Communication methods, devices, and systems

Abstract

The present application relates to the field of communication technologies and provides a communication method, apparatus, and system for improving PC5 connection switching efficiency. In this method, when a remote device establishes a first relay connection to a first relay device by using a first PC5 connection mechanism, for example, a user plane-based mechanism or a control plane-based mechanism, and the remote device plans to switch the relay connection, the remote device can establish a second relay connection to a second relay device by preferentially reusing the connection mechanism used before the relay connection switching, i.e., the first PC5 connection mechanism, to improve PC5 connection switching efficiency, reduce switching delay, and ensure the continuity of the first service obtained by the remote device from the network.

Description

TECHNICAL FIELD

[0001] This application claims the priority of Chinese Patent Application No. 202211222296.2 entitled "COMMUNICATION METHOD, APPARATUS, AND SYSTEM" filed with the China National Intellectual Property Administration on October 8, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to the field of communications, and in particular, to a communication method, apparatus, and system. BACKGROUND ART

[0003] In a communication system, when a specific user equipment (UE) 1 is located outside network coverage, when the signal strength of communication between UE1 and a radio access network (RAN) device is weak, or when another UE is required to support data transmission, UE1 can obtain services from the network side with the assistance of another UE (e.g., UE2). For example, UE1 establishes a Proximity-based communication 5 (PC5) connection with UE2 via an air interface, communicates with the network side via the PC5 connection, and obtains services provided by the network. UE1 may be regarded as a remote UE. UE2 may be regarded as a relay UE. Communication between the remote UE and the network side via the relay UE may be regarded as ProSe relay communication.

[0004] A remote UE can establish a PC5 connection to a relay UE by using either a user plane (UP)-based mechanism or a control plane (CP)-based mechanism. The UP-based mechanism obtains the relay connection key via the network's user plane, while the CP-based mechanism obtains the relay connection key via the network's control plane. However, the remote UE can also switch PC5 connections, for example, establishing a PC5 connection to a new relay UE. In this case, how to improve switching efficiency is a hot topic of current research. [Overview of the Initiative] [Means for solving the problem]

[0005] The present invention provides a communication method, apparatus, and system that improves PC5 connection switching efficiency.

[0006] To achieve the above objectives, the following technical solutions are applied in this application.

[0007] According to a first aspect, a communication method is provided. The method of the present invention includes a remote device determining priority information for a first relay service identifier when a first relay connection needs to be switched, and establishing a second relay connection to a second relay device by using a first PC5 connection mechanism based on the priority information for the first relay service identifier. The priority information for the first relay service identifier indicates that the first PC5 connection mechanism indicated by the first relay service identifier should be used preferentially. The first PC5 connection mechanism is a mechanism used by the remote device to establish a first relay connection to a first relay device. The first relay connection is used by the remote device to obtain a first service of the network via the first relay device. The second relay connection is used by the remote device to obtain a first service of the network via the second relay device.

[0008] According to the method in the first embodiment, when a remote device has established a first relay connection to a first relay device by using a first PC5 connection mechanism, for example, a user plane-based mechanism or a control plane-based mechanism, and the remote device intends to switch the relay connection, the remote device can establish a second relay connection to a second relay device by preferentially reusing the connection mechanism used before the relay connection switch, i.e., the first PC5 connection mechanism, thereby improving PC5 connection switching efficiency, reducing switching delay, and ensuring the continuity of the first service obtained from the network by the remote device.

[0009] In a possible design solution, the remote device establishing a second relay connection to a second relay device by using a first PC5 connection mechanism based on priority information of a first relay service identifier includes determining that the remote device will establish a relay connection to a second relay device by using a first PC5 connection mechanism based on priority information of a first relay service identifier, specifically by discovering a second relay device that supports the first PC5 connection mechanism and ensuring that the remote device can establish a second relay connection to the second relay device by using the first PC5 connection mechanism.

[0010] Optionally, a remote device deciding to establish a relay connection to a second relay device by using a first PC5 connection mechanism based on priority information of a first relay service identifier includes the remote device broadcasting the first relay service identifier to receive the relay service identifier of at least one relay device, the relay service identifier of at least one relay device including a relay service identifier indicating the first PC5 connection mechanism. In this way, the remote device decides to establish a relay connection to a second relay device among at least one relay device by using the first PC5 connection mechanism based on priority information of the first relay service identifier. The second relay device is a relay device corresponding to a relay service identifier indicating the first PC5 connection mechanism. It may be found that the remote device may actively broadcast the relay service identifier to increase the relay discovery probability and discover relay devices that support the first PC5 connection mechanism, such as the second relay device.

[0011] Alternatively, and optionally, a remote device deciding to establish a relay connection to a second relay device by using a first PC5 connection mechanism based on priority information of a first relay service identifier includes the remote device receiving a relay service identifier for at least one relay device, the relay service identifier for at least one relay device including a relay service identifier indicating the first PC5 connection mechanism. In this way, the remote device decides to establish a relay connection to a second relay device among at least one relay device by using the first PC5 connection mechanism based on priority information of the first relay service identifier. The second relay device is the relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism. It may be found that the remote device may alternatively and passively receive the relay service identifier to discover a relay device, e.g., a second relay device supporting the first PC5 connection mechanism, and avoid the communication overhead caused by actively broadcasting the relay service identifier.

[0012] In a possible design solution, the remote device determining the priority information for a first relay service identifier includes determining the priority information for a first relay service identifier based on first directive information from a policy-controlled network element, where the first directive information indicates establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover. In other words, in addition to establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover by default, the remote device may, alternatively and flexibly, decide whether to establish a relay connection by preferentially using the connection mechanism used before the relay connection switchover based on directives from a policy-controlled network element to meet the relay switching requirements of different services.

[0013] In a possible design solution, the remote device determines the priority information of a first relay service identifier, which includes determining the priority information of a first relay service identifier based on second instruction information from the relay server, where the second instruction information indicates establishing a relay connection by preferentially using the first PC5 connection mechanism. In other words, in addition to establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover by default, the remote device can flexibly alternatively decide, based on the relay server's instruction, whether to establish a relay connection by preferentially using the first PC5 connection mechanism, thereby achieving applicability to different switching scenarios.

[0014] Optionally, the method according to the first embodiment may further include the remote device sending a relay reselection request message to the relay server, the relay reselection request message indicating that the connection mechanism used before the relay connection switchover was the first PC5 connection mechanism. The remote device receives a relay reselection response message returned by the relay server in response to the relay reselection request message, the relay reselection response message carrying second instruction information. In other words, the remote device can obtain instructions from the relay server by reusing the relay reselection procedure to reduce the difficulty of implementation. Alternatively, the remote device may obtain instructions from the relay server via a newly defined procedure, but is not limited to this.

[0015] In a possible design solution, the remote device determining priority information for a first relay service identifier includes the remote device determining priority information for a first relay service identifier based on a first access mechanism. The first access mechanism is a mechanism used by the remote device to access the network via a first relay device. For example, the first access mechanism may be either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism. When the remote device accesses the network by using a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism, it can be understood that the remote device can establish a session between the remote device and the network in order to obtain a first service of the network. Based on this, if the remote device implements fast switching by preferentially reusing the connection mechanism used before the relay connection switchover, the remote device can continue to reuse the session before the session becomes invalid and continue to obtain a first service of the network. This can ensure continuity of service.

[0016] In a possible design solution, the priority information of the first relay service identifier further indicates that the first access mechanism should be preferred in at least one access mechanism for network access, the first access mechanism being the mechanism used by the remote device to access the network via the first relay device. The remote device establishing a second relay connection with the second relay device by using the first PC5 connection mechanism, based on the priority information of the first relay service identifier, includes the remote device deciding to establish a relay connection with the second relay device by using the first PC5 connection mechanism and access the network by using the first access mechanism, based on the priority information of the first relay service identifier. In this way, the remote device can establish a second relay connection to the second relay device by using the first PC5 connection mechanism and access the network via the second relay device by using the first access mechanism.

[0017] If a remote device accesses the network using a first access mechanism and plans to switch the relay connection, it may be found that, in order to further ensure continuity of service, the remote device may preferentially reuse the access mechanism used before the relay connection switch, i.e., the first access mechanism, to continue accessing the network.

[0018] Optionally, a remote device deciding to establish a relay connection to a second relay device by using a first PC5 connection mechanism and access the network by using a first access mechanism, based on priority information of a first relay service identifier, includes the remote device broadcasting the first relay service identifier to receive the relay service identifier of at least one relay device. The relay service identifier of at least one relay device includes a relay service identifier indicating the first PC5 connection mechanism and the first access mechanism. In this way, the remote device decides to establish a relay connection to a second relay device among at least one relay device by using the first PC5 connection mechanism and access the network by using the first access mechanism, based on priority information of the first relay service identifier. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism and the first access mechanism. It can be found that the remote device can actively broadcast the relay service identifier to discover relay devices that support the first PC5 connection mechanism and the first access mechanism, such as the second relay device, and increase the relay discovery probability.

[0019] Optionally, a remote device deciding to establish a relay connection to a second relay device by using a first PC5 connection mechanism and access the network by using a first access mechanism, based on priority information of a first relay service identifier, includes the remote device receiving a relay service identifier for at least one relay device. The relay service identifier for at least one relay device includes a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. In this way, the remote device decides to establish a relay connection to a second relay device among at least one relay device by using a first PC5 connection mechanism and access the network by using a first access mechanism, based on priority information of the first relay service identifier. The second relay device is a relay device corresponding to a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. It can be found that the remote device may alternatively and passively receive the relay service identifier to discover a relay device, e.g., a second relay device supporting a first PC5 connection mechanism and a first access mechanism, thereby avoiding the communication overhead caused by actively broadcasting the relay service identifier.

[0020] Optionally, the remote device determining the priority information for the first relay service identifier includes the remote device determining the priority information for the first relay service identifier based on third directive information from a policy-controlled network element. The third directive information indicates establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover, and accessing the network by preferentially using the access mechanism used before the relay connection switchover. In other words, based on the directive from the policy-controlled network element, the remote device can flexibly decide whether to establish a relay connection by preferentially using the connection mechanism used before the relay connection switchover, and whether to access the network by preferentially using the access mechanism used before the relay connection switchover, in order to meet the relay switching requirements of different services.

[0021] Optionally, the remote device determining the priority information for the first relay service identifier includes the remote device determining the priority information for the first relay service identifier based on fourth instruction information from the relay server. The fourth instruction information indicates establishing a relay connection by preferentially using the first PC5 connection mechanism and accessing the network by preferentially using the first access mechanism. In other words, in addition to establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover by default, the remote device can optionally flexibly decide, based on instructions from the relay server, whether to establish a relay connection by preferentially using the first PC5 connection mechanism and to establish and access the network by preferentially using the access mechanism used before the relay connection switchover, thereby achieving applicability to different switching scenarios.

[0022] Furthermore, the method according to the first embodiment may include the remote device sending a relay reselection request message to the relay server. The relay reselection request message indicates that the connection mechanism used before the relay connection switchover was the first PC5 connection mechanism and that the access mechanism used before the relay connection switchover was the first access mechanism. The remote device receives a relay reselection response message returned by the relay server in response to the relay reselection request message, and the relay reselection response message carries fourth instruction information. In other words, the remote device can obtain instructions from the relay server by reusing the relay reselection procedure to reduce the difficulty of implementation. Alternatively, the remote device may obtain instructions from the relay server via a newly defined procedure, but is not limited to this.

[0023] Optionally, the remote device determining priority information for a first relay service identifier includes the remote device determining priority information for a first relay service identifier based on a first access mechanism. For example, the first access mechanism is either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism. When a remote device accesses the network by using a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism, it can be understood that the remote device can establish a session between the remote device and the network in order to obtain a first service of the network. Based on this, if the remote device implements fast switching by preferentially reusing the connection mechanism used before the relay connection switchover, the remote device can further reuse the session to continue obtaining a first service of the network. This can ensure continuity of service.

[0024] Optionally, at least one access mechanism includes at least one of the following: a Layer 2 access mechanism, a Layer 3 protocol access mechanism, or a Layer 3 non-protocol access mechanism, to enable remote devices to flexibly access the network.

[0025] In a possible design solution, the first PC5 connection mechanism includes a mechanism for obtaining a relay connection key via the network's user plane or via the network's control plane to ensure PC5 connection security.

[0026] According to a second aspect, a communication method is provided. The method includes a remote device determining a first relay service identifier in accordance with a relay switching policy when a first relay connection needs to be switched, and establishing a second relay connection to a second relay device by using a first PC5 connection mechanism based on the first relay service identifier. The relay switching policy is to establish a relay connection by using the PC5 connection mechanism used before the relay connection switching, the first relay service identifier is for determining the first PC5 connection mechanism, the first PC5 connection mechanism is a mechanism used by the remote device to establish a first relay connection to a first relay device, and the first relay connection is used by the remote device to obtain a first service of the network through the first relay device. The second relay connection is used by the remote device to obtain a first service of the network through the second relay device.

[0027] According to the method according to the second aspect, when a remote device establishes a first relay connection to a first relay device by using a first PC5 connection mechanism, for example, a user plane-based mechanism or a control plane-based mechanism, if the remote device intends to switch the relay connection, the remote device continues to reuse the connection mechanism used before the relay connection switch, that is, the first PC5 connection mechanism, to establish a second relay connection to a second relay device, thereby improving PC5 connection switching efficiency, reducing switching delay, and ensuring the continuity of the first service obtained by the remote device from the network.

[0028] In a possible design solution, that the remote device establishes the second relay connection to the second relay device by using the first PC5 connection mechanism based on the first relay service identifier includes that the remote device determines to establish a relay connection to the second relay device by using the first PC5 connection mechanism based on the first relay service identifier, specifically, discovering the second relay device that supports the first PC5 connection mechanism, to ensure that the remote device can establish the second relay connection to the second relay device by using the first PC5 connection mechanism.

[0029] Optionally, the remote device deciding to establish a relay connection to the second relay device by using the first PC5 connection mechanism based on the first relay service identifier includes the remote device broadcasting the first relay service identifier and receiving the relay service identifiers of at least one relay device. The relay service identifiers of the at least one relay device include a relay service identifier indicating the first PC5 connection mechanism. The remote device decides to establish a relay connection to the second relay device among the at least one relay device based on the first relay service identifier. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0030] Optionally, the remote device deciding to establish a relay connection to the second relay device by using the first PC5 connection mechanism based on the first relay service identifier includes the remote device receiving the relay service identifiers of at least one relay device. The relay service identifiers of the at least one relay device include a relay service identifier indicating the first PC5 connection mechanism. The remote device decides to establish a relay connection to the second relay device among the at least one relay device based on the first relay service identifier. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0031] In possible design solutions, the method according to the second aspect may further include the remote device determining the relay switching policy based on fifth directive information from a policy-controlled network element. The fifth directive information indicates establishing a relay connection by using the connection mechanism used before the relay connection switching. In other words, in addition to establishing a relay connection by default using the connection mechanism used before the relay connection switching, the remote device may, based on the directive from the policy-controlled network element, flexibly decide whether to establish a relay connection by using the connection mechanism used before the relay connection switching to meet the relay switching requirements of different services.

[0032] In possible design solutions, the method according to the second aspect may further include the remote device determining the relay switching policy based on a first access mechanism. The first access mechanism is a mechanism used by the remote device to access the network via a first relay device. Optionally, the first access mechanism may be either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism. When the remote device accesses the network by using a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism, it can be understood that the remote device can establish a session between the remote device and the network to obtain a first service from the network. In this case, if the remote device implements fast switching by reusing the connection mechanism used before the relay connection switching, the remote device can continue to reuse the session before the session becomes invalid to obtain the first service from the network. This can ensure continuity of service.

[0033] In a possible design solution, the relay switching policy further indicates access to the network by using the access mechanism used before the relay connection switching, the first relay service identifier further indicates the first access mechanism, the first access mechanism is the mechanism used by the remote device to access the network via the first relay device. The remote device establishing a second relay connection to the second relay device by using the first PC5 connection mechanism based on the first relay service identifier includes the remote device deciding to establish a relay connection to the second relay device by using the first PC5 connection mechanism based on the first relay service identifier and to access the network by using the first PC5 connection mechanism. In this way, the remote device can establish a second relay connection to the second relay device by using the first PC5 connection mechanism and access the network via the second relay device by using the first access mechanism.

[0034] When a remote device accesses the network using a first access mechanism, and the remote device plans to switch the relay connection, it may be found that, in order to further ensure continuity of service, the remote device can continue to access the network by continuing to reuse the access mechanism used before the relay connection switch, i.e., the first access mechanism.

[0035] Optionally, a remote device decides to establish a relay connection to a second relay device by using a first PC5 connection mechanism based on a first relay service identifier, and to access the network by using the first PC5 connection mechanism, which includes the remote device broadcasting the first relay service identifier to receive the relay service identifier of at least one relay device, the relay service identifier of at least one relay device including a relay service identifier indicating the first PC5 connection mechanism and the first access mechanism. The remote device decides to establish a relay connection to a second relay device from at least one relay device based on the first relay service identifier, and to access the network by using the first PC5 connection mechanism. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0036] Optionally, a remote device decides to establish a relay connection to a second relay device by using a first PC5 connection mechanism, based on a first relay service identifier, and to access the network by using the first PC5 connection mechanism. This includes the remote device receiving a relay service identifier for at least one relay device, the relay service identifier for at least one relay device including a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. The remote device decides to establish a relay connection to a second relay device from among at least one relay device, based on the first relay service identifier, and to access the network by using the first PC5 connection mechanism. The second relay device is a relay device corresponding to a relay service identifier indicating a first PC5 connection mechanism.

[0037] Optionally, the method according to the second embodiment may further include the remote device determining a relay switching policy based on a sixth directive from a policy-controlled network element. The sixth directive indicates establishing a relay connection by using the connection mechanism used before the relay connection switching, and accessing the network by using the access mechanism used before the relay connection switching. In other words, the remote device can flexibly decide, based on the directive from the policy-controlled network element, whether to establish a relay connection by using the connection mechanism used before the relay connection switching, and whether to establish and access the network by using the access mechanism used before the relay connection switching, in order to satisfy the relay switching requirements of different services.

[0038] Optionally, the method according to the second embodiment may further include the remote device determining a relay switching policy based on the first access mechanism. For example, the first access mechanism is either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism.

[0039] Optionally, at least one access mechanism includes at least one of the following: a Layer 2 access mechanism, a Layer 3 protocol access mechanism, or a Layer 3 non-protocol access mechanism.

[0040] In a possible design solution, the first PC5 connection mechanism includes a mechanism for obtaining a relay connection key via the network's user plane, or a mechanism for obtaining a relay connection key via the network's control plane.

[0041] Furthermore, for the technical effects of the method according to the second embodiment, please refer to the technical effects of the method according to the first embodiment. Details will not be explained again in this specification.

[0042] A third aspect of the present invention provides a communication method. The method of the present invention includes a remote device establishing a first relay connection to a first relay device by using a first PC5 connection mechanism. The first relay connection is used by the remote device to obtain a first service of the network through the first relay device. When the first relay connection needs to be switched, the remote device obtains priority information of a first relay service identifier, which indicates that the first PC5 connection mechanism indicated by the first relay service identifier should be used preferentially. Based on the priority information of the first relay service identifier, the remote device establishes a second relay connection to a second relay device by using the first PC5 connection mechanism, and the second relay connection is used by the remote device to obtain a first service of the network through the second relay device.

[0043] In a possible design solution, the remote device establishes a second relay connection to a second relay device by using a first PC5 connection mechanism based on priority information of a first relay service identifier, which includes the remote device deciding to establish a relay connection to a second relay device by using a first PC5 connection mechanism based on priority information of a first relay service identifier.

[0044] Optionally, a remote device deciding to establish a relay connection to a second relay device by using a first PC5 connection mechanism based on priority information of a first relay service identifier includes the remote device broadcasting the first relay service identifier to receive the relay service identifier of at least one relay device, the relay service identifier of at least one relay device including a relay service identifier indicating the first PC5 connection mechanism. In this way, the remote device decides to establish a relay connection to a second relay device among at least one relay device by using the first PC5 connection mechanism based on priority information of the first relay service identifier. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0045] Alternatively, and optionally, a remote device deciding to establish a relay connection to a second relay device by using a first PC5 connection mechanism based on priority information of a first relay service identifier includes the remote device receiving a relay service identifier for at least one relay device, the relay service identifier for at least one relay device including a relay service identifier indicating the first PC5 connection mechanism. In this way, the remote device decides to establish a relay connection to a second relay device from at least one relay device by using the first PC5 connection mechanism based on priority information of the first relay service identifier. The second relay device is a relay device corresponding to a relay service identifier indicating the first PC5 connection mechanism.

[0046] In a possible design solution, the remote device determining the priority information for a first relay service identifier includes the remote device determining the priority information for a first relay service identifier based on first instruction information from a policy-controlled network element, where the first instruction information indicates establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover.

[0047] In a possible design solution, the remote device determining the priority information of a first relay service identifier includes the remote device determining the priority information of a first relay service identifier based on second instruction information from the relay server, where the second instruction information indicates that the relay connection should be established by preferentially using the first PC5 connection mechanism.

[0048] Optionally, a method according to a third embodiment may further include the remote device sending a relay reselection request message to the relay server, the relay reselection request message indicating that the connection mechanism used before the relay connection switchover was the first PC5 connection mechanism. The remote device receives a relay reselection response message returned by the relay server in response to the relay reselection request message, the relay reselection response message carrying second instruction information.

[0049] In a possible design solution, the remote device determines priority information for a first relay service identifier based on a first access mechanism. The first access mechanism is the mechanism used by the remote device to access the network via the first relay device. For example, the first access mechanism may be either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism.

[0050] In a possible design solution, the priority information of the first relay service identifier further indicates that the first access mechanism should be preferred in at least one access mechanism for network access, the first access mechanism being the mechanism used by the remote device to access the network via the first relay device. The remote device establishing a second relay connection with the second relay device by using the first PC5 connection mechanism, based on the priority information of the first relay service identifier, includes the remote device deciding to establish a relay connection with the second relay device by using the first PC5 connection mechanism and access the network by using the first access mechanism, based on the priority information of the first relay service identifier. In this way, the remote device can establish a second relay connection to the second relay device by using the first PC5 connection mechanism and access the network via the second relay device by using the first access mechanism.

[0051] Optionally, a remote device decides, based on priority information of a first relay service identifier, to establish a relay connection to a second relay device by using a first PC5 connection mechanism and to access the network by using a first access mechanism, which includes the remote device broadcasting the first relay service identifier to receive the relay service identifier of at least one relay device. The relay service identifier of at least one relay device includes a relay service identifier indicating the first PC5 connection mechanism and the first access mechanism. In this way, the remote device decides, based on priority information of the first relay service identifier, to establish a relay connection to a second relay device among at least one relay device by using the first PC5 connection mechanism and to access the network by using the first access mechanism. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism and the first access mechanism.

