Content for  TS 23.501  Word version:  19.2.0

Figure 4.2.4-1 depicts the 5G System roaming architecture with local breakout with service-based interfaces within the Control Plane.

Figure 4.2.4-3 depicts the 5G System roaming architecture in the case of home routed scenario with service-based interfaces within the Control Plane.

Figure 4.2.4-4 depicts 5G System roaming architecture in the case of local break out scenario using the reference point representation.

The following Figure 4.2.4-6 depicts the 5G System roaming architecture in the case of home routed scenario using the reference point representation.

The N38 reference point can be between V-SMFs in the same VPLMN, or between V-SMFs in different VPLMNs (to enable inter-PLMN mobility). For the roaming scenarios described above each PLMN implements proxy functionality to secure interconnection and hide topology on the inter-PLMN interfaces. Subscription-based routing to a particular core network as specified in clause 6.44 of TS 22.261 enables forwarding of the signalling and user traffic of certain UEs to a target PLMN that may be neither the serving PLMN nor the HPLMN of the UE. This is achieved by selecting NFs residing in the target PLMN. The NRF of the HPLMN, with optional support of the NRF in that target PLMN as specified in clause 4.17.5 of TS 23.502, is responsible to provide proper network function instance information during network function discovery and selection.

Operators can deploy UPFs supporting the Inter PLMN UP Security (IPUPS) functionality at the border of their network to protect their network from invalid inter PLMN N9 traffic in home routed roaming scenarios. The UPFs supporting the IPUPS functionality in VPLMN and HPLMN are controlled by the V-SMF and the H-SMF of that PDU Session respectively. A UPF supporting the IPUPS functionality terminates GTP-U N9 tunnels. The SMF can activate the IPUPS functionality together with other UP functionality in the same UPF, or insert a separate UPF for the IPUPS functionality in the UP path (which e.g. may be dedicated to be used for IPUPS functionality). Figure 4.2.4-9 depicts the home routed roaming architecture where a UPF is inserted in the UP path for the IPUPS functionality. Figure 4.2.4-3 depicts the home routed roaming architecture where the two UPFs perform the IPUPS functionality and other UP functionality for the PDU Session. The IPUPS functionality is specified in clause 5.8.2.14 and TS 33.501.