On the air interface, the AN may transmit service data to UE1, UE2, and UE3 separately in a unicast manner, i.e., in a PTP manner. In the schematic diagram, the service data of the UE may be different (eg, the target address is the IP address of the UE), and the service data of the UE may be respectively transmitted to the UE through independent transmission paths of the UE.

[0183] FIG. 3B is a schematic diagram of transmitting another service data according to an embodiment of the present application. The schematic diagram shown in FIG. 3B is used to transmit multicast service data. In FIG. 3B, the multicast service data may be transmitted from the CP to UE1, UE2, and UE3. The multicast service transmission path between the CP and the AN may include a transmission path between the CP and the UPF, and a transmission path between the UPF and the AN. The transmission path between the UPF and the AN may use a tunnel to transmit the multicast service data, for example, a tunnel according to the general tunnel protocol (GTP). Therefore, the transmission path between the UPF and the AN may be referred to as a multicast session tunnel, and the multicast session tunnel is shared by UE1, UE2, and UE3. On the air interface, the AN may transmit the multicast service data to UE1, UE2, and UE3 in a PTM manner. In other words, only one piece of data needs to be transmitted, and all three UEs can receive the data. In the schematic diagram, only one piece of multicast service data is transmitted from the CP to the UE on the transmission path, and multiple UEs may receive the multicast service data at the same time.

[0184] In this application, both the multicast session tunnel and the PDU session tunnel are tunnels between a user plane network element (e.g., UPF) and an access network AN (e.g., base station). The multicast session tunnel can be used to transport a multicast QoS flow of a multicast service, and the PDU session tunnel can be used to transport a unicast QoS flow of a unicast service, and can also be used to transport a unicast QoS flow corresponding to the multicast QoS flow of the multicast service.

[0185] It should be understood that the multicast QoS flow is transmitted between the UPF and the gNB1, and the data received by each UE can be referred to as multicast service data after being processed by the service data adaptation protocol (SDAP) layer, packet data convergence protocol (PDCP) layer, radio link control (RLC) layer, media access control (MAC) layer and physical layer (PHY) of the gNB1.

[0186] 2. Multicast services, multicast service flows, and multicast quality of service (QoS) flows

[0187] A multicast service may include one or more multicast service flows, which are indicated by information about the multicast service. The information about the multicast service includes at least description information of the multicast service. The description information of the multicast service may include description information of one or more multicast service flows. The description information of the multicast service flows includes at least one of a quality of service index (QoS flow identifier, QFI) that the multicast service flow needs to have, characteristic information of the multicast service flow (such as a multicast address, a target port number, and a source address of the multicast service), and a QoS requirement of the multicast service flow (such as jitter, delay, packet loss rate, and bandwidth). The QoS requirement of the multicast service flow is used to establish a multicast QoS flow. One multicast session may include one or more multicast QoS flows. In other words, a multicast service may be transmitted by using one or more multicast QoS flows in the multicast session tunnel in which the multicast session is located.

[0188] It should be understood that a PDU session is at the UE level, and a multicast session is at the service level. A PDU session of a UE can be associated with multiple multicast sessions. Specifically, a PDU session of a UE can join multiple multicast services. A multicast service can be served by a multicast session. A multicast session includes unicast or multicast tunnels from the data network to the core network and the radio access network, and unicast or multicast air interface resources allocated by the radio access network used to transmit the multicast service.

[0189] In addition to the description information of the multicast service, the multicast service information may further include information about the terminal devices, for example, identifiers of one or more terminal devices authorized (or requested) to subscribe to the multicast service, identifiers of terminal device groups, and the like.

[0190] A globally unique multicast service identifier (multicast ID, MCID) may be assigned to a multicast service, and the MCID may uniquely identify the multicast service in a PLMN. The English name MCID is not limited to this application, and the MCID may alternatively be replaced with another name, but it should be understood that the function of the MCID is to uniquely identify a multicast service. For example, the MCF shown in FIG. 2 may obtain information about the multicast service from a CP, and then send the obtained information about the multicast service to a PCF, and the PCF may generate a policy and charging control (PCC) rule based on the information about the multicast service. If the information about the multicast service may be applied to all terminal devices, the generated PCC rule may also be applied to all terminal devices. Otherwise, the generated PCC rule may be related to one or more terminal devices related to the multicast service. Optionally, if the MCF assigns an MCID to a multicast service, the MCF may send the MCID and the information about the multicast service to the PCF. Correspondingly, the PCC rule generated by the PCF for the multicast service may also include the MCID. Alternatively, the MCF may not assign an MCID to the multicast service, but the PCF may assign an MCID, and the PCF may send the MCID assigned to the multicast service to the MCF by using a response message.

[0191] 3. Multicast function of access network devices

[0192] Based on the relevant description of unicast and multicast, in this embodiment of the present application, an access network device supporting the multicast function can be understood as an access network device supporting the multicast service data transmission to a terminal device in a PTM data transmission manner, and an access network device not supporting the multicast function can be understood as an access network device not supporting the multicast service data transmission to a terminal device in a PTM data transmission manner. An access network device that does not support the multicast function can transmit the multicast service subscribed to by a terminal device by using a PDU session. An access network device that supports the multicast function can receive the multicast service data from the core network through a multicast session tunnel and transmit the multicast service data to multiple terminal devices subscribed to the multicast service.

[0193] 4. PDU session of the handed over terminal device

[0194] When a terminal device is handed over from a source access network device to a target access network device, the PDU session of the terminal device needs to be handed over from the source access network device to the target access network device. In this case, the PDU session can be referred to as the PDU session of the handed over terminal device.

[0195] In this embodiment of the present application, a PDU session being associated with a multicast service can be understood as a context of the PDU session being associated with a multicast service. Specifically, in a source access network device, a terminal device may apply to join a multicast service through a user plane or a control plane of a PDU session. Optionally, the terminal device may associate a PDU session with a multicast service by storing an identification information of the multicast service in a context of a PDU session. For example, if a terminal device joins through a user plane of a PDU session to watch CCTV1, the PDU session is associated with one multicast service. Also, if a terminal device joins to watch CCTV10, the PDU session is further associated with one multicast service. For a source access network device that supports a multicast function, after a terminal device joins a multicast service through a user plane or a control plane of a PDU session, the multicast service can be transmitted to the source access network device through a multicast session tunnel by using a multicast QoS flow, and the source access network device can transmit the multicast service data to the terminal device in an air interface point-to-point manner or an air interface point-to-multipoint manner. For a source access network device that does not support multicast function, after the terminal device subscribes to the multicast service through the user plane or control plane of the PDU session, the multicast service is transmitted to the source access network device through a PDU session tunnel by using a unicast QoS flow, and the source access network device sends the multicast service data to the terminal device in an air interface point-to-point manner.

[0196] It should be understood that after the multicast service data reaches the RAN, it is processed by the service data adaptation protocol (SDAP) layer, packet data convergence protocol (PDCP) layer, radio link control (RLC) layer, media access control (MAC) layer, and physical (PHY) layer of the RAN, and then transmitted to each UE that receives the multicast service data.

[0197] Currently, 3GPP has approved the start of a project to carry out a study on how to support multicast and broadcast functions (i.e., 5G multicast / broadcast services, 5MBS) based on the current 5G network architecture as a major research topic. In 5G or future evolved networks, access network devices supporting multicast functions will be deployed.

[0198] 4A to 4C, the procedure for a terminal device to join a multicast service is described below. For example, in FIG. 4A to FIG. 4C, an example is used for description in which terminal devices UE1, UE2, and UE3 join a multicast service.

[0199] 4A to 4C, a process of UE1 subscribing to a multicast service via a source gNB (S-gNB) and SMF1 is described in steps 401 to 410. The transmission path of the multicast service includes a transmission path between the MUF and UPF1 and a transmission path between the UPF1 and the S-gNB.

[0200] 401. UE1 sends a request to SMF1 to join a multicast service, where the request includes related information of the multicast service. The related information may be, for example, an identifier of the multicast service or multicast IP address information.

[0201] 402. SMF1 sends message #1 to MCF, where message #1 notifies MCF that UE1 will join the multicast service via S-gNB and SMF1.

[0202] 403. MCF sends message #2 to SMF1, where message #2 is used to respond to message #1 in step 402.

[0203] 404. SMF1 sends an N2 PDU session request to the S-gNB, requesting the S-gNB to allocate related air interface resources of the multicast service to UE1.

[0204] 405. The S-gNB allocates related air interface resources of the multicast service to UE1 and generates a tunnel identification information for the S-gNB.

[0205] 406. The S-gNB sends an N2 PDU session response carrying the tunnel identification information of the S-gNB to the SMF1.

[0206] 407. Perform N4 session establishment / modification between SMF1 and UPF1.

[0207] For example, SMF1 sends an N4 session establishment / modification request to UPF1, which includes the tunnel identification information of the S-gNB and the tunnel identification information assigned by SMF1 to UPF1. Then, UPF1 sends an N4 session establishment / modification response to SMF1. Then, a multicast session tunnel between the S-gNB and UPF1 is established.

[0208] 408. SMF1 sends message #3 to MCF, where message #3 requests to establish a tunnel for transmitting multicast service data between MUF and UPF1. For example, message #3 may carry a tunnel identification information assigned by SMF1 to UPF1.

[0209] 409. The MCF sends an N4 Session Establishment / Modification Request to the MUF, which includes the tunnel identification information assigned by the SMF1 to the UPF1 and further includes the tunnel identification information assigned by the MCF to the MUF. The MUF then sends an N4 Session Establishment / Modification Response to the MCF, and the tunnel between the MUF and the UPF1 is established.

[0210] 410: MCF sends message #4 to SMF1, where message #4 is used to respond to message #3 in step 408.

[0211] After step 410, a multicast service data transmission path is established from the multicast service source to the MUF, UPF1 and S-gNB. UE1 can receive the multicast service data through the multicast service data transmission path.

[0212] Please further refer to Figures 4A to 4C. After UE1 subscribes to the multicast service via the S-gNB and SMF1, UE2 may further subscribe to the multicast service via the S-gNB and SMF1. For example, the following steps 411 to 414 may be referred to.

[0213] 411: UE2 sends a request to join a multicast service to SMF1, where the request includes related information of the multicast service, where for the related information of the multicast service, please refer to the description in step 401.

[0214] 412: SMF1 sends an N2 PDU session request to the S-gNB to request the S-gNB to allocate related air interface resources of the multicast service to UE2.

[0215] UE2 also applies to join the multicast service via the S-gNB and SMF1, i.e., since both UE1 and UE2 apply to join the multicast service via the same SMF (i.e., SMF1), SMF1 only needs to request the S-gNB to allocate air interface resources for the multicast service of UE2. Specifically, the S-gNB still receives the multicast service data through the multicast session tunnel between UPF1 and the S-gNB, and transmits the multicast service data to UE2.

[0216] 413: The S-gNB allocates related air interface resources of the multicast service to the UE2.

[0217] It should be noted that since all UEs that have subscribed to the multicast service via the same SMF share a multicast session tunnel from UPF1 to the S-gNB, specifically, UE1 and UE2 share a multicast session tunnel between UPF1 and the S-gNB, in step 410, the S-gNB does not need to generate tunnel identification information.

[0218] 414. The S-gNB sends an N2 PDU session response to SMF1, responding to step 412.

[0219] After step 414, a multicast service data transmission path is established from the multicast service source to the MUF, UPF1 and S-gNB. UE2 can receive the multicast service data through the multicast service data transmission path.

[0220] Please refer to Figures 4A to 4C. UE3 may further subscribe to a multicast service. Different from UE1 and UE2 subscribing to the multicast service, UE3 subscribes to the multicast service via S-gNB and SMF2. The transmission path of the multicast service includes a transmission path between MUF and UPF2 and a transmission path between UPF2 and S-gNB. For example, the following steps 415 to 424 may be referred to.

[0221] 415: The UE 3 sends a request to join the multicast service to the SMF 2, where the request includes relevant information of the multicast service.

[0222] Since UE3 applies to join the multicast service via another SMF (i.e. SMF2), the following steps 416 to 424 need to be executed. The description of steps 416 to 424 is similar to steps 402 to 410. For details, please refer to the above description. The details will not be described again in this specification.

[0223] After step 424, a multicast service data transmission path is established from the multicast service source to the MUF, the UPF2, and the S-gNB. The UE3 can receive the multicast service data through the multicast service data transmission path.

[0224] In some embodiments, due to the mobility of the UE, the UE may be triggered to be handed over, for example, from an S-gNB to a target gNB (T-gNB). As a result, the UE leaves the multicast service to which it has subscribed in the source access network device. For example, steps 425 to 427 may be referenced.

[0225] 425: UE1 is handed over and leaves the multicast service to which it had subscribed via SMF1 and S-gNB.

[0226] 426: UE2 is handed over and leaves the multicast service to which it had subscribed via SMF1 and S-gNB.

[0227] 427: UE3 is handed over and leaves the multicast service to which it had subscribed via SMF2 and S-gNB.

[0228] The T-gNB may or may not support multicast function, which is not limited in this embodiment.

[0229] When a terminal device is handed over from a source access network device that supports multicast function to a target access network device (where the target access network device supports or does not support multicast function), how to release the multicast session tunnel between the source access network device and the core network device to reduce network resource overhead is an urgent problem to be solved.

[0230] In view of this, the embodiments of the present application provide a communication method and apparatus, in which a source access network device or a session management function network element can know that after a terminal device is handed over from a source access network device to a target access network device, other terminal devices do not receive data of a multicast service via the source access network device. In other words, the terminal device is the last terminal device that receives data of a multicast service via the source access network device, and the source access network device or the session management function network element decides to release a multicast session tunnel between the source access network device and a core network device.

[0231] Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings.

[0232] The technical solution in the present application can be used in a wireless communication system, for example, the communication system shown in Fig. 1 or the communication system shown in Fig. 2. There may be a wireless communication connection relationship between communication devices in the wireless communication system. One of the communication devices may be, for example, an access network device (for example, a source access network device) or a chip configured in an access network device (for example, a source access network device), and the other device may be, for example, a session management function network element or a chip configured in a session management function network element. This is not limited in the embodiment of the present application.

[0233] Without loss of generality, the embodiments of the present application are first described in detail by using the communication process of a terminal device as an example. It can be understood that any access network device in a wireless communication system or any chip configured in an access network device can perform communication based on the same method, and any session management function network element in a wireless communication system or any chip configured in a session management function network element can perform communication based on the same method. This is not limited in the present application.

[0234] In the following, with reference to Figs. 5A, 5B and 5C, an example scenario to which the solution in the embodiment of the present application is applied will be described.

[0235] In FIG. 5A, UE2 is handed over from S-gNB to T-gNB1, and T-gNB1 supports multicast function. There is a multicast session tunnel and a PDU session tunnel between S-gNB1 and UPF1, and there is a multicast session tunnel and a PDU session tunnel between T-gNB1 and UPF1. In this case, there is both a forwarding tunnel corresponding to the PDU session tunnel between S-gNB and T-gNB1, and a forwarding tunnel corresponding to the multicast session tunnel between S-gNB and T-gNB1. For example, UPF1 and UE2 in FIG. 5A can be UPF1 and UE2 in FIG. 4A-FIG. 4C.

[0236] Please note that in FIG. 5A, only an example in which the T-gNB1 supports the multicast function is used for explanation. However, the embodiment of the present application is not limited thereto. In another embodiment, the T-gNB1 may alternatively not support the multicast function. When the T-gNB1 does not support the multicast function, there is no multicast session tunnel between the T-gNB1 and the UPF1, and there is no forwarding tunnel corresponding to the multicast session tunnel between the S-gNB and the T-gNB1.

[0237] In Figure 5B, a UE is handed over from an S-gNB to a T-gNB, and the T-gNB does not support multicast function. There is a multicast session tunnel between the S-gNB and the MUF, a PDU session tunnel between the S-gNB and the UPF, and a PDU session tunnel between the T-gNB and the UPF. In this case, there is a forwarding tunnel corresponding to the PDU session tunnel between the S-gNB and the T-gNB, and there is no forwarding tunnel corresponding to the multicast session tunnel between the S-gNB and the T-gNB.

[0238] Please note that in FIG. 5B, only an example in which the T-gNB does not support the multicast function is used for explanation. However, the embodiment of the present application is not limited thereto. In another embodiment, the T-gNB may alternatively support the multicast function. When the T-gNB supports the multicast function, there is a multicast session tunnel between the T-gNB and the MUF, and there is a forwarding tunnel corresponding to the multicast session tunnel between the S-gNB and the T-gNB.

[0239] In FIG. 5C, a UE is handed over from an S-gNB to a T-gNB, and the T-gNB does not support multicast function. There is a multicast session tunnel between the S-gNB and the MUF, a PDU session tunnel between the S-gNB and the UPF, and a PDU session tunnel between the T-gNB and the UPF. In this case, there is an indirect forwarding tunnel between the S-gNB and the UPF corresponding to the PDU session tunnel, and there is an indirect forwarding tunnel between the UPF and the T-gNB corresponding to the PDU session tunnel. In other words, the S-gNB needs to send the PDU session that needs to be sent to the T-gNB through the indirect forwarding tunnel to the UPF, and the UPF then sends the PDU session to the T-gNB through the indirect forwarding tunnel.

[0240] Please note that in FIG. 5C, only an example in which the T-gNB does not support the multicast function is used for explanation. However, the embodiment of the present application is not limited thereto. In another embodiment, the T-gNB may alternatively support the multicast function. When the T-gNB supports a multicast session tunnel, there is a multicast session tunnel between the T-gNB and the MUF, there is an indirect forwarding tunnel corresponding to the multicast session tunnel between the S-gNB and the UPF, and there is an indirect forwarding tunnel corresponding to the multicast session tunnel between the UPF and the T-gNB. The embodiment of the present application may further be applied to a scenario in which the T-gNB supports the multicast function.

