CN118317452A - Communication method and device - Google Patents

Abstract

A communication method and device are used to solve the problem in the prior art that the user plane path is too long when a terminal accesses an isolated network (such as an IOPS network) and communicates with other terminals. In the present application, the communication method includes: a first terminal accesses the isolated network through a first access network device, wherein the isolated network is a network that provides communication services to the first terminal after the return line of the first access network device is disconnected; the first terminal establishes a LAN type session with a first core network in the isolated network, and the user plane data corresponding to the LAN type session is terminated in the isolated network; the first terminal communicates with the second terminal through the LAN type session, wherein the first terminal and the second terminal belong to the same LAN group.

Description

A communication method and device

Technical Field

The present application relates to the field of communication technology, and in particular to a communication method and device.

Background technique

The 3rd generation partnership project (3GPP) provides public safety cluster emergency communication application layer services, such as mission critical push to talk (MCPTT), mission critical video (MCVideo), mission critical data (MCData), etc. The terminal can access the data network (DN) where the public safety cluster emergency communication system is located through the mobile communication network. Usually, the mobile communication network includes a radio access network (RAN) and a macro core network, and the RAN communicates with the macro core network through a backhaul link.

Due to natural disasters and other reasons, the backhaul link between the RAN and the macro core network may be disconnected or in a limited state. In order to ensure the normal operation of the above services, the terminal can access the public safety cluster emergency communication system through the isolated E-UTRAN operation for public safety (IOPS) network. A local core network is deployed in the IOPS network, which can connect to one or more IOPS-enabled RANs to provide network coverage.

However, the way the terminal accesses the local core network is the same as the way it accesses the macro core network. When the terminal needs to communicate with other terminals, the user plane data still needs to be forwarded through N6, that is, there is a problem of too long user plane path.

Summary of the invention

The present application provides a communication method and apparatus for shortening a user plane path when a terminal accesses an isolated network (such as an IOPS network) and communicates with other terminals.

In a first aspect, the present application provides a communication method, which can be executed by a first terminal, or a module (such as a chip) in the first terminal. The following description is based on the execution of the first terminal as an example.

The communication method includes: a first terminal accesses an isolated network through a first access network device, wherein the isolated network is a network that provides communication services to the first terminal after the return line of the first access network device is disconnected; the first terminal establishes a local area network type session with a first core network in the isolated network, and user plane data corresponding to the local area network type session is terminated in the isolated network; the first terminal communicates with a second terminal through the local area network type session, wherein the first terminal and the second terminal belong to the same local area network group.

In the above technical solution, since the user plane data corresponding to the LAN type session is terminated in the isolated network, when the first terminal communicates with the second terminal, the user plane data can be transmitted directly through the isolated network, that is, it will not pass through the N6 port and does not need to be transmitted to the data network, which helps to shorten the user plane transmission path and eliminates the need to deploy a local data network in the isolated network, thereby reducing deployment costs.

In one possible implementation, when a first terminal communicates with a second terminal through a local area network type session, specifically, the first terminal may send call control request information through the local area network type session, wherein the call control request information includes a multicast address and an identifier of the second terminal; the first terminal receives response information from the second terminal to the call control request information through the local area network type session, wherein the response information includes a unicast address of the second terminal; and the first terminal transmits voice control information and/or media data with the second terminal through the local area network type session and according to the unicast address.

In the above technical solution, the control request information sent by the first terminal includes a multicast address. After obtaining the multicast address, the function in the first core network (such as the first user plane function) can forward the control request information to other terminals indicated by the multicast address according to the multicast address, without forwarding it to the data network via the N6 port; further, when the first terminal transmits the voice control information and/or media data to the second terminal according to the unicast address of the second terminal, the function in the first core network (such as the first user plane function) can forward the voice control information and/or media data to the second terminal according to the unicast address of the second terminal, without forwarding it to the data network via the N6 port; thereby helping to shorten the transmission path of the user plane and reduce deployment costs.

In a possible implementation, there is a first session of LAN type between the first terminal and the first core network; there is a second session of LAN type between the second terminal and the first core network; the access network device in the isolated network used for the second terminal to access the isolated network is the second access network device, wherein the first access network device and the second access network device may be the same access network device, or two different access network devices. The anchor user plane function corresponding to the first session and the anchor user plane function corresponding to the second session may be the same user plane function, or two different user plane functions.

When the anchor user plane function corresponding to the first session and the anchor user plane function corresponding to the second session are different user plane functions, the communication path between the first terminal and the second terminal is: the first access network device, the anchor user plane function corresponding to the first session in the first core network, the anchor user plane function corresponding to the second session in the first core network, and the second access network device. When the anchor user plane function corresponding to the first session and the anchor user plane function corresponding to the second session are the same user plane function, the communication path between the first terminal and the second terminal is: the first access network device, the anchor user plane function corresponding to the first session (or the second session) in the first core network, and the second access network device.

In the above technical solution, the communication path between the first terminal and the second terminal ends in the isolated network, that is, it does not need to go through the data network, which helps to shorten the transmission path of the user plane and reduce the deployment cost.

In one possible implementation, when the first terminal establishes a LAN type session with the first core network in the isolated network, specifically, the first terminal establishes a LAN type session with the first core network according to a user device routing selection policy that matches the isolated network. In one possible implementation, the first terminal also selects a user device routing selection policy based on one or more of the isolated network access capability information of the first terminal and an identifier of the first terminal that allows access to the isolated network. In this way, the first terminal can establish a LAN type session with the first core network according to the user device routing selection policy that matches the isolated network, and then the first terminal can communicate with the second terminal based on the established session.

In a possible implementation manner, the first terminal further receives a user equipment routing selection policy from a first policy control function of the first core network.

In the above technical solution, when the first terminal accesses the isolated network, that is, when data transmission is required through a LAN type session, a user equipment routing selection policy matching the isolated network is obtained to avoid unnecessary data transmission.

In one possible implementation, the first terminal also receives a user equipment routing selection policy from a second policy control function of a second core network in a normal network, where the normal network is a network that provides communication services to the first terminal by the first access network device before the backhaul line is disconnected. In one possible implementation, the first terminal also sends indication information to the second policy control function, where the indication information is used to indicate that the first terminal has the ability to access the isolated network. In one possible implementation, the indication information includes one or more of the isolated network access capability information of the first terminal and the identification of the first terminal that allows access to the isolated network.

In the above technical solution, the first terminal can obtain the user equipment routing selection strategy matching the isolated network when accessing the normal network, which helps the first terminal to establish a LAN type session with the first core network more quickly, and then communicate with the second terminal through the LAN type session.

In a second aspect, the present application provides a communication method, which can be executed by a first session management function.

The communication method includes: a first session management function receives a session establishment request from a first terminal, the first session management function is located in an isolated network, and the isolated network is a network that provides communication services to the first terminal after the backhaul line of a first access network device accessed by the first terminal is disconnected; the first session management function establishes a LAN type session for the first terminal according to a session policy and the session establishment request, the session policy is used to indicate the establishment of a LAN type session, and the user plane data corresponding to the LAN type session is terminated in the isolated network. In a possible implementation, the session policy includes a local session policy of the first session management function and/or a session policy of the first terminal. In a possible implementation, the first session management function also receives a session policy of the first terminal from the first terminal.

In the above technical solution, after receiving the session establishment request from the first terminal, the first session management function located in the isolated network establishes a LAN type session for the first terminal according to the session policy. Since the user plane data corresponding to the LAN type session is terminated in the isolated network, when the first terminal communicates with the second terminal based on the LAN type session, the user plane data can be directly transmitted through the isolated network, that is, it will not pass through the N6 port and does not need to be transmitted to the data network, which helps to shorten the user plane transmission path and eliminates the need to deploy a local data network in the isolated network, thereby reducing deployment costs.

In a third aspect, the present application provides a communication method, which can be executed by a policy control function.

The communication method includes: a policy control function generates a user equipment routing selection policy for a first terminal, the user equipment routing selection policy instructs the first terminal to establish a local area network type session with a first core network in an isolated network, and the isolated network is a network that provides communication services to the first terminal after a return line of a first access network device accessed by the first terminal is disconnected; the policy control function sends the user equipment routing selection policy to the first terminal.

In the above technical solution, the policy control function sends the user equipment routing selection policy to the first terminal. Accordingly, the first terminal can establish a LAN type session with the first core network according to the user equipment routing selection policy. Since the user plane data corresponding to the LAN type session is terminated in the isolated network, when the first terminal communicates with the second terminal, the user plane data can be transmitted directly through the isolated network, that is, it will not pass through the N6 port and does not need to be transmitted to the data network, which helps to shorten the user plane transmission path and eliminate the need to deploy a local data network in the isolated network, thereby reducing deployment costs.

In one possible implementation, the policy control function is a first policy control function in a first core network; when the policy control function generates a user equipment routing selection policy, specifically, the first policy control function generates a user equipment routing selection policy based on the subscription information of the first terminal and/or the local policy of the first policy control function.

In the above technical solution, the first policy control function sends the user device routing selection policy to the first terminal when the first terminal accesses the isolated network, so that the first terminal can obtain the user device routing selection policy when it needs to transmit data through a LAN type session, which helps to avoid unnecessary data transmission.

In one possible implementation, the policy control function is a second policy control function of a second core network in a normal network; when the policy control function generates a user equipment routing selection policy, specifically, the second policy control function generates a user equipment routing selection policy based on the subscription information of the first terminal and/or the indication information of the first terminal; the indication information is used to indicate that the first terminal has the ability to access the isolated network. In one possible implementation, the second policy control function also receives indication information from the first terminal. In one possible implementation, the indication information includes one or more of the isolated network access capability information of the first terminal and the identification of the first terminal allowing access to the isolated network.

In the above technical solution, the second policy control function sends a user equipment routing selection policy to the first terminal when the first terminal accesses the normal network, which helps the first terminal to establish a LAN type session with the first core network more quickly, and then communicate with the second terminal through the LAN type session.

In a fourth aspect, an embodiment of the present application provides a communication device, which has the function of implementing the first terminal in the first aspect or any possible implementation of the first aspect, and the device can be a terminal or a chip included in the terminal. The communication device can also have the function of implementing the first session management function in the second aspect or any possible implementation of the second aspect. The communication device can also have the function of implementing the policy control function in the third aspect or any possible implementation of the third aspect.

The functions of the above-mentioned communication device can be implemented by hardware, or by hardware executing corresponding software, and the hardware or software includes one or more modules or units or means corresponding to the above-mentioned functions.

In a possible implementation, the structure of the device includes a processing module and a transceiver module, wherein the processing module is configured to support the device to implement the corresponding function of the first terminal in the above-mentioned first aspect or any possible implementation of the first aspect, or to implement the corresponding function of the first session management function in the above-mentioned second aspect or any possible implementation of the second aspect, or to implement the corresponding function of the policy control function in the above-mentioned third aspect or any possible implementation of the third aspect. The transceiver module is used to support communication between the device and other communication devices, for example, when the device is a first terminal, it can be used to communicate with a second terminal. The communication device may also include a storage module, which is coupled to the processing module and stores program instructions and data necessary for the device. As an example, the processing module may be a processor, the communication module may be a transceiver, and the storage module may be a memory, and the memory may be integrated with the processor or may be set separately from the processor.

In another possible implementation, the structure of the device includes a processor and may also include a memory. The processor is coupled to the memory and can be used to execute computer program instructions stored in the memory so that the device executes the method in the first aspect or any possible implementation of the first aspect, or executes the method in the second aspect or any possible implementation of the second aspect, or executes the method in the third aspect or any possible implementation of the third aspect. Optionally, the device also includes a communication interface, and the processor is coupled to the communication interface. When the device is a network device or a terminal, the communication interface may be a transceiver or an input/output interface; when the device is a chip included in a network device or a chip included in a terminal, the communication interface may be an input/output interface of the chip. Optionally, the transceiver may be a transceiver circuit, and the input/output interface may be an input/output circuit.

In a fifth aspect, an embodiment of the present application provides a chip system, comprising: a processor, the processor being coupled to a memory, the memory being used to store programs or instructions, and when the program or instructions are executed by the processor, the chip system implements the method of the above-mentioned first aspect or any possible implementation of the first aspect, or implements the method of the above-mentioned second aspect or any possible implementation of the second aspect, or implements the above-mentioned third aspect or any possible implementation of the third aspect.

Optionally, the chip system also includes an interface circuit, which is used to interact with code instructions to the processor.

Optionally, there may be one or more processors in the chip system, and the processor may be implemented by hardware or software. When implemented by hardware, the processor may be a logic circuit, an integrated circuit, etc. When implemented by software, the processor may be a general-purpose processor implemented by reading software code stored in a memory.

Optionally, the memory in the chip system may be one or more. The memory may be integrated with the processor or may be separately provided with the processor. Exemplarily, the memory may be a non-transient processor, such as a read-only memory ROM, which may be integrated with the processor on the same chip or may be provided on different chips.

In a sixth aspect, an embodiment of the present application provides a computer-readable storage medium having a computer program or instructions stored thereon. When the computer program or instructions are executed, the computer executes the method in the first aspect or any possible implementation of the first aspect, or executes the method in the second aspect or any possible implementation of the second aspect, or executes the method in the third aspect or any possible implementation of the third aspect.

