5.34.9 Support of the Deployment Topologies with specific SMF Service Areas feature within and between PLMN(s)

When Deployments Topologies with specific SMF Service Areas need to be used in a PLMN for a S-NSSAI, all AMF serving this S-NSSAI are configured to support Deployments Topologies with specific SMF Service Areas.

NOTE 1: The specifications do not support AMF selection related with Deployment Topologies with specific SMF Service Areas.

For HR roaming, the AMF discovers at PDU Session establishment whether a H-SMF supports V-SMF change based on feature support indication received from the NRF, possibly via the SCP. When the V-PLMN requires Deployments Topologies with specific SMF Service Areas but no H-SMF can be selected that supports V-SMF change, a H-SMF not supporting V-SMF change may be selected by the VPLMN. In that case and if a V-SMF serving the full VPLMN is available, AMF should prefer to select such V-SMF.

In this release of the specifications, 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 V-SMF change but shall trigger the release of the PDU Session.

NOTE 2: The AMF can determine whether the H-SMF supports V-SMF change based on NRF look up.