A communication method, apparatus, and device

Abstract

The application discloses a communication method, device and equipment for ensuring the continuity of service transmission. The method comprises the following steps: an AS sends a service data packet of a first service to a terminal device through a multicast session; when a condition for cross-communication system switching of the terminal device is met or the terminal device performs cross-communication system switching, the terminal device can trigger the AS to send the service data packet of the first service to the terminal device through a unicast transmission mode by sending first information. In this way, the cross-communication system switching process of the terminal device does not affect the transmission of the first service of the terminal device, so that the continuity of service transmission can be ensured.

Description

Technical Field

[0001] This application relates to the field of communication technology, and in particular to a communication method, apparatus and device. Background Technology

[0002] In mobile communication systems, various service transmission methods exist. These methods can include multicast, unicast, and broadcast transmission. Multicast transmission involves one sender transmitting service data packets, which are then received by multiple receivers joining the multicast session; for example, a network device sends service data packets, and multiple terminal devices joining the multicast session receive them. Unicast transmission involves one sender transmitting service data packets, which are then received by one receiver; for example, a network device sends service data packets, and a terminal device receives them. Broadcast transmission involves one sender transmitting service data packets, which are then received by multiple receivers within the sender's coverage area; for example, a network device sends service data packets, and multiple terminal devices within the network device's coverage area receive them.

[0003] Different radio access technologies (RATs) may support different transmission methods. When a terminal device switches between two mobile communication systems using different RATs (e.g., from 5G...),... th The mobile communication system has switched from the fourth generation (4G) to 5G. th In a 4G mobile communication system, if the mobile communication system before the handover uses multicast transmission to send service data packets to the terminal device, and the mobile communication system after the handover does not support multicast transmission, the service data packets received by the terminal device may be interrupted, thereby affecting the continuity of the terminal device's service transmission. Summary of the Invention

[0004] This application provides a communication method, apparatus, and device to ensure the continuity of service transmission.

[0005] Firstly, embodiments of this application provide a communication method. This method can be applied to the following... Figure 1 and Figure 2 In the communication system shown, the method includes:

[0006] The terminal device can receive service data packets of the first service from the AS through a multicast session of the first mobile communication system; when the handover conditions for the terminal device to switch from the first mobile communication system to the second mobile communication system are met, or when the terminal device switches from the first mobile communication system to the second mobile communication system, the terminal device can send first information to the AS to trigger the AS to send the service data packets of the first service to the terminal device through unicast transmission.

[0007] Using this method, the AS sends service data packets of the first service to the terminal device through a multicast session in the first mobile communication system. When the conditions for the terminal device to perform a cross-communication system handover are met, or when the terminal device performs a cross-communication system handover, the terminal device can trigger the AS to send the service data packets of the first service to the terminal device via unicast transmission by sending the first information. Thus, the transmission of the first service of the terminal device will not be affected during the cross-communication system handover process. That is, when the conditions for the cross-communication system handover are met or during the cross-communication system handover process, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding discontinuous service transmission due to limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0008] In one possible design, after sending the first information to the AS, the terminal device can receive the service data packet of the first service from the AS via the unicast transmission method.

[0009] Optionally, the first mobile communication system is a mobile communication system using a first RAT, and the second mobile communication system is a mobile communication system using a second RAT.

[0010] Optionally, the first RAT is a 5G wireless access technology, and the second RAT is a 4G wireless access technology.

[0011] In one possible design, the terminal device may, but is not limited to, receive service data packets from the AS for the first service in the following manner:

[0012] Method 1: The terminal device can receive service data packets of the first service from the AS through the unicast transmission channel of the first mobile communication system; and / or,

[0013] Method 2: The terminal device can receive the service data packets of the first service from the AS through the unicast transmission channel of the second mobile communication system.

[0014] With this design, the terminal device can receive service data packets of the first service from the AS through the unicast transmission channel of the first mobile communication system and / or the second mobile communication system. In this way, the terminal device can flexibly receive service data packets of the first service.

[0015] In one possible design, the switching conditions may include, but are not limited to, at least one or a combination of the following:

[0016] The signal quality of the first mobile communication system is less than a first threshold.

[0017] The signal quality of the second mobile communication system is greater than the second threshold;

[0018] The signal quality of the second mobile communication system is greater than that of the first mobile communication system;

[0019] The terminal device is located within the coverage area of ​​the second mobile communication system; or,

[0020] The terminal device moves from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system.

[0021] With this design, when the terminal device determines that the conditions for cross-communication system handover are met, the terminal device can trigger the AS to send the service data packet of the first service to the terminal device via unicast transmission by sending the first information. In this way, the cross-communication system handover process of the terminal device will not affect the transmission of the first service of the terminal device. That is, when the terminal device meets the conditions for cross-communication system handover, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding the discontinuity of service transmission caused by limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0022] In one possible design, the first information may include, but is not limited to, at least one of the following:

[0023] Information used to instruct the terminal device to prepare for a handover from the first mobile communication system to the second mobile communication system;

[0024] Information used to instruct the terminal device to prepare for switching to the second mobile communication system;

[0025] Information used to instruct the terminal device to switch from the first mobile communication system to the second mobile communication system;

[0026] Information used to instruct the terminal device to switch to the second mobile communication system;

[0027] Information used to indicate that the terminal device is within the coverage area of ​​the second mobile communication system;

[0028] Information used to indicate that the terminal device moves from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system;

[0029] Information used to indicate that the signal quality of the first mobile communication system is less than a first threshold;

[0030] Information used to indicate that the signal quality of the second mobile communication system is greater than a second threshold;

[0031] Information used to indicate that the signal quality of the second mobile communication system is greater than that of the first mobile communication system;

[0032] Information used to indicate that the terminal device is about to leave the multicast session;

[0033] Information used to indicate that the terminal device will attach to or has already attached to the second mobile communication system; or,

[0034] Information used to request the AS to send the service data packet of the first service to the terminal device via unicast transmission.

[0035] In this design, the first information can have multiple forms of representation; thus, the terminal device can flexibly trigger the AS to send the service data packet of the first service to the terminal device through unicast transmission according to the multiple forms of representation of the first information.

[0036] In one possible design, after receiving a first instruction from the session management network element of the first mobile communication system, the terminal device may send first information to the AS according to the first instruction. The first instruction may indicate that the multicast session has been released; the first information may include, but is not limited to, at least one of the following: information indicating that the terminal device has left the multicast session, information indicating that the terminal device has been removed from the multicast session, information indicating that the multicast session has been released, or information indicating that the terminal device cannot receive service data packets of the first service through the multicast session.

[0037] Optionally, when the terminal device switches from the first mobile communication system to the second mobile communication system, the session management network element sends the first instruction to the terminal device.

[0038] With this design, when the terminal device switches from the first mobile communication system to the second mobile communication system, after receiving the first indication indicating that the multicast session has been released, the terminal device can trigger the AS to send the service data packet of the first service to the terminal device via unicast transmission by sending the first information. In this way, the cross-communication system handover process of the terminal device will not affect the transmission of the first service. That is, during the cross-communication system handover process of the terminal device, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding service transmission discontinuity caused by limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0039] In one possible design, the terminal device may send the first information to the AS according to the first instruction when at least one of the following conditions is met: the multicast session is not a local multicast session; or, the multicast session is a local multicast session and the terminal device is located within the service area of ​​the local multicast session.

[0040] When the above conditions are met, if the terminal device is removed from the multicast session, the terminal device still needs to acquire application layer services. When the above conditions are not met, if the terminal device is removed from the multicast session, the terminal device may not acquire application layer services. Through this design, the terminal device will only send the first information when the above conditions are met, triggering the AS to send the application layer services to the terminal device via unicast transmission; when the above conditions are not met, the terminal device does not need to send the first information, thereby saving the resources required to send the first information.

[0041] In one possible design, after receiving a handover command from the first mobile communication system, the terminal device can determine whether the multicast session has been rejected by the second mobile communication system based on the handover command. When the multicast session is rejected by the second mobile communication system, the terminal device can send the first information to the AS. The handover command is used to instruct the terminal device to switch to the second mobile communication system.

[0042] With this design, when the terminal device switches from the first mobile communication system to the second mobile communication system, if the terminal device determines that the multicast session is rejected by the second mobile communication system according to the switching command, the terminal device can trigger the AS to send the service data packet of the first service to the terminal device via unicast transmission by sending the first information. In this way, the cross-communication system handover process of the terminal device will not affect the transmission of the first service. That is, during the cross-communication system handover process of the terminal device, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding service transmission discontinuity caused by limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0043] In one possible design, the first information may include, but is not limited to, at least one of the following:

[0044] Information used to instruct the terminal device to switch from the first mobile communication system to the second mobile communication system;

[0045] Information used to instruct the terminal device to switch to the second mobile communication system;

[0046] Information used to indicate that the terminal device has switched from the first mobile communication system to the second mobile communication system;

[0047] Information used to indicate that the terminal device has switched to the second mobile communication system;

[0048] Information used to indicate that the terminal device has been attached to the second mobile communication system;

[0049] Information used to indicate that the terminal device is within the coverage area of ​​the second mobile communication system;

[0050] Information used to indicate that the terminal device moves from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system;

[0051] Information used to indicate that the terminal device has left the multicast session;

[0052] Information used to indicate that the terminal device has been removed from the multicast session;

[0053] Information used to indicate that the multicast session has been released; or,

[0054] Information used to indicate that the terminal device cannot receive service data packets of the first service through the multicast session.

[0055] In this design, the first information can have multiple forms of representation; thus, the terminal device can flexibly trigger the AS to send the service data packet of the first service to the terminal device via unicast according to the multiple forms of representation of the first information.

[0056] In one possible design, the terminal device can receive configuration information from the AS; wherein the configuration information can instruct the terminal device to send the first information to the AS when the handover conditions are met, or when the terminal device switches from the first mobile communication system to the second mobile communication system.

[0057] With this design, the terminal device sends the first information to the AS only after receiving the configuration information, thereby saving resources for sending the first information and avoiding resource waste.

[0058] Secondly, embodiments of this application provide a communication method. This method can be applied to the following... Figure 1 and Figure 2 In the communication system shown, the method includes:

[0059] An AS can send a service data packet of a first service to a terminal device through a multicast session of a first mobile communication system; after receiving first information from the terminal device, the AS can send the service data packet of the first service to the terminal device through unicast transmission according to the first information; wherein, the first information can trigger the AS to send the service data packet of the first service to the terminal device through unicast transmission.

[0060] Specifically, when the switching conditions for the terminal device to switch from the first mobile communication system to the second mobile communication system are met, or when the terminal device switches from the first mobile communication system to the second mobile communication system, the AS can receive the first information from the terminal device.

[0061] Using this method, the AS sends service data packets of the first service to the terminal device through a multicast session in the first mobile communication system. When the conditions for the terminal device to perform a cross-communication system handover are met, or when the terminal device performs a cross-communication system handover, the terminal device can trigger the AS to send the service data packets of the first service to the terminal device via unicast transmission by sending first information. Thus, the transmission of the first service of the terminal device will not be affected during the cross-communication system handover process. That is, when the conditions for the cross-communication system handover are met or during the cross-communication system handover process, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding discontinuous service transmission due to limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0062] In one possible design, the first information may include, but is not limited to, at least one of the following:

[0063] Information used to instruct the terminal device to prepare for a handover from the first mobile communication system to the second mobile communication system;

[0064] Information used to instruct the terminal device to prepare for handover to the second mobile communication system;

[0065] Information used to instruct the terminal device to switch from the first mobile communication system to the second mobile communication system;

[0066] Information used to instruct the terminal device to switch to the second mobile communication system;

[0067] Information used to indicate that the terminal device has switched from the first mobile communication system to the second mobile communication system;

[0068] Information used to indicate that the terminal device has switched to the second mobile communication system;

[0069] Information used to indicate that the terminal device is within the coverage area of ​​the second mobile communication system;

[0070] Information used to indicate that the terminal device moves from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system;

[0071] Information used to indicate that the signal quality of the first mobile communication system is less than a first threshold;

[0072] Information used to indicate that the signal quality of the second mobile communication system is greater than a second threshold;

[0073] Information used to indicate that the signal quality of the second mobile communication system is greater than that of the first mobile communication system;

[0074] Information used to indicate that the terminal device is about to leave the multicast session;

[0075] Information used to indicate that the terminal device has left the multicast session;

[0076] Information used to indicate that the terminal device has been removed from the multicast session;

[0077] Information used to indicate that the terminal device will attach to or has already attached to the second mobile communication system;

[0078] Information used to indicate that the terminal device cannot receive service data packets of the first service through a multicast session; or...

[0079] Information used to request the AS to send the service data packet of the first service to the terminal device via unicast transmission.

[0080] In this design, the first information can have multiple forms of representation; thus, the AS can flexibly determine whether it is necessary to send the service data packet of the first service to the terminal device according to the unicast transmission method.

[0081] In one possible design, the AS may, but is not limited to, send the service data packet of the first service to the terminal device in the following manner:

[0082] Method 1: Send the service data packet of the first service to the terminal device through the unicast transmission channel of the first mobile communication system; and / or,

[0083] Method 2: Send the service data packet of the first service to the terminal device through the unicast transmission channel of the second mobile communication system.

[0084] With this design, the AS can send the service data packets of the first service to the terminal device through the unicast transmission channel of the first mobile communication system and / or the second mobile communication system. This allows the AS to flexibly send the service data packets of the first service.

[0085] In one possible design, the first mobile communication system may be a mobile communication system using a first RAT, and the second mobile communication system may be a mobile communication system using a second RAT.

[0086] Optionally, the first RAT is a 5G wireless access technology, and the second RAT is a 4G wireless access technology.

[0087] In one possible design, after receiving the first information, the AS can send the service data packet of the first service to the terminal device via the unicast transmission method when at least one of the following conditions is met:

[0088] Mobile communication systems using the second RAT do not support broadcast transmission.

[0089] The terminal device is not within the broadcast area of ​​the mobile communication system using the second RAT corresponding to the first service;

[0090] The terminal device does not support broadcasting the second RAT; or,

[0091] The multicast session does not support handover from a mobile communication system using the first RAT to a mobile communication system using the second RAT.

[0092] When the above conditions are met, the terminal device cannot receive the service data packets of the first service through multicast or broadcast transmission of the second mobile communication system. Through this design, when the above conditions are met, the AS can promptly send the service data packets of the first service to the terminal device through unicast transmission. Thus, when the terminal device switches to the second mobile communication system, the terminal device can receive the service data packets of the first service through unicast transmission; the cross-communication system handover process of the terminal device will not affect the transmission of the first service. That is, when the terminal device meets the conditions for cross-communication system handover or is in the cross-communication system handover process, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding service transmission discontinuity caused by limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0093] In one possible design, when a first preset condition is met, the AS can send configuration information to the terminal device; wherein the configuration information is used to trigger the terminal device to send the first information, and the first preset condition includes at least one of the following:

[0094] The first service allows transmission via a mobile communication system using the first RAT and a mobile communication system using the second RAT;

[0095] The service area of ​​the first service overlaps with the coverage area of ​​the mobile communication system using the first RAT, and the service area of ​​the first service overlaps with the coverage area of ​​the mobile communication system using the second RAT; or

[0096] The terminal device supports having a first capability and a second capability, wherein the first capability includes the ability to receive service data packets through a multicast session of the mobile communication system using the first RAT, and the second capability includes at least one of the following: the ability to receive service data packets through a unicast transmission channel of the mobile communication system using the second RAT, and the ability to receive service data packets through a broadcast transmission channel of the mobile communication system using the second RAT.

