Generic Public Subscription Identifier (GPSI) is needed for addressing a 3GPP subscription in different data networks outside of the 3GPP system. The 3GPP system stores within the subscription data the association between the GPSI and the corresponding SUPI.
GPSIs are public identifiers used both inside and outside of the 3GPP system.
The GPSI is either an MSISDN or an External Identifier. If MSISDN is included in the subscription data, it shall be possible that the same MSISDN value is supported in both 5GS and EPS.
NOTE: There is no implied 1-to-1 relationship between GPSI and SUPI.
<GUAMI> := <MCC> <MNC> <AMF Region ID> <AMF Set ID> <AMF Pointer>
where AMF Region ID identifies the region, AMF Set ID uniquely identifies the AMF Set within the AMF Region and AMF Pointer uniquely identifies the AMF within the AMF Set.
The AMF Region ID addresses the case that there are more AMFs in the network than the number of AMFs that can be supported by AMF Set ID and AMF Pointer by enabling operators to re-use the same AMF Set IDs and AMF Pointers in different regions.
The purpose of the GUTI is to provide an unambiguous identification of the UE that does not reveal the UE or the user's permanent identity in the EPS. It also allows the identification of the MME and network. It
can be used by the network and the UE to establish the UE's identity during signalling between them in the EPS.
The GUTI has two main components:
the GUMMEI that uniquely identifies the MME which allocated the GUTI; and
the M-TMSI that uniquely identifies the UE within the MME that allocated the GUTI.