[0052] Optionally, a remote device decides, based on priority information of a first relay service identifier, to establish a relay connection to a second relay device by using a first PC5 connection mechanism and to access the network by using a first access mechanism, which includes the remote device receiving the relay service identifier of at least one relay device. The relay service identifier of at least one relay device includes a relay service identifier indicating the first PC5 connection mechanism and the first access mechanism. In this way, the remote device decides, based on priority information of the first relay service identifier, to establish a relay connection to a second relay device among at least one relay device by using the first PC5 connection mechanism and to access the network by using the first access mechanism. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism and the first access mechanism.

[0053] Optionally, the remote device determining priority information for a first relay service identifier includes the remote device determining priority information for a first relay service identifier based on third directive information from a policy-controlled network element. The third directive information indicates establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover, and accessing the network by preferentially using the access mechanism used before the relay connection switchover.

[0054] Optionally, the remote device determining priority information for a first relay service identifier includes the remote device determining priority information for a first relay service identifier based on fourth instruction information from the relay server. The fourth instruction information indicates establishing a relay connection by preferentially using the first PC5 connection mechanism and accessing the network by preferentially using the first access mechanism.

[0055] Furthermore, a third embodiment of the method may include the remote device sending a relay reselection request message to the relay server. The relay reselection request message indicates that the connection mechanism used before the relay connection switchover was the first PC5 connection mechanism and that the access mechanism used before the relay connection switchover was the first access mechanism. The remote device receives a relay reselection response message returned by the relay server in response to the relay reselection request message, and the relay reselection response message carries fourth instruction information.

[0056] Optionally, the method according to the third embodiment may further include the remote device determining priority information for a first relay service identifier based on the first access mechanism. For example, the first access mechanism is either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism.

[0057] Optionally, at least one access mechanism includes at least one of the following: a Layer 2 access mechanism, a Layer 3 protocol access mechanism, or a Layer 3 non-protocol access mechanism.

[0058] In a possible design solution, the first PC5 connection mechanism includes a mechanism for obtaining a relay connection key via the network's user plane, or a mechanism for obtaining a relay connection key via the network's control plane.

[0059] Furthermore, for the technical effects of the method according to the third embodiment, please refer to the technical effects of the method according to the first embodiment. Details will not be explained again in this specification.

[0060] According to a fourth aspect, a communication method is provided. The method of the present invention includes a remote device establishing a first relay connection to a first relay device by using a first PC5 connection mechanism. The first relay connection is used by the remote device to obtain a first service of the network through the first relay device. When the first relay connection needs to be switched, the remote device determines a first relay service identifier according to a relay switching policy and establishes a second relay connection to a second relay device by using a first PC5 connection mechanism based on the first relay service identifier. The relay switching policy indicates establishing the relay connection by using the connection mechanism used before the relay connection switch, the first relay service identifier indicates the first PC5 connection mechanism, and the second relay connection is used by the remote device to obtain a first service of the network through the second relay device.

[0061] In a possible design solution, the remote device establishes a second relay connection to a second relay device by using a first PC5 connection mechanism based on a first relay service identifier, which includes the remote device deciding to establish a relay connection to a second relay device by using a first PC5 connection mechanism based on a first relay service identifier.

[0062] Optionally, a remote device deciding to establish a relay connection to a second relay device by using a first PC5 connection mechanism based on a first relay service identifier includes the remote device broadcasting the first relay service identifier and receiving the relay service identifier of at least one relay device. The relay service identifier of at least one relay device includes a relay service identifier indicating the first PC5 connection mechanism. The remote device decides to establish a relay connection to a second relay device from among at least one relay device based on the first relay service identifier. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0063] Optionally, a remote device deciding to establish a relay connection to a second relay device by using a first PC5 connection mechanism based on a first relay service identifier includes the remote device receiving a relay service identifier for at least one relay device. The relay service identifier for at least one relay device includes a relay service identifier indicating the first PC5 connection mechanism. The remote device decides to establish a relay connection to a second relay device from among at least one relay device based on the first relay service identifier. The second relay device is the relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0064] In possible design solutions, the method according to the fourth aspect may further include the remote device determining a relay switching policy based on fifth instruction information from a policy-controlled network element. The fifth instruction information indicates establishing a relay connection by using the connection mechanism used before the relay connection switching.

[0065] In possible design solutions, the method according to the fourth aspect may further include the remote device determining the relay switching policy based on a first access mechanism. The first access mechanism is a mechanism used by the remote device to access the network via a first relay device. Optionally, the first access mechanism may be either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism.

[0066] In a possible design solution, the relay switching policy further indicates access to the network by using the access mechanism used before the relay connection switching, the first relay service identifier further indicates the first access mechanism, the first access mechanism is the mechanism used by the remote device to access the network via the first relay device. The remote device establishing a second relay connection to the second relay device by using the first PC5 connection mechanism based on the first relay service identifier includes the remote device deciding to establish a relay connection to the second relay device by using the first PC5 connection mechanism based on the first relay service identifier and to access the network by using the first PC5 connection mechanism. In this way, the remote device can establish a second relay connection to the second relay device by using the first PC5 connection mechanism and access the network via the second relay device by using the first access mechanism.

[0067] Optionally, a remote device decides to establish a relay connection to a second relay device by using a first PC5 connection mechanism based on a first relay service identifier, and to access the network by using the first PC5 connection mechanism, which includes the remote device broadcasting the first relay service identifier to receive the relay service identifier of at least one relay device, the relay service identifier of at least one relay device including a relay service identifier indicating the first PC5 connection mechanism and the first access mechanism. The remote device decides to establish a relay connection to a second relay device from at least one relay device based on the first relay service identifier, and to access the network by using the first PC5 connection mechanism. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0068] Optionally, a remote device decides to establish a relay connection to a second relay device by using a first PC5 connection mechanism, based on a first relay service identifier, and to access the network by using the first PC5 connection mechanism. This includes the remote device receiving a relay service identifier for at least one relay device, the relay service identifier for at least one relay device including a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. The remote device decides to establish a relay connection to a second relay device from among at least one relay device, based on the first relay service identifier, and to access the network by using the first PC5 connection mechanism. The second relay device is a relay device corresponding to a relay service identifier indicating a first PC5 connection mechanism.

[0069] Optionally, the method according to the fourth embodiment may further include the remote device determining a relay switching policy based on sixth directive information from a policy-controlled network element. The sixth directive information indicates establishing a relay connection by using the connection mechanism used before the relay connection switching, and accessing the network by using the access mechanism used before the relay connection switching.

[0070] Optionally, the method according to the fourth embodiment may further include the remote device determining a relay switching policy based on the first access mechanism. For example, the first access mechanism is either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism.

[0071] Optionally, at least one access mechanism includes at least one of the following: a Layer 2 access mechanism, a Layer 3 protocol access mechanism, or a Layer 3 non-protocol access mechanism.

[0072] In a possible design solution, the first PC5 connection mechanism includes a mechanism for obtaining a relay connection key via the network's user plane, or a mechanism for obtaining a relay connection key via the network's control plane.

[0073] Furthermore, for the technical effects of the method according to the fourth embodiment, please refer to the technical effects of the method according to the first embodiment. Details will not be explained again in this specification.

[0074] According to a fifth aspect, a communication device is provided. The communication device includes modules configured to perform the method according to the first aspect, for example, a transceiver module and a processing module. For example, the transceiver module is configured to perform the transceiver function of the communication device, and the processing module is configured to perform functions other than the transceiver function of the communication device.

[0075] Optionally, the transceiver module may include a transmit module and a receive module. The transmit module is configured to implement the transmit function of the communication device according to the fifth embodiment, and the receive module is configured to implement the receive function of the communication device according to the fifth embodiment.

[0076] Optionally, the communication device according to the fifth embodiment may further include a storage module that stores a program or instruction. When the processing module executes the program or instruction, the communication device is enabled to perform the method according to the first embodiment.

[0077] It can be understood that the communication device according to the fifth aspect may be a terminal, for example, a remote device, a chip (system) or other component mounted on a terminal, or a device including a terminal. This is not limited to the present application.

[0078] Furthermore, for the technical effects of the communication device according to the fifth embodiment, please refer to the technical effects of the method according to the first embodiment. Details will not be explained again in this specification.

[0079] According to a sixth aspect, a communication device is provided. The communication device includes modules configured to perform the method according to the second aspect, for example, a transceiver module and a processing module. For example, the transceiver module is configured to perform the transceiver function of the communication device, and the processing module is configured to perform functions other than the transceiver function of the communication device.

[0080] Optionally, the transceiver module may include a transmit module and a receive module. The transmit module is configured to implement the transmit function of the communication device according to the sixth embodiment, and the receive module is configured to implement the receive function of the communication device according to the sixth embodiment.

[0081] Optionally, the communication device according to the sixth embodiment may further include a storage module that stores a program or instruction. The communication device is enabled to perform the method according to the second embodiment when a processing module executes a program or instruction.

[0082] It can be understood that the communication device according to the sixth aspect may be a terminal, such as a remote device, a chip (system) or other components or elements mounted on a terminal, or a device including a terminal. This is not limited to the present application.

[0083] Furthermore, for the technical effects of the communication device according to the sixth embodiment, please refer to the technical effects of the method according to the second embodiment. Details will not be explained again in this specification.

[0084] According to the seventh aspect, a communication device is provided. The communication device includes a processor, which is configured to perform a method according to any possible implementation of the first or second aspect.

[0085] In possible design solutions, the communication device according to the seventh embodiment may further include a transceiver. The transceiver may be a transceiver circuit or an interface circuit. The transceiver may be used by the communication device according to the seventh embodiment to communicate with other communication devices.

[0086] In possible design solutions, the communication device according to the seventh aspect may further include memory. The memory and processor may be integrated or located separately. The memory may be configured to store computer programs and / or data related to the method according to either the first or second aspect.

[0087] In this embodiment of the present application, the communication device according to the seventh aspect may be a terminal according to either the first or second aspect, a chip (system) or other component or element mounted on the terminal, or a device including the terminal.

[0088] Furthermore, for the technical effects of the communication device according to the seventh embodiment, please refer to the technical effects of the method according to either the first or second embodiment. Details are again not described herein.

[0089] According to the eighth aspect, a communication device is provided. The communication device includes a processor, the processor is coupled to memory, and the processor is configured to execute a computer program stored in memory in order to enable the communication device to perform a method according to any possible implementation of the first or second aspect.

[0090] In possible design solutions, the communication device according to the eighth aspect may further include a transceiver. The transceiver may be a transceiver circuit or an interface circuit. The transceiver may be used for the communication device according to the eighth aspect to communicate with other communication devices.

[0091] In this embodiment of the present application, the communication device according to the eighth aspect may be a terminal according to either the first or second aspect, a chip (system) or other component or element mounted on the terminal, or a device including the terminal.

[0092] Furthermore, for the technical effects of the communication device according to the eighth embodiment, please refer to the technical effects of the method according to either the first or second embodiment. Details are again not described herein.

[0093] According to the ninth aspect, a communication device including a processor and memory, wherein the memory is configured to store a computer program, and when the processor executes the computer program, the communication device is enabled to perform a method according to either the first or second aspect.

[0094] In possible design solutions, the communication device according to the ninth aspect may further include a transceiver. The transceiver may be a transceiver circuit or an interface circuit. The transceiver may be used for the communication device according to the ninth aspect to communicate with other communication devices.

[0095] In this embodiment of the present application, the communication device according to the ninth aspect may be a terminal according to either the first or second aspect, a chip (system) or other component mounted on the terminal, or a device including the terminal.

[0096] Furthermore, for the technical effects of the communication device according to the ninth embodiment, please refer to the technical effects of the method according to either the first or second embodiment. Details are again not described herein.

[0097] According to a tenth aspect, a communication system is provided. The communication system includes a remote device, a first relay device, and a second relay device. The remote device, the first relay device, and the second relay device are configured to perform the method according to the third aspect or the method according to the fourth aspect.

[0098] According to the eleventh aspect, a computer-readable storage medium containing a computer program or instruction is provided, and when the computer program or instruction is executed on the computer, the computer is enabled to perform a method according to any possible implementation of the first or second aspect.

[0099] According to the twelfth aspect, a computer program product is provided, which includes a computer program or instructions. When the computer program or instructions are executed on a computer, the computer is enabled to perform a method according to any possible implementation of the first or second aspect. [Brief explanation of the drawing]

[0100] [Figure 1] This is a diagram of the 5GS architecture. [Figure 2] This is a diagram of the control plane architecture for ProSe communication. [Figure 3] This is a schematic flowchart of ProSe communication. [Figure 4] This is a diagram of the protocol stack for a Layer 2 relay mechanism. [Figure 5] This is a diagram of the protocol stack for a Layer 3 relay mechanism. [Figure 6] This is a diagram of the protocol stack for a Layer 3 relay + N3IWF mechanism. [Figure 7] This is a schematic flowchart for determining the PC5 connection mechanism and the remote end access mechanism. [Figure 8] This is a schematic flowchart of the ProSe discovery process. [Figure 9] This is a diagram of the architecture of a communication system according to one embodiment of the present invention. [Figure 10] This is flowchart 1 illustrating a communication method according to one embodiment of the present invention. [Figure 11] This is flowchart 2 of a communication method according to one embodiment of the present invention. [Figure 12] This is flowchart 3 of the communication method according to one embodiment of the present invention. [Figure 13] This is flowchart 4 of the communication method according to one embodiment of the present invention. [Figure 14] This is a schematic flowchart 5 of the communication method according to one embodiment of the present invention. [Figure 15]This is a schematic flowchart 6 of a communication method according to one embodiment of the present invention. [Figure 16] Figure 1 shows the structure of a communication device according to one embodiment of the present invention. [Figure 17] Figure 2 shows the structure of a communication device according to one embodiment of the present invention. [Modes for carrying out the invention]

[0101] To facilitate understanding, the terminology used in the embodiments of this application will be explained first.

[0102] 1. Fifth generation (5G) mobile communication system (abbreviated as 5G system (5GS)):

[0103] Figure 1 is a diagram of the 5GS architecture. As shown in Figure 1, 5GS as defined by the 3rd generation partnership project (3GPP®) includes an access network (AN) and a core network (CN), and may further include terminals.

[0104] The terminal may be a terminal with transceiver functionality, or it may be a chip or chip system installed in the terminal. The terminal may also be referred to as user equipment (UE), access terminal, subscriber unit, subscriber station, mobile station (MS), remote station, remote terminal, mobile device, user terminal, terminal, wireless communication device, user agent, or user equipment. The terminals in the embodiments of this application may include mobile phones, cellular phones, smartphones, tablet computers (Pads), wireless data cards, personal digital assistants (PDAs), wireless modems, handheld devices (handsets), laptop computers, machine-type communication (MTC) terminals, computers with wireless transceiver functionality, virtual reality (VR) terminals, augmented reality (AR) terminals, wireless terminals in industrial control, wireless terminals in self-driving, unmanned aerial vehicles, wireless terminals in remote medical care, wireless terminals in smart grids, wireless terminals in transportation safety, wireless terminals in smart cities, wireless terminals in smart homes, in-vehicle terminals, roadside units (RSUs) with terminal functionality, and the like. Alternatively, the terminal in this application may be a vehicle-mounted module, vehicle-mounted subassembly, vehicle-mounted component, vehicle-mounted chip, or vehicle-mounted unit, which is incorporated into the vehicle as one or more components or units.

[0105] An AN is configured to implement access-related functions and can provide network access to authorized users within a specific area. It can determine different quality transmission links based on user level, service requirements, etc., for the transmission of user data. The AN transfers control signals and user data between the terminal and the CN. An AN may include an access network device, which may also be referred to as a radio access network (RAN) device. The CN is primarily responsible for maintaining mobile network subscription data and providing functions such as session management, mobility management, policy management, and security authentication to terminals. CN primarily includes user plane function (UPF), authentication server function (AUSF), access and mobility management function (AMF), session management function (SMF), network slice selection function (NSSF), network exposure function (NEF), network repository function (NRF), policy control function (PCF), unified data management (UDM), unified data repository (UDR), and application function (AF).

[0106] As shown in Figure 1, the UE accesses the 5G network via the RAN device and communicates with the AMF via the N1 interface (abbreviated as N1). The RAN communicates with the AMF via the N2 interface (abbreviated as N2). The RAN communicates with the UPF via the N3 interface (abbreviated as N3). The SMF communicates with the UPF via the N4 interface (abbreviated as N4). The UPF accesses the data network (data network, DN) via the N6 interface (abbreviated as N6). In addition, control plane functions such as AUSF, AMF, SMF, NSSF, NEF, NRF, PCF, UDM, UDR, and AF shown in Figure 1 interact with each other via service-oriented interfaces. For example, a service-oriented interface provided externally by AUSF includes Nausf, a service-oriented interface provided externally by AMF includes Namf, a service-oriented interface provided externally by SMF includes Nsmf, a service-oriented interface provided externally by NSSF includes Nnssf, a service-oriented interface provided externally by NEF includes Nnef, a service-oriented interface provided externally by NRF includes Nnrf, a service-oriented interface provided externally by PCF includes Npcf, a service-oriented interface provided externally by UDM includes Nudm, a service-oriented interface provided externally by UDR includes Nudr, and a service-based interface provided by AF includes Naf.

[0107] A RAN device may be a device that provides access to a terminal. For example, in a next-generation mobile communication system, such as a 6G mobile communication system, a RAN device may include an access network device, such as a 6G base station. Alternatively, in a next-generation mobile communication system, network devices may be named in a different way, and such alternatives are within the scope of protection of embodiments of this application. This is not limited to this application. Alternatively, a RAN device may include a gNB in ​​a 5G system, such as a new radio (NR) system, or one antenna panel or group of antenna panels (including multiple antenna panels) of a base station in a 5G system, or a network node, such as a gNB, a transmission and reception point (TRP), or a transmission measurement function (TMF), or a building base band unit (BBU), a centralized unit (CU), a distributed unit (DU), an RSU with base station functionality, or a wireline access gateway included in a 5G core network. Alternatively, RAN devices may include access points (APs), wireless relay nodes, wireless backhaul nodes, or various forms of macro base stations, micro base stations (also known as small cells), relay stations, access points, wearable devices, and automotive devices within a wireless fidelity (WiFi) system.

[0108] The UPF is primarily responsible for user data processing (transfer, reception, billing, etc.). For example, the UPF can receive user data from the data network (DN) and transfer that user data to the terminal via the access network device. Alternatively, the UPF may receive user data from the terminal via the access network device and transfer the user data to the DN. The DN is a carrier network that provides data transmission services to users, such as Internet Protocol (IP) multimedia services (IMS) or the internet. The DN may be an external network of the carrier or a network managed by the carrier, and is configured to provide services to terminal devices. In a protocol data unit (PDU) session, a UPF directly connected to the DN via N6 is also called a protocol data unit session anchor (PSA).

[0109] AUSF is primarily configured to perform security authentication on the device.

[0110] AMF is primarily used for mobility management, including updating user location on mobile networks, registering users to networks, and switching users.

[0111] SMF is primarily for session management, including establishing, modifying, and releasing sessions in mobile networks. Specific functions include, for example, assigning Internet Protocol (IP) addresses to users and selecting UPF (User Processing Function) to provide data packet forwarding capabilities.

[0112] PCF primarily supports providing a unified policy framework for controlling network operations and supplying policy rules to control layer network functions, and is also responsible for obtaining user subscription information related to policy decisions. PCF can provide policies such as quality of service (QoS) policies and slice selection policies to AMF and SMF.

[0113] NSSF is primarily configured to select the network slice for a terminal.

[0114] NEF is primarily configured to support the exposure of functions and events. For example, NEF can expose some functions of a 5G network to third-party applications via an application programming interface (API), and third-party applications can obtain the functions of the 5G network by calling the APIs provided by NEF via AF, and as a result, third-party applications can control some of the behavior of the 5G network and terminals.

[0115] UDM is primarily configured to store user data, such as subscription data and authentication / authorization data.

[0116] UDRs are primarily configured to store structured data, including subscription data, policy data, publicly exposed structured data, and application-related data.

[0117] AF primarily supports interaction with CN to provide services, such as influencing data routing decisions, providing policy control functions, or offering several third-party services to the network side.

[0118] It can be understood that the functions in the embodiments of this application may also be represented as functional network elements or functional entities. For example, UPF may be represented as a UPF network element, AMF may be represented as an AMF network element, SMF may be represented as an SMF network element, and PCF may be represented as a PCF network element. The rest can be inferred by analogy and are not limited thereto.

[0119] 2. Short-range communication:

[0120] With the rapid development of mobile communications, new service types of data services such as video chat and virtual reality (VR) / augmented reality (AR) are becoming widely used. This increases the bandwidth requirements for users. From this perspective, short-range communications such as device-to-device (D2D) communication are a solution.

[0121] D2D communication enables direct communication between UEs, such as through the PC5 interface, and implements information transmission on the data plane and control plane. In this way, under the control of a cellular network, users can share frequency resources with other cellular users to effectively improve the utilization of frequency resources. D2D communication includes one-to-many communication and one-to-one communication. One-to-many communication typically corresponds to multicast and broadcast communication, while one-to-one communication typically corresponds to unicast communication. In one-to-one communication, if the transmitting UE and receiving UE are in close proximity, they can communicate directly after discovering each other.

[0122] 3. Proximity-based services (ProSe) communication:

[0123] ProSe communication, also known as short-range service communication, is a typical service scenario in D2D communication. ProSe communication can include proximity-based direct service communication and proximity-based service UE-network relay communication. In the case of proximity-based relay communication from a service UE to the network (sometimes abbreviated as ProSe communication):

[0124] Figure 2 is a diagram of the control plane architecture for ProSe communication. As shown in Figure 2, if a specific UE (shown as UE B) is located outside network coverage, if the signal for communication between UE B and the RAN device is poor, or if another UE (shown as UE A) is required to assist with data transmission, UE B can access the network with the assistance of UE A.

[0125] UE B may be referred to as a Prose remote UE or a 5G Prose remote UE, or simply as a remote UE. UE A may be referred to as a Prose UE-to-network relay or a 5G Prose UE-to-network relay, or simply as a relay UE. The remote UE and relay UE support the Prose application function, enabling the remote UE to establish a PC5 connection to the relay UE, communicate with the network via the relay UE (in other words, perform Prose communication), and obtain services provided by the network.