In the seventh aspect, an embodiment of the present application provides a computer program product. When a computer reads and executes the computer program product, the computer executes the method in the first aspect or any possible implementation of the first aspect, or executes the method in the second aspect or any possible implementation of the second aspect, or executes the method in the third aspect or any possible implementation of the third aspect.

In an eighth aspect, an embodiment of the present application provides a communication system, which includes a first terminal and a first session management function, wherein the first terminal is used to execute the method in the above-mentioned first aspect or any possible implementation of the first aspect, and the first session management function is used to execute the method in the above-mentioned second aspect or any possible implementation of the second aspect.

In the ninth aspect, an embodiment of the present application provides a communication system, which includes a first terminal and a policy control function, the first terminal is used to execute the method in the above-mentioned first aspect or any possible implementation of the first aspect, and the policy control function is used to execute the method in the above-mentioned third aspect or any possible implementation of the third aspect.

The technical effects that can be achieved in any of the fourth to ninth aspects mentioned above can refer to the description of the beneficial effects in the first to third aspects mentioned above, and will not be repeated here.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a communication system architecture;

FIG2 is a communication model between two UEs in a 5G virtual network group;

FIG3 is a schematic diagram of a process of a UE executing URSP;

FIG4 is a schematic diagram of an IOPS network architecture;

FIG5 is a schematic diagram of a process of a UE accessing a local/macro core network in IOPS mode;

FIG6 is a flow chart of a method for communication between UEs;

FIG7 is a schematic diagram of the architecture of a communication system provided by the present application;

FIG8 is a communication model between two UEs in a virtual network group provided by the present application;

FIG9 is a flow chart of a communication method provided by the present application;

FIG10 is a flow chart of another communication method provided by the present application;

FIG11 is a flow chart of another communication method provided by the present application;

FIG12 is a flow chart of a communication method in a first specific implementation scenario provided by the present application;

FIG13 is a flow chart of a communication method in a second specific implementation scenario provided by the present application;

FIG14 is a flow chart of a communication method in a third specific implementation scenario provided by the present application;

FIG15 is a schematic diagram of the structure of a communication device provided by the present application;

FIG16 is a schematic diagram of the structure of another communication device provided in the present application.

Detailed ways

For the convenience of description, the techniques and/or terms in this application are first explained as follows.

1. Fifth generation (5G) network architecture

FIG1 shows a network architecture of a 5G communication system defined by the 3rd generation partnership project (3GPP). The communication system includes: user equipment (UE), radio access network (RAN) equipment, access and mobility management function (AMF), session management function (SMF), user plane function (UPF), policy control function (PCF), unified data management function (UDM), application function (AF), network data analysis function (NWDAF) and data network (DN). Among them, each function or device can be connected through an interface, and the interface name shown in FIG1 is only an example, and the embodiment of the present application does not specifically limit this.

The following is a detailed description of some functions or devices in the communication system:

UE, which can also be called terminal equipment, terminal, mobile station (MS), mobile terminal (MT), etc., is a device that provides voice and/or data connectivity to users. For example, UE may include handheld devices, vehicle-mounted devices, etc. with wireless connection functions. At present, UE can specifically be: mobile phone, tablet computer, laptop computer, PDA, mobile internet device (MID), wearable device, virtual reality (VR) device, augmented reality (AR) device, wireless terminal in industrial control, wireless terminal in automatic driving, wireless terminal in self-driving, wireless terminal in remote medical surgery, wireless terminal in smart grid, wireless terminal in transportation safety, wireless terminal in smart city, wireless terminal in smart furniture, wireless terminal in smart office, wireless terminal in smart wear, wireless terminal in smart transportation or wireless terminal in smart home, etc. The embodiments of the present application do not limit the specific technology and specific device form adopted by the UE.

RAN, also known as RAN node (or device), is a device that provides wireless access services for UE and connects UE to the wireless network. At present, some examples of RAN nodes are: base station, transmission reception point (TRP), evolved Node B (eNB), next generation NodeB (gNB), radio network controller (RNC), Node B (NB), base station controller (BSC), base transceiver station (BTS), home base station (e.g., home evolved NodeB, or home Node B, HNB), base band unit (BBU), or wireless fidelity (Wifi) access point (AP). RAN node can also be a module or unit that completes part of the functions of a base station, for example, it can be a centralized unit (CU) or a distributed unit (DU). The CU here completes the functions of the base station's radio resource control protocol and packet data convergence protocol (PDCP), and can also complete the function of the service data adaptation protocol (SDAP); the DU completes the functions of the base station's radio link control layer and medium access control (MAC) layer, and can also complete part of the physical layer or all of the physical layer.

DN can be the internet, an IP multi-media service (IMS) network, a regional network (i.e., a local network, such as a mobile edge computing (MEC) network), etc. DN is the destination of the UE's protocol data unit (PDU) session access. DN includes an application server (AS), which provides business services for the UE.

AMF, SMF, PCF, UPF, UDM, AF and NWDAF are all functions in the core network. The core network is used to connect the UE to the DN that can realize the UE's services. The following describes the functions in the core network:

AMF can be used to manage UE access control and mobility, and can be responsible for UE registration, mobility management, UE network registration, tracking area update, reachability detection, SMF selection, mobile state transition management, etc.

SMF can be used to manage UE sessions (including session establishment, modification and release), UPF selection and reselection, UE Internet protocol (IP) address allocation, quality of service (QoS) control, etc.

PCF can be used to manage UE policies, including both mobility-related policies and PDU session-related policies, such as QoS policies and charging policies.

UPF can be responsible for processing UE messages, such as forwarding and billing of user data.

UDM stores UE’s subscription data and UE-related registration information, etc.

AF is mainly used to influence service flow routing, access network capability exposure, and policy control.

NWDAF can be used for data analysis, such as analyzing the background traffic transmission data analysis results of the UE.

In addition, the core network also includes a network repository function (NRF) network element, which is mainly used to provide registration and discovery of network functions, or for registration and discovery of services provided by network functions.

The above functions in the core network can also be called functional entities or network elements, which can be network elements implemented on dedicated hardware, software instances running on dedicated hardware, or instances of virtualized functions on an appropriate platform. For example, the above virtualization platform can be a cloud platform.

It should be noted that the communication system is not limited to the functions shown in Figure 1, and may also include other functions not shown in Figure 1, which are not listed here. The embodiment of the present application does not limit the distribution form of each function in the core network.

It should also be noted that the communication system shown in Figure 1 is a 5G network architecture and does not constitute a limitation on the 5G network. Optionally, the method of the embodiment of the present application is also applicable to various future communication systems, such as 6G or other communication networks. It should be understood that the names of all functions in this application are only examples. In future communications, such as 6G, they can also be called other names, or in future communications, such as 6G, the functions involved in this application can also be replaced by other entities or devices with the same functions, and this application does not limit this.

For the convenience of description, this application takes UE, RAN, AMF, SMF, PCF, UPF, UDM, and DN as examples.

2. 5G local area network (LAN)

5G LAN is a service provided by 5G networks, which is mainly used in scenarios such as home communications, corporate offices, factory manufacturing, Internet of Vehicles, power grid transformation, and public security agencies.

5G virtual network group (5G VN group) refers to a collection of UEs that use 5G LAN type dedicated communications. 5G LAN can provide IP type or non-IP type (such as Ethernet type) private communications for multiple UEs in the 5G VN group. The 5G VN group has a unique 5G VN group identification (5G VN group identification, 5G VN group ID). The UE in the 5G VN group has a unique generic public subscription identity (GPSI) identifier. The 5G VN group and the combination of "data network name (data network name, DNN) + single network slice selection assistance information (single network slice selection assistance information, S-NSSAI)" are mapped one to one, and each UE in the 5G VN group has a contract for 5G LAN services.

For example, based on 5G LAN, UEs in a factory form a 5G VN group, and different UEs can send Ethernet packets to each other; or, UEs (such as mobile phones, computers or laptops, etc.) of employees in a department of an enterprise form a 5G VN group, and different UEs can send IP packets to each other. 5G LAN can provide broadcast data forwarding for UEs in the 5G VN group. For example, 5G LAN can forward broadcast messages of UEs in a 5G VN group to other UEs in the 5G VN group.

In a 5G VN group, the communication model between two UEs (referred to as UE1 and UE2) can be in three modes:

Mode 1, as shown in Figure 2 (a), the communication between UE1 and UE2 is through the following devices: RAN1 accessed by UE1, intermediate UPF (I-UPF) 1 corresponding to UE1, switch in DN network, I-UPF2 corresponding to UE2, RAN2 accessed by UE2. Among them, the interface between I-UPF and switch is N6. It can also be understood that the switch realizes 5GLAN communication between UE1 and UE2.

Mode 2, as shown in Figure 2 (b), the communication between UE1 and UE2 is through the following devices: RAN1 accessed by UE1, I-UPF1 corresponding to UE1, PDU session anchor (PSA) 1 corresponding to UE1, PSA2 corresponding to UE2, and RAN2 accessed by UE2. Among them, the interface between I-UPF and PSA is N9, and the interface between the two PSAs is N19. It can also be understood that the two PSAs are used to realize 5G LAN communication between UE1 and UE2.

Mode 3, as shown in (c) of Figure 2, UE1 and UE2 communicate via the following devices: RAN1 accessed by UE1, I-UPF1 corresponding to UE1, public PSA of UE1 and UE2, RAN2 accessed by UE2. It can also be understood that one PSA is used to implement 5G LAN communication between UE1 and UE2.

3. UE route selection policy (URSP)

The UE selects a suitable PDU session for the UE's uplink service flow according to the URSP. That is, some uplink services of the UE have certain requirements on the DNN, S-NSSAI, session service continuity mode (SSC mode) and the like of the PDU session used.

The UE may trigger the establishment or modification of a PDU session during the execution of the URSP. For example, when the UE determines that there is currently no PDU session that meets the requirements, the UE will initiate the PDU session establishment process; when the UE determines that there is currently a PDU session that meets the requirements, it may directly use the existing PDU session. In conjunction with the example in Figure 3, when the UE is preparing to send data packets of application A, it determines that application A's requirements for the PDU session to be used are DNN1, S-NSSAI-a, and SSC2. Then the UE selects PDU session 2 from multiple PDU sessions as the PDU session for application A to transmit data packets.

Specifically, the URSP includes one or more URSP rules, and a URSP rule mainly includes two parts: a traffic descriptor and a route selection descriptor (RSD). The traffic descriptor includes the names or identifiers of multiple applications, and the RSD includes the NSSAI corresponding to each application, that is, the NSSAI that is not included in the traffic descriptor and can be used by the application. The URSP can refer to Table 1, the URSP rule can refer to Table 2, and the RSD can refer to Table 3.

Table 1

Table 2

table 3

Based on the above technical and/or terminological explanations, the present application is further described below in conjunction with the accompanying drawings.

The isolated E-UTRAN operation for public safety (IOPS) network refers to the ability to provide certain communication capabilities for UEs through the IOPS-enabled RAN when the backhaul link between the RAN and the macro core network is disconnected or in a restricted state (the disconnection of the backhaul link is used as an example below). Among them, the IOPS network can be applied to the public safety cluster emergency communication system. The application layer services provided by the public safety cluster emergency communication system include mission critical push to talk (MCPTT), mission critical video (MCVideo), mission critical data (MCData), future railway mobile communication system (FRMCS), etc.

As shown in Figure 4, it is a schematic diagram of the architecture of an IOPS network. As shown in Figure 4, a local core network and one or more IOPS-enabled RANs are deployed in the IOPS network (RAN1 to RAN3 are shown as examples in Figure 4, and the number of RANs in Figure 4 does not constitute a limitation to the present application). Among them, the local core network can be considered as a miniaturized core network, which includes basic network functions in a conventional core network (such as AMF, SMF, UDM). Optionally, the local core network also includes PCF, etc. Furthermore, the IOPS network also includes a local mission critical (MC) system. The local MC system is specifically a simplified public safety emergency system. The local MC system can provide UEs with services such as voice and data based on the IOPS network. The local MC system can also be called an IOPS MC system.

In conjunction with the schematic diagram of the IOPS network architecture in FIG4 , FIG5 is a schematic diagram of a process of an IOPS-enabled UE accessing a local/macro core network (ie, a normal network) in IOPS mode.

Among them, step 501 to step 504 is the IOPS startup process; step 505 to step 507 is the local core network access process; step 508 to step 513 is the normal network recovery process.

Step 501: The UE registers a mission-critical service with the macro core network, wherein the mission-critical service is, for example, an MCPPT service, an MCVideo service, an MCData service, or an FRMCS service.

Step 502: RAN detects that the backhaul link between RAN and the macro core network is disconnected.

Step 503: RAN activates the local core network and establishes an N2 connection with the local core network.

Step 504: RAN broadcasts the IOPS PLMN ID.

Step 505: After detecting the IOPS PLMN ID broadcasted by the RAN, the UE selects the IOPS PLMN ID.

Step 506: The UE registers with the local core network and establishes a PDU session with the local core network.

Step 507: The UE accesses the public safety service in the local core network.

Step 508: RAN detects that the backhaul link is restored.

Step 509: RAN disconnects the N2 connection with the local core network and deactivates the local core network.

Step 510: RAN establishes an N2 connection with the macro core network.

Step 511, RAN broadcasts a normal PLMN ID.

Step 512: After the UE detects the normal PLMN ID broadcasted by the RAN, it selects the normal PLMN ID.

Step 513: The UE registers with the macro core network and establishes a PDU session with the macro core network.