[0241] It should be further noted that the scenarios in Figures 5A, 5B, and 5C are special scenarios for facilitating the description of the technical solutions in the embodiments of the present application, and the technical solutions provided in the embodiments of the present application are not limited to Figures 5A, 5B, and 5C. In other words, the technical solutions provided in the embodiments of the present application may also be applied to other scenarios that are not listed. For example, other scenarios that are not listed may include, for example, the following three cases:

[0242] Case 1: For a PDU session of a terminal device to be handed over, in the handover process, the SMF and anchor UPF responsible for the PDU session of the terminal device to be handed over remain unchanged. For example, in the scenario in Figure 5A, the anchor UPF is UPF1 in the figure, and is UPF in Figures 5B and 5C.

[0243] Case 2: In the source access network device, for a multicast service associated with the PDU session of the terminal device to be handed over, assuming that the control plane multicast network element in charge of the group service of the source access network device is MCF-1 and the user plane multicast network element is MUF-1, MUF-1 may be connected to the anchor UPF where the PDU session of the terminal device is located (i.e., MUF is connected to UPF1 in FIG. 5A). Optionally, MUF-1 may alternatively be connected to the source access network device. In addition, MUF-1 may alternatively be connected to the source access network device by using another UPF. In other words, MUF-1 may alternatively be connected to another UPF other than the anchor UPF of the PDU session of the terminal device.

[0244] Case 3: For a target access network device, the network elements responsible for the multicast service associated with the PDU session of the terminal device to be handed over may be MCF-1 and MUF-1, or may be another MCF and another MUF. The MUF may be directly connected to the target access network device, or may be connected to the anchor UPF of the PDU session of the terminal device of the handover, or may be connected to the target access network device by using another UPF (i.e., a non-anchor UPF).

[0245] Hereinafter, a communication method provided in an embodiment of the present application will be described with reference to FIGS. 6 to 10A to 10C.

[0246] 6 is a schematic flowchart of a communication method 600 from a device interaction perspective according to an embodiment of the present application. As shown in FIG. 6, the method 600 includes steps 610 to 630.

[0247] 610: The session management function network element finds out that after the first terminal device is handed over from the first access network device to the second access network device, no terminal device has received data of the first multicast service via the first access network device.

[0248] For example, in the service layer, the first multicast service means that the data of the service can be transmitted to multiple terminal devices. For specific details about the multicast service and multicast, please refer to the above description. Details will not be described again.

[0249] The first access network device may be referred to as a source access network device, and the second access network device may be referred to as a target access network device.

[0250] For example, when the number of terminal devices subscribed to the first multicast service via the session management function network element and the source access network device is 0 after the first terminal device is handed over from the source access network device to the target access network device, the session management function network element may determine that there are no other terminal devices that receive data of the first multicast service via the source access network device after the first terminal device is handed over from the source access network device to the target access network device (in other words, there are no other terminal devices that subscribed to the first multicast service via the session management function network element and the source access network device).

[0251] In some optional embodiments, the number of terminal devices that have subscribed to the multicast service via the source access network device may be included in a Multicast Context, a Multicast Session Context, a Multicast Group Context, or a Multicast Service Context, which corresponds to the multicast service associated with the PDU session of the first terminal device. In other words, depending on whether another terminal device other than the terminal device in the Multicast Context, the Multicast Session Context, the Multicast Group Context, or the Multicast Service Context receives the first multicast service, the session management network element determines that no terminal device receives data of the first multicast service via the first access network device after the first terminal device is handed over from the first access network device to the second access network device.

[0252] In some optional embodiments, the session management function network element may further update the number of terminal devices that have subscribed to the multicast service via the session management function network element and the source access network device.

[0253] For example, after receiving a PDU session context update request, the session management network element updates the number of terminal devices subscribed to the multicast service via the session management function network element and the source access network device in the Multicast Context, Multicast Session Context, Multicast Group Context or Multicast Service Context corresponding to the multicast service associated with the PDU session of the first terminal device, for example, decrements the number of terminal devices by 1, and obtains the number of terminal devices currently subscribed to the first multicast service via the session management function network element and the source access network device.

[0254] In an example, after the first terminal device is handed over from the source access network device to the target access network device, and before the session management function network element updates the stored number of terminal devices that have subscribed to the first multicast service via the session management function network element and the access network device, the session management function network element may determine whether another terminal device receives data of the first multicast service via the source access network device. In this case, when the first terminal device is determined to be the last terminal device that has subscribed to the first multicast service via the session management function network element and the source access network device, in other words, when the terminal device (i.e., the first terminal device) that has subscribed to the first multicast service via the session management function network element and the source access network device is one, the session management function network element may know that there are no other terminal devices that receive data of the first multicast service via the source access network device.

[0255] In another example, after the first terminal device is handed over from the source access network device to the target access network device and the session management function network element updates the stored number of terminal devices that have subscribed to the multicast service via the session management function network element and the access network device, the session management function network element may determine whether another terminal device receives data of the first multicast service via the source access network device. In this case, when determining that the number of terminal devices that have subscribed to the first multicast service via the session management function network element and the source access network device is 0, the session management function network element may know that there is no other terminal device that receives data of the first multicast service via the source access network device.

[0256] 620: The session management function network element notifies the user plane function to release the first tunnel.

[0257] The first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device, which may be a UPF.

[0258] For example, the first tunnel may include a tunnel used to transmit a first multicast service between the first access network device and the UPF, i.e., a multicast session tunnel used to transmit a first multicast service. Specifically, for the multicast session tunnel, please refer to the above description. Details will not be described again.

[0259] In other words, after the first terminal device is handed over from the first access network device to the second access network device, the session management function network element may notify the user plane function to release the first tunnel after finding that the other terminal devices are not receiving data of the first multicast service through the first access network device. For example, the session management network element may send an N4 session update request to the first terminal device, carrying first information used to release the first tunnel.

[0260] For example, the first information may include an indication, a request or a notification to release the first tunnel. Optionally, the first information may alternatively include information about the first tunnel and / or identification information of the first multicast service, which is not limited in this embodiment of the present application.

[0261] For example, the first information may include an indication, a request or a notification to release the first tunnel, and may further include information about the first tunnel. Optionally, the first information may alternatively include identification information of the first multicast service, which is not limited in this embodiment of the present application.

[0262] For example, the first information may include an indication, request or notification to release the first tunnel, and may further include information about the first tunnel and identification information of the first multicast service, which is not limited in this embodiment of the present application.

[0263] The information about the first tunnel may be used to uniquely determine the first tunnel, and may be, for example, a tunnel endpoint identifier (TEID) of the first tunnel, but is not limited thereto herein. The identification information of the first multicast service may be used to uniquely determine the multicast service, and may be, for example, a multicast service ID, a multicast service name, a multicast address, or a multicast group ID, but is not limited thereto herein.

[0264] 630: The user plane function releases the first tunnel.

[0265] For example, after receiving an N4 session update request (carrying the first information) sent by a session management function network element, the user plane function may release the first tunnel and remove the associated resources of the first tunnel (e.g., remove the tunnel endpoint identifier of the first tunnel) based on, for example, the tunnel identification information in the first information.

[0266] Therefore, in this embodiment of the present application, after the first terminal device is handed over from the first access network device to the second access network device, when the other terminal devices find that they do not receive data of the first multicast service through the first access network device, the session management function network element may notify the user plane function to release the first tunnel used to transmit the first multicast service between the source access network device and the core network device, and release the multicast session tunnel between the access network device and the core network device, thereby helping to reduce network resource overhead.

[0267] In the following, a specific example of a communication method according to an embodiment of the present application is described with reference to Figures 7A and 7B. In the following embodiment, an example in which the session management function network element is an SMF, the source access network device is an S-gNB, and the user plane function is a UPF is used for description. For the implementation method of the chip in the SMF, the chip in the S-gNB, and the chip in the UPF, please refer to the specific description of the SMF, the S-gNB, and the UPF. Details will not be described again.

[0268] Optionally, in Figures 7A and 7B, the core network device further includes an AMF, an MCF, and a MUF. Alternatively, in some optional embodiments, the core network device may not include an MCF and a MUF. Rather, some functions or units in the SMF implement the functions of the MCF, and some functions or units in the UPF implement the functions of the MUF. This is not limited in this embodiment of the present application.

[0269] 7A and 7B are schematic flowcharts of another communication method 700 according to an embodiment of the present application. In the method 700, SMF1 determines whether a multicast session tunnel between the S-gNB and UPF1 needs to be released.

[0270] It should be noted that in Figures 7A and 7B, an example in which the UE to be handed over is UE2 in Figures 4A to 4C is used for description. Specifically, a process in which SMF1 determines whether to release the multicast session tunnel between the S-gNB and UPF1 after UE2 is handed over and leaves the multicast service it joined via SMF1 and S-gNB in ​​step 426 in Figures 4A to 4C is described in method 700.

[0271] In some embodiments, when the T-gNB1 to which the UE2 is handed over supports the multicast function, the method 700 is applicable to the scenario shown in Fig. 5A. In the following, the method 700 is described with reference to the scenario in Fig. 5A. As shown in Fig. 7A and Fig. 7B, the method 700 may comprise steps 701 to 716. It should be noted that the solution is also applicable to a scenario in which the T-gNB1 does not support the multicast function, and this is not limited here. The scenario shown in Fig. 5A is merely an example.

[0272] 7A and 7B show steps or operations of a communication method 700 provided in this embodiment of the present application, it should be understood that these steps or operations are merely examples. In this embodiment of the present application, other operations or variations of the operations in FIG. 7A and 7B may also be performed. In addition, the steps in the figures may be performed in a different order than presented in the figures, and not all operations in the figures may need to be performed.

[0273] Optionally, before step 701, the S-gNB may know whether the function of the T-gNB1, i.e., the function for the multicast function, is supported. For example, when there is an Xn connection between the T-gNB1 and the S-gNB, the T-gNB1 may inform the S-gNB of the capability information of the T-gNB1 by using the Xn interface, where Xn may be the interface of the Xn connection between the S-gNB and the T-gNB. For example, when the T-gNB1 supports the multicast function, the T-gNB sends the indication information #1 to the S-gNB, where the indication information #1 indicates that the T-gNB1 supports the multicast function.

[0274] 701: UE2 sends a measurement report to the S-gNB.

[0275] In response, the S-gNB receives the measurement report and decides to handover UE2 to T-gNB1.

[0276] 702: The S-gNB sends a Handover Request to the T-gNB1, where the S-gNB may know that the T-gNB1 supports multicast functionality.

[0277] For example, the handover request may include PDU session information of the handed over UE2. The PDU session information includes a PDU session identifier and QoS information corresponding to a unicast service included in the PDU session. If the PDU session of the handed over UE is further associated with a multicast service, the PDU session information further includes QoS information corresponding to the associated multicast service. For example, the QoS information of the unicast service includes a unicast QoS flow identifier (QFI) and QoS parameters corresponding to the unicast service, and the QoS information of the multicast service includes a multicast QoS flow identifier (QFI) and QoS parameters corresponding to the multicast service.

[0278] In addition, the handover request may further include the QFI of the QoS flow that the S-gNB intends to forward to the T-gNB1 and the endpoint identifier of the forwarding tunnel created by the S-gNB. For example, the QoS flow that the S-gNB intends to forward to the T-gNB1 may be a unicast QoS flow and / or a multicast QoS flow.

[0279] For example, when a service flow that the S-gNB intends to forward to the T-gNB1 includes a multicast QoS flow, the handover request may include the QFI of the multicast QoS flow and an endpoint identifier of a forwarding tunnel generated by the S-gNB corresponding to the multicast session tunnel. When a service flow that the S-gNB intends to forward to the T-gNB1 includes a unicast QoS flow, the handover request may include the QFI of the unicast QoS flow and an endpoint identifier of a forwarding tunnel generated by the S-gNB corresponding to the unicast session tunnel.

[0280] In other words, if the S-gNB intends to forward a unicast QoS flow through a forwarding tunnel corresponding to the PDU session tunnel, the handover request may include a QFI corresponding to the unicast QoS flow and an endpoint identifier generated by the S-gNB for the forwarding tunnel. If the S-gNB intends to forward a multicast QoS flow through a forwarding tunnel corresponding to the multicast session tunnel, the handover request may include a QFI corresponding to the multicast QoS flow and an endpoint identifier generated by the S-gNB for the forwarding tunnel.

[0281] It should be noted that the reason why the S-gNB needs to forward the service flow through the forwarding tunnel is because UE2 is disconnected from the S-gNB after step 704, specifically after the S-gNB delivers the handover command to UE2. In this case, UE2 cannot temporarily receive data through the S-gNB, and UE2 has not yet accessed the T-gNB1. In other words, UE2 cannot receive data through the S-gNB during this period of steps 704 and 705. Therefore, the S-gNB needs to forward this portion of data to the T-gNB1 for buffering through the forwarding tunnel. After step 705, specifically after UE2 has accessed the T-gNB1, the T-gNB1 delivers this portion of data to UE2.

[0282] 703: T-gNB1 sends a handover request ACK to the S-gNB.

[0283] For example, the T-gNB1 prepares radio resources for the UE to be handed over based on the QoS information of the unicast service and the QoS information of the multicast service received from the S-gNB. For example, the T-gNB1 may determine the number of air interface data radio bearers (DRBs) and the mapping relationship between the QFI and the DRB based on the QoS parameters corresponding to the QFI of each service flow. In addition, the T-gNB1 may further determine the configuration parameters corresponding to the DRB based on the QoS parameters corresponding to the QFI to which each DRB is mapped. The configuration parameters corresponding to the DRB are, for example, whether an acknowledged mode or a non-acknowledged mode is used by the radio link control (RLC) layer corresponding to the DRB. Finally, the T-gNB1 creates the corresponding DRB.

[0284] After preparing radio resources, the T-gNB1 sends a handover acknowledgement to the S-gNB. In some optional embodiments, the T-gNB1 may send information to the S-gNB that needs to be relayed to the UE2 via the S-gNB. For example, the T-gNB1 may send radio bearer configuration information of the T-gNB1 to the UE2 via the S-gNB. The radio bearer configuration information may be used by the UE2 to receive unicast service data and / or multicast service data delivered by the T-gNB1 after the UE2 accesses the T-gNB1.

[0285] In some optional embodiments, when the handover request at step 702 includes QFIs of service flows (including QFIs of unicast QoS flows and / or QFIs of multicast QoS flows) that the S-gNB intends to forward through the forwarding tunnel and the T-gNB1 supports data forwarding, the T-gNB1 assigns an endpoint identifier of the forwarding tunnel.

[0286] 704: The S-gNB delivers a handover command to UE2.

[0287] When the T-gNB1 requests the S-gNB to relay to the UE2 the radio bearer configuration information required by the UE2 to receive service data at the T-gNB1, the S-gNB sends the radio bearer configuration information to the UE2. After the S-gNB delivers the handover command to the UE2, the air interface connection between the UE2 and the S-gNB is temporarily disconnected.

[0288] Next, the S-gNB duplicates the multicast QoS flow received through the multicast session tunnel and forwards the duplicated multicast QoS flow to the T-gNB1.

[0289] After the air interface connection between the UE 2 and the S-gNB is disconnected, the S-gNB stops delivering the service data included in the PDU session and the multicast service data associated with the PDU session to the handed over UE 2. For example, the S-gNB stops transmitting the service data included in the PDU session to the handed over UE 2 through the PDU session tunnel, and stops forwarding the multicast service data to the handed over UE 2 through the multicast session tunnel.

[0290] For the QoS flows that the handed over UE2 needs to support forwarding, the S-gNB further needs to perform the following tasks: For the unicast QoS flows that need to be forwarded to the T-gNB1, the S-gNB forwards the unicast QoS flows to the T-gNB1 through a forwarding tunnel corresponding to the PDU session tunnel. After receiving the unicast QoS flows, the T-gNB1 buffers the unicast QoS flows.

[0291] For a multicast QoS flow that needs to be forwarded to the T-gNB1, the S-gNB first duplicates the multicast QoS flow in the multicast session tunnel, and then forwards the duplicated multicast QoS flow to the T-gNB1 through a forwarding tunnel corresponding to the multicast session tunnel. After receiving the multicast QoS flow, the T-gNB1 buffers the multicast QoS flow.

[0292] 705: UE2 accesses T-gNB1.

[0293] For example, after UE2 accesses the T-gNB1, the T-gNB1 transmits the received and buffered unicast QoS flow and / or multicast QoS flow to the UE2. In step 704, the UE2 receives corresponding service data based on the radio bearer configuration information transmitted by the S-gNB.

[0294] 706: T-gNB1 sends an N2 Path Switch Request to AMF.

[0295] For example, the request may include QFIs of unicast QoS flows that have been successfully handed over and unicast QoS flows that have failed to be handed over in the PDU session of UE2, and / or QFIs of multicast QoS flows that have been successfully handed over and multicast QoS flows that have failed to be handed over in the PDU session of UE2, for example, these QFIs may be encapsulated in an N2SM message.

[0296] In some optional embodiments, the N2 path switching request may further include an endpoint identifier of a PDU session tunnel assigned to UE2 by T-gNB1.

[0297] In some optional embodiments, the N2 path switching request may further include indication information #2, where indication information #2 indicates whether a multicast service associated with the PDU session of the UE2 to be handed over is running on the T-gNB1.

[0298] In a possible case, when the multicast service associated with the PDU session of the UE2 to be handed over is not running on the T-gNB1, it indicates that the multicast session tunnel used to transmit the multicast session between the T-gNB1 and the UPF has not yet been established. In this case, the N2 path switch request further includes an endpoint identifier of the multicast session tunnel allocated by the T-gNB1, so that the multicast session tunnel can be established between the T-gNB1 and the UPF.