[0097] With this design, the AS sets configuration information for the terminal device when the first preset condition is met. The terminal device sends the first information to the AS only after receiving the configuration information, thereby saving resources for sending the first information and avoiding resource waste.

[0098] Thirdly, embodiments of this application provide a communication method. This method can be applied to the following... Figure 1 and Figure 2 In the communication system shown, the method includes:

[0099] After receiving a second instruction from the mobility management network element in the first mobile communication system, the session management network element can remove the terminal device from the multicast session according to the second instruction; wherein, the second instruction can indicate that the multicast session of the terminal device is rejected by the second mobile communication system when the terminal device switches from the first mobile communication system to the second mobile communication system.

[0100] With this design, when the terminal device switches from the first mobile communication system to the second mobile communication system, if the multicast session of the terminal device is rejected by the second mobile communication system, the session management network element of the first mobile communication system can remove the terminal device from the multicast session. This avoids unnecessary occupation of multicast session resources by the terminal device, thereby preventing resource waste.

[0101] In one possible design, the session management network element can send a first instruction to the terminal device; wherein the first instruction can indicate that the multicast session is released.

[0102] Through this design, the session management network element can instruct the terminal device to release the multicast session. After receiving the instruction indicating the release of the multicast session, the terminal device can trigger the AS to send the service data packet of the first service to the terminal device via unicast transmission by sending the first information. In this way, the cross-communication system handover process of the terminal device will not affect the transmission of the first service. That is, during the cross-communication system handover process of the terminal device, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding the discontinuity of service transmission caused by the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0103] Optionally, the first mobile communication system may be a mobile communication system using a first RAT, and the second mobile communication system may be a mobile communication system using a second RAT.

[0104] Optionally, the first RAT is a 5G wireless access technology, and the second RAT is a 4G wireless access technology.

[0105] In one possible design, the second indication may include: information indicating that the multicast session is rejected by the second mobile communication system, or information indicating that the Quality of Service (QoS) stream of the multicast session is rejected by the second mobile communication system.

[0106] In this design, the second indication can have multiple forms; thus, the session management network element can flexibly determine whether the multicast session of the terminal device is rejected by the second mobile communication system based on the multiple forms of the second indication.

[0107] Fourthly, embodiments of this application provide a communication device including a unit for performing the steps in any of the above aspects.

[0108] Fifthly, embodiments of this application provide a communication device including at least one processing element and at least one storage element, wherein the at least one storage element is used to store programs and data, and the at least one processing element is used to read and execute the programs and data stored in the storage element, so that the methods provided in any of the above aspects of this application are implemented.

[0109] In a sixth aspect, embodiments of this application provide a communication system, including: a first AN device for performing the method provided in the first aspect, an AMF for performing the method provided in the second aspect, and a terminal device for performing the method provided in the third aspect.

[0110] In a seventh aspect, embodiments of this application also provide a computer program that, when run on a computer, causes the computer to perform the methods provided in any of the above aspects.

[0111] Eighthly, embodiments of this application also provide a computer-readable storage medium storing a computer program that, when executed by a computer, causes the computer to perform the method provided in any of the above aspects.

[0112] Ninthly, embodiments of this application also provide a chip for reading a computer program stored in a memory and executing the method provided in any of the above aspects.

[0113] In a tenth aspect, embodiments of this application also provide a chip system including a processor for supporting a computer device in implementing the methods provided in any of the foregoing aspects. In one possible design, the chip system further includes a memory for storing programs and data necessary for the computer device. The chip system may be composed of chips or may include chips and other discrete devices.

[0114] The technical effects that can be achieved by any of the fourth to tenth aspects mentioned above can be described with reference to the technical effects that can be achieved by any possible design in any of the first to third aspects mentioned above. Where there is overlap, no further discussion will be given. Attached Figure Description

[0115] Figure 1 This is an architecture diagram of a communication system;

[0116] Figure 2 This is an architecture diagram of another communication system;

[0117] Figure 3 A flowchart illustrating a communication method provided in an embodiment of this application;

[0118] Figure 4 A flowchart illustrating another communication method provided in an embodiment of this application;

[0119] Figure 5 A flowchart illustrating yet another communication method provided in an embodiment of this application;

[0120] Figure 6 A flowchart illustrating another communication method provided in an embodiment of this application;

[0121] Figure 7 A structural diagram of a communication device provided in an embodiment of this application;

[0122] Figure 8 This is a structural diagram of a communication device provided in an embodiment of this application. Detailed Implementation

[0123] This application provides a communication method, apparatus, and device to ensure the continuity of service transmission. The method, apparatus, and device are based on the same technical concept. Since the principles for solving the problem are similar, the implementations of the apparatus, device, and method can be mutually referenced, and repeated details will not be elaborated further.

[0124] The solution provided in this application embodiment allows the application server (AS) to send service data packets of a first service to the terminal device via a multicast session in the first mobile communication system. When the conditions for the terminal device to perform a cross-communication system handover are met, or when the terminal device performs a cross-communication system handover, the terminal device can trigger the AS to send the service data packets of the first service to the terminal device via unicast transmission by sending first information. Thus, the transmission of the first service of the terminal device is not affected during the cross-communication system handover process. That is, when the terminal device meets the conditions for cross-communication system handover or performs a cross-communication system handover process, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding discontinuous service transmission due to limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0125] The following explanations of some terms used in the embodiments of this application are provided to facilitate understanding by those skilled in the art.

[0126] 1) Terminal equipment is a device that provides voice and / or data connectivity to users. Terminal equipment can also be called user equipment (UE), mobile station (MS), mobile terminal (MT), etc.

[0127] For example, terminal devices can be handheld devices, in-vehicle devices, etc., with wireless connectivity. Currently, some examples of terminal devices include: mobile phones, tablets, laptops, PDAs, mobile internet devices (MIDs), wearable devices, virtual reality (VR) devices, augmented reality (AR) devices, wireless terminals in industrial control, wireless terminals in self-driving cars, wireless terminals in remote medical surgery, wireless terminals in smart grids, wireless terminals in transportation safety, wireless terminals in smart cities, wireless terminals in smart homes, and wireless terminals in the Internet of Things (IoT).

[0128] 2) Access network (AN) equipment is the device in a mobile communication system that connects terminal devices to the wireless network. As a node in the radio access network, the AN device can also be called a base station, radio access network (RAN) node (or device), access point (AP), or network device.

[0129] Currently, some examples of AN devices include: generation Node B (gNB), transmission reception point (TRP), evolved Node B (eNB), radio network controller (RNC), Node B (NB), base station controller (BSC), base transceiver station (BTS), home base station (e.g., home-evolved Node B, or home Node B, HNB), base band unit (BBU), wireless fidelity (WiFi) access point, or world interoperability for microwave access (WiMAX) base station, etc.

[0130] In another network architecture, the AN device may include centralized unit (CU) nodes and distributed unit (DU) nodes. This architecture separates the protocol layers of the AN device, with some protocol layer functions centrally controlled by the CU, and the remaining part or all of the protocol layer functions distributed in the DU, which are centrally controlled by the CU.

[0131] 3) Core network (CN) equipment refers to network elements included in the CN portion of a mobile communication system. CN equipment enables terminal devices to access different data networks and performs services such as billing, mobility management, session management, and user plane forwarding. In different mobile communication systems, the names of CN equipment with the same functions may differ. However, this application does not limit the specific name of the CN equipment having each function.

[0132] For example, in a 4G mobile communication system (i.e., Long Term Evolution, LTE), the network element responsible for access control, security control, and signaling coordination is the Mobile Management Entity (MME); the network element that serves as the local mobile management anchor point is the Serving Gateway (S-GW); the network element that serves as the anchor point for handover to external data networks and is responsible for Internet Protocol (IP) address allocation is the Packet Data Network (PDN) Gateway (P-GW); the network element that stores user-related data and subscription data is the Home Subscriber Server (HSS); and the network element responsible for policy and charging functions is called the Policy and Charging Rule Function (PCRF) network element.

[0133] For example, in a 5G mobile communication system, based on specific logical functions, the core network can be divided into the control plane (CP) and the user plane (UP). The network elements responsible for control plane functions within the core network (CN) can be collectively referred to as control plane network elements, while those responsible for user plane functions can be collectively referred to as user plane network elements. Specifically, in the user plane, the network elements that serve as interfaces to the data network and are responsible for user plane data forwarding are called user plane function (UPF) network elements. In the control plane, network elements responsible for access control and mobility management functions can be called access and mobility management function (AMF) network elements; network elements responsible for session management and execution of control policies are called session management function (SMF) network elements; network elements responsible for managing subscription data and user access authorization are called unified data management (UDM) network elements; network elements responsible for billing and policy control functions are called policy and charging function (PCF) network elements; and application function (AF) network elements are responsible for the transmission application side's requirements on the network side.

[0134] 4) A data network (DN) is a network located outside the mobile communication system that can provide services to users. For example, the DN can be a packet data network (PDN), such as the Internet, IP Multimedia Service (IMS) networks, dedicated data networks for certain applications, Ethernet, IP local area networks, etc., and this application does not limit this. Multiple services can be deployed on the DN, providing data and / or voice services to terminal devices. A DN can contain multiple application systems (ASs), each of which can provide at least one service.

[0135] 5) Session: In a mobile communication system, a session management network element establishes a connection between a terminal device, access network equipment, user plane network element, and DN for the terminal device. This connection is used to transmit user plane data between the terminal device and the DN, such as a protocol data unit (PDU) session.

[0136] Terminal devices can establish one or more PDU sessions with mobile communication systems (e.g., 5G communication systems), and each PDU session can establish one or more quality of service (QoS) flows.

[0137] Each QoS flow is used to transmit data for the same QoS requirement (reliability or latency) within a service. QoS flows can be identified by a QoS flow identifier (QFI).

[0138] Sessions can include multicast sessions and unicast sessions. When a mobile communication system session is a multicast session (e.g., a 5G multicast session), the service transmission method is multicast transmission; when a mobile communication system session is a unicast session (e.g., a 5G unicast session), the service transmission method is unicast transmission.

[0139] In this application, a multicast session can be a multicast and broadcast service (MBS) session. A unicast session can be a PDU session.

[0140] 6) Local multicast session: A multicast session implemented within a limited area. The limited area can be a geographical region, the coverage area of ​​at least one cell, or the coverage area of ​​at least one base station. When a terminal device that has joined the local multicast session moves out of the limited area, the terminal device cannot receive service data packets through the local multicast session.

[0141] 7) Bearer: A logical path in a mobile communication system, used to transmit signaling and / or data between communication devices in a mobile communication system.

[0142] In a 4G mobile communication system, the bearer between the CN device and the terminal device can be an EPS bearer. For example, a 4G unicast bearer can be an EPS unicast bearer, used to transmit service data packets between the CN device and the terminal device in a 4G mobile communication system via unicast transmission.

[0143] 8) RAT (Range Technology) refers to the communication technology used in mobile communication systems. For example, RAT can include, but is not limited to, 4G, 5G, WiMAX, and future communication technologies, such as sixth-generation (6G) technology. th 5G (Generatoin, 6G) mobile communication systems. Systems using 5G wireless access technology can be called 5G mobile communication systems, while systems using 4G wireless access technology can be called 4G mobile communication systems.

[0144] The handover of terminal devices between systems using different RATs can be called cross-communication system handover.

[0145] In this application, the 4G mobile communication system can be an evolved packet system (EPS).

[0146] In this application embodiment, the number of nouns, unless otherwise specified, refers to "singular nouns or plural nouns," that is, "one or more." "At least one" means one or more, and "more than one" means two or more. "And / or" describes the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. For example, A / B means: A or B. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items.

[0147] In addition, it should be understood that in the description of this application, the words "first" and "second" are used only for the purpose of distinguishing descriptions and should not be construed as indicating or implying relative importance, nor should they be construed as indicating or implying order.

[0148] In addition, in the embodiments of this application, "greater than" and "greater than or equal to" can be interchanged, and "less than or equal to" and "less than" can be interchanged.

[0149] In this embodiment, the coverage area of ​​the mobile communication system can be referred to as the coverage area of ​​the AN device of the mobile communication system. The signal quality of the mobile communication system can be referred to as the signal quality of the AN device of the mobile communication system. Handover to the mobile communication system can also be referred to as: handover to the AN device of the mobile communication system or handover to the cell of the mobile communication system. Handover from a first mobile communication system to a second mobile communication system can also be referred to as: handover from the AN device of the first mobile communication system to the AN device of the second mobile communication system, or handover from the cell of the first mobile communication system to the cell of the second mobile communication system. Access to the mobile communication system can also be referred to as: accessing the cell of the mobile communication system or accessing the AN device of the mobile communication system.

[0150] The communication system used in the embodiments of this application will now be described with reference to the accompanying drawings.

[0151] Figure 1 This illustration shows the architecture of a possible communication system to which the communication method provided in the embodiments of this application is applicable. For example... Figure 1As shown, the communication system comprises three parts: a terminal device (using a UE as an example in the figure), a mobile communication system, and a DN. The mobile communication system provides access and connection services to the terminal device.

[0152] A terminal device is an entity on the user side capable of receiving and transmitting wireless signals and can access the DN through a mobile communication system. For example, a terminal device can access the DN through a session between the terminal device, AN device, user plane network element, and the DN. Optionally, the terminal device can act as a relay device for a data collector or other terminal devices, enabling these devices to conduct service communication with the DN through the mobile communication system.

[0153] A mobile communication system can access at least one DN, and the same DN can also be accessed by at least one mobile communication system. The mobile communication system may include two parts: AN and CN.

[0154] Network devices deployed in the AN are called AN devices, which are specifically responsible for functions such as wireless access, air interface-side wireless resource management, quality of service (QoS) management, data compression and encryption, and user plane data forwarding.

[0155] Network elements deployed in a CN (Network Array) can be collectively referred to as CN equipment. The following section uses the CN in a 5G mobile communication system as an example to introduce the functions of the main network elements in the CN. As described above, the network elements in the CN of a 5G mobile communication system can be divided into two categories: control plane network elements and user plane network elements.

[0156] User plane network elements include user plane functions (UPFs), which are mainly responsible for service data packet forwarding, QoS control, and billing information statistics.

[0157] Control plane network elements are mainly responsible for service process interaction, issuing data packet forwarding policies to the user plane, and QoS control policies. Control plane network elements mainly include: AMF, SMF, PCF, AF, UDM, and Unified Data Repository (UDR) (not shown in the figure).

[0158] Among them, AMF is mainly responsible for the access management and mobility management of terminal devices. For example, it is responsible for the status maintenance of terminal devices, the reachability management of terminal devices, the location update of terminal devices, the network registration of terminal devices, the handover of terminal devices, and the forwarding of non-access-stratum (NAS) messages of mobility management (MM).

[0159] SMF is primarily responsible for session management of terminal devices, such as managing the establishment, modification, and release of PDU sessions, assigning Internet Protocol (IP) addresses to terminal devices, selecting UPFs that provide service packet forwarding functions, and maintaining PDU session contexts.

[0160] The PCF is primarily responsible for policy control, such as generating and / or managing user, session, and QoS stream processing policies, and sending policies to the AMF and SMF.

[0161] AF is primarily responsible for providing various business services and interacting with PCF for policy control, etc.

[0162] UDM is primarily responsible for storing user data (e.g., storing subscription information, authentication / authorization information) and managing user subscription contexts.

[0163] UDR is primarily responsible for storing business parameters.

[0164] Optionally, AS implements the function of AF.

