Communication method and communications apparatus

1. A communication method, comprising:

sending, by a mobility management network element, a first request message to a network repository network element, wherein the first request message comprises a data network name of a session that a terminal device requests to establish;

receiving, by the network repository network element, the first request message from the mobility management network element;

determining, by the network repository network element based on the first request message, at least one target session management network element from session management network elements that support the data network name;

sending, by the network repository network element, an identifier of the at least one target session management network element and information about a service area of the at least one target session management network element to the mobility management network element;

receiving, by the mobility management network element, the identifier of the at least one target session management network element and the information about the service area of the at least one target session management network element;

determining, by the mobility management network element based on first location information and the information about the service area of the at least one target session management network element, whether the at least one target session management network element supports a first location, wherein the first location information indicates the first location corresponding to an access network accessed by the terminal device;

sending, by the mobility management network element, a second request message to the network repository network element if the at least one target session management network element cannot support the first location, wherein the second request message carries the first location information;

receiving, by the network repository network element, the second request message;

sending, by the network repository network element, a second identifier of at least one fourth session management network element to the mobility management network element, wherein a type of the at least one fourth session management network element is an intermediate session management network element, and wherein the intermediate session management network element is configured to control a user-plane function network element that interfaces with the access network; and

receiving, by the mobility management network element, the second identifier of the at least one fourth session management network element from the network repository network element.

2. The communication method according to claim 1 , wherein the information about the service area of the at least one target session management network element is a range in which the at least one target session management network element can provide a service.

3. The communication method according to claim 2 , wherein the range comprises one or more tracking area identities.

4. The communication method according to claim 1 , further determining, by the network repository network element based on the first location information, the at least one fourth session management network element that supports the first location.

5. The communication method according to claim 1 , further comprising receiving, by the network repository network element, a registration request message, wherein the registration request message comprises information about a second service area of at least one session management network element, wherein the information about the second service area indicates a range supported by the at least one session management network element, and wherein the at least one session management network element comprises the at least one target session management network element.

6. The communication method according to claim 1 , further comprising:

detecting when the terminal device moves and a connection of the terminal device is switched from a source access network to a target access network;

sending, by the mobility management network element, second location information of the terminal device to the network repository network element, wherein the second location information indicates a second location corresponding to the target access network accessed by the terminal device;

receiving, by the network repository network element, the second location information;

determining, by the network repository network element based on the second location information, at least one fifth session management network element that supports the second location, wherein the at least one fifth session management network element controls a user-plane function network element that interfaces with the target access network;

sending, by the network repository network element, a third identifier of the at least one fifth session management network element to the mobility management network element; and

receiving, by the mobility management network element, the third identifier of the at least one fifth session management network element.

7. The communication method according to claim 1 , further comprising:

detecting when the terminal device moves and a connection of the terminal device is switched from a source access network to a target access network;

determining, by the mobility management network element based on a second location and information about a second service area of a source session management network element, whether to reselect a target intermediate session management network element for the terminal device, wherein the source session management network element is configured to control a user-plane function network element that interfaces with the source access network, wherein the target intermediate session management network element is configured to control a second user-plane function network element that interfaces with the target access network, and wherein the second location corresponds to the target access network accessed by the terminal device;

sending, by the mobility management network element, second location information to the network repository network element when the mobility management network element determines that the target intermediate session management network element needs to be reselected for the terminal device, wherein the second location information indicates the second location;

receiving, by the network repository network element, the second location information;

sending, by the network repository network element, a third identifier of at least one fifth session management network element to the mobility management network element, wherein the third identifier is determined based on the second location information; and

receiving, by the mobility management network element, the third identifier.

8. The communication method according to claim 7 , wherein determining to reselect the target intermediate session management network element for the terminal device comprises:

determining, by the mobility management network element, whether the source session management network element supports the second location; and

determining, by the mobility management network element, to reselect the target intermediate session management network element for the terminal device when the source session management network element cannot support the second location.

9. The communication method according to claim 1 , before sending the first request message to the network repository network element, the communication method further comprises receiving, by the mobility management network element, a protocol data unit (PDU) session establishment request.

10. The communication method according to claim 1 , wherein after receiving the identifier of the at least one fourth session management network element from the network repository network element, the communication method further comprises sending, by the mobility management network element, a session establishment request to a session management network element in the at least one fourth session management network element.

11. A communication system, comprising:

a mobility management network element configured to send a first request message, wherein the first request message carries a data network name of a session that a terminal device requests to establish; and

a network repository network element configured to:

receive the first request message from the mobility management network element;

determine, based on the first request message, at least one target session management network element from session management network elements that support the data network name; and

send an identifier of the at least one target session management network element and information about a service area of the at least one target session management network element to the mobility management network element,

wherein the mobility management network element is further configured to

receive the identifier of the at least one target session management network element and the information about the service area of the at least one target session management network element;

determine, based on the first location information and the information about the service area of the at least one target session management network element, whether the at least one target session management network element supports a first location, wherein the first location information indicates the first location corresponding to an access network accessed by the terminal device; and

send a second request message to the network repository network element if the at least one target session management network element cannot support the first location,

wherein the second request message carries the first location information,

wherein the network repository network element is further configured to,

receive the second request message; and

send a second identifier of at least one fourth session management network element to the mobility management network element, wherein a type of the at least one fourth session management network element is an intermediate session management network element, and wherein the intermediate session management network element is configured to control a user-plane function network element that interfaces with the access network.

