Communication method and apparatus

Abstract

This application relates to a communication method and an apparatus. A first message from a network device is received, the first message is for inquiring whether the first terminal device can provide a relay service, or the first message includes configuration information, and the configuration information is for configuring the first terminal device to provide a relay service for a second terminal device. A second message is sent to the network device. When the first message is for inquiring whether the first terminal device can provide a relay service, the second message indicates whether the first terminal device can provide a relay service, or when the first message includes configuration information, the second message indicates whether the configuration of the first terminal device has been completed, or indicates whether the first terminal device can provide a relay service. If the first terminal device refuses to provide a relay service, the network device can also know the case, so that the first terminal device does not need to enter an RRC re-establishment procedure and can continue to operate normally within the coverage of the network device to improve the service quality of the first terminal device.

Description

[Technical Field]

[0001] This application relates to the field of communications technology, and more particularly to communications methods and devices. [Background technology]

[0002] Currently proposed user equipment (UE) relay technologies include a relay scheme in which a remote UE appears to the radio access network (RAN). In this relay scheme, the remote UE can perform a path switch, or in other words, a link switch. For example, the remote UE may switch from a direct link to a base station to an indirect link for indirect communication with the base station. The indirect link here is a relay link. Specifically, the remote UE is connected to the base station via a relay UE.

[0003] The path switch process of the remote UE includes the process of switching from a direct link to an indirect link, the process of switching from an indirect link to a direct link, and the process of switching between indirect links. When switching to an indirect link (including switching from a direct link to an indirect link or switching between indirect links), the mainstream solutions currently being discussed are as follows: the base station configures the remote UE to perform measurements, the remote UE sends the measurement results to the base station, and the base station determines whether the remote UE should perform a path switch. If the base station determines that the remote UE should perform a path switch, the base station separately sends configuration information to the remote UE and the relay UE to configure the path switch.

[0004] In the path switch method, if the relay UE rejects the relevant configuration, for example, if the relay UE rejects providing relay service for the remote UE, the relay UE needs to perform processing based on the configuration failure case. 。r The relay UE enters a radio resource control (RRC) reestablishment procedure and can only continue to operate after the RRC reestablishment is successful, which obviously causes a degradation of the service quality of the relay UE. Summary of the Invention [Means for solving the problem]

[0005] The embodiments of this application provide a communication method and apparatus for improving the service quality of a relay UE.

[0006] According to a first aspect, a first communication method is provided. The method may be executed by a first terminal device or a chip system, which can realize the functions of the first terminal device. The first terminal device is, for example, a terminal device that provides a relay service for another terminal device in a relay scenario. The method includes: receiving a first message from a network device, the first message being for inquiring whether the first terminal device can provide the relay service, or the first message including configuration information for configuring the first terminal device to provide the relay service for a second terminal device; and sending a second message to the network device, where if the first message is for inquiring whether the first terminal device can provide the relay service, the second message indicates whether the first terminal device can provide the relay service, or if the first message includes the configuration information, the second message indicates whether configuration of the first terminal device has been completed, or the second message indicates whether the first terminal device can provide the relay service.

[0007] In this embodiment of the present application, regardless of whether the first terminal device can provide relay service for the second terminal device, the first terminal device can send a second message to the network device for notification, thereby allowing the network device to know whether the first terminal device can provide relay service for the second terminal device. Therefore, if the first terminal device refuses to provide relay service for the second terminal device, the network device can also know this case, so that the first terminal device does not need to enter an RRC re-establishment procedure and can continue to operate normally within the coverage of the network device, so as to improve the service quality of the first terminal device and reduce resources consumed in the RRC re-establishment procedure. In the following description, the RRC re-establishment procedure has the same meaning as the RRC re-establishment process.

[0008] Referring to the first aspect, in a first optional implementation of the first aspect, the second message indicates that the first terminal device determines that the configuration has failed or indicates that the first terminal device refuses to provide relay service for the second terminal device, and the method further includes a step of skipping initiating an RRC re-establishment process.

[0009] With reference to the first aspect or the first optional implementation of the first aspect, in a second optional implementation of the first aspect, when the first message is for inquiring whether the first terminal device can provide a relay service, the first message includes one or more of the following: an identifier of the second terminal device, integrity protection algorithm information or integrity protection rate information, encryption algorithm information or encryption rate information, PQI or 5QI, QoS, network slice information, or computational capability information.

[0010] The first message may include one or more of the above-mentioned information. In addition to the above-mentioned information, the first message may include other information. Based on one or more of the above-mentioned information, the first terminal device can identify capabilities that need to be met by the relay service, so that the first terminal device can more accurately determine whether the relay service can be provided.

[0011] With reference to the first aspect, the first optional implementation of the first aspect, or the second optional implementation of the first aspect, in a third optional implementation of the first aspect, the second message indicates that configuration of the first terminal device has failed or indicates that the first terminal device refuses to provide the relay service, and the second message further includes a cause value, which indicates a cause for the refusal by the first terminal device to provide the relay service.

[0012] The second message may include a cause value, which may indicate the cause of the refusal by the first terminal device to provide the relay service, so that the network device can determine the cause of the first terminal device's inability to provide the relay service. In this way, the network device can take corresponding measures. For example, the network device may again search for a terminal device that can provide the relay service for the second terminal device.

[0013] With reference to the third optional implementation of the first aspect, in a fourth optional implementation of the first aspect, the reason for refusing to provide relay service by the first terminal device is one of the following: The first terminal device does not support the configuration of the Uu interface included in the first message; The first terminal device does not support the PC5 interface configuration included in the first message; the admission control performed by the first terminal device to the second terminal device is unsuccessful; The first terminal device does not support the integrity protection algorithm included in the first message; The first terminal device does not support the 5QI or PQI included in the first message; The first terminal device is unable to identify the QoS flow ID indicated by the first message; The first terminal device does not support the network slicing indicated by the first message; The battery power of the first terminal device is insufficient; The PDCP of the first terminal device is overloaded, or The first terminal device does not support the computing capability indicated by the first message. Contains one or more of:

[0014] The above provides some reasons why the first terminal device may refuse to provide the relay service. In addition to the reasons described above, the first terminal device may refuse to provide the relay service due to other reasons. The reasons why the first terminal device may refuse to provide the relay service are not limited.

[0015] With reference to the first aspect, or any one of the first optional implementation of the first aspect to the fourth optional implementation of the first aspect, in a fifth optional implementation of the first aspect, the first message is for inquiring whether the first terminal device can provide the relay service, and the second message indicates that the first terminal device can provide the relay service, and the method further includes receiving configuration information from the network device and performing configuration based on the configuration information to provide the relay service.

[0016] If the first message is to inquire whether the first terminal device can provide the relay service, it is highly likely that the first message does not include configuration information. In this case, if the second message indicates that the first terminal device can provide the relay service, the network device may send the configuration information to the first terminal device again, so that the first terminal device can perform configuration based on the configuration information to provide the relay service.

[0017] With reference to the first aspect or any one of the first optional implementation of the first aspect to the fifth optional implementation of the first aspect, in a sixth optional implementation of the first aspect, the first message is an RRC reconfiguration message or a message for specifically inquiring whether the terminal device is capable of providing a relay service.

[0018] The first message may be realized by using an existing message, for example, by using an RRC reconfiguration message. In this way, no other messages need to be newly added, and compatibility with conventional technologies is promoted. Alternatively, the first message may be realized by using another message. For example, the first message is newly added in this embodiment of the present application, and the first message may be for inquiring whether the terminal device can provide a relay service. In this way, no existing messages need to be modified.

[0019] With reference to the first aspect or any one of the first optional implementation of the first aspect to the sixth optional implementation of the first aspect, in a seventh optional implementation of the first aspect, the second message is an RRC reconfiguration complete message or a message for specifically indicating whether the terminal device provides a relay service.

[0020] For example, regardless of whether the second message indicates success (e.g., indicates that the first terminal device can provide relay service or indicates that configuration has been completed) or failure (e.g., indicates that the first terminal device refuses to provide relay service or indicates that configuration has failed), the same message may be used as the second message. For example, an RRC reconfiguration complete message may be used, or a newly added message may be used. The same type of message or the same message may indicate success or failure, and there is no need to introduce excessive message types to reduce the message types that the network device needs to identify. Alternatively, the second message may indicate success and failure by using different messages. In this case, for example, the second message may indicate success by using an RRC reconfiguration complete message, and the second message may indicate failure by using a newly added message. Different messages indicate success and failure, respectively, allowing the network device to determine success or failure based on the type of the second message, thereby increasing the efficiency of determining success or failure by the network device.

[0021] With reference to the first aspect, or any one of the first optional implementation of the first aspect to the seventh optional implementation of the first aspect, in an eighth optional implementation of the first aspect, when the second message indicates that the configuration has failed, the second message is a failure information message or an SUI message.

[0022] If the second message can indicate success and failure by using different messages, for example, if the second message indicates failure, the second message may be a failure information message or an SUI message, or if the second message indicates success, the second message may be an RRC reconfiguration message or another message. The existing messages separately indicate success or failure, which can improve the efficiency of determining success or failure by the network device, and no new messages need to be added, promoting compatibility with conventional technologies.

[0023] According to a second aspect, a second communication method is provided. The method may be performed by a network device or a chip system, and the chip system can realize the functions of the network device. For example, the network device is an access network device, such as a base station. The method includes: sending a first message to a first terminal device, the first message being for inquiring whether the first terminal device can provide a relay service, or the first message including configuration information for configuring the first terminal device to provide a relay service for a second terminal device; and receiving a second message from the first terminal device, the first message being for inquiring whether the first terminal device can provide a relay service, the second message indicating whether the first terminal device can provide the relay service, or the first message including the configuration information, the second message indicating whether configuration of the first terminal device has been completed, or the second message indicating whether the first terminal device can provide the relay service.

[0024] Referring to the second aspect, in a first optional implementation of the second aspect, the method further includes the step of the first terminal device determining not to perform RRC re-establishment.

[0025] With reference to the second aspect or the first optional implementation of the second aspect, in the second optional implementation of the second aspect, when the first message is for inquiring whether the first terminal device can provide a relay service, the first message includes one or more of the following: an identifier of the second terminal device, PC5 or Uu interface parameters, integrity protection algorithm information or integrity protection rate information, encryption algorithm information or encryption rate information, PQI or 5QI, QoS, network slice information, or computational capability information.

[0026] With reference to the second aspect, the first optional implementation of the second aspect, or the second optional implementation of the second aspect, in a third optional implementation of the second aspect, the second message indicates that configuration of the first terminal device has failed or indicates that the first terminal device refuses to provide the relay service, and the second message further includes a cause value, which indicates a cause for the refusal by the first terminal device to provide the relay service.

[0027] With reference to the third optional implementation of the second aspect, in a fourth optional implementation of the second aspect, the reason for refusing to provide relay service by the first terminal device is one of the following: The first terminal device does not support the configuration of the Uu interface included in the first message; The first terminal device does not support the PC5 interface configuration included in the first message; the admission control performed by the first terminal device to the second terminal device is unsuccessful; The first terminal device does not support the integrity protection algorithm included in the first message; The first terminal device does not support the 5QI or PQI included in the first message; The first terminal device is unable to identify the QoS flow ID indicated by the first message; The first terminal device does not support the network slicing indicated by the first message; The battery power of the first terminal device is insufficient; The PDCP of the first terminal device is overloaded, or The first terminal device does not support the computing capability indicated by the first message. Contains one or more of:

[0028] With reference to the second aspect, or any one of the first optional implementation of the second aspect to the fourth optional implementation of the second aspect, in a fifth optional implementation of the second aspect, the first message is for inquiring whether the first terminal device can provide a relay service, the second message indicates that the first terminal device can provide a relay service, and the method further includes a step of sending configuration information to the first terminal device.

[0029] With reference to the second aspect or any one of the first optional implementation of the second aspect to the fifth optional implementation of the second aspect, in a sixth optional implementation of the second aspect, the first message is an RRC reconfiguration message.

[0030] With reference to the second aspect or any one of the first optional implementation of the second aspect to the sixth optional implementation of the second aspect, in a seventh optional implementation of the second aspect, the second message is an RRC reconfiguration complete message or a message for specifically indicating whether the terminal device provides a relay service.

[0031] With reference to the second aspect, or any one of the first optional implementation of the second aspect to the seventh optional implementation of the second aspect, in an eighth optional implementation of the second aspect, when the second message indicates that the configuration has failed, the second message is a failure information message or an SUI message.

[0032] With reference to the second aspect, or any one of the first optional implementation of the second aspect to the eighth optional implementation of the second aspect, in a ninth optional implementation of the second aspect, the second message indicates that the first terminal device refuses to provide the relay service, and the method further includes a step of sending a third message to the second terminal device, the third message indicating that the first terminal device refuses to provide the relay service or indicating that a terminal device capable of providing the relay service is to be reselected.

[0033] If the first terminal device refuses to provide the relay service, the network device may notify the second terminal device, so that the second terminal device may take corresponding measures. For example, the second terminal device may resume measurements to search for a terminal device that can provide the relay service.

[0034] With reference to the ninth optional implementation of the second aspect, in a tenth optional implementation of the second aspect, the third message further includes information about one or more terminal devices, and the one or more terminal devices are unable to provide relay services.

[0035] One or more terminal devices cannot provide relay services. Therefore, when performing measurements, the second terminal device may not need to measure the one or more terminal devices to meet the energy saving requirements of the second terminal device.

[0036] With reference to the second aspect, or any one of the first optional implementation of the second aspect to the tenth optional implementation of the second aspect, in an eleventh optional implementation of the second aspect, the method further includes: a step of receiving a fourth message from a second terminal device, where the fourth message indicates an energy saving requirement; and a step of sending first information to the second terminal device, where the first information includes information about M terminal devices, where the M terminal devices do not need to be measured or refuse to provide relay service, and M is a positive integer.

[0037] If the second terminal device has an energy saving requirement, the second terminal device may notify the network device. After learning that the second terminal device has an energy saving requirement, the network device may send first information to the second terminal device. The M terminal devices indicated by the first information may not need to be measured or may refuse to provide relay service. Therefore, after receiving the first information, when performing measurements, the second terminal device may not need to measure the M terminal devices in order to reduce power consumption caused by the measurements and meet the energy saving requirement.

[0038] With reference to the eleventh optional implementation of the second aspect, in a twelfth optional implementation of the second aspect, the fourth message further includes second information, the second information includes information about N terminal devices, and the N terminal devices refuse to provide the relay service, and N is a positive integer.

[0039] For example, if the second terminal device determines based on historical information that the N terminal devices refuse to provide relay service for the second terminal device, the second terminal device may add information about the N terminal devices to a blacklist and send the blacklist to the network device. Therefore, when configuring the second terminal device to perform measurements, the network device may consider not configuring the second terminal device to measure the N terminal devices, so as to reduce invalid measurement processes of the second terminal device.

[0040] For technical effects brought about by the second aspect or optional implementations of the second aspect, please refer to the description of the technical effects of the first aspect or corresponding implementations.

[0041] According to a third aspect, a third communication method is provided. The method may be executed by a second terminal device or a chip system, and the chip system can realize the function of the second terminal device. The second terminal device is, for example, a terminal device that needs to perform relaying by using another terminal device in a relay scenario. The method includes: transmitting measurement results to a network device, the measurement results including a measurement report for at least one terminal device; and performing a first operation when a first condition is satisfied, and skipping performing the first operation otherwise, the first operation including one or more of the following: transmitting a discovery message, measuring another terminal device, or transmitting new measurement results to the network device.

[0042] The first operation may be regarded as an operation related to the measurement process. In other words, in this embodiment of the present application, if the first condition is not met, the second terminal device may not perform the first operation. Since the second terminal device transmits the measurement result to the network device, and the network device can determine whether the second terminal device can perform path switching based on the measurement result, the decision of the network device is not significantly affected even if the second terminal device no longer performs measurements and no longer transmits new measurement results to the network device. In addition, in this manner, the measurement process of the second terminal device may be reduced, the resources consumed in the measurement process may be reduced, and the battery power of the second terminal device may be saved.

[0043] With reference to the third aspect, in a first optional implementation of the third aspect, after transmitting the measurement result to the network device, the method further includes a step of starting a timer, wherein the first condition is that the timer has expired.

[0044] In this manner, the satisfaction of the first condition means that the timer has expired, and the non-satisfaction of the first condition means that the timer has not expired. Determining whether to perform the first operation by using a timer is a simple manner, which helps promote the technical solution in this embodiment of this application to more terminal devices for use.

[0045] Referring to the third aspect, in a second optional implementation of the third aspect, the first condition is that a third message is received from the network device, and the third message indicates that the first terminal device refuses to provide the relay service, or indicates that a terminal device capable of providing the relay service is to be reselected.

[0046] In this manner, the satisfaction of the first condition means that the third message from the network device is received, and the non-satisfaction of the first condition means that the third message from the network device is not received. By using the message from the network device to determine whether to perform the first operation, the determination result can be more accurate and more compatible with the current situation.

[0047] With reference to the second optional implementation of the third aspect, in a third optional implementation of the third aspect, the third message further includes information about one or more terminal devices, and the one or more terminal devices cannot provide a relay service.

[0048] With reference to the third aspect, or any one of the first optional implementation of the third aspect to the third optional implementation of the third aspect, in a fourth optional implementation of the third aspect, the method further includes: a step of sending a fourth message to the network device, wherein the fourth message indicates an energy saving requirement; and a step of receiving first information from the network device, wherein the first information includes information about M terminal devices, and the M terminal devices do not need to be measured or refuse to provide relay service, and M is a positive integer.

[0049] With reference to the fourth optional implementation of the third aspect, in a fifth optional implementation of the third aspect, the fourth message further includes second information, the second information includes information about N terminal devices, and the N terminal devices refuse to provide the relay service, where N is a positive integer.

[0050] With reference to the third aspect, or any one of the first optional implementation of the third aspect to the fifth optional implementation of the third aspect, in a sixth optional implementation of the third aspect, the method further includes a step of receiving measurement configuration information from the network device, and a step of performing measurement based on the measurement configuration information to obtain a measurement result, and the step of sending the measurement result to the network device includes a step of sending the measurement result to the network device when a reporting condition for the measurement report is satisfied.

[0051] The network device sends measurement configuration information to the second terminal device to configure the second terminal device to perform measurements. The second terminal device may obtain measurement results after performing the measurements. The measurement results include, for example, measurement reports obtained by measuring one or more terminal devices. If a reporting condition of the measurement report is met, the second terminal device may send the measurement results to the network device, so that the network device can obtain the measurement results of the second terminal device and select a terminal device that can provide relay service for the second terminal device.

[0052] With reference to the third aspect or any one of the first optional implementation of the third aspect to the sixth optional implementation of the third aspect, in a seventh optional implementation of the third aspect, when the first operation includes sending a discovery message, the method further includes a step of sending the discovery message, and a step of stopping sending the discovery message when the first condition is not satisfied.

[0053] If the first operation includes transmitting a discovery message, if the second terminal device did not originally transmit the discovery message, when the first condition is not met, the second terminal device may continue not transmitting the discovery message, or if the second terminal device originally transmitted the discovery message, when it is determined that the first condition is not met, the second terminal device may stop transmitting the discovery message to reduce power consumption.

[0054] With reference to the third aspect or any one of the first optional implementation of the third aspect to the sixth optional implementation of the third aspect, in an eighth optional implementation of the third aspect, when the first operation includes sending new measurement results to the network device, the method further includes the steps of receiving a discovery message from a second terminal device, measuring the discovery message of the second terminal device to obtain the new measurement results, and skipping sending the new measurement results to the network device when the first condition is not satisfied and the reporting condition of the measurement report is satisfied.

[0055] If the second terminal device receives a discovery message from the first terminal device, the second terminal device may measure the discovery message to obtain a new measurement result. If the first operation includes transmitting a new measurement report to the network device (in other words, if the first operation includes transmitting a measurement report to the network device), when the first condition is not satisfied, even if the reporting condition of the measurement report is satisfied, the second terminal device does not transmit the new measurement report to the network device to reduce power consumption.

[0056] For technical effects provided by some optional implementations of the third aspect, please refer to the description of the technical effects of the corresponding implementations of the second aspect.

[0057] According to a fourth aspect, a fourth communication method is provided. The method may be executed by a second terminal device or a chip system, and the chip system can realize the function of the second terminal device. The second terminal device is, for example, a terminal device that needs to perform relaying by using another terminal device in a relay scenario. The method includes receiving configuration information from a first network device, the configuration information being for configuring the second terminal device to switch to communicate with a third network device via the first terminal device or for configuring the second terminal device to be handed over to the second network device; performing a path switch based on the configuration information; and determining that the path switch is successful when a first condition is satisfied; and otherwise determining that the path switch is unsuccessful.

