Method and apparatus for selecting radio access network device

This application relates to the field of wireless communications technologies, and provides a method for selecting a radio access network device. The method includes: obtaining, by a first RAN device, capability information of a second RAN device, where the capability information is used to indicate an LADN supported by the second RAN device; and sending, by the first RAN device, a handover request message to the second RAN device.

TECHNICAL FIELD

The present invention relates to the field of communications technologies, and in particular, to a method and an apparatus for selecting a radio access network device.

BACKGROUND

A local area data network (LADN) is a network that is mainly deployed for scenarios such as an enterprise, a stadium activity, and a concert hall and that is proposed in a 5th generation mobile communications technology (5G). The LADN is characterized by that the terminal device can access the LADN only when a terminal device is located in a service area (SA) of the LADN. When the terminal device moves out of the SA of the LADN, the terminal device cannot access the LADN network, and a session (LADN session) previously accessing the LADN is also disconnected.

Currently, when a mobile handover (HO) is performed for the terminal device, a source radio access network (RAN) device serving the terminal device makes a handover decision based on a measurement report of the terminal device, then selects a target RAN device from candidate RAN devices, and sends a handover request to the target RAN device.

However, after the mobile handover is performed for the terminal device, the terminal device may not access the LADN by using the target RAN device after the handover. As shown inFIG. 1, a RAN device1(RAN1for short) and a RAN device2(RAN2or short) are within a coverage area of an LADN SA, and a RAN device3(RAN3for short) is not within the coverage area of the LADN SA. Before the mobile handover, the terminal device is located within a coverage area of the RAN1. When the terminal device moves to coverage areas of the RAN2and the RAN3, according to the prior art, the RAN1may select the RAN3as a handover target, thereby reducing user experience.

SUMMARY

Embodiments of the present invention provide a method and an apparatus for selecting a radio access network device.

According to an aspect, an embodiment of this application provides a method for selecting a radio access network RAN device. The method includes: obtaining, by a first radio access network RAN device, capability information of a second RAN device; and sending, by the first RAN device, a handover request message to the second RAN device. The capability information is used to indicate a local area data network LADN supported by the second RAN device. For example, the capability information includes at least one of a data network name (DNN), a DNN index, an IP address or prefix, or IP routing information of the LADN.

Based on the foregoing solution, when a mobile handover is performed for a terminal device, the first RAN device may send, based on obtained capability information of a plurality of adjacent RAN devices, a handover request to the second RAN device supporting the LADN, so that a mobile terminal can access an LADN service after accessing the second RAN device, thereby improving user experience.

In a possible design, the first RAN device may obtain the capability information of the second RAN device in the following manner: The first RAN device sends a connection setup request message (for example, an Xn setup request message) to the second RAN device, and receives a connection setup response message from the second RAN device. The connection setup response message includes the capability information of the second RAN device. In this way, the first RAN device completes setup of a connection to the second RAN device, and obtains the capability information of the second RAN device from the second RAN device. Similarly, the first RAN device may obtain capability information of another adjacent RAN through a connection setup (for example, an Xn connection) process between RAN devices.

In a possible design, before the sending, by the first RAN device, a handover request message to the second RAN device, the method further includes: determining, by the first RAN device, that a terminal device accesses the LADN by using a first session. Therefore, when the terminal device accesses a specific LADN by using the first session, the first RAN device may send a handover request to a second RAN device supporting the specific LADN, so that the first session is not interrupted or suspended after the mobile terminal accesses the second RAN device. In this way, a service accessing the specific LADN is not interrupted or suspended, thereby further improving user experience.

In a possible design, the method further includes: receiving, by the first RAN device, an association between a session identifier of the first session and a first network name of the LADN from a session management function SMF network element; or receiving, by the first RAN device, a second network name from an SMF network element, and determining that the second network name is corresponding to the LADN. Therefore, the first RAN device obtains the association between the session identifier of the first session and the network name (for example, the first network name or the second network name), and may select a handover target for the terminal device based on the association when the mobile handover is performed for the terminal device.

According to another aspect, this application further discloses a communication method. The method includes: obtaining, by a second RAN device, capability information of the second RAN device from an AMF network element; and sending, by the second RAN device, the capability information of the second RAN device to a first RAN device. The capability information is used to indicate a local area data network LADN supported by the second RAN device.

Based on the foregoing solution, the second RAN device sends the capability information of the second RAN device obtained from the AMF network element to the first RAN device. After the first RAN device obtains the capability information, and when a handover target is selected for a terminal device, a RAN device (for example, the second RAN device) supporting the LADN may be preferentially handed over for the terminal device, so that the terminal device can access an LADN service after the handover, thereby improving user experience.

In a possible design, the second RAN device may obtain the capability information in the following manner: The second RAN device obtains the capability information of the second RAN device from the AMF network element in a process of setting up a connection (for example, an N2 connection) between the second RAN device and the AMF network element. In this way, the second RAN device completes setup of a connection to the AMF network element, and obtains the capability information of the second RAN device from the AMF network element. The capability information of the second RAN device may be used in a scenario in which a handover is performed for the terminal device, and is further applicable to another communication application scenario.

In a possible design, the second RAN device may send the capability information of the second RAN device to the first RAN device in the following manner: The second RAN device receives a connection setup request message (for example, an Xn setup request message) from the first RAN device, and sends a connection setup response message (an Xn setup response message) to the first RAN device, where the connection setup response message includes the capability information. In this way, the first RAN device completes setup of a connection to the second RAN device, and obtains the capability information of the second RAN device from the second RAN device.

According to still another aspect, this application further discloses a communication method. The method includes: receiving, by an AMF network element, a connection setup request message (for example, an NG setup request message) from a RAN device; and sending, by the AMF network element, capability information of the RAN device to the RAN device. The capability information is used to indicate an LADN supported by the RAN device. For example, after receiving the connection setup request message, the AMF network element searches for the capability information of the RAN device, and then sends the capability information to the RAN device.

Based on the foregoing solution, the AMF network element completes setup of a connection to the RAN device, and sends the capability information of the RAN device to the RAN device. The capability information may be used in a scenario in which a handover is performed for the terminal device. In addition, the capability information may be further applied to another communication application scenario.

In a possible design, the capability information of the RAN device includes at least one of a DNN, an IP address or prefix, or IP routing information of the first LADN. Therefore, the capability information of the RAN device may represent the LADN supported by the RAN device.

In a possible design, the capability information of the RAN device further includes a correspondence between a cell identifier or a tracking area identifier and at least one of a DNN, an IP address or prefix, or IP routing information of the first LADN. For example, when a coverage area of the LADN supported by the RAN device is in a granularity of a tracking area, the first RAN device may select a RAN device (for example, a second RAN device) supporting the first LADN as a handover target based on the correspondence between the tracking area identifier and at least one of the DNN, the IP address or prefix, or the IP routing information of the first LADN. Alternatively, when a coverage area of the LADN supported by the RAN device is in a granularity of a cell, the first RAN device may select, based on the correspondence between the cell identifier and at least one of the DNN, the IP address or prefix, or the IP routing information of the first LADN, a cell supporting the first LADN of a RAN device (for example, a second RAN device) as a target cell for the handover.

According to still another aspect, this application further discloses a communication method. The method includes: receiving, by an SMF network element, a session identifier of a first session and a network name from a terminal device; and sending, by the SMF network element, session management information to a RAN device. The session management information includes an association between the session identifier and the network name.

Based on the foregoing solution, the first RAN device preferentially selects a RAN device supporting an LADN as a handover target, so that a terminal device can access the LADN by using a target RAN device, thereby improving user experience.