[0126] The AF may be a proximity-based service application server (ProSe application server), i.e., an AF that supports proximity-based service application services. The ProSe application server has all the functions of the AF as defined in version 23.501 R-15, as well as functions related to ProSe services. The ProSe application server and UE may perform user plane communication via the route:UE-RAN-UPF-AF. The ProSe application server may further communicate with other NFs (network functions) in the CN via NEF, for example, with the PCF.

[0127] Figure 3 is a schematic flowchart of ProSe communication. As shown in Figure 3, the procedure includes the following steps.

[0128] Step 1: The remote UE retrieves the ProSe parameters.

[0129] ProSe parameters may also be parameters for implementing ProSe communication. ProSe parameters may include ProSe communication-related parameters in a UE route selection policy (URSP), such as a ProSe communication-related route selection descriptor (RSD). ProSe parameters may further include a ProSe policy. An RSD may indicate a mechanism (referred to as an access mechanism) for a remote UE to access the network, which may include at least one of the following: a Layer 2 relay mechanism, a Layer 3 relay mechanism, or a Layer 3 relay + non-3GPP interworking function (N3IWF) mechanism. It may be understood that a Layer 2 relay mechanism may also be referred to as a Layer 2 access mechanism, a Layer 3 relay mechanism may also be referred to as a Layer 3 with protocol access mechanism, and a Layer 3 relay + non-3GPP interworking function mechanism may also be referred to as a Layer 3 with non-protocol access mechanism.

[0130] Figure 4 is a diagram of the protocol stack of a Layer 2 relay mechanism. As shown in Figure 4, a Layer 2 relay mechanism is a mechanism for accessing a network via a Layer 2 relay device. In this case, the network side (e.g., RAN or AMF) can detect the presence of a remote UE. For example, a remote UE can establish a secure connection to the RAN via a PC5 connection. In this case, security between the remote UE and the RAN is established end-to-end between the packet data convergence protocol (PDCP) layer of the remote UE and the PDCP layer of the RAN. The remote UE can register with the network via ProSe communication provided by the Layer 2 relay UE, establish or modify a PDU session of the remote UE, and obtain services from the DN via the PDU session. The relay UE does not parse the PDCP layer, but transparently transmits information in the PDCP layer of the remote UE, the PDCP layer of the RAN, and layers above the PDCP layer, such as information indicating that the remote UE is registering with the network, information indicating that the remote UE is initiating the establishment or modification of a PDU session, or user plane data of the remote UE.

[0131] Figure 5 is a diagram of the protocol stack of a Layer 3 relay mechanism. As shown in Figure 5, a Layer 3 relay mechanism is a mechanism for accessing a network via a Layer 3 relay device. In this case, the network is usually unable to sense the presence of the remote UE. Security between the remote UE and the RAN is established by the segment and includes security from the PDCP layer of the remote UE to the PDCP layer of the relay UE, and security from the PDCP layer of the relay UE to the PDCP layer of the RAN. The relay UE needs to establish or modify a PDU session for the remote UE. In other words, ProSe communication provided by the Layer 3 relay UE between the remote UE and the network is implemented by multiplexing the relay UE's PDU session. Establishing or modifying a PDU session follows the definition in TS 23.502. The relay UE needs to parse the PDCP layer to decide whether to forward data to the remote UE.

[0132] Figure 6 is a diagram of the protocol stack of the Layer 3 relay + N3IWF mechanism. As shown in Figure 6, the Layer 3 relay + N3IWF mechanism is a mechanism that accesses the network by using a non-3GPP protocol via a Layer 3 relay device. The remote UE needs to establish a secure channel from the remote UE to the N3IWF by using the Layer 3 relay + N3IWF mechanism and access the network side through that secure channel. In this case, the network side can detect the presence of the remote UE. ProSe communication provided between the remote UE and the network by using the Layer 3 relay + N3IWF mechanism means that the remote UE uses a mechanism to access the network via a Layer 3 relay device, uses a non-3GPP protocol to establish a secure channel to the N3IWF, registers with the network, establishes or modifies the remote UE's PDU session, and obtains services from the DN via the PDU session.

[0133] In a Layer 2 relay mechanism, the remote UE may be referred to as a 5G ProSe Layer 2 remote UE, a ProSe Layer 2 remote UE, or a Layer 2 remote UE. Similarly, in a Layer 3 relay mechanism or a Layer 3 relay + N3IWF mechanism, the remote UE may be referred to as a 5G ProSe Layer 3 remote UE, a ProSe Layer 3 remote UE, or a Layer 3 remote UE. Similarly, in a Layer 2 relay mechanism, the relay UE may be referred to as a 5G ProSe Layer 2 relay UE, a ProSe Layer 2 relay UE, or a Layer 2 relay UE. Similarly, in a Layer 3 relay mechanism or a Layer 3 relay + N3IWF mechanism, the relay UE may be referred to as a 5G ProSe Layer 3 relay UE, a ProSe Layer 3 relay UE, or a Layer 3 relay UE.

[0134] Different RSDs may indicate different access mechanisms. For example, RSD1 indicates a Layer 2 relay mechanism, RSD2 indicates a Layer 3 relay mechanism, and RSD3 indicates a Layer 3 relay + N3IWF mechanism. Different RSDs may have usage priorities to indicate the priority of use for different access mechanisms. For example, the descending usage priority of RSD1-RSD3 is RSD1, RSD2, RSD3, indicating the descending usage priority of different access mechanisms is Layer 2 relay mechanism, Layer 3 relay mechanism, Layer 3 relay + N3IWF mechanism. In addition, an RSD may further indicate other information necessary for a remote UE to obtain services from a DN via ProSe communication, such as the data network name (data network name, DNN) or slice. This is not limited to these.

[0135] It can be understood that different URSPs can be configured for a remote UE and have usage priorities. The remote UE can select different URSPs sequentially based on the descending order of their usage priorities. The remote UE can configure different RSDs within the same URSP, and different RSDs have usage priorities. The remote UE can select different RSDs sequentially based on the descending order of their usage priorities within the same URSP.

[0136] A ProSe policy can specify a mechanism for establishing a PC5 connection (referred to as the PC5 connection mechanism) and the access mechanism described above. For example, a ProSe policy may include a relay service code (RSC), which can specify the PC5 connection mechanism and the access mechanism.

[0137] The PC5 connection mechanism may include a user plane (UP) mechanism and a control plane (CP) mechanism.

[0138] The CP-based mechanism is a mechanism for obtaining a relay connection key via the network's control plane. For example, if a remote UE needs to access the network via a relay, the remote UE can perform ProSe discovery to discover the relay UE. The remote UE can send a direct communication request message to the relay UE to initiate the establishment of a PC5 connection. In the UP-based mechanism, the direct communication request message can include the remote UE's subscription concealed identifier (SUCI) and RSC. Based on the direct communication request message, the relay UE may send a key acquisition request message to the AMF, which then verifies that the relay UE is authorized to act as a relay and sends an authentication request message to the AUSF. Based on the authentication request message, the AUSF can obtain an authentication vector from the UDM and perform ProSe authentication on the remote UE. Upon successful ProSe authentication, the remote UE and the AUSF generate a CP-PRUK and a CP-PRUK ID separately. The CP-PRUK is the root key for the PC5 connection in the CP-based mechanism, and the CP-PRUK ID is the identifier of the root key. AUSF can generate a KNR_ProSe based on CP-PRUK and send it to the relay UE. The KNR_ProSe can be key to PC5 connectivity in CP-based mechanisms. The remote UE can autonomously generate a KNR_ProSe based on CP-PRUK. In this case, both the remote UE and the relay UE can obtain a KNR_ProSe and use it to establish a PC5 secure connection.

[0139] AUSF can further store the CP-PRUK, CP-PRUK ID, the remote UE's RSC, and the remote UE's subscription permanent identifier (SUPI) within the PAnF (ProSe anchor function). The remote UE may again send a direct communication request message to the relay UE. In this case, in a CP-based mechanism, the direct communication request message may further include the CP-PRUK ID to indicate that the ProSe authentication procedure has been previously performed at the remote UE. AUSF can then directly retrieve the corresponding CP-PRUK from the PAnF based on the CP-PRUK ID and the remote UE's RSC without having to perform the ProSe authentication procedure again.

[0140] For specific procedures in CP-based mechanisms, it is understandable to refer to the relevant descriptions in TS 33.503. Further details are not provided.

[0141] The UP-based mechanism is a mechanism for obtaining relay connection keys via the network's user plane. For example, a remote UE and a relay UE are pre-configured with the remote UE's PKMF (ProSe key management function) address and the relay UE's PKMF address, respectively. The remote UE needs to obtain the UP-PRUK and UP-PRUK ID from the remote UE's PKMF by using UP signaling. The UP-PRUK is the root key for the PC5 connection in the UP-based mechanism, and the UP-PRUK ID is the identifier of the root key. If the remote UE needs to access the network via the relay, the remote UE can perform ProSe discovery to discover the relay UE. The remote UE can send a direct communication request message to the relay UE to initiate the establishment of a PC5 connection. In the UP-based mechanism, the direct communication request message may include a home public land mobile network (HPLMN) identifier, such as the UE's HPLMN ID, and the UE's SUCI (where the remote UE's SUCI can be substituted with the UP-PRUK ID). The relay UE may send a key acquisition request message to its PKMF based on a direct communication request message, and as a result, the relay UE's PKMF verifies that the relay UE is authorized to act as a relay. In this case, the relay UE's PKMF may determine the remote UE's PKMF based on the remote UE's HPLMN ID and the remote UE's SUCI (the remote UE's SUCI may be substituted with the UP-PRUK ID), and may obtain the KNRP (new radio PC5, NRP) and KNRP freshness parameter from the remote UE's PKMF. The relay UE's PKMF sends the KNRP and KNRP freshness parameter to the relay UE. The KNRP may be the key to the PC5 connection in the UP-based mechanism.After obtaining the KNRP, the relay UE sends the KNRP freshness parameters to the remote UE, which then autonomously determines the KNRP based on the UP-PRUK and KNRP freshness parameters. In this case, both the remote UE and the relay UE can obtain the KNRP and establish a PC5 secure connection by using the KNRP.

[0142] For specific procedures in the UP-based mechanism, it is understandable to refer to the relevant description in TS 33.503. Further details are not provided.

[0143] Different RSCs can represent different access mechanisms and PC5 connection mechanisms. For example, RSC1 represents a CP-based mechanism + Layer 2 relay mechanism, RSC2 represents a CP-based mechanism + Layer 3 relay mechanism, RSC3 represents a CP-based mechanism + Layer 3 relay + N3IWF mechanism, RSC4 represents a UP-based mechanism + Layer 2 relay mechanism, RSC5 represents a UP-based mechanism + Layer 3 relay mechanism, and RSC6 represents a UP-based mechanism + Layer 3 relay + N3IWF mechanism.

[0144] ProSe parameters obtained by a remote UE may have different sources, and ProSe parameters from different sources have a usage priority.

[0145] For example, a remote UE can obtain ProSe parameters from the PCF, which are indicated as ProSe parameter 1. Specifically, for the specific implementation principles of obtaining ProSe communication-related parameters in URSP from the PCF by the remote UE, please refer to the relevant description in section 4.16.11 of TS 23.502. Details are not explained. In the case of a ProSe policy, the remote UE can send a 5G ProSe policy provisioning request message to the AMF. The 5G ProSe policy provisioning request message may include 5G ProSe UE-to-network relay communication capability. For example, the remote UE may have relay communication capability to function as a Layer 2 remote UE, and / or the remote UE may have relay communication capability to function as a Layer 3 remote UE. The remote UE having relay communication capability to function as a Layer 2 remote UE means that the remote UE supports access to the network by using a Layer 2 relay mechanism. The fact that a remote UE has relay communication capabilities to function as a Layer 3 remote UE means that the remote UE supports network access by using Layer 3 relay mechanisms and Layer 3 relay + N3IWF mechanisms. The AMF can obtain the remote UE's ProSe subscription information from the UDM and, based on the remote UE's ProSe subscription information, can determine that the remote UE has 5G ProSe UE-network relay communication capabilities. In this way, the AMF can send a 5G ProSe policy provisioning request message to the PCF so that the PCF sends the ProSe policy via the UE configuration update (UCU) procedure.

[0146] The remote UE can retrieve ProSe parameters from the ProSe application server, and these ProSe parameters are shown as ProSe parameter 2.

[0147] Alternatively, the remote UE may obtain the ProSe parameters from the remote UE's universal integrated circuit card (UICC), which are denoted as ProSe parameter 3.

[0148] A remote UE may alternatively obtain ProSe parameters from its mobile equipment (ME), and these ProSe parameters are denoted as ProSe parameter 4.

[0149] In this case, the usage priority of the ProSe parameters is in descending order: ProSe parameter 1, ProSe parameter 2, ProSe parameter 3, and ProSe parameter 4. The remote UE can determine which ProSe parameter to use based on the descending order of the ProSe parameter usage priority, and the specific ProSe parameter is indicated as the target ProSe parameter.

[0150] If ProSe communication needs to be performed, the remote UE can determine the specific PC5 connection mechanism and specific access mechanism to be used based on the target ProSe parameters. For example, the remote UE can select the URSP with the highest priority based on the usage priority of the URSP. The remote UE can select the RSD with the highest priority based on the usage priority of the RSD within the URSP with the highest priority. The remote UE can then perform step 2 by traversing the ProSe policy based on the access mechanism indicated by the RSD with the highest priority, determining the RSC corresponding to the access mechanism indicated by the RSD with the highest priority, and using the RSC.

[0151] The following explanations use examples to facilitate understanding.

[0152] Figure 7 is a schematic flowchart for determining the PC5 connection mechanism and the access mechanism by the remote end. As shown in Figure 7, in descending order of URSP usage priority, the different URSPs are successively URSP1, URSP2, ..., URSP n, where n is an integer greater than 1. If ProSe communication needs to be performed, the remote UE can preferentially select URSP1 to use. Based on the descending order of RSD usage priority, the different RSDs within URSP1 are successively RSD1, RSD2, RSD3. RSD1 represents a Layer 2 relay mechanism, RSD2 represents a Layer 3 relay mechanism, and RSD3 represents a Layer 3 relay + N3IWF mechanism. The remote UE can preferentially select RSD1 to use, specifically determining that the access mechanism is a Layer 2 relay mechanism. The ProSe policy includes RSC1 through RSC6. RSC1 represents a CP-based mechanism + Layer 2 relay mechanism, RSC2 represents a CP-based mechanism + Layer 3 relay mechanism, RSC3 represents a CP-based mechanism + Layer 3 relay + N3IWF mechanism, RSC4 represents a UP-based mechanism + Layer 2 relay mechanism, RSC5 represents a UP-based mechanism + Layer 3 relay mechanism, and RSC6 represents a UP-based mechanism + Layer 3 relay + N3IWF mechanism. A remote UE can traverse the ProSe policy based on RSD1 to determine that ProSe communication can use the PC5 connection and access mechanisms indicated by RSC1 or RSC4.

[0153] Step 2: The remote UE performs ProSe discovery.

[0154] ProSe discovery is used by remote UEs to discover relay UEs. TS 23.304 defines two discovery models for ProSe discovery: model A and model B.

[0155] In Model A, the interacting UEs include an announcing UE and a monitoring UE. After obtaining the ProSe parameters, the announcing UE can proactively broadcast discovery requests to discover specific ProSe services. After obtaining the ProSe parameters, the monitoring UE can actively monitor discovery requests to discover specific ProSe services. In this way, after receiving a message broadcast by the announcing UE, the monitoring UE can determine whether the ProSe service broadcast by the announcing UE meets the monitoring UE's requirements and whether to proceed with the subsequent steps.

[0156] The above examples continue.

[0157] Figure 8 is a schematic flowchart of ProSe discovery. As shown in Figure 8, in Model A, the announcing UE can be a relay UE, and the monitoring UE can be a remote UE. The relay UE can announce a discovering announcing message, which may include RSCs supported by the relay UE, e.g., RSC1 or RSC2. After receiving the discovering announcing message, the remote UE can determine whether RSC1 or RSC2 is an RSC required by ProSe communication, e.g., RSC1 or RSC4. If the discovering announcing message carries RSC1, the remote UE determines that RSC1 is an RSC required by ProSe communication and continues with the subsequent steps. If the discovering announcing message carries RSC2, the remote UE determines that RSC2 is not an RSC required by ProSe communication and the procedure ends.

[0158] In Model B, the interacting UEs include a discoverer UE and a discoveree UE. After obtaining the ProSe parameters, the discoverer UE can proactively broadcast discovery requests to discover specific ProSe services. After obtaining the ProSe parameters, the discoveree UE can actively monitor discovery requests to discover specific ProSe services. In this way, after receiving a message broadcast by the discoverer UE, the discoveree UE can determine whether it supports the discoverer UE's ProSe services. If the discoveree UE supports the discoverer UE's ProSe services, it responds to the message broadcast by the discoverer UE; otherwise, it does not respond to the message broadcast by the discoverer UE. If the discoverer UE receives a response from the discoveree UE, it continues processing (step 3); otherwise, it terminates processing.

[0159] The above examples continue.

[0160] As shown in Figure 8, in Model B, the discovered UE can be a relay UE, and the discovering UE can be a remote UE. The remote UE can broadcast a discovering request message, which may include the RSC required by ProSe communication, e.g., RSC1 or RSC4. After receiving the discovering request message, the relay UE can decide whether it supports RSC1 or RSC4. If the relay UE determines that it supports RSC1 or RSC4, it can respond to the remote UE by sending a discovering response message indicating that it supports RSC1 or RSC4. Otherwise, the relay UE does not respond to the remote UE. For the remote UE, if it receives a discovering response message, the subsequent procedure (step 3) continues; otherwise, the procedure terminates.

[0161] Step 3: The remote UE establishes a PC5 connection with the relay UE.

[0162] The remote UE may establish a PC5 connection with the relay UE by using the PC5 connection mechanism described above. For specific implementation principles, please refer to the relevant explanations above. Further details will not be explained again.

[0163] Step 4: The remote UE communicates with the network via the relay UE.

[0164] The remote UE can access the network via the relay UE by using the access mechanism described above. For specific implementation principles, please refer to the relevant explanations above. Further details will not be provided again.

[0165] It can be noted that the above procedure defined by 3GPP primarily concerns how a remote UE accesses the network via a relay UE, and does not consider other communication scenarios for the remote UE. As a result, technical problems may arise in the above procedure. For example, in a relay switching scenario, if the remote UE needs to establish a PC5 connection to the original relay UE by using a CP-based mechanism before the relay switching and then establish a PC5 connection to the new relay UE by using a UP-based mechanism after the relay switching, the UP-based mechanism cannot be executed because the remote UE may not be able to obtain the PC5 root key from PKMF in advance after the relay switching, or the pre-obtained PC5 root key may have expired. In this case, the switching fails, and continuity of service cannot be guaranteed. If the remote UE needs to establish a PC5 connection to the original relay UE by using a CP-based mechanism before the relay switching and then establish a PC5 connection to the new relay UE by using a UP-based mechanism after the relay switching, the relay UE may need to establish a PDU session to the network. This causes additional signaling exchange and additional delays, reducing switching efficiency and making it impossible to guarantee continuity of service. Alternatively, if a remote UE needs to establish a PC5 connection to the original relay UE by using a UP-based mechanism before relay switching and then establish a PC5 connection to the new relay UE by using a CP-based mechanism after relay switching, the remote UE may need to perform ProSe authentication again. This results in unnecessary signaling exchanges, reduces switching efficiency, and compromises the ability to guarantee continuity of service.

[0166] In order to address the above technical challenges, the embodiments of this application provide the following technical solutions to ensure the reliability and efficiency of relay switching, thereby ensuring the continuity of service.

[0167] The technical solution of this application will be described below with reference to the attached drawings.

[0168] The technical solutions in the embodiments of this application can be applied to various communication systems, such as wireless fidelity (Wi-Fi) systems, vehicle-to-everything (V2X) communication systems, device-to-device (D2D) communication systems, vehicle internet communication systems, 4th generation (4G) mobile communication systems, such as long-term evolution (LTE) systems, worldwide interoperability for microwave access (WiMAX) communication systems, 5th generation (5G) systems, such as new radio (NR) systems, and future communication systems.

[0169] In this application, all aspects, embodiments, or features are presented by describing a system that may include multiple devices, components, modules, etc. It should be understood that each system may include other devices, components, modules, etc., and / or may not include all of the devices, components, modules, etc. described with reference to the accompanying drawings. In addition, combinations of these solutions may be used.

[0170] In addition, in embodiments of this application, terms such as “example” or “for example” are used to indicate that an example, illustration, or explanation is being given. Any embodiment or design solution described as “example” in this application should not be described as being preferable or having more advantages than another embodiment or design solution. More precisely, the term “example” is used to present a concept in a concrete way.

[0171] In embodiments of this application, the terms “information,” “signal,” “message,” “channel,” and “signaling” may be used interchangeably from time to time. Note that unless the difference between the terms is emphasized, the meanings expressed by the terms are consistent. The terms “of,” “corresponding / relevant,” and “corresponding” may be used interchangeably from time to time. Note that unless the difference between the terms is emphasized, the meanings expressed by the terms are consistent. In addition, “ / ” in this application may represent an “or” relationship.

[0172] The network architectures and service scenarios described in the embodiments of this application are intended to more clearly illustrate the technical solutions in the embodiments of this application and do not constitute limitations on the technical solutions provided in the embodiments of this application. Those skilled in the art will know that, with the development of network architectures and the emergence of new service scenarios, the technical solutions provided in the embodiments of this application are also applicable to similar technical problems.

[0173] To facilitate understanding of the embodiments of this application, the communication system shown in Figure 9 is used first as an example, and the communication systems available in the embodiments of this application will be described in detail. For example, Figure 9 is a diagram of the architecture of a communication system available in a communication method according to one embodiment of this application.

[0174] As shown in Figure 9, the communication system available in the 5GS described above includes a remote device and multiple relay devices such as a first relay device and a second relay device.

[0175] A remote device can establish a first relay connection to a first relay device by using a first PC5 connection mechanism. When the first relay connection needs to be switched, the remote device can determine priority information for the relay service identifier. The priority information for the relay service identifier may indicate that the first PC5 connection mechanism indicated by the relay service identifier should be used preferentially. Alternatively, the remote device may determine the first relay service identifier according to a relay switching policy. The relay switching policy may indicate that when a relay connection needs to be switched, the new relay connection should be established by using the PC5 connection mechanism used before the relay connection switch. In this way, the remote device can establish a second relay connection to a second relay device by using the first PC5 connection mechanism, based on priority information or according to the relay switching policy, thereby ensuring the reliability and efficiency of the relay switching.

[0176] It may be understood that a remote device may be understood as the remote UE described above, a relay device may be understood as the relay UE described above, or any other possible device. This is not limited to this.