[0299] In another possible case, the N2 path switch request indicates that the multicast service associated with the PDU session of the UE2 to be handed over is in a running state on the T-gNB1, or when the multicast service is running on the T-gNB1, a multicast session tunnel used to transmit the multicast session between the T-gNB1 and the UPF has been established. In this case, the N2 path switch request may not include an endpoint identifier of the multicast session tunnel.

[0300] 707: AMF sends a PDU session context update request (Nsmf_PDUSession_UpdateSMContext Request) to SMF1.

[0301] For example, the PDU session context update request includes the information contained in the N2SM message in step 706.

[0302] In some embodiments, before UE2 is handed over to T-gNB1, AMF may collect gNB capability information, including capability information on whether multicast function is supported. For example, when powered on, T-gNB1 may report to AMF whether T-gNB1 supports multicast function. In this case, the PDU session context update request may further include capability information of T-gNB1.

[0303] In response, the SMF1 receives a PDU session context update request. Then, the SMF1 determines whether to release the multicast session tunnel in the S-gNB where the multicast service associated with the PDU session of the UE2 to be handed over is located (i.e., the multicast session tunnel used to transmit the multicast service between the UPF1 and the S-gNB, where the multicast service is assumed to be transmitted in the multicast session tunnel).

[0304] In some embodiments, the SMF1 may determine whether to release the multicast session tunnel depending on whether another terminal device receives data of the multicast service via the S-gNB after the UE2 is handed over from the S-gNB to the T-gNB, or whether the UE2 is the last UE that subscribed to the multicast service via the SMF1 and the S-gNB, or whether the number of UEs that subscribed to the multicast service via the SMF1 and the S-gNB is 0 after the UE2 is handed over from the S-gNB to the T-gNB. For example, the number of UEs that subscribed to the multicast service via the SMF1 and the S-gNB may be included in the multicast service context. In other words, the SMF1 may determine whether to release the multicast session tunnel in which the multicast service is located depending on whether another UE other than the UE2 in the multicast service context requests the multicast service in the S-gNB. The multicast service context may also be referred to as a multicast session context.

[0305] For example, please refer to FIG. 4A-FIG. 4C. UE1 and UE2 subscribe to the same multicast service through SMF1 and S-gNB. In the following step 425, UE1 is handed over and leaves the multicast service subscribed to through SMF1 and S-gNB, and in step 426, UE2 is handed over and leaves the multicast service subscribed to through SMF1 and S-gNB. Therefore, after UE2 is handed over to the T-gNB, other terminal devices do not receive data of the multicast service through S-gNB, or UE2 is the last UE that subscribed to the multicast service through SMF1 and S-gNB, or the number of UEs that subscribed to the multicast service through SMF1 and S-gNB is 0. Based on this, SMF1 can determine whether to release the multicast session tunnel in which the multicast service is located.

[0306] In some optional embodiments, when the PDU session context update request includes indication information #2, the SMF may determine, based on indication information #2, whether a multicast service associated with the PDU session of the UE2 being handed over is running on T-gNB1.

[0307] In some optional embodiments, after determining to release the multicast session tunnel in which the multicast service is located, the SMF1 may generate information #1 and instruct the S-gNB to release the multicast session tunnel in which the multicast service is located. The information #1 may be an example of the first information.

[0308] For example, the information #1 may include an instruction, notification, or request to release the multicast session tunnel. Optionally, the information #1 may further include information about the multicast session tunnel (e.g., a tunnel endpoint identifier TEID of the multicast session tunnel used to determine the multicast session tunnel) and / or an identification information of the multicast service.

[0309] For example, the information #1 may include an instruction, notification or request to release the multicast session tunnel, and may further include information about the multicast session tunnel. Optionally, the information #1 may further include identification information of the multicast service.

[0310] For example, the information #1 may include an instruction, notification or request to release the multicast session tunnel, and may further include information about the multicast session tunnel and identification information of the multicast service.

[0311] 708: Perform N4 session update between SMF1 and UPF1.

[0312] For example, SMF1 may send an N4 session update request to UPF1 carrying the PDU session tunnel endpoint identifier of T-gNB1 and the PDU session tunnel endpoint identifier assigned to UPF1 by SMF1, and establish a PDU session tunnel (N4 Session Modification) between T-gNB1 and UPF1.

[0313] In some optional embodiments, in step 707, if the AMF further sends an endpoint identifier of the multicast session tunnel allocated by T-gNB1 to SMF1 (i.e., in this case, the multicast service associated with the PDU session of the UE2 to be handed over is not running on T-gNB1), SMF1 further sends an endpoint identifier of the multicast session tunnel from T-gNB1 to UPF1.

[0314] In some embodiments, in step 707, if SMF1 generates information #1, the N4 session update request may include information #1. Based on information #1, UPF1 may notify to release the tunnel used to transmit the multicast service between UPF1 and the S-gNB.

[0315] 709: SMF1 sends a first message to MCF to notify it to release the tunnel used for transmitting multicast services between MUF and UPF1, ie, the tunnel from MUF to UPF1.

[0316] 710: Perform an N4 session update between the MCF and the MUF. For example, the MCF may release the tunnel identity of UPF1 allocated by SMF1 (i.e., the tunnel identity of UPF1 used to establish a tunnel with the MUF).

[0317] 711: MCF sends a response to the first message to SMF1.

[0318] 712: SMF1 sends a PDU session context update response (Nsmf_PDUSession_UpdateSMContext Response) to AMF.

[0319] For example, SMF1 may release the tunnel identity of the MUF (i.e., the tunnel identity of UPF1 used to establish a tunnel with the MUF) allocated by the MCF.

[0320] 713: AMF sends an N2 path switch request ACK to T-gNB1.

[0321] 714: T-gNB1 sends a UE Context Release request to the S-gNB.

[0322] Therefore, in this embodiment of the present application, after UE2 is handed over from S-gNB to T-gNB1, when it determines that other terminal devices do not receive data of the multicast service through the S-gNB, SMF1 may notify UPF1 to release the first tunnel used to transmit the multicast service between the S-gNB and UPF1, and release the multicast session tunnel between the S-gNB and UPF1, thereby helping to reduce network resource overhead.

[0323] 8 is a schematic flowchart of a communication method 800 from the perspective of device interaction according to an embodiment of the present application. The method 800 may be applied to a scenario in which a first terminal device receives data of a first multicast service through a first access network device. As shown in FIG. 8, the method 800 includes steps 810 to 830.

[0324] 810: The first access network device knows that the first terminal device is the last terminal device to receive data of the first multicast service through the first access network device when the first terminal device is in a handover preparation phase in which the first terminal device is handed over from the first access network device to the second access network device. Here, "know" can also be replaced with "perceive", "find", "detect", or the like. This is not limited.

[0325] In other words, the first access network device may know that other terminal devices have not received data of the first multicast service through the first access network device after the first terminal device in the handover preparation phase is handed over to the second access network device. It should be noted that the terminal device receiving data of the first multicast service through the first access network device may be understood as the terminal device subscribing to the first multicast service through the first access network device. It may also be understood that the first terminal is the last first terminal device to receive data of the first multicast service through the first access network device known in the preparation phase, and the first terminal device is later handed over to the second access network device. It may also be understood that the first terminal device is the last first terminal device to receive data of the first multicast service through the first access network device, and the first terminal device is later handed over to the second access network device.

[0326] For example, the first access network device may be referred to as a source access network device, and the second access network device may be referred to as a target access network device.

[0327] For example, the handover here may be an Xn handover or an N2 handover.

[0328] It should be noted that the handover preparation phase may be a phase in which a source access network device, a target access network device, or a core network device (which may be, but is not limited to, AMF, SMF, UPF, or the like) prepares resources required by handover for the first terminal device. The resources required by handover may include a forwarding tunnel, radio bearer configuration information required by the first terminal device to receive service data via the target access network device, air interface resources configured by the target access network device for the first terminal device, or the like, which is not limited in this embodiment of the present application.

[0329] In the Xn handover scenario, the handover preparation phase may be a process in which the source access network device receives a measurement report of the first terminal device and makes a handover decision to the first terminal device based on the measurement report, where the decision result is handover; the source access network device sends a handover request to the target access network device and receives a handover confirmation response sent by the target access network device, for example, the process of steps 901 to 903 in the following Figures 9A and 9B.

[0330] In an N2 handover, the handover preparation phase may be a process in which a source access network device receives a measurement report of a first terminal device, and based on the measurement report, sends a handover request (handover required) to a source access and mobility management function network element, and the source access and mobility management function network element receives a UE context creation response from a target access and mobility management network element, for example, the process of steps 1001 to 1012 in the following Figures 10A to 10C.

[0331] The source access network device may know that at any point in the handover preparation phase, the first terminal device is the last terminal device that will receive data of the first multicast service via the first access network device.

[0332] For example, in an Xn handover scenario, when the source access network device receives a measurement report of the first terminal device and makes a handover decision to the first terminal device based on the measurement report, where when the decision result is handover (e.g., after step 901 in Figures 9A and 9B below), or when sending a handover request to the target access network device (e.g., after step 902 in Figures 9A and 9B below), or after receiving a handover confirmation response from the target access network device (e.g., after step 903 in Figures 9A and 9B below), the source access network device knows that the first terminal device is the last terminal device to receive data of the first multicast service via the first access network device.

[0333] In another example, in an N2 handover scenario, when receiving a measurement report of the first terminal device (e.g., after step 1001 in Figures 10A to 10C below) or after sending a handover request to the source access and mobility management function network element (e.g., after step 1002 in Figures 10A to 10C below), the source access network device may know that the first terminal device is the last terminal device to receive data of the first multicast service via the first access network device.

[0334] In some optional embodiments, in the handover preparation phase, when a first terminal device that has subscribed to the first multicast service sends a measurement report to the source access network device, the source access network device makes a handover decision for the first terminal device based on the measurement report, where the decision result is handover; the source access network device may update the number of terminal devices that have subscribed to the first multicast service via the source access network device, for example, decrement the number of terminal devices by 1. When the number of terminal devices is 0, it may be known that the first terminal device is the last terminal device that receives data of the first multicast service via the first access network device.

[0335] For example, in an Xn handover, after receiving a measurement report of the first terminal device and deciding to perform a handover (for example, after step 901 in the following FIG. 9A and FIG. 9B), or after sending a handover request to the target access network device (for example, after step 902 in the following FIG. 9A and FIG. 9B), or after receiving a handover confirmation response sent by the target access network device (for example, after step 903 in the following FIG. 9A and FIG. 9B), the source access network device may update the number of terminal devices that have subscribed to the first multicast service through the source access network device. Then, the source access network device may determine whether the first terminal device is the last terminal device that has subscribed to the first multicast service through the source access network device based on the updated number of terminal devices.

[0336] For example, in an N2 handover, after receiving a measurement report of the first terminal device, before sending a handover request to the source access and mobility management function network element, or after sending a handover request to the source access and mobility management function network element, the source access network device may update the number of terminal devices subscribed to the first multicast service via the source access network device.

[0337] For example, in an N2 handover, after receiving a measurement report of the first terminal device (e.g., after step 1001 in the following FIGS. 10A-10C) or after sending a handover request to a source access and mobility management function network element (e.g., after step 1002 in the following FIGS. 10A-10C), the source access network device may update the number of terminal devices that have subscribed to the first multicast service through the source access network device. Then, based on the updated number of terminal devices, the source access network device may determine whether the first terminal device is the last terminal device that has subscribed to the first multicast service through the source access network device.

[0338] In some optional embodiments, the number of terminal devices that have subscribed to the multicast service via the source access network device may be included in a Multicast Context, a Multicast Session Context, a Multicast Group Context, or a Multicast Service Context, which corresponds to the multicast service associated with the PDU session of the first terminal device. In other words, depending on whether another terminal device other than the terminal device in the Multicast Context, the Multicast Session Context, the Multicast Group Context, or the Multicast Service Context receives the first multicast service, the source access network device determines whether the first terminal device is the last terminal device that receives data of the first multicast service via the source access network device.

[0339] When the first terminal device is the last terminal device in a Multicast Context, a Multicast Session Context, a Multicast Group Context, or a Multicast Service Context, there is no other terminal device that receives the first multicast service through the source access network device after the terminal device leaves the source access network device. In this case, the source access network device may know that the first terminal device is the last terminal device that receives data of the first multicast service through the source access network device.

[0340] It should be noted that in this embodiment of the present application, one multicast service may correspond to one multicast session and one multicast session tunnel between one access network device and a core network device (such as MB-UPF or UPF). It should be noted here that one multicast service may alternatively correspond to multiple multicast sessions and correspond to multiple multicast session tunnels between multiple access network devices and a core network device.

[0341] 820: The first access network device sends first information to the core network device, where the first information is used to release a first tunnel, and the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device.

[0342] In some embodiments, the core network device may be a multicast user plane function network element, such as, but not limited to, a MUF, an M-UPF, an MS-UPF, or an MB-UPF. In this case, the first tunnel may include a tunnel used to transport the first multicast service between the source access network device and the multicast user plane function network element (such as, for example, a MUF, an M-UPF, an MS-UPF, or an MB-UPF) (where the tunnel is, for example, the multicast session tunnel described above).

[0343] In some embodiments, the core network device may be a user plane function network element, e.g., a UPF, in which case the first tunnel may include a tunnel used to transport the first multicast service between the source access network device and the user plane function network element (e.g., a UPF) (where the tunnel is, e.g., the multicast session tunnel described above).

[0344] It should be noted that when the core network device is a user plane function network element, the user plane function network element may include a user plane function that can be used to process a multicast service. That is, it may be considered that a user plane function (e.g., MUF, M-UPF, MS-UPF, or MB-UPF) that can be used to process a multicast service may be combined with a user plane function network element in a function network element. Correspondingly, in this case, the session management function network element may include a control plane function that can be used to process a multicast service. That is, a control plane function (e.g., MCF, M-SMF, MS-SMF, or MB-SMF) that can be used to process a multicast service may be combined with a session management function network element in a function network element.

[0345] In some embodiments, when the core network device is a multicast user plane function network element, the first access network device may first send the first information to the multicast session management function network element, which may then send the first information to the multicast user plane function network element.

[0346] In a possible implementation, the first access network device may send the first information to a multicast session management function network element via another network device (such as a second access network device, an AMF or an SMF), and the multicast session management function network element may then send the first information to a multicast user plane function network element. For example, the multicast session management function network element may be a multicast service session management function network element or a multicast control plane function network element such as an MB-SMF or an MCF. This is not limited in this embodiment of the present application. In a possible implementation, the first access network device may send the first information to a multicast session management function network element via another core network device (such as an AMF), and the multicast session management function network element may then send the first information to a multicast user plane function network element. In another possible implementation, the first access network device may send the first information directly to the multicast session management function network element, for example, by using a notification message or a request message. This is not limited.

[0347] In some embodiments, when the core network device is a user plane function network element, the first access network device may first send the first information to the session management function network element, which may then send the first information to the user plane function network element.

[0348] In a possible implementation, the first access network device sends the first information to the session management function network element via another network device (such as the second access network device or the AMF), and the session management network element then sends the first information to the user plane function network element. In a possible implementation, the first access network device sends the first information to the session management function network element via another core network device (such as the AMF), and the session management function network element then sends the first information to the user plane function network element. In another possible implementation, the first access network device may directly send the first information to the session management function network element, for example, by using a notification message or a request message. This is not limited.

[0349] In a first optional implementation scenario, for example, in an Xn handover scenario, when receiving a measurement report of a first terminal device and determining based on the measurement report that the first terminal device needs to be handed over to a second access network device or determining to send a handover request to the second access network device, the first access network device may know that the first terminal device is the last terminal device that subscribed to the first multicast service through the first access network device. In this case, the first access network device may send a handover request (e.g., a handover request) to the second access network device, where the handover request includes the first information. The handover request may request to hand over the first terminal device from the first access network device to the second access network device.

[0350] Correspondingly, after receiving the handover request from the first access network device, the second access network device may send a path switch request (e.g., N2 path switch request, N2 path switch request) to an access and mobility management function network element (e.g., AMF), where the path switch request includes the first information. Then, the access and mobility management function network element may send a PDU session context update request (e.g., Nsmf_PDUSession_UpdateSMContextRequest) to the session management function network element, where the PDU session context update request includes the first information.

[0351] Further, when the core network device in step 820 is a multicast user plane function network element, after receiving the PDU session context update request, the session management function network element may send a first message to the multicast session management function network element, where the first message includes the first information. For example, the first message may be an N16 message. After receiving the first message, the multicast session management function network element may send a fifth message to the multicast user plane function network element, where the fifth message may include the first information. For example, the fifth message may be an N4 session update request. The multicast user plane function network element may obtain the first information based on the fifth message, and further perform step 830.

[0352] When the core network device in step 820 is a user plane function network element, after receiving the PDU session context update request, the session management function network element may send an N4 session update request to the user plane function network element, where the N4 session update request may include the first information. The user plane function network element may obtain the first information based on the N4 session update request, and further perform step 830.

[0353] In a second optional implementation scenario, for example, in an N2 handover scenario, when receiving a measurement report of the first terminal device or deciding to send a handover request to the source access and mobility management function network element, the first access network device may know that the first terminal device is the last terminal device that subscribed to the first multicast service through the first access network device. In this case, the first access network device may send a handover request (e.g., a handover request) to the first access and mobility management function network element, where the handover request includes the first information. For example, the first access and mobility management function network element may be a source access and mobility management function network element.

[0354] Correspondingly, after receiving the handover request, the first access and mobility management function network element may send a UE context creation request (e.g., Namf_Communication_CreateUEContext Request) to the second access and mobility management function network element, where the UE context creation request includes the first information. Then, the second access and mobility management function network element sends a PDU session update context request to the session management function network element, where the PDU session update context request may include the first information. The second access and mobility management function network element may be referred to as a target access and mobility management function network element.

