Terminal interaction with different user plane function entities

1. A data transmission method comprising:

receiving, by a first user plane function entity, a data packet from a first terminal through an uplink path corresponding to the first terminal, wherein the data packet comprises first addressing information of a second terminal, wherein the first addressing information comprises an internet protocol (IP) or a media access control (MAC) address of the second terminal, and wherein the first user plane function entity currently serves the first terminal;

determining, by the first user plane function entity based on uplink information about the uplink path, and identity of a same mobile local area network (MLAN) in which the first terminal and the second terminal are located, wherein the uplink information about the uplink path corresponding to the first terminal comprises a first tunnel identifier of the first user plane function entity, and wherein the first tunnel identifier is allocated for the first terminal;

determining, by the first user plane function entity based on the identity of the same MLAN and the first addressing information, first path information of a second user plane function entity, wherein the second user plane function entity currently serves the second terminal, wherein the first path information comprises a second tunnel identifier of the second user plane function entity, and wherein the second tunnel identifier is allocated for a second tunnel between the first user plane function entity and the second user plane function entity;

sending, by the first user plane function entity, the data packet to the second user plane function entity based on the first path information;

receiving, by the second user plane function entity, the data packet from the first user plane function entity; and

sending, by the second user plane function entity, the data packet to the second terminal through a downlink path corresponding to the second terminal.

2. The method of claim 1 , wherein determining the identity of the same MLAN comprises determining, by the first user plane function entity based on the uplink information and a first correspondence, the identity of the same MLAN, and wherein the first correspondence is between the uplink information and the identity of the same MLAN.

3. The method of claim 1 , wherein determining the first path information comprises determining, by the first user plane function entity, the first path information based on the identity of the same MLAN, the first addressing information, and a second correspondence, and wherein the second correspondence is between the first addressing information, the first path information, and the identity of the same MLAN.

4. The method of claim 1 , further comprising determining, by the second user plane function entity based on the first path information and the first addressing information, the downlink path.

5. The method of claim 4 , wherein determining the downlink path comprises:

determining, by the second user plane function entity based on the first path information, the identity of the same MLAN; and

determining, by the second user plane function entity based on the identity of the same MLAN and the first addressing information, the downlink path.

6. The method of claim 1 , further comprising establishing, by a session management function entity, the second tunnel between the first user plane function entity and the second user plane function entity, wherein the second tunnel is at an MLAN granularity such that the tunnel is shared by any two user plane function entities.

7. The method of claim 6 , wherein establishing the second tunnel comprises:

sending, by the session management function entity, a first N4 session message to the first user plane function entity, wherein the first N4 session message comprises a second identifier of a second MLAN of the second terminal, the first addressing information, and the first path information; and

saving, by the first user plane function entity, a correspondence between the first addressing information, the first path information, and the second identifier of the second MLAN.

8. The method of claim 7 , wherein establishing the second tunnel comprises:

sending, by the session management function entity, a second N4 session message to the second user plane function entity, wherein the second N4 session message comprises a first identifier of a first MLAN of the first terminal, second addressing information of the first terminal, and second path information of the first user plane function entity;

determining, based on the first identifier and the second identifier, that the first MLAN and the second MLAN are both the same MLAN in which the first terminal and the second terminal are located; and

saving, by the first user plane function entity, a second correspondence between the second addressing information, the second path information of the first user plane function entity, and the first identifier of the first MLAN.

9. The method of claim 6 , further comprising determining, by the session management function entity, that the same MLAN comprises a cross user plane function entity scenario in which the first user plane function entity and the second user plane function entity serve different terminals in the same MLAN.

10. A data transmission system comprising:

a second user plane function entity; and

a first user plane function entity configured to:

receive a data packet from a first terminal through an uplink path corresponding to the first terminal, wherein the data packet comprises addressing information of a second terminal, wherein the first addressing information comprises an internet protocol (IP) or a media access control (MAC) address of the second terminal, and wherein the first user plane function entity currently serves the first terminal;

determine, based on uplink information about the uplink path, an identity of a same mobile local area network (MLAN) in which the first terminal and the second terminal are located, wherein the uplink information about the uplink path corresponding to the first terminal comprises a first tunnel identifier of the first user plane function entity, and wherein the first tunnel identifier is allocated for the first terminal;

determine, based on the identity of the same MLAN and the addressing information, path information of the second user plane function entity, wherein the second user plane function entity currently serves the second terminal, wherein the first path information comprises a second tunnel identifier of the second user plane function entity, and wherein the second tunnel identifier is allocated for a second tunnel bet ween the first user plane function entity and the second user plane function entity; and

send the data packet to the second user plane function entity based on the path information,

wherein the second user plane function entity is configured to:

receive the data packet from the first user plane function entity; and

send the data packet to the second terminal through a downlink path corresponding to the second terminal.

11. The data transmission system of claim 10 , wherein the first user plane function entity is further configured to determine, based on the uplink information and a first correspondence, the identity of the same MLAN, and wherein the first correspondence is between the uplink information and the identity of the same MLAN.

12. The data transmission system of claim 10 , wherein the first user plane function entity is further configured to determine the path information based on the identity of the same MLAN, the addressing information, and a second correspondence, and wherein the second correspondence is between the addressing information, the path information, and the identity of the same MLAN.

13. The data transmission system of claim 10 , wherein the second user plane function entity is further configured to determine, based on the path information and the addressing information, the downlink path.

14. The data transmission system of claim 13 , wherein the second user plane function entity is further configured to;

determine, based on the path information, the identity of the same MILAN; and

determine, based on the identity of the same MLAN and the addressing information, the downlink path.

15. The data transmission system of claim 10 , further comprising a session management function entity configured to establish the second tunnel between the first user plane function entity and the second user plane function entity, wherein the second tunnel is at an MLAN granularity such that the second tunnel is shared by any two user plane function entities.

16. The data transmission system of claim 15 , wherein the session management function entity is further configured to send an N4 session message to the first user plane function entity, wherein the N4 session message comprises a second identity of an MLAN of the second terminal, the addressing information, and the path information, and wherein the first user plane function entity is further configured to save a correspondence between the addressing information, the path information, and the second identity of the MLAN of the second terminal.

17. The data transmission system of claim 15 , wherein the session management function entity is further configured to determine that the same MLAN comprises a cross user plane function entity scenario in which the first user plane function entity and the second user plane function entity serve different terminals in the same MLAN.