Communications method and apparatus

1. A communications method, comprising:

determining, by a control function entity, a session management function entity based on at least one of a data network name, slice information, or an application function service identifier;

sending, by the control function entity to the session management function entity a first message subscribing to a terminal event, wherein the first message comprises service description information indicating a service corresponding to the terminal event; and

receiving, by the session management function entity, the first message.

2. The method of claim 1 , wherein the service description information determines an application function entity that provides a service for a terminal.

3. The method of claim 1 , wherein the first message further comprises an event correlation identifier to determine event reporting information, and event type information of the terminal event to identify the terminal event.

4. The method of claim 1 , further comprising sending, by the control function entity, a second message to an access and mobility management function entity subscribing to the terminal event, wherein the second message comprises an event correlation identifier to determine event reporting information, and event type information of the terminal event to identify the terminal event.

5. The method of claim 1 , further comprising receiving, by the control function entity, the service description information from an application function entity.

6. The method of claim 1 , wherein the event type comprises an event of terminal availability after downlink data notification failure.

7. The method of claim 1 , further comprising:

receiving, by the session management function entity, service information from a user plane function entity based on a downlink data packet; and

sending, by the session management function entity, event correlation information to a mobility management entity or a capability exposure entity when the service information matches the service description information, wherein the event correlation information determines event reporting information.

8. The method of claim 7 , wherein the method further comprises sending, by the session management function entity, a service information request to the user plane function entity.

9. The method of claim 8 , wherein sending the service information request to the user plane function entity comprises sending the service information request to the user plane function entity when unreachability information of a user equipment (UE) is received.

10. The method of claim 7 , wherein sending the event correlation information to the mobility management entity or the capability exposure entity comprises sending the event correlation information to the mobility management entity or the capability exposure entity based on the service description information and the service information, wherein the event correlation information determines the event reporting information.

11. A communications system comprising:

a session management function entity configured to receive a first message; and

a control function entity configured to:

determine the session management function entity based on at least one of a data network name, slice information, or an application function service identifier; and

send the first message to the session management function entity subscribing to a terminal event, wherein the first message comprises service description information indicating a service corresponding to the terminal event.

12. The system of claim 11 , wherein the service description information determines an application function entity that provides a service for a terminal, and wherein the communications system comprises a 5 th generation (5G) system.

13. The system of claim 11 , wherein the first message further comprises an event correlation identifier to determine event reporting information and event type information of the terminal event to identify the terminal event.

14. The system of claim 11 , the control function entity is further configured to send a second message to an access and mobility management function entity subscribing to the terminal event, wherein the second message comprises an event correlation identifier to determine event reporting information and event type information of the terminal event to identify the terminal event.

15. The system of claim 11 , the control function entity is further configured to receive the service description information from an application function entity.

16. The system of claim 11 , wherein the event type of the terminal event comprises an event of terminal availability after downlink data notification failure.

17. The system of claim 11 , wherein the session management function entity is further configured to:

receive service information from a user plane function entity based on a downlink data packet; and

send event correlation information to a mobility management entity or a capability exposure entity based on the service information, wherein the event correlation information determines event reporting information.

18. The system of claim 17 , wherein the session management function entity is further configured to send a service information request to the user plane function entity.

19. The system of claim 18 , wherein the session management function entity is further configured to send the service information request to the user plane function entity when unreachability information of a user equipment (UE) is received.

20. The system of claim 17 , wherein the session management function entity is further configured to send the event correlation information to the mobility management entity or the capability exposure entity based on the service description information and the service information, wherein the event correlation information determines the event reporting information.