Furthermore, when UE1 and UE2 access the same local core network, the communication method between UE1 and UE2 may refer to the process exemplarily shown in FIG. 6 .

Step 601, UE1 connects to the local MC system and completes secure authentication and authorization.

Step 602, UE1 sends IOPS discovery information to the local MC system, and accordingly, the local MC system receives the IOPS discovery information from UE1. The IOPS discovery message includes the IP unicast address of UE1, information of the group of interest (such as IP multicast address), and the like.

Step 603: The local MC system stores information such as the IP unicast address of UE1 and information of the group of interest.

Step 604: The local MC system sends the identifiers of other groups or the identifiers of other UEs to UE1. Correspondingly, UE1 receives the identifiers of other groups or the identifiers of other UEs from the local MC system.

Step 605: UE1 sends a call control request message to UE2 via the local MC system. Correspondingly, UE2 receives the call control request message from UE1 via the local MC system. The call control request message includes the identifier of the group to which UE2 belongs (i.e., group call) or the identifier of UE2 (i.e., single call).

Specifically, when UE1 sends a call control request message to the local MC system, the destination address (or destination IP address) of the call control request message is the IP address of the local MC system, so that the local MC system can receive the call control request message from UE1. Furthermore, when the local MC system sends a call control request message to UE2, the destination address of the call control request message is set to the IP multicast address, and accordingly, the UE (including UE2) connected to the local MC system can receive the call control request message from the local MC system.

Step 606: UE2 sends response information to UE1 via the local MC system. Correspondingly, UE1 receives response information from UE2 via the local MC system.

In a specific implementation, when the call control request information includes the identifier of the group to which UE2 belongs, the UEs in the group (including UE2) send response information to the local MC system, wherein the response information sent by each UE includes the IP unicast address of the UE. It can be understood that UEs in other groups can also receive the call control request information, and then determine that there is no need to send response information to UE1 based on the identifier of the group in the call control request information.

When the call control request information includes the identifier of UE2, UE2 sends a response message to the local MC system, wherein the response message includes the IP unicast address of UE2. It can be understood that other UEs belonging to the same group as UE2, or UEs in other groups, can also receive the call control request information, and then determine that there is no need to send a response message to UE1 based on the identifier of UE2 in the call control request information.

The destination address of the response information sent by UE2 to the local MC system is the IP address of the local MC system; the destination address of the response information sent by the local MC system to UE1 is the IP unicast address of UE1.

Step 607: UE1 sends the speech right control information to UE2 through the local MC system. Correspondingly, UE2 receives the speech right control information from UE1 through the local MC system.

The destination address of the speech right control information sent by UE1 to the local MC system is the IP address of the local MC system; the destination address of the speech right control information sent by the local MC system to UE2 is the IP unicast address of UE2.

Step 608: UE1 sends media data to UE2 via the local MC system. Correspondingly, UE2 receives media data from UE1 via the local MC system.

The destination address of media data sent by UE1 to the local MC system is the IP address of the local MC system; the destination address of media data sent by the local MC system to UE2 is the IP unicast address of UE2.

Based on the above-mentioned embodiment related to FIG. 6, it can be known that when UE1 communicates with UE2, the user plane data needs to be forwarded via the MC system. Specifically, the transmission path of the user plane data is In this way, there is a problem that the user plane path is too long.

When two UEs accessed to the local core network need to perform user plane data transmission, in order to shorten the user plane transmission path between the two UEs, as shown in FIG7 , a communication system exemplarily provided in the present application is shown, and the communication system includes a macro MC system, a macro core network, a local core network, one or more RANs (RAN1 and RAN2 are exemplarily shown in FIG7 , and the number of RANs in FIG7 does not constitute a limitation on the present application), and one or more UEs (UE1 and UE2 are exemplarily shown in FIG7 , and the number of UEs in FIG7 does not constitute a limitation on the present application).

Among them, UE1 accesses RAN1, and RAN1 is connected to the macro core network in a normal state. When the backhaul link between RAN1 and the macro core network is disconnected, RAN1 establishes a connection with the local core network, and accordingly, UE1 accesses the local core network. UE1 accesses RAN2, and RAN2 is connected to the macro core network in a normal state. When the backhaul link between RAN2 and the macro core network is disconnected, RAN2 establishes a connection with the local core network, and accordingly, UE2 accesses the local core network.

Furthermore, the PDU session between UE1 and the local core network and the PDU session between UE2 and the local core network are both local area network types (in the case of 5G, the type of the PDU session can specifically be a 5G local area network (5G LAN) type), wherein the user plane data corresponding to the local area network type PDU session is terminated in the local core network. The specific implementation method or explanation can be found in the description in the relevant embodiment of Figure 9 below.

When UE1 needs to communicate with UE2, the data of the communication can be forwarded via the UPF in the local core network without passing through the server in the local MC system. The transmission path (ie, user plane path) of the communication data between UE1 and UE2 can be seen as the dotted line in FIG7 .

Further, based on whether the RAN accessed by UE1 and UE2 is the same RAN, and whether the user plane anchor point (referred to as anchor point UPF) corresponding to the network layer session (such as PDU session) used for communication between UE1 and UE2 is the same, three possible communication models are provided as shown in FIG8. Among them, the transmission of user plane data between any two devices is based on the IP protocol.

Mode 1, as shown in (a) of FIG8 , UE1 and UE2 access the same RAN (denoted as RAN1), and the user plane anchor point corresponding to the network layer session used for communication between UE1 and UE2 is the same anchor point UPF (denoted as UPF1). Accordingly, the transmission path of the data communicated between UE1 and UE2 is:

Mode 2, as shown in (b) of FIG8 , UE1 and UE2 access different RANs, wherein UE1 accesses RAN1 and UE2 accesses RAN2, and the user plane anchor point corresponding to the network layer session used for communication between UE1 and UE2 is the same anchor point UPF (denoted as UPF1). Accordingly, the transmission path of the data communicated between UE1 and UE2 is:

Mode 3, as shown in (c) of FIG8 , UE1 and UE2 access different RANs, wherein UE1 accesses RAN1, UE2 accesses RAN2, and the user plane anchor points corresponding to the network layer sessions used for communication between UE1 and UE2 are different UPFs, wherein the user plane anchor point corresponding to the network layer session used for communication by UE1 is UPF1, and the user plane anchor point corresponding to the network layer session used for communication by UE2 is UPF2. Accordingly, the transmission path of the data communicated between UE1 and UE2 is:

In combination with FIG. 7 and FIG. 8 , FIG. 9 is a flow chart of a communication method provided by the present application, which can be performed by a first UE and a second UE. The first UE can be UE1 in FIG. 7 or 8 , and the second UE can be UE2 in FIG. 7 or 8 ; or, the first UE can be UE2 in FIG. 7 or 8 , and the second UE can be UE1 in FIG. 7 or 8 . For the convenience of description, the following description is based on the example that the first UE is UE1 and the second UE is UE2.

Further, in the following embodiments, the local core network accessed when the backhaul line of the RAN is disconnected may be referred to as the first core network, and the macro core network accessed when the backhaul line of the RAN is in a normal state may be referred to as the second core network. Further, the SMF, AMF, UPF, PCF, and NRF in the first core network may be referred to as the first SMF, the first AMF, the first UPF, the first PCF, and the first NRF, respectively, and the SMF, AMF, UPF, and PCF in the second core network may be referred to as the second SMF, the second AMF, the second UPF, and the second PCF, respectively.

Step 901: UE1 accesses an isolated network through RAN1.

It can be understood that when UE1 accesses RAN1, when the backhaul line between RAN1 and the macro core network is in a normal state, RAN1 and the macro core network can form a normal network, and the normal network can provide communication services for UE1; after the backhaul line between RAN1 and the macro core network is disconnected, RAN1 and the local core network can form an isolated network, and the isolated network can provide communication services for UE1.

Among them, the isolated network can be used to provide communication services for mission-critical services to UE1, wherein the critical tasks include MCPTT, MCVideo, MCData, FRMCS, etc. A mission-critical client (MC client) can be installed in UE1, so that critical tasks can be performed based on the isolated network. For example, if an MCPTT client is installed in UE1, when UE1 is connected to the isolated network, it can execute language services such as MCPTT single call, MCPTT group call, etc. Examples of isolated networks are IOPS networks, isolated networks based on 5G single stations, and isolated networks supported by 5G isolated base stations.

In one possible way, after RAN1 detects that the backhaul line between RAN1 and the macro core network is disconnected, RAN1 activates the isolation function and activates the N2 connection with the local core network. RAN1 broadcasts the identifier of the isolated network (such as IOPS PLMNID, 5G IOPS PLMN ID, or an identifier of an equivalent function). Optionally, RAN1 can carry the identifier of the isolated network in a system message. Correspondingly, after UE1 receives the identifier of the isolated network broadcast by RAN1, it attaches to the cell of the isolated network of RAN1 (the cell may be the same as or different from the cell in normal mode) according to the identifier of the isolated network, and further registers with the local core network, that is, accesses the isolated network.

In one possible way, UE1 is pre-configured with the identifier of the isolated network that it is allowed to access. After receiving the identifier of the isolated network broadcast by RAN1, if UE1 determines that the received identifier of the isolated network is included in the identifier of the isolated network that UE1 is allowed to access, UE1 can register with the local core network based on the received identifier of the isolated network. Alternatively, in another possible way, after UE1 receives the identifier of the isolated network broadcast by RAN1, the relevant information of the isolated network can be displayed on the user interface of UE1. Accordingly, the user using UE1 can choose whether to access the isolated network on the user interface of UE1. After UE1 obtains the instruction issued by the user to access the isolated network, it can further register with the local core network based on the identifier of the isolated network.

Optionally, UE1 can register with the isolated network according to the detected identifier of the isolated network broadcast by RAN1, and start the application logic function based on the isolated network LAN communication. Among them, the application logic function based on the isolated network LAN communication is expressed as: a communication data exchange between terminals (or application clients) that participate in the communication without the participation of a central application server is routed and forwarded using a LAN type session within the isolated network, and the application logic function based on the isolated network LAN communication can also be called an application logic function based on IP communication. Among them, UE1 starts the application logic function based on the isolated network LAN communication, which can be specifically that the application client on the UE1 (such as MCPTT client, MCVideo client, MCData client, FRMCS client, etc.) starts the application logic function based on the isolated network LAN communication. After UE1 starts the application logic function based on the isolated network LAN communication, UE1 can carry the application layer data on IP when transmitting application layer data (including application layer control signaling, application layer user plane control signaling, application layer user plane data).

Step 902: UE1 establishes a local area network type PDU session with the first core network in the isolated network.

Among them, the user plane data corresponding to the LAN type PDU session is terminated in the isolated network, that is, the user plane data of UE1 can be forwarded within the isolated network, and will not be forwarded to the external data network through the interface between the anchor point UPF and the data network (such as the N6 port).

Two possible implementations of establishing a local area network type PDU session between UE1 and the first core network are provided as follows:

Implementation method 1: The first SMF establishes a LAN type PDU session for UE1 based on a session policy, wherein the session policy may be a local session policy of the first SMF, or may be obtained by the first SMF from UE1 or PCF.

(1) When the session policy is obtained by the first SMF from the PCF:

The session policy can be used to indicate that all PDU sessions established by the first SMF for the DNN (or DNN+S-NSSI) corresponding to the critical tasks are LAN type PDU sessions.

In a specific implementation, when UE1 sends a PDU session establishment/modification request to the first SMF, the PDU session establishment/modification request carries the DNN (or DNN+S-NSSI) corresponding to the critical task, so that the first SMF establishes a LAN type PDU session for UE1 based on the DNN (or DNN+S-NSSI) corresponding to the critical task and the session policy.

Optionally, the PDU session establishment/modification request may also carry a packet filtering rule (IP packetfilter), where the packet filtering rule includes "the target address is an IP multicast address". The first SMF establishes a LAN type PDU session for UE1 based on the DNN (or DNN+S-NSSI) corresponding to the key task, the packet filtering rule, and the session policy.

Optionally, the session policy may be generated by the first PCF according to the contract information of UE1, wherein the contract information of UE1 is obtained by the first PCF from the first UDM. The contract information of UE1 includes the contract of the LAN service. Exemplarily, the contract information of UE1 includes one or more of the following: 1) The DNN (or DNN+S-NSSI) corresponding to the critical task is associated with the PDU session of the LAN type; 2) The application identifier of the critical task is associated with the PDU session of the LAN type; 3) The DNN (or DNN+S-NSSI) corresponding to the critical task and the application identifier of the critical task are associated with the PDU session of the LAN type. Optionally, the session policy may be generated by the first PCF according to the contract information of UE1 after RAN1 activates the first core network, and configured to the first SMF.

(2) When the session policy is obtained by the first SMF from UE1:

The session policy is used to indicate that all PDU sessions established by the first SMF for UE1 are LAN-type PDU sessions. It can be understood that after UE1 accesses the isolated network through RAN1, it determines that a LAN-type PDU session needs to be established, so the session policy is sent to the first SMF through RAN1 to indicate that the first SMF establishes a LAN-type PDU session for UE1. Optionally, the session policy can be included in the PDU session establishment request, or sent as a separate message by UE1 to the first SMF.

(3) When the session policy is the local session policy of the first SMF:

The session policy is used to indicate that the PDU sessions established by the first SMF for UE1 are all LAN type PDU sessions. Exemplarily, the session policy indicates that the first SMF establishes PDU sessions of the type of LAN type for all UEs, wherein UE1 belongs to any UE among all the UEs.

