Method and apparatus for improving service reliability in wireless communication system

1. A method, performed by a first session management function (SMF), for providing a continuous service to a user equipment (UE), the method comprising:

identifying, by the first SMF, triggering of an SMF change operation;

performing a subscription procedure with an access and mobility management function (AMF) for an event in which a status of the UE becomes an idle or an inactive;

in case that the status of the UE becomes the idle or the inactive, receiving, from the AMF, a notification message to report the event;

transmitting, to the AMF, a message indicating a change in a status of a protocol data unit (PDU) session so as to request a procedure of an SMF change, wherein the message indicating the change in the status of the PDU session includes a context identification (ID);

receiving a context request message requesting a context from a second SMF that is a target SMF; and

transmitting a context request response message to the second SMF.

2. The method of claim 1 , wherein the SMF change operation is triggered in response to a request by operations, administration and maintenance (OAM), and

wherein the request by the OAM includes the at least one of a second SMF ID (identification) or an SMF set ID.

3. The method of claim 1 ,

wherein the second SMF is selected by the AMF or a Service Communication Proxy (SCP) as an SMF corresponding to a second SMF ID when the message indicating the change in the status of the PDU session includes the second SMF ID; and

wherein the second SMF is selected by the AMF or the SCP as an SMF among SMFs corresponding to an SMF set ID when the message indicating the change in the status of the PDU session includes the SMF set ID.

4. The method of claim 1 ,

wherein the message indicating the change in the status of the PDU session further includes a PDU session ID; and

wherein the context request message requesting the context of the UE includes at least one of context type information or the context ID.

5. The method of claim 1 , further comprising:

transmitting, to a User Plane Function (UPF), request message for releasing a N4 session with the UPF; and

receiving, form the UPF, a response message for releasing the N4 session in response to the request message for releasing the N4 session with the UPF.

6. The method of claim 1 , further comprising:

transmitting, to the AMF, a message requesting notification of information about a change in a status of UE; and

receiving, from the AMF, a notification message indicating the change in the status of the UE.

7. A method, performed by an access and mobility management function (AMF), for providing a continuous service to a user equipment (UE), the method comprising:

performing a subscription procedure with a first session management function (SMF) for an event in which a status of the UE becomes an idle or an inactive;

in case that the status of the UE becomes the idle or the inactive, transmitting, to the first SMF, a notification message to report the event;

receiving, from the first SMF, a message indicating a change in a status of a protocol data unit (PDU) session so as to request a procedure of an SMF change, wherein the message indicating the change in the status of the PDU session includes a context identification (ID);

identifying a second SMF that is a target SMF;

transmitting, to the second SMF, a request message of requesting generation of a new session; and

receiving, from the second SMF, a response message with respect to the request message of requesting generation of the new session.

8. The method of claim 7 ,

wherein the second SMF is selected by the AMF or a Service Communication Proxy (SCP) as an SMF corresponding to a second SMF ID when the message indicating the change in the status of the PDU session includes the second SMF ID; and

wherein the second SMF is selected by the AMF or the SCP as an SMF among SMFs corresponding to an SMF set ID when the message indicating the change in the status of the PDU session includes the SMF set ID.

9. The method of claim 7 ,

wherein the message indicating the change in the status of the PDU session further includes a PDU session ID; and

wherein a context request message requesting a context of the UE includes at least one of context type information or the context ID.

10. The method of claim 7 , further comprising:

receiving, from the first SMF, a message requesting notification of information about a change in a status of UE; and

transmitting, to the first SMF, a notification message indicating the change in the status of the UE.

11. A first session management function (SMF) for providing a continuous service to a user equipment (UE), the SMF comprising:

a transceiver; and

at least one processor coupled with the transceiver and configured to:

identify, by the first SMF, triggering of an SMF change operation,

perform a subscription procedure with an access and mobility management function (AMF) for an event in which a status of the UE becomes an idle or an inactive,

in case that the status of the UE becomes the idle or the inactive, receive, from the AMF, a notification message to report the event,

transmit, to the AMF, a message indicating a change in a status of a protocol data unit (PDU) session so as to request a procedure of an SMF change, wherein the message indicating the change in the status of the PDU session includes a context identification (ID),

to receive a context request message requesting a context of from a second SMF that is a target SMF, and

transmit a context request response message to the second SMF.

12. The first SMF of claim 11 , wherein the SMF change operation is triggered in response to a request by operations, administration and maintenance (OAM), and

wherein the request by the OAM includes the at least one of a second SMF ID (identification) or an SMF set ID.

13. The first SMF of claim 11 ,

wherein the second SMF is selected by the AMF or a Service Communication Proxy (SCP) as an SMF corresponding to a second SMF ID when the message indicating the change in the status of the PDU session includes the second SMF ID; and

wherein the second SMF is selected by the AMF or the SCP as an SMF among SMFs corresponding to an SMF set ID when the message indicating the change in the status of the PDU session includes the SMF set ID.

14. The first SMF of claim 11 ,

wherein the message indicating the change in the status of the PDU session further includes a PDU session ID; and

wherein the context request message requesting the context of the UE includes at least one of context type information or the context ID.

15. The first SMF of claim 11 , wherein the at least one processor is further configured to:

transmit, to a User Plane Function (UPF), request message for releasing a N4 session with the UPF, and

receive, form the UPF, a response message for releasing the N4 session in response to the request message for releasing the N4 session with the UPF.

16. The first SMF of claim 11 , wherein the at least one processor is further configured to:

transmit, to the AMF, a message requesting notification of information about a change in a status of UE; and

receive, from the AMF, a notification message indicating the change in the status of the UE.

17. An access and mobility management function (AMF) for providing a continuous service to a user equipment (UE), the AMF comprising:

a transceiver; and

at least one processor coupled with the transceiver and configured to:

perform a subscription procedure with a first session management function (SMF for an event in which a status of the UE becomes an idle or an inactive,

in case that the status of the UE becomes the idle or the inactive, transmit, to the first SMF, a notification message to report the event,

receive, from the first SMF, a message indicating a change in a status of a protocol data unit (PDU) session so as to request a procedure of an SMF change, wherein the message indicating the change in the status of the PDU session includes a context identification (ID),

identify a second SMF that is a target SMF,

transmit, to the second SMF, a request message of requesting generation of a new session, and

receive, from the second SMF, a response message with respect to the request message of requesting generation of the new session.

18. The AMF of claim 17 ,

wherein the second SMF is selected by the AMF or a Service Communication Proxy (SCP) as an SMF corresponding to a second SMF ID when the message indicating the change in the status of the PDU session includes the second SMF ID; and

wherein the second SMF is selected by the AMF or the SCP as an SMF among SMFs corresponding to an SMF set ID when the message indicating the change in the status of the PDU session includes the SMF set ID.

19. The AMF of claim 17 ,

wherein the message indicating the change in the status of the PDU session further includes a PDU session ID; and

wherein a context request message requesting a context of the UE includes at least one of context type information or the context ID.

20. The AMF of claim 17 , wherein the at least one processor is further configured to:

receive, from the first SMF, a message requesting notification of information about a change in a status of UE, and

transmit, to the first SMF, a notification message indicating the change in the status of the UE.