[0058] In this embodiment of the present application, the second terminal device may determine whether the path switching is successful or unsuccessful based on the first condition. That is, this embodiment of the present application provides a manner for the second terminal device to determine whether the path switching is successful. If the path switching is unsuccessful, the second terminal device may perform a corresponding operation, for example, may continue to perform communication within the coverage of the source network device, or may enter a new cell through cell reselection, so as to resume the service of the second terminal device as soon as possible and improve service continuity.

[0059] With reference to the fourth aspect, in a first optional implementation of the fourth aspect, after receiving the configuration information from the first network device, the method further includes a step of starting a timer, wherein the first condition is that the timer has not expired.

[0060] In this manner, the satisfaction of the first condition means that the timer has not expired, and the non-satisfaction of the first condition means that the timer has expired. The second terminal device can determine whether the path switching is successful or unsuccessful based on the timer. The determination manner is simple and easy to implement. The technical solution in this embodiment of this application can also be applied to terminal devices with low capabilities.

[0061] With reference to the fourth aspect, in a second optional implementation of the fourth aspect, the configuration information is for configuring the second terminal device to switch to communicate with the third network device through the first terminal device, and the first condition is: Receive feedback from the first terminal device when the number of times of sending the connection establishment request message to the first terminal device is less than or equal to M, where M is the maximum number of retransmissions; A security verification is successful for the first terminal device, or The method includes sending a connection establishment request message to the first terminal device, and receiving a connection establishment response message from the first terminal device, the connection establishment response message indicating that the connection establishment is accepted.

[0062] If the second terminal device determines whether the path switching is successful based on a timer, the timer's timing duration is usually not set too short. Otherwise, the determination result of the second terminal device may be inaccurate. However, if the second terminal device does not use a timer but determines whether the path switching is successful by using one of the above conditions, a shorter time is required to make the determination, and the efficiency is higher, so that the second terminal device can take corresponding measures as soon as possible and determine whether the path switching is successful as soon as possible to reduce service interruption time.

[0063] With reference to the fourth aspect, the first optional implementation of the fourth aspect, or the second optional implementation of the fourth aspect, in a third optional implementation of the fourth aspect, it is determined that the path switching has failed, and the method further includes a step of sending failure information to the first network device through a first path, where the failure information indicates that the path switching has failed, and the first path is a communication path between the second terminal device and the first network device before the path switching, and a step of continuing to communicate with the first network device through the first path.

[0064] The first path is the communication path between the second terminal device and the first network device before the path switch. For example, the first path is the second terminal device-first network device, or the second terminal device-first network device-first network device. If the second terminal device has not disconnected from the first network device through the first path before successfully performing the path switch, the second terminal device may perform the method. After the first network device receives the failure information, the second terminal device may continue to communicate with the first network device through the first path. That is, since the original communication path has not been disconnected, the second terminal device may continue to communicate through the original communication path and does not need to reselect a communication path. In other words, the second terminal device does not initiate an RRC connection re-establishment process to improve the service continuity of the second terminal device.

[0065] With reference to the fourth aspect, the first optional implementation of the fourth aspect, or the second optional implementation of the fourth aspect, in a fourth optional implementation of the fourth aspect, it is determined that the path switching has failed, and the method further includes a step of sending an RRC connection re-establishment request message to the first network device through a first path, where the RRC connection re-establishment request message requests the first network device to re-establish the RRC connection, and the first path is a communication path between the second terminal device and the first network device before the path switching.

[0066] If the second terminal device has not disconnected from the first network device via the first path before successfully performing the path switch, the second terminal device may also perform the method to re-establish the RRC connection within the coverage of the first network device, thereby communicating with the first network device via the new connection.

[0067] With reference to the third optional implementation of the fourth aspect or the fourth optional implementation of the fourth aspect, in a fifth optional implementation of the fourth aspect, the first route is a route for connecting to the first network device via a third terminal device, or the first route is a route for connecting directly to the first network device.

[0068] With reference to the fourth aspect, the first optional implementation of the fourth aspect, or the second optional implementation of the fourth aspect, in a sixth optional implementation of the fourth aspect, it is determined that the path switch has failed, and the method further includes a step of performing cell reselection to reselect the first cell, and a step of initiating an RRC connection re-establishment process in the first cell, or a step of initiating an RRC connection establishment process in the first cell.

[0069] For example, if the second terminal device disconnects the first path between the second terminal device and the first network device, the second terminal device may perform the method. Alternatively, even if the second terminal device does not disconnect the first path between the second terminal device and the first network device, the second terminal device may also perform the method.

[0070] According to a fifth aspect, there is provided a fifth communication method. The method may be executed by a first network device or may be executed by a chip system, where the chip system can realize functions of the first network device. The method includes: receiving failure information or an RRC connection re-establishment request message from a second terminal device through a first path, where the failure information indicates that a path switch has failed, and the RRC connection re-establishment request message requests the first network device to re-establish the RRC connection, and the first path is a communication path between the second terminal device and the first network device before the path switch.

[0071] Referring to the fifth aspect, in a first optional implementation of the fifth aspect, failure information is received, and the method further includes a step of determining that the second terminal device does not initiate RRC connection re-establishment.

[0072] For the technical effects provided by the fifth aspect or the first optional implementation of the fifth aspect, please refer to the description of the technical effects of the fourth aspect or the corresponding implementation.

[0073] According to a sixth aspect, a sixth communication method is provided. The method may be executed by a second terminal device or may be executed by a chip system, and the chip system can realize the function of the second terminal device. The second terminal device is, for example, a terminal device that needs to perform relaying by using another terminal device in a relay scenario. The method includes the steps of receiving configuration information from a first network device, the configuration information being for configuring the second terminal device to switch to communicate with a third network device via the first terminal device or for configuring the second terminal device to be handed over to the second network device; performing a path switch based on the configuration information; and determining that the path switch has failed when a second condition is satisfied.

[0074] In this embodiment of the present application, the second terminal device may determine whether the path switching has failed based on a second condition. That is, this embodiment of the present application provides a manner for the second terminal device to determine whether the path switching has failed. If the path switching has failed, the second terminal device may perform a corresponding operation, for example, may continue to initiate re-establishment within the coverage of the source network device, may enter a new cell through cell reselection to perform re-establishment, may initiate re-establishment by using the first terminal device, or may select a new relay terminal device through reselection or selection of a relay terminal device and initiate re-establishment by using the relay terminal device, so as to resume service of the second terminal device as soon as possible and improve service continuity.

[0075] With reference to the sixth aspect, in a first optional implementation of the sixth aspect, after receiving the configuration information from the first network device, the method further includes a step of starting a timer, wherein the second condition is that the timer has expired.

[0076] In this manner, the satisfaction of the second condition means that the timer has expired. The second terminal device can determine whether the path switching is successful or unsuccessful based on the timer. The determination manner is simple and easy to implement. The technical solution in this embodiment of this application can also be applied to terminal devices with low capabilities.

[0077] With reference to the first implementation of the sixth aspect, in a second optional implementation of the sixth aspect, the following condition is satisfied: The establishment of a PC5 connection between the second terminal device and the first terminal device is completed; The second terminal device successfully randomly accesses the third network device; The second terminal device sends an RRC reconfiguration complete message to a lower layer of the second terminal device and receives an acknowledgement feedback from the lower layer; the second terminal device receives second instruction information from the third network device, the second instruction information indicating to the second terminal device to stop the timer; the second terminal device receives third instruction information from the first terminal device, the third instruction information instructing the second terminal device to stop a timer, or the third instruction information indicating that the first terminal device has successfully randomly accessed the third network device; the second terminal device receives fourth indication information from the first terminal device, the fourth indication information indicating that a Uu radio link failure (RLF) occurs at the first terminal device or that the first terminal device fails to randomly access the third network device; or The establishment of a PC5 connection between the second terminal device and the first terminal device fails or a PC5 RLF is determined When one or more of the following conditions are met, the timer is stopped.

[0078] If the second terminal device determines whether the path switch has failed depending on whether the timer has expired, the timing duration of the timer is usually not set too short, and the timer needs to be stopped in a timely manner to avoid the path switch being determined to have failed because the timer has not been stopped.

[0079] In a third optional implementation of the sixth aspect, with reference to the sixth aspect, the first optional implementation of the sixth aspect, or the second optional implementation of the sixth aspect, The second condition is that the timer has expired, The second condition is that the second terminal device receives fourth indication information from the first terminal device, the fourth indication information indicating that a Uu RLF occurs in the first terminal device or that the first terminal device fails to randomly access the third network device; or The second condition is that the establishment of a PC5 connection between the second terminal device and the first terminal device has failed, or the PC5 RLF has been determined.

[0080] If the second terminal device determines whether the path switching has failed based only on whether the timer has expired, the timer's timing duration is usually not set too short. When a failure occurs, the second terminal device still needs to wait. In this implementation, when a failure occurs, the failure can be determined quickly and the restart process can be started as soon as possible to improve the continuity of service for the second terminal device.

[0081] With reference to the sixth aspect, the first optional implementation of the sixth aspect, the second optional implementation of the sixth aspect, or the third optional implementation of the sixth aspect, in a fourth optional implementation of the sixth aspect, the method further includes: the second terminal device sending an RRC connection re-establishment request message to the first network device through a first path, the RRC connection re-establishment request message requesting the first network device to re-establish the RRC connection, and the first path being a communication path between the second terminal device and the first network device before the path switching.

[0082] If the second terminal device has not disconnected from the first network device via the first path before successfully performing the path switch, the second terminal device may also perform the method to re-establish an RRC connection within the coverage of the first network device, thereby communicating with the first network device via the new connection.

[0083] With reference to the fourth optional implementation of the sixth aspect, in a fifth optional implementation of the sixth aspect, the first route is a route for connecting to the first network device via a third terminal device, or the first route is a route for connecting directly to the first network device.

[0084] With reference to the sixth aspect, the first optional implementation of the sixth aspect, the second optional implementation of the sixth aspect, or the third optional implementation of the sixth aspect, in a sixth optional implementation of the sixth aspect, the method further includes a step of performing cell reselection to reselect the first cell, and a step of initiating an RRC connection reestablishment process in the first cell or initiating an RRC connection establishment process in the first cell.

[0085] For example, if the second terminal device disconnects the first path between the second terminal device and the first network device, the second terminal device may perform the method. Alternatively, even if the second terminal device does not disconnect the first path between the second terminal device and the first network device, the second terminal device may also perform the method.

[0086] According to a seventh aspect, a communication device is provided. The communication device may include a module configured to perform the method according to the first aspect or any one of optional implementations of the first aspect, and may include, for example, a processing unit and a transceiver unit. Optionally, the communication device may further include a storage unit.

[0087] For example, the processing unit is configured to receive a first message from the network device via the transceiver unit, the first message including configuration information, or the first message is for inquiring whether the communication device is capable of providing a relay service, and the configuration information is for configuring the communication device to provide a relay service for a second terminal device.

[0088] The processing unit is further configured to send a second message to the network device via the transceiver unit, wherein the second message indicates that configuration of the communication device has been completed or has failed, and the first message includes the configuration information, or the second message indicates that the communication device is capable of providing relay service or refuses to provide relay service.

[0089] According to an eighth aspect, there is provided a communication device. The communication device may include a module configured to perform the method according to the second aspect or any one of optional implementations of the second aspect, and may include, for example, a transceiver unit and a processing unit. Optionally, the communication device may further include a storage unit.

[0090] For example, the processing unit is configured to send a first message to the first terminal device via the transceiver unit, the first message including configuration information, or the first message is for inquiring whether the first terminal device is capable of providing a relay service, and the configuration information is for configuring the first terminal device to provide a relay service for the communication apparatus.

[0091] The processing unit is further configured to receive a second message from the first terminal device via the transceiver unit, the second message indicating that configuration of the first terminal device has been completed or has failed, the first message including configuration information, or the second message indicating that the first terminal device is capable of providing relay service or refuses to provide relay service.

[0092] According to a ninth aspect, there is provided a communication device. The communication device may include a module configured to perform the method according to the third aspect or any one of optional implementations of the third aspect, and may include, for example, a transceiver unit and a processing unit. Optionally, a storage unit may be further included.

[0093] For example, the processing unit is configured to transmit the measurement results to the network device via the transceiver unit, where the measurement results include a measurement report for the at least one terminal device.

[0094] The processing unit is further configured to perform a first operation when a first condition is met, and to skip performing the first operation otherwise, where the first operation includes one or more of the following: sending a discovery message, measuring another terminal device, or sending new measurement results to the network device.

[0095] According to a tenth aspect, there is provided a communication device. The communication device may include a module configured to perform the method according to the fourth aspect or any one of optional implementations of the fourth aspect, and may include, for example, a transceiver unit and a processing unit. Optionally, a storage unit may be further included.

[0096] For example, the processing unit is configured to receive configuration information from a first network device via the transceiver unit, the configuration information being for configuring the communication device to switch to communicate with a third network device via the first terminal device, or for configuring the communication device to be handed over to a second network device.

[0097] The processing unit is further configured to perform path switching based on the configuration information.

[0098] The processing unit is further configured to determine that the path switching is successful when the first condition is met, and otherwise determine that the path switching is unsuccessful.

[0099] According to an eleventh aspect, there is provided a communication device. The communication device may include a module configured to perform the method according to the fifth aspect or any one of optional implementations of the fifth aspect, and may include, for example, a transceiver unit and a processing unit. Optionally, a storage unit may be further included.

[0100] For example, the processing unit is configured to receive failure information or an RRC connection re-establishment request message from the second terminal device via the transceiver unit, where the failure information indicates that a path switch has failed, the RRC connection re-establishment request message requests the first network device to re-establish the RRC connection, and the first path is a communication path between the second terminal device and the first network device before the path switch.

[0101] According to a twelfth aspect, there is provided a communication device. The communication device may include a module configured to perform the method according to the sixth aspect or any one of optional implementations of the sixth aspect, and may include, for example, a transceiver unit and a processing unit. Optionally, a storage unit may be further included.

[0102] For example, the processing unit is configured to receive configuration information from a first network device via the transceiver unit, the configuration information being for configuring the second terminal device to switch to communicate with a third network device via the first terminal device, or for configuring the second terminal device to be handed over to the second network device.

[0103] The processing unit is further configured to perform path switching based on the configuration information.

[0104] The processing unit is further configured to determine that the path switching is successful when the first condition is met, and otherwise determine that the path switching is unsuccessful.

[0105] According to a thirteenth aspect, a chip system is provided. The chip system includes one or more processors and a communication interface. The processor is coupled to the communication interface and configured to implement a method according to the first aspect or any one of the optional implementations of the first aspect. Optionally, the chip system may further include a memory. For example, the processor may read and execute a software program stored in the memory to implement the method according to the first aspect or any one of the optional implementations of the first aspect.

[0106] According to a fourteenth aspect, a chip system is provided. The chip system includes one or more processors and a communication interface. The processor is coupled to the communication interface and configured to implement the method according to the second aspect or any one of the optional implementations of the second aspect. Optionally, the chip system may further include a memory. For example, the processor may read and execute a software program stored in the memory to implement the method according to the second aspect or any one of the optional implementations of the second aspect.

[0107] According to a fifteenth aspect, a chip system is provided. The chip system includes one or more processors and a communication interface. The processor is coupled to the communication interface and configured to implement a method according to the third aspect or any one of the optional implementations of the third aspect. Optionally, the chip system may further include a memory. For example, the processor may read and execute a software program stored in the memory to implement the method according to the third aspect or any one of the optional implementations of the third aspect.

[0108] According to a sixteenth aspect, a chip system is provided. The chip system includes one or more processors and a communication interface. The processor is coupled to the communication interface and configured to implement a method according to the fourth aspect or any one of the optional implementations of the fourth aspect. Optionally, the chip system may further include a memory. For example, the processor may read and execute a software program stored in the memory to implement the method according to the fourth aspect or any one of the optional implementations of the fourth aspect.

[0109] According to a seventeenth aspect, a chip system is provided. The chip system includes one or more processors and a communication interface. The processor is coupled to the communication interface and configured to implement a method according to the fifth aspect or any one of the optional implementations of the fifth aspect. Optionally, the chip system may further include a memory. For example, the processor may read and execute a software program stored in the memory to implement the method according to the fifth aspect or any one of the optional implementations of the fifth aspect.

[0110] According to an eighteenth aspect, a chip system is provided. The chip system includes one or more processors and a communication interface. The processor is coupled to the communication interface and configured to implement a method according to the sixth aspect or any one of the optional implementations of the sixth aspect. Optionally, the chip system may further include a memory. For example, the processor may read and execute a software program stored in the memory to implement the method according to the sixth aspect or any one of the optional implementations of the sixth aspect.

[0111] According to a 19th aspect, there is provided a first communication system, which includes the communication device according to the 7th aspect or the chip system according to the 13th aspect, and includes the communication device according to the 8th aspect or the chip system according to the 14th aspect.

[0112] According to a twentieth aspect, there is provided a second communication system, which includes the communication device according to the eighth aspect or the chip system according to the fourteenth aspect, and which includes the communication device according to the ninth aspect or the chip system according to the fifteenth aspect.

[0113] According to a 21st aspect, there is provided a third communication system, which includes the communication device according to the 10th aspect or the chip system according to the 16th aspect, and includes the communication device according to the 11th aspect or the chip system according to the 17th aspect.

[0114] According to a 22nd aspect, there is provided a fourth communication system, which includes the communication device according to the 12th aspect or the chip system according to the 18th aspect, and includes the communication device according to the 11th aspect or the chip system according to the 17th aspect.

[0115] According to a twenty-third aspect, there is provided a computer-readable storage medium configured to store a computer program, which, when executed on a computer, enables the computer to perform a method according to any one of the preceding aspects.

[0116] According to a twenty-fourth aspect, there is provided a computer program product comprising instructions, the computer program product being configured to store a computer program, which, when executed on a computer, enables the computer to perform a method according to any one of the preceding aspects.

[0117] In an embodiment of this application, if the first terminal device refuses to provide relay service for the second terminal device, the network device can also know the case, so that the first terminal device does not need to enter an RRC re-establishment procedure and can continue to operate normally within the coverage of the network device, so as to improve the service quality of the first terminal device and reduce the resources consumed in the RRC re-establishment procedure. [Brief explanation of the drawings]

[0118] [Figure 1A] FIG. 10 is a diagram of a scenario in which a remote terminal device performs a path switch. [Figure 1B] FIG. 10 is a diagram of a scenario in which a remote terminal device performs a path switch. [Figure 1C] FIG. 10 is a diagram of a scenario in which a remote terminal device performs a path switch. [Figure 1D]FIG. 10 is a diagram of a scenario in which a remote terminal device performs a path switch. [Figure 2] 10 is a flowchart of switching from a direct link to an indirect link by a remote terminal device. [Figure 3] 2 is a flowchart of a first communication method according to an embodiment of the present application. [Figure 4] 4 is a flowchart of a second communication method according to an embodiment of the present application. [Figure 5] 4 is a flowchart of a third communication method according to an embodiment of the present application. [Figure 6] 10 is a flowchart of a fourth communication method according to an embodiment of the present application. [Figure 7] 10 is a flowchart of a fifth communication method according to an embodiment of the present application. [Figure 8] 10 is a flowchart of a sixth communication method according to an embodiment of the present application. [Figure 9] 10 is a flowchart of a seventh communication method according to an embodiment of the present application. [Figure 10] 10 is a flowchart of an eighth communication method according to an embodiment of the present application. [Figure 11] 1 is a schematic block diagram of a terminal device according to an embodiment of the present application; [Figure 12] 1 is a schematic block diagram of a communication device according to an embodiment of the present application; DETAILED DESCRIPTION OF THE INVENTION

[0119] To make the objectives, technical solutions and advantages of the embodiments of this application clearer, the following further describes the embodiments of this application in detail with reference to the accompanying drawings.

[0120] To facilitate the understanding of those skilled in the art, some terms in the embodiments of this application are explained and described below.

[0121] In an embodiment of this application, the terminal device is a device having wireless transceiver functionality, and may be a fixed device, a mobile device, a handheld device (e.g., a mobile phone), a wearable device, an in-vehicle device, or a wireless device (e.g., a communication module, a modem, or a chip system) built into the aforementioned devices. Terminal devices are configured to connect people, things, machines, and the like, and can be widely used in various scenarios, including, but not limited to, the following scenarios: cellular communication, device-to-device (D2D) communication, vehicle-to-everything (V2X), machine-to-machine / machine type communication (M2M / MTC), internet of things (IoT), virtual reality (VR), augmented reality (AR), industrial control, self driving, telemedicine, smart grid, smart furniture, smart office, smart wearable, smart transportation, smart city, unmanned aerial vehicles, and robots. Terminal devices can sometimes be referred to as user equipment (UE), terminal, access station, UE station, remote station, wireless communication device, user equipment, or the like. For ease of description, in the embodiment of this application, an example in which the terminal device is a UE is used for description. A remote UE is a UE that requires other UEs to provide relay services to access the network. A relay UE is a UE that provides relay services for other UEs.