In a possible design, the method further includes: determining, by the SMF network element, that the terminal device accesses a local area data network LADN by using the first session. Therefore, when the terminal device accesses a specific LADN by using the first session, the first RAN device may send a handover request to a second RAN device supporting the specific LADN, so that the first session is not interrupted or suspended after a mobile terminal accesses the second RAN device. In this way, a service accessing the specific LADN is not interrupted or suspended, thereby further improving user experience.

In a possible design, the method further includes: the network name corresponding to the LADN is preconfigured in the SMF network element; or obtaining, by the SMF from an AMF network element, the network name corresponding to the LADN; or obtaining, by the SMF network element from a PCF network element, the network name corresponding to the LADN; or obtaining, by the SMF network element from a data management network element, the network name corresponding to the LADN. Therefore, the SMF network element may obtain the network name corresponding to the LADN.

According to still another aspect, an embodiment of this application provides a radio access network device. The radio access network device has a function of implementing behavior of the radio access network device (for example, the first RAN device) in the foregoing method. The function may be implemented by hardware, or implemented by hardware executing corresponding software. The hardware or the software includes one or more modules corresponding to the foregoing function. In a possible design, a structure of the radio access network device includes a processor and a transceiver. The processor is configured to support the radio access network device in performing a corresponding function in the foregoing method. The transceiver is configured to implement communication between the radio access network device and an access and mobility management function network element/another radio access network device (for example, a second RAN device). The radio access network device may further include a memory. The memory is configured to be coupled to the processor, and the memory stores a program instruction and data that are necessary for the radio access network device.

According to still another aspect, an embodiment of this application provides a radio access network device. The radio access network device has a function of implementing behavior of the radio access network device (for example, the second RAN device) in the foregoing method. The function may be implemented by hardware, or implemented by hardware executing corresponding software. The hardware or the software includes one or more modules corresponding to the foregoing function. In a possible design, a structure of the radio access network device includes a processor and a transceiver. The processor is configured to support the radio access network device to in performing a corresponding function in the foregoing method. The transceiver is configured to implement communication between the radio access network device and an access and mobility management function network element/another radio access network device (for example, a first RAN device). The radio access network device may further include a memory. The memory is configured to be coupled to the processor, and the memory stores a program instruction and data that are necessary for the radio access network device.

According to still another aspect, an embodiment of this application provides a communications apparatus. The communications apparatus has a function of implementing behavior of the AMF network element in the foregoing method. The function may be implemented by hardware, or implemented by hardware executing corresponding software. The hardware or the software includes one or more modules corresponding to the foregoing function. In a possible design, a structure of the communications apparatus includes a processor and a transceiver. The processor is configured to support the communications apparatus in performing a corresponding function in the foregoing method. The transceiver is configured to implement communication between the communications apparatus and a terminal device/a radio access network device (for example, a first or a second RAN device)/a session management function network element. The communications apparatus may further include a memory. The memory is configured to be coupled to the processor, and the memory stores a program instruction and data that are necessary for the communications apparatus.

According to still another aspect, an embodiment of this application provides a communications apparatus. The communications apparatus has a function of implementing behavior of the SMF network element in the foregoing method. The function may be implemented by hardware, or implemented by hardware executing corresponding software. The hardware or the software includes one or more modules corresponding to the foregoing function. In a possible design, a structure of the communications apparatus includes a processor and a transceiver. The processor is configured to support the communications apparatus in performing a corresponding function in the foregoing method. The transceiver is configured to implement communication between the communications apparatus and a terminal device/a radio access network device (for example, a first or a second RAN device)/an access and mobility management function network element. The communications apparatus may further include a memory. The memory is configured to be coupled to the processor, and the memory stores a program instruction and data that are necessary for the communications apparatus.

According to still another aspect, an embodiment of this application provides a communication method, and the method includes: receiving, by a terminal device, an association between an access network identifier and an LADN from an access network discovery network element (for example, an access network discovery and selection function network element in the 4G, or a PCF network element in the 5G); and accessing, by the terminal device based on the association, an access network corresponding to the access network identifier.

Based on the foregoing solution, when the terminal device moves and needs to reselect a non-3GPP access network, the terminal device sends, based on the obtained association between the access network identifier and a network name of the LADN, a access request to the access network device corresponding to the access network identifier. Because the access network device corresponding to the access network identifier supports the LADN, the terminal device can access an LADN service after accessing the access network device, thereby improving user experience.

In a possible design, the method further includes: before the accessing, by the terminal device based on the association between the access network identifier and the LADN, an access network corresponding to the access network identifier, determining, by the terminal device, that the terminal device accesses the LADN by using a first session. Therefore, in a scenario of the non-3GPP access network, the terminal device may access, by knowing a network name of a specific LADN that is accessed by the terminal device by using the first session and based on an obtained association between an identifier of a candidate access network that can be accessed and the network name of the LADN, an access network device supporting the specific LADN when an access network needs to be changed. Therefore, a service of the specific LADN is not interrupted, thereby improving user experience.

According to still another aspect, an embodiment of this application provides a terminal device. The terminal device has a function of implementing behavior of the terminal device in the foregoing method. The function may be implemented by hardware, or implemented by hardware executing corresponding software. The hardware or the software includes one or more modules corresponding to the foregoing function. In a possible design, a structure of the terminal device includes a processor and a transceiver. The processor is configured to support the terminal device in performing a corresponding function in the foregoing method. The transceiver is configured to implement communication between the terminal device and a radio access network device/an access and mobility management function network element/an access discovery network element. The terminal device may further include a memory. The memory is configured to be coupled to the processor, and the memory stores a program instruction and data that are necessary for the terminal device.

According to still another aspect, an embodiment of this application provides a computer readable storage medium. The computer readable storage medium stores an instruction, and when the instruction is run on a computer, the computer is enabled to perform the methods in the foregoing aspects.

According to still another aspect, an embodiment of this application provides a computer program product including an instruction. When the instruction is run on a computer, the computer performs the methods in the foregoing aspects.

According to still another aspect, this application provides a chip system. The chip system includes a processor, configured to support the radio access network device, the communications apparatus, or the terminal device in implementing the functions in the foregoing aspects, for example, generating or processing the information in the foregoing methods. In a possible design, the chip system further includes a memory. The memory is configured to store a program instruction and data that are necessary for a data sending device. The chip system may include a chip, or may include a chip and another discrete device.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The network architectures and the service scenarios described in this application are intended to describe the technical solutions in this application more clearly, and do not constitute a limitation to the technical solutions provided in this application. A person of ordinary skill in the art may know that with evolution of network architectures and emergence of new service scenarios, the technical solutions provided in this application are also applicable to similar technical problems.

FIG. 2is a schematic diagram of a 5G communications system that may be trial according to an embodiment of this application. In a 5G mobile network architecture, a control plane function and a forwarding plane function of a mobile gateway are decoupled, and a separated control plane function of the mobile gateway, and a conventional control network element mobility management entity (MME) of a 3rd generation partnership project (3GPP), and the like are combined into a unified control plane. A user plane function (UPF) network element can implement user plane functions (SGW-U and PGW-U) of a serving gateway (SGW) and a packet data network gateway (PGW). Further, a unified control plane network element may be decomposed into an access and mobility management function (AMF) network element and a session management function (SMF) network element.

In addition, the embodiments of this application are also applicable to another future-oriented communications technology. The system architectures and the service scenarios described in the embodiments of this application are intended to describe the technical solutions in the embodiments of this application more clearly, and do not constitute a limitation to the technical solutions provided in the embodiments of this application. A person of ordinary skill in the art may know that with the evolution of the network architectures and the emergence of new service scenarios, the technical solutions provided in the embodiments of this application are also applicable to similar technical problems.

As shown inFIG. 2, an embodiment of this application provides a communications system. For example, the communications system at least includes a terminal device201, a RAN device202, an AMF network element205, an SMF network element206, and a UPF network element203.

