4.23.1 General

23.5023GPPProcedures for the 5G System (5GS)Release 18TS

This clause captures changes to 5GC procedures in other clauses of this specification and new procedures to support deployments topologies with specific SMF Service Areas that are defined in clause 5.34 of TS 23.501 [2].

In the case of roaming for a Home Routed PDU Session the following cases may occur:

– A UE moves out of V-SMF serving area in the serving PLMN;

– A UE moves to another (serving) VPLMN;

– A UE moves between HPLMN and a VPLMN.

In the above cases, the procedures in clauses 4.23.2-16 for I-SMF apply for the V-SMF insertion/change/removal by replacing the I-SMF with V-SMF , and SMF with H-SMF. When an AMF detects the need to change the V-SMF while the H-SMF does not support V-SMF change, the AMF shall not trigger the V-SMF change but shall trigger the release of the PDU Session.

For an established PDU session an I-SMF is inserted if the UE is not in the SMF Service Area. In this case, when an UE moves from HPLMN to a VPLMN, a V-SMF is inserted and the I-SMF is removed. For mobility from VPLMN to HPLMN, an I-SMF is inserted and the V-SMF is removed. The procedures of this clause apply in this case, i.e. by replacing the target or new I-SMF by a V-SMF for mobility from HPLMN to VPLMN and by replacing the source or old I-SMF by a V-SMF for mobility from VPLMN to HPLMN.

For additional consideration for Home-routed PDU sessions see clause 4.23.17.

If at UE mobility the service area of the SMF does not include the location where the UE camps and the PDU Session is a MA PDU Session, then the AMF initiates the release of the MA PDU Session over all accesses served by this AMF. This applies to following procedures:

– Registration as defined in clause 4.23.3,

– Service Request as defined in clause 4.23.4,

– Xn Hand-over as defined in clause 4.23.11, or

– N2 Hand-Over as defined in clause 4.23.7.

For an established PDU Session supporting mechanisms for redundant transmission defined in clause 5.33.2 of TS 23.501 [2], or for a PDU Session supporting Time Sensitive Communications as defined in clauses 5.27 and 5.28 of TS 23.501 [2], if the UE moves out of SMF Service Area, the SMF may, based on local policy, release the PDU Session after the mobility procedure. This applies to following procedures: Registration procedure, Service Request procedure, Xn based handover procedure, N2 based handover procedure.

If dynamic CN PDB needs to be configured by the SMF and the I-SMF is involved in the PDU session, the I-SMF receives the Dynamic CN PDB value as part of QoS profile from SMF (over N16a) and forwards it to (R)AN via N2 SM message.