[0122] Network devices in embodiments of this application include, for example, access network devices and / or core network devices. An access network device is a device having wireless transceiver functionality and configured to communicate with terminal devices. Access network devices include, but are not limited to, base stations (BTSs, NodeBs, eNodeBs / eNBs, or gNodeBs / gNBs), transmission reception points (TRPs) in the aforementioned communication systems, base stations later evolved in the 3rd generation partnership project (3GPP), access nodes in wireless fidelity (Wi-Fi) systems, wireless relay nodes, wireless backhaul nodes, and the like. A base station may be a macro base station, a micro base station, a picocell base station, a small cell, a relay station, or the like. Multiple base stations may support the aforementioned networks using the same access technology or different access technologies. A base station may include one or more co-site or non-co-site transmission and reception points. Alternatively, the network device may be a radio controller, a central unit (CU), and / or a distributed unit (DU) in a cloud radio access network (CRAN) scenario. Alternatively, the network device may be a server, a wearable device, an in-vehicle device, or the like. For example, a network device in a vehicle-to-everything (V2X) technology may be a road side unit (RSU). The following describes the access network device by using an example in which the access network device is a base station. The base station may communicate with a terminal device or may communicate with the terminal device via a relay station.A terminal device may communicate with multiple base stations in different access technologies. The core network device is configured to realize functions such as mobility management, data processing, session management, and policy and charging. The names of devices realizing core network functions in systems using different access technologies may be different. This is not limited in the embodiments of this application. A 5G system is used as an example. The core network device includes an access and mobility management function (AMF), a session management function (SMF), a user plane function (UPF), or the like.

[0123] In the embodiments of this application, the communication device configured to realize the functions of the network device may be a network device, or may be a device, such as a chip system, that can support the network device in realizing the functions. The device may be installed in the network device. In the technical solutions provided in the embodiments of this application, an example in which the device configured to realize the functions of the network device is a network device is used to describe the technical solutions provided in the embodiments of this application.

[0124] In the embodiments of this application, unless otherwise specified, the quantities of nouns are "singular or plural," i.e., express "one or more." "At least one" means one or more, and "multiple" means two or more. The term "and / or" describes an association relationship between associated objects and expresses that three relationships may exist. For example, A and / or B may express the following three cases: only A exists, both A and B exist, and only B exists. A and B may be singular or plural. The character " / " generally indicates an "or" relationship between associated objects. For example, A / B indicates A or B. "At least one of" or similar expressions means any combination of these items, including any combination of singular items or multiple items. For example, at least one of a, b, or c expresses a, b, c, a and b, a and c, b and c, or a, b, and c. a, b, and c may be singular or plural.

[0125] In the embodiments of this application, sequence numbers such as "first" and "second" are used to distinguish between multiple objects and are not intended to limit the size, content, order, time sequence, priority, or importance of the multiple objects. For example, the first message and the second message may be the same message or different messages. In addition, such names do not indicate that the two messages differ in transmission order, amount of information, content, priority, importance, or the like.

[0126] Currently proposed UE relay technologies include a relay method in which the remote UE appears to the RAN, and in this relay method, the remote UE can perform path switching.

[0127] The path switch process of the remote UE includes a process of switching from a direct link to an indirect link, a process of switching from an indirect link to a direct link, and a process of switching between indirect links. See Figures 1A to 1D. Figure 1A illustrates a scenario in which the remote UE switches from an indirect link to a direct link, or a scenario in which the remote UE switches from a direct link to an indirect link. For example, the remote UE is a smartwatch. An embedded subscriber identity module (eSIM) card may be installed in the smartwatch, and the smartwatch can communicate directly with an access network device by using the eSIM card. A user carries the smartwatch to run without carrying a mobile phone. In this case, the smartwatch can directly communicate with an access network device through the Uu interface when outdoors. When the user returns home after running, the smartwatch detects the presence of the mobile phone through the sidelink (SL). In this case, in order to use the mobile phone as a relay UE, the smartwatch may automatically switch from a direct link between the smartwatch and the access network device to an indirect link for relaying performed by using the mobile phone, or the smartwatch may switch from a direct link between the smartwatch and the access network device to an indirect link for relaying performed by using the mobile phone based on user operation, thereby communicating with the network via the mobile phone, thereby reducing the power consumption of the smartwatch.

[0128] Figure 1B illustrates a scenario in which a remote UE switches between indirect links. For example, the remote UE is a smartwatch. A user owns a smartwatch and a mobile phone. Initially, the mobile phone is the relay UE of the smartwatch and provides relay services for the smartwatch. After the user enters a vehicle, the smartwatch may switch from the indirect link for relaying performed by using the mobile phone to the indirect link for relaying performed by using the vehicle to use the vehicle as a new relay UE, thereby communicating with the network through the vehicle, thereby reducing the power consumption of the smartwatch and the mobile phone.

[0129] 1C illustrates a scenario in which a remote UE switches from an indirect link to a direct link, or a scenario in which a remote UE switches from a direct link to an indirect link. For example, the remote UE is a smart watch. A user performs an outdoor activity. Because an eSIM card is installed in the smart watch, the smart watch can directly communicate with access network device 2 by using the eSIM card. Then, the user enters a vehicle, and the vehicle travels to another city. In the vehicle travel process, the smart watch automatically (or based on a user's operation) switches from the direct link for direct communication with access network device A to the indirect link for relaying performed by using the vehicle, in order to reduce the power consumption of the smart watch. Because the vehicle is in a traveling state, access network device B connected to the vehicle and access network device A may be different access network devices.

[0130] FIG. 1D illustrates a scenario in which a remote UE switches between indirect links. For example, the remote UE is a smartwatch. A user rides in vehicle A to a location. When the user enters vehicle A, the smartwatch may establish a connection to vehicle A to use vehicle A as the smartwatch's relay UE, thereby communicating with the network through vehicle A. The user then changes vehicles and enters vehicle B. During the vehicle B journey, the communication quality between the smartwatch and vehicle B gradually deteriorates. In this case, the smartwatch may automatically (or based on a user's operation) switch from the indirect link for relaying performed by using vehicle B to the indirect link for relaying performed by using vehicle B to improve the communication quality of the smartwatch. In addition, since vehicle B is in a traveling state and vehicle B may also be in a traveling state, the access network device serving vehicle B and the access network device serving vehicle B may be different access network devices.

[0131] The scenario depicted in Figures 1A and 1B is an intra-gNB switching scenario, and the scenario depicted in Figures 1C and 1D is an inter-gNB switching scenario.

[0132] When switching to an indirect link (including switching from a direct link to an indirect link or switching between indirect links), the mainstream solutions currently being discussed are as follows: the base station configures the remote UE to perform measurements, the remote UE performs measurements based on discovery messages from other UEs, the remote UE sends the measurement results to the base station, and the base station determines whether the remote UE should perform a path switch. If the base station determines that the remote UE should perform a path switch, the base station sends configuration information to the remote UE and the relay UE separately to configure the path switch. For example, the process of a remote UE switching from a direct link to an indirect link can be seen in the procedure shown in Figure 2.

[0133] S201: A remote UE performs data transmission with a base station.

[0134] S202: The base station sends an RRC message to the remote UE, and the remote UE receives the RRC message from the base station. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure or select other UEs.

[0135] S203: The remote UE measures or selects another UE. For example, the remote UE may trigger the other UE to send a discovery message, so that the remote UE measures the discovery message from the other UE to complete the measurement or selection of the other UE.

[0136] S204: The remote UE sends the measurement result to the base station, and the base station receives the measurement result from the remote UE; or the remote UE sends the selection result to the base station, and the base station receives the selection result from the remote UE. In FIG. 2, sending the measurement result is used as an example.

[0137] The measurement result may be, for example, a measurement report, or may include an ID of a relay UE. The selection result may be, for example, a result of a remote UE selecting a relay UE, or may include ID information of the relay UE. Optionally, measurement information of the remote UE may be further included.

[0138] S205: The base station determines whether the remote UE should perform path switch based on the measurement result or the selection result. If the base station determines that the remote UE should perform path switch, S206 and S207 are executed; otherwise, S206 and S207 are not executed.

[0139] S206: The base station sends an RRC reconfiguration message to the relay UE, and the relay UE receives the RRC reconfiguration message from the base station. To distinguish it from other RRC reconfiguration messages, the RRC reconfiguration message in S206 is called RRC reconfiguration message 1.

[0140] The RRC reconfiguration message 1 may include information configured by the base station for the relay UE, such as configuration information for the Uu interface and sidelink (SL) configuration information. The sidelink is a link between the remote UE and the relay UE. The relay UE provides relay service for the remote UE through the sidelink. After receiving the RRC reconfiguration message 1, the relay UE may perform configuration based on the information included in the RRC reconfiguration message 1, such as configuring the Uu link and sidelink.

[0141] S207: The base station sends an RRC reconfiguration message to the remote UE, and the remote UE receives the RRC reconfiguration message from the base station. To distinguish it from other RRC reconfiguration messages, the RRC reconfiguration message in S207 is called RRC reconfiguration message 2.

[0142] The RRC reconfiguration message 2 may include information configured by the base station for the remote UE, such as configuration information for the Uu interface and configuration information for the sidelink. After receiving the RRC reconfiguration message 2, the remote UE may perform configuration, such as configuring the Uu link and the sidelink, based on the information included in the RRC reconfiguration message 2.

[0143] According to the normal procedure, after the configuration of the remote UE and the relay UE is completed, the relay UE can provide relay service for the remote UE, so that the remote UE can communicate with the base station through the relay UE. However, it is very likely that the configuration of the relay UE fails or the relay UE refuses to provide relay service for the remote UE. In this case, the relay UE cannot notify the base station. Therefore, the relay UE needs to perform processing based on the case of configuration failure. 。rThe relay UE enters the RRC re-establishment procedure and can only continue to work after the RRC re-establishment is successful, which obviously causes a degradation of the service quality of the relay UE.

[0144] In consideration of this, a technical solution is provided in an embodiment of this application. In this embodiment, regardless of whether the first terminal device can provide relay service, the first terminal device can send a second message to the network device for notification, so that the network device can know whether the first terminal device can provide relay service. Therefore, if the first terminal device refuses to provide relay service, the network device can also know this case, so that the first terminal device does not need to interrupt the first terminal device's current communication and can continue to operate normally within the coverage of the network device, so as to improve the service quality of the first terminal device and reduce resources consumed in the RRC re-establishment procedure.

[0145] The technical solutions provided in the embodiments of this application may be applied to a 4th generation (4G) system, such as a long term evolution (LTE) system, or to a 5G system, such as a new radio (NR) system, or to a next generation mobile communication system or another similar communication system. is limitedIn addition, the technical solutions provided in the embodiments of this application may be applied to a device-to-device (D2D) scenario, for example, an NR-D2D scenario, or may be applied to a V2X scenario, for example, an NR-V2X scenario, for example, an Internet of Vehicles, for example, V2X or vehicle-to-vehicle (V2V), or may be applied to fields such as intelligent driving, driver assistance, or intelligent connected vehicles.

[0146] For application scenarios of the embodiments of this application, please refer to FIG. 1A, FIG. 1B, FIG. 1C, or FIG. 1D. The access network device in FIG. 1A to FIG. 1D is, for example, a base station. The access network device corresponds to different devices in different systems. For example, the access network device may correspond to an eNB in ​​a 4G system, and corresponds to an access network device in 5G, for example, a gNB in ​​a 5G system. Of course, the technical solutions provided in the embodiments of this application may alternatively be applied to future mobile communication systems. Therefore, the access network device in FIG. 1A to FIG. 1D may alternatively correspond to a network device in a future mobile communication system. In FIG. 1A to FIG. 1D, an example in which the access network device is a base station is used. In fact, referring to the foregoing description, the access network device may alternatively be a device such as an RSU.

[0147] With reference to the accompanying drawings, the following describes the methods provided in the embodiments of this application. In the accompanying drawings corresponding to the embodiments of this application, all steps indicated by dashed lines are optional steps.

[0148] An embodiment of this application provides a first communication method. Figure 3 is a flowchart of the method. The method relates to a process of switching to an indirect link. In the process described below, an example is used in which the method is applied to the network architecture shown in any one of Figures 1A to 1D.

[0149] If the technical solution provided in this embodiment of this application is applied to the network architecture shown in any one of Figures 1A to 1D, the second terminal device in the following description may be the remote terminal device shown in any one of Figures 1A to 1D. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1A, the first terminal device in the following description may be the relay terminal device in Figure 1A, and the network device in the following description may be the access network device in Figure 1A. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1B, the first terminal device in the following description may be the relay terminal device 1 or the relay terminal device 2 in Figure 1B, and the network device in the following description may be the access network device in Figure 1B. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1C, the first terminal device in the following description may be the relay terminal device in Figure 1C, and the network device in the following description may be the access network device 1 in Figure 1C. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1D, the first terminal device in the following description may be the relay terminal device 1 in Figure 1D, and the network device in the following description may be the access network device 1 in Figure 1D, or the first terminal in the following description may be the relay terminal device 2 in Figure 1D, and the network device in the following description may be the access network device 2 in Figure 1D. In addition, the following description uses an example in which the second terminal device is a remote UE and the first terminal device is a relay UE.

[0150] S301: A remote UE performs data transmission with a network device.

[0151] S302: The network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

[0152] Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included in, for example, a system message or another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

[0153] S303: The remote UE measures or selects another UE. For example, the remote UE may send a discovery message to trigger the other UE to send a discovery message, and the remote UE may measure the discovery message from the other UE to complete the measurement or selection of the other UE. In FIG. 3, an example in which the remote UE measures the other UE is used.

[0154] The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, such as measuring data signals from the other UEs. This is not limited here. The remote UE may select other UEs based on the measurement results.

[0155] S304: The remote UE sends the first result to the network device. Thus, the network device receives the first result from the remote UE. The first result may be, for example, a measurement result or a selection result. In FIG. 3, an example in which the first result is the measurement result is used.

[0156] The measurement result is, for example, a measurement report obtained by the remote UE by measuring at least one UE. The selection result is, for example, a result of the remote UE selecting a relay UE, and includes, for example, an ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may be further included.

[0157] If the application scenario of this embodiment of this application is to switch between indirect links, the communications between the remote UE and the network device in S301 to S304 are all performed through forwarding via the relay UE connected to the remote UE before the link switching, and the relay UE in the following description is the relay UE connected to the remote UE after the link switching.

[0158] S305: The network device determines whether the remote UE should perform path switch based on the measurement result or the selection result. If the network device determines that the remote UE should perform path switch, S306 and S307 are executed; otherwise, S306 and S307 are not executed.

[0159] S306: The network device sends a first message to the relay UE. Thus, the relay UE receives the first message from the network device. In this embodiment of the present application, the first message is, for example, an RRC reconfiguration message.

[0160] The RRC reconfiguration message may include configuration information, which may be for configuring the relay UE to provide relay service for the remote UE. For example, the configuration information may include configuration information for the Uu interface and configuration information for the sidelink. The sidelink is a link between the remote UE and the relay UE. The relay UE provides relay service for the remote UE through the sidelink. After the relay UE receives the RRC reconfiguration message, if the relay UE considers that relay service can be provided for the remote UE, the relay UE may perform configuration, for example, configure the Uu link and the sidelink, based on the configuration information included in the RRC reconfiguration message. If the relay UE refuses to provide relay service for the remote UE, the relay UE does not need to perform configuration based on the configuration information included in the RRC reconfiguration message.

[0161] In the RRC reconfiguration message, the related configuration for performing relay by the relay UE and the Uu configuration in the service of the relay UE may be indicated separately, for example, by different information elements. For example, the Uu configuration in the service of the relay UE may be carried in the original information element, and the related configuration for performing relay by the relay UE may be carried in a newly added information element, or an additional indication may be newly added for the related configuration for performing relay by the relay UE to indicate that the configuration is a configuration for supporting the relay service.

[0162] S307: The relay UE sends the second message to the network device, so that the network device receives the second message from the relay UE.

[0163] The second message may indicate that the configuration of the relay UE is completed, or may indicate that the configuration of the relay UE has failed. Alternatively, the second message may indicate that the relay UE is capable of providing relay service, or may indicate that the relay UE refuses to provide relay service. If the second message indicates that the configuration of the relay UE is completed, it may also be considered that the second message implicitly indicates that the relay UE is capable of providing relay service. If the second message indicates that the configuration of the relay UE has failed, it may also be considered that the second message implicitly indicates that the relay UE refuses to provide relay service.

[0164] In this embodiment of the application, the first message and the second message may be messages of the same type. For example, both are RRC reconfiguration type messages. The first message is an RRC reconfiguration message and the second message is an RRC reconfiguration complete message. Alternatively, the first message and the second message may be messages of different types. For example, the first message is an RRC reconfiguration message and the second message is a sidelink UE information (SUI) message.

[0165] Additionally, the second message may indicate success (including indicating that the configuration of the relay UE is completed or that the relay UE can provide relay service for the remote UE) or failure (including indicating that the configuration of the relay UE has failed or that the relay UE refuses to provide relay service for the remote UE). In this case, the second message may indicate success and failure by using the same type of message or the same message. For example, the second message may be an RRC reconfiguration complete message, and the RRC reconfiguration complete message may indicate success or failure. If the RRC reconfiguration complete message indicates failure, a first information element may be newly added to the RRC reconfiguration complete message, and the first information element indicates failure. In this case, after receiving the second message, the network device needs to analyze the message body of the second message to determine success or failure. The same type of message or the same message may indicate both success and failure, eliminating the need to use excessive types of messages, thereby simplifying the process of identifying different types of messages by the network device.

[0166] Alternatively, the second message may indicate success or failure by using a different type of message. For example, when the second message indicates success, the second message may be an RRC reconfiguration complete message. When the second message indicates failure, the second message may be an SUI message, a failure information message, or a newly added message in this embodiment of the application. For example, the second message may be a message specifically indicating whether the terminal device provides a relay service. In this case, the network device does not need to analyze the message body of the second message, but can determine success or failure based on the type information carried in the message header of the second message. This helps reduce the operational load of the network device.

[0167] For example, if the relay UE performs configuration based on the configuration information included in the RRC reconfiguration message and the relay UE determines that the configuration is successful and that the relay service can be provided, the second message may indicate that the configuration of the relay UE is completed or that the relay UE can provide the relay service. In another example, if the relay UE performs configuration based on the configuration information included in the RRC reconfiguration message and the configuration fails, the second message may indicate that the configuration of the relay UE has failed or may indicate that the relay UE refuses to provide the relay service. In another example, if the relay UE determines that some of the parameters in the configuration information included in the RRC reconfiguration message are not supported, the second message may indicate that the relay UE refuses to provide the relay service. In yet another example, if the relay UE does not perform configuration based on the configuration information included in the RRC reconfiguration message and determines that it refuses to provide the relay service, the second message may indicate that the relay UE refuses to provide the relay service.

[0168] In an optional implementation, if the second message indicates that the configuration of the relay UE has failed or that the relay UE refuses to provide relay service, the second message may further include a cause value. The cause value may indicate the cause of the refusal to provide relay service by the relay UE, thereby allowing the network device to determine the cause of the relay UE's inability to provide relay service and the network device to take corresponding measures. Alternatively, the cause value may implicitly indicate that the configuration has failed. That is, if the second message includes an indication of a cause value, it indicates that the configuration has failed or that the relay service is refused to be provided. If the second message does not include an indication of a cause value, it indicates that the configuration has succeeded or that relay service can be provided.The causes of refusal to provide relay service by a relay UE include the following: the relay UE does not support the configuration of the Uu interface (i.e., does not support the configuration of the Uu interface included in the configuration information); the relay UE does not support the configuration of the PC5 interface (i.e., does not support the configuration of the PC5 interface included in the configuration information); admission control performed by the relay UE for the remote UE fails; the configuration performed by the relay UE based on the configuration information fails; the relay UE does not support the integrity protection algorithm configured by using the configuration information (does not support the integrity protection algorithm information included in the configuration message); the relay UE does not support the 5G QoS identifier (5QI) or PC5 5G QoS identifier (PC5 5QI, PQI) configured by using the configuration information; the relay UE cannot identify the quality of service (QoS) flow ID indicated by the configuration information; the relay UE does not support the network slice indicated by the configuration information; the relay UE has insufficient battery power; This may include one or more of: the packet data convergence protocol (PDCP) of the UE is overloaded; or the relay UE does not support the computational capabilities indicated by the configuration information.For example, the reason for refusing to provide relay service by the relay UE is that the relay UE does not support configuration of the Uu interface, the reason for refusing to provide relay service by the relay UE is that the relay UE does not support configuration of the PC5 interface, the reason for refusing to provide relay service by the relay UE is that the relay UE cannot identify the QoS flow ID indicated by the configuration information, or the reason for refusing to provide relay service by the relay UE is that the relay UE does not support network slicing indicated by the configuration information and the relay UE has insufficient battery power.