The terminal device201in this system may be a terminal device supporting an LADN network. User equipment to which the present invention can be applied is not limited to a 5G network, and may be further applied to all kinds of terminal devices, including: a mobile phone, an internet of things device, a smart household device, an industrial control device, a vehicle device, and the like. The technical solutions provided in the embodiments of the present invention can be used provided that there is a requirement of the LADN network and there is a terminal device having the foregoing technical problem. The terminal device may also be referred to as a user equipment (UE) mobile station, a mobile station, a remote station, a remote terminal, an access terminal, a user terminal, a user agent, or user equipment (User Equipment). This is not limited herein. The foregoing terminal device may alternatively be a vehicle in vehicle-to-vehicle (V2V) communication or a machine in machine type communication, or the like.

The RAN device202in this system is an apparatus configured to provide a wireless communication function for the terminal device201. The RAN device may include base stations in various forms, for example, a macro base station, a micro base station (also referred to as a small cell), a relay station, an access point, and the like. In systems that use different radio access technologies, a device that has a base station function may have different names. For example, in an LTE system, the device is referred to as an evolved NodeB (eNB or eNodeB), or in a 3rd generation (3G) system, the device is referred to as a NodeB (Node B). In a new generation system, the device is referred to as a gNB (gNodeB).

The UPF network element203can implement the user plane functions (SGW-U and PGW-U) of the SGW and the PGW. The UPF network element may be connected to a same data network204(DN) or different data networks204(DN), to implement data transmission of a service. The UPF network element may also be referred to as a UPF device or a UPF entity.

The AMF network element205may be responsible for attachment, mobility management, a tracking area update procedure, and the like of the terminal device. The AMF network element may also be referred to as an AMF device or an AMF entity.

The SMF network element206may be responsible for session management of the terminal device. For example, the session management includes selection of a user plane device, reselection of a user plane device, internet protocol (IP) address assignment, quality of service (QoS) control, and session setup, modification, or releasing. The SMF network element may also be referred to as an SMF device or an SMF entity.

Optionally, the communications system further includes a policy control function (policy control function, PCF) network element207. The PCF network element207includes a policy control function and a flow-based charging control function. For example, the PCF network element207may implement a subscriber subscription data management function, a policy control function, a charging policy control function, and QoS control. The PCF network element may also be referred to as a PCF entity or a PCF device.

Optionally, the communications system further includes a data management device, for example, a unified data management (UDM) device208. The UDM device208is configured to store subscription data of a subscriber, for example, subscription data related to mobility management and subscription data related to session management. The UDM device may also be referred to as a UDM entity or a UDM network element.

The communications system is used as an example in the following, to describe the technical solutions of this application in detail by using some embodiments. The following several embodiments may be combined with each other, and a same or similar concept or process may not be described repeatedly in some embodiments.

FIG. 3is a flowchart of a method for selecting a radio access network device according to an embodiment of this application. The method may be applied to a scenario of handing over a RAN device for a terminal device by using a 3GPP access network. The method is performed by a first RAN device. For example, the first RAN device is the RAN device201inFIG. 2. As shown inFIG. 3, the method may include the following steps.

S301: A first RAN device obtains capability information of a second RAN device. The capability information of the second RAN device is used to indicate an LADN supported by the second RAN device.

For example, the capability information includes at least one of a data network name (DNN), a DNN index, an IP address or prefix, or IP routing information of the LADN. In other words, when the capability information of the second RAN device includes at least one of the DNN, the DNN index, the IP address or prefix, or the IP routing information of the LADN, the second RAN device is a RAN device supporting the LADN.

Optionally, when a coverage area of the LADN supported by the second RAN device is in a granularity of a tracking area (TA), the capability information of the second RAN device may include a correspondence between a tracking area identifier and at least one of a DNN, a DNN index, an IP address or prefix, or IP routing information of the LADN.

Alternatively, when a coverage area of the LADN supported by the second RAN device is in a granularity of a cell (that is, only a specific cell of the second RAN device supports the LADN), the capability information of the second RAN device may include a correspondence between a cell identifier and at least one of a DNN, a DNN index, an IP address or prefix, or IP routing information of the LADN.

It should be noted that the first RAN device may obtain capability information of a plurality of RAN devices adjacent to the first RAN device. The obtained capability information of the RAN devices at least includes the capability information of the second RAN device. In addition, the first RAN device may further obtain capability information of another RAN device supporting the LADN.

Optionally, when an adjacent RAN device does not feed back capability information to the first RAN device, it may be considered that the adjacent RAN device does not support the LADN.

A manner in which the first RAN device obtains the capability information of the second RAN device is further described with reference toFIG. 4.

S303: The first RAN device sends a handover request message to the second RAN device.

After obtaining the capability information of the second RAN device, the first RAN device knows that the second RAN device is a RAN device supporting the LADN. When the first RAN device determines that a handover is performed for terminal device, the first RAN device may select the second RAN device as a handover target based on the capability information of the second RAN device, and send the handover request message to the second RAN device.

Optionally, when the coverage area of the LADN supported by the second RAN device is in the granularity of the cell, the first RAN device selects, based on a cell identifier in the capability information, a cell supporting the LADN of the second RAN device as a target cell for the handover, and sends a handover request to the target cell.

Step S303is further described with reference toFIG. 7.

Therefore, according to the method in the embodiment of the present invention, when a mobile handover is performed for the terminal device, the first RAN device (namely, a source RAN device) may send, based on the obtained capability information of the plurality of adjacent RAN devices, a handover request to the second RAN device supporting the LADN, so that a mobile terminal can access an LADN service after accessing the second RAN device, thereby improving user experience. The present invention may be applied to a scenario in which the terminal device does not access the LADN before the handover, or may be applied to a scenario in which the terminal device accesses the LADN before the handover.

Optionally, before step303, the first RAN device may perform the following S302.

S302: The first RAN device determines that the terminal device accesses the LADN by using a first session.

For example, before the handover, the terminal device accesses a specific LADN by using the first session. For example, the specific LADN is an LADN1, and a network name of the LADN1is a DNN1. After making a handover decision, the first RAN device determines that the terminal device accesses the LADN1by using the first session. For example, because the first RAN device stores an association between an identifier of the first session and the DNN1of the LADN1, the first RAN device may determine that the terminal device accesses the LADN1by using the first session.

The first RAN device may select a handover target based on the DNN1and the obtained capability information of the RAN devices. For example, the capability information of the second RAN device includes the DNN1, indicating that the second RAN device supports the LADN1corresponding to the DNN1. Therefore, the first RAN device may select the second RAN device that can also support the LADN1as the handover target, and sends the handover request message to the second RAN device. If the obtained capability information of the RAN devices does not include the DNN1, the first RAN device may select a handover target RAN device from candidate RAN devices with reference to the prior art.

Therefore, based on the foregoing solution, when the terminal device accesses a specific LADN by using the first session, the first RAN device may send a handover request to a second RAN device supporting the specific LADN, so that the first session is not interrupted or suspended after a mobile terminal accesses the second RAN device. In this way, a service accessing the specific LADN is not interrupted or suspended, thereby further improving user experience.

Optionally, the method further includes any one of the following two implementations, to obtain an association between an identifier of the first session and a network name of the LADN.

In a possible implementation, the first RAN device receives the association between the session identifier of the first session and the network name of the LADN from an SMF network element (for example, the SMF network element206inFIG. 2). In this implementation, the SMF network element may determine the association between the session identifier of the first session and the network name of the LADN. Alternatively, the SMF network element obtains the association between the session identifier of the first session and the network name of the LADN from an AMF network element (for example, the AMF network element205inFIG. 2) or a PCF network element (for example, the PCF network element207inFIG. 2).

In another possible implementation, the first RAN device receives a network name corresponding to the first session from an SMF network element. In this implementation, the first RAN device determines the association between the session identifier of the first session and the network name of the LADN.