[0355] Further, when the core network device in step 820 is a multicast user plane function network element, after receiving the PDU session context update request, the session management function network element may send a first message to the multicast session management function network element, where the first message includes the first information. For example, the first message may be an N16 message. After receiving the first message, the multicast session management function network element may send a fifth message to the multicast user plane function network element, where the fifth message may include the first information. For example, the fifth message may be an N4 session update request. Correspondingly, the multicast user plane function network element may obtain the first information based on the fifth message, and further perform step 830.

[0356] When the core network device in step 820 is a user plane function network element, after receiving the PDU session context update request, the session management function network element may send a session update request (e.g., an N4 session update request) to the user plane function network element, where the session update request may include the first information. Correspondingly, the multicast user plane function network element may obtain the first information based on the session update request, and further perform step 830.

[0357] In a third optional implementation scenario, when the core network device in step 820 is a multicast user plane function network element, the first access network device may know that the first terminal device is the last terminal device that subscribed to the first multicast service through the first access network device at any time in the handover preparation phase. When or after knowing that the first terminal device is the last terminal device that subscribed to the first multicast service through the first access network device, the first access network device may send a third message to the third access and mobility management function network element, where the third message may be an N2 message, and the third message carries the first information. For example, the third access and mobility management function network element may be an access and mobility management function network element selected by the first access network device for the first multicast service when the first terminal device subscribes to the first multicast service, or another access and mobility management function network element related or unrelated to the first terminal device.

[0358] Furthermore, after receiving the third message, the third access and mobility management function network element may send a fourth message to the multicast session management function network element, where the fourth message carries the first information. For example, the fourth message may be an N11 message. After receiving the fourth message, the multicast session management function network element may send a fifth message to the multicast user plane function network element, which may carry the first information. For example, the fifth message may be an N4 session update request. Correspondingly, the multicast user plane function network element may obtain the first information based on the fifth message, and further perform step 830.

[0359] For example, when the first terminal device subscribes to a multicast service or a broadcast service, the first access network device may obtain an identifier of a multicast session management function network element. In this manner, the first access network device may select a third access and mobility management function network element based on the identifier. For example, the first access network device may query a network repository function (NRF) based on the identifier to obtain an appropriate third access and mobility management function network element.

[0360] The access and mobility management function network element associated with the first terminal device may be an access and mobility management function network element capable of providing a non-access stratum (NAS) signaling service to the first terminal device, and the access and mobility management function network element not associated with the first terminal device may be an access and mobility management function network element not capable of providing a NAS signaling service to the first terminal device.

[0361] It should be noted that the third access and mobility management function network element can be the same network element as the above-mentioned source access and mobility management function network element, or can be the same network element as the above-mentioned target access and mobility management function network element, which is not limited in this embodiment of the present application.

[0362] It should be noted that the third message, for example, the N2 message, may be an existing N2 message (specifically, an existing N2 message that additionally holds the first information) or may be a new N2 message. The new N2 message may be mainly used to release the multicast session tunnel. The new N2 message may follow the naming scheme of the service-based interface signaling message, and the specific name of the N2 message is not limited, but the function is used to notify the multicast user plane function network element to release the multicast session tunnel.

[0363] It should be noted that the fourth message, for example, the N11 message, may be an existing N11 message (specifically, an existing N11 message that additionally holds the first information) or may be a new N11 message. The new N11 message may be mainly used to release the multicast session tunnel. The new N11 message may follow the naming scheme of the service-based interface signaling message, and the specific name of the N11 message is not limited, but the function is used to notify the multicast user plane function network element to release the multicast session tunnel.

[0364] In a fourth optional implementation scenario, the first access network device may know that the first terminal device is the last terminal device that subscribed to the first multicast service through the first access network device at any time during the handover preparation phase. When or after the first access network device knows that the first terminal device is the last terminal device that subscribed to the first multicast service through the first access network device, the first access network device may directly send the first information to the core network device.

[0365] For example, when the core network device in step 820 is a multicast user plane function network element, the first access network device may directly send the first information to the multicast session management function network element, and the multicast session management function network element then sends the first information to the multicast user plane function network element (e.g., including the first information in the fifth message) and executes step 830. This is not limited thereto.

[0366] For example, when the core network device in step 820 is a user plane function network element, the first access network device may directly send the first information to the session management function network element, which then sends the first information to the user plane function network element (e.g., includes the first information in an N4 session update request) and executes step 830. This is not limited thereto.

[0367] In the first optional implementation scenario or the second optional implementation scenario, after receiving the measurement report of the first terminal device in the handover preparation phase or when deciding to send a handover request or a handover request, the first access network device knows that the first terminal device is the last terminal device that joined the first multicast service through the first access network device, and the first access network device can include the first information in the existing signaling (such as the handover request or the handover request), so that the first information is finally sent to the multicast user plane function network element or the user plane function network element, which helps to reduce network resource overhead.

[0368] In the third optional implementation scenario or the fourth optional implementation scenario, after receiving the measurement report of the first terminal device in the handover preparation phase, the first access network device knows that the first terminal device is the last terminal device that subscribed to the first multicast service through the first access network device, and after knowing, immediately sends the third message to the third access and mobility management function network element, or immediately sends the first information to the multicast session management function network element or the session management network element, so that the first access network device can know that the first terminal device is the last terminal device that subscribed to the first multicast service through the first access network device at an earlier time point in the handover preparation phase, which can help the multicast user plane function network element or the user plane function network element to obtain the first information earlier.

[0369] In the third optional implementation scenario or the fourth optional implementation scenario, when receiving the handover request acknowledgement in the handover preparation phase, the first access network device knows that the first terminal device is the last terminal device that has subscribed to the first multicast service through the first access network device. Compared with the above-mentioned knowledge that the first terminal device is the last terminal device at an earlier time point in the handover preparation phase, the first access network can now more accurately know that the first terminal device is the last terminal device that has subscribed to the first multicast service through the first access network device. This further helps to improve the reliability of the multicast service transmission.

[0370] In the present example, the first information may include an indication used to release the first tunnel and information about the first tunnel.

[0371] In another example of the present application, the first information may include an indication used to release the first tunnel and an identification of the first multicast service.

[0372] In another example of the present application, the first information may include an indication used to release the first tunnel, an identification of the first multicast service, and information about the first tunnel.

[0373] It should be noted that when the first information includes information about the first tunnel, the first information may include information about one, two or more first tunnels, and this is not limited. When the first information includes identification information of the first multicast service, the first information may include identification information of one, two or more first multicast services, and this is not limited.

[0374] The information about the first tunnel may be used to uniquely determine the first tunnel, and may be, for example, a tunnel endpoint identifier (TEID) of the first tunnel or an ID of the first tunnel, but this is not limited here. The identification information of the first multicast service may be used to uniquely determine the multicast service, and may be, for example, a multicast service ID, a multicast service name, a multicast address, a multicast group ID, a multicast broadcast session ID (MBS session ID), or a Temporary Mobile Group Identity (TMGI), but this is not limited here.

[0375] It should be noted that the first multicast service described herein may include one multicast service or multiple different multicast services. This is not limited. For example, when the source access network device has two multicast sessions corresponding to two multicast services and two multicast session tunnels, and the source access network device knows in the handover preparation phase that the terminal device to be handed over is the last terminal device to receive data of the two multicast services through the source access network device, the source access network device may send the first information to the core network device. In this case, the first information is used to release the first tunnel used to transmit data of the two multicast services between the source access network device and the core network device, the first multicast service includes two multicast services, and the first tunnel includes tunnels corresponding to the two multicast services respectively.

[0376] 830: The core network device releases the first tunnel based on the first information.

[0377] For example, the multicast user plane function network element or the user plane function network element may release the first tunnel based on the first information, for example, remove related resources of the first tunnel (for example, remove a tunnel endpoint identifier, e.g., a TEID, of the first tunnel, or remove N4 session context information related to the first tunnel of the first multicast service) (for example, including a packet detection rule (PDR) and a forwarding action rule (FAR)).

[0378] For example, when the first information includes an indication used to release the first tunnel and information about the first tunnel, the multicast user plane function network element or the user plane function network element may release the first tunnel based on the indication used to release the first tunnel and the information about the first tunnel. In an example, when the information about the first tunnel in the first information is the TEID of the first tunnel, the multicast user plane function network element or the user plane function network element may release the TEID. In another example, when the information about the first tunnel in the first information is the ID of the first tunnel, the multicast user plane function network element or the user plane function network element may determine the first tunnel based on the ID of the first tunnel, and then release the first tunnel based on the indication used to release the first tunnel, and remove the related resources of the first tunnel, such as the TEID, or the N4 session context information related to the first tunnel of the first multicast service.

[0379] In this manner, the multicast user plane function network element or the user plane function network element may release a first tunnel (e.g., which may be, but is not limited to, one or more first tunnels) corresponding to the information about the first tunnel included in the first information.

[0380] As another example, when the first information includes an indication used to release the first tunnel and an identification information of the first multicast service, the multicast user plane function network element or the user plane function network element may determine the first multicast service based on the identification information of the first multicast service, and then determine the first tunnel for transmitting data of the first multicast service between the first access network device and the core network device. Specifically, the multicast user plane function network element or the user plane function network element may determine one or more multicast sessions corresponding to the first multicast service, and one or more multicast session tunnels corresponding to the one multicast session, or multiple multicast session tunnels corresponding to the multiple multicast sessions. Here, the determined multicast session tunnel is a tunnel (i.e., the first tunnel) for transmitting data of the first multicast service between the source access network device and the core network device. Next, the multicast user plane function network element or user plane function network element may release the first tunnel based on the instruction used to release the first tunnel, in particular releasing related resources of the multicast session tunnel or multiple multicast tunnels, such as the TEID, or N4 session context information related to the first tunnel of the first multicast service.

[0381] In this way, the multicast session function network element, or the session function network element, may release all multicast session tunnels corresponding to the first multicast service indicated in the first information, i.e., the first tunnels (e.g., all the first tunnels) used to transmit data of the first multicast service between the source access network device and the core network device.

[0382] As another example, when the first information includes an indication used to release the first tunnel, an identification information of the first multicast service, and information about the first tunnel, the multicast user plane function network element or the user plane function network element may determine the first multicast service based on the identification information of the first multicast service. Then, the multicast user plane function network element or the user plane function network element may determine a first tunnel for transmitting data of the first multicast service between the first access network device and the core network device. Specifically, the multicast user plane function network element or the user plane function network element may determine one or more multicast sessions corresponding to the first multicast service, and one or more multicast session tunnels corresponding to the one multicast session, or multiple multicast session tunnels corresponding to the multiple multicast sessions. Then, the multicast user plane function network element or the user plane function network element may further determine the first tunnel from the one or more multicast session tunnels based on the information about the first tunnel in the first information. The multicast user plane function network element or user plane function network element may then release the first tunnel based on the instruction used to release the first tunnel and remove the first tunnel's associated resources, such as the TEID, or N4 session context information related to the first tunnel of the first multicast service.

[0383] In this way, the multicast user plane function network element or the user plane function network element can release the first tunnel corresponding to the information about the first tunnel included in the first information. In addition, when the first tunnel is determined based on both the identification information of the first multicast service and the information about the first tunnel, the first tunnel needs to be determined only from one or more multicast session tunnels corresponding to the first multicast service. This helps to determine the first tunnel more accurately and quickly and improve the efficiency of releasing the first tunnel.

[0384] It should be noted that when the first information includes an indication used to release the first tunnel, the identification information of the first multicast service, and the information about the first tunnel, the multicast user plane function network element or the user plane function network element may further determine the first tunnel that needs to be released based on only one of the identification information of the first multicast service and the information about the first tunnel. For example, when determining the first tunnel based only on the identification information of the first multicast service, the multicast user plane function network element or the user plane function network element may ignore the information about the first tunnel included in the first information. In another example, when determining the first tunnel based only on the information about the first tunnel, the multicast user plane function network element or the user plane function network element may ignore the identification information of the first multicast service included in the first information.

[0385] Therefore, in this embodiment of the present application, in a handover preparation phase in which the first terminal device is handed over from the first access network device to the second access network device, the first access network device can know that the first terminal device is the last terminal device to receive data of the first multicast service through the first access network device, and can send the first information to release the first tunnel used to transmit data of the first multicast service between the first access network device and the core network device, thereby helping to reduce network resource overhead.

[0386] In the following, a specific example of the communication method according to the present embodiment of the present application will be described with reference to Figures 9A and 9B and 10A to 10C. In Figures 9A and 9B and 10A to 10C, an example in which the multicast session management function network element is the MCF and the source access network device is the S-gNB is used for description. For the implementation method of the chip in the MCF and the chip in the S-gNB, please refer to the specific description of the MCF and the S-gNB. Details will not be described again.

[0387] Optionally, in Figures 9A and 9B or 10A-10C, the core network device further includes an AMF, an SMF, a UPF, and a MUF. Alternatively, in some optional embodiments, the core network device may not include an MCF and a MUF. Rather, some functions or units in the SMF implement the functions of the MCF, and some functions or units in the UPF implement the functions of the MUF. This is not limited in this embodiment of the present application.

[0388] 9A and 9B are schematic flowcharts of another communication method 900 according to an embodiment of the present application. The handover type in the method 900 is an Xn handover. The S-gNB determines whether to release the multicast session tunnel between the S-gNB and the MUF.

[0389] Please note that in Figures 9A and 9B, an example in which the multicast session tunnel between the S-gNB and the MUF is released is used for illustration. This solution is also suitable for releasing the multicast session tunnel between the S-gNB and the UPF, and some simple adaptations may be required. Figures 9A and 9B and some simple adaptations fall within the scope of protection of this application.

[0390] In some embodiments, when a UE receives multicast service data via an S-gNB (or, in other words, the UE subscribes to a multicast service via an S-gNB), the UE's PDU session is associated with the multicast service.

[0391] When the T-gNB to which the UE is handed over does not support the multicast function, the method 900 is applicable to the scenario shown in Figure 5B. In the following, the method 900 will be described with reference to the scenario in Figure 5B. As shown in Figures 9A and 9B, the method 900 may comprise steps 901 to 916. It should be noted that the solution is also applicable to a scenario in which the T-gNB supports the multicast function, and is not limited thereto here. The scenario shown in Figure 5B is merely an example.

[0392] 9A and 9B show steps or operations of a communication method 900 provided in this embodiment of the present application, it should be understood that these steps or operations are merely examples. In this embodiment of the present application, other operations or variations of the operations in FIG. 9A and 9B may also be performed. In addition, the steps in the figures may be performed in a different order than presented in the figures, and not all operations in the figures may need to be performed.

[0393] Optionally, before step 901, the S-gNB may know whether the function of the T-gNB, i.e., the function for the multicast function, is supported. For example, when there is an Xn connection between the T-gNB and the S-gNB, the T-gNB may inform the S-gNB of the capability information of the T-gNB by using the Xn interface, where Xn may be the interface of the Xn connection between the S-gNB and the T-gNB. For example, when the T-gNB does not support the multicast function, the T-gNB sends the indication information #1 to the S-gNB, where the indication information #1 indicates that the T-gNB does not support the multicast function. Alternatively, in some embodiments, when the T-gNB does not support the multicast function, the T-gNB may not send the indication information #1 to the S-gNB. Correspondingly, if the S-gNB does not receive the indication information #1, the T-gNB may be considered as not supporting the multicast function.

[0394] Here, first, according to the definition of the handover preparation phase of Xn handover in 3GPP technical specification (TS) 38.300, the handover preparation phase includes steps 901 to 903 in the procedure shown in Figures 9A and 9B. The handover preparation phase can be understood as a phase in which an S-gNB, a T-gNB, or a core network device prepares resources required for handover for a UE to be handed over (e.g., may include a forwarding tunnel, radio bearer configuration information required by the UE to receive service data after the UE accesses the T-gNB, or air interface resources configured by the T-gNB for the UE to be handed over).

[0395] 901: The UE sends a measurement report to the S-gNB. In response, the S-gNB receives the measurement report and decides to hand over the UE to the T-gNB.

[0396] In some optional embodiments, after receiving the measurement report sent by the UE, the S-gNB may update (e.g., decrease by one) the number of UEs in the Multicast Context, Multicast Service Context, Multicast Group Context, or Multicast Session Context corresponding to the multicast service (i.e., the multicast service or multicast group that the UE joins via the S-gNB) associated with the PDU session of the UE to be handed over. If the current UE to be handed over is the last UE in the aforementioned context (in other words, after the UE leaves, no other UEs receive the multicast service at the S-gNB), the S-gNB may know that the UE is the last UE to receive data of the multicast service via the S-gNB. In this case, the S-gNB may decide to release the multicast session tunnel between the S-gNB and the core network device (e.g., the MUF in FIG. 5B).

[0397] Here, the multicast service may be an example of the first multicast service in FIG. 8, and the multicast session tunnel may be an example of the first tunnel in FIG.

[0398] For example, the number of UEs that have subscribed to a multicast service via an S-gNB (which may also be understood as the number of UEs that receive the multicast service via an S-gNB) may be included in the multicast session context (also referred to as a multicast service context, a multicast context, or a multicast group context) of the multicast service. In other words, depending on whether another UE other than the UE in the context receives the multicast service at the S-gNB, the S-gNB may decide whether to release the multicast session tunnel in which the multicast service is located.

[0399] Here, it should be noted that at the granularity of a base station (in other words, in units of a base station), one multicast service may correspond to one multicast session, in other words, a multicast session tunnel between a base station (e.g., S-gNB) and a core network device (such as MUF or UPF). Here, it should be noted that one multicast service may also correspond to multiple multicast / broadcast sessions. This is not limited here. This solution uses a one-to-one correspondence as an example, and this solution is also applicable to a one-to-many correspondence.