[0169] If the second message indicates success and failure by using the same type of message or the same message, optionally, if the second message indicates failure, a first information element and a second information element may be newly added to the second message, where the first information element may indicate failure and the second information element is for carrying a cause value. For example, the second message is an RRC reconfiguration complete message, and the RRC reconfiguration complete message may indicate success or failure. If the RRC reconfiguration complete message indicates failure, a first information element and a second information element may be newly added to the RRC reconfiguration complete message, where the first information element indicates failure and the second information element is for carrying a cause value.

[0170] Alternatively, if the second message indicates success and failure by using a different type of message, optionally, if the second message indicates failure, a third information element may be added to the second message, where the third information element is for carrying a cause value. For example, when the second message indicates success, the second message may be an RRC reconfiguration complete message. When the second message indicates failure, the second message may be an SUI message, and a third information element may be newly added to the SUI message, where the third information element may carry a cause value. Because the second message indicates success and failure by using a different type of message, it can be known that the second message implicitly indicates failure. In this case, a small amount of information element is newly added to the second message. This helps reduce transmission overhead.

[0171] S308: The relay UE does not initiate the RRC re-establishment process.

[0172] If the second message indicates that the configuration of the relay UE has failed or that the relay UE refuses to provide relay service, S308 may be executed. In this case, since the network device knows that the relay UE does not provide relay service, the relay UE does not need to initiate an RRC re-establishment process and continues to perform normal communication with the network device. Therefore, the service quality of the relay UE is improved and resources consumed in the RRC re-establishment procedure are reduced. It may be understood that the relay UE not initiating an RRC re-establishment process may mean that the relay UE continues to communicate with the network device through the existing RRC connection.

[0173] The relay UE not initiating the RRC re-establishment process may be expressed as follows: The relay UE continues to apply the configuration of the connection between the relay UE and the network device before the first message is received. In other words, the status of the connection between the relay UE and the network device does not change. In other words, if the configuration of the connection between the relay UE and the network device (in other words, the status of the connection) does not change, it may implicitly indicate that the relay UE does not initiate RRC re-establishment.

[0174] However, if the second message indicates that the configuration of the relay UE is completed or that the relay UE can provide relay service, S207 shown in Figure 2 may be executed. In addition, after the configuration of the remote UE is also completed, the relay UE can provide relay service.

[0175] Alternatively, S207 shown in FIG. 2 may occur even if the second message indicates that the configuration of the relay UE has failed or that the relay UE refuses to provide relay service. For example, S207 is executed before the network device receives the second message. In this case, the remote UE needs to determine that the path switch has failed. How the remote UE determines that the path switch has failed will be described in the following embodiments.

[0176] In this embodiment of the present application, regardless of whether the relay UE can provide relay service, the relay UE can send a second message to the network device for notification, so that the network device can know whether the relay UE can provide relay service. Therefore, if the relay UE refuses to provide relay service, the network device can also know this case, so that the relay UE does not need to enter the RRC re-establishment procedure and can continue to operate normally within the coverage of the network device, so as to improve the service quality of the relay UE and reduce the resources consumed in the RRC re-establishment procedure.

[0177] An embodiment of this application provides a second communication method. Figure 4 is a flowchart of the method. The method relates to a process of switching to an indirect link. In the process of the following description, an example is used in which the method is applied to the network architecture shown in any one of Figures 1A to 1D. For the devices in Figures 1A to 1D that are the relay UE, remote UE, and network device in this embodiment of this application, please refer to the description of the first communication method.

[0178] S401: A remote UE performs data transmission with a network device.

[0179] S402: The network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

[0180] Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included in, for example, a system message or another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, such as measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

[0181] S403: The remote UE measures or selects another UE. For example, the remote UE may send a discovery message to trigger the other UE to send a discovery message, so that the remote UE can measure the discovery message from the other UE to complete the measurement or selection of the other UE. In FIG. 4, an example in which the remote UE measures the other UE is used.

[0182] The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, such as data signals from the other UEs, which is not limited here. The remote UE may select other UEs based on the measurement results.

[0183] S404: The remote UE sends the first result to the network device. Thus, the network device receives the first result from the remote UE. The first result is, for example, a measurement result or a selection result. In FIG. 4, an example in which the first result is the measurement result is used.

[0184] The measurement result is, for example, a measurement report obtained by measuring at least one UE. The selection result is a result of selecting a relay UE by a remote UE, for example, including an ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may be further included.

[0185] If the application scenario of this embodiment of this application is to switch between indirect links, the communications between the remote UE and the network device in S401 to S404 are all performed through forwarding via the relay UE connected to the remote UE before the link switching, and the relay UE in the following description is the relay UE connected to the remote UE after the link switching.

[0186] S405: The network device determines whether the remote UE should perform path switch based on the measurement result or the selection result. If the network device determines that the remote UE should perform path switch, proceed to S406; otherwise, the subsequent steps are not executed.

[0187] S406: The network device sends a first message to the relay UE. Accordingly, the relay UE receives the first message from the network device. The first message may be for inquiring whether the relay UE can provide a relay service. In this embodiment of the present application, the first message may be, for example, an RRC reconfiguration message, or the first message may be a message newly added in this embodiment of the present application, specifically for inquiring whether the terminal device can provide a relay service.

[0188] In this embodiment of the present application, the network device does not first send configuration information to the relay UE, but first inquires whether the relay UE can provide relay service by using a first message. If the relay UE can provide relay service, the network device may send configuration information to the relay UE, thereby making the transmission of the configuration information more effective. Alternatively, the network device sends one or more sets of configuration information to the relay UE to inquire whether the relay UE can provide relay service based on the corresponding configuration.

[0189] In an optional implementation, the first message may include one or more of the following: an identifier of the remote UE, integrity protection algorithm information or rate information, encryption algorithm information or rate information, PQI or 5QI, QoS, network slice information, configuration information, or computing capability information. For example, the first message includes an identifier of the remote UE, the first message includes a PQI, the first message includes configuration information, or the first message includes an identifier of the remote UE and network slice information. The first message may be for implicitly inquiring whether the relay UE can provide a relay service by using one or more of the foregoing included in the first message. Alternatively, the first message may further include inquiry information in addition to one or more of the foregoing, where the inquiry information is for inquiring whether the relay UE can provide a relay service. For a description of the configuration information, please refer to the embodiment shown in FIG. 3.

[0190] Integrity protection algorithm information or rate information, encryption algorithm information or rate information, configuration information, PQI or 5QI, QoS, network slice information, computing capability information, and the like are all capabilities required by the remote UE, or in other words, capabilities required by the relay UE to perform relaying. The first message includes information about the relevant capabilities required by the relay UE to perform relaying, thereby allowing the relay UE to better determine whether it can provide relay service for the remote UE. For example, if the relay UE does not have the capabilities indicated by the first message, the relay UE can determine to refuse to provide relay service for the remote UE, thereby making the relay UE's decision more accurate. In an embodiment of this application, the UE identifier is, for example, the UE ID, and the UE ID is, for example, the UE's Layer 2 ID or the ID of an application (APP) installed for the UE that requires relay service.

[0191] S407: The relay UE sends a second message to the network device. Thus, the network device receives the second message from the relay UE. The second message may indicate that the relay UE can provide the relay service, or may indicate that the relay UE refuses to provide the relay service.

[0192] In an optional implementation, when the first message includes one or more sets of configuration information, if the second message indicates that the relay UE can provide a relay service, the second message may further include first indication information indicating the configuration information for which the relay UE can provide the relay service, that is, the first indication information indicates that the UE can provide the relay service for one or more sets of configuration information.

[0193] In an optional implementation, if the second message indicates that the relay UE refuses to provide the relay service, the second message may further include a cause value. The cause value may indicate the reason for the refusal of the relay UE to provide the relay service, so that the network device can determine the reason when the relay UE cannot provide the relay service, and the network device can take corresponding measures. Causes for refusing to provide relay service by the relay UE may include one or more of the following: the relay UE does not support the configuration of the Uu interface (i.e., does not support the configuration of the Uu interface included in the first message); the relay UE does not support the configuration of the PC5 interface (i.e., does not support the configuration of the PC5 interface included in the first message); admission control performed by the relay UE for the remote UE fails; the relay UE does not support the integrity protection algorithm configured by using the first message; the relay UE does not support the 5QI or PQI configured by using the first message; the relay UE cannot identify the QoS flow ID indicated by the first message; the relay UE does not support the network slicing indicated by the first message; the relay UE has insufficient battery power; the relay UE's PDCP is overloaded; or the relay UE does not support the computing capability indicated by the first message.For example, the reason for refusing to provide relay service by the relay UE is that the relay UE does not support configuration of the Uu interface, the reason for refusing to provide relay service by the relay UE is that the relay UE does not support configuration of the PC5 interface, the reason for refusing to provide relay service by the relay UE is that the relay UE cannot identify the QoS flow ID indicated by the first message, or the reason for refusing to provide relay service by the relay UE is that the relay UE does not support network slicing indicated by the first message and the battery power of the relay UE is insufficient.

[0194] For further details of S407, such as the implementation of the second message, please refer to S307 in the embodiment shown in FIG.

[0195] If the second message indicates that the relay UE can provide relay service and does not include configuration information, the process may proceed to S408 and S409. Alternatively, if the second message indicates that the relay UE can provide relay service and includes configuration information, the process may proceed to S409, and S408 does not need to be executed. If the second message indicates that the relay UE refuses to provide relay service, S410 may be executed. In addition, if the second message indicates that the relay UE refuses to provide relay service, the network device knows that the relay UE does not provide relay service, so the relay UE does not need to initiate an RRC re-establishment process and continues to perform normal communication with the network device. Therefore, the service quality of the relay UE is improved, and resources consumed in the RRC re-establishment procedure are reduced.

[0196] The relay UE not initiating the RRC re-establishment process may be expressed as follows: The relay UE continues to apply the configuration of the connection between the relay UE and the network device before the first message is received. In other words, the status of the connection between the relay UE and the network device does not change. In other words, if the configuration of the connection between the relay UE and the network device (in other words, the status of the connection) does not change, it may implicitly indicate that the relay UE does not initiate RRC re-establishment.

[0197] S408: The network device sends an RRC reconfiguration message to the relay UE. Thus, the relay UE receives the RRC reconfiguration message from the network device. To distinguish it from other RRC reconfiguration messages, the RRC reconfiguration message in S408 is referred to as RRC reconfiguration message 1.

[0198] The RRC reconfiguration message 1 may include configuration information. For example, the configuration information is referred to as configuration information 1. The configuration information 1 includes, for example, configuration information of the Uu interface and configuration information of the sidelink. The sidelink is a link between the remote UE and the relay UE. The relay UE provides a relay service for the remote UE through the sidelink. If the relay UE can provide a relay service for the remote UE, the network device may send the configuration information 1 to the relay UE. After receiving the RRC reconfiguration message 1, the relay UE may perform configuration, for example, configure the Uu link and the sidelink, based on the configuration information 1.

[0199] In this embodiment of the present application, the network device sends configuration information 1 after the relay UE determines that relay service can be provided, but the configuration of the relay UE may still fail. For example, the relay UE enters an area with a weak signal, or the relay UE still does not support some of the parameters included in configuration information 1, and some of the parameters are not included in the first message. In this case, if the configuration of the relay UE fails, the relay UE may send a second message to the network device. In this case, the second message may indicate that the configuration has failed.

[0200] S409: The network device sends an RRC reconfiguration message to the remote UE, and the remote UE receives the RRC reconfiguration message from the network device. To distinguish it from other RRC reconfiguration messages, the RRC reconfiguration message in S409 is referred to as RRC reconfiguration message 2.

[0201] The RRC reconfiguration message 2 may include information configured by the network device for the remote UE. For example, the information included in the RRC reconfiguration message 2 is referred to as configuration information 2, and the configuration information 2 may include configuration information of the Uu interface and configuration information of the sidelink. If the relay UE can provide relay service for the remote UE, the network device may send the configuration information 2 to the remote UE. After receiving the RRC reconfiguration message 2, the remote UE may perform configuration, for example, configure the Uu link and the sidelink, based on the configuration information 2.

[0202] After the configuration of the remote UE and the relay UE is completed, the relay UE can provide a relay service for the remote UE, so that the remote UE can communicate with a network device through the relay UE.

[0203] S410: The relay UE does not initiate the RRC re-establishment process.

[0204] If the second message indicates that the configuration of the relay UE has failed or that the relay UE refuses to provide relay service, S410 may be executed. In this case, the network device knows that the relay UE does not provide relay service, so the relay UE does not need to initiate an RRC re-establishment process and continues to perform normal communication with the network device, so as to improve the service quality of the relay UE and reduce resources consumed in the RRC re-establishment procedure.

[0205] For further details of S410, please refer to S308 in the embodiment shown in FIG.

[0206] In this embodiment of the present application, the network device may inquire whether the relay UE can provide a relay service by using a first message. For example, the first message is a message for specifically inquiring whether the terminal device can provide a relay service, and the second message is not an RRC reconfiguration complete message. In this case, in this embodiment of the present application, it is equivalent to not using a message in the RRC re-establishment process and not changing the existing RRC re-establishment procedure. In this way, the technical solution in this embodiment of the present application can be better compatible with existing technologies.

[0207] Next, a problem is considered. From the above procedure, it can be known that the remote UE needs to measure other UEs to realize path switching. If the reporting condition for the measurement report is met, the remote UE can transmit the measurement result to the network device. Regardless of whether the remote UE transmits the measurement result to the network device, the measurement process may be performed continuously, which consumes a high battery power of the remote UE. In addition, the remote UE usually performs measurements based on a discovery message. In this case, the other UE (e.g., a relay UE) needs to send a discovery message, so that the remote UE performs measurements based on the discovery message. However, it is possible that one UE does not continuously send discovery messages. Therefore, the remote UE needs to first send a discovery message to the other UE, which requests a corresponding service (e.g., a relay service). After receiving the discovery message, the other UE sends a discovery message to the remote UE if the service can be provided. In this case, the remote UE can perform measurements based on the received discovery message. It may be noted that in order to stimulate the relay UE to send a discovery message to the remote UE, the remote UE may need to send the discovery message multiple times and receive the discovery message multiple times, which also requires consuming a large amount of resources.

[0208] To solve this problem, an embodiment of this application provides a third communication method. According to this method, measurement resources can be saved and battery power of a remote UE can be saved. Figure 5 is a flowchart of the method. The method may relate to a process of switching from a direct link to an indirect link, a process of switching between direct links, a process of switching from an indirect link to a direct link, or a process of switching between indirect links. In the process described below, an example is used in which the method is applied to the network architecture shown in any one of Figures 1A to 1D.

[0209] If the technical solution provided in this embodiment of this application is applied to the network architecture shown in any one of Figures 1A to 1D, the second terminal device in the following description may be the remote terminal device shown in any one of Figures 1A to 1D. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1A, the first terminal device in the following description may be the relay terminal device in Figure 1A, and the network device in the following description may be the access network device in Figure 1A. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1B, the first terminal device in the following description may be the relay terminal device 1 or the relay terminal device 2 in Figure 1B, and the network device in the following description may be the access network device in Figure 1B. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1C, the first terminal device in the following description may be the relay terminal device in Figure 1C, and the network device in the following description may be the access network device 1 or the access network device 2 in Figure 1C. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in FIG. 1D, the first terminal device in the following description may be the relay terminal device 1 in FIG. 1D, and the network device in the following description may be the access network device 1 in FIG. 1D, or the first terminal in the following description may be the relay terminal device 2 in FIG. 1D, and the network device in the following description may be the access network device 2 in FIG. 1D.

[0210] In addition, in the following description, an example is used in which the second terminal device is a remote UE and the first terminal device is a relay UE. The relay terminal device 1 and the relay terminal device 2 in FIG. 5 simply indicate that there may be multiple UEs that can serve as relay UEs, and the remote UE may measure multiple UEs when performing measurements.

[0211] S501: A remote UE performs data transmission with a network device.

[0212] S502: The network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

[0213] Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included in, for example, a system message or another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

[0214] S503: The remote UE measures or selects other UEs. For example, the remote UE may send a discovery message to trigger other UEs to send discovery messages, so that the remote UE can measure the discovery messages from other UEs to complete the measurement or selection of the other UEs. In FIG. 5, an example in which the remote UE measures other UEs is used.

[0215] The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, such as measuring data signals from the other UEs, which is not limited here. The remote UE may select other UEs based on the measurement results.

[0216] S504: The remote UE sends the first result to the network device. Thus, the network device receives the first result from the remote UE. The first result is, for example, a measurement result or a selection result. In FIG. 5, an example in which the first result is the measurement result is used.

[0217] The measurement result may include, for example, a report of measuring at least one UE by the remote UE. The selection result may include, for example, a result of selecting a relay UE by the remote UE, and may include, for example, an ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may also be included.

[0218] In this embodiment of this application, after the remote UE sends the measurement result, when the first condition is not met, the remote UE does not perform the first operation, and the first operation can be considered to be an operation related to the measurement process.

[0219] The first operation may include one or more of the following: sending a discovery message, measuring other UEs, or sending the new first result to the network device (in other words, sending the first result to the network device). For example, the first operation includes sending a discovery message, the first operation includes measuring other UEs, and the first operation includes sending the new first result to the network device, or the first operation includes sending a discovery message and measuring other UEs.

[0220] For example, if the first operation includes transmitting a discovery message, does not include measuring other UEs, and does not include transmitting a new first result to the network device, the remote UE may not transmit the discovery message if the first condition is not met (e.g., if the remote UE has previously transmitted a discovery message, the remote UE stops transmitting the discovery message if the first condition is not met). However, if the remote UE receives a discovery message from another UE, the remote UE may still perform measurement based on the received discovery message and measurement configuration information at S502 to obtain new measurement results. When a reporting condition for the measurement report is met, the remote UE may further transmit a new first result to the network device. Alternatively, if the first operation includes measuring other UEs, does not include transmitting a discovery message, and does not include transmitting a new first result to the network device, the remote UE may not measure the other UE if the first condition is not met. Because other UEs do not need to be measured, the remote UE may not need to send a discovery message, or the remote UE may send a discovery message but not need to perform measurements even if the remote UE receives a discovery message from the other UE. In addition, because other UEs do not need to be measured and therefore do not need to send a new first result to the network device, the remote UE does not obtain a measurement report. Alternatively, if the first operation includes sending new measurement results to the network device but does not include sending a discovery message and does not include measuring other UEs, the remote UE may or may not send a discovery message if the first condition is not met.In addition, if the remote UE receives a discovery message from another UE, the remote UE may still perform measurements based on the received discovery message, but a measurement report may not be formed after the remote UE performs the measurements. That is, the measurements may be performed, but the measurement report may not be obtained. Alternatively, if the remote UE performs measurements, the remote UE may instead obtain a measurement report. However, even if the reporting condition for the measurement report is met, the remote UE does not send the measurement report to the network device.

[0221] In this embodiment of the application, the first condition is related to a timer, see the description below.

[0222] S505: The remote UE starts a timer.

[0223] For example, when S504 is completed, i.e., when transmitting the measurement result to the network device is completed, the remote UE may start a timer. The first condition being satisfied means, for example, that the timer has expired, and the first condition not being satisfied means, for example, that the timer has not expired.

[0224] S506: When the timer has not expired, the remote UE does not perform the first action.

[0225] In other words, in this embodiment of the present application, if the timer has not expired, the remote UE does not need to perform the first operation. Because the remote UE has sent the measurement result to the network device, and the network device can determine whether the remote UE can perform a path switch based on the measurement result, the decision of the network device is not significantly affected even if the remote UE does not perform measurements and does not send new measurement results to the network device. In addition, this method can reduce the measurement process of the remote UE, reduce resources consumed in the measurement process, and save battery power of the remote UE.

[0226] S507: When the timer expires, the remote UE may perform a first action.

[0227] If the timer expires and the remote UE does not receive configuration information (for configuring the remote UE to perform a path switch) from the network device, the remote UE may continue to perform the first operation to send new measurement results to the network device again. Of course, here it is simply described that if the timer expires and the remote UE does not receive configuration information (for configuring the remote UE to perform a path switch) from the network device, the remote UE may perform the first operation. However, whether to perform the first operation depends on the implementation of the remote UE. Here, it is simply described a possibility and does not constitute a limitation on the behavior of the remote UE. For example, if the timer expires, the remote UE may measure other UEs. When the reporting condition for the measurement report is met, the remote UE sends new measurement results to the network device. If the network device determines, based on the new measurement results, that the remote UE can perform a path switch, the network device may send configuration information separately to the remote UE and the relay UE (in the case of switching to an indirect link).

[0228] In this embodiment of the present application, after transmitting the measurement result to the network device, the remote UE may start a timer. When the timer has not expired, the remote UE may not need to perform measurement-related operations, so as to reduce the measurement process of the remote UE and save resources required in the measurement process. In addition, since the remote UE reduces related operations, the battery power of the remote UE may also be saved.