[0177] The interaction procedure between network elements / devices in the communication system described above will be specifically explained below with reference to Figures 10 to 12, using embodiments of the method. The communication method according to the embodiments of this application can be applied to the communication system described above and can be specifically applied to various scenarios in the communication system described above. A specific explanation is provided below.

[0178] Scenario 1:

[0179] Figure 10 is a schematic flowchart 1 of a communication method according to one embodiment of the present application. This communication method is applicable to the communication system described above and relates to the interaction between a remote UE, a first relay UE, a second relay UE, a PCF, and a ProSe application server. In Scenario 1, the remote UE can establish a first relay connection to the first relay UE by using a first PC5 connection mechanism. When the first relay connection needs to be switched, the remote UE can establish a second relay connection to the second relay UE by preferentially using the first PC5 connection mechanism, thereby ensuring the reliability and efficiency of relay switching and thus ensuring continuity of service.

[0180] Specifically, as shown in Figure 10, the communication procedure is as follows.

[0181] S1001: The remote UE retrieves ProSe parameters from the PCF.

[0182] ProSe parameters can include ProSe communication-related parameters within URSP, such as ProSe communication-related RSDs. ProSe parameters can further include ProSe policies. For specific implementation principles, please refer to the relevant explanation in "3. ProSe Communication" above. Further details will not be explained again.

[0183] S1002: The remote UE obtains the first instruction information from the PCF.

[0184] The first instruction information may indicate that a relay connection should be established by preferentially using the PC5 connection mechanism used before the relay connection switchover. The relay connection may be a connection established between the remote UE and the relay UE, such as a PC5 connection, or any other possible connection. This is not limited. The PC5 connection mechanism may be a CP-based mechanism, a UP-based mechanism, or any other possible mechanism. This is not limited. The first instruction information may be configured locally on the PCF, or it may be obtained by the PCF from another network element, such as a UDR. This is not limited.

[0185] The remote UE can obtain the first instruction information by reusing the procedure for obtaining ProSe parameters from the PCF, in other words, S1001 and S1002 can be executed together. For example, if the PCF provides a ProSe policy to the remote UE via the UCU procedure for the remote UE's 5G ProSe policy provisioning request message, the PCF may further provide the first instruction information by reusing the UCU procedure. Alternatively, S1001 and S1002 may be executed separately. For example, if the PCF determines that the first instruction information in the ProSe parameters for the UE has been updated, the PCF may, instead, proactively provide the first instruction information to the UE.

[0186] The first instruction information is an exemplary name and may be replaced with any other possible name, such as, for example, the first fast switching instruction or the first fast switching instruction. This is not limited to this.

[0187] It can be further understood that S1002 is an optional step. For example, when a relay connection needs to be switched, the remote UE may, by default, establish the relay connection by preferentially using the PC5 connection mechanism used before the relay connection switch (this is indicated as the remote UE configuring the first policy by default). Alternatively, when the remote UE accesses the network by using a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism, when a relay connection needs to be switched, the remote UE may, by default, establish the relay connection by preferentially using the PC5 connection mechanism used before the relay connection switch (this is indicated as the remote UE configuring the second policy by default). When the network is accessed by using a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism, the establishment of a PDU session to obtain services from the network is requested by the remote UE from the network. In this case, fast switching can be implemented by using the PC5 connection mechanism used before the relay connection switch, and as a result, the remote UE can establish a new PDU session by reusing the user plane resources of the PDU session, thereby ensuring continuity of service.

[0188] S1003: The remote UE establishes a first relay connection to the first relay UE by using the first PC5 connection mechanism.

[0189] The first PC5 connection mechanism may be a UP-based mechanism or a CP-based mechanism. This is not limited to this. A UP-based mechanism may also be referred to as a mechanism that obtains a relay connection key (e.g., the root key for the PC5 connection) via the network's user plane, and a CP-based mechanism may also be referred to as a mechanism that obtains a relay connection key via the network's control plane. For specific implementation principles, please refer to "3. ProSe Communication" above, or the UP-based mechanism and the CP-based mechanism may be replaced with any possible description. This is not limited to this.

[0190] The network may be, but is not limited to, a home public land mobile network (HPLMN) of a remote UE, or a visited public land mobile network (VPLMN) of a remote UE. Services obtained from the network by the remote UE may be several services with high real-time performance and high data capacity requirements, such as extended reality (XR) services, specifically virtual reality (VR) services, or other services, such as audio services. This is not limited to such services.

[0191] The remote UE can determine a first PC5 connection mechanism based on ProSe parameters, such as ProSe communication-related RSDs and ProSe policies, and establish a first relay connection to the first relay UE by using the first PC5 connection mechanism. For specific implementation principles, please refer to the relevant explanation in "3. ProSe Communication" above. Details will not be explained again. When the remote UE establishes a first relay connection to the first relay UE, the remote UE can access the network through the first relay UE by using the first access mechanism and obtain a first service, such as an XR service, or any other possible service from the network. This is not limited to these. The first access mechanism may be any one of the following: a Layer 2 access mechanism, a Layer 3 protocol access mechanism, or a Layer 3 non-protocol access mechanism.

[0192] It can be understood that the execution sequence of S1003 and S1002 is not limited.

[0193] S1004: The remote UE determines that the first relay connection needs to be switched.

[0194] A remote UE can determine, based on the current service status, whether the first relay connection needs to be switched over. For example, if the remote UE determines that the current quality of service of the first relay connection is poor, e.g., the current packet loss rate of the service is high and the service reliability requirements cannot be met, or the current delay of the service is high and the service delay requirements cannot be met, then it may determine that the first relay connection needs to be switched over to establish a relay connection with a better quality of service through the switchover, in order to obtain the service.

[0195] S1005: The remote UE sends a relay reselection request message to the ProSe application server. The ProSe application server receives the relay reselection request message from the remote UE.

[0196] A relay reselection request message may indicate that the PC5 connection mechanism used before the relay connection switchover is the first PC5 connection mechanism. For example, a relay reselection request message may include a remote UE identifier, e.g., a GPSI or application layer user identifier used by the UE, and a first relay service identifier, e.g., an RSC or any other possible identifier. The first relay service identifier may indicate the first PC5 connection mechanism. Optionally, a relay reselection request message may further include a first relay UE identifier, and by using the remote UE identifier and the first relay UE identifier, may indicate that the relay connection established before the relay connection switchover is the first relay connection. Optionally, a relay reselection request message may not carry the first relay service identifier but may carry other identification information indicating the first PC5 connection mechanism, for example. Optionally, a relay reselection request message may further indicate that the relay connection established before the relay connection switchover is the first relay connection.

[0197] S1006: The ProSe application server sends a relay reselection response message to the remote UE. The remote UE receives the relay reselection response message from the ProSe application server.

[0198] A relay reselection response message may respond to a relay reselection request message. For example, a relay reselection response message may include second instruction information, such as a first relay service identifier, to indicate that a relay connection will be established by preferentially using a first PC5 connection mechanism.

[0199] It can be understood that the relay reselection response message may alternatively indicate that a relay connection should be established by not preferentially using the first PC5 connection mechanism, by not carrying the second instruction information. Alternatively, the ProSe application server may indicate that a relay connection should be established by not preferentially using the first PC5 connection mechanism, by not sending a relay reselection response message when a relay connection needs to be switched.

[0200] It can be understood that the second instruction information may, alternatively, be any other possible information element. This is not limited to the second instruction information being an exemplary name and may be replaced with any other possible name, such as second fast switching instruction or second fast switching instruction. This is not limited to the second instruction information being an exemplary name and may be replaced with any other possible name, such as second fast switching instruction or second fast switching instruction.

[0201] It can be further understood that steps S1005 and S1006 are optional. For example, steps S1005 and S1006 do not need to be performed if the remote UE has obtained the first instruction information, or if the remote UE has configured the first or second policy by default.

[0202] S1007: The remote UE determines the priority information for the relay service identifier.

[0203] A relay service identifier may be at least one relay service identifier (including the first relay service identifier) ​​that indicates at least one PC5 connection mechanism (including the first PC5 connection mechanism) for establishing a relay connection, i.e., at least one PC5 connection mechanism supported by the remote UE, for example: at least one of the following: UP-based mechanisms or CP-based mechanisms. For example, each of the at least one relay service identifier may indicate one corresponding PC5 connection mechanism. The remote UE can determine the relay service identifier according to the ProSe policy. For example, the remote UE can determine at least one PC5 connection mechanism supported by the remote UE according to the ProSe policy, and determine the relay service identifier corresponding to each of the at least one PC5 connection mechanism to obtain at least one relay service identifier. It may be understood that the at least one relay service identifier may also be referred to as a relay service identifier list, a relay service identifier set, etc., but is not limited to this.

[0204] To facilitate understanding, one example is used for explanation.

[0205] A ProSe policy includes UP-based and CP-based mechanisms. A remote UE can assign RSC-UP to a UP-based mechanism and RSC-CP to a CP-based mechanism. In this case, at least one relay service identifier includes RSC-UP and RSC-CP. It should be understood that RSC-UP and RSC-CP may be substituted for any other possible representation. For example, RSC-UP may be replaced with RSC1, and RSC-CP may be replaced with RSC2, but this is not limited to these.

[0206] The priority information for a relay service identifier can indicate the usage priority of at least one relay service identifier, that is, the usage priority of at least one PC5 connection mechanism indicated by at least one relay service identifier. The PC5 connection mechanism with the higher usage priority must be used preferentially. In this case, the priority information for the first relay service identifier may indicate that the first PC5 connection mechanism indicated by the first relay service identifier must be used preferentially, in other words, that the first PC5 connection mechanism may have the highest usage priority.

[0207] Where possible, the priority information of the relay service identifier may be explicit. By using a mapping relationship, a mapping relationship can be established between the priority information of the relay service identifier and at least one relay service identifier to indicate the usage priority of each of at least one PC5 connection mechanisms.

[0208] The above examples continue.

[0209] The priority information for relay service identifiers is listed in descending order of priority, with priority 1 followed by priority 2, and the corresponding relationships can be enumerated in Table 1.

[0210] [Table 1]

[0211] If the first PC5 connection mechanism is a UP-based mechanism, the mapping relationship can indicate that priority 1 corresponds to RSC-UP and priority 2 corresponds to RSC-CP. Specifically, it can be seen that the relay connection is established by preferentially using the UP-based mechanism, and if the UP-based mechanism cannot be used, the relay connection is established by using the CP-based mechanism. Priority information can also be understood as the sequence number of the relay service identifier in the mapping relationship table. For example, priority 1 is sequence number 0 and priority 2 is sequence number 1.

[0212] Alternatively, the priority information of the relay service identifier may be implicit. The priority information of the relay service identifier can be represented by a sequence of at least one relay service identifier. In other words, a sequence of at least one relay service identifier can implicitly indicate the usage priority of at least one PC5 connection mechanism.

[0213] The above examples continue.

[0214] Priority information for relay service identifiers can be listed in Table 2.

[0215] [Table 2]

[0216] If the first PC5 connection mechanism is a UP-based mechanism, it may be found that a top-to-bottom sequence of at least one relay service identifier may indicate a descending order of usage priority, specifically indicating that the relay connection will be established by using the UP-based mechanism preferentially, and if the UP-based mechanism is unavailable, that the relay connection will be established by using the CP-based mechanism. It may be understood that a bottom-to-top sequence of at least one relay service identifier may alternatively indicate a descending order of usage priority, but is not limited to this.

[0217] Optionally, the remote UE may determine the priority information of the relay service identifiers based on the first instruction information. For example, the remote UE may determine the priority of each of at least one relay service identifiers based on the first instruction information, and determine that the first PC5 connection mechanism will be used before relay connection switching, thereby obtaining the priority information of the relay service identifiers. Alternatively, the remote UE may determine the priority information of the relay service identifiers based on the second instruction information. For example, the remote UE may determine the priority of each of at least one relay service identifiers based on the second instruction information, thereby obtaining the priority information of the relay service identifiers. Alternatively, the remote UE may determine the priority information of the relay service identifiers according to the first policy. For example, the remote UE may determine the priority of each of at least one relay service identifiers based on the first policy, and determine that the first PC5 connection mechanism will be used before relay connection switching, thereby obtaining the priority information of the relay service identifiers. Alternatively, the remote UE may determine the priority information of the relay service identifiers according to the second policy. For example, a remote UE can determine the priority of each of at least one relay service identifier based on a second policy, and the network can be accessed by using a first PC5 connection mechanism before relay connection switching, and by using a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism before relay switching, thereby obtaining the relay service identifier priority information.

[0218] After S1007, the remote UE can perform relay UE discovery, which may be implemented in Model B, for example, via S1008 to S1010 below, or in Model A, for example, via S1011 and S1012 below. Further details are provided below.

[0219] S1008: The remote UE transmits at least one relay service identifier.

[0220] A remote UE can broadcast at least one relay service identifier (including a first relay service identifier). For example, a remote UE can send at least one discovery request message, each discovery request message can carry one corresponding relay service identifier within at least one relay service identifier to indicate one corresponding PC5 connection mechanism. Alternatively, a remote UE can send one discovery request message, each discovery request message can carry at least one relay service identifier, each relay service identifier can indicate at least one PC5 connection mechanism.

[0221] It may be understood that S1008 may be executed multiple times to increase the probability of finding the relay UE.

[0222] S1009: The remote UE receives the relay service identifier of at least one relay UE.

[0223] The relay service identifier of at least one relay UE can indicate at least one PC5 connection mechanism, i.e., a PC5 connection mechanism supported by at least one relay UE. The relay service identifier of at least one relay device may or may not include a relay service identifier indicating a first PC5 connection mechanism.

[0224] Specifically, after receiving a discovery request message, the relay UE can determine whether it has locally stored the relay service identifier contained in the discovery request message. If the relay UE has locally stored the relay service identifier carried in the discovery request message, it can determine that it supports the PC5 connection mechanism supported by the remote UE and, for example, choose to feed back the relay service identifier corresponding to the PC5 connection mechanism supported by the relay UE to the remote UE, and send a discovery response message carrying the relay service identifier. Otherwise, the relay UE can choose not to send a discovery response message to the remote UE. In this way, the remote UE can receive relay service identifiers from at least one relay UE.

[0225] The above examples continue.

[0226] A remote UE can broadcast discovery request message 1 and discovery request message 2, where discovery request message 1 carries RSC-UP and discovery request message 2 carries RSC-CP. Relay UE 1 supports the UP-based mechanism. Based on the received discovery request messages 1 and 2, relay UE 1 may decide to respond to discovery request 1 by sending discovery response message 1. Discovery response message 1 may carry RSC-UP. Relay UE 2 supports the CP-based mechanism and may decide to respond to discovery request 2 by sending discovery response message 2 based on the received discovery request messages 1 and 2. Discovery response message 2 may carry RSC-CP. Relay UE 3 supports both the CP-based and UP-based mechanisms and may send discovery response message 3 based on the received discovery request messages 1 and 2. Discovery response message 3 may carry RSC-CP and RSC-UP. Relay UE4 supports both CP-based and UP-based mechanisms and can respond to discovery request 1 by sending discovery response message 4 and to discovery request 2 by sending discovery response message 5, based on the discovery request message 1 and discovery request message 2 received. Discovery response message 4 can carry RSC-UP, and discovery response message 5 can carry RSC-CP. In this case, the remote UE can receive six RSCs, including three RSC-CPs and three RSC-UPs.

[0227] S1010: The remote UE determines, based on the priority information of the relay service identifier, that a relay connection should be established to the second relay UE by using the first PC5 connection mechanism.

[0228] The remote UE can determine the priority of at least one relay UE's received relay service identifiers based on the relay service identifier priority information and select the relay service identifier with the highest priority to use.

[0229] If the relay service identifier of at least one relay device includes a relay service identifier indicating a first PC5 connection mechanism, the highest priority relay service identifier is the relay service identifier indicating the first PC5 connection mechanism, and the relay UE corresponding to the relay service identifier indicating the first PC5 connection mechanism may be a second relay UE, in other words, the relay service identifier indicating the first PC5 connection mechanism is the relay service identifier of the second relay UE. In other words, a remote UE may decide, based on the priority information of the first relay service identifier, to establish a relay connection to the second relay UE in at least one relay UE by using the first PC5 connection mechanism.

[0230] If the relay service identifier of at least one relay device does not include a relay service identifier indicating a first PC5 connection mechanism, it can be understood that the relay service identifier with the highest priority may be a relay service identifier with the highest priority indicating another PC5 connection mechanism.

[0231] If multiple relay service identifiers with the highest priority exist, the remote UE may choose any one of the multiple relay service identifiers to use, or it may choose the first relay service identifier received from among the multiple relay service identifiers to use. This is not limited to this.

[0232] The above examples continue.

[0233] The remote UE may select three RSC-UPs from the six received RSCs based on the priority of the RSC-UPs, which is higher than the priority of the RSC-CPs. Of the three RSC-UPs to be used, it may further select the first RSC-UP received, for example, the RSC-UP of relay UE1, or it may select any one of the three RSC-UPs.

[0234] S1008-S1010 are procedures for Model B, and it can be further understood that the remote UE may use Model B by default, or may decide to use Model B based on other conditions. For example, when a relay connection needs to be switched, and the relay connection is established by preferentially using the PC5 connection mechanism that was in use before the relay connection switch, the remote UE decides to use Model B.

[0235] S1011: The remote UE receives the relay service identifier of at least one relay UE.

[0236] The relay service identifier of at least one relay UE can indicate at least one PC5 connection mechanism, i.e., a PC5 connection mechanism supported by at least one relay UE. For example, each of the at least one relay UE can send a discovery announcement message, which can carry the relay service identifier of the relay UE to indicate the PC5 connection mechanism supported by the relay UE. In response, a remote UE receives a discovery announcement message from at least one relay UE and obtains the relay service identifier of at least one relay UE.

[0237] Since the remote UE does not pre-transmit at least one relay service identifier supported by the remote UE, it can be understood that it does not specifically indicate the PC5 connection mechanism supported by the remote UE, in which case the PC5 connection mechanism indicated by the relay service identifier of at least one relay UE may or may not include the PC5 connection mechanism supported by the remote UE.

[0238] The above examples continue.

[0239] Relay UE1 supports the UP-based mechanism and can announce discovery announcement message 1, which can carry RSC-UP. Relay UE2 supports the CP-based mechanism and can announce discovery announcement message 2, which can carry RSC-CP. Relay UE3 supports both the CP-based and UP-based mechanisms and can announce discovery announcement message 3, which can carry RSC-CP and RSC-UP. Relay UE4 supports both the CP-based and UP-based mechanisms and can announce discovery announcement messages 4 and 5, which can carry RSC-UP and RSC-CP. In this case, the remote UE can receive six RSCs, including three RSC-CPs and three RSC-UPs.

[0240] S1012: The remote UE decides to establish a relay connection with the second relay UE by using the first PC5 connection mechanism, based on the priority information of the relay service identifier.

[0241] The remote UE can determine, based on at least one local relay service identifier (for example, in S1007), whether the relay service identifier of at least one relay UE contains a relay service identifier within at least one relay service identifier. If the relay service identifier of at least one relay UE does not contain a relay service identifier within at least one relay service identifier, the remote UE can perform processing based on existing logic. If the relay service identifier of at least one relay UE contains a relay service identifier within at least one relay service identifier, the remote UE can mark the relay service identifiers within at least one relay service identifier based on the priority information of the relay service identifiers and select the relay service identifier with the highest priority to use. For specific implementation principles, please refer to the relevant explanation in S1010. Further details will not be explained again.

[0242] The above examples continue.

[0243] The remote UE can determine that all six received RSCs belong to at least one relay service identifier, based on the RSC-UPs and RSC-CPs included in at least one relay service identifier. Based on the fact that the priority of the RSC-UPs is higher than the priority of the RSC-CPs, the remote UE selects three RSC-UPs from the six received RSCs, and of the two RSC-UPs to use, it may further select the first RSC-UP received, for example, the RSC-UP of relay UE1, or it may select any one of the two RSC-UPs.

[0244] S1011 and S1012 are procedures in Model A, and it should be understood that the remote UE may use Model A by default. Alternatively, the remote UE may decide to use Model A based on other conditions. For example, when a relay connection needs to be switched, the remote UE may decide to use Model A if the relay connection is established by preferentially using the PC5 connection mechanism that was in use before the relay connection switch. Alternatively, the remote UE may randomly select either Model A or Model B.

[0245] S1013: The remote UE establishes a second relay connection to the second relay UE by using the first PC5 connection mechanism.

[0246] For the specific implementation principles of S1013, please refer to the relevant explanation in "3. ProSe Communication" above. Further details will not be explained again.

[0247] Scenario 2:

[0248] Figure 11 is a schematic flowchart 2 of a communication method according to one embodiment of the present application. This communication method is applicable to the communication system described above and relates to the interaction between a remote UE, a first relay UE, a second relay UE, a PCF, and a ProSe application server. In Scenario 2, the remote UE can establish a first relay connection to the first relay UE by using a first PC5 connection mechanism and access the first network via the first relay UE by using a first access mechanism. When the first relay connection needs to be switched, the remote UE can ensure the reliability and efficiency of relay switching and therefore the continuity of service by preferentially using the first PC5 connection mechanism to establish a second relay connection to the second relay UE and preferentially using the first access mechanism to access the first network via the first relay UE.

[0249] Specifically, as shown in Figure 11, the procedure for the communication method is as follows.

[0250] S1101: The remote UE retrieves ProSe parameters from the PCF.

[0251] ProSe parameters can include ProSe communication-related parameters within URSP, such as ProSe communication-related RSDs. ProSe parameters can further include ProSe policies. For specific implementation principles, please refer to the relevant explanation in "3. ProSe Communication" above. Further details will not be explained again.

[0252] S1102: The remote UE obtains third instruction information from the PCF.

[0253] The third instruction information may indicate that the relay connection will be established by preferentially using the PC5 connection mechanism used before the relay connection switchover, and that the network will be accessed by preferentially using the access mechanism used before the relay connection switchover. For specific implementation principles of the relay connection and PC5 connection mechanism, see the relevant explanation in S1002. Details will not be explained again. The access mechanism may be a mechanism used by the remote UE to access the network via the relay UE, and may include, for example, at least one of the following: a Layer 2 relay mechanism, a Layer 3 relay mechanism, or a Layer 3 relay + N3IWF mechanism. The third instruction information may be configured locally on the PCF, or it may be obtained by the PCF from another network element, such as a UDR. This is not limited to this.

[0254] The remote UE can obtain third instruction information by reusing the procedure for obtaining ProSe parameters from the PCF, in other words, S1101 and S1102 can be executed together. For example, if the PCF provides a ProSe policy to the remote UE via the UCU procedure for the remote UE's 5G ProSe policy provisioning request message, the PCF may further provide third instruction information by reusing the UCU procedure. Alternatively, S1101 and S1102 may be executed separately. For example, if the PCF determines that third instruction information in the ProSe parameters for the UE has been updated, the PCF may, instead, proactively provide the third instruction information to the UE.