When the first SMF establishes a LAN type PDU session for UE1, specifically, the first SMF sends an N4 message to the first UPF corresponding to UE1 (referred to as anchor UPF1), so that the first SMF and anchor UPF1 establish an N4 session that complies with the N4 message, wherein the N4 message is used to instruct anchor UPF1 to comply with the routing and forwarding rules of the LAN type, that is, anchor UPF1 can perform user plane routing locally without routing to the server in the data network domain. Optionally, the routing and forwarding rules are used to instruct anchor UPF1 that when receiving user plane data whose source address is the unicast address of UE1 (i.e., from UE1) and whose destination address is the IP multicast address, if the anchor UPF corresponding to the UE with the IP multicast address is also anchor UPF1, then anchor UPF1 sends the user plane data to the RAN accessed by the other UE; if the UE with the IP multicast address corresponds to other anchor UPF, then anchor UPF1 sends the user plane data to the anchor UPF corresponding to the other UE. Furthermore, if there are multiple first UPFs in the first core network, the first SMF needs to establish group-level N4 sessions with the multiple first UPFs respectively, and establish an N19 connection between every two first UPFs in the multiple first UPFs for LAN type user plane routing.

Optionally, after establishing a LAN-type PDU session for UE1, the first SMF may send a completion indication to UE1. The completion indication is used to inform UE1 that a LAN-type session already exists with the first core network. UE1 can transmit data through the LAN-type session with other UEs (such as UE2, see the description in the following embodiments for details) that also have LAN-type sessions with the first core network.

In addition, the first SMF can also establish a PDU session in the prior art for UE1, and then UE1 can also send a PDU session modification request to the first SMF, and the PDU session modification request provides a packet filtering rule (IP packet filter), and the packet filtering rule further includes "the target address is an IP multicast address". The first SMF can send an N4 message to the anchor UPF1 according to the obtained packet filtering rule, and the N4 message is used to update the user plane routing rule of the anchor UPF1. For example, the updated routing forwarding rule of the anchor UPF1 is used to indicate that when the anchor UPF1 receives user plane data whose source address is the unicast address of UE1 and the destination address is the IP multicast address, if the anchor UPF corresponding to the UE with the IP multicast address is also the anchor UPF1, then the anchor UPF1 sends the user plane data to the RAN accessed by the other UE; if the UE with the IP multicast address corresponds to other anchor UPFs, then the anchor UPF1 sends the user plane data to the anchor UPF corresponding to the other UE. Optionally, when there are multiple first UPFs in the first core network, the first SMF can also update the user plane routing rules of other first UPFs, so that when the other first UPF receives user plane data from UE1 with the destination address being an IP multicast address, it can send the user plane data to the UE corresponding to the first UPF.

It should be pointed out that there may be multiple first SMFs in the first core network. When the first AMF receives a PDU session establishment request from UE1, the first AMF needs to select a first SMF from the multiple first SMFs. The selected first SMF is used to establish a LAN type PDU session for UE1.

Optionally, the first AMF is set to select the same first SMF for the same DNN (or DNN+SNSSAI). Taking DNN+SNSSAI as an example, in a specific implementation, the first AMF includes the following correspondence: DNN1+SNSSAI1 corresponds to the first SMF1. When the first AMF receives a PDU session establishment request from UE1, the first AMF obtains DNN1+SNSSAI1 from the PDU session establishment request, and then sends the PDU session establishment request to the first SMF1. The first SMF1 establishes a LAN type PDU session for UE1.

Exemplarily, all UEs accessing the isolated network can use the same DNN+SNSSAI; or, UEs corresponding to the same service layer group (e.g., MCPTT group, MCVideo group, MCData group) use the same DNN+SNSSAI, while UEs corresponding to different service layer groups use different DNN+SNSSAI; or, UEs corresponding to an organization (e.g., MC organization) use an independent DNN+SNSSAI, and UEs corresponding to different organizations use different DNN+SNSSAI.

Optionally, a first SMF (referred to as the first SMF1) is registered in the NRF, and the first SMF1 is used to establish a LAN type PDU session for a UE using DNN (or DNN+SNSSAI) that is connected to an isolated network. When the first AMF receives a PDU session establishment request from UE1, the first AMF obtains the identifier of the first SMF1 from the NRF, and then sends the PDU session establishment request to the first SMF1 based on the identifier of the first SMF1, and the first SMF1 establishes a LAN type PDU session for UE1.

Implementation method 2: UE1 establishes a local area network type session with the first core network according to the URSP matching the isolated network.

The URSP matching the isolated network may be obtained by UE1 from the first PCF, or may be obtained by UE1 from the second PCF. The following is an explanation of the following situations:

Case 1: The URSP matching the isolated network is obtained by UE1 from the first PCF.

In one possible example, UE1 receives a URSP from the first PCF that matches the isolated network, and then establishes a LAN type session with the first core network based on the URSP. In another possible example, UE1 receives multiple URSPs from the first PCF, UE1 selects a URSP that matches the isolated network from the multiple URSPs, and then establishes a LAN type session with the first core network based on the selected URSP.

Optionally, UE1 may select a URSP matching the isolated network from the multiple URSPs according to one or more of UE1's isolated network access capability information and UE1's identification of allowing access to the isolated network. The isolated network access capability information is used to indicate whether UE1 can access an isolated network type network.

Exemplarily, after UE1 determines that UE1 can access a network of the isolated network type according to the isolated network access capability information, UE1 selects a URSP matching the isolated network type from the multiple URSPs.

The isolation network access capability information may be indicated by an element information. Exemplarily, the element information may occupy one or more bits.

For example, the isolated network access capability information of UE1 is indicated by a bit. When the value of the bit is 1, the isolated network access capability information indicates that UE1 has the ability to access an isolated network type network; when the value of the bit is 0, the isolated network access capability information indicates that UE1 does not have the ability to access an isolated network type network. Further, UE1 receives two URSPs (recorded as the first URSP to the second URSP) from the first PCF, wherein the first URSP matches the isolated network type network, and the second URSP matches the non-isolated network type network (i.e., a normal network). When UE1 determines that the value of the bit occupied by the isolated network access capability information is 1, UE1 selects the first URSP, and then establishes a LAN type session with the first core network according to the first URSP.

As another example, different isolated networks may be matched with different URSPs, and UE1 selects a URSP that matches the identifier of UE1 that is allowed to access the isolated network from the multiple URSPs according to the identifier of UE1 that is allowed to access the isolated network.

For example, UE1 receives three URSPs (recorded as URSP1 to URSP3) from the first PCF, wherein URSP1 to URSP3 match isolated networks 1 to 3 respectively. Further, after UE1 determines that the identifier that allows UE1 to access the isolated network is the identifier of isolated network 1, UE1 establishes a local area network type session with the first core network according to URSP1.

In the present application, the URSP matching the isolated network may be generated by the first PCF according to the subscription information of UE1 and/or the local policy of the first PCF.

In one possible manner, the first PCF obtains the subscription information of UE1 from the first UDM, determines one or more isolated networks that UE1 is allowed to access based on the subscription information of UE1, and then generates URSPs that match the one or more isolated networks that UE1 is allowed to access. For example, the first PCF determines that the isolated networks that UE1 is allowed to access are isolated network 1 to isolated network 3 based on the subscription information of UE1, and the first PCF generates URSP1 to URSP3 that match isolated network 1 to isolated network 3 respectively.

In another possible manner, the first PCF generates a URSP (such as a first URSP) that matches the network of the isolated network type according to the local policy of the first PCF. It can be understood that the first PCF is a PCF in the local core network, so the first PCF can directly generate a URSP that matches the network of the isolated network type.

Optionally, a route selection validation criteria is added to the URSP generated by the first PCF, wherein the route selection validation criteria includes an item including information about the isolated network. The information about the isolated network may be an indication information indicating that the UE may use the URSP in any isolated network.

In one possible process, after UE1 determines that it has access to the isolated network, it initiates a registration process. In the registration process, UE1 sends a registration request to the first AMF; the first AMF responds to the registration request and sends a UE policy control create request to the first PCF; the first PCF responds to the UE policy control create request and sends a response message of the UE policy control create request to the first AMF (UE policy controlcreate response). Furthermore, the first PCF generates a URSP that matches the isolated network, and sends the generated URSP to the UE in the UE configuration update process. Optionally, the registration request includes UE1's isolated network access capability information, and the first AMF obtains UE1's isolated network access capability information from the registration request, and then carries UE1's isolated network access capability information in the UE policy control create request.

Case 2: The URSP matching the isolated network is obtained by UE1 from the second PCF.

The implementation manner in which UE1 obtains the URSP matching the isolated network from the second PCF can be referred to the description in the above situation 1, where "first PCF" can be replaced by "second PCF".

In the present application, the URSP matching the isolated network may be generated by the second PCF according to indication information, wherein the indication information is used to indicate whether UE1 has the ability to access the isolated network.

In a specific implementation, when UE1 resides in the second core network, it sends an indication message to the second PCF; accordingly, after receiving the indication message, the second PCF generates a URSP matching the isolated network according to the indication message. The indication message includes one or more of the isolated network access capability information of UE1 and the identifier of UE1 allowing access to the isolated network. The isolated network access capability information is used to indicate whether UE1 can access a network of the isolated network type.

In one possible manner, the indication information includes the isolated network access capability information of UE1. After receiving the indication information, the second PCF determines, based on the isolated network access capability information in the indication information, that UE1 has the ability to access a network of the isolated network type, and generates a URSP that matches the network of the isolated network type. For example, the isolated network access capability information of UE1 is indicated by a bit. When the value of the bit is 1, the isolated network access capability information indicates that UE1 has the ability to access a network of the isolated network type; when the value of the bit is 0, the isolated network access capability information indicates that UE1 does not have the ability to access a network of the isolated network type. Furthermore, when the second PCF determines that the value of the bit occupied by the isolated network access capability information is 1, a URSP that matches the network of the isolated network type (such as the first URSP) is generated.

In another possible manner, the indication information includes the identifiers of one or more isolated networks that UE1 is allowed to access. After receiving the indication information, the second PCF generates a URSP matching each isolated network according to the identifiers of one or more isolated networks that UE1 is allowed to access in the indication information. For a specific example, see the implementation method in which the first PCF generates a URSP according to the subscription information of UE1 in situation 1.

In one possible process, when UE1 resides in the second core network, UE1 sends a registration request to the second AMF; the second AMF sends a UE policy control creation request to the second PCF in response to the registration request; the second PCF sends a response message of the UE policy control creation request to the second AMF in response to the UE policy control creation request. Furthermore, the second PCF generates a URSP that matches the isolated network, and sends the generated URSP to the UE in the UE configuration update process. Optionally, the registration request includes indication information, and the first AMF obtains the indication information from the registration request, and then carries the indication information in the UE policy control creation request.

Step 903: UE1 communicates with UE2 via a LAN type session, wherein UE1 and UE2 belong to the same LAN group (or called virtual network group).

It is noted in advance that UE2 can access RAN2. After the backhaul line between RAN2 and the second core network is disconnected, RAN2 and the first core network can form an isolated network, which can provide communication services for UE2. RAN2 broadcasts the identifier of the isolated network, UE2 receives the identifier of the isolated network broadcast by RAN2, and accesses the isolated network according to the identifier of the isolated network. The specific implementation method can be found in the description of step 901, and "UE1" can be replaced with "UE2", and "RAN1" can be replaced with "RAN2".

Furthermore, UE2 establishes a LAN type PDU session with the first core network in the isolated network, or, after establishing the PDU session in the existing scheme with the first core network in the isolated network, UE2 sends a PDU session modification message to the first SMF, and the first SMF updates the user plane routing rules in the first UPF (referred to as anchor point UPF2) corresponding to UE2's PDU session according to UE2's PDU session modification message, wherein the user plane routing rules in the updated anchor point UPF2 are used to instruct the anchor point UPF2 to send the user plane data to the RAN accessed by other UEs (such as UE1) or the anchor point UPF corresponding to other UEs (such as UE1) when receiving user plane data with a source address as UE2's IP unicast address and a destination address as an IP multicast address. Among them, UE2 establishes a LAN type PDU session with the first core network in the isolated network, or UE2 initiates the update process of the user plane routing rules. Please refer to the description in step 902, and "UE1" can be replaced with "UE2", "RAN1" can be replaced with "RAN2", and "anchor point UPF1" can be replaced with "anchor point UPF2".

In this application, UE1 and UE2 are connected to the same isolated network, and RAN1 and RAN2 can be the same RAN or different RANs. The PDU session between UE1 and the first core network can be called PDU session 1, and the PDU session between UE2 and the first core network can be called PDU session 2. The anchor point UPF1 corresponding to PDU session 1 (or UE1) and the anchor point UPF2 corresponding to PDU session 2 (or UE2) are the same first UPF or different first UPFs.

Optionally, the first SMF may further update the user plane routing rules in the anchor point UPF1, wherein the updated user plane routing rules in the anchor point UPF1 are not only used to instruct the anchor point UPF1 to send the user plane data to the RAN accessed by other UEs or the anchor point UPF corresponding to other UEs when receiving user plane data with a source address of UE1's IP unicast address and a destination address of IP multicast address, but also used to instruct the anchor point UPF1 to send the user plane data to RAN accessed by UE1 when receiving user plane data with a source address of UE2's IP unicast address and a destination address of IP multicast address.