Optionally, the first RAN device may further store the association between the session identifier of the first session and the network name of the LADN. The foregoing implementations are further described with reference toFIG. 5andFIG. 6.

FIG. 4shows a communication method according to an embodiment of this application. As shown inFIG. 4, the method may include the following steps.

S401: A second RAN device sends a connection setup request message to an AMF network element. Correspondingly, the AMF network element receives the connection setup request message from the second RAN device.

The connection setup request message is used to request to set up a device connection between the second RAN device and the AMF network element. This may occur when the device is powered on. Specifically, the connection between the second RAN device and the AMF may be an N2 connection. For example, the connection setup request message may be an NG setup request message.

S402: After receiving the connection setup request message, the AMF network element sends a connection setup response message to the second RAN device. Correspondingly, the second RAN device receives the connection setup response message from the AMF network element. The connection setup response message includes capability information of the second RAN device. The capability information is used to indicate an LADN supported by the second RAN device.

For example, the connection setup response message may be an NG setup response message.

For example, after receiving the connection setup request message, the AMF network element searches for the capability information of the second RAN device. A manner in which the AMF network element obtains the capability information of the second RAN device includes any one of the following:

In a possible implementation, capability information of RAN devices (including the capability information of the second RAN device) is preconfigured on the AMF network element. For example, capability information of an AMF (in other words, an LADN supported by the AMF device and an SA corresponding to the LADN) is configured in the AMF network element. The RAN devices may report respective location information to the AMF device, and the AMF device determines, based on the location information reported by the RAN devices and a distribution status of the SA of the LADN, an LADN supported by the RAN devices, in other words, determines the capability information of the RAN devices. For example, the connection setup request message carries location information of the second RAN device. After receiving the connection setup request message, the AMF network element determines the LADN supported by the second RAN device, and sends the capability information of the second RAN device to the second RAN device by using the connection setup response message.

In another possible implementation, the AMF network element obtains capability information of RAN devices (including the capability information of the second RAN device) from a PCF network element (for example, the PCF network element207inFIG. 2) in a process of setting up a connection (for example, an N15 connection) between the AMF network element and the PCF network element.

In addition, the AMF network element may alternatively obtain the capability information of the second RAN device in another manner. This is not limited in this application.

For example, the foregoing steps S401and S402may be performed when the second RAN device is powered on.

In this way, the second RAN device completes setup of a connection to the AMF network element, and obtains the capability information of the second RAN device from the AMF network element. The capability information of the second RAN device may be used in a scenario in which a handover is performed for the terminal device, and is further applicable to another communication application scenario. This is not limited in the present invention.

Optionally, in S403, after receiving the connection setup response message from the AMF network element, the second RAN device stores the capability information of the second RAN device.

Further, after obtaining the capability information of the second RAN device, the second RAN device may send the capability information to a first RAN device. The specific process is as follows.

S404: The first RAN device sends a connection setup request message to the second RAN device. Correspondingly, the second RAN device receives the connection setup request message from the first RAN device.

The connection setup request message is used to request to set up a device connection between the first RAN device and the second RAN device. This may occur when the device is powered on. For example, the connection between the first RAN device and the second RAN device may be an Xn connection. For example, the connection setup request message may be an Xn setup request message.

S405: After receiving the connection setup request message sent by the first RAN device, the second RAN device sends a connection setup response message to the first RAN device. Correspondingly, the first RAN device receives the connection setup response message from the second RAN device. The connection setup response message includes the capability information of the second RAN device obtained by the second RAN device. For example, the connection setup response message may be an Xn setup response message.

S406: After receiving the connection setup response message from the second RAN device, the first RAN device stores an association between the capability information of the second RAN device and identification information of the second RAN device. The identification information of the second RAN device is used to indicate the second RAN device.

In this way, the first RAN device completes setup of a connection to the second RAN device, and obtains the capability information of the second RAN device from the second RAN device. Similarly, the first RAN device may obtain capability information of another adjacent RAN through a connection setup process between RAN devices. The method is not limited to an application scenario of the embodiment of this application, and is further applicable to another communication application scenario.

Based on the foregoing solution, the second RAN device obtains the capability information of the second RAN device from the AMF network element, and sends the capability information to the first RAN device. In this way, after the first RAN device obtains the capability information, and when a handover target is selected for the terminal device, a RAN device (for example, the second RAN device) supporting the LADN may be preferentially handed over for the terminal device, so that the terminal device can access an LADN service after the handover, thereby improving user experience.

Optionally, the first RAN device may also obtain capability information of the first RAN device in a manner similar to S401and S402. In addition, in step S404, the connection setup request message sent by the first RAN device to the second RAN device may further carry the capability information of the first RAN device. In other words, in a process of setting up a connection between two RAN devices, the two RAN devices may notify each other of capability information of the two RAN devices, that is, notify each other of network names of LADNs respectively supported by the two RAN devices.

FIG. 5andFIG. 6respectively show still another communication method according to an embodiment of this application. The method inFIG. 5orFIG. 6may be performed in a session (for example, a first session) setup procedure. The difference lies in that: in an example inFIG. 5, an SMF network element determines an association between a session identifier of the first session and a network name of an LADN. However, in an example inFIG. 6, a first RAN device determines an association between a session identifier of the first session and a network name of an LADN.

As shown inFIG. 5, the method may include the following steps.

S501: A terminal device sends a session setup request message to an AMF network element by using a first RAN device. Correspondingly, the AMF network element receives the session setup request message from the first RAN device. The session setup request message is used to request to set up a first session. For example, the terminal device sends a non-access stratum (NAS) message to the AMF network element. The NAS message includes a session identifier (session ID) of the first session, a network name, and session management (SM) information (for example, N1 SM information). The session management information includes the session setup request message.

For example, the network name includes at least one of a DNN, a DNN index, an IP address or prefix, or IP routing information.

S502: After receiving the session setup request message, the AMF network element selects an SMF network element, and sends the session identifier of the first session, the network name, and the session management information to the SMF network element.

S503: After receiving the session identifier of the first session, the network name, and the session management information, the SMF network element selects a UPF network element, and sends a user plane connection setup request message to the UPF network element, to set up a connection (for example, an N4 connection) between the SMF network element and the UPF network element. Correspondingly, the UPF network element receives the user plane connection setup request message from the SMF network element. For example, the user plane connection setup request message may be an N4 session setup request message.

S504: After receiving the user plane connection setup request message, the UPF network element sends a user plane connection setup response message to the SMF network element. Correspondingly, the SMF network element receives the user plane connection setup response message from the UPF network element. For example, the user plane connection setup response message may be an N4 session setup response message.

S505: The SMF network element knows that the terminal device accesses an LADN by using the first session.

For example, the SMF network element may obtain that the terminal device accesses the LADN by using the first session in any one of the following manners.

Manner1: The SMF network element determines that the terminal device accesses the LADN by using the first session.

For example, the SMF network element determines, based on the network name carried in step S502and an obtained network name corresponding to the LADN, whether the terminal device accesses the LADN by using the first session. For example, if the obtained network name corresponding to the LADN includes the network name carried in step S502, the SMF network element determines that the terminal device accesses the LADN by using the first session.

For example, the SMF network element may obtain the network name corresponding to the LADN in any one of the following manners.(a1) The network name corresponding to the LADN is preconfigured in the SMF network element.(a2) The SMF network element obtains the network name corresponding to the LADN from the AMF network element.(a3) The SMF network element obtains the network name corresponding to the LADN from a PCF network element.

(a4) The SMF network element obtains the network name corresponding to the LADN from a data management device (for example, the UDM device208inFIG. 2).

In addition, the SMF network element may alternatively obtain the network name corresponding to the LADN in another manner. This is not limited in this application.