[0165] When implementing multicast and / or broadcast services (e.g., MBS), in Figure 1 Based on the architecture shown, the communication system can also include communication equipment for multicast and / or broadcast services. The following uses MBS as an example, combined with... Figure 2 The document provides a detailed description of the communication equipment involved in multicast and / or broadcast services.

[0166] The communication system may also include: multicast broadcast SMF (MB-SMF) and multicast broadcast UPF (MB-UPF).

[0167] Optionally, the communication system further includes at least one of the following: a multicast and broadcast service function (MBSF) or a multicast and broadcast service transport function (MBSTF).

[0168] MB-SMF is an entity that supports broadcast features and can also perform functions similar to SMF. MB-SMF is primarily responsible for: managing MBS sessions (e.g., controlling the QoS of MBS sessions and configuring MB-UPF); interacting with AN devices to control the transmission of broadcast streams (e.g., interacting with AN devices to interact with broadcast session-specific functions); interacting with AN devices to control the transmission of multicast streams (e.g., interacting with AN devices to interact with multicast session-specific functions); and interacting with SMF to associate multicast sessions with unicast sessions (e.g., PDU sessions).

[0169] MB-UPF is the data plane gateway for 5G multicast and / or broadcast services. Its main responsibilities include: interacting with MB-SMF to obtain data forwarding rules; transmitting service data packets to AN devices through shared delivery mode; and transmitting service data packets to UPF through individual delivery mode.

[0170] The MBSF is primarily responsible for: implementing service layer functions; interacting with the 4G mobile communication system to provide Multimedia Broadcast / Multicast Service (MBMS); interacting with the AF and / or MB-SMF to support multicast session operations, determining transmission parameters and multicast session types; selecting the MB-SMF; controlling the MBSTF; and determining the sender's IP multicast address, etc.

[0171] MBSTF is primarily responsible for: serving as the anchor point for MBS data; serving as the source for IP multicast; supporting common transmission functions such as frames, multistreams, and forward error correction (FEC); and sending objects or object flows for input files via multicast or broadcast.

[0172] in addition, Figure 1 Some of the communication devices in the architecture shown can also perform functions for multicast and / or broadcast services. This will be explained in detail below.

[0173] The PCF is an optional network element used for multicast and / or broadcast services. For example, when using policy charging control (PCC), the PCF can be used to implement multicast and / or broadcast services. The PCF is mainly responsible for: QoS processing of MBS sessions; providing policy information to the MB-SMF; and obtaining QoS information through interaction with the UDR.

[0174] The SMF is primarily responsible for: discovering the MB-SMF; authenticating UE Join MBS sessions; managing the context of MBS sessions through interaction with the MB-SMF; and establishing multicast transmission channels through interaction with the RAN.

[0175] The UPF is primarily responsible for: receiving service data packets of MBS sessions transmitted in independent transmission mode by interacting with the MB-UPF; and transmitting service data packets of MBS sessions transmitted in independent transmission mode to terminal devices through the PDU session.

[0176] The AMF is primarily responsible for: signaling routing (e.g., signaling routing from AN devices to MB-SMF); and selecting AN devices for broadcast service packets.

[0177] The AF / AS is primarily responsible for: providing service information to CN equipment (e.g., 5G CN equipment) and requesting multicast and / or broadcast services; instructing MBS session operations with CN equipment, etc.

[0178] The AN device is primarily responsible for: processing QoS flows for multicast sessions; sending data to terminal devices via point-to-multipoint (PTM) and / or point-to-point (PTP); configuring the access stratum to receive broadcast streams; switching between PTM and PTP; supporting interface switching for multicast sessions, such as supporting Xn and N2 switching of multicast sessions; processing session signaling; and establishing air interface broadcast and / or multicast resources, etc.

[0179] UDM is primarily responsible for: subscription / contract management of multicast sessions, etc.

[0180] The UDR is primarily responsible for: managing service parameters, which may include: QoS requirements and information on serving MB-SMF; and managing terminal device authorization for multicast sessions, etc.

[0181] The terminal equipment is mainly responsible for: receiving service data packets of MBS sessions via PTM and / or PTP; receiving broadcast service data packets via PTM; processing QoS; initiating session join and / or session leave for the MBS session; and managing resources on the terminal equipment side of the multicast session.

[0182] Figure 1 and Figure 2The document also demonstrates the interfaces between multiple communication devices in the communication system. N1 is the interface between the UE and the core network control plane; the UE and AMF can interact through the N1 interface. N2 is the interface between the access network equipment and the core network control plane; the access network equipment and AMF can interact through the N2 interface. N3 is the communication interface between the access network equipment and the UPF, used for transmitting user data. N4 is the interface between the SMF and the UPF, used for policy configuration of the UPF, etc. N5 is the interface between the PCF and the AF. N6 is the interface between the UPF and the DN. N7 is the interface between the SMF and the PCF. N8 is the interface between the AMF and the UDM. N10 is the interface between the UDM and the SMF. N11 is the interface between the AMF and the SMF. N25 is the interface between the PCF and the UDM. The interfaces between the various control plane network elements in the CN can be implemented using corresponding service-oriented interfaces, such as... Figure 2 As shown.

[0183] It should be noted that, Figure 1 and Figure 2 The communication system shown is not intended to limit the scope of communication systems applicable to the embodiments of this application. Therefore, the communication method provided in the embodiments of this application can also be applied to various communication systems, such as: LTE communication systems, 5G communication systems, 6G communication systems, future communication systems, vehicle-to-everything (V2X), LTE-V (LTE-V), vehicle-to-vehicle (V2V), vehicle-to-vehicle (V2V), vehicle-to-everything (V2V), machine-type communications (MTC), internet of things (IoT), LTE-M (LTE-Machine-to-Machine), machine-to-machine (M2M), and the Internet of Things. Furthermore, it should be noted that the embodiments of this application do not limit the names of the network elements in the communication system. For example, in different communication systems, each network element may have other names; and for example, when multiple network elements are integrated into the same physical device, that physical device may also have other names.

[0184] Figure 1 and Figure 2 The communication system shown can support multiple multicast transmission modes, specifically including: shared transmission mode and independent transmission mode. The following section, with reference to the accompanying drawings, describes... Figure 1 and Figure 2 The multicast transmission methods supported by the communication system shown are explained below:

[0185] Method 1: Shared transmission method.

[0186] Shared transmission refers to transmitting service data through a shared transmission channel, which can be shared by multiple terminal devices. This shared transmission channel can include two parts: the transmission channel between the user plane network element (e.g., MB-UPF) and the AN device, and the transmission channel between the AN device and the terminal device.

[0187] In one implementation, assuming a shared transmission method is used to transmit service data, the transmission channel (or transmission tunnel, such as a tunnel based on the General Packet Radio Service Tunneling Protocol, or GTP) between the user plane network element (e.g., MB-UPF) and the AN device, as well as the air interface transmission channel between the AN device and the terminal device, are shared by multiple terminal devices that have joined the multicast session.

[0188] For example, when multiple terminal devices (e.g., UEa, UEb, and UEc) join a multicast session through the same AN ​​device (taking the first AN device as an example), the MB-UPF can send a service data packet to the first AN device through a transmission channel between the MB-UPF corresponding to the multicast session and the first AN device. The first AN device can then send the service data packet to the multiple terminal devices through a shared transmission channel between the first AN device and the terminal devices that have joined the multicast session. Correspondingly, the multiple terminal devices can receive the service data packet through this transmission channel.

[0189] Method 2: Independent transmission method.

[0190] Independent transmission mode refers to transmitting service data through a dedicated transmission channel. This dedicated transmission channel can be exclusively used by a single terminal device, meaning that the single terminal device uses this dedicated transmission channel alone. This dedicated transmission channel can include two parts: a user plane network element (e.g., a unicast UPF, which can be...). Figure 1 The transmission channel between the UPF and AN devices, and the transmission channel between the AN devices and the terminal devices.

[0191] In one implementation, assuming that an independent transmission method is used to transmit service data, the user plane network element (e.g., unicast UPF, where the unicast UPF can be...) Figure 1 The transmission channel between the UPF and AN devices, as well as the air interface transmission channel between the AN devices and the terminal devices, can be dedicated to a single terminal device joining a multicast session.

[0192] For example, when multiple terminal devices (e.g., UEd and UEe) join a multicast session through the same AN ​​device (taking the second AN device as an example), the MB-UPF can send a service data packet to the unicast UPF through a transmission channel between the MB-UPF and the unicast UPF corresponding to the multicast session. Then, the unicast UPF can send the service data packet to UEd and UEe respectively through dedicated transmission channels for UEd and UEe. Specifically, the unicast UPF can send a service data packet to the second AN device through a dedicated transmission channel between the unicast UPF and the second AN device; the second AN device can send a service data packet to UEd through a dedicated transmission channel between the second AN device and UEd. The data transmission path is: MB-UPF → unicast UPF → second AN device → UEd. The unicast UPF can send a service data packet to the second AN device through a dedicated transmission channel between the unicast UPF and the second AN device; the second AN device can send a service data packet to UEe through a dedicated transmission channel between the second AN device and UEe. The data transmission path is: MB-UPF → unicast UPF → second AN device → UEe.

[0193] It should be noted that the transmission method of service data can be determined based on the multicast support capability of the AN device (e.g., whether it supports multicast or not). For example, when multiple terminal devices (e.g., UEa, UEb, UEc, UEd, and UEe) join a multicast session through different AN devices, for instance, UEa, UEb, and UEc join the multicast session through a first AN device, while UEd and UEe join the multicast session through a second AN device. When the first AN device supports multicast, UEa, UEb, and UEc can receive service data packets using method 1 described above. When the second AN device does not support multicast, UEd and UEe can receive service data packets using method 2 described above.

[0194] When the AN device supports multicast, a shared transmission mode can be used, meaning that the transmission channel between the user plane network element (e.g., MB-UPF) and the AN device, as well as the air interface transmission channel between the AN device and the terminal device, can be shared by multiple terminal devices that have joined the multicast session. When the AN device does not support multicast, an independent transmission mode can be used, meaning that the transmission channel between the user plane network element (e.g., unicast UPF) and the AN device, as well as the air interface transmission channel between the AN device and the terminal device, is dedicated to a single terminal device.

[0195] The solution provided in this application will be described below with reference to the accompanying drawings.

[0196] This application provides a communication method that can be applied to... Figure 1 or Figure 2 The communication system shown below. See below. Figure 3 The flowchart shown below provides a detailed explanation of the method's process.

[0197] S301: AS sends the service data packet of the first service to the terminal device through the multicast session of the first mobile communication system.

[0198] Accordingly, the terminal device receives service data packets of the first service from the AS through the multicast session of the first mobile communication system.

[0199] The first service may include, but is not limited to, at least one of the following: voice service, data service, or video service. The terminal device may be any terminal device that has joined the multicast session. Furthermore, the terminal device may be a member of the multicast group corresponding to the multicast session; this application does not impose any restrictions on this.

[0200] Specifically, after the terminal device accesses the first mobile communication system, the AS can send the service data packets of the first service to the terminal device through the multicast session of the first mobile communication system.

[0201] Specifically, step S301 can be implemented in the following way:

[0202] Method 1: The AS sends the service data packet of the first service to the terminal device through the first multicast session in the first mobile communication system.

[0203] The first multicast session is a multicast session between the multicast user plane network element in the first mobile communication system, the AN device in the first mobile communication system accessed by the terminal device, and the terminal device.

[0204] The multicast user plane network element can be MB-UPF.

[0205] The transmission channel between the MB-UPF and the AN device corresponding to the first multicast session, and the air interface transmission channel between the AN device and the terminal device corresponding to the first multicast session, can be shared by the terminal device and other terminal devices joining the first multicast session. In this case, the AS can send the service data packets of the first service to the terminal device through a shared transmission method, i.e., through the first multicast session.

[0206] Specifically, the AS can send a service data packet of the first service to the MB-UPF. The MB-UPF sends the service data packet of the first service to the terminal device through the transmission channel between the MB-UPF and the AN device corresponding to the first multicast session, and the air interface transmission channel between the AN device and the terminal device corresponding to the first multicast session.

[0207] Optionally, the first multicast session may or may not be a local multicast session.

[0208] Method 2: The AS sends the service data packet of the first service to the terminal device through the second multicast session in the first mobile communication system.

[0209] The second multicast session is a multicast session between a multicast user plane network element in the first mobile communication system, a unicast user plane network element in the first mobile communication system accessed by the terminal device, an AN device in the first mobile communication system accessed by the terminal device, and the terminal device.

[0210] The multicast user plane network element can be an MB-UPF, and the user plane network element can be a unicast UPF.

[0211] Specifically, the transmission channel between the unicast UPF and the AN device corresponding to the second multicast session, and the air interface transmission channel between the AN device and the terminal device corresponding to the second multicast session, can be exclusively used by the terminal device joining the second multicast session. In this case, the AS can send the service data packets of the first service to the terminal device through the aforementioned independent transmission method, i.e., through the second multicast session.

[0212] Specifically, the AS can send a service data packet of the first service to the multicast UPF corresponding to the second multicast session, and the multicast UPF can send a service data packet of the first service to the unicast UPF corresponding to the second multicast session. Then, the unicast UPF can send a service data packet of the first service to the terminal device through the dedicated transmission channel between the unicast UPF corresponding to the second multicast session and the AN device, and the dedicated air interface transmission channel between the AN device corresponding to the second multicast session and the terminal device.

[0213] Optionally, the second multicast session may or may not be a local multicast session.

[0214] S302: When the handover conditions for the terminal device to switch from the first mobile communication system to the second mobile communication system are met, or when the terminal device switches from the first mobile communication system to the second mobile communication system, the terminal device sends first information to the AS.

[0215] The first information can be used to trigger the AS to send the service data packet of the first service to the terminal device via unicast transmission.

[0216] Specifically, the first information can be a message that triggers the AS to send the service data packet of the first service to the terminal device via unicast transmission, or it can be an information element in the message. Specifically, when the first information is an information element, it can reuse information elements from an existing message, or it can be a new information element from an existing message. For example, the information element can be a first indication field; when this field takes a first value, it can trigger the AS to send the service data packet of the first service to the terminal device via unicast transmission.

[0217] Accordingly, the AS receives the first information from the terminal device.

[0218] The first mobile communication system and the second mobile communication system may use different or the same Radio Access Technology (RAT), and this application does not impose any restrictions on this. Specifically, the first mobile communication system may be a mobile communication system using a first RAT, and the second mobile communication system may be a mobile communication system using a second RAT. For example, the first RAT may be 5G radio access technology, and the second RAT may be 4G radio access technology; that is, the first mobile communication system is a 5G mobile communication system, and the second mobile communication system is a 4G mobile communication system. Obviously, the second RAT may be 5G radio access technology, and the first RAT may be 4G radio access technology; this application does not impose any restrictions on this.

[0219] It should be noted that the switching of the terminal device from the first mobile communication system to the second mobile communication system may include, but is not limited to, the following scenarios:

[0220] 1. The terminal device may be switching from an AN device of the first mobile communication system to an AN device of the second mobile communication system;

[0221] 2. The terminal device has been switched from the AN device of the first mobile communication system to the AN device of the second mobile communication system;

[0222] 3. The terminal device has been switched from the AN device of the first mobile communication system to the AN device of the second mobile communication system, and is switching from the CN device of the first mobile communication system to the CN device of the second mobile communication system;

[0223] 4. The terminal device has been switched from the AN device of the first mobile communication system to the AN device of the second mobile communication system, and has been switched from the CN device of the first mobile communication system to the CN device of the second mobile communication system.

