Clock source determining method and apparatus

1. A method, comprising:

receiving, by a session management network element, a session request from a mobility management network element, wherein the session request comprises information about a network slice and a data network name (DNN), and the session request requests to create a session;

determining, by the session management network element, clock source information corresponding to both the information about the network slice and the DNN; and

sending, by the session management network element, the clock source information to an access network device, wherein the clock source information is usable by the access network device to perform clock synchronization with a terminal device; and

wherein the terminal device accesses a visited network, and the session management network element is located in the visited network.

2. The method according to claim 1 , further comprising:

receiving, by the session management network element from a network management system, a correspondence among the information about the network slice, the DNN, and the clock source information.

3. The method according to claim 1 , further comprising:

obtaining, by the session management network element from a data management network element, a correspondence among the information about the network slice, the DNN, and the clock source information.

4. The method according to claim 1 , further comprising:

receiving, by the access network device, the clock source information corresponding to both the information about the network slice and the DNN; and

performing, by the access network device, clock synchronization with the terminal device based on the clock source information.

5. The method according to claim 4 , further comprising:

receiving, by the access network device, the information about the network slice and the DNN from the session management network element.

6. The method according to claim 4 , further comprising:

receiving, by the access network device, the information about the network slice and the DNN from the session management network element via the mobility management network element, wherein the information about the network slice is information about a network slice that is allowed to be accessed by the terminal device, and the DNN is supported by the network slice that is allowed to be accessed by the terminal device.

7. A system, comprising:

a session management network element;

a mobility management network element; and

an access network device;

wherein the session management network element is configured to:

receive, from a network management system, a correspondence among information about a network slice, a data network name, and clock source information;

receive a session request from the mobility management network element, wherein the session request comprises the information about the network slice and the DNN, and the session request requests to create a session;

determine clock source information corresponding to both the information about the network slice and the DNN; and

send the clock source information to the access network device; and

wherein the access network device is configured to:

receive the clock source information; and

perform clock synchronization with a terminal device.

8. The system according to claim 7 , wherein the terminal device accesses a visited network, and the session management network element is located in the visited network.

9. An apparatus, comprising:

a receiver;

a transmitter;

a processor; and

a non-transitory computer-readable storage medium storing a program to be executed by the processor, the program including instructions for:

receiving a request message from a terminal device, wherein the request message requests to register with a network;

determining, based on subscription information of the terminal device, information about a network slice that is allowed to be accessed by the terminal device and a data network name (DNN) supported by the network slice that is allowed to be accessed by the terminal device, wherein determining the information about the network slice that is allowed to be accessed by the terminal device and the DNN supported by the network slice that is allowed to be accessed by the terminal device comprises:

obtaining, from a data management network element, information about a network slice to which the terminal device subscribes and a DNN supported by the network slice to which the terminal device subscribes; and

determining, based on the information about the network slice to which the terminal device subscribes and the DNN supported by the network slice to which the terminal device subscribes, the information about the network slice that is allowed to be accessed by the terminal device and the DNN supported by the network slice that is allowed to be accessed by the terminal device;

obtaining, from the data management network element, a correspondence among the information about the network slice that is allowed to be accessed by the terminal device, the DNN supported by the network slice that is allowed to be accessed by the terminal device, and clock source information; and

determining the clock source information corresponding to both the information about the network slice that is allowed to be accessed by the terminal device and the DNN supported by the network slice that is allowed to be accessed by the terminal device; and

wherein the transmitter is configured to send the clock source information to an access network device, wherein the clock source information is usable by the access network device to perform clock synchronization with the terminal device.

10. The apparatus according to claim 9 , wherein the request message comprises requested network slice selection assistance information.

11. The apparatus according to claim 9 , wherein the request message is received in a registration procedure of the terminal device.

12. The apparatus according to claim 9 , wherein the data management network element is a unified data management (UDM) network element.

13. The method according to claim 1 , wherein the session request carries an identifier of the terminal device.

14. The system according to claim 7 , wherein the session request carries an identifier of the terminal device.

15. The method according to claim 1 , further comprising:

sending, by the session management network element, an identifier to a unified data management (UDM) network element; and

receiving, by the session management network element, subscription data from the UDM network element.

16. The system according to claim 7 , wherein the session management network element is further configured to:

send an identifier to a unified data management (UDM) network element; and

receive subscription data from the UDM network element.

17. The method according to claim 1 , wherein the clock source information comprises an identifier of the clock source information.

18. The system according to claim 7 , wherein the clock source information comprises an identifier of the clock source information.