Manner2: The SMF network element knows that the terminal device accesses the LADN by using the first session from the AMF network element.

For example, the network name corresponding to the LADN is preconfigured in the AMF network element. The AMF network element may determine, based on the network name carried in step S501and the preconfigured network name corresponding to the LADN, whether the terminal device accesses the LADN by using the first session. For example, if the preconfigured network name corresponding to the LADN includes the network name carried in step S501, the AMF network element determines that the terminal device accesses the LADN by using the first session. The AMF network element may send, to the SMF network element, indication information used to instruct the terminal device to access the LADN by using the first session, so that the SMF network element knows, based on the indication information, that the terminal device accesses the LADN by using the first session.

Manner3: The SMF network element knows that the terminal device accesses the LADN by using the first session from the PCF network element.

For example, the SMF network element sends the network name carried in step S502to the PCF network element, and the PCF network element determines, based on the network name sent by the SMF network element and the obtained network name corresponding to the LADN, whether the terminal device accesses the LADN by using the first session. For example, if the obtained network name corresponding to the LADN includes the network name sent by the SMF network element, the PCF network element determines that the terminal device accesses the LADN by using the first session. The PCF network element may send, to the SMF network element, indication information used to instruct the terminal device to access the LADN by using the first session, so that the SMF network element knows, based on the indication information, that the terminal device accesses the LADN by using the first session.

For example, the PCF network element may obtain the network name corresponding to the LADN in any one of the following manners.(b1) The network name corresponding to the LADN is preconfigured in the PCF network element.(b2) The PCF network element obtains the network name corresponding to the LADN from the AMF network element.(b3) The PCF network element obtains the network name corresponding to the LADN from a UDM network element.

In any one of the manners mentioned above, the SMF network element knows that the terminal device accesses the LADN by using the first session.

Optionally, the SMF network element stores an association between a session identifier of the first session and a network name of the LADN. For example, if the session identifier of the first session is a session ID1, and the network name of the LADN is a DNN1, the SMF network element stores an association between the session ID1and the DNN1, as shown in Table 1.

Optionally, when the terminal device simultaneously initiates a plurality of sessions, the SMF network element stores a plurality of groups of associations between the session identifier and the network name.

It should be noted that Table 1 is merely an example. The association between the session identifier and the network name of the LADN in this application is not limited to Table 1. All correspondences fall within the protection scope of this application provided that the correspondence indicates a correspondence between the session identifier and the network name of the LADN.

In addition, it should be noted that an execution time of step S505is not limited in the present invention, and step S505can be performed provided that the SMF obtains the network name in S502.

S506: After knowing that the terminal device accesses the LADN by using the first session, the SMF network element sends the association between the session identifier of the first session and the network name of the LADN to the AMF network element.

Optionally, the SMF network element sends SM information such as an N2 SM information to the AMF network element. The N2 SM information includes an association between the session identifier and a first network name of the LADN.

Optionally, if the SMF network element determines, in step S505, that a data network accessed by the terminal device by using the first session is not the LADN, the SMF network element does not need to send the association between the session identifier and the network name to the AMF network element/the first RAN device.

S507: After receiving the association between the session identifier of the first session and the first network name of the LADN, the AMF network element forwards a session request message to the first RAN device. The session request message includes the association between the session identifier of the first session and the first network name of the LADN. Correspondingly, the first RAN device receives the session request message from the AMF network element. For example, the session request message may be an N2 session request message.

Optionally, in S508, after receiving the association between the session identifier of the first session and the network name of the LADN, the first RAN device stores the association between the session identifier and the network name of the LADN. The association is used to select a handover target for the terminal device when a mobile handover is performed for the terminal device.

In this way, the first RAN device receives the association between the session identifier of the first session and the network name of the LADN from the SMF network element. After step S508, for performing subsequent steps of a session setup process, refer to the prior art. Details are not described herein again.

FIG. 6shows still another communication method according to an embodiment of this application. An SMF network element is shown inFIG. 6. The method may include the following steps.

S601: A terminal device sends a session setup request message to an AMF network element by using a first RAN device. Correspondingly, the AMF network element receives the session setup request message from the first RAN device. The session setup request message is used to request to set up a first session.

S602: After receiving the session setup request message, the AMF network element selects an SMF network element, and sends a session identifier of the first session, a network name, and session management information to the SMF network element.

S603: After receiving the session identifier of the first session, the network name, and the session management information, the SMF network element selects a UPF network element, and sends a user plane connection setup request message to the UPF network element, to set up a connection between the SMF network element and the UPF network element. Correspondingly, the UPF network element receives the user plane connection setup request message from the SMF network element.

S604: After receiving the user plane connection setup request message, the UPF network element sends a user plane connection setup response message to the SMF network element. Correspondingly, the SMF network element receives the user plane connection setup response message from the UPF network element.

Steps S601to S604are the same as steps S501to S504inFIG. 5, and details are not described herein again.

S605: After receiving the session setup response message, the SMF network element sends the session identifier of the first session and the network name that are carried in step S602to the AMF network element.

Optionally, the SMF network element sends SM information such as an N2 SM information to the AMF network element. The N2 SM information includes the session identifier and the network name. A difference between step S605and step S506inFIG. 5lies in that, in an example inFIG. 5, the SMF network element sends the association between the session identifier and the network name of the LADN to the first RAN device only after knowing that the terminal device accesses the LADN by using the first session. However, in an example inFIG. 6, the SMF network element neither determines nor knows whether the terminal device accesses the LADN by using the first session, and the SMF network element may directly send the received session identifier and network name to the first RAN device, and then the first RAN device determines whether the network name is corresponding to the LADN.

S606: After receiving the session identifier and the network name, the AMF network element sends a session request message to the first RAN device. The session request message includes the session identifier and the network name.

For example, the session request message may be an N2 session request message.

S607: After receiving the session request message, the first RAN device determines that the terminal device accesses the LADN by using the first session.

For example, the first RAN device obtains capability information of the first RAN device in a manner similar to steps S401and S402, to know the network name corresponding to the LADN. The first RAN device determines, based on the session identifier of the first session and the network name that are obtained in step S606, whether the terminal device accesses the LADN by using the first session. For example, if the obtained network name corresponding to the LADN includes the network name carried in step S606, the first RAN device determines that the terminal device accesses the LADN by using the first session.

Optionally, in S608, after determining that the terminal device accesses the LADN by using the first session, the first RAN device stores the association between the session identifier of the first session and the network name of the LADN. The association is used to select a handover target for the terminal device when a mobile handover is performed for the terminal device.

In this way, the first RAN device determines the association between the session identifier of the first session and the network name of the LADN from the SMF network element. After step S608, for performing subsequent steps of a session setup process, refer to the prior art. Details are not described herein again.

FIG. 7shows a handover method according to an embodiment of this application. As shown inFIG. 7, the method may include the following steps.

S701: A first RAN device sends measurement control information to a terminal device, to obtain a measurement report of the terminal device.

Optionally, the measurement control information may include at least one of an object that needs to be measured, a cell list, or a reporting mode.

S702: The terminal device performs measurement based on the received measurement control information, and then sends the measurement report to the first RAN device. The measurement report includes a candidate RAN device and a cell identifier within a coverage area of each RAN device in the candidate RAN devices.

The candidate RAN device is a RAN device that can be accessed by the terminal device. A quantity of candidate RAN devices is not limited in this application, and at least one RAN device in the candidate RAN devices supports an LADN service.

S703: The first RAN device makes a handover decision based on the received measurement report.

For example, after the first RAN device decides, based on the measurement report, to perform a handover for terminal device, the first RAN device searches, based on capability information of another RAN device obtained in a process of setting up a connection to the another RAN device, for whether there is a RAN device (for example, the second RAN device) supporting a LADN in the candidate RAN devices. In this way, the first RAN device selects the second RAN device as a handover target. Therefore, after accessing the second RAN device, a mobile terminal can access the LADN service, thereby improving user experience.

