C.0 Requirements for 5G steering of roaming over the control plane

23.1223GPPNon-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle modeRelease 17TS

In addition to the requirements specified in 3GPP TS 22.011 [9] clause 3.2.2.8, 3GPP TS 22.261 [74] clause 6.30 and 3GPP TS 23.501 [62] clause 5.30.2.2, the requirements in this clause apply.

The UE supporting N1 mode shall support the control plane solution for steering of roaming in 5GS. If the HPLMN or subscribed SNPN supports and wants to use the control plane solution for steering of roaming in 5GS, then the HPLMN or subscribed SNPN shall provide the steering of roaming information to the UE using the control plane mechanism defined in this annex.

The VPLMN shall transparently relay the steering of roaming information received from the HPLMN to the UE. The UE shall be able to detect whether the VPLMN removed the steering of roaming information during the initial registration procedure in the VPLMN. The UE shall be able to detect whether the VPLMN altered the steering of roaming information. If the UE detects that the VPLMN altered or removed the steering of roaming information then the UE shall consider the current VPLMN as the lowest priority PLMN and perform PLMN selection as defined in this annex.

The non-subscribed SNPN shall transparently relay the steering of roaming information received from the HPLMN or subscribed SNPN to the UE. The UE shall be able to detect whether the non-subscribed SNPN removed the steering of roaming information during the initial registration procedure in the non-subscribed SNPN. The UE shall be able to detect whether the non-subcribed SNPN altered the steering of roaming information. If the UE detects that the non-subscribed SNPN altered or removed the steering of roaming information then the UE shall consider the current SNPN as the lowest priority SNPN and perform SNPN selection as defined in this annex.