[0229] An embodiment of this application provides a fourth communication method. Figure 6 is a flowchart of the method. The method may relate to a process of switching from a direct link to an indirect link, a process of switching between direct links, a process of switching from an indirect link to a direct link, or a process of switching between indirect links. In the process described below, an example is used in which the method is applied to the network architecture shown in any one of Figures 1A to 1D. For the contents of the devices in Figures 1A to 1D that are the relay UE, remote UE, and network device in this embodiment of this application, please refer to the description of the third communication method.

[0230] In addition, in the following description, an example is used in which the second terminal device is a remote UE and the first terminal device is a relay UE. The relay terminal device 1 and the relay terminal device 2 in FIG. 6 simply indicate that there may be multiple UEs that can serve as relay UEs, and the remote UE may measure multiple UEs when performing measurements. In the following description, the relay UE that serves as the first terminal device is, for example, the relay terminal device 1.

[0231] S601: A remote UE performs data transmission with a network device.

[0232] S602: The network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

[0233] Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included in, for example, a system message or another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

[0234] S603: The remote UE measures or selects another UE. For example, the remote UE may send a discovery message to trigger the other UE to send a discovery message, and the remote UE may measure the discovery message from the other UE to complete the measurement or selection of the other UE. In FIG. 6, an example in which the remote UE measures the other UE is used.

[0235] The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, such as measuring data signals from the other UEs. This is not limited here. The remote UE may select other UEs based on the measurement results.

[0236] S604: The remote UE sends the first result to the network device. Thus, the network device receives the first result from the remote UE. The first result is, for example, a measurement result or a selection result. In FIG. 6, an example in which the first result is the measurement result is used.

[0237] The measurement result may include, for example, a report of measuring at least one UE by the remote UE. The selection result may include, for example, a result of selecting a relay UE by the remote UE, and may include, for example, an ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may also be included.

[0238] In this embodiment of the present application, after the remote UE sends the first result, if the first condition is not met, the remote UE does not perform the first operation, and the first operation can be considered to be an operation related to the measurement process. For a description of the first operation, please refer to the embodiment shown in FIG. 3.

[0239] In this embodiment of the application, the first condition relates to messages from network devices, see the description below.

[0240] S605: The network device determines whether the remote UE should perform path switch based on the measurement result or the selection result. If the network device determines that the remote UE should perform path switch, S606 and S607 are executed, or S608 and S609 are executed. If the network device determines that the remote UE should not perform path switch, the subsequent steps may not be executed, or S610 may be executed.

[0241] S606: The network device sends a first message to the relay UE, so that the relay UE receives the first message from the network device.

[0242] For further details of S606, please refer to S306 in the embodiment shown in FIG.

[0243] S607: The relay UE sends the second message to the network device, so that the network device receives the second message from the relay UE.

[0244] The second message may indicate that the configuration of the relay UE has been completed, or may indicate that the configuration of the relay UE has failed. Alternatively, the second message may indicate that the relay UE is able to provide the relay service, or may indicate that the relay UE refuses to provide the relay service. For example, in this embodiment of the present application, the second message indicates that the configuration of the relay UE has failed, or indicates that the relay UE refuses to provide the relay service.

[0245] For further details of S607, please refer to S307 in the embodiment shown in FIG.

[0246] S608: The network device sends a first message to the relay UE, so that the relay UE receives the first message from the network device. The first message may be for inquiring whether the relay UE can provide a relay service.

[0247] For further details of S608, please refer to S406 in the embodiment shown in FIG.

[0248] S609: The relay UE sends the second message to the network device, so that the network device receives the second message from the relay UE.

[0249] The second message may indicate that the configuration of the relay UE has been completed, or may indicate that the configuration of the relay UE has failed. Alternatively, the second message may indicate that the relay UE is able to provide the relay service, or may indicate that the relay UE refuses to provide the relay service. For example, in this embodiment of the present application, the second message indicates that the configuration of the relay UE has failed, or indicates that the relay UE refuses to provide the relay service.

[0250] For further details of S609, please refer to S407 in the embodiment shown in FIG.

[0251] Processes S606 and S607 are parallel to processes S608 and S609, and only one of the processes needs to be executed.

[0252] S610: The network device sends a third message to the remote UE. Accordingly, the remote UE receives the third message from the network device. The third message may indicate that the relay UE refuses to provide the relay service, or may indicate that the relay UE reselects a UE that can provide the relay service. The third message may be, for example, an RRC message, or another message.

[0253] S611: The remote UE performs a first operation.

[0254] In this embodiment of the present application, if the remote UE receives the third message from the network device, the first condition is deemed to be met and the first operation may be performed. If the remote UE does not receive the third message from the network device, the first condition is deemed not to be met. When the first condition is not met, the remote UE does not need to perform the first operation to reduce the measurement process of the remote UE and save resources required in the measurement process. In addition, since the remote UE reduces measurement-related operations, the battery power of the remote UE may also be saved. However, when the first condition is met, the remote UE knows that a UE capable of providing relay service needs to be reselected. In this case, the remote UE may trigger a measurement process to select another relay UE.

[0255] In an optional implementation, after S604 is executed or before S604 is executed, the remote UE may further send a fourth message to the network device. The fourth message may indicate an energy saving requirement. This may be understood as the fourth message indicating that the remote UE has an energy saving requirement. In this case, after receiving the fourth message, the network device may determine that the remote UE has an energy saving requirement. In this case, optionally, the network device may further send first information to the remote UE. Thus, the remote UE receives the first information from the network device. The first information may be included in the third message or may be transmitted using another message. The first information may include information about M UEs. The information about the UEs may be, for example, UE identifiers, where M is a positive integer. The M UEs are UEs that do not need to be measured or UEs that refuse to provide relay service. If the remote UE receives the first information, the remote UE does not need to measure the M UEs. This reduces the measurement process of the remote UE and reduces the power consumption of the remote UE, so as to meet the energy saving requirements of the remote UE.

[0256] Optionally, the fourth message may further include information about N UEs. The information about the UEs may be, for example, UE identifiers, where N is a positive integer. The N UEs may be, for example, UEs that refuse to provide relay service. For example, if the remote UE determines, based on historical information, that N UEs have refused to provide relay service for the remote UE, the remote UE may add information about the N UEs to a blacklist and send the blacklist to the network device. In this way, when configuring the remote UE to perform measurements, the network device may consider not configuring the remote UE to measure N UEs to reduce invalid measurement processes of the remote UE. If the fourth message includes information about N UEs and the network device sends the first information, M UEs may be determined by the network device based on N UEs and some other factors. For example, M UEs is N UEs. In this case, M=N. Alternatively, M UEs and N UEs are disjoint. Alternatively, the M UEs and the N UEs have some intersection but are not exactly the same.

[0257] In this embodiment of the present application, if the remote UE does not receive a third message from the network device after the remote UE transmits the measurement result to the network device, the remote UE may not need to perform measurement-related operations, so as to reduce the measurement process of the remote UE and save the resources required in the measurement process. In addition, since the remote UE reduces related operations, the battery power of the remote UE may also be saved.

[0258] Next, another problem is considered. Currently, the remote UE can either succeed or fail in a path switch. However, when the remote UE fails in a path switch, the remote UE cannot make a decision. Specifically, the remote UE cannot determine when the path switch has failed. A possible consequence is that the remote UE cannot continue to operate.

[0259] Therefore, an embodiment of this application provides a fifth communication method. According to this method, the remote UE can determine when the path switch has failed, so that the operation of the remote UE can continue. Figure 7 is a flowchart of the method. The method may relate to a process of switching from an indirect link to a direct link. In the process described below, an example is used in which the method is applied to the network architecture shown in Figure 1A or Figure 1C.

[0260] If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1A, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs the path switch are the same network device. In this case, the first terminal device in the following description may be the relay terminal device in Figure 1A, the second terminal device in the following description may be the remote terminal device in Figure 1A, the network device in the following description may be the access network device in Figure 1A, and the network device is both the source network device and the target network device. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1C, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs the path switch are different network devices. In this case, the first terminal device in the following description may be the relay terminal device in Figure 1C, the second terminal device in the following description may be the remote terminal device in Figure 1C, and the network device in the following description (which is also called the first network device, and the first network device is the source network device) may be the access network device 1 in Figure 1C. In addition, the following further relates to the target network device, which may be called the second network device, and may be the access network device 2 in Figure 1C.

[0261] In addition, the following description uses an example in which the second terminal device is a remote UE and the first terminal device is a relay UE. In addition, this embodiment of the present application uses an example in which the source network device and the target network device are different network devices.

[0262] S701: A remote UE performs data transmission with a source network device.

[0263] S702: The source network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the source network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure a reference signal from the source network device.

[0264] S703: The remote UE measures a reference signal from the network device.

[0265] For example, the remote UE may receive a synchronization signal block (SSB) or a channel state information reference signal (CSI-RS) from the source network device, and the remote UE may measure the strength of the received signal to complete measurements for the source network device. In addition, the remote UE may further measure a target network device. For example, the remote UE receives an SSB or a CSI-RS from the target network device. The remote UE may measure the strength of the received signal to complete measurements for the target network device.

[0266] S704: The remote UE sends the measurement result to the source network device. Thus, the source network device receives the measurement result from the remote UE. The measurement result includes, for example, a measurement report obtained by measuring at least one frequency or cell.

[0267] The communication between the remote UE and the source network device in S701 to S704 is performed through forwarding via the relay UE.

[0268] S705: The source network device makes a handover decision. The source network device determines whether the remote UE can perform a path switch based on the measurement result. In this embodiment of the present application, the source network device determines whether the remote UE can be handed over from the relay UE to the target network device based on the measurement result. If the source network device determines that the remote UE can be handed over from the relay UE to the target network device, S706 is executed.

[0269] S706: The source network device sends a handover request message to the target network device. Accordingly, the target network device receives the handover request message from the source network device. The handover request message may indicate that the remote UE should be handed over to the target network device.

[0270] S707: The target network device sends a handover request acknowledgement message to the source network device. Accordingly, the source network device receives the handover request acknowledgement message from the target network device. The handover request acknowledgement message may indicate that the remote UE is allowed to be handed over to the target network device, or may indicate that the remote UE is not allowed to be handed over to the target network device.

[0271] If the handover request acknowledge message indicates that the remote UE is allowed to be handed over to the target network device, proceed to S708; otherwise, the subsequent steps are not executed.

[0272] If the target network device and the source network device are the same network device, after S705, S706 and S707 do not need to be executed, and proceed to S708.

[0273] S708: The source network device sends an RRC reconfiguration message to the remote UE, so that the remote UE receives the RRC reconfiguration message from the source network device.

[0274] The RRC reconfiguration message may include configuration information. The configuration information may be for configuring the remote UE to be handed over to the target network device. For example, the configuration information may include configuration information for the Uu interface. The configuration information for the Uu interface may include an identifier of the target network device, a user ID (e.g., C-RNTI) used by the relay UE during access, and a timer configured to determine whether the access is successful, such as the duration of T304. Optionally, a random access resource configuration and a contention-free preamble configuration for the relay UE to access the network device may be further included.

[0275] S709: The remote UE performs a path switch based on the configuration information. For example, the remote UE performs configuration based on the configuration information, and the remote UE initiates random access to the target network device. If the remote UE succeeds in the random access, the remote UE is successfully handed over to the target network device.

[0276] When the first condition is met and the remote UE successfully accesses the target network device, the remote UE may determine that the path switch is successful. If the first condition is not met and the remote UE fails to access the target network device, the remote UE determines that the path switch is unsuccessful.

[0277] In this embodiment of the application, the first condition may relate to a timer, see the description below.

[0278] S710: The remote UE starts a timer.

[0279] For example, the remote UE may start a timer after S708 is executed, or in other words, after the remote UE receives configuration information from the source network device. The timer may be T304 or another newly introduced timer, which is not limited here.

[0280] S711: The remote UE initiates random access to the target network device.

[0281] If the remote UE successfully accesses the target network device before the timer expires, the remote UE determines that the path switch is successful. If the remote UE has not successfully accessed the target network device when the timer expires, the remote UE determines that the path switch has failed. In this embodiment of the present application, whether the path switch is successful is determined by using a timer. This method is simple and easy to implement. The timing duration of the timer can be determined by the remote UE. For example, the remote UE can determine the time for accessing the network device based on historical information and set that time as the timing duration of the timer. Alternatively, the timing duration of the timer can be configured by the network device and notified to the remote UE in S708. Alternatively, the timing duration of the timer can be specified in a protocol. If the random access is successful, the timer can be stopped to avoid timer expiration.

[0282] If the remote UE successfully accesses the target network device before the timer expires, the remote UE may perform normal communication within the coverage of the target network device, and subsequent steps do not need to be performed. If the remote UE has not successfully accessed the target network device when the timer expires, the following steps may be performed.

[0283] S712: The remote UE sends failure information to the source network device through the first path. Thus, the source network device receives the failure information from the remote UE through the first path. The failure information may indicate that the path switch has failed. The failure information may be, for example, an RRC message. For example, the failure information may be a failure information message, a master cell group failure information (MCG failure information) message, an RRC reconfiguration complete message, or a UE information response message, or may be another newly added RRC message. This is not limited here.

[0284] The first path is a communication path between the remote UE and the source network device before the remote UE performs a path switch. Since this embodiment of this application is used as an example of a scenario in which the remote UE switches from an indirect link to a direct link, the first path is a communication path in which the remote UE is connected to the source network device via the relay UE. In other words, the first path is remote UE-relay UE-source network device.

[0285] If the remote UE has not disconnected from the source network device through the first path before successfully performing the path switch, the remote UE may perform S712. After the source network device receives the failure information, the remote UE may continue to communicate with the source network device through the first path. That is, because the remote UE has not disconnected the original communication path, the remote UE may continue to perform communication through the original communication path and does not need to reselect a communication path. In other words, the remote UE does not initiate an RRC connection re-establishment process to improve the service continuity of the remote UE.

[0286] S713: The remote UE sends an RRC connection re-establishment request message to the source network device through a first path, so that the source network device receives the RRC connection re-establishment request message from the remote UE.

[0287] S712 and S713 are parallel steps, and only one of S712 and S713 needs to be executed. If the remote UE has not disconnected from the source network device through the first path before successfully executing the path switch, the remote UE may alternatively execute S713 to re-establish an RRC connection within the coverage of the source network device, thereby communicating with the source network device through the new connection.

[0288] S714: The remote UE performs cell reselection.

[0289] The remote UE may enter an RRC idle state and perform cell reselection in the RRC idle state, eg, the cell reselected by the remote UE is referred to as the first cell.

[0290] S715: The remote UE initiates an RRC connection reestablishment process in the first cell, or initiates an RRC connection establishment process in the first cell.

[0291] If the first cell stores the context of the remote UE, the remote UE may initiate an RRC connection re-establishment process in the first cell. If the first cell does not store the context of the remote UE, the remote UE may initiate an RRC connection establishment process in the first cell. For example, the remote UE may initiate an RRC connection re-establishment process in the first cell. If the first cell stores the context of the remote UE, the RRC connection re-establishment process of the remote UE has a high probability of success. If the first cell does not store the context of the remote UE and the context of the remote UE cannot be obtained through the interface of the network device, the RRC connection re-establishment process of the remote UE may fail. If the RRC connection re-establishment process of the remote UE fails, the remote UE restarts the RRC connection establishment process in the first cell. Alternatively, since the first cell does not store the context of the remote UE, the remote UE may directly initiate an RRC connection establishment process in the first cell to reduce the probability of RRC re-establishment failing.

[0292] The three solutions S712, S713, and S714, and S715 are parallel, and only one of the three solutions needs to be performed.

[0293] In this embodiment of the present application, the remote UE may determine whether the path switch is successful or unsuccessful based on a timer. The determination method is simple and easy to implement. The technical solution in this embodiment of the present application may also be applied to UEs with low capabilities. In addition, if the path switch fails, the remote UE may perform a corresponding operation, for example, continue communication within the coverage of the source network device, or enter a new cell through cell reselection, so as to resume the service of the remote UE as soon as possible and improve service continuity.

[0294] An embodiment of this application provides a sixth communication method. According to this method, the remote UE can also determine when the path switch has failed, so that the operation of the remote UE can continue. Figure 8 is a flowchart of the method. The method may relate to a process of switching between indirect links or a process of switching from a direct link to an indirect link. In the process described below, an example is used in which the method is applied to the network architecture shown in any one of Figures 1A to 1D.

[0295] If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1A, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs the path switch are the same network device. In this case, the first terminal device in the following description may be the relay terminal device in Figure 1A, the second terminal device in the following description may be the remote terminal device in Figure 1A, the network device in the following description may be the access network device in Figure 1A, and the network device is both the source network device and the target network device. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1B, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs the path switch are the same network device. In this case, the first terminal device in the following description may be the relay terminal device 1 or the relay terminal device 2 in Figure 1B, the second terminal device in the following description may be the remote terminal device in Figure 1B, the network device in the following description may be the access network device in Figure 1B, and the network device is both the source network device and the target network device. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1C, it indicates that the source network device before the remote UE performs path switch and the target network device after the remote UE performs path switch are different network devices.In this case, the first terminal device in the following description may be the relay terminal device in FIG. 1C, the second terminal device in the following description may be the remote terminal device in FIG. 1C, and the network device in the following description (which is also referred to as the first network device, and the first network device is the source network device) may be the access network device in FIG. 1C. In addition, the following also relates to a target network device, which may be referred to as the second network device and may be the access network device 2 in FIG. 1C. Alternatively, the source network device may be the access network device 2 in FIG. 1C, and the target network device may be the access network device 1 in FIG. 1C. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in FIG. 1D, it indicates that the source network device before the remote UE performs path switch and the target network device after the remote UE performs path switch are different network devices. In this case, the first terminal device in the following description may be the relay terminal device 1 in Figure 1D, the second terminal device in the following description may be the remote terminal device in Figure 1D, and the network device in the following description (which is also called the first network device, and the first network device is the source network device) may be the access network device 1 in Figure 1D. In addition, the following further relates to a target network device, which may be called the second network device and may be the access network device 2 in Figure 1D. Alternatively, the first terminal device may be the relay terminal device 2 in Figure 1D, the source network device may be the access network device 2 in Figure 1D, and the target network device may be the access network device 1 in Figure 1D.

[0296] In addition, the following description uses an example in which the second terminal device is a remote UE and the first terminal device is a relay UE. In addition, this embodiment of the present application uses an example in which the source network device and the target network device are different network devices.

[0297] S801: A remote UE performs data transmission with a source network device.

[0298] S802: The source network device sends an RRC message to the remote UE. Thus, the remote UE receives the RRC message from the source network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

[0299] Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included in, for example, a system message or another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

[0300] S803: The remote UE measures or selects another UE. For example, the remote UE may send a discovery message to trigger the other UE to send a discovery message, so that the remote UE may measure the discovery message from the other UE to complete the measurement or selection of the other UE. In FIG. 8, an example in which the remote UE measures the other UE is used.

[0301] The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, such as measuring data signals from the other UEs. This is not limited here. The remote UE may select other UEs based on the measurement results.

[0302] S804: The remote UE sends the first result to the network device. Thus, the network device receives the first result from the remote UE. The first result may be, for example, a measurement result or a selection result. In FIG. 8, an example in which the first result is the measurement result is used.

[0303] The measurement result may include, for example, a report of measuring at least one UE by the remote UE. The selection result may include, for example, a result of selecting a relay UE by the remote UE, and may include, for example, an ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may also be included.

[0304] If the application scenario of this embodiment of this application is to switch between indirect links, the communications between the remote UE and the network device in S801 to S804 are all performed through forwarding via the relay UE connected to the remote UE before the link switching, and the relay UE in the following description is the relay UE connected to the remote UE after the link switching.

[0305] S805: The source network device makes a handover decision. Based on the measurement result, the source network device determines whether the remote UE can perform a path switch. In this embodiment of the present application, based on the measurement result, the source network device determines whether the remote UE can be handed over from the relay UE to the target network device. If the source network device determines that the remote UE can be handed over from the relay UE to the target network device, S806 is executed.

[0306] S806: The source network device sends a handover request message to the target network device. Accordingly, the target network device receives the handover request message from the source network device. The handover request message may indicate that the remote UE should be handed over to the target network device. The target network device serves the relay UE. Because the remote UE will switch to performing communication via the relay UE, the source network device will request handover from the target network device serving the relay UE.

[0307] S807: The target network device sends an RRC reconfiguration message to the relay UE. Thus, the relay UE receives an RRC reconfiguration message from the target network device. For example, the RRC reconfiguration message is called RRC reconfiguration message 1.

[0308] The RRC reconfiguration message may, for example, include configuration information, and the RRC reconfiguration message may, for example, implement the function of the first message in the embodiment shown in Figure 3. Alternatively, the RRC reconfiguration message may, for example, be for inquiring whether the relay UE can provide a relay service, and the RRC reconfiguration message may, for example, implement the function of the first message in the embodiment shown in Figure 4.