[0224] This application does not limit the specific scenario in which the terminal device switches from the first mobile communication system to the second mobile communication system.

[0225] S303: The AS sends the service data packet of the first service to the terminal device via unicast transmission based on the first information.

[0226] Accordingly, the terminal device receives the service data packet of the first service from the AS via the unicast transmission method.

[0227] Based on the method provided in the above embodiments, the AS sends service data packets of the first service to the terminal device through a multicast session in the first mobile communication system. When the conditions for the terminal device to perform a cross-communication system handover are met, or when the terminal device performs a cross-communication system handover, the terminal device can trigger the AS to send the service data packets of the first service to the terminal device through unicast transmission by sending the first information. In this way, the transmission of the first service of the terminal device will not be affected during the cross-communication system handover process. That is, when the conditions for the cross-communication system handover are met or during the cross-communication system handover process, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding discontinuous service transmission due to limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0228] The following is a detailed description of step S302, which states that "when the handover conditions for the terminal device to switch from the first mobile communication system to the second mobile communication system are met, the terminal device sends first information to the AS".

[0229] The switching conditions may include, but are not limited to, at least one or a combination of the following: Condition 1: The signal quality of the first mobile communication system is less than a first threshold; Condition 2: The signal quality of the second mobile communication system is greater than a second threshold; Condition 3: The signal quality of the second mobile communication system is greater than the signal quality of the first mobile communication system; Condition 4: The terminal device is located within the coverage area of ​​the second mobile communication system; or, Condition 5: The terminal device moves from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system, etc.

[0230] It should be noted that the above switching conditions can be the switching conditions between AN devices in the prior art, and this application does not limit them.

[0231] Optionally, the switching condition is configured for the terminal device by the AN device to which the terminal device is connected. For example, the terminal device can obtain the switching condition from the AN device during the registration process.

[0232] The following explains how the terminal device determines whether the switching conditions are met.

[0233] Regarding condition 1:

[0234] The terminal device can determine whether condition 1 is met based on the signal quality of the first mobile communication system detected by the terminal device. Specifically, when the signal quality of the first mobile communication system detected by the terminal device is less than the first threshold, the terminal device can determine that condition 1 is met; otherwise, the terminal device determines that condition 1 is not met. The signal quality of the first mobile communication system detected by the terminal device can be the signal quality of the service data packets of the first mobile communication system (e.g., the service data packets of the first service), or the signal quality of the control signals of the first mobile communication system (e.g., signals including downlink control information (DCI) or reference signals). The first threshold can be pre-configured, or it can be configured by the AN device accessed by the terminal device and sent to the terminal device.

[0235] Regarding condition 2:

[0236] The terminal device can determine whether condition 2 is met based on the signal quality of the second mobile communication system detected by the terminal device. Specifically, when the signal quality of the second mobile communication system detected by the terminal device is greater than the second threshold, the terminal device can determine that condition 2 is met; otherwise, the terminal device determines that condition 2 is not met. The signal quality of the second mobile communication system detected by the terminal device can be the signal quality of a reference signal of the second mobile communication system. The second threshold can be pre-configured, or it can be configured by the AN device accessed by the terminal device and sent to the terminal device.

[0237] Regarding condition 3:

[0238] The terminal device can determine whether condition 3 is met based on the signal quality of the first mobile communication system and the signal quality of the second mobile communication system detected by the terminal device. Specifically, if the signal quality of the second mobile communication system detected by the terminal device is greater than the signal quality of the first mobile communication system detected by the terminal device, the terminal device can determine that condition 3 is met; otherwise, the terminal device determines that condition 3 is not met. The method by which the terminal device detects the signal quality of the first mobile communication system can be referred to the description of condition 1, and the method by which the terminal device detects the signal quality of the second mobile communication system can be referred to the description of condition 2, and will not be repeated here.

[0239] Optionally, for conditions 1-3 above, the signal quality is the signal strength. The parameters used to represent or indicate the signal strength may include, but are not limited to, at least one of the following: reference signal receiving power (RSRP), reference signal receiving quality (RSRQ), or received signal strength indication (RSSI).

[0240] Regarding condition 4:

[0241] The terminal device can determine whether condition 4 is met based on whether it can detect the signal of the second mobile communication system. Specifically, the signal of the second mobile communication system can be a system message of the second mobile communication system (e.g., a system information block (SIB)). When the terminal device can detect the system message of the second mobile communication system (e.g., an SIB), the terminal device can determine that it is within the coverage area of ​​the second mobile communication system, thus satisfying condition 4. When the terminal device cannot detect the system message of the second mobile communication system (e.g., an SIB), the terminal device determines that it is not within the coverage area of ​​the second mobile communication system, thus not satisfying condition 4.

[0242] Regarding condition 5:

[0243] The terminal device can determine whether condition 5 is met based on whether it can detect the signal of the second mobile communication system and whether it can detect the signal of the first mobile communication system. Specifically, when the terminal device can detect the system message (e.g., SIB) of the second mobile communication system, and the terminal device changes from being able to detect the signal of the first mobile communication system to not being able to detect the signal of the first mobile communication system, the terminal device can determine that it has moved from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system, thus satisfying condition 5; otherwise, the terminal device can determine that condition 5 is not satisfied. The signal of the first mobile communication system may include at least one of the following: the system message (e.g., SIB) of the first mobile communication system, and service data packets. Optionally, the first information includes, but is not limited to, at least one of the following: information indicating that the terminal device is preparing to switch from the first mobile communication system to the second mobile communication system; information indicating that the terminal device is preparing to switch to the second mobile communication system; information indicating that the terminal device will switch from the first mobile communication system to the second mobile communication system; information indicating that the terminal device will switch to the second mobile communication system; information indicating that the terminal device is within the coverage area of ​​the second mobile communication system; information indicating that the terminal device moves from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system; information indicating that the signal quality of the first mobile communication system is less than a first threshold; information indicating that the signal quality of the second mobile communication system is greater than a second threshold; information indicating that the signal quality of the second mobile communication system is greater than the signal quality of the first mobile communication system; information indicating that the terminal device is about to leave the multicast session; information indicating that the terminal device will attach to or has already attached to the second mobile communication system; or, information requesting the AS to send the service data packet of the first service to the terminal device via unicast transmission.

[0244] Based on the method provided in the above embodiments, the AS sends the service data packet of the first service to the terminal device through a multicast session in the first mobile communication system. When the conditions for the terminal device to perform cross-communication system handover are met, the terminal device can trigger the AS to send the service data packet of the first service to the terminal device through unicast transmission by sending the first information. Thus, the transmission of the first service of the terminal device will not be affected during the cross-communication system handover process. That is, during the cross-communication system handover process, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding discontinuous service transmission due to limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0245] The following is a detailed explanation of step S302, which states that "when the terminal device switches from the first mobile communication system to the second mobile communication system, the terminal device sends first information to the AS".

[0246] Optionally, the terminal device sends the first information to the AS based on information received when switching from the first mobile communication system to the second mobile communication system. The received information may be a first indication from the session management network element of the first mobile communication system, wherein the first indication is used to indicate that the multicast session is released. Alternatively, the received information may be a handover command from the first mobile communication system. The specific implementation process is described below in conjunction with implementation methods one and two.

[0247] Implementation Method 1: The terminal device can send the first information to the AS according to a first instruction from the session management network element of the first mobile communication system. The first instruction can indicate that the multicast session is released. The session management network element can be an SMF (Service Management Function).

[0248] Optionally, the first indication can be a dedicated message for releasing a multicast session, or it can be an information element in a message. For example, the first indication can be an information element in a PDU session modification command.

[0249] Additionally, the first indication may include identification information of the multicast session (e.g., a temporary mobile group identity (TMGI)).

[0250] In this first implementation, the AS sends service data packets for the first service to the terminal device through a multicast session in the first mobile communication system. When the terminal device is removed from the multicast session, the terminal device can trigger the AS to send service data packets for the first service to the terminal device via unicast transmission by sending the first information. Thus, the transmission of the first service is not affected during the cross-communication system handover process of the terminal device. That is, during the cross-communication system handover process of the terminal device, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding discontinuous service transmission due to limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0251] Optionally, in the above implementation method one, the terminal device sends the first information to the AS according to the first instruction from the session management network element of the first mobile communication system, in the following manner:

[0252] Method 1: After receiving a first instruction from the session management network element indicating that the multicast session has been released, the terminal device can send the first information to the AS.

[0253] Method 2: When the second preset condition is met, the terminal device may send the first information to the AS after receiving the first instruction; when the second preset condition is not met, the terminal device may not send the first information to the AS after receiving the first instruction.

[0254] It should be noted that this application does not restrict the execution order of determining whether the second preset condition is met and receiving the first instruction. For example, the terminal device may determine whether the second preset condition is met after receiving the first instruction; or, the terminal device may determine whether the second preset condition is met before receiving the first instruction.

[0255] The second preset condition may include, but is not limited to, at least one of the following: Condition 1: The multicast session is not a local multicast session; or, Condition 2: The multicast session is a local multicast session, and the terminal device is located within the service area of ​​the local multicast session.

[0256] The following explains how the terminal device determines whether the second preset condition is met.

[0257] Regarding condition one:

[0258] In some possible ways, the terminal device can determine whether condition one is met based on the type of the multicast session. Specifically, when the type of the multicast session is a local multicast session, the terminal device can determine that the multicast session is a local multicast session, i.e., condition one is not met; when the type of the multicast session is not a local multicast session, the terminal device can determine that the multicast session is not a local multicast session, i.e., condition one is met. The type of the multicast session can be obtained by the terminal device during session establishment or can be carried in the service data packets of the multicast session.

[0259] In other possible approaches, the terminal device can determine whether condition one is satisfied based on whether the context of the multicast session contains parameters of a local multicast session (e.g., MBS service area). Specifically, when the terminal device receives a multicast session whose context contains parameters of a local multicast session (e.g., MBS service area), the terminal device can determine that the multicast session is a local multicast session, i.e., condition one is not satisfied; when the terminal device receives a multicast session whose context does not contain parameters of a local multicast session (e.g., MBS service area), the terminal device can determine that the multicast session is not a local multicast session, i.e., condition one is satisfied. The context of the multicast session can be obtained by the terminal device during session establishment or can be carried in the service data packets of the multicast session.

[0260] Regarding condition two:

[0261] The terminal device can determine whether condition two is met by means of the following method.

[0262] Method A: The terminal device can determine whether condition two is met based on the type of the multicast session, the location information of the terminal device, and the service area of ​​the local multicast session.

[0263] Specifically, when the type of the multicast session is a local multicast session, and the service area of ​​the local multicast session includes the location or area indicated by the location information of the terminal device, the terminal device can determine that the multicast session is the local multicast session, and the terminal device is located within the service area of ​​the local multicast session, that is, condition two is satisfied; otherwise, the terminal device can determine that condition two is not satisfied.

[0264] The type of the multicast session can be obtained by the terminal device during the session establishment process, or it can be carried in the service data packets of the multicast session.

[0265] The location information of the terminal device may be at least one of the following: the global positioning system (GPS) information of the terminal device, the information of the cell where the terminal device is located, the tracking area (TA) information of the terminal device, and the information of the AN device connected to the terminal device.

[0266] The terminal device obtains information (e.g., MBS service area) for indicating the service area of ​​the local multicast session in the following ways: the terminal device obtains information for indicating the service area of ​​the local multicast session during the session establishment process; or, after determining that the multicast session is the local multicast session, the terminal device requests information for indicating the service area of ​​the local multicast session from the first mobile communication system.

[0267] The information used to indicate the service area of ​​the local multicast session may include at least one of the following: one or more AN device identifiers (IDs), one or more cell identifiers (cellIDs), and one or more tracking area identifiers (TAIs). When the information indicating the service area of ​​the local multicast session includes one or more AN device identifiers, the coverage area of ​​the AN device indicated by the one or more AN device identifiers is the service area of ​​the local multicast session. When the information indicating the service area of ​​the local multicast session includes one or more cell identifiers, the coverage area of ​​the cell indicated by the one or more cell identifiers is the service area of ​​the local multicast session. When the information indicating the service area of ​​the local multicast session includes one or more TAIs, the area indicated by the one or more TAIs is the service area of ​​the local multicast session.

[0268] Method B: The terminal device can determine whether condition two is met based on the context of the multicast session, the location information of the terminal device, and the service area of ​​the local multicast session.

[0269] Specifically, when the terminal device receives parameters of the local multicast session (e.g., MBS service area) in the context of the multicast session, and the service area of ​​the local multicast session includes the location or area indicated by the location information of the terminal device, the terminal device can determine that the multicast session is the local multicast session, and the terminal device is located within the service area of ​​the local multicast session, that is, condition two is satisfied; otherwise, the terminal device can determine that condition two is not satisfied.

[0270] The context of the multicast session can be obtained by the terminal device during session establishment, or it can be carried in the service data packets of the multicast session. The location information of the terminal device can be referenced in method A, and the service area of ​​the local multicast session can also be referenced in method A; further details are omitted here.

[0271] When the second preset condition is met, if the terminal device is removed from the multicast session, the terminal device still needs to acquire application layer services; when the second preset condition is not met, if the terminal device is removed from the multicast session, the terminal device may not acquire application layer services. Through this design, the terminal device will only send the first information when the second preset condition is met, triggering the AS to transmit the application layer services to the terminal device via unicast transmission; when the second preset condition is not met, the terminal device does not need to send the first information, thereby saving the resources required to send the first information.

[0272] Optionally, in the first implementation, the first information includes, but is not limited to, at least one of the following: information indicating that the terminal device has left the multicast session; information indicating that the terminal device has been removed from the multicast session; information indicating that the multicast session has been released; information indicating that the terminal device cannot receive service data packets of the first service through the multicast session; information indicating that the terminal device is preparing to switch from the first mobile communication system to the second mobile communication system; information indicating that the terminal device is preparing to switch to the second mobile communication system; information indicating that the terminal device will switch from the first mobile communication system to the second mobile communication system; information indicating that the terminal device will switch ... Information indicating that the terminal device is located within the coverage area of ​​the second mobile communication system; information indicating that the terminal device moves from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system; information indicating that the signal quality of the first mobile communication system is less than a first threshold; information indicating that the signal quality of the second mobile communication system is greater than a second threshold; information indicating that the signal quality of the second mobile communication system is greater than the signal quality of the first mobile communication system; information indicating that the terminal device is about to leave the multicast session; information indicating that the terminal device will attach to or has already attached to the second mobile communication system; or, information requesting the AS to send the service data packet of the first service to the terminal device via unicast transmission.

[0273] Optionally, in one implementation scenario of the above-described method one, the method further includes: after receiving a second instruction from a mobility management network element (AMF) in the first mobile communication system, the session management network element may, according to the second instruction, remove the terminal device from the multicast session. The second instruction may indicate that the multicast session of the terminal device is rejected by the second mobile communication system when the terminal device switches from the first mobile communication system to the second mobile communication system. Specifically, after receiving the second instruction, when the session management network element determines, according to the second instruction, that the multicast session of the terminal device is rejected by the second mobile communication system when the terminal device switches from the first mobile communication system to the second mobile communication system, the session management network element may remove the terminal device from the multicast session. The mobility management network element may be an AMF.

[0274] Specifically, when the second indication is used to instruct the terminal device to switch from the first mobile communication system to the second mobile communication system, and the multicast session of the terminal device is rejected by the second mobile communication system, the session management network element can also send the first indication to the terminal device. In other words, the second indication can trigger the session management network element to send the first indication to the terminal device.

