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5GS – General Registration – 02 of 24
Signalling flow for TS 23.502 General Register: access network connect


Step 1, verbatim
UE to (R)AN: AN message (AN parameters, RM-NAS Registration Request (Registration type, SUCI or SUPI or 5G‑GUTI, last visited TAI (if available), Security parameters, Requested NSSAI, Mapping Of Requested NSSAI, UE 5GC Capability, PDU Session status, PDU Session(s) to be re-activated, Follow on request, and MICO mode preference)).
In case of NG-RAN, the AN parameters include e.g. SUCI or SUPI or the 5G‑GUTI, the Selected PLMN ID and Requested NSSAI, the AN parameters also include Establishment cause. The Establishment cause provides the reason for requesting the establishment of an RRC connection.
The Registration type indicates if the UE wants to perform an Initial Registration (i.e. the UE is in RM-DEREGISTERED state), a Mobility Registration Update (i.e. the UE is in RM-REGISTERED state and initiates a Registration procedure due to mobility), a Periodic Registration Update (i.e. the UE is in RM-REGISTERED state and initiates a Registration procedure due to the Periodic Registration Update timer expiry, see clause 4.2.2.2.1) or an Emergency Registration (i.e. the UE is in limited service state). The UE performing an Initial Registration (i.e., the UE is in RM-DEREGISTERED state) to a PLMN for which the UE does not already have a 5G‑GUTI, the UE shall include its SUCI or SUPI in the Registration Request. The SUCI is included if and only if the home network has provisioned the public key to protect SUPI in the UE (as defined in TS 33.501 [15]). If the UE previously received a UE Configuration Update Command indicating that the UE needs to re-register and the 5G‑GUTI is invalid, the UE performs an Initial Registration and shall include the SUPI in the Registration Request message. For an Emergency Registration, the SUPI shall be included if the UE does not have a valid 5G‑GUTI available; the PEI shall be included when the UE has no SUPI and no valid 5G‑GUTI. In other cases, the 5G‑GUTI is included and it indicates the last serving AMF. If the UE is already registered via a non-3GPP access in a PLMN different from the new PLMN (i.e. not the registered PLMN or an equivalent PLMN of the registered PLMN) of the 3GPP access, the UE shall not provide over the 3GPP access the 5G‑GUTI allocated by the AMF during the Registration procedure over the non-3GPP access. Also, if the UE is already registered via a 3GPP access in a PLMN (i.e. the registered PLMN), different from the new PLMN (i.e. not the registered PLMN or an equivalent PLMN of the registered PLMN) of the non-3GPP access, the UE shall not provide over the non-3GPP access the 5G‑GUTI allocated by the AMF during the Registration procedure over the 3GPP access. The UE may provide the UE's usage setting based on its configuration as defined in TS 23.501 [2] clause 5.16.3.7. In case of Initial Registration or Mobility Registration Update, the UE includes the Mapping Of Requested NSSAI, which is the mapping of each S‑NSSAI of the Requested NSSAI to the S‑NSSAIs of the Configured NSSAI for the HPLMN, to ensure that the network is able to verify whether the S‑NSSAI(s) in the Requested NSSAI are permitted based on the Subscribed S‑NSSAIs.
If available, the last visited TAI shall be included in order to help the AMF produce Registration Area for the UE.
The Security parameters are used for Authentication and integrity protection, see TS 33.501 [15]. Requested NSSAI indicates the Network Slice Selection Assistance Information (as defined in clause 5.15 of TS 23.501 [2]). The PDU Session status indicates the previously established PDU Sessions in the UE. When the UE is connected to the two AMFs belonging to different PLMN via 3GPP access and non-3GPP access then the PDU Session status indicates the established PDU Session of the current PLMN in the UE. The PDU Session(s) to be re-activated is included to indicate the PDU Session(s) for which the UE intends to activate UP connections. A PDU Session corresponding to a LADN shall not be included in the PDU Session(s) to be re-activated when the UE is outside the area of availability of the LADN. The Follow on request is included when the UE has pending uplink signalling and the UE doesn't include PDU Session(s) to be re-activated, or the Registration type indicates the UE wants to perform an Emergency Registration.