Optionally, after the first RAN device decides, based on the measurement report, to perform a handover for terminal device, the first RAN device first determines that the terminal device accesses the LADN by using a first session. For example, the first RAN device may determine, based on the obtained association between the session identifier of the first session and the network name of the LADN in the process inFIG. 5orFIG. 6that the terminal device accesses the LADN by using the first session. The first RAN device determines whether there is a RAN device (for example, the second RAN device) whose capability information includes the network name in the candidate RAN devices. The first RAN device may obtain capability information of the RAN devices by performing steps S401to S406. If there is the RAN device whose capability information includes the network name in the candidate RAN devices, the first RAN device selects the RAN device as a handover target. Therefore, after the mobile terminal accesses the second RAN device, a service accessing a specific LADN is not interrupted or suspended, thereby further improving user experience.

Further, when a coverage area of the LADN supported by the RAN device is in a granularity of a cell, the first RAN device selects a cell that supports the LADN and that is of the RAN device as a target cell for the handover.

If there is no RAN device whose capability information includes the network name in the candidate RAN devices, a handover target may be selected from the candidate RAN devices with reference to the prior art.

For example, capability information of the candidate RAN devices stored in the first RAN device may be shown in the following Table 2.

As shown in the foregoing Table 2, the candidate RAN devices include a RAN1, a RAN2, a RAN3, and a RAN4. Identifiers of the RAN1, the RAN2, the RAN3, and the RAN4are respectively an ID1, an ID2, an ID3, and an ID4. The first RAN device stores capability information of the four candidate RAN devices. For example, the capability information is a DNN. Capability information of the RAN1includes a DNN1, indicating that the RAN1supports an LADN1corresponding to the DNN1. Capability information of the RAN2includes a DNN2and a cell identifier of a cell1, indicating that the LADN2uses a cell as a granularity and that the cell (cell1) of the RAN2supports an LADN corresponding to the DNN2. Capability information of the RAN3includes the DNN2and a DNN3, indicating that the RAN3separately supports the LADN2corresponding to the DNN2and an LADN3corresponding to the DNN3. In addition, because there is no capability information of the RAN4in the first RAN device, it may be considered that the RAN4does not support an LADN.

It is assumed that a network name corresponding to the first session of the terminal device is the DNN1. When a mobile handover is performed for the terminal device, the first RAN device selects, based on the obtained capability information, the RAN1whose capability information includes the DNN1as a handover target.

Alternatively, if a network name corresponding to the first session of the terminal device is the DNN2. When a mobile handover is performed for the terminal device, the first RAN device selects one RAN device as a handover target from the RAN2and the RAN3whose capability information includes the DNN2. Further, when selecting the RAN2as a handover target, the first RAN device may further select the cell1as a target cell for the handover.

Alternatively, if a network name corresponding to the first session of the terminal device is a DNN4. When a mobile handover is performed for the terminal device, there is no RAN device whose capability information includes the DNN4in the candidate RAN devices. In this case, the first RAN device preferentially selects the RAN3whose capability information includes the DNN2and the DNN3as a handover target. In this way, it can be ensured that after the mobile handover is performed for the terminal device, the terminal device can access the LADN2corresponding to the LADN2or the LADN3corresponding to the DNN3, thereby improving user experience.

Alternatively, it is assumed that the first session of the terminal device is not an LADN session. In this scenario, the first RAN device may select a handover target with reference to the scenario in which the network name corresponding to the first session is the DNN4. Details are not described herein again.

S704: The first RAN device sends a handover request to a target RAN (for example, the second RAN device).

S705: After receiving the handover request, the target RAN device performs handover processing such as parameter check and resource reservation. After the processing succeeds, the target RAN device sends a handover response message to the first RAN device.

In this way, a handover process from the first RAN device to the target RAN device is completed.

FIG. 8shows still another communication method according to an embodiment of this application.FIG. 8is described with reference toFIG. 5andFIG. 6. As shown inFIG. 8, the method may include the following steps.

S801: An SMF network element receives a session identifier of a first session and a network name from a terminal device.

The SMF may obtain the session identifier of the first session and the network name by using step S502inFIG. 5or step S602inFIG. 6. Details are not described herein again.

S803: After receiving the session identifier of the first session and the network name, the SMF network element sends session management information to the first RAN device. The session management information includes an association between the session identifier of the first session and the network name.

For step S803, refer to the description of step S506inFIG. 5or the description of S605inFIG. 6. Details are not described herein again.

Therefore, according to the method in the embodiment of this application, the first RAN device preferentially selects a RAN device supporting an LADN as a handover target, so that the terminal device can access the LADN by using a target RAN device, thereby improving user experience.

Optionally, before S803, the method may further include the following steps.

S802: After receiving the session identifier of the first session and the network name, the SMF network element determines that the terminal device accesses a local area data network LADN by using the first session.

For a specific process of determining, by the SMF network element, that the terminal device accesses the LADN by using the first session and a manner of obtaining, by the SMF network element, the network name corresponding to the LADN, refer to S505. Details are not described herein again.

Therefore, the first RAN device obtains the association between the session identifier of the first session and the network name, and when a mobile handover is performed for the terminal device, the first RAN device determines, based on the association, whether the terminal device has a session for accessing the LADN. When the terminal device has the session for accessing the LADN, the first RAN device selects a RAN device supporting the LADN as the handover target.

This application further provides a method for selecting a radio access network device. The method is applicable to a scenario of a non-3GPP access network. As shown inFIG. 9, the method may include the following steps.

S901: An access discovery network element sends access network information to a terminal device. Correspondingly, the terminal device receives the access network information from the access discovery network element. The access network information includes an association between an access network identifier and a network name of an LADN.

For example, the access discovery network element may be an access network discovery and selection function (ANDSF) network element in a 4th generation mobile communications system (4G), or may be a PCF network element (for example, the PCF network element207inFIG. 2) in a 5th generation mobile communications system (5G), or may be a network element that can provide access network information for a terminal device in a future communications system. This is not limited herein. There may be one or more access discovery network elements. A quantity of the access discovery network elements is not limited in this application either.

An access network identifier may be used to identify different access networks. For example, the access network identifier may be a service set identifier (SSID).

Optionally, the access network information further includes an access technology type of the access network. For example, the access technology type includes a wireless local area network (WLAN), a worldwide interoperability for microwave access network (WiMAX), or the like.

S902: After receiving the access network information, the terminal device obtains the association between the access network identifier and the network name of the LADN.

In this application, there may be one or more access discovery network elements. The terminal device may obtain one or a plurality of groups of associations between the access network identifier and the network name of the LADN. For example, in an implementation, the terminal device may obtain the plurality of groups of associations between the access network identifier and the network name of the LADN from one access discovery network element. In another implementation, the terminal device may obtain the plurality of groups of associations between the access network identifier and the network name of the LADN from a plurality of access discovery network elements. For example, the association between the access network identifier and the network name of the LADN obtained by the terminal device may be shown in the following Table 3.

As shown in Table 3, the terminal device obtains two groups of associations between the access network identifier and the network name of the LADN. For example, the access network identifier is an SSID. Identifiers of an access network1and an access network2are respectively an SSID1and an SSID2. Network names of an LADN1, an LADN2, and an LADN3are respectively a DNN1, a DNN2, and a DNN3. The association between the access network identifier and the network name of the LADN in Table 3 represents that an access network1corresponding to the SSID1supports the LADN1; and an access network2corresponding to the SSID2supports the LADN2and the LADN3.

S904: The terminal device accesses, based on the association between the access network identifier and the network name of the LADN in S902, an access network device corresponding to the access network identifier.