[0275] Optionally, the second indication is a dedicated message or an information element within a message. For example, the second indication could be an information element in a PDU session update session management context request (Nsmf_PDUsession_updateSMcontext request).

[0276] Additionally, the second indication may include: information indicating that the multicast session is rejected by the second mobile communication system, or information indicating that the quality of service (QoS) flow (e.g., MBS QoS flow) of the multicast session is rejected by the second mobile communication system.

[0277] The information used to indicate that the multicast session was rejected by the second mobile communication system may include at least one of the following: indication information of a session rejected by the second mobile communication system, information indicating that an MBS session was rejected by the second mobile communication system, and indication information of a session accepted by the second mobile communication system. The information used to indicate that the QoS flow of the multicast session was rejected by the second mobile communication system may include at least one of the following: indication information of the QoS flow of a session rejected by the second mobile communication system, and indication information of the QoS flow of a session accepted by the second mobile communication system.

[0278] The following example, based on the content of the second instruction, illustrates how the session management network element determines, according to the second instruction, that the multicast session of the terminal device is rejected by the second mobile communication system when the terminal device switches from the first mobile communication system to the second mobile communication system.

[0279] For example, when the second indication contains indication information of a session rejected by the second mobile communication system, and the session rejected by the second mobile communication system includes the multicast session of the terminal device, the session management network element can determine that the multicast session of the terminal device is rejected by the second mobile communication system.

[0280] For example, when the second indication includes information indicating that the MBS session is rejected by the second mobile communication system, and the multicast session is an MBS session, the session management network element can determine that the multicast session is rejected by the second mobile communication system.

[0281] For example, when the second indication contains indication information of a session accepted by the second mobile communication system, and the session accepted by the second mobile communication system does not include the multicast session of the terminal device, the session management network element can determine that the multicast session is rejected by the second mobile communication system.

[0282] For example, when the second indication includes indication information of the QoS flow of a session rejected by the second mobile communication system, and the QoS flow of the session rejected by the second mobile communication system includes the QoS flow of the multicast session of the terminal device, the session management network element can determine that the QoS flow of the multicast session is rejected by the second mobile communication system, and thus determine that the multicast session is rejected by the second mobile communication system.

[0283] For example, when the second indication includes indication information of the QoS flow of the session accepted by the second mobile communication system, and the QoS flow of the session accepted by the second mobile communication system does not include the QoS flow of the multicast session, the session management network element can determine that the QoS flow of the multicast session is rejected by the second mobile communication system, and thus determine that the multicast session is rejected by the second mobile communication system.

[0284] Using this method, when the terminal device switches from the first mobile communication system to the second mobile communication system, if the multicast session of the terminal device is rejected by the second mobile communication system, the session management network element of the first mobile communication system can remove the terminal device from the multicast session. This avoids unnecessary occupation of multicast session resources by the terminal device, thereby preventing resource waste.

[0285] Optionally, in another implementation scenario of the first embodiment described above, the method further includes: before sending the first instruction to the terminal device, the session management network element may receive a third instruction from the multicast session management network element. The third instruction may indicate that the multicast session is released. The session management network element may remove the terminal device from the multicast session according to the third instruction, that is, after receiving the third instruction, the session management network element removes the terminal device from the multicast session. The multicast session management network element may be an MB-SMF.

[0286] Optionally, when the third indication is used to indicate that the multicast session is released, the session management network element may send the first indication to the terminal device. That is, the third indication may trigger the session management network element to send the first indication to the terminal device.

[0287] Optionally, the third indication is a dedicated message or an information element within a message. For example, the third indication can be an information element in an MBS session context notification (Nmbsmf_MBSSession_ContextStatusNotify).

[0288] Optionally, the third indication includes indication information of the terminal device (e.g., the identifier of the terminal device) and identification information of the multicast session (e.g., TMGI).

[0289] Using this method, the session management network element of the first mobile communication system can remove the terminal device from the multicast session after receiving an instruction from the multicast session management network element. This avoids unnecessary occupation of multicast session resources by the terminal device, thereby preventing resource waste.

[0290] Implementation Method Two: The terminal device can send the first information to the AS according to a handover command from the first mobile communication system. The handover command is used to instruct the terminal device to switch to the second mobile communication system.

[0291] Optionally, after receiving the handover command, the terminal device determines whether the multicast session has been rejected by the second mobile communication system based on the handover command; if the determination result is yes, the terminal device may send the first information to the AS; otherwise, the terminal device may not send the first information to the AS.

[0292] The following example illustrates how the terminal device determines whether the multicast session has been rejected by the second mobile communication system based on the switching command.

[0293] For example, when the switching command contains indication information of a session accepted by the second mobile communication system, and the session accepted by the second mobile communication system does not include the multicast session, the terminal device determines that the multicast session is rejected by the second mobile communication system.

[0294] For example, when the switching command contains indication information of the QoS flow of the session accepted by the second mobile communication system, and the QoS flow of the session accepted by the second mobile communication system does not contain the QoS flow of the multicast session, the terminal device can determine that the QoS flow of the multicast session is rejected by the second mobile communication system, thereby determining that the multicast session is rejected by the second mobile communication system.

[0295] For example, when the switching command includes a QoS stream that needs to be forwarded, and the QoS stream that needs to be forwarded does not include the QoS stream of the multicast session, the terminal device can determine that the multicast session is rejected by the second mobile communication system. In other words, the terminal device can determine that the QoS stream corresponding to the multicast session cannot be switched to the second mobile communication system, or determine that the QoS stream corresponding to the multicast session is rejected by the second mobile communication system.

[0296] For example, when the switching command contains bearer information of the second mobile communication system, and the bearer indicated by the bearer information of the second mobile communication system does not include the bearer corresponding to the multicast session, the terminal device can determine that the multicast session is rejected by the 4G mobile communication system.

[0297] In this second implementation, when the terminal device switches from the first mobile communication system to the second mobile communication system, if the terminal device determines that the multicast session is rejected by the second mobile communication system according to the switching command, the terminal device can trigger the AS to send the service data packet of the first service to the terminal device via unicast transmission by sending the first information. Thus, the transmission of the first service of the terminal device will not be affected during the cross-communication system handover process. That is, during the cross-communication system handover process, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding discontinuous service transmission due to limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0298] Optionally, in this second implementation, the first information includes, but is not limited to, at least one of the following: information indicating that the terminal device will switch from the first mobile communication system to the second mobile communication system; information indicating that the terminal device will switch to the second mobile communication system; information indicating that the terminal device has switched from the first mobile communication system to the second mobile communication system; information indicating that the terminal device has switched to the second mobile communication system; information indicating that the terminal device has attached to the second mobile communication system; information indicating that the terminal device is within the coverage area of ​​the second mobile communication system; information indicating that the terminal device has moved from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system; information indicating that the terminal device has left the multicast session; information indicating that the terminal device has been removed from the multicast session; information indicating that the multicast session has been released; information indicating that the terminal device cannot receive the service data packets of the first service through the multicast session; or, information requesting the AS to send the service data packets of the first service to the terminal device via unicast transmission.

[0299] Accordingly, in step S302, the first information received by the AS may include, but is not limited to, at least one of the following: information indicating that the terminal device is preparing to switch from the first mobile communication system to the second mobile communication system; information indicating that the terminal device is preparing to switch to the second mobile communication system; information indicating that the terminal device will switch from the first mobile communication system to the second mobile communication system; information indicating that the terminal device will switch to the second mobile communication system; information indicating that the terminal device has switched from the first mobile communication system to the second mobile communication system; information indicating that the terminal device has switched to the second mobile communication system; information indicating that the terminal device is within the coverage area of ​​the second mobile communication system; information indicating that the terminal device moves from the coverage area of ​​the first mobile communication system to... Information regarding the coverage area of ​​the second mobile communication system; information indicating that the signal quality of the first mobile communication system is less than a first threshold; information indicating that the signal quality of the second mobile communication system is greater than a second threshold; information indicating that the signal quality of the second mobile communication system is greater than the signal quality of the first mobile communication system; information indicating that the terminal device is about to leave the multicast session; information indicating that the terminal device has already left the multicast session; information indicating that the terminal device has been removed from the multicast session; information indicating that the terminal device will attach to or has already attached to the second mobile communication system; information indicating that the terminal device cannot receive the service data packets of the first service through the multicast session; or, information requesting the AS to send the service data packets of the first service to the terminal device via unicast transmission.

[0300] Optionally, in the above embodiments, when the first information includes: information for instructing the terminal device to prepare to switch from the first mobile communication system to the second mobile communication system, or information for instructing the terminal device to prepare to switch to the second mobile communication system, the terminal device is in the handover preparation stage.

[0301] When the first information includes information indicating that the terminal device will switch from the first mobile communication system to the second mobile communication system, or information indicating that the terminal device will switch to the second mobile communication system, the terminal device is switching from the AN device of the first mobile communication system to the AN device of the second mobile communication system; or, the terminal device has switched from the AN device of the first mobile communication system to the AN device of the second mobile communication system, but has not yet switched from the CN device of the first mobile communication system to the CN device of the second mobile communication system.

[0302] When the first information includes: information indicating that the terminal device has switched from the first mobile communication system to the second mobile communication system, or information indicating that the terminal device has switched to the second mobile communication system, the terminal device has switched from the AN device of the first mobile communication system to the AN device of the second mobile communication system, but has not switched from the CN device of the first mobile communication system to the CN device of the second mobile communication system; or, the terminal device has switched from the AN device of the first mobile communication system to the AN device of the second mobile communication system, and has also switched from the CN device of the first mobile communication system to the CN device of the second mobile communication system.

[0303] Optionally, in one implementation scenario of the above embodiments, the method further includes: when the first preset condition is met, the AS sends configuration information to the terminal device.

[0304] The configuration information can be used to instruct the terminal device to send first information to the AS when the handover conditions for switching from the first mobile communication system to the second mobile communication system are met, or when the terminal device switches from the first mobile communication system to the second mobile communication system. The configuration information can be a message or an information element within a message. Specifically, when the configuration information is an information element, it can reuse information elements from existing messages or use new information elements from existing messages. For example, the information element can be a second indication field. When this field takes a second value, it can instruct the terminal device to send first information to the AS when the handover conditions for switching from the first mobile communication system to the second mobile communication system are met, or when the terminal device switches from the first mobile communication system to the second mobile communication system.

[0305] Further, S302 may include: when the terminal device meets the handover conditions, or when the terminal device switches from the first mobile communication system to the second mobile communication system, if the terminal device has received the configuration information, then sending the first information to the AS.

[0306] Using this method, the AS sets configuration information for the terminal device when the first preset condition is met. The terminal device sends the first information to the AS only after receiving the configuration information, thereby saving resources for sending the first information and avoiding resource waste.

[0307] Optionally, the first preset condition includes, but is not limited to, at least one of the following:

[0308] Condition A: The first service is permitted to be transmitted using both the mobile communication system using the first RAT and the mobile communication system using the second RAT;

[0309] Condition B: The service area of ​​the first service overlaps with the coverage area of ​​the mobile communication system using the first RAT, and the service area of ​​the first service overlaps with the coverage area of ​​the mobile communication system using the second RAT; or

[0310] Condition C: The terminal device supports having a first capability and a second capability, wherein the first capability includes the ability to receive service data packets through a multicast session of the mobile communication system using the first RAT, and the second capability includes at least one of the following: the ability to receive service data packets through a unicast transmission channel of the mobile communication system using the second RAT, and the ability to receive service data packets through a broadcast transmission channel of the mobile communication system using the second RAT.

[0311] The following explains how the AS determines whether the first preset condition is met.

[0312] Regarding condition A:

[0313] In some possible ways, the AS can determine whether condition A is met by interacting with a mobile communication system using the first RAT and a mobile communication system using the second RAT.

[0314] For example, before transmitting the service data packet of the first service through the first mobile communication system, the AS can interact with the first mobile communication system to determine whether the first mobile communication system is allowed to transmit the first service, thereby determining whether the mobile communication system using the first RAT is allowed to transmit the first service. After receiving the first information, the AS can interact with the second mobile communication system to determine whether the mobile communication system using the second RAT is allowed to transmit the first service. In this way, the AS can determine whether condition A is met.

[0315] In some other possible ways, the AS can determine whether condition A is met based on the characteristics of the first service.

[0316] For example, when the first service is a voice service, and both the mobile communication system using the first RAT and the mobile communication system using the second RAT can support the voice service, the AS determines that condition A is met.

[0317] For example, when the first service is a video service, the mobile communication system using the first RAT supports video services, and the mobile communication system using the second RAT does not support video services, the AS determines whether condition A is satisfied.

[0318] Regarding condition B:

[0319] The AS can obtain the coverage area of ​​the mobile communication system using the first RAT by interacting with it; and can obtain the coverage area of ​​the mobile communication system using the second RAT by interacting with it. When the coverage area of ​​the mobile communication system using the first RAT intersects with the service area of ​​the first service, and the coverage area of ​​the mobile communication system using the second RAT intersects with the service area of ​​the first service, the AS determines that condition B is satisfied; otherwise, the AS determines that condition B is not satisfied.

[0320] Regarding condition C:

[0321] The AS can determine whether the terminal device supports the first capability and the second capability based on the capability information reported by the terminal device, thereby determining whether condition C is met. For example, when the capabilities reported by the terminal device to the AS include the first capability and the second capability, the AS can determine that condition C is met; when the capabilities reported by the terminal device to the AS do not include the first capability or the second capability, the AS can determine that condition C is not met.

[0322] Optionally, step S303 can be implemented as follows:

[0323] Method 1: After receiving the first information, the AS can send the service data packet of the first service to the terminal device through the unicast transmission method.

[0324] Method 2: When the third preset condition is met, the AS can send the service data packet of the first service to the terminal device through the unicast transmission method after receiving the first information.

[0325] It should be noted that this application does not restrict the execution order of determining whether the third preset condition is met and receiving the first information. For example, the AS can determine whether the third preset condition is met after receiving the first information; or, for another example, the AS can determine whether the third preset condition is met before receiving the first information.

[0326] The third preset condition may include, but is not limited to, at least one of the following: Condition a: The mobile communication system using the second RAT does not support broadcast transmission; Condition b: The terminal device is not in the broadcast area of ​​the mobile communication system using the second RAT corresponding to the first service; Condition c: The terminal device does not support broadcasting of the second RAT; or, Condition d: The multicast session does not support switching from the mobile communication system using the first RAT to the mobile communication system using the second RAT.

[0327] The following explains how the AS determines whether the third preset condition is met.

[0328] Regarding condition a:

[0329] The AS can determine whether the mobile communication system using the second RAT supports broadcast transmission by interacting with the mobile communication system using the second RAT.

[0330] Regarding condition b:

[0331] The AS can obtain the broadcast area of ​​the mobile communication system using the second RAT by interacting with the mobile communication system using the second RAT; and obtain the location information of the terminal device by interacting with the terminal device; when the terminal device is located in the overlapping area of ​​the broadcast area of ​​the mobile communication system using the second RAT and the service area of ​​the first service, the AS can determine that condition b is met; otherwise, condition b is not met.

[0332] Regarding condition c:

[0333] The AS can determine whether the terminal device supports broadcasting of the second RAT based on the capability information reported by the terminal device, thereby determining whether condition c is met. For example, when the capability information reported by the terminal device indicates that the terminal device does not support broadcasting, the AS can determine that condition c is met; otherwise, the AS can determine that condition c is not met. As another example, when the capabilities supported by the terminal device, as indicated by the capability information reported by the terminal device, do not include broadcasting capabilities, the AS can determine that condition c is met; otherwise, the AS can determine that condition c is not met.

