AMF node, NSSF node, target SMF node and methods performed in a communications network

1. A method performed by an Access and mobility Management Function, AMF, node for allocating a target network slice instance to serve a Protocol Data Unit, PDU, session for a User Equipment, UE, in a communications network, the method comprising:

receiving, from a Network Slice Selection Function, NSSF, node, information about a decision to change an allocation of a first network slice instance that is serving the PDU session for the UE to the target network slice instance, and an identifier of the target network slice instance,

retrieving, from a first Session Management Function, SMF, node of the first network slice instance, a UE context related to the UE and the PDU session,

transmitting, towards a target SMF node of the target network slice instance, information about the retrieved UE context and Access Network, AN, tunnel information to be used for the PDU session,

receiving from the target SMF node, target Core Network, CN, tunnel information to be used for the PDU session,

allocating the target network slice instance to route data flows pertaining to the PDU session by transmitting towards an Access Network, AN, node, the target CN tunnel information to be used for the PDU session.

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

selecting the target SMF node of the target network slice instance.

3. The method according to claim 1 , wherein the AN tunnel information to be used for the PDU session relates to an address of the AN tunnel comprising a Tunnel Endpoint Identifier, TEID, and an IP address and an IP port number that is used by the AN node for the PDU Session.

4. The method according to claim 1 , wherein the target CN tunnel information to be used for the PDU session relates to an address of the CN tunnel comprising a Tunnel Endpoint Identifier, TEID, an IP address and an IP port number to be used by a target User Plane Function, UPF, node (162) of the target network slice instance for the PDU Session.

5. The method according to claim 1 , wherein the information transmitted towards the AN node further comprises information about which data flows of the PDU Session should be routed through the target CN tunnel.

6. The method according to claim 1 , wherein the information transmitted towards a target SMF node of the target network slice instance , further comprises information about which data flows of the PDU Session that should be routed through the target AN tunnel.

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

transmitting a response to the NSSF node comprising an acknowledgement of the decision to change an allocation of the first network slice instance to the target network slice instance.

8. A computer program product comprising a non-transitory computer readable medium storing computer readable program code, the computer readable program code operable, when executed by processing circuitry proeessor to perform actions according to claim 1 .

9. A Network Slice Selection Function, NSSF, node configured to assist an Access and mobility Management Function, AMF, node to allocate a target network slice instance to serve a Protocol Data Unit, PDU, session for a User Equipment, UE, in a communications network , wherein the NSSF node further is configured to:

receive from a Network Data Analytics Function, NWDAF, node an indication of a traffic behaviour of data packets transmitted in the PDU session,

decide to change an allocation of a first network slice instance that is adapted to serve the PDU session, to the target network slice instance , based on policy rules and the received indication adapted to indicate the traffic behaviour,

assist the AMF node to allocate the target network slice instance to serve the PDU session for the UE by transmitting to the AMF node , information about the decision to change the allocation of the PDU session for the UE from the first network slice instance to the target network slice instance , and an identifier of the target network slice instance.

10. A method performed by a Network Slice Selection Function, NSSF, node for assisting an Access and mobility Management Function, AMF, node to allocate a target network slice instance to serve a Protocol Data Unit, PDU, session for a User Equipment, UE, in a communications network , the method comprising:

receiving, from a Network Data Analytics Function, NWDAF, node, an indication indicating a traffic behaviour of data packets transmitted in the PDU session,

deciding to change an allocation of a first network slice instance that is serving the PDU session, to the target network slice instance , based on policy rules and the received indication indicating the traffic behaviour,

assisting the AMF node to allocate the target network slice instance to serve the PDU session for the UE by transmitting to the AMF node , information about the decision to change the allocation of the PDU session for the UE from the first network slice instance to the target network slice instance , and an identifier of the target network slice instance .

11. A computer program product comprising a non-transitory computer readable medium storing computer readable program code, the computer readable program code operable, when executed by processing circuitry to perform actions according to claim 10 .