12. The communication system according to claim 11 , wherein the service area of the at least one target session management network element is a range in which the at least one target session management network element can provide a service.

13. The communication system according to claim 11 , wherein the network repository network element is further configured to determine, based on the first location information, the at least one fourth session management network element that supports the first location, and wherein the mobility management network element is further configured to receive the second identifier of the at least one fourth session management network element.

14. The communication system according to claim 11 , wherein the network repository network element is further configured to receive a registration request message, wherein the registration request message comprises information about a second service area of at least one session management network element, wherein the information about the second service area indicates a range supported by the at least one session management network element, and wherein the at least one session management network element comprises the at least one target session management network element.

15. The communication system according to claim 11 , wherein the mobility management network element is further configured to send second location information of the terminal device to the network repository network element, wherein the second location information indicates a second location corresponding to a target access network accessed by the terminal device,

wherein the network repository network element is further configured to:

receive the second location information;

determine, based on the second location information, at least one fifth session management network element that supports the second location, wherein the at least one fifth session management network element controls a user-plane function network element that interfaces with the target access network; and

send a third identifier of the at least one fifth session management network element to the mobility management network element, and

wherein the mobility management network element is further configured to receive the third identifier of the at least one fifth session management network element.

16. The communication system according to claim 11 , wherein the mobility management network element is further configured to receive the second identifier of the at least one fourth session management network element from the network repository network element.

17. The communication system according to claim 11 , wherein the mobility management network element is further configured to:

determine, based on a second location and information about a second service area of a source session management network element, whether to reselect a target intermediate session management network element for the terminal device, wherein the source session management network element is configured to control a user-plane function network element that interfaces with a source access network, wherein the target intermediate session management network element is configured to control a second user-plane function network element that interfaces with a target access network, and wherein the second location is a location corresponding to the target access network accessed by the terminal device; and

send second location information to the network repository network element when determining that the target intermediate session management network element needs to be reselected for the terminal device, wherein the second location information indicates the second location corresponding to the target access network accessed by the terminal device,

wherein the network repository network element is further configured to receive the second location information, and send a third identifier of at least one fifth session management network element to the mobility management network element, wherein the third identifier of the at least one fifth session management network element is determined based on the second location information, and

wherein the mobility management network element is further configured to receive the third identifier of the at least one fifth session management network element.

18. The communication system according to claim 17 , wherein the mobility management network element is configured to:

determine whether the source session management network element supports the second location; and

determine to reselect the target intermediate session management network element for the terminal device when the source session management network element cannot support the second location.

19. A mobility management network element, comprising:

at least one processor; and

a memory coupled to the at least one processor and storing computer-executable instructions that, when executed by the at least one processor, cause the mobility management network element to:

send a first request message to a network repository network element, wherein the first request message comprises a data network name of a session that a terminal device requests to establish;

receive, from the network repository network element, an identifier of at least one target session management network element and information about a service area of the at least one target session management network element, wherein the at least one target session management network element supports the data network name;

determine, based on first location information and the information about the service area of the at least one target session management network element, whether the at least one target session management network element supports a first location, wherein the first location information indicates the first location corresponding to an access network accessed by the terminal device;

send a second request message to the network repository network element if the at least one target session management network element cannot support the first location, wherein the second request message comprises the first location information; and

receive an identifier of at least one fourth session management network element from the network repository network element, wherein a type of the at least one fourth session management network element is an intermediate session management network element, and wherein the intermediate session management network element is configured to control a user-plane function network element that interfaces with the access network.

20. The mobility management network element according to claim 19 , wherein the computer-executable instructions, when executed by the at least one processor, further cause the mobility management network element to receive a protocol data unit (PDU) session establishment request.

21. The mobility management network element according to claim 19 , wherein the computer-executable instructions, when executed by the at least one processor, further cause the mobility management network element to send a session establishment request to a session management network element in the at least one fourth session management network element.

22. A communication method, comprising:

sending, by a mobility management net ork element, a first request message to a network repository network element, wherein the first request message comprises a data network name of a session that a terminal device requests to establish;

receiving, by the mobility management network element, from the network repository network element, an identifier of at least one target session management network element and information about a service area of the at least one target session management network element, wherein the at least one target session management network element supports the data network name;

determining, by the mobility management network element, based on first location information and the information about the service area of the at least one target session management network element, whether the at least one target session management network element supports a first location, wherein the first location information indicates the first location corresponding to an access network accessed by the terminal device;

sending, by the mobility management network element, a second request message to the network repository network element if the at least one target session management network element cannot support the first location, wherein the second request message comprises the first location information; and

receiving, by the mobility management network element, an identifier of at least one fourth session management network element from the network repository network element, wherein a type of the at least one fourth session management network element is an intermediate session management network element, and wherein the intermediate session management network element is configured to control a user-plane function network element that interfaces with the access network.

23. The communication method according to claim 22 , further comprising receiving, by the mobility management network element, a protocol data unit (PDU) session establishment request.

24. The communication according to claim 22 , further comprising

sending, by the mobility management network element, a session establishment request to a session management network element in the at least one fourth session management network element.

25. The communication method according to claim 22 , wherein the information about the service area of the at least one target session management network element is a range in which the at least one target session management network element can provide a service.

26. The communication method according to claim 25 , wherein the range comprises one or more tracking area identities.