[0255] The third instruction information is an exemplary name and may be replaced with any other possible name, such as, for example, a third fast switching instruction or a third fast switching instruction. This is not limited to this.

[0256] It can be further understood that S1102 is an optional step. For example, when a relay connection needs to be switched, the remote UE may, by default, establish the relay connection by preferentially using the PC5 connection mechanism used before the relay connection switch, and access the network by preferentially using the access mechanism used before the relay connection switch (this is shown as the remote UE configuring a third policy by default). Alternatively, when the relay connection needs to be switched when the remote UE accesses the network using a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism, the remote UE may, by default, establish the relay connection by preferentially using the PC5 connection mechanism used before the relay connection switch, and access the network by preferentially using the access mechanism used before the relay connection switch (this is shown as the remote UE configuring a fourth policy by default).

[0257] S1103: The remote UE establishes a first relay connection to the first relay UE by using the first PC5 connection mechanism.

[0258] S1104: The remote UE determines that the first relay connection needs to be switched.

[0259] For specific implementation principles of S1103 and S1104, please refer to the relevant explanations in S1003 and S1004. Further details will not be provided again.

[0260] S1105: The remote UE sends a relay reselection request message to the ProSe application server. The ProSe application server receives the relay reselection request message from the remote UE.

[0261] The relay re-selection request message can indicate that the PC5 connection mechanism used before the relay connection switchover is the first PC5 connection mechanism, and optionally further indicate that the relay connection established before the relay connection switchover is the first relay connection. For specific implementation principles, please refer to the relevant explanation in S1005. Further details will not be explained again.

[0262] Optionally, the relay reselection request message may further indicate that the access mechanism used before the relay connection switchover was the first access mechanism. The first access mechanism can be used by a remote UE to access the network. For example, if a remote UE establishes a first relay connection to the first relay UE, the remote UE can access the first network through the first relay UE by using the first access mechanism to obtain services, e.g., XR services, or any other possible services from the first network. This is not limited to these. The first access mechanism may be any one of the following: a Layer 2 relay mechanism, a Layer 3 relay mechanism, or a Layer 3 relay + N3IWF mechanism.

[0263] A relay reselection request message can indicate that the access mechanism used before the relay connection switchover was the first access mechanism by reusing the first relay service identifier within the relay reselection request message. This can reduce overhead. Alternatively, another information element, such as the identifier of the first access mechanism, can indicate that the access mechanism used before the relay connection switchover was the first access mechanism, to improve the flexibility of indication. This is not limited to this.

[0264] S1106: The ProSe application server sends a relay reselection response message to the remote UE. The remote UE receives the relay reselection response message from the ProSe application server.

[0265] A relay reselection response message may respond to a relay reselection request message. For example, a relay reselection response message may include fourth directive information, such as a first relay service identifier, indicating that a relay connection is established by preferentially using a first PC5 connection mechanism and that the network is accessed by preferentially using a first access mechanism.

[0266] It should be understood that establishing a relay connection by preferentially using the first PC5 connection mechanism and accessing the network by preferentially using the first access mechanism is just one example, and not limited to it. In some scenarios, the relay reselection response message may alternatively indicate, by carrying other directive information, that the relay connection be established by not preferentially using the first PC5 connection mechanism and / or that the network be accessed by not preferentially using the first access mechanism. For example, the other directive information may be a relay service identifier that specifically indicates the first PC5 connection mechanism, indicating that the relay connection be established by preferentially using the first PC5 connection mechanism and that the network is accessed without preferentially using the first access mechanism. For example, the other directive information may alternatively be a relay service identifier that specifically indicates the first access mechanism, indicating that the network is accessed by preferentially using the first access mechanism and that the relay connection is established without preferentially using the first PC5 connection mechanism. Alternatively, the relay reselection response message may indicate that a relay connection is established by not preferentially using the first PC5 connection mechanism, by not carrying any instructional information, and that access to the network is accessed by not preferentially using the first access mechanism.

[0267] It can be understood that the fourth instruction information may, alternatively, be any other possible information element. This is not limited to the fourth instruction information. The fourth instruction information is an exemplary name and may be replaced with any other possible name, such as fourth fast switching instruction or fourth fast switching instruction. This is not limited to the fourth instruction information.

[0268] It can be further understood that S1105 and S1006 are optional steps. For example, if the remote UE obtains third instruction information, or if the remote UE has configured a fourth policy by default, S1105 and S1106 do not need to be performed.

[0269] S1107: The remote UE determines the priority information for the relay service identifier.

[0270] A relay service identifier may be at least one relay service identifier (including a first relay service identifier) ​​and may indicate at least one PC5 connection mechanism (including a first PC5 connection mechanism) for establishing a relay connection, which may include, for example, at least one of the following: UP-based mechanisms or CP-based mechanisms, and may further indicate at least one access mechanism for accessing the network, which may include, for example, at least one of the following: Layer 2 relay mechanisms, Layer 3 relay mechanisms, or Layer 3 relay + N3IWF mechanisms. For example, each relay service identifier may indicate one corresponding PC5 connection mechanism and one corresponding access mechanism. A remote UE can determine at least one relay service identifier based on the ProSe policy and ProSe communication-related parameters in the URSP. For example, a remote UE can determine at least one PC5 connection mechanism supported by the remote UE according to the ProSe policy and determine at least one access mechanism supported by the remote UE based on ProSe communication-related parameters, for example, the ProSe communication-related RSD in the URSP. A remote UE can assign one relay service identifier to each combination of at least one access mechanism and at least one PC5 connection mechanism in order to obtain at least one relay service identifier.

[0271] To facilitate understanding, one example is used for explanation.

[0272] The ProSe policy includes UP-based and CP-based mechanisms. The ProSe communication-related RSDs include RSD1, RSD2, and RSD3. RSD1 represents a Layer 2 relay mechanism, RSD2 represents a Layer 3 relay mechanism, and RSD3 represents a Layer 3 relay + N3IWF mechanism. In this case, there are six possible combinations of access mechanisms and PC5 connection mechanisms, including combination 1 (UP-based mechanism and Layer 2 relay mechanism), combination 2 (UP-based mechanism and Layer 3 relay mechanism), combination 3 (UP-based mechanism and Layer 3 relay + N3IWF mechanism), combination 4 (CP-based mechanism and Layer 2 relay mechanism), combination 5 (CP-based mechanism and Layer 3 relay mechanism), and combination 6 (CP-based mechanism and Layer 3 relay + N3IWF mechanism). The remote UE assigns the corresponding RSC to each of the six combinations. For example, a remote UE assigns RSC-UP-1 to combination 1, RSC-UP-2 to combination 2, RSC-UP-3 to combination 3, RSC-CP-1 to combination 4, RSC-CP-2 to combination 5, and RSC-CP-3 to combination 4. In this case, at least one relay service identifier includes RSC-UP-1, RSC-UP-2, RSC-UP-3, RSC-CP-1, RSC-CP-2, and RSC-CP-3.

[0273] It should be understood that RSC-UP-1, RSC-UP-2, RSC-UP-3, RSC-CP-1, RSC-CP-2, and RSC-CP-3 may be substituted for other expressions. For example, RSC-UP-1 can be replaced with RSC1, RSC-UP-2 with RSC2, RSC-UP-3 with RSC3, RSC-CP-1 with RSC4, RSC-CP-2 with RSC5, and RSC-CP-3 with RSC6. This is not limited to these.

[0274] The priority information for the relay service identifier may indicate the usage priority of at least one relay service identifier, that is, the usage priority of at least one PC5 connection mechanism indicated by at least one relay service identifier, and the usage priority of at least one access mechanism indicated by at least one relay service identifier. The PC5 connection mechanism and access mechanism with higher priority must be used preferentially. Specifically, for each combination of at least one PC5 connection mechanism and at least one access mechanism, the combination with the higher usage priority must be used preferentially. In this case, the priority information for the first relay service identifier may indicate that the first PC5 connection mechanism and first access mechanism indicated by the first relay service identifier must be used preferentially, or in other words, that the combination of the first PC5 connection mechanism and the first access mechanism may have the highest usage priority.

[0275] Where possible, the priority information of a relay service identifier may be explicit. A mapping relationship may be established between the priority information of a relay service identifier and at least one relay service identifier, and by using this mapping relationship, the usage priority of each combination of at least one PC5 connection mechanism and at least one access mechanism can be indicated.

[0276] The above examples continue.

[0277] The priority information for relay service identifiers is listed in descending order of priority, from priority 1 to priority 6, and the corresponding relationships can be enumerated in Table 3.

[0278] [Table 3]

[0279] When the first PC5 connection mechanism is a UP-based mechanism, the mapping relationship may indicate that priority 1 corresponds to RSC-UP-1, priority 2 corresponds to RSC-UP-2, and priority 3 corresponds to RSC-UP-3. Specifically, it can be appreciated that the mapping relationship may indicate that a relay connection is established by preferentially using the UP-based mechanism, and based on using the UP-based mechanism, a Layer 2 relay mechanism, a Layer 3 relay mechanism, or a Layer 3 relay + N3IWF mechanism are used sequentially in descending order of priority. In addition, the mapping relationship may further indicate that priority 4 corresponds to RSC-CP-1, priority 5 corresponds to RSC-CP-2, and priority 6 corresponds to RSC-CP-3. Specifically, when the UP-based mechanism cannot be used, the mapping relationship may indicate that a relay connection is established by using a CP-based mechanism, and based on using the CP-based mechanism, a Layer 2 relay mechanism, a Layer 3 relay mechanism, or a Layer 3 relay + N3IWF mechanism are used sequentially in descending order of priority.

[0280] The priority information may also be understood as the sequence number of the relay service identifier in the mapping relationship table. For example, priority 1 is sequence number 0, and priority 2 is sequence number 1. The rest can be inferred by analogy.

[0281] In another possible manner, the priority information of the relay service identifier may alternatively be implicit information, and may be represented by a sequence of at least one relay service identifier. In other words, the sequence of the at least one relay service identifier may implicitly indicate the usage priority of each combination of at least one PC5 connection mechanism and at least one access mechanism.

[0282] The above example is continued.

[0283] The at least one relay service identifier may be listed in Table 4.

[0284] [Table 4]

[0285] If the first PC5 connection mechanism is a UP-based mechanism, it may be found that the top-to-bottom sequence of at least one relay service identifier may indicate descending order of usage priority. See the relevant explanation in Table 3 for the meaning of descending priority. Further details are not provided. It may be understood that the bottom-to-top sequence of at least one relay service identifier may alternatively indicate descending order of usage priority. This is not limited to this.

[0286] Optionally, the remote UE may determine the priority information of relay service identifiers based on first instruction information. For example, the remote UE may determine the priority of each of at least one relay service identifier based on the first instruction information, and the network may be established and accessed by using the first PC5 connection mechanism before relay connection switching and using the first access mechanism before relay connection switching to obtain the priority information of relay service identifiers. Alternatively, the remote UE may determine the priority information of relay service identifiers based on second instruction information. For example, the remote UE can determine the priority of each of at least one relay service identifier based on the second instruction information to obtain the priority information of relay service identifiers. Alternatively, the remote UE may determine the priority information of relay service identifiers according to the first policy. For example, the remote UE may determine the priority of each of at least one relay service identifier based on the first policy, and the network may be established and accessed by using the first PC5 connection mechanism before relay connection switching and using the first access mechanism before relay connection switching to obtain the priority information of relay service identifiers. Alternatively, the remote UE may determine the priority information of the relay service identifiers according to a second policy. For example, the remote UE may determine the priority of each of at least one relay service identifier based on the second policy, and the network may be accessed by using a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism before the relay connection switchover to obtain the priority information of the relay service identifiers.

[0287] In this case, the priority of the relay service identifier indicating the first PC5 connection mechanism may be higher than the priority of the relay service identifiers indicating other PC5 connection mechanisms. Based on this, the priority of multiple relay service identifiers indicating the same PC5 connection mechanism can be determined based on the access mechanism indicated by the multiple relay service identifiers. In this case, the priority of the relay service identifier indicating the first access mechanism may be higher than the priority of the relay service identifiers indicating other access mechanisms. In other words, in at least one relay service identifier, the priority of the relay service identifier indicating both the first PC5 connection mechanism and the first access mechanism may be the highest.

[0288] After S1107, the remote UE can perform relay UE discovery, which may be implemented in Model B, for example, via S1108 to S1110 below, or in Model A, for example, via S1111 and S1112 below. Further details are provided below.

[0289] S1108: The remote UE transmits at least one relay service identifier.

[0290] A remote UE can broadcast at least one relay service identifier (including a first relay service identifier). For example, a remote UE can send at least one discovery request message, each discovery request message can carry one corresponding relay service identifier within at least one relay service identifier to indicate one corresponding PC5 connection mechanism and one corresponding access mechanism. Alternatively, a remote UE can send one discovery request message, each discovery request message can carry at least one relay service identifier, each relay service identifier can indicate at least one PC5 connection mechanism and at least one access mechanism.

[0291] It may be understood that S1108 may be executed multiple times to increase the probability of finding the relay UE.

[0292] S1109: The remote UE receives the relay service identifier of at least one relay UE.

[0293] The relay service identifier of at least one relay UE may indicate at least one combination of PC5 connection and access mechanisms, i.e., a PC5 connection and access mechanism supported by at least one relay UE. The relay service identifier of at least one relay device may or may not include a relay service identifier indicating a first PC5 connection and a first access mechanism.

[0294] Specifically, after receiving a discovery request message, the relay UE can determine whether it has locally stored the relay service identifier contained in the discovery request message. If the relay UE has locally stored the relay service identifier carried in the discovery request message, it can determine that it supports the PC5 connection and access mechanisms supported by the remote UE and, for example, choose to feed back the relay service identifier corresponding to the PC5 connection and access mechanisms supported by the relay UE to the remote UE, and send a discovery response message carrying the relay service identifier. Otherwise, the relay UE can choose not to send a discovery response message to the remote UE. In this way, the remote UE can receive relay service identifiers from at least one relay UE.

[0295] The above examples continue.

[0296] A remote UE can broadcast discovery request message 1 to discovery request message 6. Discovery request message 1 carries RSC-UP-1, discovery request message 2 carries RSC-UP-2, discovery request message 3 carries RSC-UP-3, discovery request message 4 carries RSC-CP-1, discovery request message 5 carries RSC-CP-2, and discovery request message 6 carries RSC-CP-3. Relay UE1 supports UP-based and Layer 2 relay mechanisms. Based on the received discovery request message 1, relay UE1 may decide to send discovery response message 1 carrying RSC-UP-1 in response to discovery request 1. Relay UE1 does not respond to discovery request messages 2 through 6. Relay UE2 supports CP-based and Layer 2 relay mechanisms. Based on the received discovery request message 4, relay UE2 may decide to send discovery response message 2 carrying RSC-CP in response to discovery request 4. Relay UE2 does not respond to discovery request messages 1 through 5, and discovery request message 6. Relay UE3 supports CP-based, UP-based, and Layer 2 relay mechanisms. Based on the received discovery request messages 1 and 4, Relay UE3 may decide to send discovery response message 3 carrying RSC-CP-1 and RSC-UP-1 in response to discovery request 1 and discovery request 4. Relay UE3 does not respond to discovery request messages 2, 3, 5, and 6. Relay UE4 supports CP-based, UP-based, and Layer 2 relay mechanisms. Based on the received discovery request messages 1 and 4, Relay UE4 may decide to send discovery response message 4 carrying RSC-UP-1 in response to discovery request 1 and discovery response message 5 carrying RSC-CP-1 in response to discovery request 4. In this case, the remote UE can receive six RSCs, including three RSC-CP-1s and three RSC-UP-1s.

[0297] S1110: The remote UE decides to establish a relay connection with the second relay UE by using the first PC5 connection mechanism and to access the network by using the first access mechanism, based on the priority information of the relay service identifier.

[0298] The remote UE can determine the priority of at least one relay UE's received relay service identifiers based on the relay service identifier priority information and select the relay service identifier with the highest priority to use.

[0299] If the relay service identifier of at least one relay device includes a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism, the relay service identifier with the highest priority may be the relay service identifier indicating the first PC5 connection mechanism and the first access mechanism. In this case, the relay service identifier indicating the first PC5 connection mechanism and the first access mechanism is the relay service identifier of the second relay UE. In other words, a remote UE may decide, based on the priority information of the first relay service identifier, to establish a relay connection to the second relay UE within at least one relay UE by using the first PC5 connection mechanism.

[0300] If the relay service identifiers of the at least one relay device do not include a relay service identifier indicating the first PC5 connection mechanism and the first access mechanism, and if the relay service identifiers of the at least one relay device include a relay service identifier indicating the first PC5 connection mechanism, it can be appreciated that the relay service identifier with the highest priority is within the relay service identifiers indicating the first PC5 connection mechanism, and may be the relay service identifier indicating the access mechanism with the highest priority. Alternatively, if the relay service identifiers of the at least one relay device include neither a relay service identifier indicating the first PC5 connection mechanism nor a relay service identifier indicating the first PC5 connection mechanism, the relay service identifier with the highest priority may be a relay service identifier indicating another PC5 connection mechanism and another access mechanism with the highest priority.

[0301] It can be further appreciated that when there are multiple relay service identifiers with the highest priority, the remote UE may select any one of the multiple relay service identifiers to use, or may select the first received relay service identifier from the multiple relay service identifiers to use. This is not limited.

[0302] The above example continues.

[0303] The remote UE selects three RSC-UP-1 among the six received RSCs based on the priority of RSC-UP-1 that is higher than the priority of RSC-CP-1, and among the three RSC-UP-1 to be used, may further select the first received RSC-UP-1, for example, RSC-UP-1 of relay UE1, or may select and use any one of the three RSC-UP-1.

[0304] S1108-S1110 are procedures for Model B, and it can be further understood that the remote UE may use Model B by default, or may decide to use Model B based on other conditions. For example, if the relay connection needs to be switched and the relay connection is established by preferentially using the PC5 connection mechanism used before the relay connection switch, the remote UE will decide to use Model B. In another example, if the relay connection needs to be switched and the relay connection is established by preferentially using the PC5 connection mechanism used before the relay connection switch, and the network is accessed by preferentially using the access mechanism used before the relay connection switch, the remote UE will decide to use Model B.

[0305] S1111: The remote UE receives the relay service identifier of at least one relay UE.

[0306] The relay service identifier of at least one relay UE can indicate at least one PC5 connection mechanism and at least one access mechanism, i.e., a PC5 connection mechanism and access mechanism supported by at least one relay UE. For example, each of the at least one relay UE can send a discovery announcement message, which can carry the relay service identifier of the relay UE to indicate the PC5 connection mechanism and access mechanism supported by the relay UE. In response, a remote UE receives a discovery announcement message from at least one relay UE and obtains the relay service identifier of at least one relay UE.

[0307] Since the remote UE does not pre-transmit (for example, in S1107) at least one relay service identifier supported by the remote UE, it can be understood that it does not specifically indicate the PC5 connection and access mechanisms supported by the remote UE, in which case the PC5 connection mechanisms indicated by the relay service identifier of at least one relay UE may or may not include the PC5 connection and access mechanisms supported by the remote UE.

[0308] The above examples continue.

[0309] Relay UE1 supports UP-based and Layer 2 relay mechanisms and can announce discovery announcement message 1, which can carry RSC-UP-1. Relay UE2 supports CP-based and Layer 2 relay mechanisms and can announce discovery announcement message 2, which can carry RSC-CP-1. Relay UE3 supports CP-based, UP-based, and Layer 2 relay mechanisms and can announce discovery announcement message 3, which can carry RSC-CP-1 and RSC-UP-1. Relay UE4 supports CP-based and UP-based mechanisms and can announce discovery announcement message 4 and discovery announcement message 5, which can carry RSC-UP and RSC-CP. In this case, the remote UE receives six RSCs, including three RSC-CP-1s and three RSC-UP-1s.

[0310] S1112: The remote UE decides to establish a relay connection with the second relay UE by using the first PC5 connection mechanism and to access the network by using the first access mechanism, based on the priority information of the relay service identifier.

[0311] The remote UE can determine, based on at least one local relay service identifier (for example, in S1107), whether the relay service identifier of at least one relay UE contains a relay service identifier within at least one relay service identifier. If the relay service identifier of at least one relay UE does not contain a relay service identifier within at least one relay service identifier, the remote UE can perform processing based on existing logic. If the relay service identifier of at least one relay UE contains a relay service identifier within at least one relay service identifier, the remote UE can mark the relay service identifiers within at least one relay service identifier based on the priority information of the relay service identifiers and select the relay service identifier with the highest priority to use. For specific implementation principles, please refer to the relevant explanation in S1110. Details will not be explained again.

[0312] The above examples continue.

[0313] The remote UE can determine that all six received RSCs belong to at least one relay service identifier, based on the RSC-UP-1 through RSC-UP-3 and RSC-CP-1 through RSC-CP-3 contained in at least one relay service identifier. The remote UE can then select three RSC-UP-1s from the six received RSCs based on the priority of RSC-UP-1, which is higher than the priority of RSC-CP-1, and may further select the first RSC-UP-1 received, for example, the RSC-UP-1 of relay UE1, from the three RSC-UP-1s to use, or it may select and use any one of the three RSC-UP-1s.

[0314] S1111 and S1112 are procedures in Model A, and it should be understood that the remote UE may use Model A by default. Alternatively, the remote UE may decide to use Model A based on other conditions. For example, if the relay connection needs to be switched and the relay connection is established by preferentially using the PC5 connection mechanism used before the relay connection switch, the remote UE will decide to use Model A. In another example, if the relay connection needs to be switched and the relay connection is established by preferentially using the PC5 connection mechanism used before the relay connection switch, and the network is accessed by preferentially using the access mechanism used before the relay connection switch, the remote UE will decide to use Model A. Alternatively, the remote UE may randomly select either Model A or Model B.

[0315] Furthermore, for the specific implementation principles of S1112, please refer to the related explanation in S1110. Further details will not be explained again.

[0316] S1113: The remote UE establishes a second relay connection to the second relay UE by using the first PC5 connection mechanism.

[0317] When a remote UE establishes a second relay connection to a second relay UE, the remote UE can access the first network through the second relay UE by using the first access mechanism to obtain services, such as XR services, or any other possible services from the first network. This is not limited to these services.

[0318] For the specific implementation principles of S1113, please refer to the relevant explanation in "3. ProSe Communication" above. Further details will not be explained again.

