AMF Node, NSSF Node, Target SMF Node and Methods Performed in a Communications Network

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.

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.

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.