12. A method performed by a target Session Management Function, SMF, node of a target network slice instance for assisting an Access and mobility Management Function, AMF, node to allocate the target network slice instance to serve a Protocol Data Unit, PDU, session for a User Equipment, UE, in a communications network, the method comprising:

receiving, from the AMF node, information about a UE context related to the UE and Access Network, AN, tunnel information to be used for the PDU session,

transmitting, towards a target User Plane Function, UPF, node of the target network slice instance, the received AN tunnel information to be used for the PDU session,

receiving, from the target UPF node, target Core Network, CN, tunnel information to be used for the PDU session,

transmitting, towards the AMF node, the received target CN tunnel information to be used for the PDU session.

13. The method according to claim 12 , further comprising:

selecting the target UPF node of the target network slice instance .

14. A computer program product comprising a non-transitory computer readable medium storing computer readable program code, the computer readable program code operable, when executed by processing circuitry to perform actions according claim 12 .

15. A target Session Management Function, SMF, node of a target network slice instance, the SMF node configured to assist an Access and mobility Management Function, AMF, node to allocate the target network slice instance to serve a Protocol Data Unit, PDU, session for a User Equipment, UE, in a communications network, wherein the SMF node further is configured to:

receive, from the AMF node , information about a UE context related to the UE and Access Network, AN, tunnel information adapted to be used for the PDU session,

transmit, towards a target User Plane Function, UPF, node of the target network slice instance , the received AN tunnel information adapted to be used for the PDU session,

receive, from the target UPF node , target Core Network, CN, tunnel information adapted to be used for the PDU session,

transmit, towards the AMF node, the received target CN tunnel information adapted to be used for the PDU session.

16. The SMF node according to claim 15 , is further configured to:

select the target UPF node of the target network slice instance.

17. An Access and mobility Management Function, AMF, node configured to allocate a target network slice instance to serve a Protocol Data Unit, PDU, session for a User Equipment, UE, in a communications network, wherein the AMF further is configured to:

receive from a Network Slice Selection Function, NSSF, node, information about a decision to change an allocation of a first network slice instance, which is adapted to serve the PDU session, to the target network slice instance, and an identifier of the target network slice instance,

retrieve from a first Session Management Function, SMF, node of the first network slice instance, a UE context adapted to be related to the UE and the PDU session,

transmit towards a target SMF node of the target network slice instance, information about the retrieved UE context and an Access Network, AN, tunnel information adapted to be used for the PDU session,

receive from the target SMF node, target Core Network, CN, tunnel information adapted to be used for the PDU session,

allocate the target network slice instance to route data flows pertaining to the PDU session by transmitting towards an Access Network, AN, node the target CN tunnel information adapted to be used for the PDU session.

18. The AMF node according to claim 17 , is further configured to:

select the target SMF node of the target network slice instance .

19. The AMF node according to claim 17 , wherein the AN tunnel information to be used for the PDU session, is adapted to relate to an address of the AN tunnel comprising a Tunnel Endpoint Identifier, TEID, and an IP address and an IP port number to be used by the AN node for the PDU Session.

20. The AMF node according to claim 17 , wherein the target CN tunnel information to be used for the PDU session is adapted to relate to an address of the CN tunnel comprising a Tunnel Endpoint Identifier, TEID, an IP address and an IP port number to be used by a target User Plane Function, UPF, node of the target network slice instance for the PDU Session.

21. The AMF node according to claim 17 , wherein the information transmitted towards the AN node is further adapted to comprise information about which data flows of the PDU Session should be routed through the target CN tunnel.

22. The AMF node according to claim 17 , wherein the information transmitted towards a target SMF node of the target network slice instance, is further adapted to comprise information about which data flows of the PDU Session should be routed through the target AN tunnel.

23. The AMF node according to claim 17 , is further configured to:

transmit a response to the NSSF node adapted to comprise an acknowledgement of the decision to change an allocation of the first network slice instance to the target network slice instance.