Optionally, when the anchor point UPF1 and the anchor point UPF2 are different first UPFs, the first SMF may further update the user plane routing rules in the anchor point UPF2. The user plane routing rules in the updated anchor point UPF2 instruct the anchor point UPF2 to send the user plane data to the RAN accessed by other UEs or the anchor point UPF corresponding to other UEs when receiving user plane data with the source address being the IP unicast address of UE2 and the destination address being the IP multicast address. It is also used to instruct the anchor point UPF2 to send the user plane data to RAN accessed by UE2 when receiving user plane data with the source address being the IP unicast address of UE1 and the destination address being the IP multicast address.

Based on the user plane routing rules in the above-mentioned anchor point UPF1 and the user plane routing rules in the anchor point UPF2, it can be understood that the endpoints of the user plane data corresponding to PDU session 1 and PDU session 2 are both in the isolated network, and UE1 and UE2 can communicate with each other based on PDU session 1 and PDU session 2, and during the communication process, the data only needs to be forwarded through the anchor point UPF1 and the anchor point UPF2, and does not need to be forwarded through the data network.

In a specific implementation, a multicast address is pre-set in UE1 or UE2, and the multicast address is, for example, an IP multicast address. Optionally, the IP multicast address is based on the granularity of a LAN group, or a key business, or a MC system, or even the entire isolated network.

Specifically, when the IP multicast address is based on the granularity of the LAN group, each LAN group corresponds to an IP multicast address. For example, LAN group 1 corresponds to IP multicast address 1, LAN group 2 corresponds to IP multicast address 2, and LAN group 3 corresponds to IP multicast address 3. At least two UEs belonging to LAN group 1 can communicate based on IP multicast address 1. LAN group 2 and LAN group 3 are similar to LAN group 1. Furthermore, one or more LAN groups may correspond to a service group, and the service group may be, for example, an MCPTT group, an MCVideo group, an MCData group, or an FRMCS group. For example, LAN group 1 and LAN group 2 in the above example correspond to the MCPTT group, and LAN group 3 corresponds to the MCVideo group.

When the IP multicast address is based on the granularity of key services, each key service corresponds to an IP multicast address. For example, the key services include MCPTT, MCVideo, MCData or FRMCS, MCPTT corresponds to IP multicast address 1, MCVideo corresponds to IP multicast address 2, MCData corresponds to IP multicast address 3, RMCS corresponds to IP multicast address 4, and at least two UEs installed with the client corresponding to MCPTT can communicate based on IP multicast address 1. MCVideo, MCData or FRMCS are similar to MCPTT.

When the IP multicast address is based on the granularity of the MC system (or organization, the terms are interchangeable) in the normal network, each MC system corresponds to an IP multicast address, for example, MC system 1 in the normal network corresponds to IP multicast address 1, and MC system 2 in the normal network corresponds to IP multicast address 2. When entering the isolated network state, at least two UEs belonging to MC system 1 can communicate based on IP multicast address 1, and MC system 2 is similar.

When the IP multicast address is based on the granularity of the entire isolated network, the UE can pre-configure (or obtain from the first core network such as the first PCF, or the second core network such as the second PCF) the relationship between the isolated network identifier and the IP multicast address. Accordingly, at least two UEs connected to the isolated network can communicate based on the IP multicast address corresponding to the isolated network.

In a specific implementation, during the communication between UE1 and UE2, UE1 may first initiate a call process to UE2, and after UE1 obtains the unicast address of UE2, transmit media data or voice control information to UE2.

When the anchor point UPF1 corresponding to PDU session 1 and the anchor point UPF2 corresponding to PDU session 2 are the same first UPF, the flowchart of the communication between UE1 and UE2 can be seen in Figure 10.

Step 1001: UE1 sends a call control request message via PDU session 1.

In the present application, UE1 sends call control request information through PDU session 1. Specifically, UE1 sends call control request information through the user plane (QoS flow) corresponding to PDU session 1, that is, UE1 sends call control request information to RAN1, RAN1 sends the call control request information to the anchor point UPF1, and accordingly, the anchor point UPF1 receives the call control request information. For the convenience of description, the following is an example of UE1 sending call control request information through PDU session 1.

The packet header of the call control request information includes a destination address and a source address, wherein the destination address is specifically an IP multicast address, and the source address is specifically an IP unicast address of UE1.

In one possible example, the payload of the call control request information includes the identifier of the UE initiating the call (i.e., the identifier of UE1) and the identifier of the called UE, wherein the identifier of the called UE may be one or more, and the one or more identifiers of the called UE include the identifier of UE2.

In another possible example, the payload of the call control request information includes the identifier of the UE initiating the call (i.e., the identifier of UE1) and the identifier of the called LAN group, wherein the identifier of the called LAN group may be one or more, and the one or more identifiers of the called LAN groups include the identifier of the LAN group to which UE2 is located.

The UE identifier may be a permanent identity identifier of the UE, a generic public subscription identity (GPSI), a client identifier corresponding to an application client on the UE, or a user identifier corresponding to an application client on the UE.

Optionally, UE1, as the initiator of the call, can periodically send call control request information. For example, since the UE connected to the isolated network may change, when UE1 sends call control request information at two different times, the UE that responds to the call control request information may be the same or different. Optionally, when UE1 is the talker of the current call, UE1 can periodically send call control request information. When other UEs in the call become speakers, the other UEs are responsible for periodically sending call control request information. The speaker refers to the role in the call that determines whether to grant the floor request sent by the call participants. Generally, there can be only one speaker in a call, but there can be multiple speakers in specific scenarios. For example, there can be multiple speakers at the same time in a railway cluster communication scenario. At this time, multiple speakers can periodically send call control request information.

Step 1002: The anchor point UPF1 sends a call control request message through PDU session 2 according to the IP multicast address in the call control request message.

Specifically, the anchor point UPF1 obtains the IP multicast address from the packet header of the call control request information, and then sends the call control request information through the PDU session 2 according to the IP multicast address and the routing forwarding rule in the anchor point UPF1.

In the present application, the anchor point UPF1 sends the call control request information through the PDU session 2. Specifically, the anchor point UPF1 sends the call control request information through the user plane (QoS flow) corresponding to the PDU session 2, that is, the anchor point UPF1 sends the call control request information to RAN2, and RAN2 then sends the call control request information to UE2. Correspondingly, UE2 receives the call control request information. For the convenience of description below, the anchor point UPF1 sending the call control request information through the PDU session 2 is taken as an example.

It should be supplemented that the call control request information can be received not only by UE2, but also by other UEs configured with the IP multicast address. Specifically, when the IP multicast address is based on the granularity of the LAN group, other UEs (including UE2) other than UE1 in the LAN group corresponding to the IP multicast address can receive the call control request information; when the IP multicast address is based on the granularity of the key business, other UEs (including UE2) other than UE1 with the key business client corresponding to the IP multicast address can receive the call control request information; when the IP multicast address is based on the granularity of the MC system, other UEs (including UE2) other than UE1 connected to the MC system corresponding to the IP multicast address can receive the call control request information; when the IP multicast address is based on the granularity of the key business, other UEs (including UE2) other than UE1 connected to the isolated network can receive the call control request information.

Further, the other UE configured with the IP multicast address is, for example, UE3, and UE3 establishes PDU session 3 with the first core network, and UE3 is connected to RAN3. Exemplarily, when the anchor point UPF3 corresponding to PDU session 3 is the same as the anchor point UPF1, the anchor point UPF1 can send the call control request information through PDU session 3 (or, through the user plane corresponding to PDU session 3) according to the IP multicast address in the call control request information. Specifically, the anchor point UPF1 sends the call control request information to RAN3 according to the IP multicast address and the routing forwarding rules in the anchor point UPF1, and RAN3 then sends the call control request information to UE3. Correspondingly, UE3 receives the call control request information. When the anchor point UPF3 corresponding to PDU session 3 is different from the anchor point UPF1, the anchor point UPF1 can specifically send the call control request information to the anchor point UPF3 according to the IP multicast address and the routing forwarding rules in the anchor point UPF1. Subsequently, anchor UPF3 sends the call control request information through PDU session 3 according to the IP multicast address in the call control request information. Specifically, anchor UPF3 sends the call control request information to RAN3, and RAN3 then sends the call control request information to UE3. Accordingly, UE3 receives the call control request information.

Furthermore, after other UEs configured with the IP multicast address receive the call control request information, they obtain the identifiers of one or more called UEs from the payload of the call control request information, or obtain the identifiers of one or more called LAN groups, and then determine whether they are the target UE called by UE1. If so, they perform the same action as UE2 in the following step 1003. Otherwise, it is determined that the call control request information is not used to call themselves, and the call control request information can be discarded.

Taking UE3 as an example, UE3 obtains the identifiers of one or more called UEs from the payload of the call control request information. If it is determined that the identifier of UE3 is included in the identifiers of one or more called UEs, it is determined that it is the target UE called by UE1; if it is determined that the identifier of UE3 is not included in the identifiers of one or more called UEs, it is determined that it is not the target UE called by UE1.

Alternatively, UE3 obtains the identifiers of one or more called LAN groups from the payload of the call control request information. If it is determined that the identifier of the LAN group to which UE3 is located is included in the identifiers of one or more called LAN groups, it determines that it is the target UE called by UE1; if it is determined that the identifier of the LAN group to which UE3 is located is not included in the identifiers of one or more called UEs, it determines that it is not the target UE called by UE1.

Step 1003: UE2 sends a response message according to the identifier of UE2 in the call control request message through PDU session 2. Specifically, UE2 obtains the identifier of UE2 from the payload in the call control request message.

Further, in the present application, UE2 sends response information through PDU session 2. Specifically, UE2 sends response information through the user plane corresponding to PDU session 2, that is, UE2 sends response information to RAN2, RAN2 sends the response information to the anchor point UPF1, and accordingly, the anchor point UPF1 receives the response information. For the convenience of description below, UE2 sending response information through PDU session 2 is taken as an example.

In a possible implementation, before UE2 sends a response message through PDU session 2, UE2 may trigger an update process for the routing forwarding rules of the anchor UPF1. For example, UE2 obtains the IP unicast address of UE1 from the packet header of the call control request information, and then initiates a PDU session modification request for PDU session 2 (recorded as PDU session modification request 2) to the first SMF, wherein the PDU session modification request 2 includes "the IP unicast address of the destination address being UE1". For example, the packet filtering rule of the PDU session modification request 2 includes the "IP unicast address of the destination address being UE1". After the first SMF receives the session modification request 2, the first SMF updates the routing forwarding rules of the anchor UPF1 through the N4 message, wherein the updated routing forwarding rules of the anchor UPF1 are used to indicate that: when the anchor UPF1 receives user plane data whose source address is the IP unicast address of UE2 and whose destination address is the IP unicast address of UE1, the anchor UPF1 needs to forward the user plane data to UE1 through PDU session 1 (specifically, the user plane corresponding to PDU session 1). Further, when UE2 sends a response message through PDU session 2, the destination address in the packet header of the response message is the IP unicast address of UE1, and the source address is the IP unicast address of UE2.

In a possible implementation, the PDU session modification request 2 also includes "the IP unicast address with the destination address being UE2". For example, the packet filtering rules of the PDU session modification request 2 include the "IP unicast address with the destination address being UE2". Furthermore, the first SMF also updates the routing and forwarding rules of the anchor point UPF1 through the N4 message, wherein the routing and forwarding rules of the anchor point UPF1 after the update are also used to indicate: when user plane data with the source address being the IP unicast address of UE1 and the destination address being the IP unicast address of UE2 is received, the anchor point UPF1 needs to send the user plane data to UE2 through PDU session 2.

Step 1004: The anchor point UPF1 sends the response information through PDU session 1 according to the IP unicast address of UE1 in the response information. Specifically, the anchor point UPF1 obtains the IP unicast address of UE1 from the packet header of the response information, and sends the response information through PDU session 1 according to the IP unicast address of UE1 and the routing forwarding rule of the anchor point UPF1.

In the present application, the anchor point UPF1 sends the response information through the PDU session 1. Specifically, the anchor point UPF1 sends the response information through the user plane corresponding to the PDU session 1, that is, UPF1 sends the response information to RAN1, and RAN1 sends the response information to UE1. Correspondingly, UE1 receives the response information. For the convenience of description below, the anchor point UPF1 sending the response information through the PDU session 1 is taken as an example.

In addition, in the above steps 1002 to 1004, before UE2 sends the response information through PDU session 2, it is also possible not to trigger the update process of the routing forwarding rules of the anchor UPF2, but UE2 obtains the identifier of UE1 from the payload of the call control request information, and carries the identifier of UE1 in the payload of the response information. At this time, the payload of the response information includes the identifier of UE1 and the identifier of UE2 to indicate that the response information is sent by UE2 to UE1. Furthermore, the destination address in the packet header of the response information is an IP multicast address, and the source address is the IP unicast address of UE2. Based on the destination address and source address in the response information and the routing forwarding rules of the anchor UPF2, the anchor UPF2 sends the response information to the anchor UPF corresponding to the UE configured with the IP multicast address, or sends the response information to the RAN to which the UE configured with the IP multicast address accesses. It can also be understood that the response information can be received not only by UE1, but also by other UEs (such as UE3) configured with the IP multicast address (for specific implementation methods, see the description of UE3 receiving the call control request information in step 1002). Further, since the payload of the response information includes the identifier of UE1, after receiving the response information, UE1 can determine that the response information is sent to itself, while other UEs configured with the IP multicast address can determine that the response information is not sent to themselves after receiving the response information, and thus can discard the response information.