[0400] 902: The S-gNB sends a Handover Request to the T-gNB, where the S-gNB may know that the T-gNB does not support multicast functionality.

[0401] For example, the handover request may include PDU session information of the handed over UE, including a PDU session identifier and QoS information corresponding to the unicast service included in the PDU session. For details, please refer to the description in step 702. For the sake of brevity, the details will not be described again in this specification.

[0402] It should be noted that in step 902, if the PDU session of the current UE to be handed over is associated with a multicast service, the S-gNB may map the multicast QoS flow to a unicast QoS flow based on the mapping relationship between the multicast QoS flow QFI and the unicast QoS flow QFI, i.e., in this case, the unicast QoS flow included in the PDU session further includes the unicast QoS flow to which the multicast QoS flow is mapped.

[0403] In addition, the handover request may further include an identifier of a service flow that the S-gNB intends to forward through a forwarding tunnel corresponding to the PDU session tunnel. Specifically, in the scenario of FIG. 5B, since the T-gNB does not support multicast function, only a forwarding tunnel corresponding to the PDU session tunnel can be established between the S-gNB and the T-gNB. In this case, if a multicast QoS flow needs to be forwarded through the forwarding tunnel, the handover request may include a QFI of a unicast QoS flow corresponding to the multicast QoS flow.

[0404] In some optional embodiments, when deciding to release the multicast session tunnel in step 901, the S-gNB may generate information #2 used to release the multicast session tunnel used to transmit data of the multicast service between the S-gNB and a core network device (such as the UPF or MUF, where the MUF is used as an example). In this case, the handover request may further include information #2.

[0405] In a particular example, for a multicast session tunnel in the downlink direction (i.e., the transmission direction from the MUF to the S-gNB), the S-gNB may generate information #2 after the S-gNB determines or decides to release, or can release, the multicast session tunnel between the S-gNB and the MUF.

[0406] For example, the information #2 may include an instruction used to release the multicast session tunnel and information about the multicast session tunnel, or the information #2 may include an instruction used to release the multicast session tunnel and identification information of a multicast service, or the information #2 may include an instruction used to release the multicast session tunnel, information about the multicast session tunnel, and identification information of a multicast service, which is not limited in this embodiment of the present application.

[0407] 903: The T-gNB sends a handover request acknowledgment (handover request ACK) to the S-gNB.

[0408] For example, the T-gNB prepares radio resources for the handed-over UE based on the QoS information of the unicast service (including the mapped unicast QoS flow) received from the S-gNB. For example, the T-gNB may determine the number of air interface data radio bearers (DRBs) and the mapping relationship between the QFI and the DRB based on the QoS parameters corresponding to the QFI of each service flow. In addition, the T-gNB may further determine the configuration parameters corresponding to the DRB based on the QoS parameters corresponding to the QFI to which each DRB is mapped. The configuration parameters corresponding to the DRB are, for example, whether an acknowledged mode or a non-acknowledged mode is used by the radio link control (RLC) layer corresponding to the DRB. Finally, the T-gNB creates the corresponding DRB.

[0409] After preparing radio resources, the T-gNB sends a handover request ACK to the S-gNB. In some optional embodiments, the T-gNB may send information to the S-gNB that needs to be relayed to the UE via the S-gNB. For example, the T-gNB may send radio bearer configuration information of the T-gNB to the UE via the S-gNB. The radio bearer configuration information may be used by the UE to receive unicast service data and / or multicast service data transmitted by the T-gNB after the UE accesses the T-gNB.

[0410] In some optional embodiments, when the handover request in step 902 includes QFIs of service flows (including QFIs of unicast QoS flows and / or QFIs of multicast QoS flows) that the S-gNB intends to forward through the forwarding tunnel and the T-gNB supports data forwarding, the T-gNB assigns an endpoint identifier for the forwarding tunnel.

[0411] In some optional embodiments, when skipping the determination of whether to release the multicast session tunnel after receiving the measurement report transmitted by the UE in step 901, the S-gNB may update the number of UEs in the multicast session context (also referred to as the multicast service context, the multicast context, or the multicast group context) corresponding to the multicast service associated with the PDU session of the UE to be handed over (e.g., decrement the number of UEs by one) after receiving the handover request acknowledgment. If the current UE to be handed over is the last UE in the context (in other words, there is no other UE to receive the multicast service at the base station after the UE leaves), the S-gNB knows that the UE is the last UE to receive data of the multicast service through the S-gNB. In this case, the S-gNB may decide to release the multicast session tunnel between the S-gNB and the core network device (e.g., the MUF in FIG. 5B).

[0412] For example, the number of UEs that have subscribed to the multicast service via the S-gNB (which may also be understood as the number of UEs that receive the multicast service via the S-gNB) and / or the identification information of the UEs may be included in the multicast session context (or referred to as a multicast service context, a multicast context, or a multicast group context). In other words, depending on whether another UE other than the UE in the multicast session context (or referred to as a multicast service context, a multicast context, or a multicast group context) receives the multicast service via the S-gNB, the S-gNB may decide whether to release the multicast session tunnel in which the multicast service is located.

[0413] For example, if the S-gNB decides to release the multicast session tunnel after receiving the handover request acknowledgment, the S-gNB may generate information #2. In this case, the S-gNB may transmit information #2 to the T-gNB, for example, by using separate signaling. This is not limited here. Specifically, for the information #2, please refer to the above description. Details will not be described again.

[0414] 904: The S-gNB sends a handover command to the UE. For the handover command, see the description of step 704.

[0415] Next, the S-gNB duplicates the multicast QoS flow received through the multicast session tunnel, maps the duplicated multicast QoS flow, and forwards the mapped duplicated multicast QoS flow to the T-gNB.

[0416] Different from "S-gNB duplicates the multicast QoS flow received through the multicast session tunnel and forwards the duplicated multicast QoS flow to T-gNB1" in Figures 7A and 7B, since the T-gNB does not support the multicast function in this procedure, for the multicast QoS flow that needs to be forwarded, the S-gNB may first duplicate the multicast QoS flow in the multicast session tunnel of the S-gNB, and then map the multicast QoS flow to the unicast QoS flow based on the mapping relationship between the multicast QoS flow and the unicast QoS flow. Then, the unicast QoS flow is forwarded to the T-gNB through a forwarding tunnel corresponding to the PDU session tunnel between the S-gNB and the T-gNB. After receiving the unicast QoS flow through the forwarding tunnel, the T-gNB buffers the unicast QoS flow.

[0417] 905: The UE accesses the T-gNB. Specifically, for step 905, please refer to the description of step 705. Details will not be described again.

[0418] 906: The T-gNB sends an N2 Path Switch Request to the AMF.

[0419] For example, the request includes the QFIs of the unicast QoS flows that have been successfully handed over and the QFIs of the unicast QoS flows that have not been handed over in the PDU session of the UE (wherein the QFIs of the unicast QoS flows to which the multicast QoS flows are mapped are included). For example, these QFIs may be encapsulated in an N2SM message.

[0420] In some optional embodiments, the N2 path switching request may further include an endpoint identifier of a PDU session tunnel assigned to the UE by the T-gNB.

[0421] In some optional embodiments, when receiving information #2 transmitted by the S-gNB, the T-gNB further includes information #2 in the N2 path switching request.

[0422] 907: The AMF sends a PDU session context update request (Nsmf_PDUSession_UpdateSMContext Request) to the SMF.

[0423] For example, the PDU session context update request includes the information contained in the N2SM message in step 906.

[0424] In some optional embodiments, before the UE is handed over to the T-gNB, the AMF may collect capability information of the gNB (e.g., including capability information of whether the multicast function is supported). For example, when powered on, the T-gNB may report to the AMF whether the T-gNB supports the multicast function. In this case, the PDU session context update request may further include the capability information of the T-gNB.

[0425] In some embodiments, when the AMF receives information #2 sent by the S-gNB in ​​step 906 (i.e., information #2 sent by the S-gNB to the T-gNB and then relayed by the T-gNB to the AMF), the AMF may include information #2 in a PDU session context update request.

[0426] 908: Perform N4 session update (N4 session modification) between the SMF and the UPF.

[0427] 909: The SMF sends a first message to the MCF. For example, the first message may be an N16 message.

[0428] In some embodiments, when the SMF receives information #2 sent by the S-gNB in ​​step 907, the first message sent by the SMF to the MCF may include information #2.

[0429] 910: Perform an N4 session update (N4 session modification) between the MCF and the MUF.

[0430] For example, the MCF sends an N4 session update request to the MUF. In some embodiments, if the MCF receives information #2 sent by the S-gNB in ​​step 909, the MCF may include information #2 in the N4 session update request. After receiving information #2, the MUF releases the associated multicast session tunnel. For example, the MUF may remove the associated resources of the tunnel based on the corresponding tunnel identification information.

[0431] For example, a multicast / broadcast service usually only has a downlink. When a shared tunnel between the S-gNB and the MUF is established, the MUF configures a tunnel endpoint identifier TEID generated by the S-gNB and a PDR configured by the MCF for the MUF. In this way, the MUF can transmit data of the multicast service to the S-gNB. Thus, the release here can be to remove the associated TEID or to remove the PDR associated with the first multicast service. Note that the multicast service data in the entire document can be replaced with the multicast / broadcast service data.

[0432] In an example, when the information #2 includes an indication used to release the multicast session tunnel and information about the multicast session tunnel, the MUF may release the first tunnel based on the indication and the information about the multicast session tunnel. For example, when the information about the multicast session tunnel in the information #2 is the TEID of the multicast session tunnel, the MUF may release the TEID. In another example, when the information about the multicast session tunnel is the ID of the multicast session tunnel, the MUF may determine the multicast session tunnel based on the ID of the multicast session tunnel, and then release the multicast session tunnel based on the indication in the information #2, for example, remove the related resources of the multicast session tunnel, for example, the TEID, or remove the PDR related to the first multicast service.

[0433] In another example, when information #2 includes an indication used to release a multicast session tunnel and an identification information of a multicast service, the MUF may determine a multicast service based on the identification information of the multicast service, and then determine a multicast session tunnel for transmitting data of the multicast service between the S-gNB and the MUF. Specifically, the MUF may determine one or more multicast sessions corresponding to the multicast service, and one or more multicast session tunnels corresponding to the one multicast session, or multiple multicast session tunnels corresponding to the multiple multicast sessions. Then, the MUF may release the multicast session tunnel based on the indication in information #2, specifically, release related resources, such as TEIDs, of the one or more multicast session tunnels, or remove the PDR associated with the first multicast service.

[0434] In another example, when the information #2 includes an indication used to release the multicast session tunnel, an identification information of the multicast service, and information about the multicast session tunnel, the MUF may determine the multicast service based on the identification information of the multicast service. Then, the MUF may determine a multicast session tunnel for transmitting data of the multicast service between the S-gNB and the MUF based on the information about the multicast session tunnel in the information #2. Specifically, the MUF may determine one or more multicast sessions corresponding to the first multicast service, and one or more multicast session tunnels corresponding to the one multicast session, or multiple multicast session tunnels corresponding to the multiple multicast sessions. Then, the MUF may further determine the multicast session tunnel from the one or more multicast session tunnels based on the information about the multicast session tunnel in the information #2. Then, the multicast user plane function network element or the user plane function network element may release the multicast session tunnel based on the indication in the information #2, for example, remove related resources of the multicast session tunnel, for example, the TEID, or remove the PDR related to the first multicast service.

[0435] The MUF may then send an N4 session update response to the MCF.

[0436] 911: The MCF sends a response to the first message to the SMF. Optionally, the response to the first message may include response information for information #2. In addition, it should be noted that the necessity of a response message is limited here, in other words, a response message may not be sent.

[0437] Specifically, for steps 908 to 911, please refer to the description of steps 708 to 711. Details will not be described again in this specification.

[0438] 912: The SMF sends a PDU session context update response (Nsmf_PDUSession_UpdateSMContext Response) to the AMF.

[0439] In some embodiments, in addition to the existing information elements included in the signaling specified in the protocol, if the SMF receives a response information element related to the release of the multicast session tunnel in step 911, for example, response information for information #2, optionally, the PDU session context update response may further include a response information element.

[0440] 913: The AMF sends an N2 path switch request ACK to the T-gNB.

[0441] In some embodiments, in addition to the existing information elements specified in the protocol and included in the signaling, if a response information element related to the release of the multicast session tunnel, e.g., response information for information #2, is included in step 912, optionally the N2 path switch confirmation response may further include a response information element.

[0442] 914: The T-gNB sends a UE Context Release request to the S-gNB.

[0443] In some embodiments, in addition to existing information elements included in the signaling as specified in the protocol, if a response information element related to the release of the multicast session tunnel, e.g., response information for information #2, is included in step 913, optionally the N2 path switch confirmation response further includes a response information element.

[0444] Please note that in the embodiment shown in Figures 9A and 9B, only the example in which the T-gNB does not support the multicast function is used for explanation. However, the embodiment of the present application is not limited thereto. For example, the T-gNB may further support the multicast function. In this case, the S-gNB needs to duplicate and forward the multicast QoS flow received through the multicast session tunnel to the T-gNB, that is, the multicast QoS flow does not need to be mapped to a unicast QoS flow. For details, please refer to the description of Figures 7A and 7B. The details will not be described again.

[0445] In the above steps 906, 907 or 909, the information #2 is included as an information element in existing signaling and transmitted to the MCF, however, the embodiment of the present application is not limited thereto.

[0446] In some optional embodiments, the S-gNB may further execute step 915. Specifically, the S-gNB sends a notification message directly to the MCF, where the notification message instructs the MCF to release the multicast session tunnel in which the multicast service is located, i.e., the multicast session tunnel used to transmit the multicast service between the S-gNB and the MUF. In this case, the message in steps 902, 906, 907, 909 or 910 may not include information #2. Specifically, the S-gNB does not include information #2 in the existing signaling as an information element, but notifies the MCF by using a separate signaling to release the multicast session tunnel.

[0447] For example, the signaling may include an instruction used to release a multicast session tunnel and information about the multicast session tunnel, or the signaling may include an instruction used to release a multicast session tunnel and identification information of a multicast service, or the signaling may include an instruction used to release a multicast session tunnel, information about the multicast session tunnel, and identification information of a multicast service, which is not limited in this embodiment of the present application.

[0448] In a possible implementation, step 915 may be performed after the S-gNB decides to release the multicast session tunnel used to transmit the multicast service between the S-gNB and the MUF, and may be performed, for example, between steps 901 and 914, or after step 914. This is not limiting in this embodiment of the present application.

[0449] 916: Release the multicast session tunnel between the S-gNB and the MCF.

[0450] For example, after receiving the signaling at stage 915, the MCF may send the signaling to the MUF, and the MUF may release a multicast session tunnel used to transmit the multicast service between the S-gNB and the MUF based on the signaling.

[0451] In addition, in some other optional embodiments, when the UE subscribes to a multicast service, the MCF may also subscribe to a multicast session tunnel release notification from the S-gNB. In other words, when the S-gNB determines that the multicast session tunnel between the S-gNB and a core network device (such as a MUF or a UPF) needs to be released in the handover process, the S-gNB may send a release notification to the MCF. In this case, the signaling in steps 901 to 914 may be performed based on the existing normal handover procedure and does not need to include additional information, such as information #2.

[0452] In some optional embodiments, when the S-gNB decides or determines to release or is able to release the S-gNB's multicast session tunnel during the handover preparation phase (specific manners are described in steps 901 to 903 and will not be described again here), the S-gNB may further perform steps 917 to 919.

[0453] 917: The S-gNB sends a third message to the AMF, where the third message may be an N2 message, and the third message carries information #2.

[0454] Here, it should be noted that the AMF in step 917 may be the same AMF as the AMF in the handover procedure in Figures 9A and 9B (i.e., the AMF responsible for the UE to be handed over), or may be another AMF. This is not limited. In addition, the N2 message may be an existing N2 message (i.e., holding information #2), or may be a new N2 message (e.g., mainly used to release the multicast session tunnel, where the new N2 message follows the naming scheme of the service-based interface signaling message, and the specific name of the N2 message is not limited, but the function is to notify the MUF to release the multicast session tunnel). This is not limited in this embodiment of the present application.

[0455] 918: The AMF sends a fourth message to the MCF, where the fourth message may be an N11 message, and the fourth message carries information #2. For example, the N11 message may be an existing N11 message (i.e., carrying information #2), or may be a new N11 message (e.g., mainly used to release a multicast session tunnel, where the new N11 message follows the naming scheme of the service-based interface signaling message, and the specific name of the N11 message is not limited, but the function is to notify the MUF to release the multicast session tunnel).

[0456] 919: Perform N4 Session Modification between the MCF and the MUF. For example, the MCF sends a fifth message to the MUF, where the fifth message may be an N4 Session Update Request, the fifth message holds information #2, and the MUF releases the multicast session tunnel based on the information #2. Then, the MUF sends a response to the fifth message to the MCF, which may be an N4 Session Update Response.

[0457] It should be further noted that, in the handover procedure shown in Figures 9A and 9B, if the S-gNB notifies the MUF to release the multicast session tunnel through steps 917 to 919, after the S-gNB decides or resolves to release or may release the multicast session tunnel of the source base station in the handover preparation phase, the S-gNB performs steps 917 to 919 to notify the MUF to release the multicast session tunnel, i.e., information #2 and the response to the release of the associated multicast session tunnel are no longer retained in the handover procedure (e.g., steps 906 to 914).