[0309] S808: The relay UE sends a second message to the target network device. Thus, the target network device receives the second message from the relay UE. If the RRC reconfiguration message in S807 implements the function of the first message in the embodiment shown in FIG. 3, the second message in S808 may implement the function of the second message in the embodiment shown in FIG. 3. Alternatively, if the RRC reconfiguration message in S807 implements the function of the first message in the embodiment shown in FIG. 4, the second message in S808 may implement the function of the second message in the embodiment shown in FIG. 4. S808 may be an optional step. The transmission is not performed, the relay UE determines that the reconfiguration has failed, and the relay UE is triggered to enter an RRC connection re-establishment procedure.

[0310] In this embodiment of the present application, for example, the second message indicates that the configuration has failed or that the relay UE refuses to provide relay service. For further details, see S306 or S307 in the embodiment shown in Figure 3, or S406 or S407 in the embodiment shown in Figure 4.

[0311] S809: The target network device sends a handover request acknowledgement message to the source network device, so that the source network device receives the handover request acknowledgement message from the target network device.

[0312] The handover request acknowledge message may indicate that the remote UE is allowed to be handed over to the target network device, or may indicate that the remote UE is not allowed to be handed over to the target network device. In this embodiment of the application, the second message indicates that the configuration has failed or that the relay UE refuses to provide relay service, so the handover request acknowledge message may indicate that the remote UE is not allowed to be handed over to the target network device.

[0313] S807 follows S806, and S810 follows S809. However, the order of S807 and S809 is not limited. For example, the target network device may configure the relay UE and then perform S809, or may first perform S809 and then query the relay UE or configure the relay UE. If the target network device and the source network device are the same network device, S806 and S809 do not need to be performed.

[0314] S810: The source network device sends an RRC reconfiguration message to the remote UE. Thus, the remote UE receives the RRC reconfiguration message from the source network device. For example, the RRC reconfiguration message is called RRC reconfiguration message 2.

[0315] The RRC reconfiguration message may include configuration information, which may be for configuring the remote UE to switch to an indirect path and communicate with the target network device through the relay UE. For example, the configuration information may include configuration information for the Uu interface, which may include information about the Uu configuration of the relay UE, and the configuration information may further include a user ID (e.g., the ID is a cell radio network temporary identifier (C-RNTI)) for access of the relay UE, or may further include a random access resource configuration and a contention-free preamble configuration for the relay UE to access the network device. In another example, the configuration information may include configuration information for the remote UE, which may include a user ID (e.g., a C-RNTI) of the remote UE or may include configuration information of the PC5 of the remote UE. For example, the PC5 configuration information of the remote UE includes one or more of the following: configuration information of the PC5 radio link control (RLC), a logical channel ID (LCID) corresponding to the PC5 RLC entity, or a correlation between the LCID corresponding to the PC5 RLC entity and a data radio bearer (DRB) ID. In another example, the configuration information may include information related to a timer, which may be used by the remote UE to determine whether a path switch has failed. The timer may be, for example, timer T304 or another newly introduced timer, which is not limited here. The source network device may choose to configure different timers depending on whether the remote UE should perform a path switch or a general switch.For example, if the remote UE is to perform a path switch, a new timer may be configured for the remote UE. If the remote UE is to perform a general switch, timer T304 may be configured for the remote UE. Alternatively, the source network device may configure timer T304 for the remote UE by using a general RRC reconfiguration message without using an RRC reconfiguration with sync message. The source network device may add a new information element, for example, a fourth information element, to the RRC reconfiguration message to indicate that the remote UE needs to switch to an indirect path (i.e., a path for communicating with the network via a relay), and the fourth information element may include the configured timer. The ID of the remote UE may also be included in the fourth information element. This is not limited here. The related information of the timer included in the configuration information may include the timer duration, the timer duration and an offset duration, or the offset duration. The offset duration may be determined based on the status of the relay UE. For example, the offset duration may be set differently in three cases where the relay UE is in the RRC idle state, the RRC inactive state, and the RRC connected state. For example, when the relay UE is in the RRC connected state, the offset duration may be set to be short or even 0. If the remote UE performs a path switch to access the network via the relay UE in the RRC connected state, the relay UE in the RRC connected state does not need to perform a random access process for the Uu interface. If the remote UE performs a path switch to access the network via the relay UE in the RRC idle state or the RRC inactive state, the relay UE in the RRC idle state or the RRC inactive state does not need to perform a random access process for the Uu interface.Therefore, when the remote UE performs different path switches, the duration for establishing a connection between the remote UE and the network device may also be different. For example, the remote UE determines the duration of a timer configured to determine whether a path switch has failed as follows: The duration of the timer received by the remote UE is X. If the relay UE is in an RRC idle state, the offset duration is Y, where Y is greater than 0. If the relay UE is in an RRC connected state, the offset duration is 0. When the remote UE switches to access the network through the relay UE, if the relay UE is in an RRC idle state, the duration of the timer used by the remote UE to determine whether a path switch has failed is set to X+Y. If the relay UE is in an RRC connected state, the duration of the timer used by the remote UE to determine whether a path switch has failed is set to X+0. In other words, the offset duration may be determined based on the status of the relay UE, so as to effectively reduce the duration that the remote UE needs to wait when switching to the relay UE in the RRC connected state fails, thereby allowing the remote UE to enter the status recovery process as soon as possible.

[0316] S811: The remote UE performs a path switch based on the configuration information. For example, the remote UE performs configuration based on the configuration information, and the remote UE requests a connection to the relay UE. If the connection between the remote UE and the relay UE is successfully established, the remote UE successfully switches to communicating with the network through the relay UE. When a first condition is met and the connection between the remote UE and the relay UE is successfully established, the remote UE may determine that the path switch is successful. If the first condition is not met and the connection between the remote UE and the relay UE is unsuccessful, the remote UE determines that the path switch is unsuccessful.

[0317] In this embodiment of the application, the first condition may relate to a timer, see the description below.

[0318] S812: The remote UE starts a timer.

[0319] For example, after S810 is executed, or in other words, after the remote UE receives configuration information (for example, the configuration information is included in an RRC reconfiguration message that does not carry a synchronization reconfiguration information element, an RRC reconfiguration message that carries a fourth information element, or an RRC reconfiguration message that carries a synchronization reconfiguration information element) from the source network device, the remote UE may start a timer. The timer may be timer T304 or another newly introduced timer. This is not limited here. The timing duration and / or offset duration of the timer may be configured by using the RRC reconfiguration message in S810, by using a broadcast message, or by the relay UE. The remote UE may determine the timing duration of the timer based on the configured timing duration and / or offset duration of the timer. For example, the remote UE directly determines the timing duration of the timer based on the RRC reconfiguration message. In another example, the remote UE determines the timing duration of the timer based on a broadcast message. In another example, the remote UE determines the timing duration of the timer based on the timing duration configured by using the broadcast message and the offset duration configured by using the RRC reconfiguration message. For example, the timing duration of the timer is the sum of the timing duration configured by using the broadcast message and the offset duration configured by using the RRC reconfiguration message. In yet another example, the remote UE determines the timing duration of the timer based on the timing duration configured by using the RRC reconfiguration message or the broadcast message and the offset duration configured by using the PC5 RRC message received from the relay UE.For example, the timing duration of the timer is the sum of the timing duration configured by using an RRC reconfiguration message or a broadcast message and the offset duration configured by using a PC5 RRC message. Because the offset duration is set based on the status of the relay UE, this can better help the remote UE determine the required waiting time to determine whether the path switch has failed.

[0320] S813: The remote UE requests the relay UE to establish a connection. For example, the remote UE sends a connection establishment request to the relay UE. After the relay UE receives the connection establishment request, the relay UE replies to the remote UE with a connection establishment response message, and if the connection establishment response message indicates that the connection establishment is allowed, the connection establishment between the remote UE and the relay UE is successful. After the relay UE receives the connection establishment request, the relay UE replies to the remote UE with a connection establishment response message, and if the connection establishment response message indicates that the connection establishment is not allowed, or if the relay UE replies without a connection establishment response message, the connection establishment between the remote UE and the relay UE is unsuccessful.

[0321] The timer for the first condition, i.e., the timer started in S812, may be stopped when certain conditions are met. For example, the timer may be stopped when any one of the first stop condition, the second stop condition, the third stop condition, or the fourth stop condition is met. The following briefly describes these stop conditions.

[0322] For example, the first stop condition is as follows: A PC5 RRC connection between the remote UE and the relay UE is successfully established. In this case, the timer may be stopped. For example, if the remote UE receives a connection establishment response message returned by the relay UE, and the connection establishment response message indicates that the connection establishment is allowed, the remote UE may stop the timer.

[0323] If the connection between the remote UE and the relay UE is successfully established before the timer expires, the remote UE determines that the path switch is successful. If the connection between the remote UE and the relay UE is not established when the timer expires, the remote UE determines that the path switch has failed. In this embodiment of the application, whether the path switch is successful is determined by using a timer. This method is simple and easy to implement. The timing duration of the timer can be determined by the remote UE. Alternatively, see the description of S810 and S812. For example, the remote UE can determine the time to establish a connection to another UE based on historical information and set that time as the timing duration of the timer. Alternatively, the timing duration of the timer can be configured by the network device and notified to the remote UE. Alternatively, the timing duration of the timer can be specified in a protocol.

[0324] If the connection between the remote UE and the relay UE is successfully established before the timer expires, the remote UE may perform normal communication via the relay UE, and subsequent steps do not need to be performed. However, if the connection between the remote UE and the relay UE is not established when the timer expires, the subsequent steps may be performed.

[0325] For example, the second stop condition is as follows: The RRC layer of the remote UE sends an RRC reconfiguration complete message to a lower layer of the remote UE, and the RRC layer receives an acknowledgement feedback from the lower layer. The lower layer here is, for example, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, or a media access control (MAC) layer. If the timer of the remote UE expires, the remote UE determines that the path switch has failed. In this embodiment of the present application, whether the path switch is successful is determined by using a timer. This method is simple and easy to implement. The timer setting method is similar to that in the first stop condition. The details will not be described again here. If the timer of the remote UE expires, the remote UE can proceed to the subsequent step.

[0326] For example, the third stop condition is as follows: The remote UE receives an acknowledgement indication from the relay UE, and the acknowledgement indication is sent by the source network device, for example, via the relay UE. If the timer of the remote UE expires, the remote UE determines that the path switch has failed. In this embodiment of the present application, whether the path switch is successful is determined by using a timer. This method is simple and easy to implement. The timer setting method is similar to that in the first stop condition. The details will not be described again here. If the timer of the remote UE expires, the remote UE can proceed to the subsequent step.

[0327] For example, the fourth stop condition is as follows: the remote UE receives indication information from the relay UE, the indication information is carried, for example, by using a PC5 RRC message, and the indication information indicates to the remote UE to stop a timer or indicates that the relay UE has successfully accessed the network device.

[0328] The relay UE may determine when to send the indication information to the remote UE based on the status of the relay UE. For example, if the relay UE is in an RRC connected state, the relay UE may send the indication information to the remote UE when or after a connection to the remote UE is successfully established. If the relay UE is in an RRC idle state or an RRC inactive state, the relay UE may send indication information to the remote UE when random access is completed, or may send indication information to the remote UE when it determines that the RRC connection has been successfully established or resumed (e.g., after successfully receiving an RRC setup message, an RRC establishment, or an RRC resume message), or may send indication information to the remote UE when it determines that the RRC connection has been successfully established or resumed (e.g., after the relay UE stops timer T300 or timer T319). If the timer of the remote UE expires, the remote UE determines that the path switch has failed. In this embodiment of the present application, whether the path switch is successful is determined by using a timer. This scheme is simple and easy to implement. The timer setting method is similar to that in the first stop condition, and the details will not be described again here. If the timer of the remote UE expires, it can proceed to the next step.

[0329] S814: The remote UE sends failure information to the source network device through the first path. Thus, the source network device receives the failure information from the remote UE through the first path. The failure information may indicate that the path switch has failed.

[0330] The first path is a communication path between the remote UE and the source network device before the remote UE performs a path switch. If this embodiment of this application is applied to a scenario in which the remote UE switches between indirect links, the first path is a communication path in which the remote UE is connected to the source network device via a relay UE. That is, the first path is remote UE-relay UE-source network device. In this case, the relay UE is a relay UE connected to the remote UE before the remote UE performs a path switch. However, if this embodiment of this application is applied to a scenario in which the remote UE switches from a direct link to an indirect link, the first path is a communication path in which the remote UE is directly connected to the source network device. That is, the first path is remote UE-source network device.

[0331] For further details of S814, please refer to S712 in the embodiment shown in FIG.

[0332] S815: The remote UE sends an RRC connection re-establishment request message to the source network device through the first path. Thus, the source network device receives the RRC connection re-establishment request message from the remote UE. Alternatively, after performing relay reselection, the remote UE may select another relay UE and initiate RRC connection re-establishment by using the other relay UE.

[0333] S814 and S815 are parallel steps, and only one of S814 and S815 needs to be executed. If the remote UE has not disconnected from the source network device through the first path before successfully executing the path switch, the remote UE may alternatively execute S815 to re-establish an RRC connection within the coverage of the source network device, thereby communicating with the source network device through the new connection.

[0334] S816: The remote UE performs cell reselection.

[0335] The remote UE may enter an RRC idle state and perform cell reselection in the RRC idle state, eg, the cell reselected by the remote UE is referred to as the first cell.

[0336] S817: The remote UE initiates an RRC connection reestablishment process in the first cell, or initiates an RRC connection establishment process in the first cell.

[0337] The three solutions S814, S815, and S816 and S817 are parallel, and only one of the three solutions needs to be performed.

[0338] For further details of S817, please refer to S715 in the embodiment shown in FIG.

[0339] In this embodiment of the present application, the remote UE may determine whether the path switch is successful or unsuccessful based on a timer. The determination method is simple and easy to implement. The technical solution in this embodiment of the present application may also be applied to UEs with low capabilities. In addition, if the path switch fails, the remote UE may perform a corresponding operation, for example, continue communication within the coverage of the source network device, or enter a new cell through cell reselection, so as to resume the service of the remote UE as soon as possible and improve service continuity.

[0340] An embodiment of this application provides a seventh communication method. According to this method, the remote UE can also determine when the path switch has failed, so that the operation of the remote UE can continue. FIG. 9 is a flowchart of the method. The method may relate to a process of switching between indirect links or a process of switching from a direct link to an indirect link. In the process described below, an example is used in which the method is applied to the network architecture shown in any one of FIGS. 1A to 1D. For the devices in FIGS. 1A to 1D that are the relay UE, remote UE, and network device in this embodiment of this application, please refer to the description of the sixth communication method. The relay terminal device 1 and relay terminal device 2 in FIG. 9 simply indicate that there may be multiple UEs that can serve as relay UEs, and the remote UE may measure multiple UEs when performing measurements.

[0341] In this embodiment of this application, an example is used in which the source network device and the target network device are the same network device. In addition, the following description uses an example in which the second terminal device is a remote UE and the first terminal device is a relay UE.

[0342] S901: A remote UE performs data transmission with a network device.

[0343] S902: The network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

[0344] Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included in, for example, a system message or another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

[0345] S903: The remote UE measures or selects another UE. For example, the remote UE may send a discovery message to trigger the other UE to send a discovery message, so that the remote UE may measure the discovery message from the other UE to complete the measurement or selection of the other UE. In FIG. 9, an example in which the remote UE measures the other UE is used.

[0346] The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, such as measuring data signals from the other UEs. This is not limited here. The remote UE may select other UEs based on the measurement results.

[0347] S904: The remote UE sends the first result to the network device. Thus, the network device receives the first result from the remote UE. The first result is, for example, a measurement result or a selection result. In FIG. 9, an example in which the first result is the measurement result is used.

[0348] The measurement result is, for example, a measurement report obtained by the remote UE by measuring at least one UE. The selection result is, for example, a result of the remote UE selecting a relay UE, and includes, for example, an ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may be further included.

[0349] If the application scenario of this embodiment of this application is to switch between indirect links, the communications between the remote UE and the network device in S901 to S904 are all performed through forwarding via the relay UE connected to the remote UE before the link switching, i.e., the relay terminal device 2 in Figure 9, and the relay UE in the following description is the relay UE connected to the remote UE after the link switching, i.e., the relay terminal device 1 in Figure 9.

[0350] S905: The network device determines whether the remote UE should perform path switch based on the measurement result or the selection result. If the network device determines that the remote UE should perform path switch, the subsequent steps are executed; otherwise, the subsequent steps are not executed.

[0351] S906: The network device sends a first message to the relay UE, so that the relay UE receives the first message from the network device.

[0352] For further details of S906, please refer to S306 in the embodiment shown in FIG.

[0353] S907: The relay UE sends a second message to the network device, so that the network device receives the second message from the relay UE.

[0354] The second message may indicate that the configuration of the relay UE has been completed, or may indicate that the configuration of the relay UE has failed. Alternatively, the second message may indicate that the relay UE is able to provide the relay service, or may indicate that the relay UE refuses to provide the relay service. For example, in this embodiment of the present application, the second message indicates that the configuration of the relay UE has failed, or indicates that the relay UE refuses to provide the relay service.

[0355] For further details of S907, please refer to S307 in the embodiment shown in FIG.

[0356] S908: The network device sends a first message to the relay UE, so that the relay UE receives the first message from the network device. The first message may be for inquiring whether the relay UE can provide a relay service.

[0357] For further details of S908, please refer to S406 in the embodiment shown in FIG.

[0358] S909: The relay UE sends a second message to the network device, so that the network device receives the second message from the relay UE.

[0359] The second message may indicate that the configuration of the relay UE has been completed, or may indicate that the configuration of the relay UE has failed. Alternatively, the second message may indicate that the relay UE is able to provide the relay service, or may indicate that the relay UE refuses to provide the relay service. For example, in this embodiment of the present application, the second message indicates that the configuration of the relay UE has failed, or indicates that the relay UE refuses to provide the relay service.

[0360] For further details of S909, please refer to S407 in the embodiment shown in FIG.

[0361] Processes S906 and S907 are parallel to processes S908 and S909, and only one of the processes needs to be executed.

[0362] Alternatively, steps S906 to S909 may not be performed. Instead, the network device normally sends an RRC reconfiguration message to the relay UE in an existing manner, where the RRC reconfiguration message includes configuration information. After receiving the RRC reconfiguration message, the relay UE may perform the configuration. If the configuration is successful, the relay UE may send an RRC reconfiguration complete message to the network device. If the configuration fails or the relay UE refuses to provide relay service, the relay UE may enter an RRC reestablishment process.

[0363] S910: The network device sends an RRC reconfiguration message to the remote UE, so that the remote UE receives the RRC reconfiguration message from the network device.

[0364] The RRC reconfiguration message may include configuration information for configuring the remote UE to switch to communicating with the target network device through the relay UE. For example, the configuration information may include configuration information for the Uu interface.

[0365] S911: The remote UE performs a path switch based on the configuration information. For example, the remote UE performs configuration based on the configuration information, and the remote UE requests a connection to the relay UE. If the connection between the remote UE and the relay UE is successfully established, the remote UE successfully switches to communication with the network via the relay UE.

[0366] When the first condition is met, the remote UE may determine that the path switch is successful. If the first condition is not met, the remote UE may determine that the path switch is unsuccessful.

[0367] In this embodiment of the present application, the first condition not being met may be the failure to establish a direct communication connection, for example, including condition 1, condition 2, or condition 3.

[0368] Condition 1: A feedback is received from the relay UE when the number of times a connection establishment request message is sent to the relay UE is less than or equal to M, where M is the maximum number of retransmissions. The prerequisite for using condition 1 is that if the relay UE does not accept the establishment of a connection to the remote UE, the relay UE does not reply to the remote UE with a connection establishment response message.

[0369] The remote UE may send a connection establishment request message to the relay UE by using a retransmission mechanism. That is, if the connection establishment request message is unsuccessful the first time it is sent, the connection establishment request message may be retransmitted again. However, the number of retransmissions is limited, where M is the maximum number of retransmissions. If the remote UE still does not receive feedback from the relay UE after sending the connection establishment request message to the relay UE M times, this indicates that the connection establishment has failed. Therefore, if the number of times the connection establishment request message is sent to the relay UE is M or less and feedback is received from the relay UE, this indicates that the connection establishment has been successful. If the number of times the connection establishment request message is sent to the relay UE is M or more and feedback is still not received from the relay UE, this indicates that the connection establishment has failed. If the connection establishment has failed, the remote UE cannot communicate through the relay UE, and the path switch has failed. Therefore, Condition 1 may be for determining whether the path switch is successful.

[0370] Condition 2: Security verification for the relay UE is successful.

