5.3.13 Lists of 5GS forbidden tracking areas

If the UE is not operating in SNPN access operation mode, the UE shall store a list of "5GS forbidden tracking areas for roaming", as well as a list of "5GS forbidden tracking areas for regional provision of service". Otherwise the UE shall store a list of "5GS forbidden tracking areas for roaming":

• per SNPN; and
• if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, per entry of the "list of subscriber data" or, if the UE supports access to an SNPN using credentials from a credentials holder, PLMN subscription;

and store a list of "5GS forbidden tracking areas for regional provision of service":

• per SNPN; and
• if the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, per entry of the "list of subscriber data" or, if the UE supports access to an SNPN using credentials from a credentials holder, PLMN subscription.

Within the 5GS, these lists are managed independently per access type, i.e. 3GPP access or wireline access. These lists shall be erased when:

• the UE is switched off, the UICC containing the USIM is removed, an entry of the "list of subscriber data" with the subscribed SNPN identity identifying the current SNPN is updated or, if the UE supports access to an SNPN using credentials from a credentials holder, the entry of the "list of subscriber data" associated with the lists is updated; and
• periodically (with a period in the range 12 to 24 hours).

Over 3GPP access, when the lists are erased, the UE performs cell selection according to 3GPP TS 38.304 [28] or 3GPP TS 36.304 [25C]. If the UE is not operating in SNPN access operation mode a tracking area shall be removed from the list of "5GS forbidden tracking areas for roaming", as well as the list of "5GS forbidden tracking areas for regional provision of service", if the UE receives the tracking area in the TAI list or the Service area list of "allowed tracking areas" in REGISTRATION ACCEPT message or a CONFIGURATION UPDATE COMMAND message.

The UE operating in SNPN access operation mode shall remove a tracking area from the list of "5GS forbidden tracking areas for roaming" as well as the list of "5GS forbidden tracking areas for regional provision of service" for:

• the selected SNPN; and
• when the UE supports access to an SNPN using credentials from a credentials holder, equivalent SNPNs or both, for the selected entry of the "list of subscriber data" or, when the UE supports access to an SNPN using credentials from a credentials holder, the selected PLMN subscription;

if the UE receives the tracking area in the TAI list or the Service area list of "allowed tracking areas" in REGISTRATION ACCEPT message or a CONFIGURATION UPDATE COMMAND message.

If the UE supports access to an SNPN providing access for localized services in SNPN, the access for localized services in SNPN is enabled and the validity information of:

• any SNPN identified by the "credentials holder controlled prioritized list of preferred SNPNs for access for localized services in SNPN" changes from not met to met; or
• any GIN (broadcasted by an SNPN) identified by "credentials holder controlled prioritized list of preferred GINs for access for localized services in SNPN" changes from not met to met,

the UE shall remove the tracking area(s) which are included in the location validity information of the SNPN in a) or b), if any, from the list of "5GS forbidden tracking areas for roaming" as well as the list of "5GS forbidden tracking areas for regional provision of service" for that SNPN and for the selected entry of the "list of subscriber data" or PLMN subscription.

The UE shall not remove the tracking area from "5GS forbidden tracking areas for roaming" or "5GS forbidden tracking areas for regional provision of service" if the UE is registered for emergency services.

In N1 mode over 3GPP access, the UE shall update the suitable list whenever a REGISTRATION REJECT, SERVICE REJECT or DEREGISTRATION REQUEST message is received with the 5GMM cause #12 "tracking area not allowed", #13 "roaming not allowed in this tracking area", #15 "no suitable cells in tracking area", or #62 "no network slices available".

In N1 mode over 3GPP access, if the UE receives the "5GS forbidden tracking areas for roaming" IE or the "5GS forbidden tracking areas for regional provision of service" IE in the REGISTRATION REJECT, SERVICE REJECT, DEREGISTRATION REQUEST, REGISTRATION ACCEPT or SERVICE ACCEPT message, the UE update the suitable list with the received TAI(s) belonging to the serving PLMN or equivalent PLMN(s) and ignore the TAI(s) which do not belong to the serving PLMN or equivalent PLMN(s) included in the IE.

If the UE receives ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message provided with S-NSSAI and the PLMN ID in the Protocol configuration options IE or Extended protocol configuration options IE (see clause 6.5.1.3 of 3GPP TS 24.301 [15]), the UE may remove the corresponding tracking area from the "5GS forbidden tracking areas for roaming".

Over wireline access, the 5G-RG, the W-AGF acting on behalf of an FN-RG or the W-AGF acting on behalf of an N5GC device shall update the suitable list whenever a REGISTRATION REJECT, SERVICE REJECT or DEREGISTRATION REQUEST message is received with the 5GMM cause #12 "tracking area not allowed" or #13 "roaming not allowed in this tracking area".

NOTE: In this release of the specification, for untrusted non-3GPP access and trusted non-3GPP access, neither the list of "5GS forbidden tracking areas for roaming" nor the list of "5GS forbidden tracking areas for regional provision of service" is maintained by the UE since the UE is not able to determine the corresponding TAI.

Each list shall accommodate 40 or more TAIs. When the list is full and a new entry has to be inserted, the oldest entry shall be deleted.