According to the embodiment of the present invention, when the terminal device moves and needs to reselect a non-3GPP access network, the terminal device sends, based on the obtained association between the access network identifier and a network name of the LADN, an access request to the access network device corresponding to the access network identifier. Because the access network device corresponding to the access network identifier supports the LADN, the terminal device can access an LADN service after the access network is changed, thereby improving user experience. The embodiment of the present invention may be applied to a scenario in which the terminal device does not access the LADN before the access network of the terminal device is changed, or may be applied to a scenario in which the terminal device accesses the LADN before the access network of the terminal device is changed for the terminal device.

Optionally, before step S904, the terminal device performs S903.

S903: The terminal device knows that the terminal device accesses the LADN by using a first session.

In a possible implementation, for a process in which the SMF network element knows that the terminal device accesses the LADN by using the first session, refer to steps S501to S505. Then, the SMF network element sends, to the terminal device by using the AMF network element and the RAN device, indication information used to instruct the terminal device to access the LADN by using the first session.

Optionally, if the SMF network element determines, in step S505, that a data network accessed by the terminal device by using the first session is not the LADN, the SMF network element does not need to send the network name to the terminal device. In another possible implementation, the terminal device may determine the LADN accessed by using the first session. For example, in a registration procedure, the terminal device obtains, from the AMF device, the network name corresponding to the LADN, and then performs matching the network name corresponding to the LADN with a network name of an LADN corresponding to the first session. If the network name corresponding to the LADN includes the network name of the LADN corresponding to the first session, or the network name corresponding to the LADN is the same as the network name of the LADN corresponding to the first session, the terminal device determines to access the LADN by using the first session.

Therefore, in step S904, when the terminal device accesses a specific LADN by using the first session, the terminal device may send, by knowing that the terminal device accesses the LADN by using the first session and based on the association between the access network identifier and the network name of the LADN that are obtained by the terminal device, a access request to a non-3GPP access network device that supports the specific LADN and that is corresponding to the access network identifier. Therefore, after the terminal device accesses the access network device, a service accessing the specific LADN is not interrupted, thereby further improving user experience.

For example, the terminal device knows, in step S903, that the network name of the LADN accessed by the terminal device by using the first session is the DNN1, and the terminal device obtains, in step S902, an association between the identifier SSID1and the DNN1, where the DNN1is corresponding to the LADN1. In this case, the terminal device selects and accesses an access network device, supporting the LADN1, whose identifier is the SSID1.

Therefore, based on the foregoing solution, in a scenario of the non-3GPP access network, the terminal device may access, by knowing a network name of a specific LADN that is accessed by the terminal device by using the first session and based on an obtained association between an identifier of a candidate access network that can be accessed and the network name of the LADN, an access network device supporting the specific LADN. Therefore, after the terminal device accesses the access network, a specific LADN service is not interrupted, thereby improving user experience. In the foregoing embodiments provided in this application, the solutions of the method for selecting the radio access network device provided in the embodiments of this application are separately described from a perspective of the network elements and from a perspective of interaction between the network elements. It may be understood that, to implement the foregoing functions, the network elements such as the radio access network device, the communications apparatus, or the terminal device include corresponding hardware structures and/or software modules for performing the functions. A person skilled in the art should easily be aware that, in combination with the examples described in the embodiments disclosed in this specification, units, and algorithms steps may be implemented by hardware or a combination of hardware and computer software in this application. Whether a function is performed by hardware or hardware driven by computer software depends on particular applications and design constraints of the technical solutions. A person skilled in the art may use different methods to implement the described functions for each particular application, but it should not be considered that the implementation goes beyond the scope of this application.

For example, when the foregoing network elements implement the corresponding functions by using the software modules, a radio access network device may include a receiving module1001and a sending module1003, as shown inFIG. 10A. Optionally, the radio access network device further includes a processing module1002. The radio access network device may be configured to perform operations of the first RAN device inFIG. 3toFIG. 8. For example, the receiving module1001is configured to receive capability information of a second RAN device from the second RAN device, where the capability information is used to indicate a local area data network LADN supported by the RAN device; and the sending module1003is configured to send a handover request message to the second RAN device.

Therefore, when a mobile handover is performed for a terminal device, the radio access network device may send, based on obtained capability information of a plurality of adjacent RAN devices, a handover request to the second RAN device supporting the LADN, so that a mobile terminal can access an LADN service after accessing the second RAN device, thereby improving user experience.

Optionally, the sending module1003is configured to send a connection setup request message to the second RAN device; and the receiving module is configured to receive a connection setup response message from the second RAN device, where the connection setup response message includes the capability information of the second RAN device.

Optionally, before the sending module1003sends the handover request message to the second RAN device, the processing module1002is configured to determine that a terminal device accesses the LADN by using a first session.

Optionally, the receiving module1001is further configured to receive an association between a session identifier of the first session and a first network name of the LADN from a session management function SMF network element; or the receiving module1001is further configured to receive a second network name from an SMF network element, and the processing module1002is further configured to determine that the second network name is corresponding to the LADN.

Therefore, when the terminal device accesses a specific LADN by using the first session, the first RAN device may send a handover request to a second RAN device supporting the specific LADN, so that the first session is not interrupted or suspended after a mobile terminal accesses the second RAN device. In this way, a service accessing the specific LADN is not interrupted or suspended, thereby further improving user experience.

In addition, the receiving module1001, the processing module1002, and the sending module1003in the radio access network device may further implement other operations or functions of the first RAN device in the foregoing methods. Details are not described herein again.

FIG. 10Bis another possible schematic structural diagram of a radio access network device in the foregoing embodiments. As shown inFIG. 10B, the radio access network device includes a transceiver1004and a processor1005. For example, the processor1005is configured to support the radio access network device in performing a corresponding function of the first RAN device in the foregoing method. The transceiver1004is configured to implement communication between the first RAN device and an access and mobility management function network element/another radio access network device (for example, a second RAN device). The radio access network device may further include a memory1006. The memory is configured to be coupled to the processor, and the memory stores a program instruction and data that are necessary for the radio access network device.

As shown inFIG. 11A, a radio access network device may include a receiving module1101and a sending module1103. Optionally, the radio access network device further includes a processing module1102. The radio access network device may be configured to perform operations of the second RAN device inFIG. 3,FIG. 4, andFIG. 7. For example, the receiving module1101is configured to receive capability information of the radio access network device from an AMF network element, where the capability information is used to indicate a local area data network LADN supported by the radio access network device; and the sending module1103is configured to send the capability information to a first RAN device.

Therefore, the radio access network device sends the capability information of the radio access network device obtained from the AMF network element to the first RAN device. After the first RAN device obtains the capability information, and when a handover target is selected for a terminal device, a RAN device (for example, the second radio access network device) supporting the LADN may be preferentially handed over the terminal device, so that the terminal device can access an LADN service after the handover, thereby improving user experience.

Optionally, the receiving module1101is configured to receive the capability information of the radio access network device from the AMF network element in a process of setting up a connection between the radio access network device and the AMF network element.

Optionally, the receiving module1101is configured to receive a connection setup request message from the first RAN device; and the sending module1103is configured to send a connection setup response message to the first RAN device, where the connection setup response message includes the capability information.

In addition, the receiving module1101, the processing module1102, and the sending module1103in the radio access network device may further implement other operations or functions of the second RAN device in the foregoing methods. Details are not described herein again.

FIG. 11Bis another possible schematic structural diagram of a radio access network device in the foregoing embodiments. As shown inFIG. 11B, the radio access network device includes a transceiver1104and a processor1105. For example, the processor1105is configured to support the radio access network device in performing a corresponding function of the second RAN device in the foregoing method. The transceiver1104is configured to implement communication between the second RAN device and an access and mobility management function network element/another radio access network device (for example, a first RAN device). The radio access network device may further include a memory1106. The memory is configured to be coupled to the processor, and the memory stores a program instruction and data that are necessary for the radio access network device.

