Intra-rat handover for next generation system

1 . A method of operating a session management function (SMF) entity in a wireless communication system, the method comprising:

receiving, from an access and mobility management function (AMF), an N11 message including a list of bearers to be switched;

determining whether a source user plane function (UPF) entity can continue to serve a user equipment (UE) based on the N11 message;

selecting a target UPF based on UPF selection criteria, in case that the source UPF entity cannot continue to serve the UE;

allocating tunnel information associated with an uplink (UL) and tunnel information associated with a downlink (DL);

transmitting, to the target UPF, an N4 session establishment request message including the tunnel information associated with the UL and the tunnel information associated with the DL; and

transmitting, to the AMF, an N11 acknowledge (ACK) message based on the N11 message, the N11 ACK message including the tunnel information associated with the UL.

2 . The method of claim 1 , further comprising:

receiving, from the target UPF, an N4 session establishment response message as a response to the N4 session establishment request message;

starting a timer based on receiving the N4 session establishment response message; and

performing a source UPF release procedure in case that the timer is expired.

3 . The method of claim 1 , further comprising:

transmitting, to a UPF with a protocol data unit (PDU) session anchor (PSA), an N4 session modification request message; and

receiving, from the UPF with the PSA, an N4 session modification response message as a response to the N4 session modification request message.

4 . The method of claim 3 , the N11 ACK message is transmitted to the AMF, after receipt of the N4 session modification response message.

5 . The method of claim 1 , wherein and the UPF selection criteria comprise at least one of:

information on a dynamic load of at least one UPF;

information on a relative static capacity of at least one UPF;

information on a location of at least one UPF available at the SMF;

information on capability of at least one UPF and functionality required for a particular UE session;

information on a local operator policy; or

information on deployment of at least one UPF.

6 . A method of operating an access and mobility management function (AMF) entity in a wireless communication system, the method comprising:

transmitting, to a session management function (SMF), an N11 message including a list of bearers to be switched;

in response to the SMF determining that a source user plane function cannot continue to serve a user equipment (UE) based on the N11 message and selecting a target UPF based on UPF selection criteria, receiving, from the SMF, an N4 session establishment request message including tunnel information associated with an uplink (UL) and tunnel information associated with a downlink (DL); and

receiving, from the SMF, an N11 acknowledge (ACK) message including the tunnel information associated with the UL.

7 . The method of claim 6 , wherein the N11 message includes at least one session to be switched and the at least one session is associated with the UE.

8 . An apparatus for a session management function (SMF) in a wireless communication system, the apparatus comprising:

a network node configured to:

receive, from an access and mobility management function (AMF), an N11 message including a list of bearers to be switched,

determine whether a source user plane function (UPF) entity can continue to serve a user equipment (UE) based on the N11 message,

select a target UPF entity based on UPF selection criteria, in case that the source UPF entity cannot continue to serve the UE,

allocate tunnel information associated with an uplink (UL) and tunnel information associated with a downlink (DL),

transmit, to the target UPF, an N4 session establishment request message including the tunnel information associated with the UL and the tunnel information associated with the DL, and

transmit, to the AMF, an N11 acknowledge (ACK) message based on the N11 message, the N11 ACK message including the tunnel information associated with the UL.

9 . The apparatus of claim 8 , wherein the network node is further configured to:

receive, from the target UPF entity, an N4 session establishment response message as a response to the N4 session establishment request message,

start a timer based on receiving the N4 session establishment response message, and

perform a source UPF release procedure in case that the timer is expired.

10 . The apparatus of claim 8 , wherein the network node is further configured to:

transmit, to a UPF with a protocol data unit (PDU) session anchor (PSA), an N4 session modification request message, and

receive, from the UPF with the PSA, an N4 session modification response message as a response to the N4 session modification request message.

11 . The apparatus of claim 10 , wherein the N11 ACK message is transmitted to the AMF, after receipt of the N4 session modification response message.

12 . The apparatus of claim 8 , wherein the UPF selection criteria comprises at least one of:

information on a dynamic load of at least one UPF;

information on a relative static capacity of at least one UPF;

information on a location of at least one UPF available at the SMF;

information on capability of at least one UPF and functionality required for a particular UE session;

information on a local operator policy; or

information on deployment of at least one UPF.

13 . An apparatus for an access and mobility management function (AMF) entity in a wireless communication system, the apparatus comprising:

network node configured to:

transmit, to a session management function (SMF), an N11 message including a list of bearers to be switched

in response to the SMF determining that a source user plane function cannot continue to serve a user equipment (UE) based on the N11 message and selecting a target UPF based on UPF selection criteria, receive, from the SMF, an N4 session establishment request message including tunnel information associated with an uplink (UL) and tunnel information associated with a downlink (DL), and

receive, from the SMF, an N11 acknowledge (ACK) message including the tunnel information associated with the UL.

14 . The AMF of claim 13 , wherein the N11 message includes at least one session to be switched and the at least one session is associated with the UE.