[0334] Regarding condition d:

[0335] In some possible ways, the AS can determine whether the mobile communication system using the second RAT supports multicast by interacting with the mobile communication system using the second RAT. When the mobile communication system using the second RAT does not support multicast, the AS can determine that condition d is met, that is, the multicast session does not support handover from the mobile communication system using the first RAT to the mobile communication system using the second RAT.

[0336] In other possible approaches, the AS can determine whether condition d is met based on first information from the terminal device. For example, when the first information contains predetermined indication information, the AS determines that condition d is met. The predetermined indication information may include at least one of the following: information indicating that the terminal device has left the multicast session; information indicating that the terminal device has been removed from the multicast session; information indicating that the multicast session has been released; or information indicating that the terminal device cannot receive service data packets of the first service through the multicast session.

[0337] In some other possible ways, after determining that the multicast session is rejected by the second mobile communication system using the second RAT, the CN device (e.g., AMF or SMF) of the first mobile communication system may send an indication message to the AS indicating that the multicast session does not support handover from the mobile communication system using the first RAT to the mobile communication system using the second RAT, so that the AS can determine that condition d is met.

[0338] When the third preset condition is met, the terminal device cannot receive the service data packets of the first service through multicast or broadcast transmission of the second mobile communication system. Using this method, when the third preset condition is met, the AS can promptly send the service data packets of the first service to the terminal device through unicast transmission. Thus, when the terminal device switches to the second mobile communication system, the AS can send the service data packets of the first service to the terminal device through unicast transmission; the handover process between the terminal device and the communication system will not affect the transmission of the first service of the terminal device. That is, during the handover process, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding discontinuous service transmission due to limitations such as the multicast support capability of the target communication system, thereby improving the continuity of service transmission.

[0339] Optionally, in step S303, unicast transmission is used to transmit service data via a unicast transmission channel. Specifically, when unicast transmission is used, the AS sends the service data packet of the first service to the terminal device through the unicast transmission channel. For example, the AS can send the service data packet of the first service to the terminal device through the unicast transmission channel between the user plane network element and the AN device accessed by the terminal device, and through the unicast transmission channel between the AN device accessed by the terminal device and the terminal device.

[0340] The unicast transmission channel can be at least one of the following: the transmission channel corresponding to the unicast session, or the transmission channel corresponding to the unicast bearer.

[0341] Optionally, in step S303, the AS sends the service data packet of the first service to the terminal device via unicast transmission, including: the AS sending the service data packet of the first service to the terminal device through the unicast transmission channel of the first mobile communication system, and correspondingly, the terminal device receiving the service data packet of the first service from the AS through the unicast transmission channel of the first mobile communication system; and / or, the AS sending the service data packet of the first service to the terminal device through the unicast transmission channel of the second mobile communication system, and correspondingly, the terminal device receiving the service data packet of the first service from the AS through the unicast transmission channel of the second mobile communication system.

[0342] The following describes "the AS sending the service data packet of the first service to the terminal device through the unicast transmission channel of the first mobile communication system".

[0343] The unicast transmission channel of the first mobile communication system may include: a unicast transmission channel between the unicast UPF in the first mobile communication system and the AN device in the first mobile communication system accessed by the terminal device, and a unicast transmission channel between the AN device in the first mobile communication system accessed by the terminal device and the terminal device. The unicast transmission channel of the first mobile communication system is dedicated to the terminal device. In this case, the AS can send the service data packet of the first service to the unicast UPF through the transmission channel between the AS and the unicast UPF; the unicast UPF can send the service data packet of the first service to the terminal device through the unicast transmission channel of the first mobile communication system.

[0344] For example, when the first mobile communication system is a 5G mobile communication system, the unicast transmission channel of the first mobile communication system is the transmission channel corresponding to the 5G unicast session. The 5G unicast session can be a unicast user plane network element (e.g., unicast UPF) in the first mobile communication system, an AN device in the first mobile communication system accessed by the terminal device, and a unicast session between the terminal device and the terminal device. The transmission channel between the unicast user plane network element and the AN device corresponding to the unicast session, and the air interface transmission channel between the AN device and the terminal device corresponding to the unicast session, can be dedicated to the terminal device. The unicast transmission channel of the first mobile communication system can include: the transmission channel between the unicast user plane network element and the AN device corresponding to the unicast session, and the air interface transmission channel between the AN device and the terminal device corresponding to the unicast session. In this case, the AS can send the service data packet of the first service to the unicast UPF through the transmission channel between the AS and the unicast UPF; the unicast UPF can send the service data packet of the first service to the terminal device through the unicast transmission channel of the first mobile communication system.

[0345] The following describes "the AS sending the service data packet of the first service to the terminal device through the unicast transmission channel of the second mobile communication system".

[0346] The unicast transmission channel of the second mobile communication system may include: a unicast transmission channel between the S-GW in the second mobile communication system and the AN device in the second mobile communication system accessed by the terminal device, and a unicast transmission channel between the AN device in the second mobile communication system accessed by the terminal device and the terminal device. The unicast transmission channel of the second mobile communication system is dedicated to the terminal device. In this case, the AS can send the service data packet of the first service to the S-GW through the transmission channel between the AS and the S-GW; the S-GW can send the service data packet of the first service to the terminal device through the unicast transmission channel of the second mobile communication system.

[0347] For example, when the second mobile communication system is a 4G mobile communication system, the unicast transmission channel of the second mobile communication system is the transmission channel corresponding to the 4G unicast bearer. The unicast bearer includes the S-GW in the second mobile communication system, the AN device in the second mobile communication system accessed by the terminal device, and the unicast bearer between the terminal device and the unicast bearer. The transmission channel between the S-GW and the AN device corresponding to the unicast bearer, and the air interface transmission channel between the AN device and the terminal device corresponding to the unicast bearer, can be dedicated to the terminal device. The unicast transmission channel of the second mobile communication system may include: the transmission channel between the S-GW and the AN device corresponding to the unicast bearer, and the air interface transmission channel between the AN device and the terminal device corresponding to the unicast bearer. In this case, the AS can send the service data packet of the first service to the S-GW through the transmission channel between the AS and the S-GW; the S-GW can send the service data packet of the first service to the terminal device through the unicast transmission channel of the second mobile communication system.

[0348] This application also provides a communication method. This method can be applied to... Figure 1 or Figure 2 In the communication system shown, in this method, before the terminal device performs a cross-communication system handover (i.e., the handover preparation phase), the terminal device can send first information to the AS. After receiving the first information, the AS can send service data packets to the terminal device via unicast transmission. See below. Figure 4 The flowchart shown illustrates an embodiment of this application, using a handover between 5G and 4G mobile communication systems as an example. For ease of description, the terminal device is UE as an example below.

[0349] S401: The AS sends the service data packet of the first service to the UE through a 5G multicast session. Correspondingly, the UE receives the service data packet of the first service from the AS through a 5G multicast session.

[0350] For details on S401, please refer to S301; it will not be repeated here.

[0351] Figure 4 The diagram illustrates one implementation of S401: the AS sends a service data packet of the first service to the MB-UPF, and the MB-UPF sends the service data packet of the first service to the UE through the transmission channel between the MB-UPF corresponding to the 5G multicast session and the AN device accessed by the UE, and the air interface transmission channel between the AN device corresponding to the 5G multicast session and the UE.

[0352] S402: When the handover conditions for the UE to switch from a 5G mobile communication system to a 4G mobile communication system are met, the UE generates first information.

[0353] The specific content of the handover conditions and the first information can be found in S302, and the process by which the UE determines whether the handover conditions are met can also be found in S302, which will not be repeated here.

[0354] Optionally, the first information is generated by the client implementing the first service in the UE.

[0355] Specifically, step S402 is implemented in the following way:

[0356] Implementation method 1: When the switching conditions for the UE to switch from the 5G mobile communication system to the 4G mobile communication system are met, the UE generates the first information.

[0357] Implementation Method 2: When the handover conditions for the UE to switch from a 5G mobile communication system to a 4G mobile communication system are met, the UE generates the first information only if it receives configuration information from the AS. The specific content of the configuration information can be... Figure 3 The method shown will not be elaborated here.

[0358] S403: The UE sends the first information to the AS. Correspondingly, the AS receives the first information from the UE.

[0359] Specifically, S403 can be implemented in the following ways:

[0360] Method a: After generating the first information, the UE sends the first information to the AS.

[0361] Method b: When the UE receives configuration information from the AS, after generating the first information, the UE can send the first information to the AS. The specific content of the configuration information can be found in [reference needed]. Figure 3 The method shown will not be elaborated here.

[0362] It should be noted that this application does not restrict the execution order of receiving the configuration information of the AS and generating the first information. For example, the terminal device may first receive the configuration information of the AS and then generate the first information; or, the terminal device may first generate the first information and then receive the configuration information of the AS.

[0363] S404: The AS determines, based on the first information, whether to send the service data packet of the first service to the UE via unicast transmission.

[0364] In some possible implementations, after receiving the first information, the AS can determine that it needs to send the service data packet of the first service to the UE via unicast transmission.

[0365] In other possible implementations, when a preset condition is met, the AS, after receiving the first information, can determine to send the service data packet of the first service to the UE via the unicast transmission method; when the preset condition is not met, the AS, after receiving the first information, can determine not to send the service data packet of the first service to the UE via the unicast transmission method. The specific content of the preset condition can be referred to the third preset condition in S303, and will not be repeated here.

[0366] S405: The AS sends the service data packet of the first service to the UE via unicast transmission. Correspondingly, the UE receives the service data packet of the first service from the AS via the unicast transmission.

[0367] The use of unicast transmission can be manifested by using a unicast transmission channel to transmit service data. Specifically, when using unicast transmission, the AS can send the service data packets of the first service to the UE through the unicast transmission channel. Optionally, the unicast transmission channel includes at least one of the following: a transmission channel corresponding to a 5G unicast session, and a transmission channel corresponding to a 4G unicast bearer.

[0368] In some possible implementations, the AS can send the service data packets of the first service to the UE through the transmission channel corresponding to the 5G unicast session.

[0369] Figure 4 The implementation is illustrated below. Specifically, the AS can send the service data packet of the first service to the unicast UPF through the transmission channel between the AS and the unicast UPF; the unicast UPF can send the service data packet of the first service to the UE through the transmission channel between the unicast UPF corresponding to the 5G unicast session and the AN device, and the transmission channel between the AN device corresponding to the 5G unicast session and the UE. For details of this implementation, please refer to S303, which will not be repeated here.

[0370] In this implementation, before the UE disconnects from the 5G mobile communication system, the AS can switch the transmission mode of the service data packets for the UE's first service to unicast transmission mode. Thus, when the UE switches from the 5G mobile communication system to the 4G mobile communication system, the traditional method for switching from the 5G mobile communication system to the 4G mobile communication system can be used. The UE's first service transmission will not be affected during the cross-communication system handover process. That is, when the UE meets the conditions for cross-communication system handover, the AS switches the transmission mode of the UE's corresponding first service from shared or independent transmission mode to unicast transmission mode, avoiding service transmission discontinuity caused by limitations such as the multicast support capability of the target communication system. This maintains the continuity of service transmission and, consequently, the continuity of application layer services.

[0371] In some other possible implementations, the AS can send the service data packets of the first service to the UE through the corresponding transmission channel of the 4G unicast bearer. For details, please refer to S303, which will not be repeated here.

[0372] This application provides a communication method in which the AS (Automatic Service Provider) sends service data packets of the first service to the UE (User Equipment) via a 5G multicast session. When the handover conditions for the UE to switch from a 5G mobile communication system to a 4G mobile communication system are met, the UE can trigger the AS to send the service data packets of the first service to the UE via unicast transmission by sending the first information. Thus, the transmission of the UE's first service is not affected during the UE's cross-communication system handover process. That is, when the UE meets the cross-communication system handover conditions, the AS switches the transmission mode of the UE's corresponding first service from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding discontinuous service transmission due to limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0373] This application also provides a communication method. This method can be applied to... Figure 1 or Figure 2 In the communication system shown, in this method, when a terminal device performs a cross-communication system handover, the terminal device can send first information to the AS according to an instruction from a Session Management Network (SMF). After receiving the first information, the AS can send service data packets to the terminal device via unicast transmission. See below. Figure 5 The flowchart shown illustrates an embodiment of this application, using a handover between 5G and 4G mobile communication systems as an example. For ease of description, the terminal device is UE as an example below.

[0374] S501: The first UE receives a service data packet for the first service from the AS via a 5G multicast session. Correspondingly, the AS sends the service data packet for the first service to the first UE via the 5G multicast session.

[0375] For details on S501, please refer to S401; it will not be repeated here.

[0376] S502: When the first UE switches from a 5G mobile communication system to a 4G mobile communication system, the AMF sends a PDU session update session management context request (Nsmf_PDUsession_updateSMcontext request) to the SMF. Correspondingly, the SMF receives the PDU session update session management context request from the AMF.

[0377] The PDU session update session management context request may include a second indication. This second indication may indicate that when the first UE switches from the 5G mobile communication system to the 4G mobile communication system, the multicast session is rejected by the 4G mobile communication system (e.g., the multicast session is rejected by the AN device of the 4G mobile communication system). The specific content of the second indication can be found in S302, and will not be repeated here.

[0378] Optionally, before the AMF sends the session context update request to the SMF, the AMF determines, based on the first message from the MME, that the multicast session has been rejected by the 4G mobile communication system.

[0379] For example, when the first message contains indication information of a session rejected by the 4G mobile communication system, and the session rejected by the 4G mobile communication system includes the multicast session of the first UE, the AMF can determine that the multicast session of the first UE is rejected by the 4G mobile communication system.

[0380] For example, when the first message contains indication information of a session accepted by the 4G mobile communication system, and the session accepted by the 4G mobile communication system does not include the multicast session, the AMF can determine that the multicast session is rejected by the 4G mobile communication system.

[0381] For example, when the first message contains indication information of the QoS flow of a session rejected by the 4G mobile communication system, and the QoS flow of the session rejected by the 4G mobile communication system includes the QoS flow of the first UE's multicast session, the AMF can determine that the first UE's multicast session has been rejected by the 4G mobile communication system.

[0382] For example, when the first message contains indication information of the QoS flow of a session accepted by the 4G mobile communication system, and the QoS flow of the session accepted by the 4G mobile communication system does not contain the QoS flow of the multicast session, the AMF can determine that the multicast session is rejected by the 4G mobile communication system.

[0383] Optionally, the PDU session update session management context request may further include at least one of the following: N2 SM information from the AN device of the 4G mobile communication system, and N2 SM information from the AN device of the 5G mobile communication system.

[0384] S503: The SMF determines, according to the second instruction, to remove the first UE from the multicast session.

[0385] When the SMF determines, according to the second instruction, that the multicast session has been rejected by the 4G mobile communication system, the SMF determines that the first UE needs to be removed from the multicast session. The method by which the SMF determines that the multicast session has been rejected by the 4G mobile communication system can be found in S302, and will not be repeated here.

[0386] After the SMF determines that the first UE needs to be removed from the multicast session, the first UE can be removed from the multicast session via S504-S508, S511-S514.

[0387] S504: The SMF sends an MBS session notification request (MBS_session_notificationrRequest) to the AMF. Correspondingly, the AMF receives the MBS session notification request from the SMF.

[0388] The MBS session notification request may include at least one of the following: indication information of the first UE (e.g., the identifier of the first UE) and identification information of the multicast session (e.g., TMGI).

[0389] S505: The AMF sends an MBS session notification response to the SMF. Correspondingly, the SMF receives the MBS session notification response from the AMF.

