Inter-plmn Roaming Mobility Support

The Inter-plmn roaming mobility is a feature that allows a UE to move from their home network (H-PLMN) to a partner network (V-PLMN) and vice versa while maintaining an ongoing seamless data transfer.

The SMF supports home-routed roaming Inter-plmn scenarios when the UE moves from the home network to the visitor network and vice versa.

SMF supports the following functionalities:

  • Handovers from H-PLMN to V-PMLN and vice versa.

  • Enabling and disabling of inter-plmn handover functionalities through a CLI.

  • Advertises Deployments Topologies with specific SMF Service Areas (DTSSA) in supported features on N11 and N16 interfaces.

  • Creates Secondary PDRs for secondary RATs for homer calls for efficient Inter-RAT handoffs.

During Inter-plmn mobility, vSMF:

  • Selects operator policy based on the configured subscriber policy.

  • Selects V-UPF and V-CHF based on the configuration.

  • Uses roaming status that is configured under the Operator policy to override the HRT roaming request to treat the UE as Local Breakout (LBO).

N4 Changes

The SMF supports re-creating of PDRs rather than changing the associations.

  • 5G roaming: For 5G roaming, when the 5G UE moves from a homer to a roamer, and vice versa, N3 PDRs is created and deleted. The S5 and N9 Secondary PDRs get recreated with an existing FTEID.

  • 4G roaming: For 4G roaming, when the 4G UE moves from a homer to roamer and vice versa, S5 and N9 PDRs get recreated with existing FTEIDs. The N3 PDRs get freshly created and deleted.

  • Inter-RAT roaming: The SMF deletes older RAT PDRs and creates new RAT PDRs for Inter-RAT scenarios. SMF also recreates the S5 and N9 PDRs with existing FTEIDs.