International Mobile Subscriber Identity (IMSI) is defined in TS 23.003
IMSI is permanent subscriber data. IMSI is stored in HLR, HSS, CSS, VLR, SGSN, S4-SGSN, GGSN, MME, S-GW, P-GW, ePDG, SCEF and SMLC. For Anonymous Access, IMSI is not used in SGSN nor in GGSN. The IMSI serves as the root of the subscriber data pseudo-tree.
For emergency attached UEs without IMSI (e.g; UICCless UE) or with an unauthenticated IMSI, IMEI is used instead of IMSI to identify the UE.
The Network Access Mode (NAM) defines if the subscriber is registered to get access to the CS domain (non-GPRS/EPS), to the PS domain (GPRS/EPS) or to both domains using 3GPP access networks. NAM describes the first level of the subscriber data pseudo-tree below the IMSI root. It is permanent subscriber data stored in the HSS/HLR and the SGSN with the Gs interface option, and the MME with the SGs interface option.
For an emergency attached UE with an unauthenticated IMSI, the IMSI Unauthenticated indicator is set to reflect that the IMSI is unauthenticated. See TS 23.401
, TS 23.060
and TS 23.402
The IMSI Unauthenticated indicator is a temporary subscriber data stored in the MME, S-GW, P-GW, SGSN, S4-SGSN, GGSN and ePDG.