As shown inFIG. 12A, a communications apparatus may include a receiving module1201and a sending module1203. Optionally, the communications apparatus further includes a processing module1202. The communications apparatus may be configured to perform operations of the AMF network element inFIG. 4. For example, the receiving module1201is configured to receive a connection setup request message from a RAN device; and the sending module1203is configured to send capability information of the RAN device to the RAN device, where the capability information is used to indicate an LADN supported by the RAN device.

Therefore, the communications apparatus completes setup of a connection to the RAN device, and sends the capability information of the RAN device to the RAN device. The capability information may be used in a scenario in which a handover is performed for a terminal device. In addition, the capability information is further applicable to another communication application scenario.

Optionally, the capability information includes at least one of a data network name DNN, an internet protocol IP address or prefix, or IP routing information of the LADN. Therefore, the capability information of the RAN device may be used to represent the LADN supported by the RAN device.

Optionally, the capability information includes a correspondence between a cell identifier or a tracking area identifier and at least one of a DNN, an IP address or prefix, or IP routing information of the LADN.

In addition, the receiving module1201, the processing module1202, and the sending module1203in the communications apparatus may further implement other operations or functions of the AMF in the foregoing methods. Details are not described herein again.

FIG. 12Bis another possible schematic structural diagram of a communications apparatus in the foregoing embodiments. As shown inFIG. 12B, the communications apparatus includes a transceiver1204and a processor1205. For example, the processor1205is configured to support the communications apparatus in performing a corresponding function of the AMF network element in the foregoing method. The transceiver1204is configured to implement communication between the AMF network element and a terminal device/a radio access network device/a session management function network element. The communications apparatus may further include a memory1206. The memory is configured to be coupled to the processor, and the memory stores a program instruction and data that are necessary for the communications apparatus.

As shown inFIG. 13A, a communications apparatus may include a receiving module1301and a sending module1303. Optionally, the communications apparatus further includes a processing module1302. The communications apparatus may be configured to perform operations of the SMF network element inFIG. 5,FIG. 6, andFIG. 8. For example, the receiving module1301is configured to receive a session identifier of a first session and a network name from a terminal device; and the sending module1303is configured to send session management information to a radio access network RAN device, where the session management information includes an association between the session identifier and the network name.

Based on the foregoing solution, the first RAN device preferentially selects a RAN device supporting an LADN as a handover target, so that the terminal device can access the LADN by using a target RAN device, thereby improving user experience.

Optionally, the processing module1302is configured to determine that a terminal device accesses the LADN by using a first session. Based on the foregoing solution, when the terminal device accesses a specific LADN by using the first session, the first RAN device may send a handover request to a second RAN device supporting the specific LADN, so that the first session is not interrupted or suspended after a mobile terminal accesses the second RAN device. In this way, a service accessing the specific LADN is not interrupted or suspended, thereby further improving user experience.

Optionally, the processing module1302is configured to preconfigure the network name corresponding to the LADN; or the receiving module1301is configured to receive the network name corresponding to the LADN from an AMF network element; or the receiving module1301is further configured to receive the network name corresponding to the LADN from a PCF network element; or the receiving module1301is further configured to receive the network name corresponding to the LADN from a data management network element.

In addition, the receiving module1301, the processing module1302, and the sending module1303in the communications apparatus may further implement other operations or functions of the SMF in the foregoing methods. Details are not described herein again.

FIG. 13Bis another possible schematic structural diagram of a communications apparatus in the foregoing embodiments. As shown inFIG. 13B, the communications apparatus includes a transceiver1304and a processor1305. For example, the processor1305is configured to support the communications apparatus in performing a corresponding function of the SMF network element in the foregoing method. The transceiver1304is configured to implement communication between the SMF network element and a terminal device/a radio access network device/an access and mobility management function network element. The communications apparatus may further include a memory1306. The memory is configured to be coupled to the processor, and the memory stores a program instruction and data that are necessary for the communications apparatus.

As shown inFIG. 14A, a terminal device may include a receiving module1401and a processing module1402. Optionally, the terminal device further includes a sending module1403. The terminal device may be configured to perform an operation of the terminal device inFIG. 9. For example, the receiving module1401is configured to receive an association between an access network identifier and an LADN from an access network discovery network element (for example, an access network discovery and selection function network element in the 4G, or a PCF network element in the 5G); and the processing module1402is configured to access, based on the association between the access network identifier and the LADN, an access network corresponding to the access network identifier.

Based on the foregoing solution, when the terminal device moves and needs to reselect a non-3GPP access network, the terminal device sends, based on the obtained association between the access network identifier and a network name of the LADN, an access request to the access network device corresponding to the access network identifier. Because the access network device corresponding to the access network identifier supports the LADN, the terminal device can access an LADN service after the access network is changed, thereby improving user experience.

Optionally, before the terminal device accesses, based on the association between the access network identifier and the LADN, an access network corresponding to the access network identifier, the processing module1402is configured to determine that the terminal device accesses the LADN by using a first session. Therefore, in a scenario of the non-3GPP access network, the terminal device may access, by knowing a network name of a specific LADN that is accessed by the terminal device by using the first session and based on an obtained association between an identifier of a candidate access network that can be accessed and the network name of the LADN, an access network device supporting the specific LADN. Therefore, after an access network of the terminal device is changed, a service of the specific LADN is not interrupted, thereby improving user experience.

In addition, the receiving module1401, the processing module1402, and the sending module1403in the terminal device may further implement other operations or functions of the terminal device in the foregoing methods. Details are not described herein again.

FIG. 14Bis another possible schematic structural diagram of a terminal device in the foregoing embodiments. As shown inFIG. 14B, the terminal device includes a transceiver1404and a processor1405. For example, the processor1405is configured to support the terminal device in performing a corresponding function of the terminal device in the foregoing method. The transceiver1404is configured to implement communication between the terminal device and an access discovery network element. The terminal device may further include a memory1406. The memory is configured to be coupled to the processor, and the memory stores a program instruction and data that are necessary for the terminal device. It may be understood thatFIG. 10B,FIG. 11B,FIG. 12B,FIG. 13B, andFIG. 14Bshow merely simplified designs of the foregoing devices. In actual application, each of the foregoing devices may include any quantities of transmitters, receivers, processors, controllers, memories, communications units, and the like. All devices that can implement this application fall within the protection scope of this application.

The controller/processor configured to perform the radio access network device in this application may be a central processing unit (CPU), a 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 transistor logic device, a hardware component, or any combination thereof. The processor may implement or execute various example logical blocks, modules, and circuits described with reference to content disclosed in this application. Alternatively, the processor may be a combination of processors implementing a computing function, for example, a combination of one or more microprocessors, or a combination of the DSP and a microprocessor.

Method or algorithm steps described in combination with the content disclosed in this application may be implemented by hardware, or may be implemented by a processor by executing a software instruction. The software instruction may be formed by a corresponding software module. The software module may be located in a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a removable magnetic disk, a CD-ROM, or a storage medium of any other form known in the art. For example, a storage medium is coupled to a processor, so that the processor can read information from the storage medium or write information into the storage medium. Certainly, the storage medium may be a component of the processor. The processor and the storage medium may be located in the ASIC. In addition, the ASIC may be located in the radio access network device. Certainly, the processor and the storage medium may alternatively exist in the radio access network device as discrete components.

The objectives, technical solutions, and benefits of the present invention are further described in detail in the foregoing specific embodiments. It should be understood that the foregoing descriptions are merely specific embodiments of the present invention, but are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

The objectives, technical solutions, and benefits of the present invention are further described in detail in the foregoing specific embodiments. It should be understood that the foregoing descriptions are merely specific embodiments of the present invention, but are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.