[0319] The specific procedures of the communication method according to the embodiment of the present invention have been described in detail above with reference to Figures 10 and 11 in Scenario 1 and Scenario 2. The overall procedures of the communication method in Scenario 1 and Scenario 2 will now be described in detail with reference to Figure 12.

[0320] Figure 12 is a schematic flowchart 3 of a communication method according to one embodiment of the present application. The communication method is applicable to the communication system described above and mainly concerns the interaction between a remote device (e.g., remote UE), a first relay device (e.g., first relay UE), and a second relay device (e.g., second relay UE).

[0321] Specifically, as shown in Figure 12, the communication procedure is as follows.

[0322] S1201: The remote device establishes a first relay connection with the first relay device by using the first PC5 connection mechanism.

[0323] The first PC5 connection mechanism may include a mechanism for obtaining a relay connection key via the network's user plane, i.e., a user-plane based mechanism, or a mechanism for obtaining a relay connection key via the network's control plane, i.e., a control-plane based mechanism. The first relay connection may be used by a remote device to obtain a first service from the network via a first relay device. For example, a remote device may access the network via the first relay connection by using the first access mechanism within at least one access mechanism to obtain a first service from the network. Optionally, at least one access mechanism may include at least one of the following: a Layer 2 access mechanism, a Layer 3 protocol access mechanism, or a Layer 3 non-protocol access mechanism, to allow the remote device flexible access to the network.

[0324] Furthermore, for the specific implementation principles of S1201, please refer to the related explanations in S1001 and S1003. Further details will not be explained again.

[0325] S1202: When the first relay connection needs to be switched, the remote device obtains priority information for the first relay service identifier.

[0326] The priority information of the first relay service identifier may indicate that the first PC5 connection mechanism indicated by the first relay service identifier should be used preferentially. For specific implementation principles, see the relevant explanations in S1004 and S1007. Further details will not be explained again. Optionally, the priority information of the first relay service identifier may further indicate that the first access mechanism in at least one access mechanism for accessing the network should be used preferentially. For specific implementation principles, see the relevant explanations in S1104 and S1107. Further details will not be explained again.

[0327] S1203: The remote device establishes a second relay connection to the second relay device by using the first PC5 connection mechanism based on the priority information of the first relay service identifier.

[0328] The second relay device may be a relay device that supports the first PC5 connection mechanism, i.e., a relay device corresponding to a relay service identifier indicating the first PC5 connection mechanism. The second relay connection may be used by a remote device to obtain the first service of the network via the second relay device.

[0329] Method 1: The first PC5 connection mechanism, indicated by the relay service identifier, must be used preferentially.

[0330] The remote device can determine, based on the priority information of the first relay service identifier, to establish a relay connection to the second relay device by using the first PC5 connection mechanism; in other words, it can discover the second relay device that supports the first PC5 connection mechanism, thereby ensuring that the remote device can establish a second relay connection to the second relay device by using the first PC5 connection mechanism.

[0331] For example, a remote device may broadcast a first relay service identifier to receive the relay service identifier of at least one relay device. The relay service identifier of at least one relay device includes a relay service identifier indicating a first PC5 connection mechanism. In this way, the remote device may decide to establish a relay connection to a second relay device among the at least one relay device by using the first PC5 connection mechanism, based on the priority information of the first relay service identifier. The second relay device is the relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism. It may be found that the remote device may actively broadcast the relay service identifier to increase the relay discovery probability and discover relay devices that support the first PC5 connection mechanism, such as the second relay device.

[0332] As another example, a remote device may receive a relay service identifier for at least one relay device. The relay service identifier for at least one relay device includes a relay service identifier indicating a first PC5 connection mechanism. In this way, the remote device may decide, based on the priority information of the first relay service identifier, to establish a relay connection to a second relay device among the at least one relay device by using the first PC5 connection mechanism. The second relay device is the relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism. It may be found that the remote device can alternatively and passively receive the relay service identifier to discover a relay device, e.g., a second relay device supporting the first PC5 connection mechanism, thereby avoiding the communication overhead that would result from actively broadcasting the relay service identifier.

[0333] For the specific implementation principles of Method 1, please refer to the relevant explanations in S1008-S1013. Further details will not be explained again.

[0334] Method 2: The first PC5 connection mechanism, indicated by the relay service identifier, must be used preferentially, and of at least one access mechanism, the first access mechanism for accessing the network must be used preferentially.

[0335] The remote device may decide to establish a relay connection to the second relay device by using the first PC5 connection mechanism, based on the priority information of the first relay service identifier, access the network by using the first access mechanism, and establish a second relay connection to the second relay device by using the first PC5 connection mechanism. In addition, the remote device may further access the network via the second relay device by using the first access mechanism. If the remote device intends to switch relay connections when it has accessed the network by using the first access mechanism, it may be found that, in order to further ensure continuity of service, the remote device may continue to access the network by preferentially reusing the access mechanism used before the relay connection switch, i.e., the first access mechanism.

[0336] For example, a remote device may broadcast a first relay service identifier to receive the relay service identifier of at least one relay device. The relay service identifier of at least one relay device includes a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. In this way, based on the priority information of the first relay service identifier, the remote device may decide to establish a relay connection to a second relay device among the at least one relay device by using the first PC5 connection mechanism and to access the network by using the first access mechanism. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism and the first access mechanism. It may be found that the remote device may actively broadcast the relay service identifier to increase the relay discovery probability and discover a relay device that supports the first PC5 connection mechanism and the first access mechanism, such as a second relay device.

[0337] As another example, a remote device may receive a relay service identifier for at least one relay device. The relay service identifier for at least one relay device includes a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. In this way, based on the priority information of the first relay service identifier, the remote device may decide to establish a relay connection to a second relay device among the at least one relay device by using the first PC5 connection mechanism and to access the network by using the first access mechanism. The second relay device is the relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism and the first access mechanism. It may be found that the remote device may alternatively and passively receive the relay service identifier to discover a relay device, e.g., a second relay device supporting the first PC5 connection mechanism and the first access mechanism, thereby avoiding the communication overhead caused by actively broadcasting the relay service identifier.

[0338] For the specific implementation principles of Method 2, please refer to the relevant explanations in S1108 to S1113. Further details will not be explained again.

[0339] In conclusion, when a remote device establishes a first relay connection to a first relay device using a first PC5 connection mechanism, such as a user-plane based mechanism or a control-plane based mechanism, and the remote device intends to switch the relay connection, the remote device can establish a second relay connection to a second relay device by preferentially reusing the connection mechanism used before the relay connection switch, i.e., the first PC5 connection mechanism, thereby improving PC5 connection switching efficiency, reducing switching delay, and ensuring the continuity of the first service obtained from the network by the remote device.

[0340] In a possible design solution, referring to Method 1 described above, the remote device can determine priority information for a first relay service identifier based on first directive information from a policy-controlled network element. The first directive information may indicate establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover. In other words, in addition to establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover by default, the remote device may, alternatively and flexibly, decide whether to establish a relay connection by preferentially using the connection mechanism used before the relay connection switchover based on the directive from the policy-controlled network element to meet the relay switching requirements of different services.

[0341] Alternatively, the remote device can determine the priority information of the first relay service identifier based on second instruction information from the relay server, which indicates establishing the relay connection by preferentially using the first PC5 connection mechanism. In other words, in addition to establishing the relay connection by preferentially using the connection mechanism used before the relay connection switchover by default, the remote device can flexibly decide, based on the relay server's instructions, whether to establish the relay connection by preferentially using the first PC5 connection mechanism, thereby achieving applicability to different switching scenarios.

[0342] Specifically, the remote device sends a relay reselection request message to the relay server, indicating that the connection mechanism used before the relay connection switchover was the first PC5 connection mechanism. The remote device receives a relay reselection response message returned by the relay server in response to the relay reselection request message, and the relay reselection response message carries second instruction information. In other words, the remote device can obtain instructions from the relay server by reusing the relay reselection procedure to reduce the difficulty of implementation. Alternatively, the remote device may obtain instructions from the relay server via a newly defined procedure, but is not limited to this.

[0343] Alternatively, the remote device may determine priority information for the first relay service identifier based on a first access mechanism. The first access mechanism is a mechanism used by the remote device to access the network via the first relay device. For example, the first access mechanism may be either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism. When the remote device accesses the network by using a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism, it can be understood that the remote device can establish a session between the remote device and the network in order to obtain the first service from the network. Based on this, if the remote device implements fast switching by preferentially reusing the connection mechanism used before the relay connection switchover, the remote device can continue to reuse the session before the session becomes invalid, thereby continuing to obtain the first service from the network. This can ensure continuity of service.

[0344] For specific implementation principles of the design solution, it may be helpful to refer to the relevant explanations in S1002, S1005, and S1006. Further details will not be provided again.

[0345] In possible design solutions, referring to Method 2 described above, the remote device can determine priority information for the first relay service identifier based on third directive information from a policy-controlled network element. The third directive information may indicate establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover, and accessing the network by preferentially using the access mechanism used before the relay connection switchover. In other words, based on the directives of the policy-controlled network element, the remote device can flexibly decide whether to establish a relay connection by preferentially using the connection mechanism used before the relay connection switchover, and whether to establish and access the network by preferentially using the access mechanism used before the relay connection switchover, in order to satisfy the relay switching requirements of different services.

[0346] Alternatively, the remote device may determine the priority information of the first relay service identifier based on a fourth instruction from the relay server. The fourth instruction may indicate establishing a relay connection by preferentially using the first PC5 connection mechanism and accessing the network by preferentially using the first access mechanism. In other words, in addition to establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover by default, the remote device can optionally flexibly decide, based on the instructions from the relay server, whether to establish a relay connection by preferentially using the first PC5 connection mechanism and whether to establish and access the network by preferentially using the access mechanism used before the relay connection switchover, thereby achieving applicability to different switching scenarios.

[0347] Specifically, a remote device can send a relay reselection request message to the relay server. The relay reselection request message indicates that the connection mechanism used before the relay connection switchover was the first PC5 connection mechanism, and that the access mechanism used before the relay connection switchover was the first access mechanism. The remote device receives a relay reselection response message from the relay server in response to the relay reselection request message. The relay reselection response message carries fourth instruction information. In other words, to reduce implementation complexity, the remote device can obtain instructions from the relay server by reusing the relay reselection procedure. Alternatively, the remote device may obtain instructions from the relay server via a newly defined procedure, but is not limited to this.

[0348] Alternatively, the remote device may determine priority information for the first relay service identifier based on a first access mechanism. For example, the first access mechanism is either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism. When the remote device accesses the network by using a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism, it can be understood that the remote device can establish a session between the remote device and the network in order to obtain the first service from the network. Based on this, if the remote device implements fast switching by preferentially reusing the connection mechanism used before the relay connection switchover, the remote device can further reuse the session to continue obtaining the first service from the network. This can ensure continuity of service.

[0349] For specific implementation principles of the design solution, it may be helpful to refer to the relevant explanations in S1102, S1105, and S1106. Further details will not be explained again.

[0350] The procedure shown in Figure 11 can be understood as primarily describing the following process: the remote device establishes a first relay connection with a first relay device, and then switches to establishing a second relay connection with a second relay device. This process can also be understood as follows: the remote device switches from a state of establishing a relay connection with the first relay device to a state of establishing a relay connection with the second relay device; in other words, the remote device switches from a state of connection with the first relay device to a state of connection with the second relay device.

[0351] Scenario 3:

[0352] Figure 13 is a schematic flowchart 4 of a communication method according to one embodiment of the present application. This communication method is applicable to the communication system described above and relates to the interaction between a remote UE, a first relay UE, a second relay UE, a PCF, and a ProSe application server. In Scenario 3, the remote UE can establish a first relay connection to the first relay UE by using the first PC5 connection mechanism. When the first relay connection needs to be switched, the remote UE can establish a second relay connection to the second relay UE by using the first PC5 connection mechanism to ensure the reliability and efficiency of relay switching and thus ensure continuity of service.

[0353] Specifically, as shown in Figure 13, the communication procedure is as follows.

[0354] S1301: The remote UE retrieves ProSe parameters from the PCF.

[0355] ProSe parameters can include ProSe communication-related parameters within URSP, such as ProSe communication-related RSDs. ProSe parameters can further include ProSe policies. For specific implementation principles, please refer to the relevant explanation in "3. ProSe Communication" above. Further details will not be explained again.

[0356] S1302: The remote UE obtains the fifth instruction information from the PCF.

[0357] The fifth instruction may indicate that the relay connection is established by using the PC5 connection mechanism used before the relay connection switching. For specific implementation principles of the relay connection and the PC5 connection mechanism, please refer to the relevant explanation in S1002. Further details will not be explained again.

[0358] The remote UE can obtain the fifth instruction information by reusing the procedure for obtaining ProSe parameters from the PCF, in other words, S1301 and S1302 can be executed together. For example, if the PCF provides a ProSe policy to the remote UE via the UCU procedure for the remote UE's 5G ProSe policy provisioning request message, the PCF may further provide the fifth instruction information by reusing the UCU procedure. Alternatively, S1301 and S1302 may be executed separately. For example, if the PCF determines that the fifth instruction information in the ProSe parameters for the UE has been updated, the PCF may, instead, proactively provide the fifth instruction information to the UE.

[0359] The remote UE can determine the relay switching policy based on the fifth instruction information, for example, it can determine the relay switching policy based on the instructions in the fifth instruction information. The relay switching policy can indicate that when a relay connection needs to be switched, the relay connection should be established by using the PC5 connection mechanism used before the relay connection switch, or when the network is accessed using a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism, the relay connection should be established by using the PC5 connection mechanism used before the relay connection switch if a relay connection needs to be switched.

[0360] The fifth instruction information is an illustrative name and can be replaced with any other possible name, such as fifth fast switching instruction or fifth fast switching instruction. This is not limited to this. In addition, S1302 is an optional step. For example, a remote UE may configure a relay switching policy by default.

[0361] S1303: The remote UE establishes a first relay connection to the first relay UE by using the first PC5 connection mechanism.

[0362] S1304: The remote UE determines that the first relay connection needs to be switched.

[0363] S1305: The remote UE sends a relay reselection request message to the ProSe application server. The ProSe application server receives the relay reselection request message from the remote UE.

[0364] For specific implementation principles of S1303 to S1305, please refer to the related explanations in S1003 to S1005. Further details will not be explained again.

[0365] S1306: The ProSe application server sends a relay reselection response message to the remote UE. The remote UE receives the relay reselection response message from the ProSe application server.

[0366] A relay reselection response message may respond to a relay reselection request message. For example, a relay reselection response message may include a relay switching policy to indicate that a relay connection will be established by using a first PC5 connection mechanism.

[0367] It can be understood that, when a relay connection needs to be switched, it is an example, and not an limitation, that a remote UE decides to establish a relay connection by using a first PC5 connection mechanism in accordance with the relay switching policy in the relay reselection response message. Alternatively, the relay reselection response message may indicate that the relay connection will be established without using the first PC5 connection mechanism by not carrying a relay switching policy. Alternatively, the ProSe application server may indicate that it will establish a relay connection without using the first PC5 connection mechanism by not sending a relay reselection response message. Optionally, the relay reselection response message may further carry another relay switching policy, which may indicate that the relay connection will be established by using a different PC5 connection mechanism than the first PC5 connection mechanism.

[0368] It can be further understood that steps S1305 and S1306 are optional. For example, if a remote UE configures a relay switching policy by default, steps S1305 and S1306 may not be performed.

[0369] S1307: The remote UE determines the first relay service identifier according to the relay switching policy.

[0370] A first relay service identifier (e.g., a first RSC) can indicate a first PC5 connection mechanism.

[0371] In a possible way, the relay switching policy may indicate that when a relay connection needs to be switched, the relay connection should be established by using the PC5 connection mechanism that was used before the relay connection switch. Based on this, the remote UE may determine, based on the instructions of the relay switching policy, that a first PC5 connection mechanism was used before the relay connection switch, and determine a first relay service identifier, for example, a first relay service identifier corresponding to the first PC5 connection mechanism.

[0372] Alternatively, the relay switching policy could indicate that when the network is accessed using a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism, and the relay connection needs to be switched, the relay connection should be established by using the PC5 connection mechanism used before the relay connection switch. Based on this, the remote UE can determine, based on the instructions of the relay switching policy, whether the network is accessed using a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism before the relay connection switch. If the network is accessed without using a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism, the remote UE performs processing based on existing logic. If the network is accessed using a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism, the remote UE can determine, based on the instructions of the relay switching policy, that a first PC5 connection mechanism is used before the relay connection switch, and can determine a first relay service identifier indicating the first PC5 connection mechanism.

[0373] After S1307, the remote UE can perform relay UE discovery, which may be implemented in Model B, for example, via S1308 to S1310 below, or in Model A, for example, via S1311 and S1312 below. Further details are provided below.

[0374] S1308: The remote UE transmits the first relay service identifier.

[0375] A remote UE can transmit a first relay service identifier in a broadcast manner. For example, a remote UE can send a discovery request message carrying the first relay service identifier to indicate a first PC5 connection mechanism.

[0376] It may be understood that S1308 may be executed multiple times to increase the probability of finding the relay UE.

[0377] S1309: The remote UE receives the relay service identifier of at least one relay UE.

[0378] The relay service identifier of at least one relay UE may indicate at least one PC5 connection mechanism, i.e., a PC5 connection mechanism supported by at least one relay UE. The relay service identifier of at least one relay device may include a relay service identifier indicating a first PC5 connection mechanism.

[0379] Specifically, with respect to a relay UE, after receiving a discovery request message, the relay UE can determine, based on a first relay service identifier carried in the discovery request message, whether it locally stores a relay service identifier indicating a first PC5 connection mechanism. If the relay UE locally stores a relay service identifier indicating a first PC5 connection mechanism, the relay UE may determine that it supports the first PC5 connection mechanism supported by the remote UE and may choose to provide feedback to the remote UE, for example, by sending a discovery response message carrying the relay service identifier indicating the first PC5 connection mechanism; otherwise, the relay UE may choose not to provide feedback to the remote UE. In this way, the remote UE can receive relay service identifiers from at least one relay UE.

[0380] The above examples continue.

[0381] A remote UE can broadcast a discovery request message carrying an RSC-UP to indicate that it supports the UP-based mechanism. Relay UE1 supports the UP-based mechanism and can send discovery response message 1 carrying an RSC-UP based on the received discovery request message. Relay UE2 supports the CP-based mechanism and therefore does not need to respond to the discovery request message. Relay UE3 supports both the CP-based and UP-based mechanisms and can send discovery response message 2 carrying an RSC-UP based on the received discovery request message. In this case, the remote UE can receive two RSCs, each containing two RSC-UPs.

[0382] S1310: The remote UE decides to establish a relay connection with the second relay UE by using the first PC5 connection mechanism.

[0383] A remote UE may decide to establish a relay connection to a second relay UE within at least one relay UE based on a first relay service identifier. For example, a remote UE may decide, based on the first relay service identifier, that at least one relay UE supports a first PC5 connection mechanism, and then determine the second relay UE from at least one relay UE. For example, at least one relay UE is one relay UE, and the remote UE may determine that this relay UE is the second relay UE. As another example, at least one relay UE may be multiple relay UEs, and the remote UE may determine that any of the multiple relay UEs is the second relay UE, or that the relay UE from which the discovery response message was first received is the second relay UE, or the remote UE may select the relay UE with the best signal quality among the multiple relay UEs as the second relay UE.

[0384] The above examples continue.

[0385] For two received RSC-UPs, the remote UE may decide to select the first RSC-UP received, for example, the RSC-UP of relay UE1, and establish a relay connection to relay UE1 by using the UP-based mechanism, or it may select either of the two RSC-UPs to be used. This is not limited to the remote UE.

[0386] S1308-S1310 are procedures for Model B, and it should be understood that the remote UE may use Model B by default, or may decide to use Model B based on other conditions. For example, if a relay connection needs to be switched, and the relay connection is established by using the PC5 connection mechanism that was used before the relay connection switch, the remote UE will decide to use Model B.

[0387] S1311: The remote UE receives the relay service identifier of at least one relay UE.

[0388] For the specific implementation principles of S1311, please refer to the related explanation in S1011. Further details will not be explained again.

[0389] S1312: The remote UE decides to establish a relay connection with the second relay UE by using the first PC5 connection mechanism.

[0390] The remote UE can determine, based on the first relay service identifier, whether the relay service identifier of at least one relay UE includes a relay service identifier indicating the first PC5 connection mechanism. If the relay service identifier of at least one relay UE does not include a relay service identifier indicating the first PC5 connection mechanism, the remote UE can perform processing based on existing logic. If the relay service identifier of at least one relay UE includes a relay service identifier indicating the first PC5 connection mechanism, the remote UE can establish a relay connection with the second relay UE by using the first PC5 connection mechanism, based on the determination that the relay UE corresponding to the relay service identifier indicating the first PC5 connection mechanism is the second relay UE. For specific implementation principles, please refer to the relevant explanation in S1310. Further details will not be explained again.

[0391] S1311 and S1312 are procedures in Model A, and it should be understood that the remote UE may use Model A by default. Alternatively, the remote UE may decide to use Model A based on other conditions. For example, if the relay connection needs to be switched, and the relay connection is established by using the PC5 connection mechanism that was in use before the relay connection switch, the remote UE will decide to use Model A. Alternatively, the remote UE may randomly select either Model A or Model B.

[0392] S1313: The remote UE establishes a second relay connection to the second relay UE by using the first PC5 connection mechanism.

[0393] For the specific implementation principles of S1313, it is understandable to refer to the related explanation in S1013. Further details will not be explained again.

[0394] Scenario 4:

[0395] Figure 14 is a schematic flowchart 5 of a communication method according to one embodiment of the present application. This communication method is applicable to the communication system described above and relates to the interaction between a remote UE, a first relay UE, a second relay UE, a PCF, and a ProSe application server. In Scenario 4, the remote UE can establish a first relay connection to the first relay UE by using a first PC5 connection mechanism and access the first network through the first relay UE by using a first access mechanism. When the first relay connection needs to be switched, the remote UE can establish a second relay connection to the second relay UE by using a first PC5 connection mechanism and access the first network through the first relay UE by using a first access mechanism, thereby ensuring the reliability and efficiency of relay switching and thus ensuring continuity of service.

[0396] Specifically, as shown in Figure 14, the communication procedure is as follows.

[0397] S1401: The remote UE retrieves ProSe parameters from the PCF.

[0398] ProSe parameters can include ProSe communication-related parameters within URSP, such as ProSe communication-related RSDs. ProSe parameters can further include ProSe policies. For specific implementation principles, please refer to the relevant explanation in "3. ProSe Communication" above. Further details will not be explained again.

[0399] S1402: The remote UE obtains the sixth instruction information from the PCF.