[0371] After the remote UE sends a connection establishment request message to the relay UE, if the relay UE agrees to establish a connection, the relay UE sends security-related parameters to the remote UE, and the remote UE needs to perform configuration based on the security-related parameters. However, the configuration of the remote UE may fail. For example, if some parameters (e.g., integrity protection algorithm) sent by the relay UE cannot be supported by the remote UE, the configuration of the remote UE may fail. If the remote UE fails to perform configuration based on the security parameters, security verification for the relay UE is deemed to have failed. If the remote UE successfully performs configuration based on the security parameters, security verification for the relay UE is deemed to have succeeded. If the security verification for the relay UE is successful, the remote UE may perform communication via the relay UE, and path switch is successful. If the security verification for the relay UE fails, the remote UE cannot perform communication via the relay UE, and path switch is failed. Therefore, condition 2 may be to determine whether the path switch is successful.

[0372] Condition 3: A connection establishment request message is sent to a relay UE, a connection establishment response message is received from the relay UE, and the connection establishment response message may indicate that the connection establishment is accepted (or permitted). The prerequisite for using condition 3 is that the relay UE replies to the remote UE with a connection establishment response message, regardless of whether the relay UE accepts the establishment of a connection to the remote UE.

[0373] The remote UE sends a connection establishment request message to the relay UE. The relay UE replies with a connection establishment response message. If the connection establishment response message indicates that the connection establishment is accepted, the remote UE may perform communication via the relay UE, and the path switch is successful. However, if the connection establishment response message indicates that the connection establishment is not accepted, the remote UE cannot perform communication via the relay UE, and the path switch is unsuccessful. Therefore, condition 3 can also be used to determine whether the path switch is successful.

[0374] Which of the three conditions above is used by the remote UE to determine whether the path switch is successful may be determined by the remote UE, configured by a network device, or specified in a protocol. By using the above conditions, the remote UE can flexibly and quickly determine whether the path switch is successful. If the path switch fails, compared to a solution in which whether the path switch is successful is determined by using a timer, this solution can enable the remote UE to quickly enter a link resumption step to reduce or avoid communication interruptions and improve service continuity.

[0375] Alternatively, in this embodiment of the present application, the remote UE may not use the aforementioned conditions, but may determine whether the path switch is successful by using a timer. For the manner of performing the determination by using a timer, please refer to the description of the embodiment shown in Figure 8.

[0376] In addition, optionally, in the embodiment shown in Figure 8, the remote UE may alternatively not use a timer to determine whether the path switch is successful, but may use one of the three conditions mentioned above to determine whether the path switch is successful. For the determination manner, please refer to the description in this embodiment of this application.

[0377] If the remote UE determines that the path switch has failed, the remote UE may perform normal communication via the relay UE, and the subsequent steps do not need to be performed. If the remote UE determines that the path switch has failed, the remote UE may proceed to the following steps.

[0378] S912: The remote UE sends failure information to the network device through the first path. Thus, the network device receives the failure information from the remote UE through the first path. The failure information may indicate that the path switch has failed.

[0379] The first path is a communication path between the remote UE and the network device before the remote UE performs a path switch. If this embodiment of this application is applied to a scenario in which the remote UE switches between indirect links, the first path is a communication path in which the remote UE is connected to the network device via a relay UE. That is, the first path is remote UE-relay UE-network device. In this case, the relay UE is a relay UE connected to the remote UE before the remote UE performs a path switch. However, if this embodiment of this application is applied to a scenario in which the remote UE switches from a direct link to an indirect link, the first path is a communication path in which the remote UE is directly connected to the network device. That is, the first path is remote UE-network device.

[0380] For further details of S912, please refer to S712 in the embodiment shown in FIG.

[0381] S913: The remote UE sends an RRC connection re-establishment request message to the source network device through a first path, so that the source network device receives the RRC connection re-establishment request message from the remote UE.

[0382] S912 and S913 are parallel steps, and only one of S912 and S913 needs to be executed. If the remote UE has not disconnected from the source network device through the first path before successfully executing the path switch, the remote UE may alternatively execute S912 to re-establish an RRC connection within the coverage of the source network device, thereby communicating with the source network device through the new connection.

[0383] S914: The remote UE performs cell reselection.

[0384] The remote UE may enter an RRC idle state and perform cell reselection in the RRC idle state, eg, the cell reselected by the remote UE is referred to as the first cell.

[0385] S915: The remote UE initiates an RRC connection reestablishment process in the first cell, or initiates an RRC connection establishment process in the first cell.

[0386] The three solutions S912, S913, and S914, and S915 are parallel, and only one of the three solutions needs to be implemented.

[0387] For further details of S915, please refer to S715 in the embodiment shown in FIG.

[0388] In this embodiment of the present application, the remote UE may determine whether the path switch is successful or unsuccessful based on different conditions. Compared with the method of determining whether the path switch is successful by using a timer, performing the determination by using the above conditions can reduce the time required for the determination process and improve the efficiency of the determination, so that the remote UE can more quickly know whether the path switch is successful so as to take corresponding measures more quickly and reduce the service interruption time. In addition, if the path switch fails, the remote UE may perform corresponding operations, such as continuing to perform communication within the coverage of the source network device, or entering a new cell through cell reselection, so as to resume the service of the remote UE as soon as possible and improve service continuity.

[0389] Next, an embodiment of this application provides an eighth communication method. According to this method, the remote UE can also determine when the path switch has failed, so that the operation of the remote UE can continue. Figure 10 is a flowchart of the method. The method may relate to a process of switching between indirect links, or a process of switching from a direct link to an indirect link. In the process described below, an example is used in which the method is applied to the network architecture shown in any one of Figures 1A to 1D.

[0390] If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1A, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs the path switch are the same network device. In this case, the first terminal device in the following description may be the relay terminal device in Figure 1A, the second terminal device in the following description may be the remote terminal device in Figure 1A, the network device in the following description may be the access network device in Figure 1A, and the network device is both the source network device and the target network device. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1B, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs the path switch are the same network device. In this case, the first terminal device in the following description may be the relay terminal device 1 or the relay terminal device 2 in Figure 1B, the second terminal device in the following description may be the remote terminal device in Figure 1B, the network device in the following description may be the access network device in Figure 1B, and the network device is both the source network device and the target network device. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in Figure 1C, it indicates that the source network device before the remote UE performs path switch and the target network device after the remote UE performs path switch are different network devices.In this case, the first terminal device in the following description may be the relay terminal device in FIG. 1C, the second terminal device in the following description may be the remote terminal device in FIG. 1C, and the network device in the following description (which is also referred to as the first network device, and the first network device is the source network device) may be the access network device in FIG. 1C. In addition, the following also relates to a target network device, which may be referred to as the second network device and may be the access network device 2 in FIG. 1C. Alternatively, the source network device may be the access network device 2 in FIG. 1C, and the target network device may be the access network device 1 in FIG. 1C. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in FIG. 1D, it indicates that the source network device before the remote UE performs path switch and the target network device after the remote UE performs path switch are different network devices. In this case, the first terminal device in the following description may be the relay terminal device 1 in Figure 1D, the second terminal device in the following description may be the remote terminal device in Figure 1D, and the network device in the following description (which is also called the first network device, and the first network device is the source network device) may be the access network device 1 in Figure 1D. In addition, the following further relates to a target network device, which may be called the second network device and may be the access network device 2 in Figure 1D. Alternatively, the first terminal device may be the relay terminal device 2 in Figure 1D, the source network device may be the access network device 2 in Figure 1D, and the target network device may be the access network device 1 in Figure 1D.

[0391] In the following description, an example is used in which the second terminal device is a remote UE and the first terminal device is a relay UE. In addition, in this embodiment of the present application, an example is used in which the source network device and the target network device are different network devices.

[0392] S1001: A remote UE performs data transmission with a source network device.

[0393] S1002: The source network device sends an RRC message to the remote UE. Thus, the remote UE receives the RRC message from the source network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

[0394] Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included in, for example, a system message or another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

[0395] S1003: The remote UE measures or selects another UE. For example, the remote UE may send a discovery message to trigger the other UE to send a discovery message, so that the remote UE may measure the discovery message from the other UE to complete the measurement or selection of the other UE. In FIG. 10, an example in which the remote UE measures the other UE is used.

[0396] The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, such as measuring data signals from the other UEs. This is not limited here. The remote UE may select other UEs based on the measurement results.

[0397] S1004: The remote UE sends the first result to the network device. Thus, the network device receives the first result from the remote UE. The first result is, for example, a measurement result or a selection result. In FIG. 10, an example in which the first result is the measurement result is used.

[0398] The measurement result may include, for example, a report of measuring at least one UE by the remote UE. The selection result may include, for example, a result of selecting a relay UE by the remote UE, and may include, for example, an ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may also be included.

[0399] If the application scenario of this embodiment of this application is to switch from a direct link to an indirect link, the measurement result may further include a result of measuring a serving cell, i.e., a result of measuring a network device. If the application scenario of this embodiment of this application is to switch between indirect links, the communications between the remote UE and the network device in S1001 to S1004 are all performed through forwarding via a relay UE connected to the remote UE before the link switch, and the relay UE in the following description is the relay UE connected to the remote UE after the link switch. The first result may further include a result of measuring the relay UE connected to the remote UE before the link switch.

[0400] S1005: The source network device makes a handover decision. The source network device determines whether the remote UE can perform a path switch based on the measurement result. In this embodiment of the present application, the source network device determines whether the remote UE can be handed over from the relay UE to the target network device based on the measurement result. If the source network device determines that the remote UE can be handed over from the relay UE to the target network device, S1006 is executed.

[0401] S1006: The source network device sends a handover request message to the target network device. Accordingly, the target network device receives the handover request message from the source network device. The handover request message may indicate that the remote UE should be handed over to the target network device. The target network device serves the relay UE. Because the remote UE will switch to performing communication via the relay UE, the source network device will request handover from the target network device serving the relay UE.

[0402] S1007: The target network device sends an RRC reconfiguration message to the relay UE. Thus, the relay UE receives an RRC reconfiguration message from the target network device. For example, the RRC reconfiguration message is called RRC reconfiguration message 1.

[0403] The RRC reconfiguration message, for example, includes configuration information, and the RRC reconfiguration message, for example, realizes the function of the first message in the embodiment shown in Fig. 3. Alternatively, the RRC reconfiguration message, for example, is for inquiring whether the relay UE can provide a relay service, and the RRC reconfiguration message, for example, realizes the function of the first message in the embodiment shown in Fig. 4. Alternatively, after the configuration is performed by using the RRC reconfiguration message, if the relay UE cannot configure the relevant configuration, the relay UE triggers a reconfiguration failure, and then the relay UE enters an RRC connection re-establishment procedure.

[0404] S1008: The relay UE sends a second message to the target network device. Thus, the target network device receives the second message from the relay UE. If the RRC reconfiguration message at S1007 implements the function of the first message in the embodiment shown in Figure 3, the second message at S1008 may implement the function of the second message in the embodiment shown in Figure 3. Alternatively, if the RRC reconfiguration message at S1007 implements the function of the first message in the embodiment shown in Figure 4, the second message at S1008 may implement the function of the second message in the embodiment shown in Figure 4.

[0405] In this embodiment of the present application, for example, the second message indicates that the configuration has failed or that the relay UE refuses to provide relay service. For further details, see S306 or S307 in the embodiment shown in FIG. 3, or S406 or S407 in the embodiment shown in FIG. 4. If the configuration performed by using the configuration message in S1007 has failed, S1008 may be an optional step. The sending is not performed, the relay UE determines that the reconfiguration has failed, and the relay UE is triggered to enter an RRC connection re-establishment procedure.

[0406] S1009: The target network device sends a handover request acknowledge message to the source network device, so that the source network device receives the handover request acknowledge message from the target network device.

[0407] The handover request acknowledge message may indicate that the remote UE is allowed to be handed over to the target network device, or may indicate that the remote UE is not allowed to be handed over to the target network device. In this embodiment of the application, the second message indicates that the configuration has failed or that the relay UE refuses to provide relay service, so the handover request acknowledge message may indicate that the remote UE is not allowed to be handed over to the target network device.

[0408] S1007 follows S1006, and S1010 follows S1009. However, the order of S1007 and S1009 is not limited. For example, the target network device may configure the relay UE and then perform S1009, or may first perform S1009 and then query the relay UE or configure the relay UE. If the target network device and the source network device are the same network device, S1006 and S1009 do not need to be performed.

[0409] S1010: The source network device sends an RRC reconfiguration message to the remote UE. Thus, the remote UE receives the RRC reconfiguration message from the source network device. For example, the RRC reconfiguration message is called RRC reconfiguration message 2.

[0410] The RRC reconfiguration message may include configuration information, which may be for configuring the remote UE to switch to an indirect path and communicate with the target network device through the relay UE. For further content of S1010, such as the implementation of the configuration information, see S810 in the embodiment shown in FIG. 8.

[0411] S1011: The remote UE performs a path switch based on the configuration information. For example, the remote UE performs a configuration based on the configuration information, and the remote UE requests a connection to the relay UE. If a second condition is met, it may be determined that the remote UE has failed the path switch.

[0412] In this embodiment of the present application, the second condition may be related to a timer and a received indication. For example, if a configured timer expires, if the establishment of a connection between the remote UE and the relay UE fails before the timer expires, or if an RLF indication sent by the relay UE is received before the timer expires, the remote UE determines that the path switch has failed. For details, see the description below.

[0413] S1012: The remote UE starts a timer.

[0414] For example, the remote UE may start a timer after S1010 is executed, or in other words, after the remote UE receives configuration information (the configuration information may be included in a general RRC reconfiguration message) from the source network device. The timer may be, for example, timer T304, or another newly introduced timer. This is not limited here. For details such as the configuration method of parameters such as the timing duration of the timer, please refer to S812 in the embodiment shown in FIG. 8. In addition, the timer may be stopped in a specific scenario. For specific stopping conditions, please refer to the following description in S1013.

[0415] S1013: The remote UE requests the relay UE to establish a connection. For example, the remote UE sends a connection establishment request to the relay UE. After the relay UE receives the connection establishment request, the relay UE replies to the remote UE with a connection establishment response message, and if the connection establishment response message indicates that the connection establishment is allowed, the connection establishment between the remote UE and the relay UE is successful. After the relay UE receives the connection establishment request, the relay UE replies to the remote UE with a connection establishment response message, and if the connection establishment response message indicates that the connection establishment is not allowed, or if the relay UE replies without a connection establishment response message, the connection establishment between the remote UE and the relay UE is unsuccessful.

[0416] BelowWhen one or more of the following scenarios occur, it may be directly determined that the establishment of the connection between the remote UE and the relay UE has failed. When it is determined that the connection establishment has failed, it may be determined that the path switch has failed. Optionally, the configured timer may be stopped. In other words, when one or more of the following scenarios occur, it may be determined that the connection establishment has failed without waiting for the timer, thereby reducing the waiting time of the remote UE. Optionally, if it is determined that the connection establishment has failed, the remote UE may be further triggered to perform RRC re-establishment.

[0417] Scenario 1: When the number of times of sending a connection establishment request message to a relay UE reaches M, no feedback is still received from the relay UE, and M is the maximum number of retransmissions.

[0418] The remote UE may send a connection establishment request message to the relay UE by using a retransmission mechanism. That is, if the connection establishment request message is sent unsuccessfully once, the connection establishment request message may be retransmitted again. However, the number of retransmissions is limited, where M is the maximum number of retransmissions. If the remote UE still does not receive feedback from the relay UE after sending the connection establishment request message to the relay UE M times, it indicates that the connection establishment has failed. If the number of times the connection establishment request message is sent to the relay UE is greater than M and no feedback is still received from the relay UE, it indicates that the connection establishment has failed. If the connection establishment has failed, the remote UE cannot perform communication via the relay UE, and the path switch has failed.

[0419] Scenario 2: The security verification performed by the remote UE against the relay UE fails.

[0420] After the remote UE sends a connection establishment request message to the relay UE, if the relay UE agrees to establish a connection, the relay UE sends security-related parameters to the remote UE, and the remote UE needs to perform configuration based on the security-related parameters. However, the configuration of the remote UE may fail. For example, if some parameters (e.g., integrity protection algorithm) sent by the relay UE cannot be supported by the remote UE, the configuration of the remote UE may fail. If the remote UE fails to perform configuration based on the security parameters, security verification with the relay UE is considered to have failed. If the remote UE successfully performs configuration based on the security parameters, security verification with the relay UE is considered to have succeeded. If security verification with the relay UE fails, the remote UE cannot perform communication via the relay UE. This indicates that connection establishment has failed and path switch has failed.

[0421] Scenario 3: A connection establishment request message is sent to a relay UE, and a connection establishment response message is received from the relay UE, and the connection establishment response message may indicate that the connection establishment is rejected.

[0422] The remote UE sends a connection establishment request message to the relay UE. The relay UE replies with a connection establishment response message, and if the connection establishment response message indicates that the connection establishment is accepted, the remote UE can perform communication via the relay UE. However, if the connection establishment response message indicates that the connection establishment is not accepted, the remote UE cannot perform communication via the relay UE. This indicates that the connection establishment has failed and the path switch has failed.

[0423] In addition, the timer related to the second condition, i.e., the timer started in S1012, may be stopped when certain conditions are met. For example, the timer may be stopped when any one of the first stop condition, the second stop condition, the third stop condition, the fourth stop condition, or the fifth stop condition is met. For the first to fourth stop conditions, please refer to the description of S813 in the embodiment shown in Figure 8. The fifth stop condition will be briefly described below.

[0424] For example, the fifth stop condition is as follows: the remote UE determines that the establishment of a connection to the relay UE has failed, or determines a PC5 RLF between the remote UE and the relay UE, the remote UE receives a Uu RLF indication from the relay UE, or the remote UE receives an access failure indication from the relay UE. If the fifth stop condition is met, the remote UE may stop the timer and determine that the path switch has failed. If the timer of the remote UE has expired, the remote UE determines that the path switch has failed. In this embodiment of the present application, whether the path switch has been successful is determined by using a timer. This method is simple and easy to implement. The timer setting method is similar to that in the first stop condition. The details will not be described again here. The fifth stop condition includes multiple conditions. The condition is introduced to quickly determine whether the path switch has failed before the timer expires, reduce the waiting time of the remote UE, and accelerate the speed at which the remote UE resumes service.

[0425] After it is determined that the path switch has failed, subsequent steps may be taken.

[0426] S1013a: If the configuration information in S1010 includes the configuration information of the relay UE, the remote UE sends the configuration information to the relay UE. Thus, the relay UE receives the configuration information from the remote UE. The configuration information sent by the remote UE to the relay UE may be the configuration information in S1010, or may be the configuration information of the relay UE included in the configuration information in S1010.

[0427] S1013b: If the connection between the relay UE and the remote UE is successfully established, the remote UE sends an RRC reconfiguration complete message to the network device via the relay UE, and the network device receives the RRC reconfiguration complete message from the relay UE.

[0428] The configuration sent by the remote UE to the relay UE is a default PC5 RLC configuration. The PC5 RLC configuration may include a default LCID, a default parameter configuration, and the like. The default parameter configuration is used, thereby triggering entry into the RRC connected state, so the relay UE can successfully receive an RRC reconfiguration complete message from the remote UE even in an RRC idle state or an RRC inactive state. If the establishment of the PC5 connection fails in S1013, S1013b may not be successfully executed.

[0429] S1013c: If the relay UE is in an RRC idle state or an RRC inactive state, after receiving a first PC5 message from the remote UE, access to the target network device is triggered.

[0430] S1014: The remote UE sends failure information to the source network device through the first path. Thus, the source network device receives the failure information from the remote UE through the first path. The failure information may indicate that the path switch has failed.

[0431] The first path is a communication path between the remote UE and the source network device before the remote UE performs a path switch. If this embodiment of this application is applied to a scenario in which the remote UE switches between indirect links, the first path is a communication path in which the remote UE is connected to the source network device via a relay UE. That is, the first path is remote UE-relay UE-source network device. In this case, the relay UE is a relay UE connected to the remote UE before the remote UE performs a path switch. However, if this embodiment of this application is applied to a scenario in which the remote UE switches from a direct link to an indirect link, the first path is a communication path in which the remote UE is directly connected to the source network device. That is, the first path is remote UE-source network device.

[0432] For further details of S1014, please refer to S712 in the embodiment shown in FIG.

[0433] S1015: The remote UE sends an RRC connection re-establishment request message to the source network device through a first path. Thus, the source network device receives the RRC connection re-establishment request message from the remote UE. Alternatively, after performing relay re-selection, the remote UE selects another relay UE and initiates connection re-establishment.

[0434] S1014 and S1015 are parallel steps, and only one of S1014 and S1015 needs to be executed. If the remote UE has not disconnected from the source network device through the first path before successfully executing the path switch, the remote UE may alternatively execute S1015 to re-establish an RRC connection within the coverage of the source network device, thereby communicating with the source network device through the new connection.

[0435] S1016: The remote UE performs cell reselection.

[0436] The remote UE may enter an RRC idle state and perform cell reselection in the RRC idle state, e.g., the cell reselected by the remote UE is referred to as the first cell.

[0437] S1017: The remote UE initiates an RRC connection re-establishment process in the first cell, or initiates an RRC connection establishment process in the first cell.