[0458] Therefore, in this embodiment of the present application, in the handover preparation phase in which a UE is handed over from an S-gNB to a T-gNB, when it determines that there are no other UEs receiving a multicast service via the S-gNB in ​​a multicast session context (or a multicast service context, a multicast context, a multicast group context, or a multicast session context), the S-gNB may notify the core network device (such as a MUF or a UPF) to release a multicast session tunnel used to transmit the multicast service between the S-gNB and the core network device, for example, by using existing signaling or separate signaling to notify the release of the tunnel, and release the multicast session tunnel between the S-gNB and the core network device (such as a MUF or a UPF). This helps to reduce network resource overhead.

[0459] 10A-10C are schematic flowcharts of another communication method 1000 according to an embodiment of the present application. The handover in the method 1000 is an N2 handover. The S-gNB decides whether to release the multicast session tunnel between the S-gNB and the MUF.

[0460] Please note that in Figures 10A-10C, an example in which the multicast session tunnel between the S-gNB and the MUF is released is used for illustration. This solution is also suitable for releasing the multicast session tunnel between the S-gNB and the UPF, and some simple adaptations may be required. Figures 10A-10C and some simple adaptations belong to the protection scope of this application.

[0461] In some embodiments, when a UE receives multicast service data via an S-gNB (or, in other words, the UE subscribes to a multicast service via an S-gNB), the UE's PDU session is associated with the multicast service.

[0462] When the T-gNB to which the UE is handed over does not support the multicast function, the method 1000 is applicable to the scenario shown in FIG. 5C. In the following, the method 1000 is described with reference to the scenario in FIG. 5C. As shown in FIG. 10A to FIG. 10C, the method 1000 may comprise steps 1001 to 1017. It should be noted that the solution is also applicable to a scenario in which the T-gNB supports the multicast function, and is not limited thereto here. The scenario shown in FIG. 5C is merely an example.

[0463] 10A-10C show steps or operations of a communication method 1000 provided in this embodiment of the present application, it should be understood that these steps or operations are merely examples. In this embodiment of the present application, other operations or variations of the operations in FIG. 10A-10C may also be performed. In addition, the steps in the figures may be performed in a different order than presented in the figures, and not all operations in the figures may need to be performed.

[0464] Optionally, before step 1001, the S-gNB may know whether the function of the T-gNB, i.e., the function for the multicast function, is supported. For example, when there is an Xn connection between the T-gNB and the S-gNB, the T-gNB may inform the S-gNB of the capability information of the T-gNB by using the Xn interface, where Xn may be the interface of the Xn connection between the S-gNB and the T-gNB. For example, when the T-gNB does not support the multicast function, the T-gNB sends the indication information #1 to the S-gNB, where the indication information #1 indicates that the T-gNB does not support the multicast function. Alternatively, in some embodiments, when the T-gNB does not support the multicast function, the T-gNB may not send the indication information #1 to the S-gNB. Correspondingly, if the S-gNB does not receive the indication information #1, the T-gNB may be considered as not supporting the multicast function.

[0465] Here, first, according to the definition of the handover preparation phase of N2 handover in 3GPP technical specification (TS) 23.502, the handover preparation phase includes steps 1001 to 1012 in the procedure shown in Fig. 10A to Fig. 10C. The handover preparation phase can be understood as a phase in which an S-gNB, a T-gNB, or a core network device prepares resources required for handover for a UE to be handed over (e.g., may include information about a forwarding tunnel, radio bearer configuration information required by the UE to receive service data after the UE accesses the T-gNB, or air interface resources configured by the T-gNB for the terminal device to be handed over).

[0466] 1001: The UE sends a measurement report to the S-gNB. In response, the S-gNB receives the measurement report and decides to hand over the UE to the T-gNB.

[0467] In some optional embodiments, after receiving the measurement report sent by the UE, the S-gNB may update the number of UEs in the multicast session context (or multicast service context, multicast context, or multicast group context) corresponding to the multicast service associated with the PDU session of the UE to be handed over (e.g., decrease the number of UEs by 1). If the current UE to be handed over is the last UE in the aforementioned context (in other words, after the UE leaves, no other UEs receive the multicast service at the base station), the S-gNB may know that the UE is the last UE to receive data of the multicast service via the S-gNB. In this case, the S-gNB may decide to release the multicast session tunnel between the S-gNB and the core network device (e.g., the MUF in FIG. 5C).

[0468] Here, the multicast service may be an example of the first multicast service in FIG. 8, and the multicast session tunnel may be an example of the first tunnel in FIG.

[0469] For example, the number of UEs that have subscribed to the multicast service via the S-gNB (which may also be understood as the number of UEs that receive the multicast service via the S-gNB) and / or the identification information of the UEs may be included in the multicast session context (or the multicast service context, the multicast context, or the multicast group context). In other words, depending on whether another UE other than the UE in the multicast session context (or the multicast service context, the multicast context, or the multicast group context) receives the multicast service via the S-gNB, the S-gNB may decide whether to release the multicast session tunnel in which the multicast service is located.

[0470] Here, it should be noted that at the granularity of a base station (in other words, in units of a base station), one multicast service may correspond to one multicast session, in other words, a multicast session tunnel between a base station (e.g., S-gNB) and a core network device (such as MUF or UPF). Here, it should be noted that one multicast service may also correspond to multiple multicast / broadcast sessions. This is not limited here. This solution uses a one-to-one correspondence as an example, and this solution is also applicable to a one-to-many correspondence.

[0471] 1002: The S-gNB sends a handover request (Handover Required) to the S-AMF.

[0472] For example, the "handover request" includes the PDU session information of the UE to be handed over and the associated multicast service information (including the associated multicast service identifier), where the PDU session information includes the PDU session identifier and QoS information corresponding to the unicast service flow included in the PDU session. The QoS information of the unicast service flow includes the QFI and QoS parameters. If the PDU session of the current UE to be handed over is associated with a multicast service, the S-gNB may map the multicast QoS flow to the unicast QoS flow based on the mapping relationship between the multicast QoS flow QFI and the unicast QoS flow QFI.

[0473] In addition, the handover request may further include SM N2 information. If the SM N2 information indicates that there is no direct forwarding tunnel between the S-gNB and the T-gNB, it indicates that an indirect forwarding tunnel can be established between the S-gNB and the T-gNB. In this case, the SM N2 information may include indirect forwarding tunnel information allocated by the S-gNB.

[0474] The "handover request" may further include an identifier of the service flow that the S-gNB intends to forward through the forwarding tunnel. If a multicast QoS flow needs to be forwarded through the forwarding tunnel, the handover request includes the QFI of the unicast QoS flow corresponding to the multicast QoS flow.

[0475] In some optional embodiments, when deciding to release the multicast session tunnel in step 1001, the S-gNB may generate information #2 used to release the multicast session tunnel used to transmit data of the multicast service between the S-gNB and a core network device (such as UPF or MCF, where MUF is used as an example). In this case, the handover request may include information #2. Specifically, for information #2, please refer to the description in step 902 of Figures 9A and 9B. Details will not be described again.

[0476] 1003: The S-AMF selects a target AMF (i.e., a Target-AMF or a T-AMF) based on the target cell ID, where the T-AMF is connected to the T-gNB.

[0477] 1004: The S-AMF sends a UE context creation request (Namf_Communication_CreateUEContext Request) to the T-AMF, where the request may include context information of the UE to be handed over that is stored in the S-AMF, and may further include information sent by the S-gNB to the S-AMF in step 1002.

[0478] Optionally, when the S-gNB is in step 1002 and transmits information #2 to the S-AMF, the S-AMF transmits information #2 to the T-AMF in step 1004.

[0479] 1005: The T-AMF sends a PDU session context update request (Nsmf_PDUSession_UpdateSMContext Request) to the SMF, including the information sent by the S-gNB to the S-AMF in step 1002. Optionally, if information #2 is included in step 1004, the PDU session context update request further carries information #2.

[0480] 1006: Perform N4 session update (N4 session modification) between the SMF and the UPF.

[0481] For example, the SMF sends an N4 session update request to the UPF. Optionally, the N4 session update request carries the indirect forwarding tunnel information assigned to the S-gNB. The UPF then returns an N4 session update response to the SMF. Optionally, the N4 session update response includes the indirect forwarding tunnel information assigned by the UPF, which is used to establish the indirect forwarding tunnel between the S-gNB and the T-gNB shown in FIG. 5C.

[0482] 1007: The SMF sends a PDU session context update response (Nsmf_PDUSession_UpdateSMContext Response) to the T-AMF. The message may include QoS information of the unicast QoS flow of the PDU session. The QoS information includes a QFI and corresponding QoS parameters. The unicast QoS flow includes a unicast QoS flow to which the multicast QoS flow is mapped.

[0483] 1008: The T-AMF sends a Handover Request to the T-gNB. The message may include QoS information of the unicast QoS flow included in the PDU session (including QoS information of the unicast QoS flow to which the multicast QoS flow is mapped). The T-gNB allocates radio resources to the unicast QoS flow based on the QoS information of the QoS flow. Optionally, if the S-gNB supports the establishment of an indirect forwarding tunnel, the Handover Request includes the indirect forwarding tunnel information allocated by the S-gNB and the indirect forwarding tunnel information allocated by the UPF.

[0484] 1009: The T-gNB sends a handover request acknowledgment (Handover Request ACK) to the T-AMF.

[0485] For example, the handover request acknowledgment may include the QFIs of unicast QoS flows that have been successfully handed over and / or failed to be handed over (e.g., the handover failure occurs because the T-gNB cannot allocate radio resources to the unicast QoS flows due to insufficient resources), the radio bearer configurations that the UE needs to access the T-gNB to receive the service data, and the like. In addition, since there is an indirect forwarding tunnel between the S-gNB and the T-gNB, the T-gNB further includes information about the indirect forwarding tunnel (specifically, used to establish a forwarding tunnel with the UPF) in the handover request acknowledgment, and then sends the tunnel information to the UPF through steps 1009 to 1018.

[0486] 1010: The T-AMF sends a PDU session context update request (Nsmf_PDUSession_UpdateSMContext Request) to the SMF, including relevant information included in the handover request acknowledgment in step 1009.

[0487] 1011: The SMF sends a PDU session context update response (Nsmf_PDUSession_UpdateSMContext Response) to the T-AMF. Optionally, the response further includes indirect forwarding tunnel information of the UPF.

[0488] 1012: The T-AMF sends a UE context creation response (Nsmf_PDUSession_UpdateSMContext Response) including the information in step 1011 to the S-AMF.

[0489] 1013: The S-AMF sends a handover command including the information in step 1012 to the S-gNB.

[0490] Optionally, if information #2 is not generated in step 1001 (in other words, the S-gNB does not generate information #2 after receiving the signaling in step 1001, i.e., the signaling does not hold information #2 in steps 1001 to 1005), after the S-gNB receives the handover command, the S-gNB may update the number of UEs in the multicast session context corresponding to the multicast service associated with the PDU session of the UE to be handed over (e.g., decrease the number of UEs by 1). If the current UE to be handed over is the last UE in the multicast session context (or multicast service context, multicast context, or multicast group context) (in other words, after the UE has left, no other UEs have received the multicast service at the base station), the S-gNB knows that the UE is the last UE to receive data of the multicast service via the S-gNB. In this case, the S-gNB may decide to release the multicast session tunnel between the S-gNB and the core network device (e.g., the MUF in FIG. 5C).

[0491] For example, the number of UEs that have subscribed to a multicast service via an S-gNB (which may also be understood as the number of UEs that receive multicast service data via an S-gNB) may be included in the multicast session context (or multicast service context, multicast context, or multicast group context) of the multicast service. In other words, depending on whether another UE other than the UE in the multicast session context (or multicast service context, multicast context, or multicast group context) receives data of the multicast service via the S-gNB, the S-gNB may decide whether to release the multicast session tunnel in which the multicast service is located.

[0492] For example, after receiving the handover command, if it decides to release the multicast session tunnel, the S-gNB may generate information #2 that is used to request, instruct or notify a core network device (such as MCF or MUF, where MUF is used as an example) to release the multicast session tunnel where the multicast service is located. Specifically, for information #2, please refer to the above description. Details will not be described again. Then, the S-gNB may include information #2 in signaling and send the signaling to a session management function network element.

[0493] 1014: The S-gNB sends a handover command to the UE, including radio bearer configuration information required by the UE to access the target base station (here, the radio bearer configuration information includes radio bearer configuration information required for the unicast QoS flow and the radio bearer configuration information of the unicast QoS flow to which the multicast QoS flow is mapped).

[0494] Next, the S-gNB duplicates the multicast QoS flow received through the multicast session tunnel, maps the duplicated multicast QoS flow, and forwards the mapped duplicated multicast QoS flow to the T-gNB through the indirect forwarding tunnel.

[0495] 1015: The UE accesses the T-gNB. The T-gNB transmits the received and buffered unicast QoS flow and / or multicast QoS flow to the UE. The UE receives the corresponding service data based on the radio bearer configuration information transmitted by the S-gNB in ​​step 1014.

[0496] 1016: The T-gNB sends a Handover Notify to the T-AMF, where the notification indicates that the UE has successfully handed over to the T-gNB.

[0497] 1017: The T-AMF sends a PDU session context update request (Nsmf_PDUSession_UpdateSMContext) to the SMF, which holds information about the PDU session tunnel allocated by the T-gNB. Optionally, information about the indirect forwarding tunnel created by the T-gNB is further held.

[0498] 1018: The SMF sends a first message to the MCF. For example, the first message may be an N16 message.

[0499] In some embodiments, when the SMF receives information #2 sent by the S-gNB in ​​step 1005, the first message sent by the SMF to the MCF may include information #2.

[0500] The description of steps 1019 to 1021 is similar to that of steps 910 to 912. Details will not be described again in this specification.

[0501] 1022: Continue to perform subsequent handover procedures based on the N2 handover procedures specified in the 3GPP technical specifications.

[0502] Please note that in the embodiment shown in Figures 10A to 10C, only the example in which the T-gNB does not support the multicast function is used for explanation. However, the embodiment of the present application is not limited thereto. For example, the T-gNB may further support the multicast function. In this case, the S-gNB needs to duplicate and forward the multicast QoS flow received through the multicast session tunnel to the T-gNB, that is, the multicast QoS flow does not need to be mapped to a unicast QoS flow. For details, please refer to the description of Figures 7A and 7B. The details will not be described again.

[0503] In the preceding steps (steps 1002, 1004, 1005, 1007, 1008, 1016, 1017 and 1019) or (steps 1016, 1017 and 1018), the S-gNB includes information #2 in existing signaling and transmits information #2 to the MCF, which further transmits information #2 to the MUF via step 1019. However, the embodiments of the present application are not limited thereto.

[0504] In some optional embodiments, the S-gNB may further execute step 1023. Specifically, the S-gNB directly sends a notification message to the MCF, where the notification message instructs the MCF to release the multicast session tunnel in which the multicast service is located, i.e., the multicast session tunnel used to transmit the multicast service between the S-gNB and the MUF. In this case, the message in step (1002, 1004, 1005, 1007, 1008, 1016, 1017, 1018, or 1019) may not include information #2. Specifically, the S-gNB does not include related instruction information to release the multicast session tunnel as an information element in the existing signaling, but notifies the MCF to release the multicast session tunnel by using a separate signaling.

[0505] For example, the signaling may include an instruction used to release a multicast session tunnel and information about the multicast session tunnel, or the signaling may include an instruction used to release a multicast session tunnel and identification information of a multicast service, or the signaling may include an instruction used to release a multicast session tunnel, information about the multicast session tunnel, and identification information of a multicast service, which is not limited in this embodiment of the present application.

[0506] In a possible implementation, step 1023 may be performed after the S-gNB decides to release the multicast session tunnel used to transmit the multicast service between the S-gNB and the MUF, and may be performed, for example, between steps 1001 and 1022 or after step 1022. This is not limited in this embodiment of the present application.

[0507] 1024: Release the multicast session tunnel between the S-gNB and the MCF.

[0508] For example, after receiving the signaling at step 1023, the MCF may send the signaling to the MUF, and the MUF may release a multicast session tunnel used to transmit the multicast service between the S-gNB and the MUF based on the signaling.

[0509] In addition, in some other optional embodiments, when the UE subscribes to a multicast service, the MCF may also subscribe to a multicast session tunnel release notification from the S-gNB. In other words, when the S-gNB determines that the multicast session tunnel between the S-gNB and a core network device (such as a MUF or a UPF) needs to be released in the handover process, the S-gNB may send a release notification to the MCF. In this case, the signaling in steps 1001 to 1022 may be performed based on the existing normal handover procedure and does not need to include additional information, such as information #2.

[0510] In some optional embodiments, when the S-gNB decides or determines to release or is able to release the S-gNB's multicast session tunnel during the handover preparation phase (specific manners are described in steps 1001 to 1012 and will not be described again here), the S-gNB may further perform steps 1025 to 1027.

[0511] 1025: The S-gNB sends a third message to the S-AMF, where the third message may be an N2 message, and the third message carries information #2.

[0512] It should be noted here that the S-AMF in step 1025 may be the same AMF as the S-AMF in the handover procedure in FIG. 10A-FIG. 10C (i.e., the S-AMF in charge of the UE to be handed over), or may be another AMF. This is not limited. In addition, the N2 message may be an existing N2 message (i.e., holding information #2), or may be a new N2 message (e.g., mainly used to release the multicast session tunnel, where the new N2 message follows the naming scheme of the service-based interface signaling message, and the specific name of the N2 message is not limited, but the function is to notify the MUF to release the multicast session tunnel). This is not limited in this embodiment of the present application.

[0513] 1026: The S-AMF sends a fourth message to the MCF, where the fourth message may be an N11 message, and the N11 message carries information #2. For example, the N11 message may be an existing N11 message (i.e., carrying information #2), or may be a new N11 message (e.g., mainly used to release a multicast session tunnel, where the new N11 message follows the naming scheme of the service-based interface signaling message, and the specific name of the N11 message is not limited, but the function is to notify the MUF to release the multicast session tunnel).