[0390] S506: The SMF sends an N1N2 message transfer (Namf_Communicate_N1N2MessageTransfer) message to the AMF. Correspondingly, the AMF receives the N1N2 message transfer message from the SMF.

[0391] The N1N2 message transfer message can be invoked by the SMF for the first UE.

[0392] Optionally, the N1N2 message transfer message includes at least one of the following: an N1 SM container and N2 SM information. The N1 SM container may indicate the release of the multicast session (e.g., releasing the MBS session); the N2 SM information may indicate that the AN device of the 5G mobile communication system (i.e., the source AN device of the first UE) removes the first UE from the multicast session.

[0393] S507: The AMF sends an N2 request to the AN device. Correspondingly, the AN device receives the N2 request from the AMF.

[0394] Optionally, the N2 request includes the N2 SM information. The AN device can remove the first UE from the multicast session based on the N2 SM information; that is, the AN device removes the first UE from the multicast session after receiving the N2 SM information.

[0395] Optionally, the N2 request may also include the N1 SM container.

[0396] S508: The AN device sends a PDU session modification command to the first UE. Correspondingly, the first UE receives the PDU session modification command from the AN device.

[0397] The PDU session modification command may include the N1 SM container.

[0398] S509: The first UE sends the first information to the AS.

[0399] The first UE can send the first information to the AS after determining that the multicast session has been released based on the N1 SM container. Specifically, the first UE can determine that the multicast session has been released upon receiving the N1 SM container; then, the first UE can send the first information to the AS.

[0400] The first UE can send the first information to the AS through a client on the first UE.

[0401] Optionally, the specific content of the first information is as described in S302, and the method by which the first UE sends the first information to the AS is as described in S302, which will not be repeated here.

[0402] In addition, the first information may include, but is not limited to, at least one of the following: indication information of the first UE (e.g., the identifier of the first UE) and identification information of the multicast session (e.g., TMGI).

[0403] S510: AS determines, based on the first information, whether to send the service data packet of the first service to the first UE via unicast transmission.

[0404] For details on S510, please refer to S404; it will not be repeated here.

[0405] S511: The AN device executes the resource modification process.

[0406] Specifically, when the AN device determines that there is no joined UE among the UEs accessing the AN device, the AN device can release the resources of the multicast session. Specifically, the AN device can release the radio resources corresponding to the 5G multicast session between the AN device and the UE.

[0407] S512: The AN device initiates a downlink tunnel release procedure (DL tunnel release).

[0408] When the AN device determines that there is no UE among the UEs connected to the AN device that has joined the multicast session, it can initiate a downlink tunnel release procedure for the multicast session.

[0409] For example, when the AN device exclusively uses the transmission channel (or transmission tunnel) between the AN device and the MB-UPF, the AN device can initiate a downlink tunnel release procedure from the AN device to the MB-UPF to release the transmission channel between the AN device and the MB-UPF for the multicast session.

[0410] For example, when the AN device shares the transmission channel (or transmission tunnel) between the AN device and the MB-UPF with other AN devices through a multicast tree, the AN device can leave the multicast tree corresponding to the multicast session by initiating a downlink tunnel release procedure from the AN device to the MB-UPF.

[0411] S513: The AN device sends an N2 response to the AMF. Correspondingly, the AMF receives the N2 response from the AN device.

[0412] Optionally, when there is no UE among the UEs managed by the AMF that has joined the multicast session, the AMF deletes the context of the multicast session after receiving the N2 response.

[0413] S514: The AMF sends a PDU session update SM context (Nsmf_PDU session_updateSM context) message to the SMF. Correspondingly, the SMF receives the PDU session update SM context message from the AMF.

[0414] The PDU session update SM context message may include the N2 response.

[0415] Optionally, after receiving the PDU session update SM context message, the SMF removes the first UE from the multicast session.

[0416] Optionally, when there are no UEs in the UEs managed by the SMF that have joined the multicast session, the SMF deletes the context of the multicast session after receiving the PDU session update SM context message.

[0417] S515: The AS sends service data packets to the first UE via unicast transmission. Correspondingly, the first UE receives service data packets for the first service from the AS via the unicast transmission.

[0418] For details on S515, please refer to S405, which will not be repeated here. The following only explains the differences from S405.

[0419] When the AS sends the service data packet of the first service to the first UE through a 5G unicast session, the UE can switch over based on the traditional handover process from the 5G mobile communication system to the 4G mobile communication system. For example, the AN device accessed by the first UE can initiate the handover process from the 5G mobile communication system to the 4G mobile communication system for the 5G unicast session.

[0420] This application provides a communication method in which the AS sends service data packets of a first service to the first UE via a 5G multicast session. When the first UE receives an instruction to release the multicast session, the first UE can trigger the AS to send the service data packets of the first service to the first UE via unicast transmission by sending the first information. Thus, the transmission of the first service of the first UE will not be affected during the cross-communication system handover process of the first UE. That is, during the cross-communication system handover process of the first UE, the AS switches the transmission mode of the first service corresponding to the first UE from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding discontinuous service transmission due to limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0421] This application provides a communication method. This method can be applied to... Figure 1 or Figure 2 In the communication system shown, in this method, when a terminal device performs a cross-communication system handover, the terminal device can send first information to the AS according to the handover command. After receiving the first information, the AS can send service data packets to the terminal device via unicast transmission. See below. Figure 6 The flowchart shown illustrates an embodiment of this application, using a handover between 5G and 4G mobile communication systems as an example. For ease of description, the terminal device is UE as an example below.

[0422] S601: The UE receives a service data packet for the first service from the AS via a 5G multicast session. Correspondingly, the AS sends the service data packet for the first service to the UE via the 5G multicast session.

[0423] For details on S601, please refer to S401; it will not be repeated here.

[0424] S602: The AN device to which the UE accesses (i.e., the source AN device) receives a first handover command from the AMF. Accordingly, the AMF sends the first handover command to the source AN device.

[0425] The AMF can send the first handover command to the source AN device when the UE switches from the 5G mobile communication system to the 4G mobile communication system. The source AN device can be an AN device within the 5G mobile communication system.

[0426] Optionally, the first switching command includes at least one of the following: a pass-through container, data forwarding tunnel information, information on the QoS flow to be forwarded, and bearer information of the 4G mobile communication system.

[0427] The following example illustrates the parameters included in the first switching command.

[0428] For example, the transparent transmission container may contain access information of the 4G mobile communication system. The access information of the 4G mobile communication system may include: the identifier of the target AN device in the 4G mobile communication system.

[0429] For example, the data forwarding tunnel information may include a tunnel identifier between the source AN device and the target AN device used to forward the UE's service data packets. The source AN device can forward the UE's service data packets to the target AN device according to the data forwarding tunnel information. Specifically, the source AN device sends the UE's service data packets to the target AN device through the tunnel corresponding to the tunnel identifier.

[0430] For example, the information of the QoS flow to be forwarded can be the identifier of the QoS flow to be forwarded. When the QoS flow to be forwarded does not include the QoS flow of the multicast session, the multicast session is rejected by the 4G mobile communication system.

[0431] For example, the bearer information of the 4G mobile communication system can be an EPS bearer ID. When the bearer information of the 4G mobile communication system does not include a bearer corresponding to the multicast session, the multicast session is rejected by the 4G mobile communication system.

[0432] S603: The source AN device sends a second handover command to the UE. Correspondingly, the UE receives the second handover command from the source AN device.

[0433] The content of the first switching command and the content of the second switching command may be the same or different.

[0434] Optionally, the second switching command may include at least one of the following: access information of the 4G mobile communication system, information of the QoS flow to be forwarded, and bearer information of the 4G mobile communication system.

[0435] S604: After the UE determines that the multicast session has been rejected by the 4G mobile communication system according to the second handover command, the UE sends the first information to the AS.

[0436] Optionally, the UE determines that the multicast session is rejected by the 4G mobile communication system based on the QoS flow information to be forwarded in the second handover command or the bearer information of the 4G mobile communication system. The determination method can be found in S302, and will not be repeated here.

[0437] Optionally, the UE sends the first information to the AS when the UE switches from the 5G mobile communication system to the 4G mobile communication system. Alternatively, the UE sends the first information to the AS after the UE switches from the 5G mobile communication system to the 4G mobile communication system.

[0438] For details of S604, please refer to S302; it will not be repeated here.

[0439] S605: The UE sends a handover confirmation to the target AN device in the 4G mobile communication system.

[0440] Optionally, the UE sends the handover confirmation to the target device based on the access information of the 4G mobile communication system in the second handover command, so as to access the target AN device.

[0441] For example, when the access information of the 4G mobile communication system contains information for indicating the target AN device (e.g., the identifier of the target AN device), the UE determines the target AN device based on the information for indicating the target AN device and sends the handover confirmation to the target AN device.

[0442] For example, when the access information of the 4G mobile communication system contains information indicating resources for accessing the target AN device, the UE sends the handover request to the target AN device on the resources.

[0443] S606: AS determines, based on the first information, whether to send the service data packet of the first service to the UE via unicast transmission.

[0444] For details on S606, please refer to S404; it will not be repeated here.

[0445] S607: The AS sends the service data packet of the first service to the UE via unicast transmission. Correspondingly, the UE receives the service data packet of the first service from the AS via the unicast transmission.

[0446] For details on S607, please refer to S405; it will not be repeated here.

[0447] It should be noted that this application does not restrict the execution order of any step S604, S606, and S607, or S605. For example, S604 can be executed first, followed by S605; or S605 can be executed first, followed by S604; or S605 can be executed first, followed by S606; or S606 can be executed first, followed by S605; or S605 can be executed first, followed by S607; or S607 can be executed first, followed by S605.

[0448] This application provides a communication method in which an AS receives service data packets of a first service from a UE via a 5G multicast session. When the UE receives a second handover command, the UE can trigger the AS to send the service data packets of the first service to the UE via unicast transmission by sending first information according to the second handover command. In this way, the transmission of the UE's first service will not be affected during the UE's cross-communication system handover process. That is, during the cross-communication system handover process of the terminal device, the AS switches the transmission mode of the first service corresponding to the terminal device from shared transmission mode or independent transmission mode to unicast transmission mode, avoiding discontinuous service transmission due to limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0449] Based on the same technical concept, this application also provides a communication device, the structure of which is as follows: Figure 7 As shown, it includes a communication unit 701 and a processing unit 702. The communication device 700 can be applied to... Figure 1 The terminal equipment or SMF in the communication system shown, or applied to Figure 2 The terminal device, AS, or SMF in the communication system shown can implement the communication methods provided in the embodiments and examples of this application. The functions of each unit in the device 700 are described below.

[0450] The communication unit 701 is used to receive and send data.

[0451] When the communication device 700 is applied to the terminal device (in a scenario where the AS interacts with the terminal device), the AS, or the SMF, the communication unit 701 can be implemented through a physical interface, a communication module, a communication interface, or an input / output interface. The communication device 700 can connect to a network cable or electrical cable through this communication unit to establish a physical connection with other devices.

[0452] When the communication device 700 is applied to the terminal device (in a scenario where the AN device interacts with the terminal device), the communication unit 701 can be implemented by a transceiver, for example, a mobile communication module.

[0453] The mobile communication module can provide solutions for wireless communication applications, including 2G / 3G / 4G / 5G, on the terminal device. The mobile communication module may include at least one antenna, at least one filter, a switch, a power amplifier, a low-noise amplifier (LNA), etc. The terminal device can access and interact with the AN device in the AN through the mobile communication module; the AN device can also communicate with the accessed terminal device through the mobile communication module.

[0454] In one embodiment, the communication device 700 is applied to Figure 3 , Figure 4 , Figure 5 or Figure 6 The terminal device shown in the embodiments of this application (e.g., Figure 3 Terminal equipment, Figure 4 and 6 UE, Figure 5 (The first UE). The specific functions of the processing unit 702 in this embodiment will be described below.

[0455] The processing unit 702 is configured to: receive service data packets of a first service from an application server AS through a multicast session of a first mobile communication system via the communication unit 701; and send first information to the AS through the communication unit 701 when the handover conditions for the terminal device to switch from the first mobile communication system to the second mobile communication system are met, or when the terminal device switches from the first mobile communication system to the second mobile communication system, wherein the first information is used to trigger the AS to send the service data packets of the first service to the terminal device via unicast transmission.

[0456] Optionally, the processing unit 702 is specifically configured to: after sending the first information to the AS, receive the service data packet of the first service from the AS through the communication unit 701 via the unicast transmission method.

[0457] Optionally, the processing unit 702 is specifically configured to: receive service data packets of the first service from the AS through the unicast transmission channel of the first mobile communication system via the communication unit 701; and / or, receive service data packets of the first service from the AS through the unicast transmission channel of the second mobile communication system via the communication unit 701.

[0458] Optionally, the switching conditions include at least one or a combination of the following:

[0459] The signal quality of the first mobile communication system is less than a first threshold.

[0460] The signal quality of the second mobile communication system is greater than the second threshold;

[0461] The signal quality of the second mobile communication system is greater than that of the first mobile communication system;

[0462] The terminal device is located within the coverage area of ​​the second mobile communication system; or,

[0463] The terminal device moves from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system.

[0464] Optionally, the first information includes at least one of the following:

[0465] Information used to instruct the terminal device to prepare for a handover from the first mobile communication system to the second mobile communication system;

[0466] Information used to instruct the terminal device to prepare for switching to the second mobile communication system;

[0467] Information used to instruct the terminal device to switch from the first mobile communication system to the second mobile communication system;

[0468] Information used to instruct the terminal device to switch to the second mobile communication system;

[0469] Information used to indicate that the terminal device is within the coverage area of ​​the second mobile communication system;

[0470] Information used to indicate that the terminal device moves from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system;

[0471] Information used to indicate that the signal quality of the first mobile communication system is less than a first threshold;

[0472] Information used to indicate that the signal quality of the second mobile communication system is greater than a second threshold;

[0473] Information used to indicate that the signal quality of the second mobile communication system is greater than that of the first mobile communication system;

[0474] Information used to indicate that the terminal device is about to leave the multicast session;

[0475] Information used to indicate that the terminal device will attach to or has already attached to the second mobile communication system; or,

[0476] Information used to request the AS to send the service data packet of the first service to the terminal device via unicast transmission.

[0477] Optionally, the processing unit 702 is specifically used for:

[0478] The communication unit 701 receives a first instruction from the session management network element of the first mobile communication system; wherein the first instruction is used to indicate that the multicast session is released;

[0479] According to the first instruction, the first information is sent to the AS through the communication unit 701; wherein the first information includes at least one of the following: information indicating that the terminal device has left the multicast session, information indicating that the terminal device has been removed from the multicast session, information indicating that the multicast session has been released, or information indicating that the terminal device cannot receive the service data packets of the first service through the multicast session.

[0480] Optionally, the processing unit 702 is specifically configured to: send the first information to the AS via the communication unit 701 according to the first instruction when at least one of the following conditions is met:

[0481] The multicast session is not a local multicast session; or...

[0482] The multicast session is a local multicast session, and the terminal device is located within the service area of ​​the local multicast session.

[0483] Optionally, the processing unit 702 is specifically used for:

[0484] The communication unit 701 receives a handover command from the first mobile communication system; wherein the handover command is used to instruct the terminal device to switch to the second mobile communication system;

[0485] Based on the switching command, it is determined that the multicast session was rejected by the second mobile communication system;

[0486] The first information is sent to the AS through the communication unit 701.