[0438] The three solutions S1014, S1015, and S1016, and S1017 are parallel, and only one of the three solutions needs to be implemented.

[0439] For further details of S1017, please refer to S715 in the embodiment shown in FIG.

[0440] In this embodiment of the present application, the remote UE may determine whether the path switch is successful or unsuccessful based on a timer. The determination method is simple and easy to implement. The technical solution in this embodiment of the present application may also be applied to UEs with low capabilities. In addition, if the path switch fails, the remote UE may perform a corresponding operation, for example, continue communication within the coverage of the source network device, or enter a new cell through cell reselection, so as to resume the service of the remote UE as soon as possible and improve service continuity.

[0441] The following describes an apparatus configured to perform the above-mentioned method in the embodiments of this application with reference to the accompanying drawings. Therefore, all of the above content can be used in the subsequent embodiments. The repeated content will not be described again.

[0442] An embodiment of the present application provides a communication device, which may be a terminal device or a circuit, and which may be configured to perform the operations performed by the terminal device in the above-mentioned method embodiments.

[0443] When the communication device is a terminal device, FIG. 11 is a simplified schematic diagram of the structure of the terminal device. For ease of understanding and illustration, FIG. 11 uses an example in which the terminal device is a mobile phone. As shown in FIG. 11, the terminal device includes a processor, a memory, a radio frequency circuit, an antenna, and an input / output device. The processor is mainly configured to process communication protocols and communication data, control the terminal device, execute software programs, process data of the software programs, etc. The memory is mainly configured to store software programs and data. The radio frequency circuit is mainly configured to convert between baseband signals and radio frequency signals and process radio frequency signals. The antenna is mainly configured to transmit and receive radio frequency signals in the form of electromagnetic waves. The input / output device, such as a touch screen, a display, or a keyboard, is mainly configured to receive data input by a user and output data to the user. It should be noted that some types of terminal devices may not have input / output devices.

[0444] When data needs to be transmitted, the processor performs baseband processing on the data to be transmitted and outputs the baseband signal to the radio frequency circuit. After performing radio frequency processing on the baseband signal, the radio frequency circuit transmits the radio frequency signal in the form of electromagnetic waves through an antenna. When data is transmitted to a terminal device, the radio frequency circuit receives the radio frequency signal through the antenna, converts the radio frequency signal into a baseband signal, and outputs the baseband signal to the processor. The processor converts the baseband signal into data and processes the data. For ease of explanation, FIG. 11 shows only one memory and one processor. In an actual terminal device product, there may be one or more processors and one or more memories. The memory may also be referred to as a storage medium, a storage device, or the like. The memory may be located independently of the processor or integrated with the processor. This is not limited to this embodiment of the present application.

[0445] In this embodiment of the present application, the antenna and radio frequency circuit having receiving and transmitting functions may be regarded as a transceiver unit of the terminal device (the transceiver unit may be one functional unit, and the functional unit may realize the transmitting function and the receiving function, or the transceiver unit may include two functional units, i.e., a receiving unit capable of realizing the receiving function and a transmitting unit capable of realizing the transmitting function), and the processor having processing functions may be regarded as a processing unit of the terminal device. As shown in FIG. 11, the terminal device includes a transceiver unit 1110 and a processing unit 1120. The transceiver unit may also be referred to as a transceiver, a transceiver device, or the like. The processing unit may also be referred to as a processor, a processing board, a processing module, a processing device, or the like. Optionally, a component in the transceiver unit 1110 configured to realize the receiving function may be regarded as a receiving unit, and a component in the transceiver unit 1110 configured to realize the transmitting function may be regarded as a transmitting unit. That is, the transceiver unit 1110 includes a receiving unit and a transmitting unit. A transceiver unit may sometimes be referred to as a transceiver, a transceiver circuit, or the like. A receiving unit may sometimes be referred to as a receiver, a receiver circuit, or the like. A transmitting unit may sometimes be referred to as a transmitter, a transmitter circuit, or the like.

[0446] It should be understood that the transceiver unit 1110 is configured to perform transmission and reception operations on the first terminal device side or the second terminal device side in any one of the embodiments represented in FIG. 3 to the embodiments represented in FIG. 10, and the processing unit 1120 is configured to perform operations other than transmission and reception operations on the first terminal device side or the second terminal device side in any one of the embodiments represented in FIG. 3 to the embodiments represented in FIG. 10.

[0447] When the communication device is a chip-type device or circuit, the device may include a transceiver unit and a processing unit. The transceiver unit may be an input / output circuit and / or a communication interface. The processing unit may be an integrated processor, a microprocessor, or an integrated circuit.

[0448] FIG. 12 is a schematic block diagram of another communication device 1200 according to an embodiment of the present application. For example, the communication device 1200 is, for example, a terminal device or a network device. For example, the communication device 1200 can implement the function of the first terminal device in the embodiment shown in FIG. 3 or the embodiment shown in FIG. 4, or the function of the network device in the embodiment shown in FIG. 3 or the embodiment shown in FIG. 4. Alternatively, the communication device 1200 can implement the function of the second terminal device in the embodiment shown in FIG. 5 or the embodiment shown in FIG. 6, or the function of the network device in the embodiment shown in FIG. 5 or the embodiment shown in FIG. 6. Alternatively, the communication device 1200 can implement the function of the second terminal device in any one of the embodiments shown in FIG. 7 to FIG. 9, or the function of the first network device in any one of the embodiments shown in FIG. 7 to FIG. 9 (in the embodiment shown in FIG. 9, the source network device and the target network device are the same network device, and both may be referred to as the first network device). Alternatively, the communication device 1200 can implement the functionality of the second terminal device in the embodiment shown in FIG. 10, or can implement the functionality of the first network device in the embodiment shown in FIG.

[0449] The communication device 1200 includes a transceiver unit 1220 and a processing unit 1210. Optionally, the communication device 1200 may further include a storage unit, which may be in communication with the processing unit 1210 and is not shown in FIG. 12 . Alternatively, the communication device 1200 may not include a storage unit, and the storage unit may be located outside the communication device 1200. For example, the communication device 1200 may be a terminal device, a chip used in a terminal device, or another combined component or part having the functionality of a first terminal device or a second terminal device. Alternatively, the communication device 1200 may be a network device, a chip used in a network device, or another combined component or part having the functionality of a network device. When the communication device 1200 is a terminal device or a network device, the processing unit 1210 may include a processor, such as a baseband processor. The baseband processor may include one or more central processing units (CPUs). The transceiver unit 1220 may be a transceiver. The transceiver may include an antenna, a radio frequency circuit, and the like. The transceiver may include a transmitter and a receiver, or the transceiver may realize the functions of the transmitter and the receiver. Alternatively, the transmitter and the receiver may be two functional modules separately deployed, but the two functional modules are collectively referred to as a transceiver in this embodiment of the application. When the communication device 1200 is a part having the functions of a terminal device or a network device, the transceiver unit 1220 may be a radio frequency unit, and the processing unit 1210 may be a processor, for example, a baseband processor. When the communication device 1200 is a chip system, the transceiver unit 1220 may be an input / output interface of the chip (e.g., a baseband chip), and the processing unit 1210 may be a processor of the chip system and may include one or more central processing units.It should be understood that the processing unit 1210 in this embodiment of the application may be realized by a processor or processor-related circuit components, and the transceiver unit 1220 may be realized by a transceiver or transceiver-related circuit components.

[0450] In implementation, when the communication apparatus 1200 is configured to realize the functionality of the first terminal device in the embodiment shown in Figure 3, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the first terminal device in the embodiment shown in Figure 3, e.g., S308, and / or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the first terminal device in the embodiment shown in Figure 3, e.g., S303, S306, and S307, and / or may be configured to support other processes of the technology herein.

[0451] In implementation, when communications apparatus 1200 is configured to realize the functionality of the network device in the embodiment depicted in Figure 3, processing unit 1210 may be configured to perform all operations other than the transmit and receive operations performed by the network device in the embodiment depicted in Figure 3, e.g., S305, and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receive and transmit operations performed by the network device in the embodiment depicted in Figure 3, e.g., S301, S302, S304, S306, and S307, and / or may be configured to support other processes of the technology herein.

[0452] In implementation, when the communication apparatus 1200 is configured to realize the functionality of the first terminal device in the embodiment depicted in Figure 4, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the first terminal device in the embodiment depicted in Figure 4, e.g., S410, and / or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the first terminal device in the embodiment depicted in Figure 4, e.g., S403, S406, S407, and S408, and / or may be configured to support other processes of the technology herein.

[0453] In implementation, when communications apparatus 1200 is configured to realize the functionality of the network device in the embodiment depicted in Figure 4, processing unit 1210 may be configured to perform all operations other than the transmit and receive operations performed by the network device in the embodiment depicted in Figure 4, e.g., S405, and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receive and transmit operations performed by the network device in the embodiment depicted in Figure 4, e.g., S401, S402, S404, S406, S407, S408, and S409, and / or may be configured to support other processes of the technology herein.

[0454] In implementation, when the communication apparatus 1200 is configured to realize the functionality of the second terminal device in the embodiment depicted in Figure 5, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the second terminal device in the embodiment depicted in Figure 5, e.g., S505, S506, and S507, and / or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the second terminal device in the embodiment depicted in Figure 5, e.g., S501, S502, S503, and S504, and / or may be configured to support other processes of the technology herein.

[0455] In implementation, when communications apparatus 1200 is configured to realize the functionality of the network device in the embodiment depicted in Figure 5, processing unit 1210 may be configured to perform all operations other than the transmit and receive operations performed by the network device in the embodiment depicted in Figure 5 and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receive and transmit operations performed by the network device in the embodiment depicted in Figure 5, e.g., S501, S502, and S504, and / or may be configured to support other processes of the technology herein.

[0456] In implementation, when communication apparatus 1200 is configured to realize the functionality of the second terminal device in the embodiment depicted in Figure 6, processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the second terminal device in the embodiment depicted in Figure 6, e.g., S611, and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the second terminal device in the embodiment depicted in Figure 6, e.g., S601, S602, S603, S604, and S610, and / or may be configured to support other processes of the technology herein.

[0457] In implementation, when communications apparatus 1200 is configured to realize the functionality of the network device in the embodiment depicted in Figure 6, processing unit 1210 may be configured to perform all operations other than the transmit and receive operations performed by the network device in the embodiment depicted in Figure 6, e.g., S605, and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receive and transmit operations performed by the network device in the embodiment depicted in Figure 6, e.g., S601, S602, S604, and S606 to S610, and / or may be configured to support other processes of the technology herein.

[0458] In implementation, when communication apparatus 1200 is configured to realize the functionality of the second terminal device in the embodiment depicted in Figure 7, processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the second terminal device in the embodiment depicted in Figure 7, e.g., S709, S710, and S714, and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the second terminal device in the embodiment depicted in Figure 7, e.g., S701, S702, S703, S704, S708, S711, S712, S713, and S715, and / or may be configured to support other processes of the technology herein.

[0459] In implementation, when communications apparatus 1200 is configured to realize the functionality of the first network device in the embodiment depicted in Figure 7, processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the first network device in the embodiment depicted in Figure 7, e.g., S705, and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the first network device in the embodiment depicted in Figure 7, e.g., S701, S702, S704, S706, S707, S708, S712, S713, and S715, and / or may be configured to support other processes of the technology herein.

[0460] In implementation, when communication apparatus 1200 is configured to realize the functionality of the second terminal device in the embodiment depicted in Figure 8, processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the second terminal device in the embodiment depicted in Figure 8, e.g., S811, S812, and S816, and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the second terminal device in the embodiment depicted in Figure 8, e.g., S801, S802, S803, S804, S810, S813, S814, S815, and S817, and / or may be configured to support other processes of the technology herein.

[0461] In implementation, when communications apparatus 1200 is configured to realize the functionality of the first network device in the embodiment depicted in Figure 8, processing unit 1210 may be configured to perform all operations other than the transmit and receive operations performed by the first network device in the embodiment depicted in Figure 8, e.g., S805, and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receive and transmit operations performed by the first network device in the embodiment depicted in Figure 8, e.g., S801, S802, S804, S806, S809, S810, S814, S815, and S817, and / or may be configured to support other processes of the technology herein.

[0462] In implementation, when communication apparatus 1200 is configured to realize the functionality of the second terminal device in the embodiment depicted in Figure 9, processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the second terminal device in the embodiment depicted in Figure 9, e.g., S911 and S914, and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the second terminal device in the embodiment depicted in Figure 9, e.g., S901, S902, S903, S904, S910, S912, S913, and S915, and / or may be configured to support other processes of the technology herein.

[0463] In implementation, when communications apparatus 1200 is configured to realize the functionality of the first network device in the embodiment depicted in Figure 9, processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the first network device in the embodiment depicted in Figure 9, e.g., S905, and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the first network device in the embodiment depicted in Figure 9, e.g., S901, S902, S904, S906 to S910, S912, S913, and S915, and / or may be configured to support other processes of the technology herein.

[0464] In implementation, when communication apparatus 1200 is configured to realize the functionality of the second terminal device in the embodiment shown in Figure 10, processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the second terminal device in the embodiment shown in Figure 10, e.g., S1011, S1012, and S1016, and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the second terminal device in the embodiment shown in Figure 10, e.g., S1001, S1002, S1003, S1004, S1010, S1013, S1013a, S1013b, S1013c, S1014, S1015, and S1017, and / or may be configured to support other processes of the technology herein.

[0465] In implementation, when communications apparatus 1200 is configured to realize the functionality of the first network device in the embodiment depicted in Figure 10, processing unit 1210 may be configured to perform all operations other than the transmit and receive operations performed by the first network device in the embodiment depicted in Figure 10, e.g., S1005, and / or may be configured to support other processes of the technology herein. Transceiver unit 1220 may be configured to perform all receive and transmit operations performed by the first network device in the embodiment depicted in Figure 10, e.g., S1001, S1002, S1003, S1004, S1010, S1013, S1013a, S1013b, S1013c, S1014, S1015, and S1017, and / or may be configured to support other processes of the technology herein.

[0466] Additionally, the transceiver unit 1220 may be a single functional module, and the functional module may complete both transmission and reception operations. For example, the transceiver unit 1220 may be configured to perform all transmission and reception operations performed by a terminal device or a network device in any one of the embodiments illustrated in FIG. 3 to FIG. 10. For example, when performing reception operations, the transceiver unit 1220 may be considered a reception unit, and when performing transmission operations, the transceiver unit 1220 may be considered a transmission unit. Alternatively, the transceiver unit 1220 may be two functional modules. The transceiver unit 1220 may be considered a general term for the two functional modules. The two functional modules include a reception unit and a transmission unit. The transmission unit is configured to complete transmission operations. For example, the transmission unit may be configured to perform all transmission operations performed by a terminal device or a network device in any one of the embodiments illustrated in FIG. 3 to FIG. 10. The reception unit is configured to complete reception operations. For example, the receiving unit may be configured to perform all receiving operations performed by a terminal device or a network device in any one of the embodiments shown in Figure 3 to the embodiments shown in Figure 10.

[0467] For specific functions that can be realized by the processing unit 1210 and the transceiver unit 1220, please refer to the description of the operations performed by the terminal device in any one of the embodiments represented in Figure 3 to Figure 10, or refer to the description of the operations performed by the network device in any one of the embodiments represented in Figure 3 to Figure 10. Details will not be described again.

[0468] It should be understood that the processor referred to in the embodiments of this application may be a CPU, or 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, a discrete gate or transistor logic device, a discrete hardware component, or the like. The general-purpose processor may be a microprocessor, or the processor may be any conventional processor or the like.

[0469] It should be noted that when the processor is a general-purpose processor, a DSP, an ASIC, an FPGA or another programmable logic device, a discrete gate or transistor logic device, or a discrete hardware component, the memory (storage module) may be integrated into the processor.

[0470] It should be noted that memory, as used herein, is intended to include, without being limited to, these and any other suitable types of memory.

[0471] It should be understood that the sequence numbers of the above processes do not mean the execution order in the embodiments of this application. The execution order of the processes should be determined based on the functions and internal logic of the processes, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0472] In combination with the examples described in the embodiments disclosed in this specification, those skilled in the art can recognize that the steps of the units and algorithms can be realized by electronic hardware or a combination of computer software and electronic hardware. Whether a function is performed by hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to realize the functions for each specific application, but the implementation should not be considered beyond the scope of this application.

[0473] In some embodiments provided in this application, it should be understood that the disclosed systems, devices, and methods may be realized in other manners. For example, the device embodiments described above are merely examples. For example, the division into units is merely a logical division of functions, and other divisions may occur during actual implementation. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not implemented. In addition, mutual couplings or direct couplings or communication connections shown or discussed may be realized through some interfaces. Indirect couplings or communication connections between devices or units may be realized in electronic, mechanical, or other forms.

[0474] Units described as separate parts may or may not be physically separate, and parts shown as units may or may not be physical units, i.e., located in one location or distributed across multiple network units. Some or all of the units may be selected based on actual requirements to achieve the objectives of the solutions in the embodiments.

[0475] In addition, the functional units in the embodiments of this application may be integrated into one processing unit, each of the units may exist physically alone, or two or more units may be integrated into one unit.

[0476] When the functions are realized in the form of a software functional unit and sold or used as an independent product, the functions may be stored in a computer-readable storage medium. Based on such understanding, the technical solutions in this application, the parts contributing to the prior art, or some of the technical solutions may be realized in the form of a software product. A computer software product is stored in a storage medium and includes some instructions for instructing a computer device (which may be a personal computer, a server, a network device, or the like) to perform all or some of the steps of the method in the embodiments of this application. The aforementioned computer-readable storage medium may be any available medium that can be accessed by a computer. By way of example, and not limitation, a computer-readable medium may include random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM), universal serial bus flash disk, removable hard disk, another compact disc storage, magnetic disk storage medium, another magnetic storage device, or any other medium capable of containing or storing contemplated program code in the form of instructions or data structures that can be accessed by a computer.Additionally, by way of example and not limitation, many forms of RAM may be used, 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), or direct rambus random access memory (DR RAM).

[0477] The above description is merely a specific implementation of this application, and the protection scope of the embodiments of this application is not limited thereto. Any modifications or substitutions that are easily understood by those skilled in the art within the technical scope disclosed in the embodiments of this application shall fall within the protection scope of the embodiments of this application. Therefore, the protection scope of the embodiments of this application shall be subject to the protection scope of the claims. [Explanation of symbols]

[0478] 1110 Transceiver Unit 1120 Processing Unit 1200 Communication Equipment 1210 Processing Unit 1220 Transceiver Unit

Claims

1. A communication method applied to a second terminal device, comprising: receiving configuration information from a first network device, the configuration information for configuring the second terminal device to switch to communicate with a third network device via the first terminal device, the configuration information including information about a first timer, the information about the first timer being for path switching; starting the first timer, establishing a connection to a second terminal device, said connection being used by said second terminal device to communicate with a third network device via said first terminal device; sending an RRC reconfiguration complete message to the first terminal device, wherein the RRC reconfiguration complete message is communicated by using a default PC5 RLC configuration, and the RRC reconfiguration complete message is for triggering the first terminal device, which is in an RRC idle state or an RRC inactive state, to enter an RRC connected state.

2. the RRC reconfiguration complete message is an RRC reconfiguration complete message sent by the second terminal device to the third network device; The method of claim 1 further comprising:

3. the configuration information includes the information about the first timer, The method of claim 1 , further comprising: configuring, by the second terminal device, the first timer based on the information about the first timer.

4. The method is performed under the following conditions: The second terminal device sends the RRC reconfiguration complete message to a lower layer of the second terminal device and receives an acknowledgement feedback from the lower layer, wherein the lower layer is an RLC layer. The method of claim 1 , further comprising stopping the first timer when one or more of the following conditions are satisfied:

5. The method comprises: The method of claim 1 , further comprising the step of performing a re-establishment of a connection between the second terminal device and the first network device when the first timer expires.

6. The method of claim 1, wherein the step of performing a re-establishment of a connection between the second terminal device and the first network device comprises: performing a re-establishment of the connection between the second terminal device and the first network device by using a relay device; or 6. The method of claim 5, comprising performing a re-establishment of a connection between the second terminal device and the first network device by using a cell.

7. A communication method applied to a first network device, comprising: A method comprising: a step of sending configuration information to a second terminal device, the configuration information being for configuring the second terminal device to switch to communicate with a third network device via a first terminal device, the configuration information including information about a first timer, the information about the first timer being for path switching.

8. 8. The method of claim 7, wherein the information about the first timer is for configuring the first timer, and when the first timer expires, the second terminal device determines that the path switch has failed.

9. A communication device comprising a transceiver unit and a processing unit, said transceiver unit being coupled to said processing unit, said communication device being capable of performing the method of any one of claims 1 to 8.

10. 9. A computer-readable storage medium configured to store a computer program, the computer program, when executed in a computer, enabling the computer to perform the method of any one of claims 1 to 8.

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