[0514] 1027: Perform N4 Session Modification between the MCF and the MUF. For example, the MCF sends a fifth message to the MUF, where the fifth message may be an N4 Session Update Request, and the fifth message carries information #2. The MUF releases the multicast session tunnel based on the information #2, and then sends a response to the fifth message, which may be an N4 Session Update Response, to the MCF.

[0515] Here, it should be further noted that when the S-gNB notifies the MUF to release the multicast session tunnel through steps 1025 to 1027, in the handover procedure shown in Figures 10A to 10C, after the S-gNB decides or resolves to release the multicast session tunnel of the source base station in the handover preparation phase, or may release it, the S-gNB performs steps 1025 to 1027 to notify the MUF to release the multicast session tunnel, i.e., information #2 and the response to the release of the associated multicast session tunnel are no longer retained in the handover procedure.

[0516] Therefore, in this embodiment of the present application, in the handover preparation phase in which a UE is handed over from an S-gNB to a T-gNB, when it determines that there are no other UEs receiving a multicast service via the S-gNB in ​​a multicast session context (or a multicast service context, a multicast context, or a multicast group context), the S-gNB may notify the core network device (such as a MUF or a UPF) to release the multicast session tunnel used to transmit the multicast service between the S-gNB and the core network device, for example, by using existing signaling or separate signaling to notify the release of the tunnel, and release the multicast session tunnel between the S-gNB and the core network device (such as a MUF or a UPF). This helps to reduce network resource overhead.

[0517] According to the above method, FIG. 11 is a schematic diagram of a wireless communication device 1100 according to an embodiment of the present application.

[0518] The apparatus 1100 may be an access network device or may be a chip or circuit, such as a chip or circuit that may be located in an access network device.

[0519] Alternatively, the apparatus 1100 may be an access and mobility management function network element, or may be a chip or circuit, for example a chip or circuit that may be located in an access and mobility management function network element.

[0520] Alternatively, the apparatus 1100 may be a session management function network element, or may be a chip or circuit, for example a chip or circuit that may be located in a session management function network element.

[0521] Alternatively, the apparatus 1100 may be a multicast session management function network element or may be a chip or circuit, for example a chip or circuit that may be located in a multicast session management function network element.

[0522] Alternatively, the apparatus 1100 may be a multicast user plane function network element, or may be a chip or circuit, for example a chip or circuit that may be located in a multicast user plane function network element.

[0523] The apparatus 1100 may include a processing unit 1110 (ie, an example of a processor) and a transceiver unit 1130 .

[0524] Optionally, the transceiver unit 1130 may be implemented by using a transceiver, a transceiver-related circuit, or an interface circuit.

[0525] Optionally, the device 1100 may further include a storage unit 1120. In a possible manner, the storage unit 1120 is configured to store instructions. Optionally, the storage unit 1120 may alternatively be configured to store data or information. The storage unit 1120 may be implemented by using a memory.

[0526] In a possible design, the processing unit 1110 may be configured to execute instructions stored in the memory unit 1120 to enable the apparatus 1100 to implement steps performed by the access network device in the aforementioned methods.

[0527] Furthermore, the processing unit 1110, the storage unit 1120, and the transceiver unit 1130 may communicate with each other through an internal connection path and transmit control signals and / or data signals. For example, the storage unit 1120 may be configured to store a computer program, and the processing unit 1110 may be configured to call up the computer program from the storage unit 1120 and execute the computer program, and control the transceiver unit 1130 to receive signals and / or transmit signals, and may realize the steps of an access network device, an access and mobility management function network element, a session management function network element, a multicast session management function network element, or a multicast user plane function network element in the above-mentioned method. The storage unit 1120 may be integrated into the processing unit 1110 or may be located separately from the processing unit 1110.

[0528] Optionally, if the apparatus 1100 is a communication device, the transceiver unit 1130 may include a receiver and a transmitter. The receiver and the transmitter may be the same physical entity or different physical entities. When the receiver and the transmitter are the same physical entity, they may be collectively referred to as a transceiver.

[0529] Optionally, if the apparatus 1100 is a chip or a circuit, the transceiver unit 1130 includes an input interface and an output interface.

[0530] In implementation, the functionality of the transceiver unit 1130 may be considered to be implemented by using a transceiver circuit or a dedicated transceiver chip, and the processing unit 1110 may be considered to be implemented by using a dedicated processing chip, a processing circuit, a processing unit, or a general-purpose chip.

[0531] In another implementation, the communication device (such as an access network device, an access and mobility management function network element, a session management function network element, a multicast session management function network element, or a multicast user plane function network element) provided in this embodiment of the present application may be considered to be implemented by using a general-purpose computer, that is, the program codes for implementing the functions of the processing unit 1110 and the transceiver unit 1130 are stored in the storage unit 1120, and the general-purpose processing unit implements the functions of the processing unit 1110 and the transceiver unit 1130 by executing the codes in the storage unit 1120.

[0532] In some embodiments, when the apparatus 1100 is a first access network device or may be a chip or circuit disposed in the first access network device, the processing unit 1110 is configured to know that when the first terminal device is in a handover preparation phase in which the first terminal device is handed over from the first access network device to the second access network device, the first terminal device is the last terminal device to receive data of the first multicast service via the first access network device; the transceiver unit 1130 is configured to transmit first information, where the first information is used to release a first tunnel, and the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device.

[0533] Optionally, the transceiver unit 1130 is specifically configured to send a handover request to the second access network device, where the handover request requests to handover the first terminal device from the first access network device to the second access network device, and the handover request includes the first information.

[0534] Optionally, the transceiver unit 1130 is specifically configured to send a handover request to the first access and mobility management function network element, where the handover request includes the first information.

[0535] Optionally, the transceiver unit 1130 is specifically configured to send a third message to a third access and mobility management function network element, where the third message includes the first information, and the third access and mobility management function network element is an access and mobility management function network element selected by the first access network device for the first multicast service when the first terminal device joins the first multicast service.

[0536] Optionally, the processing unit 1110 is further configured to update a number of terminal devices that have subscribed to the first multicast service via the first access network device.

[0537] Optionally, the first information includes an instruction used to release the first tunnel and information about the first tunnel; the first information includes an instruction used to release the first tunnel and identification information of the first multicast service; or the first information includes an instruction used to release the first tunnel, identification information of the first multicast service, and information about the first tunnel.

[0538] Optionally, the core network device comprises a multicast user plane function network element or a user plane function network element.

[0539] The functions and operations of the modules or units in the apparatus 1100 listed above are merely illustrative examples. When the apparatus 1100 is configured in or is a first access network device, the modules or units in the apparatus 1100 may be configured to perform the operations or processing performed by the first access network device in the aforementioned method.

[0540] In some embodiments, when the apparatus 1100 is a second access network device or may be a chip or circuit disposed in the second access network device, the transceiver unit 1130 is configured to receive a handover request from the first access network device, where the handover request requests to handover the first terminal device from the first access network device to the second access network device, the handover request includes first information, where the first information is used to release a first tunnel, where the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device, and the transceiver unit 1130 is further configured to send a path switch request to the access and mobility management function network element, where the path switch request includes the first information.

[0541] The functions and operations of the modules or units in the apparatus 1100 listed above are merely illustrative examples. When the apparatus 1100 is configured in or is a second access network device, the modules or units in the apparatus 1100 may be configured to perform the operations or processing performed by the second access network device in the aforementioned method.

[0542] In some embodiments, when the apparatus 1100 is an access and mobility management function network element or may be a chip or circuit disposed in an access and mobility management function network element, the transceiver unit 1130 is configured to receive a path switch request from a second access network device, where the path switch request includes first information, the first information being used to release a first tunnel, the first tunnel being used to transmit data of a first multicast service between the first access network device and the core network device; the transceiver unit 1130 is further configured to send a protocol data unit PDU session context update request to the session management function network element, where the PDU session context update request includes the first information.

[0543] The functions and operations of the modules or units in the device 1100 listed above are merely illustrative examples. When the device 1100 is configured in or is an access and mobility management function network element, the modules or units in the device 1100 may be configured to perform the operations or processing performed by the access and mobility management function network element in the above-mentioned method.

[0544] In some embodiments, when the apparatus 1100 is a session management function network element or may be a chip or circuit disposed in a session management function network element, the transceiver unit 1130 is configured to receive a protocol data unit PDU session context update request from the access and mobility management function network element, where the PDU session context update request includes first information, where the first information is used to release a first tunnel, where the first tunnel is used to transmit data of a first multicast service between the first access network device and the core network device, and the transceiver unit 1130 is further configured to send a first message to the multicast session management function network element, where the first message includes the first information.

[0545] Optionally, the first message may be an N16 message.

[0546] In some embodiments, when the apparatus 1100 is a session management function network element or may be a chip or circuit disposed in a session management function network element, the transceiver unit 1130 is configured to receive a protocol data unit PDU session context update request from the access and mobility management function network element, where the PDU session context update request includes first information, where the first information is used to release a first tunnel, where the first tunnel is used to transmit data of a first multicast service between the first access network device and the core network device, and the transceiver unit 1130 is further configured to send the session update request to the user plane function network element, where the session update request includes the first information.

[0547] The functions and operations of the modules or units in the apparatus 1100 listed above are merely illustrative examples. When the apparatus 1100 is configured in or is a session management function network element, the modules or units in the apparatus 1100 may be configured to perform the operations or processing performed by the session management function network element in the above-mentioned manner.

[0548] In some embodiments, when the apparatus 1100 is a multicast session management function network element or may be a chip or circuit arrangement in a multicast session management function network element, the transceiver unit 1130 is configured to receive a first message from the session management function network element, where the first message includes first information, where the first information is used to release a first tunnel, where the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device, and the transceiver unit 1130 is further configured to send a fifth message to the multicast user plane function network element, where the fifth message includes the first information.

[0549] Optionally, the first message is an N16 message.

[0550] Optionally, the fifth message is an N4 session update request.

[0551] The functions and operations of the modules or units in the apparatus 1100 listed above are merely examples for illustration. When the apparatus 1100 is configured in or is a multicast session management function network element, the modules or units in the apparatus 1100 may be configured to perform the operations or processing performed by the multicast session management function network element in the above-mentioned manner.

[0552] In some embodiments, when the apparatus 1100 is a first access and mobility management function network element or may be a chip or circuit disposed in the first access and mobility management function network element, the transceiver unit 1130 is configured to receive a handover request from the first access network device, the handover request including first information, the first information being used to release a first tunnel, the first tunnel being used to transmit data of the first multicast service between the first access network device and the core network device; the transceiver unit 1130 is further configured to send a user equipment (UE) context creation request to the second access and mobility management function network element, where the UE context creation request includes the first information.

[0553] The functions and operations of the modules or units in the apparatus 1100 listed above are merely illustrative examples. When the apparatus 1100 is configured in or is a first access and mobility management function network element, the modules or units in the apparatus 1100 may be configured to perform the operations or processing performed by the first access and mobility management function network element in the above-mentioned method.

[0554] In some embodiments, when the apparatus 1100 is a second access and mobility management function network element or may be a chip or circuit disposed in the second access and mobility management function network element, the transceiver unit 1130 is configured to receive a user equipment (UE) context creation request from the first access and mobility management function network element, where the UE context creation request includes first information, the first information being used to release a first tunnel, the first tunnel being used to transmit data of the first multicast service between the first access network device and the core network device; the transceiver unit 1130 is further configured to send a protocol data unit (PDU) session context update request to the session management function network element, where the PDU session context update request includes the first information.

[0555] The functions and operations of the modules or units in the device 1100 listed above are merely examples for illustration. When the device 1100 is configured in or is a second access and mobility management function network element, the modules or units in the device 1100 may be configured to perform the operations or processing performed by the second access and mobility management function network element in the above-mentioned method.

[0556] In some embodiments, when the apparatus 1100 is a third access and mobility management function network element or may be a chip or circuit disposed in the third access and mobility management function network element, the transceiver unit 1130 is configured to receive a third message from the first access network device, where the third message includes first information, where the first information is used to release a first tunnel, where the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device, and when the first terminal device joins the first multicast service, the third access and mobility management function network element is an access and mobility management function network element selected by the first access network device for the first multicast service; the transceiver unit 1130 is further configured to send a fourth message to the multicast session management function network element, where the fourth message includes the first information.

[0557] Optionally, the third message is an N2 message.

[0558] Optionally, the fourth message is an N11 message.

[0559] The functions and operations of the modules or units in the device 1100 listed above are merely examples for illustration. When the device 1100 is configured in or is a third access and mobility management function network element, the modules or units in the device 1100 may be configured to perform the operations or processing performed by the third access and mobility management function network element in the above-mentioned method.

[0560] In some embodiments, when the apparatus 1100 is a multicast session management function network element or may be a chip or circuit disposed in the multicast session management function network element, the transceiver unit 1130 is configured to receive a fourth message from a third access and mobility management function network element, where the fourth message includes first information, the first information is used to release a first tunnel, the first tunnel is used to transmit data of the first multicast service between the first access network device and the core network device, and when the first terminal device joins the first multicast service, the third access and mobility management function network element is an access and mobility management function network element selected by the first access network device for the first multicast service; the transceiver unit 1130 is further configured to send a fifth message to the multicast user plane function network element, where the fifth message includes the first information.

[0561] Optionally, the fifth message is an N4 session update request.

[0562] Optionally, the fourth message is an N11 message.

[0563] The functions and operations of the modules or units in the apparatus 1100 listed above are merely examples for illustration. When the apparatus 1100 is configured in or is a multicast session management function network element, the modules or units in the apparatus 1100 may be configured to perform the operations or processing performed by the multicast session management function network element in the above-mentioned manner.

[0564] In some embodiments, when the apparatus 1100 is a multicast user plane function network element or may be a chip or circuit disposed in the multicast user plane function network element, the transceiver unit 1130 is configured to receive a fifth message from the multicast session management function network element, where the fifth message includes first information, the first information being used to release a first tunnel, the first tunnel being used to transmit data of the first multicast service between the first access network device and the core network device; the transceiver unit 1130 is further configured to release the first tunnel based on the first information.

[0565] Optionally, the transceiver unit 1130 is specifically configured to receive a fifth message from the multicast session management function network element, where the fifth message includes the first information.

[0566] Optionally, the fifth message is an N4 session update request.

[0567] The functions and operations of the modules or units in the apparatus 1100 listed above are merely illustrative examples. When the apparatus 1100 is configured in or is a multicast user plane function network element, the modules or units in the apparatus 1100 may be configured to perform the operations or processing performed by the multicast user plane function network element in the above-mentioned manner.

[0568] In some embodiments, when the apparatus 1100 is a user plane function network element or may be a chip or circuit disposed in a user plane function network element, the transceiver unit 1130 is configured to receive a session update request from the session management network element, where the session update request includes first information, the first information being used to release a first tunnel, the first tunnel being used to transmit data of the first multicast service between the first access network device and the core network device; the transceiver unit 1130 is further configured to release the first tunnel based on the first information.

[0569] The units in the above embodiments may also be referred to as modules, circuits, or components.

[0570] For the concepts, explanations, detailed descriptions and other steps of the apparatus 1100 related to the technical solutions according to the embodiments of the present application, please refer to the content descriptions in the above method or other embodiments, and the details will not be described again in this specification.

[0571] FIG. 12 is a schematic diagram of a structure of a network device 1200 according to an embodiment of the present application, which may be configured to implement the functions of an access network device (such as a first access network device or a second access network device) in the aforementioned method. The network device 1200 includes a remote radio unit (RRU) 1210 and one or more radio frequency units, such as one or more baseband units (BBUs) (which may also be referred to as digital units (DUs)) 1220. The RRU 1210 may also be referred to as a transceiver unit, a transceiver machine, a transceiver circuit, a transceiver, etc., and may include at least one antenna 1211 and a radio frequency unit 1212. The RRU 1210 is mainly configured to receive and transmit radio frequency signals, and perform conversion between radio frequency signals and baseband signals, for example, configured to transmit signaling messages in the aforementioned embodiment to terminal devices. The BBU 1220 is mainly configured to perform baseband processing, control a base station, etc. The RRU 1210 and the BBU 1220 may be physically co-located or physically separated (i.e., in a distributed base station).

[0572] The BBU 1220 is the control center of the base station, which may also be referred to as a processing unit, and is mainly configured to implement baseband processing functions such as channel encoding, multiplexing, modulation, spreading, etc. For example, the BBU (processing unit) 1220 may be configured to control the access network device and perform operation procedures related to the access network device in the above-mentioned method embodiments.

[0573] In an example, the BBU 1220 may include one or more boards, which may jointly support a radio access network of a single access standard (such as an LTE system or a 5G system) or may each support a radio access network of a different access standard. The BBU 1220 further includes a memory 1221 and a processor 1222. The memory 1221 is configured to store necessary instructions and data. The processor 1222 is configured to control the access network device to perform necessary operations, for example, to control the access network device to perform operation procedures related to the access network device in the embodiment of the method described above. The memory 1221 and the processor 1222 may be responsible for one or more boards. In other words, the memory and the processor may be separately disposed on each board. Alternatively, the multiple boards may share the same memory and processor. In addition, necessary circuits may be further disposed on each board.

[0574] In a possible implementation, with the development of system-on-chip (SoC) technology, all or part of the functions of the portion 1220 and the portion 1210 may be implemented by using SoC technology, for example, by using a base station function chip. The base station function chip integrates devices such as a processor, a memory, and an antenna port. The program of the base station related function is stored in the memory. The processor executes the program to implement the base station related function. Optionally, the base station function chip may also read an external memory of the chip and implement the base station related function.