[0400] The sixth instruction information may indicate that the relay connection will be established by using the PC5 connection mechanism used before the relay connection switchover, and that the network will be accessed by using the access mechanism used before the relay connection switchover. For specific implementation principles of the relay connection and PC5 connection mechanism, please refer to the relevant explanation in S1002. Details will not be explained again. For specific implementation principles of the access mechanism, please refer to the relevant explanation in S1102. Details will not be explained again.

[0401] The remote UE may obtain the sixth instruction information by reusing the procedure for obtaining ProSe parameters from the PCF, in other words, S1401 and S1402 may be executed together. For example, if the PCF provides a ProSe policy to the remote UE via the UCU procedure in response to the remote UE's 5G ProSe policy provisioning request message, the PCF may further provide the sixth instruction information by reusing the UCU procedure. Alternatively, S1401 and S1402 may be executed separately. For example, if the PCF determines that the sixth instruction information in the UE's ProSe parameters has been updated, the PCF may, instead, proactively provide the sixth instruction information to the UE.

[0402] The remote UE can determine the relay switching policy based on the sixth instruction information, for example, it can determine the relay switching policy based on the instructions in the sixth instruction information. The relay switching policy may indicate that the relay connection will be established by using the PC5 connection mechanism used before the relay connection switching, and that the network will be accessed by using the access mechanism used before the relay connection switching. If the network is accessed by using a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism, the policy may indicate that the relay connection will be established by using the PC5 connection mechanism used before the relay connection switching, and that the network will be accessed by using the access mechanism used before the relay connection switching.

[0403] The sixth instruction information is an illustrative name and can be replaced with any other possible name, such as sixth fast switching instruction or sixth fast switching instruction. This is not limited to this. In addition, S1402 is an optional step. For example, a remote UE may configure a relay switching policy by default.

[0404] S1403: The remote UE establishes a first relay connection to the first relay UE by using the first PC5 connection mechanism.

[0405] S1404: The remote UE determines that the first relay connection needs to be switched.

[0406] S1405: The remote UE sends a relay reselection request message to the ProSe application server. The ProSe application server receives the relay reselection request message from the remote UE.

[0407] For specific implementation principles of S1403 and S1404, please refer to the relevant explanations for S1003 and S1004. For specific implementation principles of S1405, please refer to the relevant explanation for S1105. Further details will not be explained again.

[0408] S1406: The ProSe application server sends a relay reselection response message to the remote UE. The remote UE receives the relay reselection response message from the ProSe application server.

[0409] A relay reselection response message may respond to a relay reselection request message. For example, a relay reselection response message may include a relay switching policy to indicate that when a relay connection needs to be switched, the relay connection should be established by using a first PC5 connection mechanism and the network should be accessed by using a first access mechanism.

[0410] It should be understood that, when a relay connection needs to be switched, establishing a relay connection by using the first PC5 connection mechanism and accessing the network by using the first access mechanism is one example, but not limited to this. Alternatively, the relay reselection response message may indicate, by carrying other directive information, that when a relay connection needs to be switched, the relay connection should be established without using the first PC5 connection mechanism and / or the network should be accessed without using the first access mechanism. For example, the other directive information may be a relay service identifier specifically indicating the first PC5 connection mechanism, indicating that the relay connection should be established by using the first PC5 connection mechanism and the network should be accessed without using the first access mechanism. As another example, the other directive information may, alternatively, be a relay service identifier specifically indicating the first access mechanism, indicating that the network should be accessed by using the first access mechanism and the relay connection should be established without using the first PC5 connection mechanism. Alternatively, the relay reselection response message may indicate that the relay connection should be established without using the first PC5 connection mechanism and the network should be accessed without using the first access mechanism by not carrying any directive information. Alternatively, the relay reselection response message may carry an alternative relay switching policy, which may indicate establishing a relay connection by using a different PC5 connection mechanism than the first PC5 connection mechanism, and accessing the network by using a different access mechanism than the first access mechanism.

[0411] It can be further understood that steps S1405 and S1406 are optional. For example, if a remote UE configures a relay switching policy by default, steps S1405 and S1406 may not be performed.

[0412] S1407: The remote UE determines the first relay service identifier according to the relay switching policy.

[0413] The first relay service identifier (e.g., the first RSC) may indicate the first PC5 connection mechanism and the first access mechanism.

[0414] In a possible way, a relay switching policy can indicate that when a relay connection needs to be switched, the relay connection should be established by using the PC5 connection mechanism used before the relay connection switch, and the network should be accessed by using the access mechanism used before the relay connection switch. Based on this, the remote UE can determine a first relay service identifier based on the instructions of the relay switching policy, deciding that a first PC5 connection mechanism and a first access mechanism were used before the relay connection switch, for example, determining a first relay service identifier corresponding to the first PC5 connection mechanism and the first access mechanism.

[0415] Alternatively, the relay switching policy could indicate that when the network is accessed using a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism, and the relay connection needs to be switched, the relay connection should be established using the PC5 connection mechanism used before the relay connection switch, and the network should be accessed using the access mechanism used before the relay connection switch. Based on this, the remote UE can determine, based on the instructions of the relay switching policy, whether the network is accessed using a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism before the relay connection switch, in other words, whether the first PC5 connection mechanism is a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism. If the first PC5 connection mechanism is neither a Layer 2 relay mechanism nor a Layer 3 relay + N3IWF mechanism, the remote UE performs processing based on existing logic. If the first PC5 connection mechanism is a Layer 2 relay mechanism or a Layer 3 relay + N3IWF mechanism, the remote UE may, based on the instructions of the relay switching policy, decide that the first PC5 connection mechanism is to be used before relay connection switching, and determine the first relay service identifier, for example, the first relay service identifier corresponding to the first PC5 connection mechanism and the first access mechanism.

[0416] After S1407, the remote UE can perform relay UE discovery, which may be implemented in Model B, for example, via S1408 to S1410 below, or in Model A, for example, via S1411 and S1412 below. Further details are provided below.

[0417] S1408: The remote UE transmits the first relay service identifier.

[0418] A remote UE can transmit a first relay service identifier in a broadcast manner. For example, a remote UE can transmit a discovery request message carrying the first relay service identifier to indicate a first PC5 connection mechanism and a first access mechanism.

[0419] It may be understood that S1408 may be repeated multiple times to increase the probability of finding the relay UE.

[0420] S1409: The remote UE receives the relay service identifier of at least one relay UE.

[0421] The relay service identifier of at least one relay UE may indicate at least one PC5 connection mechanism and at least one access mechanism, i.e., a PC5 connection mechanism and access mechanism supported by at least one relay UE. The relay service identifier of at least one relay device may include a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism.

[0422] Specifically, for a relay UE, after receiving a discovery request message, the relay UE can determine, based on a first relay service identifier carried in the discovery request message, whether it locally stores a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. If the relay UE locally stores a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism, the relay UE may determine that it supports the first PC5 connection mechanism and the first access mechanism supported by the remote UE and may choose to provide feedback to the remote UE, for example, by sending a discovery response message carrying a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism; otherwise, the relay UE may choose not to provide feedback to the remote UE. In this way, the remote UE can receive relay service identifiers from at least one relay UE.

[0423] The above examples continue.

[0424] A remote UE can broadcast a discovery request message carrying an RSC-UP-1 to indicate that the remote UE supports UP-based and Layer 2 relay mechanisms. Relay UE1 supports UP-based and Layer 2 relay mechanisms. Based on the received discovery request message, relay UE1 can send discovery response message 1 carrying an RSC-UP-1. Relay UE2 supports CP-based and Layer 2 relay mechanisms and may not respond to a discovery request message. Relay UE3 supports CP-based, UP-based, and Layer 2 relay mechanisms. Based on the received discovery request message, relay UE3 can send discovery response message 2 carrying an RSC-UP-1. In this case, the remote UE can receive two RSCs, each containing two RSC-UP-1s.

[0425] S1410: The remote UE decides to establish a relay connection with the second relay UE by using the first PC5 connection mechanism and to access the network by using the first access mechanism.

[0426] A remote UE may decide to establish a relay connection to a second relay UE within at least one relay UE based on a first relay service identifier. For example, a remote UE may determine the second relay UE from at least one relay UE by deciding that at least one relay UE all support the first PC5 connection mechanism and the first access mechanism, based on the first relay service identifier. The specific implementation principle is the same as that described in the relevant section of S1310. For further details, please refer to the relevant section for understanding, as further details will not be explained again here.

[0427] S1408-S1410 are procedures for Model B, and it should be understood that the remote UE may use Model B by default, or may decide to use Model B based on other conditions. For example, when a relay connection needs to be switched, and the relay connection is established by using the PC5 connection mechanism that was used before the relay connection switch, and the network is accessed by using the access mechanism that was used before the relay connection switch, the remote UE will decide to use Model B.

[0428] S1411: The remote UE receives the relay service identifier of at least one relay UE.

[0429] For the specific implementation principles of S1411, please refer to the related explanation in S1111. Further details will not be explained again.

[0430] S1412: The remote UE decides to establish a relay connection with a second relay UE in at least one relay UE by using the first PC5 connection mechanism and to access the network by using the first access mechanism.

[0431] The remote UE can determine, based on the first relay service identifier, whether the relay service identifier of at least one relay UE contains the first relay service identifier. If the relay service identifier of at least one relay UE does not contain the first relay service identifier, the remote UE can perform processing based on existing logic. If the relay service identifier of at least one relay UE contains the first relay service identifier, the remote UE may, based on the determination that the relay UE corresponding to the first relay service identifier is the second relay UE, decide to establish a relay connection with the second relay UE at at least one relay UE by using the first PC5 connection mechanism and to access the network by using the first access mechanism. The specific implementation principles are similar to those in the relevant description of S1310. For further details, please refer to the relevant description, as further details will not be explained again.

[0432] S1411 and S1412 are procedures in Model A, and it should be understood that the remote UE may use Model A by default. Alternatively, the remote UE may decide to use Model A based on other conditions. For example, the remote UE may decide to use Model A when a relay connection needs to be switched over, and the relay connection is established by using the PC5 connection mechanism used before the relay connection switchover, and the network is accessed by using the access mechanism used before the relay connection switchover. Alternatively, the remote UE may randomly select either Model A or Model B.

[0433] S1413: The remote UE establishes a second relay connection to the second relay UE by using the first PC5 connection mechanism.

[0434] For the specific implementation principles of S1413, it is understandable to refer to the related explanation in S1113. Further details will not be explained again.

[0435] In some other scenarios, it may be further understood that when the first relay connection needs to be switched, the remote UE may establish a second relay connection to the second relay UE by using the first PC5 connection mechanism, and may preferentially use the first access mechanism. In this case, the relay service identifier list may contain at least one relay service identifier, each relay service identifier may indicate one corresponding PC5 access mechanism within the first PC5 connection mechanism and at least one access mechanism. The relay service identifier priority information may indicate the priority of at least one relay service identifier, i.e., the priority of use of at least one access mechanism. For specific implementation principles of the scenarios, please refer to the relevant descriptions of Scenario 2 and Scenario 3. Further details will not be explained again.

[0436] The above describes in detail the specific procedures of the communication method according to the embodiment of the present invention in Scenario 3 and Scenario 4 with reference to Figures 13 and 14. The overall procedures of the communication method in Scenario 3 and Scenario 4 will now be described in detail with reference to Figure 15.

[0437] Figure 15 is a schematic flowchart 6 of a communication method according to one embodiment of the present application. The communication method is applicable to the communication system described above and mainly concerns the interaction between a remote device (e.g., remote UE), a first relay device (e.g., first relay UE), and a second relay device (e.g., second relay UE).

[0438] Specifically, as shown in Figure 15, the communication procedure is as follows.

[0439] S1501: The remote device establishes a first relay connection with the first relay device by using the first PC5 connection mechanism.

[0440] The first PC5 connection mechanism may include a mechanism for obtaining a relay connection key via the network's user plane, i.e., a user-plane based mechanism, or a mechanism for obtaining a relay connection key via the network's control plane, i.e., a control-plane based mechanism. The first relay connection may be used by a remote device to obtain a first service from the network via a first relay device. For example, a remote device may access the network via the first relay connection by using the first access mechanism within at least one access mechanism to obtain a first service from the network. Optionally, at least one access mechanism may include at least one of the following: a Layer 2 access mechanism, a Layer 3 protocol access mechanism, or a Layer 3 non-protocol access mechanism, to allow the remote device flexible access to the network.

[0441] Furthermore, for the specific implementation principles of S1501, please refer to the related explanations in S1301 and S1303. Details will not be explained again.

[0442] S1502: When the first relay connection needs to be switched over, the remote device determines the first relay service identifier according to the relay switching policy.

[0443] The relay switching policy may indicate that the relay connection is established by using the connection mechanism used before the relay connection switching, and the first relay service identifier may indicate the first PC5 connection mechanism. For specific implementation principles, see the relevant explanations in S1304 and S1307. Further details will not be explained again. Optionally, the relay switching policy may further indicate that the network is accessed by using the access mechanism used before the relay connection switching. In this case, the first relay service identifier further indicates the first access mechanism. For specific implementation principles, see the relevant explanations in S1404 and S1407. Further details will not be explained again.

[0444] S1503: The remote device establishes a second relay connection to the second relay device based on the first relay service identifier.

[0445] The second relay device may be a relay device that supports the first PC5 connection mechanism, i.e., a relay device corresponding to a relay service identifier indicating the first PC5 connection mechanism. The second relay connection may be used by a remote device to obtain the first service of the network via the second relay device.

[0446] Method 3: The relay connection is established by using the connection mechanism that was used before the relay connection switchover.

[0447] The remote device decides to establish a relay connection to a second relay device by using a first PC5 connection mechanism based on a first relay service identifier; in other words, it can discover a second relay device that supports the first PC5 connection mechanism to ensure that the remote device can establish a second relay connection to the second relay device by using the first PC5 connection mechanism.

[0448] For example, a remote device can broadcast a first relay service identifier to receive the relay service identifier of at least one relay device. The relay service identifier of at least one relay device may include a relay service identifier indicating a first PC5 connection mechanism. Based on the first relay service identifier, the remote device can decide to establish a relay connection to a second relay device among the at least one relay device. The second relay device is the relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0449] In another example, a remote device receives a relay service identifier for at least one relay device. The relay service identifier for at least one relay device may include a relay service identifier indicating a first PC5 connection mechanism. Based on the first relay service identifier, the remote device may decide to establish a relay connection to a second relay device from among the at least one relay device. The second relay device is the relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0450] For the specific implementation principles of Method 3, please refer to the relevant explanations in S1308 to S1313. Further details will not be explained again.

[0451] Method 4: The relay connection is established by using the connection mechanism used before the relay connection switchover, and the network is accessed by using the access mechanism used before the relay connection switchover.

[0452] A remote device can decide to establish a relay connection to a second relay device by using a first PC5 connection mechanism, based on a first relay service identifier, and to access the network by using the first PC5 connection mechanism. In this way, the remote device can establish a second relay connection to the second relay device by using the first PC5 connection mechanism and access the network through the second relay device by using the first access mechanism. When the remote device accesses the network by using the first access mechanism, if the remote device plans to switch the relay connection, it can be found that, in order to further ensure continuity of service, the remote device can continue to access the network by continuing to reuse the access mechanism used before the relay connection switch, i.e., the first access mechanism.

[0453] For example, a remote device can broadcast a first relay service identifier to receive the relay service identifier of at least one relay device, where the relay service identifier of at least one relay device may include a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. Based on the first relay service identifier, the remote device may decide to establish a relay connection to a second relay device among the at least one relay device and access the network by using the first PC5 connection mechanism. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0454] In another example, a remote device may receive a relay service identifier for at least one relay device, the relay service identifier for at least one relay device may include a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. Based on the first relay service identifier, the remote device may decide to establish a relay connection to a second relay device among the at least one relay device and access the network using the first PC5 connection mechanism. The second relay device is the relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0455] For the specific implementation principles of Method 4, please refer to the relevant explanations in S1408-S1413. Further details will not be explained again.

[0456] In conclusion, when a remote device establishes a first relay connection to a first relay device using a first PC5 connection mechanism, such as a user-plane based mechanism or a control-plane based mechanism, and the remote device intends to switch the relay connection, the remote device can improve PC5 connection switching efficiency, reduce switching delay, and ensure the continuity of the first service obtained from the network by the remote device by continuing to reuse the connection mechanism used before the relay connection switch, i.e., the first PC5 connection mechanism.

[0457] In a possible design solution, referring to Method 3 described above, the remote device can determine the relay switching policy based on a fifth directive from the policy control network element. The fifth directive may indicate establishing a relay connection by using the connection mechanism used before the relay connection switch. In other words, in addition to establishing a relay connection by using the connection mechanism used before the relay connection switch by default, the remote device can, based on the directive from the policy control network element, flexibly decide whether to establish a relay connection by using the connection mechanism used before the relay connection switch to meet the relay switching requirements of different services.

[0458] Alternatively, the remote device may determine the relay switching policy based on a first access mechanism. The first access mechanism is the mechanism used by the remote device to access the network via a first relay device. Optionally, the first access mechanism may be either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism. When the remote device accesses the network by using a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism, it can be understood that the remote device may establish a session between the remote device and the network to obtain a first service from the network. In this case, if the remote device implements fast switching by reusing the connection mechanism used before the relay connection switching, the remote device may continue to reuse the session before the session becomes invalid to obtain the first service from the network. This can ensure continuity of service.

[0459] For specific implementation principles of the design solution, it may be helpful to refer to the relevant explanations in S1302, S1305, and S1306. Further details will not be explained again.

[0460] In a possible design solution, referring to Method 4 described above, the remote device can determine the relay switching policy based on a sixth directive from the policy-controlled network element. The sixth directive indicates establishing a relay connection by using the connection mechanism used before the relay connection switch, and accessing the network by using the access mechanism used before the relay connection switch. In other words, based on the directive from the policy-controlled network element, the remote device can flexibly decide whether to establish a relay connection by using the connection mechanism used before the relay connection switch, and whether to establish and access the network by using the access mechanism used before the relay connection switch, in order to meet the relay switching requirements of different services.

[0461] Alternatively, the remote device may determine the relay switching policy based on a first access mechanism. For example, the first access mechanism is either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism. Optionally, at least one access mechanism includes at least one of the following: a Layer 2 access mechanism, a Layer 3 protocol access mechanism, or a Layer 3 non-protocol access mechanism.

[0462] For specific implementation principles of the design solution, it may be helpful to refer to the relevant explanations in S1402, S1405, and S1406. Further details will not be explained again.

[0463] The procedure shown in Figure 15 can be understood as primarily describing the following process: the remote device establishes a first relay connection with a first relay device, and then switches to establishing a second relay connection with a second relay device. This process can also be understood as follows: the remote device switches from a state of establishing a relay connection to the first relay device to a state of establishing a relay connection to the second relay device; in other words, the remote device switches from a state of connection to the first relay device to a state of connection to the second relay device.

[0464] The communication method according to an embodiment of the present invention has been described in detail above with reference to Figures 10 to 15. Hereinafter, the communication device configured to implement the communication method according to an embodiment of the present invention will be described in detail with reference to Figures 16 and 17.

[0465] Figure 16 is a structural diagram 1 of a communication device according to one embodiment of the present application. For example, as shown in Figure 16, the communication device 1600 includes a transceiver module 1601 and a processing module 1602. In Figure 16, only the main components of the communication device are shown for the sake of clarity.

[0466] In some embodiments, the communication device 1600 may be used in the communication system shown in Figure 9 and perform functions of a remote UE or remote device in the manner shown in Figures 10 to 12.

[0467] For example, when the first relay connection needs to be switched, the processing module 1602 is configured to determine priority information for the first relay service identifier and, based on the priority information for the first relay service identifier, to control the transceiver module 1601 to establish a second relay connection to the second relay device by using the first PC5 connection mechanism. The priority information for the first relay service identifier indicates that the first PC5 connection mechanism indicated by the first relay service identifier should be used preferentially. The first PC5 connection mechanism is a mechanism used by the communication device 1600 to establish a first relay connection with the first relay device. The first relay connection is used by the communication device 1600 to obtain a first service of the network via the first relay device. The second relay connection is used by the communication device 1600 to obtain a first service of the network via the second relay device.

[0468] In a possible design solution, the processing module 1602 is further configured to decide to establish a relay connection to a second relay device by using a first PC5 connection mechanism based on priority information of a first relay service identifier, and to control the transceiver module 1601 by using the first PC5 connection mechanism to establish a second relay connection to the second relay device.

[0469] Optionally, the transceiver module 1601 is further configured to broadcast a first relay service identifier to receive a relay service identifier of at least one relay device, the relay service identifier of at least one relay device including a relay service identifier indicating a first PC5 connection mechanism. In this way, the processing module 1602 is further configured to decide, based on priority information of the first relay service identifier, to establish a relay connection to a second relay device among the at least one relay device by using the first PC5 connection mechanism. The second relay device is a relay device corresponding to a relay service identifier indicating the first PC5 connection mechanism.

[0470] Alternatively, and optionally, the transceiver module 1601 is further configured to receive a relay service identifier for at least one relay device, the relay service identifier for at least one relay device including a relay service identifier indicating a first PC5 connection mechanism. In this way, the processing module 1602 is further configured to decide, based on priority information of the first relay service identifier, to establish a relay connection to a second relay device among the at least one relay device by using the first PC5 connection mechanism. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0471] In a possible design solution, the processing module 1602 is further configured to determine priority information for a first relay service identifier based on first instruction information from a policy-controlled network element, where the first instruction information indicates establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover.

[0472] In a possible design solution, the processing module 1602 is further configured to determine priority information for a first relay service identifier based on second instruction information from the relay server, where the second instruction information indicates that the relay connection should be established by preferentially using the first PC5 connection mechanism.

[0473] Optionally, the transceiver module 1601 is further configured to send a relay reselection request message to the relay server, the relay reselection request message indicating that the connection mechanism used before the relay connection switchover was the first PC5 connection mechanism. The transceiver module 1601 is further configured to receive a relay reselection response message returned by the relay server in response to the relay reselection request message, the relay reselection response message carrying second instruction information.

[0474] In a possible design solution, the processing module 1602 is further configured to determine priority information for a first relay service identifier based on a first access mechanism. The first access mechanism is a mechanism used by the communication device 1600 to access the network via a first relay device. For example, the first access mechanism may be either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism.

[0475] In a possible design solution, priority information of the first relay service identifier further indicates that the first access mechanism should be used preferentially in at least one access mechanism for network access, the first access mechanism being the mechanism used by the communication device 1600 to access the network via the first relay device. The processing module 1602 is further configured to decide, based on the priority information of the first relay service identifier, to establish a relay connection to the second relay device by using the first PC5 connection mechanism and to access the network by using the first access mechanism. In this way, the processing module 1602 is further configured to control the transceiver module 1601 by using the first PC5 connection mechanism to establish a second relay connection to the second relay device and to access the network via the second relay device by using the first access mechanism.

