Similar to GUMMEI in LTE network, 5G network defines identifiers to identify various units of network. Similar to MME in EPC, 5G core supports Access and Mobility Management Function i.e. known as AMF. One PLMN may have many AMFs in its network. In order to manage all AMFs, new terms such as AMF region id, AMF set id and AMF pointer have been introduced.
In EPC, MMEs belonging to a network managed by MME group id and MME code. Once you add MCC and MNC before MME group id and MME code, it becomes globally unique MME identifier.
Similar to EPC, 5G network constructs globally unique AMF identifier as below:
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It is used to route the initial NAS message from NG-RAN to AMF. When UE provides GUAMI in rrc connection along with very first NAS message, RAN prepares and sends the received the NAS message to the right AMF node (selection based on received GUAMI).
It is also useful when UE first registers to AMF through 3GPP access and then it again registers to same AMF using non-3GPP access. In this case when second registration goes through N3IWF, UE provides AMF Id so that its request gets forwarded to right AMF.