[0575] It should be understood that the structure of the network device shown in Fig. 12 is only a possible form and does not constitute any limitation to this embodiment of the present application. The present application does not exclude the possibility that other forms of base station structures may appear in the future.

[0576] It should be understood that the processor in the embodiments of the present application may be a central processing unit (CPU). The processor may also be another general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), or another programmable logic device, a discrete gate or transistor logic device, a discrete hardware device, or the like. The general-purpose processor may be a microprocessor, or the processor may be any conventional processor or the like.

[0577] It will be understood that the memory in the present embodiment of the present application may be volatile or non-volatile memory, or may include volatile and non-volatile memory. The non-volatile memory may be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. The volatile memory may be random access memory (RAM) used as an external cache. Many forms of random access memories (RAM) are available, such as, for example and without limitation, static random access memory (static RAM, SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (synchronous DRAM, SDRAM), double data rate synchronous dynamic random access memory (DDR SDRAM), enhanced synchronous dynamic random access memory (enhanced SDRAM, ESDRAM), synchlink dynamic random access memory (synchlink DRAM, SLDRAM), and direct rambus random access memory (direct rambus RAM, DR RAM).

[0578] All or some of the above-mentioned embodiments may be implemented by software, hardware, firmware, or any combination thereof. When software is used to implement the embodiments, the above-mentioned embodiments may be implemented in the form of a computer program product, either completely or partially. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded and executed on a computer, the procedures or functions according to the embodiments of the present application are generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or may be transmitted from a computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from a website, computer, server, or data center to another website, computer, server, or data center in a wired (e.g., infrared, radio, and microwave, or the like) manner. The computer-readable storage medium may be any available medium that can be accessed by a computer or by a data storage device that integrates one or more available media, such as a server or data center. The available media may be magnetic media (e.g., floppy disk, hard disk, or magnetic tape), optical media (e.g., DVD), or semiconductor media. The semiconductor media may be a solid-state drive.

[0579] An embodiment of the present application further provides a computer-readable medium. The computer-readable medium stores a computer program. When the computer program is executed by a computer, the steps performed by the access network device, the access and mobility management function network element, the session management function network element, the multicast session management function network element, or the multicast user plane function network element in any one of the previous embodiments are implemented.

[0580] An embodiment of the present application further provides a computer program product, which, when executed by a computer, implements the steps performed by an access network device, an access and mobility management function network element, a session management function network element, a multicast session management function network element, or a multicast user plane function network element in any one of the previous embodiments.

[0581] The embodiment of the present application further provides a system chip. The system chip includes a communication unit and a processing unit. The processing unit may be, for example, a processor. The communication unit may be, for example, an input / output interface, a pin, or a circuit. The processing unit may execute computer instructions, so that the chip in the communication device executes the steps performed by the access network device, the access and mobility management function network element, the session management function network element, the multicast session management function network element, or the multicast user plane function network element provided in the embodiment of the present application.

[0582] Optionally, the computer instructions are stored in a storage unit.

[0583] The embodiments in the present application may be used independently or in combination, and there is no limitation thereon.

[0584] Furthermore, aspects or features of the present application may be implemented as a method, apparatus, or article of manufacture using standard programming and / or engineering techniques. The term "article of manufacture" as used herein encompasses a computer program accessible from any computer-readable component, carrier, or medium. For example, a computer-readable medium may include, but is not limited to, a magnetic storage component (e.g., a hard disk, a floppy disk, or a magnetic tape), an optical disk (e.g., a compact disc (CD) or a digital versatile disc (DVD)), or a smart card and a flash memory component (e.g., an erasable programmable read-only memory (EPROM), card, stick, or key drive). Furthermore, various storage media described herein may represent one or more devices configured to store information and / or other machine-readable media. The term "machine-readable medium" may include, but is not limited to, wireless channels, as well as various other media capable of storing, containing, and / or retaining instructions and / or data.

[0585] In the embodiment of the present application, it should be understood that the sequence numbers of the above processes do not mean the execution order. The execution order of the processes should be determined based on the functions and internal logic of the processes, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0586] It should be further understood that in the above illustrated embodiments, first and second are merely intended to distinguish different objects and should not constitute any limitation to the present application, e.g., distinguishing between different access network devices and different access and mobility management function network elements.

[0587] It should be further understood that the term "and / or" describes a correspondence relationship for describing related objects and represents that three relationships may exist. For example, A and / or B may represent the following three cases: only A is present, both A and B are present, and only B is present. The character " / " usually indicates an "or" relationship between related objects. The term "at least one" means one or more. The term "at least one of A and B", which is similar to the term "A and / or B", describes a correspondence relationship between related objects and represents that three relationships may exist. For example, at least one of A and B may represent the following three cases: only A is present, both A and B are present, and only B is present.

[0588] In combination with the examples described in the embodiments disclosed herein, those skilled in the art can recognize that the units and algorithm steps can be implemented by electronic hardware or a combination of computer software and electronic hardware. Whether these functions are performed by hardware or software depends on the specific application and the design constraints of the technical solution. Those skilled in the art may use different methods to implement the described functions for each specific application, but such implementation should not be considered as going beyond the scope of this application.

[0589] Those skilled in the art can clearly understand that for the purpose of simple and concise description, the detailed operation processes of the above-mentioned systems, devices and units are referred to the corresponding processes in the above-mentioned method embodiments, and the details will not be described again in this specification.

[0590] In some embodiments provided in the present application, it should be understood that the disclosed system, device, and method can be implemented in other ways. For example, the described device embodiment is merely an example. For example, the division into multiple units is merely a logical division of functions, and other divisions may be possible in actual implementation. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not implemented. In addition, the shown or described mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. Indirect couplings or communication connections between devices or units may be implemented in electronic, mechanical, or other forms.

[0591] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, in other words, located in one location or distributed over multiple network units. Some or all of these units may be selected based on actual requirements to achieve the objectives of the solutions of each embodiment.

[0592] In addition, the functional units in the embodiments of the present application may be integrated into one processing unit, or each of those units may exist physically alone, or two or more units may be integrated into one unit.

[0593] When these functions are implemented in the form of software functional units and sold or used as independent products, these functions may be stored in a computer-readable storage medium. Based on such understanding, the technical solutions of the present application may be essentially implemented in the form of a software product, or the part that contributes to the prior art may be implemented in the form of a software product. The computer software product is stored in a storage medium and includes a plurality of instructions for instructing a computer device (which may be a personal computer, a server, a network device, etc.) to execute all or part of the steps of the method described in the embodiments of the present application. The aforementioned storage medium includes any medium that can store program code, such as a USB flash drive, a removable hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0594] The above description is merely a specific implementation example of the present application, and is not intended to limit the protection scope of the present application. Any variations or replacements that a person skilled in the art can easily think of within the technical scope disclosed in this application shall be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims. [Other possible items] (Item 1) when the first terminal device is in a handover preparation phase in which the first terminal device is handed over from the first access network device to a second access network device by a first access network device, the first terminal device knows that the first terminal device is the last terminal device to receive data of a first multicast service via the first access network device; and transmitting first information by the first access network device, where the first information is used to release a first tunnel, the first tunnel being used to transport the data of the first multicast service between the first access network device and the core network device; A communication method comprising: (Item 2) The step of transmitting first information by the first access network device further comprises: sending, by the first access network device, a handover request to the second access network device, where the handover request requests handing over the first terminal device from the first access network device to the second access network device, and the handover request includes the first information; The method according to item 1, comprising: (Item 3) The step of transmitting first information by the first access network device further comprises: sending, by the first access network device, a handover request to a first access and mobility management function network element, where the handover request includes the first information; The method according to item 1, comprising: (Item 4) the step of transmitting the first information by the first access network device includes transmitting, by the first access network device, a third message to a third access and mobility management function network element, where the third message includes the first information; The method according to item 1, comprising: (Item 5) 5. The method according to any one of claims 1 to 4, further comprising updating, by the first access network device, the number of terminal devices that have subscribed to the first multicast service via the first access network device. (Item 6) the first information includes instructions used to release the first tunnel and information about the first tunnel; the first information includes an indication used to release the first tunnel and an identification of the first multicast service; or 6. The method according to any one of claims 1 to 5, wherein the first information includes an instruction used to release the first tunnel, an identification of the first multicast service, and information about the first tunnel. (Item 7) 7. The method according to any one of claims 1 to 6, wherein the core network device includes a multicast user plane function network element or a user plane function network element. (Item 8) receiving, by a second access network device, a handover request from a first access network device, where the handover request requests a handover of a first terminal device from the first access network device to the second access network device, the handover request including first information, the first information being used to release a first tunnel, the first tunnel being used to transmit data of a first multicast service between the first access network device and a core network device; and sending, by the second access network device, a reroute request to an access and mobility management function network element, where the reroute request includes the first information; A communication method comprising: (Item 9) receiving, by an access and mobility management function network element, a path switching request from a second access network device, where the path switching request includes first information, the first information being used to release a first tunnel, the first tunnel being used to transmit data of a first multicast service between the first access network device and a core network device; and sending, by the access and mobility management function network element, a protocol data unit (PDU) session context update request to a session management function network element, where the PDU session context update request includes the first information; A communication method comprising: (Item 10) receiving, by a session management function network element, a protocol data unit (PDU) session context update request from an access and mobility management function network element, where the PDU session context update request includes first information, and the first information is used to release a first tunnel, the first tunnel being used to transmit data of a first multicast service between a first access network device and a core network device; and sending, by the session management function network element, a first message to a multicast session management function network element, where the first message includes the first information; A communication method comprising: (Item 11) receiving, by a session management function network element, a protocol data unit (PDU) session context update request from an access and mobility management function network element, where the PDU session context update request includes first information, the first information being used to release a first tunnel, the first tunnel being used to transmit data of a first multicast service between a first access network device and a core network device; and sending, by the session management function network element, a session update request to a user plane function network element, where the session update request includes the first information; A communication method comprising: (Item 12) receiving, by a multicast session management function network element, a first message from the session management function network element, where the first message includes first information, the first information is used to release a first tunnel, the first tunnel being used to transmit data of a first multicast service between a first access network device and a core network device; and sending, by the multicast session management function network element, a fifth message to a multicast user plane function network element, where the fifth message includes the first information; A communication method comprising: (Item 13) receiving, by a first access and mobility management function network element, a handover request from a first access network device, where the handover request includes first information, the first information is used to release a first tunnel, the first tunnel being used to transmit data of a first multicast service between the first access network device and a core network device; and sending, by the first access and mobility management function network element, a create user equipment (UE) context request to a second access and mobility management function network element, where the create UE context request includes the first information; A communication method comprising: (Item 14) receiving, by a second access and mobility management function network element, a create user equipment (UE) context request from a first access and mobility management function network element, where the create UE context request includes first information, the first information is used to release a first tunnel, the first tunnel is used to transmit data of a first multicast service between a first access network device and a core network device; and sending, by the second access and mobility management function network element, a protocol data unit (PDU) session context update request to a session management function network element, where the PDU session context update request includes the first information; A communication method comprising: (Item 15) receiving, by a third access and mobility management function network element, a third message from a first access network device, where the third message includes first information, and the first information is used to release a first tunnel, the first tunnel being used to transmit data of a first multicast service between the first access network device and a core network device; and sending, by the third access and mobility management function network element, a fourth message to a multicast session management function network element, where the fourth message includes the first information; A communication method comprising: (Item 16) receiving, by the multicast session management function network element, a fourth message from a third access and mobility management function network element, where the fourth message includes first information, the first information is used to release a first tunnel, the first tunnel being used to transmit data of the first multicast service between the first access network device and the core network device; and sending, by the multicast session management function network element, a fifth message to a multicast user plane function network element, where the fifth message includes the first information; A communication method comprising: (Item 17) receiving, by the multicast user plane function network element, a fifth message from the multicast session management function network element, where the fifth message includes first information, the first information is used to release a first tunnel, the first tunnel being used to transport data of a first multicast service between a first access network device and a core network device; and releasing, by the multicast user plane function network element, the first tunnel based on the first information. A communication method comprising: (Item 18) receiving, by a user plane function network element, a session update request from a session management network element, where the session update request includes first information, the first information being used to release a first tunnel, the first tunnel being used to transport data of a first multicast service between a first access network device and a core network device; and releasing, by the user plane function network element, the first tunnel based on the first information. A communication method comprising: (Item 19) the first information includes instructions used to release the first tunnel and information about the first tunnel; Item 19. The method of item 17 or 18, wherein the step of releasing the first tunnel comprises releasing the first tunnel based on the instruction used to release the first tunnel and the information about the first tunnel. (Item 20) the first information includes an instruction used to release the first tunnel and an identification of the first multicast service; The step of releasing the first tunnel comprises: determining the first multicast service based on the identification information of the first multicast service; determining the first tunnel for transmitting the data of the first multicast service between the first access network device and the core network device; and releasing the first tunnel based on the indication used to release the first tunnel. 19. The method according to item 17 or 18, comprising: (Item 21) the first information includes an instruction used to release the first tunnel, an identification of the first multicast service, and information about the first tunnel; The step of releasing the first tunnel comprises: determining the first multicast service based on the identification information of the first multicast service; determining the first tunnel from tunnels for transporting the data of the first multicast service between the first access network device and the core network device based on the information about the first tunnel; and releasing the first tunnel based on the indication used to release the first tunnel. 19. The method according to item 17 or 18, comprising: (Item 22) 22. A wireless communication device comprising a unit configured to perform the method according to any one of items 1 to 21. (Item 23) A communication device comprising a processor, the processor being configured to call a computer program from a memory, to execute the computer program, and to perform the method according to any one of claims 1 to 21. (Item 24) 24. The communication device of claim 23, further comprising the memory. (Item 25) A communications chip, 22. A communications chip comprising: a processor and a communications interface; the processor is configured to call instructions from the communications interface and execute the instructions; and when the processor executes the instructions, the method of any one of items 1 to 21 is implemented. (Item 26) An apparatus configured to carry out the method according to any one of items 1 to 7, an apparatus configured to carry out the method according to items 8, 9 and 10, and an apparatus configured to carry out the method according to any one of items 17, 19, 20 or 21; An apparatus configured to perform the method according to any one of items 1 to 7, an apparatus configured to perform the method according to items 8, 9, 11 and 12, and an apparatus configured to perform the method according to any one of items 18 to 21; An apparatus configured to carry out the method according to any one of items 1 to 7, an apparatus configured to carry out the method according to items 13, 14 and 10, and an apparatus configured to carry out the method according to any one of items 17, 19, 20 or 21; An apparatus configured to carry out the method according to any one of items 1 to 7, an apparatus configured to carry out the method according to items 13, 14, 11 and 12, and an apparatus configured to carry out the method according to any one of items 18 to 21; or A device configured to carry out the method according to any one of items 1 to 7, a device configured to carry out the method according to items 15 and 16, and a device configured to carry out the method according to any one of items 17, 19, 20 or 21. A communication system comprising:

Claims

1. when the first terminal device is in a handover preparation phase in which the first terminal device is handed over from the first access network device to a second access network device by a first access network device, the first terminal device knows that the first terminal device is the last terminal device to receive data of a first multicast service via the first access network device; and transmitting first information by the first access network device when the first access network device knows that the first terminal device is the last terminal device to receive data of the first multicast service via the first access network device, wherein the first information is used to release a first tunnel, the first tunnel being used to transport the data of the first multicast service between the first access network device and a multicast user plane function network element. A communication method comprising:

2. the step of transmitting the first information by the first access network device includes the step of transmitting a third message by the first access network device to a third access and mobility management function network element, where the third message includes the first information; The communication method of claim 1 , comprising:

3. The communication method according to claim 1 or 2, further comprising a step of updating, by the first access network device, a number of terminal devices which have subscribed to the first multicast service via the first access network device.

4. knowing that the first terminal device is the last terminal device to receive data of a first multicast service via the first access network device when the first terminal device is in a handover preparation phase in which the first terminal device is handed over from the first access network device to a second access network device by the first access network device; sending a third message by the first access network device when the first access network device learns that the first terminal device is the last terminal device to receive data of the first multicast service via the first access network device, where the third message includes first information used to release a first tunnel, the first tunnel being used to transport the data of the first multicast service between the first access network device and a multicast user plane function network element; receiving, by a third access and mobility management function network element, the third message from the first access network device; and sending, by the third access and mobility management function network element, a fourth message to a multicast session management function network element, where the fourth message includes the first information; receiving, by the multicast session management function network element, the fourth message; sending, by the multicast session management function network element, a fifth message to the multicast user plane function network element, where the fifth message includes the first information; receiving, by the multicast user plane function network element, the fifth message; and releasing, by the multicast user plane function network element, the first tunnel based on the first information. A communication method comprising:

5. The method of claim 4, further comprising updating, by the first access network device, a number of terminal devices that have subscribed to the first multicast service via the first access network device.

6. The communication method according to claim 1 , wherein the first tunnel is a multicast session tunnel shared by terminal devices.

7. The method of claim 1 , wherein the first information comprises a request used to release the first tunnel and an identification of the first multicast service.

8. 8. The method according to claim 1, wherein the number of terminal devices subscribed to the first multicast service via the first access network device is included in a multicast context, a multicast session context, a multicast group context, or a multicast service context corresponding to the first multicast service associated with a PDU session of the first terminal device.

9. A wireless communication device comprising a unit adapted to carry out the communication method according to any one of claims 1 to 3.

10. A communication device comprising at least one processor, the at least one processor being configured to retrieve a computer program from a memory, to execute the computer program, and to perform the communication method according to any one of claims 1 to 3.

11. The communication device of claim 10 , further comprising the memory.

12. A program for causing an apparatus to execute the communication method according to any one of claims 1 to 3.

13. A communication system adapted to carry out the communication method according to claim 4 or 5.

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