Method and apparatus for session management function reselection

1 . A method performed by an access and mobility function, comprising:

selecting a second session management function (SMF) to serve a session of a user equipment, wherein the session of the UE is currently served by a first SMF and an access network;

sending a create session management context request comprising a reason of selecting the second SMF to serve the session of the UE to the second SMF, the reason indicating that the session of the UE is still served by the access network;

receiving a create session management context response comprising a session resource modify request from the second SMF, the session resource modify request comprising access network tunnel information of the access network; and

sending the session resource modify request to the access network.

2 . The method according to claim 1 , wherein the reason of selecting the second SMF to serve the session of the UE is based on a single-network slice selection assistance information (S-NSSAI) value.

3 . The method according to claim 1 , wherein the session resource modify request is a protocol data unit (PDU) session resource modify request.

4 . The method according to claim 1 , wherein the create session management context request is a Nsmf_PDUSession_CreateSMContext Request and the create session management context response is a Nsmf_PDUSession_CreateSMContext Response.

5 . The method according to claim 1 , wherein the session of the UE comprises a PDU session of the UE.

6 . The method according to claim 1 , wherein the create session management context request is sent after a completion of Evolved Packet System (EPS) to fifth generation system (5GS) Mobility Registration Procedure using N26 interface or EPS to 5GS handover using N26 interface.

7 . The method according to claim 1 , wherein the first SMF comprises a first intermediate SMF and the second SMF comprises a second intermediate SMF.

8 . The method according to claim 1 , wherein the first SMF comprises a first visited SMF and the second SMF comprises a second visited SMF.

9 . A method performed by a second session management function, the method comprising:

receiving a create session management context request comprising a reason of selecting the second SMF to serve a session of a user equipment (UE) from an access and mobility function, the session of the UE being currently served by a first SMF and an access network, the reason indicating that the session of the UE is still served by the access network;

sending a session context request comprising the reason of selecting the second SMF to serve the session of the UE to the first SMF;

receiving a session context response comprising the session management context of the session of the UE and tunnel information of the access network from the first SMF; and

sending a create session management context response comprising a session resource modify request to the access and mobility function, the session resource modify request comprising the access network tunnel information of the access network received from the first SMF.

10 . The method according to claim 9 , wherein the reason of selecting the second SMF to serve the session of the UE is based on a single-network slice selection assistance information (S-NSSAI) value.

11 . The method according to claim 10 , wherein the session resource modify request is a protocol data unit (PDU) session resource modify request.

12 . The method according to claim 9 , wherein the create session management context request is a Nsmf_PDUSession_CreateSMContext Request and the create session management context response is a Nsmf_PDUSession_CreateSMContext Response.

13 . The method according to claim 9 , wherein the session of the UE is a PDU session of the UE.

14 . The method according to claim 9 , wherein the create session management context request is received after a completion of Evolved Packet System (EPS) to fifth generation system (5GS) Mobility Registration Procedure using N26 interface or EPS to 5GS handover using N26 interface.

15 . The method according to claim 9 , wherein the session context request is a Nsmf_PDUSession_Context Request and the session context response is a Nsmf_PDUSession_Context Response.

16 . The method according to claim 9 , wherein the first SMF comprises a first intermediate SMF and the second SMF comprises a second intermediate SMF.

17 . The method according to claim 9 , wherein the first SMF comprises a first visited SMF and the second SMF comprises a second visited SMF.

18 . An access and mobility function, comprising:

a processor; and

a memory coupled to the processor, the memory containing instructions executable by the processor, whereby the access and mobility function is operative to:

select a second session management function (SMF) to serve a session of a user equipment (UE), the session of the UE being currently served by a first SMF and an access network;

send a create session management context request comprising a reason of selecting the second SMF to serve the session of the UE to the second SMF, the reason indicating that the session of the UE is still served by the access network;

receive a create session management context response comprising a session resource modify request from the second SMF, the session resource modify request comprising access network tunnel information of the access network; and

send the session resource modify request to the access network.

19 . The access and mobility function according to claim 18 , wherein the access and mobility function is configured such that the reason of selecting the second SMF to serve the session of the UE is based on a single-network slice selection assistance information (S-NSSAI) value.

20 . A second session management function (SMF), comprising:

a processor; and

a memory coupled to the processor, the memory containing instructions executable by the processor, whereby the second SMF is operative to:

receive a create session management context request comprising a reason of selecting the second SMF to serve a session of a user equipment (UE) from an access and mobility function, the session of the UE being currently served by a first SMF and an access network, the reason indicating that the session of the UE is still served by the access network;

send a session context request comprising the reason of selecting the second SMF to serve the session of the UE to the first SMF;

receive a session context response comprising the session management context of the session of the UE and tunnel information of the access network from the first SMF; and

send a create session management context response comprising a session resource modify request to the access and mobility function, the session resource modify request comprises comprising access network tunnel information of the access network received from the first SMF.

21 . The second SMF according to claim 20 , wherein the second SMF is configured such that the reason of selecting the second SMF to serve the session of the UE is based on a single-network slice selection assistance information (S-NSSAI) value.

22 . The access and mobility function according to claim 18 , wherein the create session management context request is a Nsmf_PDUSession_CreateSMContext Request and the create session management context response is a Nsmf_PDUSession_CreateSMContext Response.

23 . The second SMF according to claim 20 , wherein the create session management context request is a Nsmf_PDUSession_CreateSMContext Request and the create session management context response is a Nsmf_PDUSession_CreateSMContext Response.