[0476] Optionally, the transceiver module 1601 is further configured to broadcast a first relay service identifier and receive a relay service identifier of at least one relay device. The relay service identifier of at least one relay device includes a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. In this way, the processing module 1602 is further configured to decide, based on priority information of the first relay service identifier, to establish a relay connection to a second relay device among the at least one relay device by using the first PC5 connection mechanism and to access the network by using the first access mechanism.

[0477] Optionally, the transceiver module 1601 is further configured to receive a relay service identifier for at least one relay device. The relay service identifier for at least one relay device includes a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. In this way, the processing module 1602 is further configured to determine, based on priority information of the first relay service identifier, to establish a relay connection to a second relay device among the at least one relay device by using the first PC5 connection mechanism and to access the network by using the first access mechanism. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism and the first access mechanism.

[0478] Optionally, the processing module 1602 is further configured to determine priority information for a first relay service identifier based on third instruction information from a policy-controlled network element. The third instruction information indicates establishing a relay connection by preferentially using the connection mechanism used before the relay connection switchover, and accessing the network by preferentially using the access mechanism used before the relay connection switchover.

[0479] Optionally, the processing module 1602 is further configured to determine priority information for the first relay service identifier based on fourth instruction information from the relay server. The fourth instruction information indicates establishing a relay connection by preferentially using the first PC5 connection mechanism and accessing the network by preferentially using the first access mechanism.

[0480] Furthermore, the transceiver module 1601 is configured to send a relay reselection request message to the relay server. The relay reselection request message indicates that the connection mechanism used before the relay connection switchover was the first PC5 connection mechanism and that the access mechanism used before the relay connection switchover was the first access mechanism. The transceiver module 1601 is further configured to receive a relay reselection response message returned by the relay server in response to the relay reselection request message, the relay reselection response message carrying fourth instruction information.

[0481] Optionally, the processing module 1602 is further configured to determine priority information for a first relay service identifier based on a first access mechanism. For example, the first access mechanism is either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism.

[0482] Optionally, at least one access mechanism includes at least one of the following: a Layer 2 access mechanism, a Layer 3 protocol access mechanism, or a Layer 3 non-protocol access mechanism.

[0483] In a possible design solution, the first PC5 connection mechanism includes a mechanism for obtaining a relay connection key via the network's user plane, or a mechanism for obtaining a relay connection key via the network's control plane.

[0484] Optionally, the transceiver module 1601 may include a transmit module (not shown in Figure 16) and a receive module (not shown in Figure 16). The transmit module is configured to implement the transmit function of the communication device 1600, and the receive module is configured to implement the receive function of the communication device 1600.

[0485] Optionally, the communication device 1600 may further include a storage module (not shown in Figure 16) that stores a program or instruction. The communication device 1600 enables the processing module 1602 to perform the functions of a remote UE or remote device in the manner shown in Figures 10 to 12, among the methods described above, when executing a program or instruction.

[0486] It can be understood that the communication device 1600 may be a terminal, for example, a remote UE or remote device, a chip (system) or another component or element that can be located within the terminal, or a device including a terminal. This is not limited to the present application.

[0487] Furthermore, for the technical effects of the communication device 1600, please refer to the technical effects of the communication method shown in Figures 10 to 12. Further details will not be explained again in this specification.

[0488] In some embodiments, the communication device 1600 may be used in the communication system shown in Figure 9, and perform functions of a remote UE or remote device in the manner shown in Figures 13 to 15.

[0489] For example, when a first relay connection needs to be switched, the processing module 1602 is configured to determine a first relay service identifier according to a relay switching policy and to control the transceiver module 1601 to establish a second relay connection to a second relay device by using a first PC5 connection mechanism based on the first relay service identifier. The relay switching policy indicates that the relay connection should be established by using the connection mechanism used before the relay connection switch, the first relay service identifier indicates a first PC5 connection mechanism, the first PC5 connection mechanism is a mechanism used by a remote device to establish a first relay connection to a first relay device, and the first relay connection is used by a remote device to obtain a first service of the network via the first relay device. The second relay connection is used by a remote device to obtain a first service of the network via the second relay device.

[0490] In a possible design solution, the processing module 1602 is further configured to determine, based on a first relay service identifier, to establish a relay connection to a second relay device by using a first PC5 connection mechanism. The processing module 1602 is further configured to control the transceiver module 1601 by using the first PC5 connection mechanism to establish a second relay connection to the second relay device.

[0491] Optionally, the transceiver module 1601 is further configured to broadcast a first relay service identifier and receive a relay service identifier of at least one relay device. The relay service identifier of at least one relay device includes a relay service identifier indicating a first PC5 connection mechanism. The processing module 1602 is further configured to decide, based on the first relay service identifier, to establish a relay connection to a second relay device from among the at least one relay device. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0492] Optionally, the transceiver module 1601 is further configured to receive a relay service identifier for at least one relay device. The relay service identifier for at least one relay device includes a relay service identifier indicating a first PC5 connection mechanism. The processing module 1602 is further configured to decide, based on the first relay service identifier, to establish a relay connection to a second relay device from among the at least one relay device. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0493] In a possible design solution, the processing module 1602 is further configured to determine the relay switching policy based on a fifth instruction from a policy control network element. The fifth instruction indicates establishing the relay connection by using the connection mechanism used before the relay connection switching.

[0494] In possible design solutions, processing module 1602 is further configured to determine a relay switching policy based on a first access mechanism. The first access mechanism is a mechanism used by a remote device to access the network via a first relay device. Optionally, the first access mechanism may be either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism.

[0495] In a possible design solution, the relay switching policy further indicates access to the network by using the access mechanism used before the relay connection switching, and the first relay service identifier further indicates the first access mechanism. The processing module 1602 is further configured to decide, based on the first relay service identifier, to establish a relay connection to the second relay device by using the first PC5 connection mechanism and to access the network by using the first PC5 connection mechanism. In this way, the processing module 1602 is further configured to control the transceiver module 1601 by using the first PC5 connection mechanism to establish a second relay connection to the second relay device and to access the network through the second relay device by using the first access mechanism.

[0496] Optionally, the transceiver module 1601 is further configured to broadcast a first relay service identifier to receive a relay service identifier for at least one relay device, the relay service identifier for at least one relay device including a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. The processing module 1602 is further configured to determine, based on the first relay service identifier, to establish a relay connection to a second relay device among the at least one relay device and to access the network by using the first PC5 connection mechanism. The second relay device is a relay device corresponding to a relay service identifier indicating the first PC5 connection mechanism.

[0497] Optionally, the transceiver module 1601 is further configured to receive a relay service identifier for at least one relay device, the relay service identifier for at least one relay device including a relay service identifier indicating a first PC5 connection mechanism and a first access mechanism. The processing module 1602 is further configured to determine, based on the first relay service identifier, to establish a relay connection to a second relay device among the at least one relay device and to access the network by using the first PC5 connection mechanism. The second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism.

[0498] Optionally, the processing module 1602 is further configured to determine a relay switching policy based on a sixth instruction from a policy control network element. The sixth instruction indicates establishing a relay connection by using the connection mechanism used before the relay connection switching, and accessing the network by using the access mechanism used before the relay connection switching.

[0499] Optionally, the processing module 1602 is further configured to determine a relay switching policy based on a first access mechanism. For example, the first access mechanism is either a Layer 2 access mechanism or a Layer 3 non-protocol access mechanism.

[0500] Optionally, at least one access mechanism includes at least one of the following: a Layer 2 access mechanism, a Layer 3 protocol access mechanism, or a Layer 3 non-protocol access mechanism.

[0501] In a possible design solution, the first PC5 connection mechanism includes a mechanism for obtaining a relay connection key via the network's user plane, or a mechanism for obtaining a relay connection key via the network's control plane.

[0502] Optionally, the transceiver module 1601 may include a transmit module (not shown in Figure 16) and a receive module (not shown in Figure 16). The transmit module is configured to implement the transmit function of the communication device 1600, and the receive module is configured to implement the receive function of the communication device 1600.

[0503] Optionally, the communication device 1600 may further include a storage module (not shown in Figure 16) that stores a program or instruction. When the processing module 1602 executes a program or instruction, the communication device 1600 enables the execution of functions of a remote UE or remote device in the manner shown in Figures 13 to 15, among the methods described above.

[0504] It can be understood that the communication device 1600 may be a terminal, for example, a remote UE or remote device, a chip (system) or another component or element that can be located within the terminal, or a device including a terminal. This is not limited to the present application.

[0505] Furthermore, for the technical effects of the communication device 1600, please refer to the technical effects of the communication method shown in Figures 13 to 15. Further details will not be explained again in this specification.

[0506] Figure 17 is a diagram of the structure of a communication device according to one embodiment of the present invention. For example, the communication device may be a terminal, or a chip (system) or other components mounted on a terminal. As shown in Figure 17, the communication device 1700 may include a processor 1701. Optionally, the communication device 1700 may further include a memory 1702 and / or a transceiver 1703. The processor 1701 is coupled to the memory 1702, and the transceiver 1703 may be connected, for example, via a communication bus.

[0507] The following will provide a detailed explanation of each component of the communication device 1700 with reference to Figure 17.

[0508] The processor 1701 is the control center of the communication device 1700, and may be a single processor or a collective term for multiple processing elements. For example, the processor 1701 may be one or more central processing units (CPUs), which may be application-specific integrated circuits (ASICs), or it may be configured as one or more integrated circuits implementing embodiments of the present application, such as one or more digital signal processors (DSPs), or one or more field programmable gate arrays (FPGAs).

[0509] The processor 1701 can optionally run or execute a software program stored in memory 1702, or retrieve data stored in memory 1702 to perform various functions of the communication device 1700, for example, by performing the communication methods shown in Figures 10 to 15.

[0510] In one specific implementation, the processor 1701 may include one or more CPUs, for example, CPU 0 and CPU 1 shown in Figure 17.

[0511] In a specific implementation, in one embodiment, the communication device 1700 may alternatively include a plurality of processors, for example, processors 1701 and 1704 shown in Figure 17. Each of the processors may be a single-core (single-CPU) processor or a multi-core (multi-CPU) processor. A processor as used herein may be one or more devices, circuits, and / or processing cores configured to process data (e.g., computer program instructions).

[0512] Memory 1702 is configured to store a software program for executing the solution of this application, and processor 1701 controls its execution. For specific implementation details, please refer to the embodiments of the method described above. Further details are not described herein.

[0513] Optionally, the memory 1702 may be a read-only memory (ROM), another type of static storage device capable of storing static information and instructions, a random access memory (RAM), or another type of dynamic storage device capable of storing information and instructions, or an electrically erasable programmable read-only memory (EEPROM), a compact disc read-only memory (CD-ROM), or another compact disc storage device, an optical disc storage device (including compact discs, laser discs, optical discs, digital multipurpose discs, Blu-ray discs, etc.), a magnetic disk storage medium, or another magnetic storage device, or any other medium accessible to the computer that may be configured to carry or store program code intended in the form of instruction structures or data structures. The memory 1702 may be integrated with the processor 1701 or exist independently, and may be coupled to the processor 1701 via an interface circuit of a communication device 1700 (not shown in Figure 17). This is not specifically limited to this embodiment of the present application.

[0514] The transceiver 1703 is configured to communicate with other communication devices. For example, the communication device 1700 may be a terminal, and the transceiver 1703 may be configured to communicate with a network device or other terminal devices. In another example, the communication device 1700 may be a network device, and the transceiver 1703 may be configured to communicate with a terminal or another network device.

[0515] Optionally, the transceiver 1703 may include a receiver and a transmitter (not shown separately in Figure 17). The receiver is configured to implement a receiving function, and the transmitter is configured to implement a transmitting function.

[0516] Optionally, the transceiver 1703 may be integrated with the processor 1701 or exist independently, and may be coupled to the processor 1701 via an interface circuit of the communication device 1700 (not shown in Figure 17). This is not specifically limited to this embodiment of the present application.

[0517] It should be understood that the structure of the communication device 1700 shown in Figure 17 is not limiting to communication devices. Actual communication devices may contain more or fewer components than those shown in the figure, may combine several components, or may have different arrangements of components.

[0518] Furthermore, for the technical effects of the communication device 1700, please refer to the technical effects of the method in the embodiment of the method described above. Details will not be explained again in this specification.

[0519] It should be understood that the processor in the embodiments of this application may be a central processing unit (CPU), or the processor may be another general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), or another programmable logic device, discrete gate or transistor logic device, discrete hardware component, etc. The general-purpose processor may be a microprocessor, or the processor may be any conventional processor, etc.

[0520] It can be further understood that the memory in the embodiments of this application may be volatile memory or non-volatile memory, or may include both volatile and non-volatile memory. Non-volatile memory may be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. Volatile memory may be random access memory (RAM) used as an external cache. Many forms of random access memory (RAM), such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), double data rate synchronous dynamic random access memory (DDR SDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchlink dynamic random access memory (SLDRAM), and direct rambus random access memory (DR RAM), may be used, but not as an example.

[0521] All or part of the embodiments described above can be implemented by software, hardware (e.g., circuitry), firmware, or any combination thereof. When software is used to implement the embodiments, the embodiments described above can be implemented, in whole or in part, in the form of a computer program product. A computer program product includes one or more computer instructions or computer programs. When the program instructions or computer programs are loaded into a computer and executed, all or part of the procedures or functions according to the embodiments of this application are generated. The computer may be a general-purpose computer, a dedicated computer, a computer network, or other programmable device. Computer instructions may be stored in a computer-readable storage medium and may be transmitted from one computer-readable storage medium to another. For example, computer instructions may be transmitted by wire (e.g., infrared, wireless, or microwave) from one website, computer, server, or data center to another website, computer, server, or data center. The computer-readable storage medium may be any available medium accessible to a computer, or a data storage device integrating one or more available media, such as a server or data center. The usable media may be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., DVDs), or semiconductor media. Semiconductor media may include solid-state drives.

[0522] In this specification, the term "and / or" describes only the relationship between associated objects, and it should be understood that three relationships may exist. For example, A and / or B can represent three cases: when only A exists, when both A and B exist, and when only B exists. A and B may be singular or plural. In addition, the letter " / " in this specification usually indicates an "or" relationship between associated objects, but may alternatively indicate an "and / or" relationship. See the context for details.

[0523] In this application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following items" or similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, at least one of a, b, or c could be a, b, c, ab, ac, bc, or abc, where a, b, and c may be singular or plural.

[0524] It should be understood that the sequence numbers of the processes described above do not represent the execution sequences in the various embodiments of this application. The execution sequences of the processes should be determined according to the function and internal logic of the processes and should not be interpreted as any limitation on the implementation processes of the embodiments of this application.

[0525] Those skilled in the art will recognize, in combination with the examples described in the embodiments disclosed herein, that units and algorithmic steps can be implemented by electronic hardware or by a combination of computer software and electronic hardware. Whether a function is performed by hardware or software depends on the design constraints of the particular application and technical solution. Those skilled in the art may use different methods to implement the described functions for each particular application, but such implementations should not be considered to exceed the scope of this application.

[0526] For the sake of a convenient and concise explanation, it will be readily apparent to those skilled in the art that the detailed working processes of the above-described systems, apparatus, and units are described by referring to the corresponding processes in the embodiments of the methods described above. Further details are not described herein.

[0527] It should be understood that, in some embodiments provided in this application, the systems, apparatus, and methods disclosed may be implemented in other ways. For example, the embodiments of the apparatus described are merely examples. For example, the division into units is merely a logical functional division, and other divisions may be used in actual implementations. For example, multiple units or components may be coupled or integrated into another system, or some features may be ignored or not performed. In addition, the mutual coupling, direct coupling, or communication connection shown or described may be implemented by using some interfaces. Indirect coupling or communication connection between apparatus or units may be implemented in an electrical, mechanical, or other form.

[0528] Units described as separate parts may or may not be physically separate, and parts shown as units may or may not be physical units; in other words, they may be located in one location or distributed across multiple network units. Some or all of the units may be selected based on the actual requirements for achieving the objectives of the solution of the embodiment.

[0529] In addition, the functional units in the embodiments of this application may be integrated into a single processing unit, each unit may exist physically independently, or two or more units may be integrated into a single unit.

[0530] When a function is implemented in the form of a software function unit and sold or used as an independent product, the function may be stored on a computer-readable storage medium. Based on this understanding, the technical solutions of this application, in essence, may be implemented in the form of a software product, with some parts contributing to the prior art or some parts of the technical solutions. A computer software product is stored on a storage medium and includes several instructions for instructing a computer device (which may be a personal computer, server, network device, etc.) to perform all or some of the steps of the method described in the embodiments of this application. The storage medium includes any medium capable of storing program code, such as a USB flash drive, removable hard disk, read-only memory (ROM), random access memory (RAM), magnetic disk, optical disk, etc.

[0531] The above description is merely a specific implementation of the present application and is not intended to limit the scope of protection of this application. Any modification or substitution that is readily understood by a person skilled in the art within the technical scope disclosed herein shall be included in the scope of protection of this application. Accordingly, the scope of protection of this application shall be subject to the scope of protection of the claims. [Explanation of Symbols]

[0532] 1600 Communication equipment 1601 Transceiver Module 1602 Processing Module 1700 Communication equipment 1701 Processor 1702 memory 1703 Transceiver 1704 Processor

Claims

1. A method of communication, Steps include: when a first relay connection needs to be switched, the device determines a first relay service identifier according to a relay switching policy, wherein the relay switching policy is to establish the relay connection by using the PC5 connection mechanism used before the relay connection switch, the first relay service identifier is for determining the first PC5 connection mechanism, the first PC5 connection mechanism is a mechanism used by the device to establish the first relay connection to a first relay device, the first PC5 connection mechanism includes a mechanism for obtaining a relay connection key via the user plane of the network or a mechanism for obtaining a relay connection key via the control plane of the network, and the first relay connection is used by the device to obtain a first service of the network via the first relay device; The steps include: establishing a second relay connection to a second relay device by using the first PC5 connection mechanism based on the first relay service identifier, wherein the second relay connection is used by the device to obtain the first service of the network via the second relay device; and Methods that include...

2. The step of establishing a second relay connection to a second relay device by using the first PC5 connection mechanism based on the first relay service identifier using the apparatus is: The device determines, based on the first relay service identifier, to establish a relay connection to the second relay device by using the first PC5 connection mechanism. The method according to claim 1, including the method described in claim 1.

3. The step of determining, by the apparatus, to establish a relay connection to the second relay device by using the first PC5 connection mechanism based on the first relay service identifier, The device broadcasts the first relay service identifier, The device receives a relay service identifier for at least one relay device, wherein the relay service identifier for the at least one relay device includes a relay service identifier indicating the first PC5 connection mechanism. The steps include: determining, based on the first relay service identifier, that the apparatus establishes the relay connection to the second relay device among the at least one relay device, wherein the second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism; The method according to claim 2, including the method described in claim 2.

4. The step of determining, by the apparatus, to establish a relay connection to the second relay device by using the first PC5 connection mechanism based on the first relay service identifier, The device receives a relay service identifier for at least one relay device, wherein the relay service identifier for the at least one relay device includes a relay service identifier indicating the first PC5 connection mechanism. The steps include: determining, based on the first relay service identifier, that the apparatus establishes the relay connection to the second relay device among the at least one relay device, wherein the second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism; The method according to claim 2, including the method described in claim 2.

5. The device determines the relay switching policy based on a fifth instruction information from a policy control network element, wherein the fifth instruction information indicates that the relay connection is established by using the connection mechanism used before the relay connection switching. The method according to claim 2, further comprising:

6. The step of determining the relay switching policy based on a first access mechanism using the apparatus, wherein the first access mechanism is a mechanism used by the apparatus to access the network via a first relay device. The method according to claim 2, further comprising:

7. The method according to claim 6, wherein the first access mechanism is one of the following mechanisms: a Layer 2 access mechanism and a Layer 3 non-3GPP access mechanism.

8. The relay switching policy further indicates that the network is accessed by using the access mechanism used before the relay connection switching, the first relay service identifier further indicates the first access mechanism, the first access mechanism is a mechanism used by the device to access the network via the first relay device, The step of establishing a second relay connection to a second relay device by using the first PC5 connection mechanism based on the first relay service identifier using the apparatus is: The device determines, based on the first relay service identifier, to establish the relay connection to the second relay device by using the first PC5 connection mechanism and to access the network by using the first access mechanism. The method according to claim 1, including the method described in claim 1.

9. The step of the device determining, based on the first relay service identifier, to establish the relay connection to the second relay device by using the first PC5 connection mechanism and to access the network by using the first access mechanism, The device broadcasts the first relay service identifier, The steps include: receiving a relay service identifier for at least one relay device using the aforementioned device, wherein the relay service identifier for the at least one relay device includes a relay service identifier indicating the first PC5 connection mechanism and the first access mechanism; The steps include: determining to establish the relay connection to the second relay device among the at least one relay device based on the first relay service identifier using the apparatus, and accessing the network by using the first access mechanism, wherein the second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism; and The method according to claim 8, including the method described in claim 8.

10. The step of the device determining, based on the first relay service identifier, to establish the relay connection to the second relay device by using the first PC5 connection mechanism and to access the network by using the first access mechanism, The steps include: receiving a relay service identifier for at least one relay device using the aforementioned device, wherein the relay service identifier for the at least one relay device includes a relay service identifier indicating the first PC5 connection mechanism and the first access mechanism; The steps include: determining to establish the relay connection to the second relay device among the at least one relay device based on the first relay service identifier using the apparatus, and accessing the network by using the first access mechanism, wherein the second relay device is a relay device corresponding to the relay service identifier indicating the first PC5 connection mechanism; and The method according to claim 8, including the method described in claim 8.

11. The device determines the relay switching policy based on a sixth instruction information from a policy control network element, wherein the sixth instruction information indicates that the relay connection is established by using the connection mechanism used before the relay connection switching, and the network is accessed by using the access mechanism used before the relay connection switching. The method according to claim 8, further comprising:

12. The device determines the relay switching policy based on the first access mechanism. The method according to claim 8, further comprising:

13. The method according to claim 1, wherein the device is a remote user device (UE) or a chip of the remote UE.

14. A communication device configured to perform the method described in any one of claims 1 to 13.

15. A computer-readable storage medium, wherein the computer-readable storage medium includes a computer program or instructions, and when the computer program or instructions are executed on the computer, the computer is enabled to perform the method according to any one of claims 1 to 13.

16. A computer program product comprising a computer program or instruction, wherein when the computer program or instruction is executed on a computer, the computer is enabled to perform the method according to any one of claims 1 to 13.

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