UE1 can also initiate a PDU session modification request (recorded as PDU session modification request 1) to the first SMF, where the PDU session modification request 1 includes "the destination address is the IP unicast address of UE2". For example, the packet filtering rule of the PDU session modification request 1 carries the "destination address is the IP unicast address of UE2". Furthermore, after the first SMF receives the session modification request 1, the first SMF updates the routing forwarding rules of the anchor point UPF1 through the N4 message, wherein the updated routing forwarding rules of the anchor point UPF1 are used to indicate: when the anchor point UPF1 receives user plane data whose source address is the IP unicast address of UE1 and whose destination address is the IP unicast address of UE2, the anchor point UPF1 needs to send the user plane data to RAN2, that is, send it to UE2 through the user plane corresponding to the PDU session 2.

Optionally, the PDU session modification request 1 also includes "the IP unicast address of the destination address being UE1", for example, the packet filtering rule of the PDU session modification request 1 carries the "IP unicast address of the destination address being UE1". Accordingly, the first SMF further updates the routing and forwarding rules of the anchor point UPF1 through the N4 message, wherein the routing and forwarding rules of the anchor point UPF1 after the update are also used to indicate that: when the anchor point UPF1 receives user plane data whose source address is the IP unicast address of UE2 and whose destination address is the IP unicast address of UE1, the anchor point UPF1 needs to send the user plane data to RAN1, that is, to UE1 through the user plane corresponding to the PDU session 1.

Based on the above steps 1001 to 1004, UE1 obtains the IP unicast address of UE2, UE2 also obtains the IP unicast address of UE1, and the routing forwarding rules in the anchor point UPF1 have been updated. UE1 can send UE1's media data or voice control information to UE2's IP unicast address, and accordingly, UE2 can receive the media data or voice control information from UE1. And/or, UE2 can send UE2's media data or voice control information to UE1's IP unicast address, and accordingly, UE1 can receive the media data or voice control information from UE2. It should be noted that when the call control request information indicates a single call, UE1 can communicate with UE2 one-to-one, and when exchanging media data or voice control information, the target address can use the other party's IP unicast address; when the call control request information indicates a group call, the destination address used by each UE participating in the group call to send media data is the IP multicast address.

As follows, it is explained by taking UE1 sending the media data of UE1 to the IP unicast address of UE2 as an example, and the details can be referred to the following steps 1005 and 1006.

Step 1005, UE1 sends the media information of UE1 through PDU session 1. Specifically, UE1 sends the media information of UE1 through the user plane (QoS flow) corresponding to PDU session 1, that is, UE1 sends the media information of UE1 to RAN1, RAN1 sends the media information of UE1 to the anchor point UPF1, and accordingly, the anchor point UPF1 receives the media information of UE1. Among them, the source address in the packet header of the media information is the IP unicast address of UE1, the destination address is the IP unicast address of UE2, and the payload of the media information includes media data.

Step 1006, the anchor point UPF1 sends the media information through PDU session 2 according to the IP unicast address of UE2 in the media information. Specifically, the anchor point UPF1 obtains the IP unicast address of UE2 from the packet header of the media information, and then sends the media information through the user plane corresponding to PDU session 2 according to the IP unicast address of UE2 and the updated routing forwarding rule in the anchor point UPF1, that is, the anchor point UPF1 sends the media information to RAN2, and RAN2 sends the media information to UE2, and accordingly, UE2 receives the media information.

In the above technical solution, the anchor point UPF1 (or anchor point UPF2) performs the local forwarding function based on the updated routing forwarding rules. Taking media information as an example, after receiving the media information from UE1, the anchor point UPF1 directly forwards the media information to UE2 through PDU session 2, without sending the media information to the MC system first, and then the MC system sends it to the anchor point UPF1, and then the anchor point UPF1 sends it to UE2, thus shortening the transmission path of the user plane. And there is no need to deploy a local MC system in the first core network (i.e., the local core network), saving the hardware deployment cost. In addition, after receiving the media information from UE1, the anchor point UPF1 directly forwards the media information to UE2 through PDU session 2 according to the IP unicast address of UE2, and will not send it to other UEs that are not part of the call (such as UE3 above), thus helping to ensure the security of the media information.

When the anchor point UPF1 corresponding to PDU session 1 and the anchor point UPF2 corresponding to PDU session 2 are different first UPFs, the flowchart of the communication between UE1 and UE2 can be seen in Figure 11.

Step 1101, UE1 sends a call control request message through PDU session 1. Specifically, UE1 sends the call control request message to RAN1, and RAN1 sends the call control request message to anchor point UPF1. Accordingly, anchor point UPF1 receives the call control request message. For specific implementation, please refer to the description in step 1001.

Step 1102: anchor point UPF1 sends the call control request information to anchor point UPF2 according to the IP multicast address in the call control request information. Specifically, anchor point UPF1 obtains the IP multicast address from the packet header of the call control request information, and then sends the call control request information to anchor point UPF2 according to the IP multicast address and the routing forwarding rule in anchor point UPF1. Accordingly, anchor point UPF2 receives the call control request information from anchor point UPF1.

Among them, an N19 connection is established between the anchor point UPF1 and the anchor point UPF2, so that the anchor point UPF1 can directly send the call control request information to the anchor point UPF2 through the N19 connection.

Step 1103, anchor UPF2 sends the call control request information through PDU session 2 according to the IP multicast address in the call control request information. Specifically, anchor UPF2 obtains the IP multicast address from the packet header of the call control request information, and then sends the call control request information to RAN2 according to the IP multicast address and the routing forwarding rule in anchor UPF2. RAN2 then sends the call control request information to UE2. Accordingly, UE2 receives the call control request information.

It should be supplemented that the call control request information can be received not only by UE2, but also by other UEs configured with the IP multicast address. For details, please refer to the description in step 1002.

Step 1104, UE2 sends a response message through PDU session 2 according to the identifier of UE2 in the call control request message. Specifically, UE2 obtains the identifier of UE2 from the payload in the call control request message, determines that the call control request message is for calling UE2, and then sends the response message to RAN2, which sends the response message to the anchor point UPF1, and accordingly, the anchor point UPF2 receives the response message.

In a possible implementation, before UE2 sends the response information through PDU session 2, UE2 may initiate a process of updating the routing forwarding rule of the anchor point UPF2.

Specifically, UE2 obtains the unicast address of UE1 from the packet header of the call control request information, and then initiates a PDU session modification request for PDU session 2 (recorded as PDU session modification request 2) to the first SMF, wherein the packet filtering rule in the PDU session modification request 2 includes "the destination address is the IP unicast address of UE1". After the first SMF receives the session modification request 2, the first SMF updates the routing forwarding rules of the anchor point UPF2 through the N4 message, wherein the updated routing forwarding rules of the anchor point UPF2 are used to indicate that: when the anchor point UPF2 receives user plane data whose source address is the IP unicast address of UE2 and whose destination address is the IP unicast address of UE1, the anchor point UPF2 needs to send the user plane data to the anchor point UPF1. Optionally, the first SMF also updates the routing forwarding rules of the anchor point UPF1 through the N4 message, wherein the routing forwarding rules of the anchor point UPF1 after the update are used to indicate that: when the anchor point UPF1 receives user plane data whose source address is the IP unicast address of UE2 and the destination address is the IP unicast address of UE1, the anchor point UPF1 needs to send the user plane data to UE1. Further, when UE2 sends a response message through PDU session 2, the destination address in the packet header of the response message is the IP unicast address of UE1, and the source address is the IP unicast address of UE2.

Optionally, the packet filtering rules in the PDU session modification request 2 also include "the destination address is the IP unicast address of UE2", and the first SMF further updates the routing forwarding rules of the anchor point UPF2 through the N4 message, wherein the routing forwarding rules of the anchor point UPF2 after the update are also used to indicate: when receiving user plane data whose source address is the IP unicast address of UE1 and the destination address is the IP unicast address of UE2, the anchor point UPF2 needs to send the user plane data to UE2 through PDU session 2. Optionally, the first SMF also updates the routing forwarding rules of the anchor point UPF1 through the N4 message, wherein the routing forwarding rules of the anchor point UPF1 after the update are used to indicate: when the anchor point UPF1 receives user plane data whose source address is the IP unicast address of UE1 and the destination address is the IP unicast address of UE2, the anchor point UPF1 needs to send the user plane data to the anchor point UPF2.

Step 1105: anchor point UPF2 sends response information to anchor point UPF1 according to the IP unicast address of UE1. Specifically, anchor point UPF2 obtains the IP unicast address of UE1 from the packet header of the response information, and sends the response information to anchor point UPF1 according to the IP unicast address of UE1 and the routing forwarding rule in anchor point UPF2. Accordingly, anchor point UPF1 receives the response information from anchor point UPF2.

Among them, an N19 connection is established between the anchor point UPF1 and the anchor point UPF2, so that the anchor point UPF2 can directly send the response information to the anchor point UPF1 through the N19 connection.

Step 1106: The anchor point UPF1 sends the response information through PDU session 1 according to the IP unicast address of UE1 in the response information. Specifically, the anchor point UPF1 obtains the IP unicast address of UE1 from the packet header of the response information, and according to the IP unicast address of UE1 and the routing forwarding rule of the anchor point UPF1, UPF1 sends the response information to RAN1. RAN1 then sends the response information to UE1. Accordingly, UE1 receives the response information.

In addition, in the above steps 1104 to 1106, before sending the response information through PDU session 2, UE2 may not initiate the update process of the routing forwarding rules of the anchor UPF2, but UE2 obtains the identifier of UE1 from the payload of the call control request information, and carries the identifier of UE1 in the payload of the response information. At this time, the payload of the response information includes the identifier of UE1 and the identifier of UE2 to indicate that the response information is sent by UE2 to UE1. Furthermore, the destination address in the packet header of the response information is an IP multicast address, and the source address is the IP unicast address of UE2. Based on the destination address and source address in the response information and the routing forwarding rules of the anchor UPF2, the anchor UPF2 sends the response information to the anchor UPF corresponding to the UE configured with the IP multicast address, or sends the response information to the RAN to which the UE configured with the IP multicast address accesses. It can also be understood that the response information can be received not only by UE1, but also by other UEs configured with the IP multicast address (for specific implementation methods, see the description of UE3 receiving the call control request information in step 1002). Further, since the payload of the response information includes the identifier of UE1, after receiving the response information, UE1 can determine that the response information is sent to itself, while other UEs configured with the IP multicast address can determine that the response information is not sent to themselves after receiving the response information, and thus can discard the response information.

UE1 can also initiate a session modification request (denoted as PDU session modification request 1) to the first SMF. The packet filtering rule in the session modification request 1 includes "the destination address is the IP unicast address of UE2". After the first SMF receives the session modification request 1, the first SMF updates the routing forwarding rule of the anchor point UPF1 through the N4 message, wherein the updated routing forwarding rule of the anchor point UPF1 is used to indicate that: when the anchor point UPF1 receives user plane data whose source address is the IP unicast address of UE1 and whose destination address is the IP unicast address of UE2, the anchor point UPF1 needs to send the user plane data to the anchor point UPF2. Optionally, the first SMF also updates the routing forwarding rule of the anchor point UPF2 through the N4 message, wherein the updated routing forwarding rule of the anchor point UPF2 is used to indicate that: when the anchor point UPF2 receives user plane data whose source address is the IP unicast address of UE1 and whose destination address is the IP unicast address of UE2, the anchor point UPF2 needs to send the user plane data to RAN2, that is, send it to UE2 through the user plane corresponding to the PDU session 2.

Optionally, the packet filtering rules in the PDU session modification request 1 also include "the destination address is the IP unicast address of UE1", and the first SMF further updates the routing forwarding rules of the anchor point UPF1 through the N4 message, wherein the updated routing forwarding rules of the anchor point UPF1 are also used to indicate: when the anchor point UPF1 receives user plane data whose source address is the IP unicast address of UE2 and whose destination address is the IP unicast address of UE1, the anchor point UPF1 needs to send the user plane data to RAN1, that is, send it to UE1 through the user plane corresponding to the PDU session 1. Optionally, the first SMF also updates the routing forwarding rules of the anchor point UPF2 through the N4 message, wherein the updated routing forwarding rules of the anchor point UPF2 are used to indicate: when the anchor point UPF2 receives user plane data whose source address is the IP unicast address of UE2 and whose destination address is the IP unicast address of UE1, the anchor point UPF2 needs to send the user plane data to the anchor point UPF1.

Based on the above steps 1101 to 1106, UE1 obtains the IP unicast address of UE2, UE2 also obtains the IP unicast address of UE1, and the routing forwarding rules in the anchor points UPF1 and UPF2 have been updated. UE1 can send UE1's media data or voice control information to UE2's IP unicast address, and accordingly, UE2 can receive UE1's media data or voice control information. And/or, UE2 can send UE2's media data or voice control information to UE1's IP unicast address, and accordingly, UE1 can receive UE2's media data or voice control information.

As follows, it is explained by taking UE1 sending the media data of UE1 to the IP unicast address of UE2 as an example, and the details can be referred to the following steps 1107 to 1109.