[0487] Optionally, the first information includes at least one of the following:

[0488] Information used to instruct the terminal device to switch from the first mobile communication system to the second mobile communication system;

[0489] Information used to instruct the terminal device to switch to the second mobile communication system;

[0490] Information used to indicate that the terminal device has switched from the first mobile communication system to the second mobile communication system;

[0491] Information used to indicate that the terminal device has switched to the second mobile communication system;

[0492] Information used to indicate that the terminal device has been attached to the second mobile communication system;

[0493] Information used to indicate that the terminal device is within the coverage area of ​​the second mobile communication system;

[0494] Information used to indicate that the terminal device moves from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system;

[0495] Information used to indicate that the terminal device has left the multicast session;

[0496] Information used to indicate that the terminal device has been removed from the multicast session;

[0497] Information used to indicate that the multicast session has been released; or,

[0498] Information used to indicate that the terminal device cannot receive service data packets of the first service through the multicast session.

[0499] Optionally, the first mobile communication system is a mobile communication system using a first RAT, and the second mobile communication system is a mobile communication system using a second RAT.

[0500] In one embodiment, the communication device 700 is applied to Figure 3 , Figure 4 , Figure 5 or Figure 6 In the AS shown in the embodiment of this application, the specific functions of the processing unit 702 in this embodiment will be described below.

[0501] The processing unit 702 is configured to: send a service data packet of a first service to a terminal device through a multicast session of a first mobile communication system via the communication unit 701; receive first information from the terminal device via the communication unit 701; wherein the first information is used to trigger the AS to send the service data packet of the first service to the terminal device via unicast transmission; and send the service data packet of the first service to the terminal device via unicast transmission according to the first information via the communication unit 701.

[0502] Optionally, the first information includes at least one of the following:

[0503] Information used to instruct the terminal device to prepare for a handover from the first mobile communication system to the second mobile communication system;

[0504] Information used to instruct the terminal device to prepare for handover to the second mobile communication system;

[0505] Information used to instruct the terminal device to switch from the first mobile communication system to the second mobile communication system;

[0506] Information used to instruct the terminal device to switch to the second mobile communication system;

[0507] Information used to indicate that the terminal device has switched from the first mobile communication system to the second mobile communication system;

[0508] Information used to indicate that the terminal device has switched to the second mobile communication system;

[0509] Information used to indicate that the terminal device is within the coverage area of ​​the second mobile communication system;

[0510] Information used to indicate that the terminal device moves from the coverage area of ​​the first mobile communication system to the coverage area of ​​the second mobile communication system;

[0511] Information used to indicate that the signal quality of the first mobile communication system is less than a first threshold;

[0512] Information used to indicate that the signal quality of the second mobile communication system is greater than a second threshold;

[0513] Information used to indicate that the signal quality of the second mobile communication system is greater than that of the first mobile communication system;

[0514] Information used to indicate that the terminal device is about to leave the multicast session;

[0515] Information used to indicate that the terminal device has left the multicast session;

[0516] Information used to indicate that the terminal device has been removed from the multicast session;

[0517] Information used to indicate that the terminal device will attach to or has already attached to the second mobile communication system;

[0518] Information used to indicate that the terminal device cannot receive service data packets of the first service through a multicast session; or...

[0519] Information used to request the AS to send the service data packet of the first service to the terminal device via unicast transmission.

[0520] Optionally, the processing unit 702 is specifically configured to: send the service data packet of the first service to the terminal device through the unicast transmission channel of the first mobile communication system via the communication unit 701; and / or send the service data packet of the first service to the terminal device through the unicast transmission channel of the second mobile communication system via the communication unit 701.

[0521] Optionally, the first mobile communication system is a mobile communication system using a first RAT, and the second mobile communication system is a mobile communication system using a second RAT.

[0522] Optionally, the processing unit 702 is specifically configured to: after receiving the first information, send the service data packet of the first service to the terminal device via the unicast transmission method through the communication unit 701 when at least one of the following conditions is met:

[0523] Mobile communication systems using the second RAT do not support broadcast transmission.

[0524] The terminal device is not within the broadcast area of ​​the mobile communication system using the second RAT corresponding to the first service;

[0525] The terminal device does not support broadcasting the second RAT; or,

[0526] The multicast session does not support handover from a mobile communication system using the first RAT to a mobile communication system using the second RAT.

[0527] In one embodiment, the communication device 700 is applied to Figure 5 The SMF shown in this embodiment of the application is described below. The specific functions of the processing unit 702 in this embodiment will be described in detail below.

[0528] The processing unit 702 is configured to: receive a second instruction from a mobility management network element in the first mobile communication system via the communication unit 701, wherein the second instruction is configured to instruct the terminal device that its multicast session is rejected by the second mobile communication system when the terminal device switches from the first mobile communication system to the second mobile communication system; and remove the terminal device from the multicast session according to the second instruction.

[0529] Optionally, the processing unit 702 is specifically used to: send a first indication to the terminal device through the communication unit 701, the first indication being used to indicate that the multicast session is released.

[0530] Optionally, the second indication includes: information indicating that the multicast session is rejected by the second mobile communication system, or information indicating that the Quality of Service (QoS) stream of the multicast session is rejected by the second mobile communication system.

[0531] Optionally, the first mobile communication system is a mobile communication system using a first RAT, and the second mobile communication system is a mobile communication system using a second RAT.

[0532] It should be noted that the module division in the above embodiments of this application is illustrative and only represents one logical functional division. In actual implementation, there may be other division methods. Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, exist as separate physical entities, or have two or more units integrated into one unit. The integrated units described above can be implemented in hardware or as software functional units.

[0533] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0534] Based on the same technical concept, this application also provides a communication device, which can be applied to, for example... Figure 1 The terminal equipment or SMF in the communication system shown, or applied to Figure 2 The terminal equipment, AS, or SMF in the communication system shown can implement the communication methods provided in the embodiments and examples of this application, and have... Figure 7 The function of the communication device shown. (See also...) Figure 8 As shown, the communication device 800 includes a communication module 801, a processor 802, and a memory 803. The communication module 801, the processor 802, and the memory 803 are interconnected.

[0535] Optionally, the communication module 801, the processor 802, and the memory 803 are interconnected via a bus 804. The bus 804 can be a peripheral component interconnect (PCI) bus or an extended industry standard architecture (EISA) bus, etc. The bus can be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Figure 8 The bus is represented by a single thick line, but this does not mean that there is only one bus or one type of bus.

[0536] The communication module 801 is used to receive and send data, enabling communication and interaction with other devices. For example, when the communication device 800 is applied to the terminal device (in a scenario where the AS interacts with the terminal device), the AS, or the SMF, the communication module 801 can be implemented through a physical interface, a communication module, a communication interface, or an input / output interface. As another example, when the communication device 800 is applied to the terminal device (in a scenario where the AN device interacts with the terminal device), the communication module 801 can also be implemented through a transceiver.

[0537] In one embodiment, the communication device 800 is applied to Figure 3 , Figure 4 , Figure 5 or Figure 6 The terminal device shown in the embodiments of this application (e.g., Figure 3 Terminal equipment, Figure 4 and 6 UE, Figure 5 The first UE). The processor 802 is specifically used for:

[0538] The communication module 801 receives service data packets of the first service from the application server AS through a multicast session of the first mobile communication system; when the handover conditions for the terminal device to switch from the first mobile communication system to the second mobile communication system are met, or when the terminal device switches from the first mobile communication system to the second mobile communication system, the communication module 801 sends first information to the AS, wherein the first information is used to trigger the AS to send the service data packets of the first service to the terminal device through unicast transmission.

[0539] In one embodiment, the communication device 800 is applied to Figure 3 , Figure 4 , Figure 5 or Figure 6In the AS shown in the embodiment of this application, the processor 802 is specifically used for:

[0540] The communication module 801 sends a service data packet of the first service to the terminal device through a multicast session of the first mobile communication system; the communication module 801 receives first information from the terminal device; wherein the first information is used to trigger the AS to send the service data packet of the first service to the terminal device through unicast transmission; according to the first information, the communication module 801 sends the service data packet of the first service to the terminal device through unicast transmission.

[0541] In one embodiment, the communication device 800 is applied to Figure 5 In the SMF shown in the embodiment of this application, the processor 802 is specifically used for:

[0542] The communication module 801 receives a second instruction from a mobility management network element in the first mobile communication system. The second instruction is used to instruct the terminal device that its multicast session is rejected by the second mobile communication system when it switches from the first mobile communication system to the second mobile communication system. According to the second instruction, the terminal device is removed from the multicast session.

[0543] The specific functions of the processor 802 can be found in the descriptions of the communication methods provided in the embodiments and examples of this application above. Figure 7 The specific functional description of the communication device 700 in the embodiments of this application is shown below and will not be repeated here.

[0544] The memory 803 is used to store program instructions and data. Specifically, the program instructions may include program code, which includes computer operation instructions. The memory 803 may include random access memory (RAM) and may also include non-volatile memory, such as at least one disk storage device. The processor 802 executes the program instructions stored in the memory 803 and uses the data stored in the memory 803 to implement the above functions, thereby realizing the communication method provided in the embodiments of this application.

[0545] It is understood that this application Figure 8The memory 803 can be volatile memory or non-volatile memory, or may include both. The non-volatile memory can 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 can be random access memory (RAM), which is used as an external cache. By way of example, but not limitation, many forms of RAM are available, such as Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM), Synchronous DRAM (SDRAM), Double Data Rate SDRAM (DDR SDRAM), Enhanced Synchronous DRAM (ESDRAM), Synchlink DRAM (SLDRAM), and Direct Rambus RAM (DR RAM). It should be noted that the memory used in the systems and methods described herein is intended to include, but is not limited to, these and any other suitable types of memory.

[0546] Based on the above embodiments, this application also provides a computer program that, when run on a computer, causes the computer to execute the communication method provided in the above embodiments.

[0547] Based on the above embodiments, this application also provides a computer-readable storage medium storing a computer program, which, when executed by a computer, causes the computer to perform the communication method provided in the above embodiments.

[0548] The storage medium can be any available medium that a computer can access. For example, but not limited to, a computer-readable medium can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage media or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer.

[0549] Based on the above embodiments, this application also provides a chip for reading computer programs stored in a memory and implementing the communication method provided in the above embodiments.

[0550] Based on the above embodiments, this application provides a chip system including a processor for supporting a computer device in implementing the functions involved in the service equipment, forwarding equipment, or site equipment in the above embodiments. In one possible design, the chip system further includes a memory for storing necessary programs and data of the computer device. This chip system may be composed of chips or may include chips and other discrete components.

[0551] In summary, this application provides a communication method, apparatus, and device. In this method, an AS (Automatic System) sends service data packets of a first service to a terminal device through a multicast session in a first mobile communication system. When the conditions for the terminal device to perform a cross-communication system handover are met, or when the terminal device performs a cross-communication system handover, the terminal device can trigger the AS to send the service data packets of the first service to the terminal device via unicast transmission by sending first information. Thus, the transmission of the first service of the terminal device is not affected during the cross-communication system handover process. That is, when the conditions for the cross-communication system handover are met or during the cross-communication system handover process, the AS switches the transmission mode of the first service corresponding to the terminal device from a shared transmission mode or an independent transmission mode to a unicast transmission mode, avoiding discontinuous service transmission due to limitations such as the multicast support capability of the target communication system, thereby ensuring the continuity of service transmission.

[0552] In the various embodiments of this application, unless otherwise specified or in case of logical conflict, the terminology and / or descriptions of different embodiments are consistent and can be referenced by each other. The technical features of different embodiments can be combined to form new embodiments according to their inherent logical relationship.

[0553] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0554] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to this application. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0555] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0556] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0557] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A communication method, characterized in that, The method includes: (The method is applied to a terminal device or a chip in a terminal device.) Receive service data packets from the first service of the application server AS through a multicast session of the first mobile communication system. When the terminal device switches from the first mobile communication system to the second mobile communication system, it sends first information to the AS. The first information includes information indicating that the terminal device has switched from the first mobile communication system to the second mobile communication system. The first information is also used to trigger the AS to send the service data packet of the first service to the terminal device via unicast transmission. The first mobile communication system is a mobile communication system using a first radio access technology (RAT), and the second mobile communication system is a mobile communication system using a second RAT. After sending the first information to the AS, the service data packet of the first service from the AS is received through the unicast transmission channel of the second mobile communication system.

2. The method according to claim 1, characterized in that, The method further includes: Receive a first instruction from the session management network element of the first mobile communication system; wherein the first instruction is used to indicate that the multicast session is released; Sending first information to the AS includes: According to the first instruction, the first information is sent to the AS; wherein the first information includes at least one of the following: information indicating that the terminal device has left the multicast session, information indicating that the terminal device has been removed from the multicast session, information indicating that the multicast session has been released, or information indicating that the terminal device cannot receive the service data packets of the first service through the multicast session.

3. The method according to claim 2, characterized in that, Sending the first information to the AS according to the first instruction includes: The first information is sent to the AS according to the first instruction when at least one of the following conditions is met: The multicast session is not a local multicast session; or... The multicast session is a local multicast session, and the terminal device is located within the service area of ​​the local multicast session.

4. The method according to claim 1, characterized in that, When the terminal device switches from the first mobile communication system to the second mobile communication system, it sends first information to the AS, including: Receive a handover command from the first mobile communication system; wherein the handover command is used to instruct the terminal device to switch to the second mobile communication system; Based on the switching command, it is determined that the multicast session was rejected by the second mobile communication system; Send the first information to the AS.

5. A communication method, characterized in that, The method, which applies to a chip in an application server AS or AS, includes: The service data packets of the first service are sent to the terminal device through a multicast session of the first mobile communication system. The system receives first information from the terminal device; wherein the first information includes information indicating that the terminal device has switched from the first mobile communication system to the second mobile communication system, the first information is used to trigger the AS to send the service data packet of the first service to the terminal device via unicast transmission, and the first information is sent by the terminal device when the terminal device switches from the first mobile communication system to the second mobile communication system; wherein the first mobile communication system is a mobile communication system using a first radio access technology (RAT), and the second mobile communication system is a mobile communication system using a second RAT; Based on the first information, the service data packet of the first service is sent to the terminal device via unicast transmission; The step of sending the service data packet of the first service to the terminal device via unicast transmission includes: sending the service data packet of the first service to the terminal device via the unicast transmission channel of the second mobile communication system.

6. The method according to claim 5, characterized in that, The step of sending the service data packet of the first service to the terminal device via unicast transmission based on the first information includes: After receiving the first information, the service data packet of the first service is sent to the terminal device via the unicast transmission method when at least one of the following conditions is met: Mobile communication systems using the second RAT do not support broadcast transmission. The terminal device is not within the broadcast area of ​​the mobile communication system using the second RAT corresponding to the first service; The terminal device does not support broadcasting the second RAT; or, The multicast session does not support handover from a mobile communication system using the first RAT to a mobile communication system using the second RAT.

7. A communication device, applied to a terminal equipment, characterized in that, include: The communication unit is used to receive and send data; A processing unit is configured to execute the method as described in any one of claims 1-4 via the communication unit.

8. A communication device applied to an application server AS, characterized in that, include: The communication unit is used to receive and send data; A processing unit is configured to execute the method as described in any one of claims 5-6 via the communication unit.

9. A communication system, characterized in that, include: A terminal device for implementing the method as described in any one of claims 1-4; An application server AS is used to implement the method as described in any one of claims 5-6.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when run on a computer, causes the computer to perform the method described in any one of claims 1-6.

11. A chip, characterized in that, The chip is coupled to a memory, and the chip reads a computer program stored in the memory to execute the method described in any one of claims 1-6.

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