IMSI:-

IMSI stands for International Mobile subscriber Identity.

  • It is a globally unique permanent subscriber identity associated with the USIM.
  • An IMSI is stored on the USIM and by the UDM(user data management) network function.

Structure of IMSI:

  • MCC (Mobile country code): ITU is responsible for allocating MCC.
  • MNC (Mobile network code): The national administrator is responsible for allocating the MNC. [PLMN = MCC + MNC].
  • MSIN (Mobile Subscriber Identification Number): The MSIN is allocated by the service provider (ISP).

The subscriber is identified within the home PLMN using the Mobile Subscriber Identification Number (MSIN).

IMEI:-

IMEI stands for International Mobile Equipment Identity.

  • It is a permanent identity belonging to a device. It is stored in the device hardware and by UDM.

Structure of IMEI:

TAC (Type Allocation Code): This identifies the UE model, as well as a specific version of a UE model. GSM Association (GSMA) is responsible for TAC allocation.

SNR (Serial Number): unique identification of a device with a specific TAC, i.e. all the UE's having the same TAC will get the different serial number.

CD (Check Digit): It is calculated from a combination of the TAC and Serial Number. CD provides a mechanism for detecting data entry errors, e.g. when the IMEI is manually entered into a system.

SUPI and SUCI:-

SUPI (5G subscription permanent identity): It can be either IMSI or NAI (Network access identifier).

SUCI (Subscription Concealed Identifier): This allows the SUPI to be signalled without exposing the identity of the user.

5G-GUTI:-

5G-GUTI stands for 5G-Globally Unique Temporary Identifier. AMF is responsible for its allocation, it is a temporary identity.

Structure of the 5G-GUTI:

5G-GUTI and 4G-GUTI comparison
  • AMF Identifier = AMF Region ID + AMF Set ID + AMF Pointer.
  • GUAMI = AMF Identifier + MCC + MNC.

5G-S-TMSI:-

It is shortened version of the 5G-GUTI i.e. without PLMN(MNC + MCC) and AMF Region Identifier.

  • It is more efficient to use the 5G-S-TMSI rather than the 5G-GUTI.
  • Because of its smaller size help in the reduction of signalling overhead.