Step 1107, UE1 sends the media information of UE1 through PDU session 1. Specifically, UE1 sends the media information of UE1 to RAN1, and RAN1 sends the media information of UE1 to anchor point UPF1. Accordingly, anchor point UPF1 receives the media information of UE1. The source address in the packet header of the media information is the IP unicast address of UE1, the destination address is the IP unicast address of UE2, and the payload of the media information includes media data.

Step 1108, anchor point UPF1 sends the media information to anchor point UPF2 according to the IP unicast address of UE2 in the media information. Specifically, anchor point UPF1 obtains the IP unicast address of UE2 from the packet header of the media information, and then sends the media information to anchor point UPF2 according to the IP unicast address of UE2 and the updated routing forwarding rule in anchor point UPF1. Accordingly, anchor point UPF2 receives the media information from anchor point UPF1.

Step 1109: The anchor UPF2 sends the media information through PDU session 2 according to the IP unicast address of UE2 in the media information. Specifically, the anchor UPF2 obtains the IP unicast address of UE2 from the packet header of the media information, and then sends the media information to RAN2 according to the IP unicast address of UE2 and the updated routing forwarding rule in the anchor UPF2. RAN2 then sends the media information to UE2. Accordingly, UE2 receives the media information.

In the above technical solution, an N19 connection is established between the anchor point UPF1 and the anchor point UPF2, and the anchor point UPF1 and the anchor point UPF2 can transmit data to each other based on the N19 connection, so as to realize data forwarding in the local core network. Taking media information as an example, after receiving the media information from UE1, the anchor point UPF1 directly forwards the media information to the anchor point UPF2 based on the N19 connection, and the anchor point UPF2 then forwards the media information to UE2, without the need for the anchor point UPF1 to first send the media information to the local MC system through the N6 connection, and the local MC system then forwards the media information to the anchor point UPF2 through the N6 connection, and then the anchor point UPF2 sends the media information to UE2, thus shortening the transmission path of the user plane. And there is no need to deploy the local MC system in the first core network (i.e., the local core network), saving the deployment cost of hardware. In addition, the media information of UE1 can be directly passed to UE2, and will not be received by other UEs that are not part of the call (such as UE3 above), so as to help ensure the security of media information.

In combination with the above-mentioned related embodiments of Figures 9 to 11, the following Figures 12 to 14 provide communication methods in three specific implementation scenarios.

Figure 12 shows a communication method in which a first SMF establishes a LAN type session based on a session policy.

Step 1201: RAN1 detects that the backhaul link between RAN1 and the second core network is disconnected, RAN1 activates the connection with the first core network, and forms an isolated network with the first core network.

Step 1202: RAN1 broadcasts the identifier of the isolated network. Correspondingly, UE1 detects the identifier of the isolated network broadcast by RAN1. The identifier of the isolated network is, for example, an IOPS PLMN ID.

Step 1203: UE1 registers with the first core network according to the identifier of the isolated network.

Step 1204: The first PCF sends the session policy to the first SMF. Correspondingly, the first SMF receives the session policy from the first PCF and saves the session policy.

In step 1205, UE1 sends a PDU session establishment request to the first SMF, wherein the PDU session establishment request carries a DNN or carries a DNN+S-NSSAI. Accordingly, the first SMF receives the PDU session establishment request from UE1. In this application, the order between step 1204 and step 1205 is not limited.

Step 1206: The first SMF establishes a LAN type PDU session for UE1 according to the session policy and the DNN (or DNN+S-NSSAI) in the PDU session establishment request.

Step 1207 : UE1 starts the application logic function based on the isolated network LAN communication. Here, step 1207 may be after step 1202 and before step 1208 .

Step 1208: UE1 communicates with UE2 via a local area network type session.

Among them, the specific implementation methods of steps 1201 to 1203 and step 1207 can refer to the description in step 901; the specific implementation methods of steps 1204 to 1206 can refer to the description of implementation method 1 in step 902; the specific implementation method of step 1208 can refer to the description in step 903.

FIG. 13 is a communication method in which a UE establishes a LAN type session with a first core network based on a URSP from a first PCF that matches an isolated network.

Step 1301: RAN1 detects that the backhaul link between RAN1 and the second core network is disconnected. RAN1 activates the first core network and forms an isolated network with the first core network.

Step 1302: RAN1 broadcasts the identifier of the isolated network. Correspondingly, UE1 detects the identifier of the isolated network broadcast by RAN1. The identifier of the isolated network is, for example, an IOPS PLMN ID.

Step 1303: UE1 sends a registration request to the first AMF. Correspondingly, the first SMF receives the registration request from UE1.

Step 1304: The first AMF sends a UE policy control creation request to the first PCF. Correspondingly, the first PCF receives the UE policy control creation request from the first AMF.

Step 1305: The first PCF sends a creation response to the UE policy control creation request to the first AMF. Correspondingly, the first AMF receives a creation response to the UE policy control creation request from the first PCF.

Step 1306: The first PCF generates a URSP matching the isolated network according to the subscription information of UE1 and/or the local policy of the first PCF.

Step 1307: The first PCF sends a URSP matching the isolated network to UE1. Correspondingly, UE1 receives the URSP matching the isolated network from the first PCF.

Step 1308: UE1 establishes a local area network type PDU session with the first core network according to the URSP matching the isolated network.

Step 1309 : UE1 starts the application logic function based on the isolated network LAN communication. Here, step 1309 may be after step 1302 and before step 1308 .

Step 1310: UE1 communicates with UE2 via a local area network type session.

Among them, the specific implementation methods of steps 1301, 1302, and 1309 can refer to the description in step 901; the specific implementation methods of steps 1303 to 1308 can refer to the description of the first PCF generating URSP in implementation method 2 in step 902; the specific implementation method of step 1310 can refer to the description in step 903.

FIG. 14 is a communication method in which a UE establishes a LAN type session with a first core network based on a URSP from a second PCF that matches an isolated network.

Step 1401, UE1 sends a registration request to the second AMF. Correspondingly, the second AMF receives the registration request from UE1. The registration request includes indication information, which includes one or more of the isolated network access capability information of UE1 and the identifier of the UE1 that allows access to the isolated network.

Step 1402: The second AMF sends a UE policy control creation request to the second PCF. Correspondingly, the second PCF receives the UE policy control creation request from the second AMF. The UE policy control creation request includes indication information.

Step 1403: The second PCF sends a creation response to the UE policy control creation request to the second AMF. Correspondingly, the second AMF receives a creation response to the UE policy control creation request from the second PCF.

Step 1404: The second PCF generates a URSP matching the isolated network according to the instruction information.

Step 1405: The second PCF sends a URSP matching the isolated network to UE1. Correspondingly, UE1 receives the URSP matching the isolated network from the second PCF.

Step 1406: RAN1 detects that the backhaul link between RAN1 and the second core network is disconnected, RAN1 activates the first core network, and forms an isolated network with the first core network.

Step 1407: RAN1 broadcasts the identifier of the isolated network. Correspondingly, UE1 detects the identifier of the isolated network broadcast by RAN1. The identifier of the isolated network is, for example, an IOPS PLMN ID.

Step 1408: UE1 registers to the first core network.

Step 1409: UE1 establishes a LAN type PDU session with the first core network according to the URSP matching the isolated network.

Step 1410 : UE1 starts the application logic function based on the isolated network LAN communication. Here, step 1410 may be after step 1407 and before step 1411 .

Step 1411, UE1 communicates with UE2 via a local area network type session.

Among them, the specific implementation method of steps 1401 to 1405 can refer to the description of the second PCF generating URSP in implementation method 2 in step 902; the specific implementation method of steps 1406 to 1410 can refer to the description in step 901; the specific implementation method of step 1411 can refer to the description in step 903.

In the method embodiments related to Figures 9 to 14 above, "UE1" can be replaced with "first terminal", "UE2" can be replaced with "second terminal", "RAN1" can be replaced with "first access network device", "RAN2" can be replaced with "second access network device", "first SMF" can be replaced with "first session management function", "first PCF" can be replaced with "first policy control function", "second PCF" can be replaced with "second policy control function", "PDU session" can be replaced with "session", "PDU session 1" can be replaced with "first session", "PDU session 2" can be replaced with "second session", etc.

The various embodiments described herein may be independent solutions or may be combined according to internal logic, and all of these solutions fall within the protection scope of this application.

In the embodiments provided by the present application, the methods provided by the embodiments of the present application are introduced from the perspective of interaction between various devices. In order to implement the functions in the methods provided by the embodiments of the present application, the terminal, the session management function or the policy control function may include a hardware structure and/or a software module, and the functions are implemented in the form of a hardware structure, a software module, or a hardware structure plus a software module. Whether one of the functions is executed in the form of a hardware structure, a software module, or a hardware structure plus a software module depends on the specific application and design constraints of the technical solution.

The division of modules in the embodiments of the present application is schematic and is only a logical function division. There may be other division methods in actual implementation. In addition, each functional module in each embodiment of the present application may be integrated into a processor, or may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated modules may be implemented in the form of hardware or in the form of software functional modules.

Based on the above content and the same concept, Figures 15 and 16 are schematic diagrams of the structures of possible communication devices provided by the present application. These communication devices can be used to implement the functions of the first terminal or the first session management function or the policy control function (i.e., the first policy control function or the second policy control function) in the above method embodiment, and thus can also achieve the beneficial effects of the above method embodiment.

In the present application, the communication device can be a terminal as shown in Figure 1 or a module (such as a chip) applied to the terminal, or it can be a session management function as shown in Figure 1 or a module (such as a chip) applied to the session management function, or it can be a policy control function as shown in Figure 1 or a module (such as a chip) applied to the policy control function.

As shown in FIG. 15 , the communication device 1500 includes a processing module 1501 and a transceiver module 1502 .

When the communication device 1500 is used to implement the functions of UE1 in the method embodiments shown in FIG. 9 to FIG. 14 above:

Processing module 1501 is used to access the isolated network through the first access network device. The isolated network is a network that provides communication services to the device after the return line of the first access network device is disconnected; processing module 1501 is also used to establish a LAN type session with the first core network in the isolated network, and the user plane data corresponding to the LAN type session is terminated in the isolated network; transceiver module 1502 is used to communicate with the second terminal through the LAN type session, wherein the device and the second terminal belong to the same LAN group.

In one possible implementation, when the transceiver module 1502 communicates with the second terminal through a LAN type session, it is specifically used to: send call control request information through a LAN type session, the call control request information including a multicast address and an identifier of the second terminal; receive response information from the second terminal to the call control request information through a LAN type session, the response information including a unicast address of the second terminal; and transmit voice control information and/or media data to the second terminal through a LAN type session according to the unicast address.

In one possible implementation, there exists a first session of a LAN type between the apparatus and the first core network; there exists a second session of a LAN type between the second terminal and the first core network; the communication path between the apparatus and the second terminal is: a first access network device in the isolated network, an anchor user plane function corresponding to the first session in the first core network, an anchor user plane function corresponding to the second session in the first core network, and a second access network device in the isolated network for the second terminal to access the isolated network.

In a possible implementation, when the processing module 1501 establishes a LAN type session with the first core network in the isolated network, it is specifically used to: establish a LAN type session with the first core network according to a user equipment routing selection policy matching the isolated network.

In a possible implementation, the processing module 1501 is further configured to: select a user equipment routing selection strategy according to one or more of the isolated network access capability information of the device and an identifier of the device that is allowed to access the isolated network.

In a possible implementation, the transceiver module 1502 is further configured to: receive a user equipment routing selection policy from a first policy control function of the first core network.

In one possible implementation, the transceiver module 1502 is also used to: receive a user equipment routing selection policy from a second policy control function of a second core network in a normal network, where the normal network is a network where the first access network device provides communication services to the device before the backhaul line is disconnected.

In a possible implementation, the transceiver module 1502 is further used to: send indication information to the second policy control function, where the indication information is used to indicate that the device has the ability to access the isolated network.

In a possible implementation manner, the indication information includes one or more of the isolated network access capability information of the device and an identification of the device that is allowed to access the isolated network.

When the communication device 1500 is used to implement the function of the first SMF in the method embodiments shown in FIG. 9 to FIG. 14 above:

The transceiver module 1502 is used to receive a session establishment request from the first terminal. The device is located in an isolated network. The isolated network is a network that provides communication services to the first terminal after the backhaul line of the first access network device accessed by the first terminal is disconnected; the processing module 1501 is used to establish a local area network type session for the first terminal according to the session policy and the session establishment request. The session policy is used to indicate the establishment of a local area network type session. The user plane data corresponding to the local area network type session is terminated in the isolated network.

In a possible implementation, the session policy includes a local session policy of the device and/or a session policy of the first terminal.

In a possible implementation manner, the transceiver module 1502 is further configured to: receive a session policy of the first terminal from the first terminal.

When the communication device 1500 is used to implement the function of the PCF in the method embodiments shown in FIG. 9 to FIG. 14 above:

The processing module 1501 is used to generate a user equipment routing selection policy for the first terminal, the user equipment routing selection policy instructs the first terminal to establish a local area network type session with the first core network in the isolated network, and the isolated network is a network that provides communication services to the first terminal after the return line of the first access network device accessed by the first terminal is disconnected; the transceiver module 1502 is used to send the user equipment routing selection policy to the first terminal.

In one possible implementation, the device is the first policy control function (i.e., the first PCF) in the first core network; when generating a user equipment routing selection policy, the processing module 1501 is specifically used to: generate a user equipment routing selection policy based on the subscription information of the first terminal and/or the local policy of the device.

