Communications system, communication method, and apparatus thereof

1. A communications system, comprising: a multicast session management network element, an access and mobility management network element and a user plane function network element, wherein

the multicast session management network element is configured to: send a first multicast session request to the access and mobility management network element, wherein the first multicast session request carries a multicast session context, and the first multicast session request is used to request to establish a multicast session based on the multicast session context; and send a second multicast session request to the user plane function network element, wherein the second multicast session request carries user plane forwarding-related information, and the user plane forwarding-related information is used to indicate a user plane forwarding rule of the multicast session;

the access and mobility management network element is configured to: receive the first multicast session request, and send the first multicast session request to an access network node; and

the user plane function network element is configured to: receive the second multicast session request, and set, based on the user plane forwarding-related information, the user plane forwarding rule of the multicast session.

2. The communications system according to claim 1 , further comprising a multicast service control network element, wherein

the multicast service control network element is configured to send a multicast service transmission request to the multicast session management network element, wherein the multicast service transmission request carries service description information of a multicast service;

the multicast session management network element is further configured to: receive the multicast service transmission request, and send the first multicast session request and the second multicast session request based on the multicast service transmission request; and

the multicast session management network element is further configured to send a multicast service transmission response to the multicast service control network element, wherein the multicast service transmission response carries multicast transmission information of the multicast service.

3. The communications system according to claim 2 , wherein the multicast service control network element is further configured to: determine to transmit the multicast service by using a multicast transmission manner, and send the multicast service transmission request to the multicast session management network element after the determining to transmit the multicast service by using a multicast transmission manner.

4. The communications system according to claim 2 , wherein the multicast transmission information of the multicast service comprises at least one of a multicast transmission stream identifier and a user plane receiving address that are of the multicast service; and

the multicast service control network element is further configured to send a service receiving indication message to a terminal, wherein the service receiving indication message carries at least one of the multicast transmission stream identifier and the user plane receiving address, and the service receiving indication message is used to instruct the terminal to receive data of the multicast service.

5. The communications system according to claim 1 , wherein the first multicast session request carries an access network node side user plane multicast receiving address, and the second multicast session request carries the access network node side user plane multicast receiving address of the access network node; and

the multicast session management network element is further configured to allocate the access network node side user plane multicast receiving address to the multicast session.

6. The communications system according to claim 1 , wherein

the user plane function network element is further configured to: allocate an access network node side user plane multicast receiving address to the multicast session, and send the access network node side user plane multicast receiving address to the multicast session management network element; and

the multicast session management network element is further configured to: receive the access network node side user plane multicast receiving address, and add the access network node side user plane multicast receiving address to the first multicast session request.

7. The communications system according to claim 1 , further comprising the access network node, wherein

the access network node is configured to: receive the first multicast session request from the access and mobility management network element, and send a first multicast session response to the access and mobility management network element, wherein the first multicast session response carries path information of the access network node, and the path information comprises at least one of a downlink receiving address and a tunnel identifier;

the access and mobility management network element is further configured to: receive the first multicast session response, and send the first multicast session response to the multicast session management network element; and

the multicast session management network element is further configured to: receive the first multicast session response, and add the path information of the access network node to the second multicast session request.

8. The communications system according to claim 1 , further comprising the access network node, wherein

the user plane function network element is further configured to forward, based on the user plane forwarding rule of the multicast session, data to the access network node by using the multicast session; and

the access network node is further configured to: receive the data forwarded by the user plane function network element, and broadcast the data.

9. A multicast session management network element, comprising: a processor and a memory, wherein

the memory is configured to store an instruction;

the processor is configured to read the instruction stored in the memory, to perform the following operations:

sending a first multicast session request to an access and mobility management network element, wherein the first multicast session request carries a multicast session context, and the first multicast session request is used to request to establish a multicast session based on the multicast session context; and

sending a second multicast session request to a user plane function network element, wherein the second multicast session request carries user plane forwarding-related information, and the user plane forwarding-related information is used to indicate a user plane forwarding rule of the multicast session.

10. The multicast session management network element according to claim 9 , wherein the processor is further configured to:

receive a multicast service transmission request from a multicast service network element;

send a multicast service transmission response to the multicast service network element, wherein the multicast service transmission response carries multicast transmission information of the multicast service;

the sending a first multicast session request to an access and mobility management network element comprises:

sending, based on the multicast service transmission request, the first multicast session request to the access and mobility management network element; and

the sending a second multicast session request to a user plane function network element comprises:

sending, based on the multicast service transmission request, the second multicast session request to the user plane function network element.

11. The multicast session management network element according to claim 9 , wherein the processor is further configured to:

allocate an access network node side user plane multicast receiving address to the multicast session, wherein the first multicast session request and the second multicast session request carry the access network node side user plane multicast receiving address.

12. The multicast session management network element according to claim 9 , wherein the processor is further configured to:

receive an access network node side user plane multicast receiving address from the user plane function network element, and add the access network node side user plane multicast receiving address to the first multicast session request.

13. The multicast session management network element according to claim 9 , wherein the processor is further configured to:

receive a first multicast session response from the access and mobility management network element, wherein the first multicast session response carries path information of the access network node; and add the path information of the access network node to the second multicast session request, wherein the path information comprises at least one of a downlink receiving address and a tunnel identifier.

14. A user plane function network element, comprising a processor and a memory, wherein

the memory is configured to store an instruction;

the processor is configured to read the instruction stored in the memory, to perform the following operations:

receiving a multicast session request from a multicast session management network element, wherein the multicast session request carries user plane forwarding-related information and carries path information of the access network node, and the path information comprises at least one of a downlink receiving address and a tunnel identifier; and

setting a user plane forwarding rule of a multicast session based on the user plane forwarding-related information.

15. The user plane function network element according to claim 14 , wherein the processor is further configured to:

allocate a user plane receiving address to the multicast session; and

send a multicast session response to the multicast session management network element, wherein the multicast session response carries the user plane receiving address.

16. The user plane function network element according to claim 14 , wherein the processor is further configured to:

allocate an access network node side user plane multicast receiving address to the multicast session; and

send the access network node side user plane multicast receiving address to the multicast session management network element.

17. The user plane function network element according to claim 16 , wherein the multicast session request carries path information of the access network node, and the path information comprises at least one of a downlink receiving address and a tunnel identifier.