Network handover method and related device

1. A network handover method, comprising:

receiving, by a source mobility management function entity in a source system from a source radio access network node in the source system, a user terminal handover required message that carries a target base station identifier in a target system;

determining, by the source mobility management function entity based on the target base station identifier, to trigger a handover of a user terminal from the source system to the target system;

sending, by the source mobility management function entity, a first message for requesting a session management context to a source session management function entity in the source system;

receiving, by the source mobility management function entity, a second message from the source session management function entity, wherein the second message comprises a session management context of the user terminal in the target system; and

sending, by the source mobility management function entity, a relocation request to a target mobility management function entity in the target system, wherein the relocation request is used to instruct to perform the handover on the user terminal, wherein the relocation request carries the target base station identifier, the session management context of the user terminal in the target system, and a mobility management context of the user terminal in the target system, wherein the source system is a 5 th generation (5G) network, and wherein the target system is a 4 th generation (4G) network.

2. The network handover method according to claim 1 , wherein the first message comprises a 5G-to-4G network handover indication, and the 5G-to-4G network handover indication is for determining that an operation is a 5G-to-4G network handover.

3. The network handover method according to claim 1 , wherein before sending, by the source mobility management function entity, the relocation request to the target mobility management function entity, the method further comprises:

obtaining, by the source mobility management function entity, a mobility management context of the user terminal in the source system; and

mapping, by the source mobility management function entity, the mobility management context of the user terminal in the source system to the mobility management context of the user terminal in the target system.

4. A network handover device, comprising:

a memory; and

a processor coupled to the memory and configured to execute instructions stored on the memory such that when executed by the processor, cause the network handover device to:

receive, from a source radio access network node in a source system, a user terminal handover required message that carries a target base station identifier in a target system;

determine, based on the target base station identifier, to trigger a handover of a user terminal from the source system to the target system;

send a first message for requesting a session management context to a source session management function entity in the source system;

receive a second message from the source session management function entity, wherein the second message comprises a session management context of the user terminal in the target system; and

send a relocation request to a target mobility management function entity in the target system, wherein the relocation request is used to instruct to perform the handover on the user terminal,

wherein the relocation request carries the target base station identifier, the session management context of the user terminal in the target system, and a mobility management context of the user terminal in the target system, wherein the source system is a 5 th generation (5G) network, and wherein the target system is a 4 th generation (4G) network.

5. The network handover device according to claim 4 , wherein the first message comprises a 5G-to-4G network handover indication, and the 5G-to-4G network handover indication is for determining that an operation is a 5G-to-4G network handover.

6. The network handover device according to claim 4 , wherein before sending the relocation request to the target mobility management function entity, the network handover device is configured to:

obtain a mobility management context of the user terminal in the source system; and

map the mobility management context of the user terminal in the source system to the mobility management context of the user terminal in the target system.

7. A method, comprising:

receiving, by a source mobility management function entity in a source system from a source radio access network node in the source system, a user terminal handover required message that carries a target base station identifier in a target system;

determining, by the source mobility management function entity based on the target base station identifier, to trigger a handover of a user terminal from the source system to the target system;

sending, by the source mobility management function entity, a first message for requesting a session management context to a source session management function entity in the source system;

sending, by the source session management function entity, a second message to the source mobility management function entity, wherein the second message comprises a session management context of the user terminal in the target system; and

sending, by the source mobility management function entity, a relocation request to a target mobility management function entity in the target system, wherein the relocation request is used to instruct to perform the handover on the user terminal, wherein the relocation request carries the target base station identifier, the session management context of the user terminal in the target system, and a mobility management context of the user terminal in the target system, wherein the source system is a 5 th generation (5G) network, and wherein the target system is a 4 th generation (4G) network.

8. The method according to claim 7 , wherein the first message comprises a 5G-to-4G network handover indication.

9. The method according to claim 8 , further comprising determining, by the source session management function entity, that the handover is a 5G-to-4G network handover based on the 5G-to-4G network handover indication.

10. The method according to claim 9 , further comprising:

obtaining, by the source session management function entity, a session management context of the user terminal in the source system; and

mapping, by the source session management function entity, the session management context of the user terminal in the source system to the session management context of the user terminal in the target system.

11. The method according to claim 10 , further comprising:

obtaining, by the source mobility management function entity, a mobility management context of the user terminal in the source system; and

mapping, by the source mobility management function entity, the mobility management context of the user terminal in the source system to the mobility management context of the user terminal in the target system.

12. A system, comprising:

a source mobility management function entity in a source system, wherein the source mobility management function entity is configured to:

receive, from a source radio access network node in the source system, a user terminal handover required message that carries a target base station identifier in a target system;

determine based on the target base station identifier to trigger a handover of a user terminal from the source system to the target system; and

send a first message for requesting a session management context; and

a source session management function entity in the source system, wherein the source session management function entity is configured to send a second message to the source mobility management function entity, wherein the second message comprises a session management context of the user terminal in the target system,

wherein the source mobility management function entity is further configured to send a relocation request to a target mobility management function entity in the target system, wherein the relocation request is used to instruct to perform the handover on the user terminal, wherein the relocation request carries the target base station identifier, the session management context of the user terminal in the target system, and a mobility management context of the user terminal in the target system, wherein the source system is a 5 th generation (5G) network, and wherein the target system is a 4 th generation (4G) network.

13. The system according to claim 12 , wherein the first message comprises a 5G-to-4G network handover indication.

14. The system according to claim 13 , wherein the source session management function entity is further configure to determine that the handover is a 5G-to-4G network handover based on the 5G-to-4G network handover indication.

15. The system according to claim 14 , wherein the source session management function entity is further configured to:

obtain a session management context of the user terminal in the source system; and

map the session management context of the user terminal in the source system to the session management context of the user terminal in the target system.

16. The system according to claim 15 , wherein the source mobility management function entity is further configured to:

obtain a mobility management context of the user terminal in the source system; and

map the mobility management context of the user terminal in the source system to the mobility management context of the user terminal in the target system.

17. A non-transitory computer readable storage medium storing an instruction, which when executed by a processor, causes an apparatus comprising the processor to:

receive, from a source radio access network node in a source system, a user terminal handover required message that carries a target base station identifier in a target system;

determine, based on the target base station identifier, to trigger a handover of a user terminal from the source system to the target system;

send a first message for requesting a session management context to a source session management function entity in the source system;

receive a second message from the source session management function entity, wherein the second message comprises a session management context of the user terminal in the target system; and

send a relocation request to a target mobility management function entity in the target system, wherein the relocation request is used to instruct to perform the handover on the user terminal, wherein the relocation request carries the target base station identifier, the session management context of the user terminal in the target system, and a mobility management context of the user terminal in the target system, wherein the source system is a 5 th generation (5G) network, and wherein the target system is a 4 th generation (4G) network.

18. The non-transitory computer readable storage medium according to claim 17 , wherein the instruction, when executed by the processor, further causes the apparatus to:

obtain a mobility management context of the user terminal in the source system; and

map the mobility management context of the user terminal in the source system to the mobility management context of the user terminal in the target system.

19. The non-transitory computer readable storage medium according to claim 17 , wherein the first message comprises a 5G-to-4G network handover indication, and wherein the 5G-to-4G network handover indication is for the source session management function entity to determine that the handover is a 5G-to-4G network handover.