In one possible implementation, the device is a second policy control function (i.e., a second PCF) of a second core network in a normal network; when generating a user equipment routing selection policy, the processing module 1501 is specifically used to: generate a user equipment routing selection policy based on the subscription information of the first terminal and/or the indication information of the first terminal; the indication information is used to indicate that the first terminal has the ability to access the isolated network. In one possible implementation, the transceiver module 1502 is also used to: receive indication information from the first terminal. In one possible implementation, the indication information includes one or more of the isolated network access capability information of the first terminal and the identification of the first terminal that allows access to the isolated network.

As shown in FIG15, a device 1600 provided in an embodiment of the present application is shown. The device shown in FIG15 may be a hardware circuit implementation of the device shown in FIG15. The device may be applicable to the flowchart shown above to perform the functions of the first terminal or the first session management function or the policy control function (i.e., the first policy control function or the second policy control function) in the above method embodiment.

For ease of explanation, FIG15 shows only the main components of the device.

The device 1600 shown in FIG15 includes a communication interface 1610, a processor 1620 and a memory 1630, wherein the memory 1630 is used to store program instructions and/or data. The processor 1620 may operate in conjunction with the memory 1630. The processor 1620 may execute program instructions stored in the memory 1630. When the instructions or programs stored in the memory 1630 are executed, the processor 1620 is used to execute the operations performed by the processing module 1501 in the above embodiment, and the communication interface 1610 is used to execute the operations performed by the transceiver module 1502 in the above embodiment.

The memory 1630 is coupled to the processor 1620. The coupling in the embodiment of the present application is an indirect coupling or communication connection between devices, units or modules, which can be electrical, mechanical or other forms, for information exchange between devices, units or modules. At least one of the memories 1630 may be included in the processor 1620.

In the embodiment of the present application, the communication interface may be a transceiver, a circuit, a bus, a module or other types of communication interfaces. In the embodiment of the present application, when the communication interface is a transceiver, the transceiver may include an independent receiver, an independent transmitter, or a transceiver with integrated transceiver functions or a communication interface.

The device 1600 may further include a communication line 1640. The communication interface 1610, the processor 1620, and the memory 1630 may be interconnected via the communication line 1640; the communication line 1640 may be a peripheral component interconnect (PCI) bus or an extended industry standard architecture (EISA) bus. The communication line 1640 may be divided into an address bus, a data bus, a control bus, and the like. For ease of representation, FIG15 is represented by only one thick line, but it does not mean that there is only one bus or one type of bus.

Based on the above content and the same concept, an embodiment of the present application provides a computer-readable storage medium on which a computer program or instruction is stored. When the computer program or instruction is executed, the computer executes the actions of the first terminal, the first session management function or the policy control function in the above method embodiment.

Based on the above content and the same concept, an embodiment of the present application provides a computer program product. When a computer reads and executes the computer program product, the computer executes the actions of the first terminal, the first session management function or the policy control function in the above method embodiment.

Based on the above content and the same concept, an embodiment of the present application provides a communication system, which includes the first terminal and the first session management function in the above method embodiment.

Based on the above content and the same concept, an embodiment of the present application provides a communication system, which includes the first terminal and the policy control function in the above method embodiment.

In the present application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b or c can be represented by: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple. "And/or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and/or B can be represented by: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. In the text description of the present application, the character "/" generally indicates that the previous and next associated objects are in an "or" relationship; in the formula of the present application, the character "/" indicates that the previous and next associated objects are in a "division" relationship.

It is understood that the various numbers involved in the embodiments of the present application are only for the convenience of description and are not used to limit the scope of the embodiments of the present application. The size of the sequence number of the above-mentioned processes does not mean the order of execution, and the execution order of each process should be determined by its function and internal logic.

Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the protection scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims (38)

1. A communication method, comprising: The first terminal accesses an isolated network through a first access network device, where the isolated network is a network that provides communication services for the first terminal after a backhaul line of the first access network device is disconnected; The first terminal establishes a local area network type session with the first core network in the isolated network, and user plane data corresponding to the local area network type session is terminated in the isolated network; The first terminal communicates with the second terminal through the LAN type session, wherein the first terminal and the second terminal belong to the same LAN group. 2. The method according to claim 1, wherein the first terminal communicates with the second terminal through the LAN type session, comprising: The first terminal sends call control request information through the local area network type session, where the call control request information includes a multicast address and an identifier of the second terminal; The first terminal receives, through the local area network type session, response information of the second terminal to the call control request information, wherein the response information includes a unicast address of the second terminal; The first terminal transmits the speech right control information and/or the media data to the second terminal through the local area network type session and according to the unicast address. 3. The method according to claim 1 or 2, characterized in that a first session of the local area network type exists between the first terminal and the first core network; A second session of the local area network type exists between the second terminal and the first core network; The communication path between the first terminal and the second terminal is: The first access network device in the isolated network, the anchor user plane function corresponding to the first session in the first core network, the anchor user plane function corresponding to the second session in the first core network, and the second access network device in the isolated network used for the second terminal to access the isolated network. 4. The method according to any one of claims 1 to 3, wherein the first terminal establishes a local area network type session with the first core network in the isolated network, comprising: The first terminal establishes the local area network type session with the first core network according to a user equipment routing selection policy that matches the isolated network. 5. The method according to claim 4, further comprising: The first terminal selects the user equipment routing selection strategy according to one or more of the isolated network access capability information of the first terminal and an identification of the first terminal allowed to access the isolated network. 6. The method according to claim 4 or 5, further comprising: The first terminal receives the user equipment routing selection policy from a first policy control function of the first core network. 7. The method according to claim 4 or 5, further comprising: The first terminal receives the user equipment routing selection policy from a second policy control function of a second core network in a normal network, where the normal network is a network where the first access network device provides communication services for the first terminal before the backhaul line is disconnected. 8. The method according to claim 7, further comprising: The first terminal sends indication information to the second policy control function, where the indication information is used to indicate that the first terminal has the ability to access the isolated network. 9. The method as claimed in claim 8 is characterized in that the indication information includes one or more of the isolated network access capability information of the first terminal and the identification of the first terminal allowed to access the isolated network. 10. A communication method, comprising: A first session management function receives a session establishment request from a first terminal, where the first session management function is located in an isolated network, where the isolated network is a network that provides communication services to the first terminal after a backhaul line of a first access network device accessed by the first terminal is disconnected; The first session management function establishes a LAN type session for the first terminal according to a session policy and the session establishment request, wherein the session policy is used to indicate the establishment of a LAN type session, and user plane data corresponding to the LAN type session is terminated in the isolated network. 11. The method of claim 10, wherein the session policy comprises a local session policy of the first session management function and/or a session policy of the first terminal. 12. The method according to claim 10 or 11, further comprising: A first session management function receives a session policy for the first terminal from the first terminal. 13. A communication method, comprising: The policy control function generates a user equipment routing selection policy for the first terminal, wherein the user equipment routing selection policy instructs the first terminal to establish a local area network type session with a first core network in an isolated network, wherein the isolated network is a network that provides communication services for the first terminal after a backhaul line of a first access network device accessed by the first terminal is disconnected; The policy control function sends the user equipment routing policy to the first terminal. 14. The method according to claim 13, wherein the policy control function is a first policy control function in the first core network; The policy control function generates a user equipment routing selection policy, including: The first policy control function generates the user equipment routing policy according to the subscription information of the first terminal and/or the local policy of the first policy control function. 15. The method according to claim 13, wherein the policy control function is a second policy control function of a second core network in a normal network; The policy control function generates a user equipment routing selection policy, including: The second policy control function generates a routing selection policy for the user equipment according to the subscription information of the first terminal and/or the indication information of the first terminal; The indication information is used to indicate that the first terminal has the ability to access the isolated network. 16. The method of claim 15, further comprising: The second policy control function receives the indication information from the first terminal. 17. The method according to claim 15 or 16, characterized in that the indication information includes one or more of the isolated network access capability information of the first terminal and the identification of the first terminal allowed to access the isolated network. 18. A communication device, comprising: A processing module, configured to access an isolated network through a first access network device, wherein the isolated network is a network that provides communication services for the device after a backhaul line of the first access network device is disconnected; The processing module is further configured to establish a local area network type session with the first core network in the isolated network, wherein user plane data corresponding to the local area network type session is terminated in the isolated network; A transceiver module is used to communicate with a second terminal through the local area network type session, wherein the device and the second terminal belong to the same local area network group. 19. The device according to claim 18, wherein the transceiver module, when communicating with the second terminal through the local area network type session, is specifically used to: Sending a call control request message through the local area network type session, wherein the call control request message includes a multicast address and an identifier of the second terminal; receiving, through the local area network type session, response information of the second terminal to the call control request information, the response information including a unicast address of the second terminal; The voice control information and/or media data are transmitted to the second terminal through the local area network type session and according to the unicast address. 20. The device according to claim 18 or 19, characterized in that a first session of the local area network type exists between the device and the first core network; A second session of the local area network type exists between the second terminal and the first core network; The communication path between the device and the second terminal is: The first access network device in the isolated network, the anchor user plane function corresponding to the first session in the first core network, the anchor user plane function corresponding to the second session in the first core network, and the second access network device in the isolated network used for the second terminal to access the isolated network. 21. The device according to any one of claims 18 to 20, characterized in that the processing module, when establishing a local area network type session with the first core network in the isolated network, is specifically used to: The local area network type session is established with the first core network according to a user equipment routing selection policy that matches the isolated network. 22. The device according to claim 21, wherein the processing module is further configured to: The user equipment routing selection strategy is selected according to one or more of the isolated network access capability information of the device and an identification of the device that is allowed to access the isolated network. 23. The device according to claim 21 or 22, characterized in that the transceiver module is further used for: The user equipment routing policy is received from a first policy control function of the first core network. 24. The device according to claim 21 or 22, characterized in that the transceiver module is further used for: The user equipment routing selection policy is received from a second policy control function of a second core network in a normal network, where the normal network is a network where the first access network device provides communication services for the device before the backhaul line is disconnected. 25. The device according to claim 24, wherein the transceiver module is further used for: Sending indication information to the second policy control function, wherein the indication information is used to indicate that the device has the ability to access the isolated network. 26. The device as claimed in claim 25 is characterized in that the indication information includes one or more of the isolated network access capability information of the device and the identification of the device allowed to access the isolated network. 27. A communication device, comprising: A transceiver module, configured to receive a session establishment request from a first terminal, wherein the device is located in an isolated network, and the isolated network is a network that provides communication services to the first terminal after a backhaul line of a first access network device accessed by the first terminal is disconnected; A processing module is used to establish a local area network type session for the first terminal according to a session policy and the session establishment request, wherein the session policy is used to indicate the establishment of a local area network type session, and user plane data corresponding to the local area network type session is terminated in the isolated network. 28. The device of claim 27, wherein the session policy comprises a local session policy of the device and/or a session policy of the first terminal. 29. The device according to claim 27 or 28, characterized in that the transceiver module is further used for: A session policy for the first terminal is received from the first terminal. 30. A communication device, comprising: a processing module, configured to generate a user equipment routing selection policy for a first terminal, wherein the user equipment routing selection policy instructs the first terminal to establish a local area network type session with a first core network in an isolated network, wherein the isolated network is a network that provides communication services for the first terminal after a backhaul line of a first access network device accessed by the first terminal is disconnected; The transceiver module is used to send the user equipment routing selection policy to the first terminal. 31. The device of claim 30, wherein the device is a first policy control function in the first core network; When generating a user equipment routing selection strategy, the processing module is specifically used to: The user equipment routing selection policy is generated according to the subscription information of the first terminal and/or the local policy of the device. 32. The device according to claim 30, characterized in that the device is a second policy control function of a second core network in a normal network; When generating a user equipment routing selection strategy, the processing module is specifically used to: The user equipment routing selection policy is generated according to the subscription information of the first terminal and/or the indication information of the first terminal; the indication information is used to indicate that the first terminal has the ability to access the isolated network. 33. The device according to claim 32, wherein the transceiver module is further used for: The indication information is received from the first terminal. 34. The device as described in claim 32 or 33 is characterized in that the indication information includes one or more of the isolated network access capability information of the first terminal and the identification of the first terminal allowed to access the isolated network. 35. A communication device, characterized in that it comprises a processor, the processor is connected to a memory, the memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory, so that the device performs the method as described in any one of claims 1 to 9, or, so that the device performs the method as described in any one of claims 10 to 12, or, so that the device performs the method as described in any one of claims 13 to 17. 36. A computer-readable storage medium, characterized in that a computer program or instruction is stored in the computer-readable storage medium, and when the computer program or instruction is executed by a communication device, it implements the method as described in any one of claims 1 to 9, or implements the method as described in any one of claims 10 to 12, or implements the method as described in any one of claims 13 to 17. 37. A computer program product, characterized in that the computer program product comprises a computer program or instructions, and when the computer program or instructions are executed by a communication device, it implements the method as described in any one of claims 1 to 9, or implements the method as described in any one of claims 10 to 12, or implements the method as described in any one of claims 13 to 17. 38. A communication system, characterized in that it comprises a communication device as claimed in any one of claims 18 to 26, and a communication device as claimed in any one of claims 27 to 29; or, it comprises a communication device as claimed in any one of claims 18 to 26, and a communication device as claimed in any one of claims 30 to 34.