Method and apparatus for session management

1. A method implemented at a first network function (NF), comprising:

detecting that a path between the first NF and a second NF is failed or the second NF is failed, wherein the second NF maintains one or more data network connections or sessions established between one or more user equipments (UEs) and one or more data networks;

selecting an available second NF for the at least one of the one or more data network connections or sessions;

sending at least one address or address range of at least one UE corresponding to the at least one of the one or more data network connections or sessions and a respective priority metric of the at least one address or address range to the available second NE; and

the respective priority metric being associated with a valid time, and responsive to the valid time expiring, applying a predefined priority metric to the at least one address or address range, the respective priority metric having a higher priority than a priority of the predefined priority metric, the higher priority indicating a shorter path toward the at least one address or address range.

2. The method according to claim 1 , wherein the steps of selecting and sending are performed in a planned way or in response to receiving a signaling.

3. The method according to claim 1 , wherein the at least one address or address range and the respective priority metric are notified to the one or more data networks by the available second NF to enable the one or more data networks at least one of to route and forward traffic for the at least one UE to the available second NF instead of the second NF.

4. The method according to claim 1 , wherein the one or more data network connections or sessions pass through a tunnel between the second NF and a fourth NF, the method further comprises:

sending a tunnel identifier of the fourth NF to the available second NF;

receiving a tunnel identifier of the available second NF from the available second NF; and

sending the tunnel identifier of the available second NF to the fourth NF.

5. The method according to claim 4 , wherein the first NF comprises a Session Management Function (SMF), the second NF comprises a User Plane Function (UPF), and the fourth NF comprises another UPF.

6. The method according to claim 4 , wherein sending the tunnel identifier of the available second NF to the fourth NF comprises:

sending the tunnel identifier of the available second NF to a third NF, the third NF configured to send the tunnel identifier of the available second NF to the fourth NF.

7. The method according to claim 6 , wherein the first NF comprises a packet data network gateway control plane (PGW-C) or a Session Management Function (SMF), the second NF comprises a packet data network gateway user plane (PGW-U) or a User Plane Function (UPF), the third NF comprises a control plane of a serving gateway (SGW-C) or an Access and Mobility Management Function (AMF), and the fourth NF comprises a user plane of a serving gateway (SGW-U) or a (Radio) Access Network ((R)AN).

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

detecting that the path between the first NF and the second NF is recovered or the second NF is recovered; and

sending at least one session deletion request to the second NF to cleanup at least one session between the first NF and the second NF.

9. A method implemented at an available second network function (NF), comprising:

receiving at least one address or address range of at least one user equipment (UE) corresponding to at least one of one or more data network connections or sessions and a respective priority metric of the at least one address or address range from a first NF, wherein the second NF maintains the one or more data network connections or sessions established between one or more UEs and one or more data networks;

notifying the at least one address or address range and the respective priority metric to the one or more data networks;

the respective priority metric being associated with a valid time, and

responsive to the valid time expiring, applying a predefined priority metric to the at least one address or address range, the respective priority metric having a higher priority than a priority of the predefined priority metric, the higher priority indicating a shorter path toward the at least one address or address range.

10. The method according to claim 9 , wherein the at least one address or address range and the respective priority metric can enable the one or more data networks at least one of to route and forward traffic for the at least on UE to the available second NF instead of the second NF.

11. The method according to claim 9 , wherein the one or more data network connections or sessions pass through a tunnel between the second NF and a fourth NF, the method further comprising

receiving a tunnel identifier of the fourth NF from the first NF; and

sending a tunnel identifier of the available second NF to the first NF, the first NF configured to send the tunnel identifier of the available second NF to the fourth NF.

12. The method according to claim 11 , wherein the first NF comprises a Session Management Function (SMF), the second NF comprises a User Plane Function (UPF), and the fourth NF comprises a UPF.

13. The method according to claim 11 , wherein the tunnel identifier of the available second NF is sent by the first NF to a third second NF which will send the tunnel identifier of the available second NF to the fourth NF.

14. The method according to claim 13 , wherein the first NF comprises a packet data network gateway control plane (PGW-C) or a Session Management Function (SMF), the second NF comprises a packet data network gateway user plane (PGW-U) or a User Plane Function (UPF), the third NF comprises a control plane of a serving gateway (SGW-C) or an Access and Mobility Management Function (AMF), and the fourth NF comprises a user plane of a serving gateway (SGW-U) or a (Radio) Access Network ((R)AN).

15. An apparatus implemented at a first network function (NF), comprising:

a processor; and

a memory coupled to the processor, said memory containing instructions executable by said processor, whereby said apparatus is configured to:

detect that a path between the first NF and a second NF is failed or the second NF is failed, wherein the second NF maintains one or more data network connections or sessions established between one or more user equipments (UEs) and one or more data networks;

select an available second NF for the at least one of the one or more data network connections or sessions;

send at least one address or address range of at least one UE corresponding to the at least one of the one or more data network connections or sessions and a respective priority metric of the at least one address or address range to the available second NE;

the respective priority metric being associated with a valid time, and responsive to the valid time expiring, applying a predefined priority metric to the

at least one address or address range, the respective priority metric having a higher priority than a priority of the predefined priority metric, the higher priority indicating a shorter path toward the at least one address or address range.

16. An apparatus implemented at an available second network function (NF), comprising:

a processor; and

a memory coupled to the processor, said memory containing instructions executable by said processor, whereby said apparatus is configured to:

receive at least one address or address range of at least one user equipment (UE) corresponding to at least one of one or more data network connections or sessions and a respective priority metric of the at least one address or address range from a first NF, wherein a second NF maintains the one or more data network connections or sessions established between one or more UEs and one or more data networks;

notify the at least one address or address range and the respective priority metric to the one or more data networks;

of the respective priority metric being associated with a valid time, and

responsive to the valid time expiring, applying a predefined priority metric to the

at least one address or address range, the respective priority metric having a higher priority than a priority of the predefined priority metric, the higher priority indicating a shorter path toward the at least one address or address range.