Section: 4.7.4 Limited service state over non-3GPP access
Content: There are a number of situations in which the UE is unable to obtain normal service from a PLMN over non-3GPP access and the UE enters the limited service state over non-3GPP access. These include: a) no USIM in the ME; b) an "illegal UE" or "illegal ME" is received when registration, network-initiated de-registration or service request is performed (any USIM in the ME is then considered "invalid"); c) a "5GS services not allowed" is received when a registration, network-initiated de-registration or service request is performed; d) a "PLMN not allowed" is received when registration, network-initiated de-registration or service request is performed; e) a "Tracking area not allowed" is received when a registration, network-initiated de-registration or service request is performed; f) a "Roaming not allowed in this tracking area" is received when a registration, network-initiated de-registration or service request is performed; g) void; or h) a "Serving network not authorized" is received when a registration or service request is performed. In limited service state with a valid USIM in the UE, the network selection is performed as defined in 3GPP TS 24.502[ Access to the 3GPP 5G Core Network (5GCN) via non-3GPP access networks ]  [18]. With the exception of performing initial registration for emergency services, no registration requests are made until a valid USIM is present. For registration for emergency services, the PLMN of the current N3IWF or TNGF is considered as the selected PLMN for the duration the UE is registered for emergency services.