Identifiers are used who uniquely recognize the entity. Send all the connection characteristics are tied to this identity. For example, if the device identity can be used it will be fine if it is a blacklisted device or not. Subscription identity is used to define if the subscription allows a certain 5G service or not. There are two different identities in the 5G system as follows
i) Device Identity
ii) Subscription Identity

Device Identity

In a 5G system, the device identifier is called PEI or Permanent Equipment Identifier. Every device in the 5G network has a unique PEI. This is stored in the device whether it is a 5G smartphone or self-driving car it contains or stores the PEI. It can take two possible formats inside the system


It is a 15 digit number with three different columns. TAC type allocation code is issued by the central body across the globe in a global contest and then using these 8 digits, the manufacturer can then assign a 6 digit serial number corresponding to phones they manufacture. Then we have one digit code, but tech desert which is used to see when the people report the lost device.


IMSI is a hardware number if we need software information then we use the same digit I am EISV this is along with a serial number it also has SVN or software version number, which is used to identify which is what is the software whether in the current device

Note: PEI is transmitted only after the encryption parameter is set, so it’s always transmitted securely. So nobody can eavesdrop on the network and identify this network. There is one exception when a device is trying to make an emergency call then it may not have time to authenticate itself and it may not have the necessary encryption parameters in place. So under this scenario, PEI is transmitted without interruption and this is an exceptional case.

Subscription Identifier 

i) SUPI (Subscription Permanent Identity) or IMSI

It can take two formats such as

a) IMSI 

b) NAI

If an operator has a 5G system, it will use IMSI. Suppose in some cases they have Wi-Fi or non-3GPP for supporting 5G connectivity then they will use an NAI. IMSI has 15 or 16 digits it has three components such as MCC, MNC, and MSIN. Mobile country code(MCC) is used to know the country, Mobile Network Code(MNC) to know which operator of that country, and Mobile Subscriber Identification Number(MSIN) to know which subscriber of that operator in that country. NAI is used for the non-3GPP like Wi-Fi even if IMSI can be transmitted in this format 


Note: IMSI is stored in a SIM card or embedded SIM card in the device.

ii) SUCI (Subscription Concealed Identity)

Suppose there is a scenario where your device is looking for good signal strength and gets connected to the hacker’s base station. They will track your location and other information easily through the subscriber identity. To prevent this problem in the 5G system, the subscription identity as we have seen previously as SUPI is never transmitted unencrypted over the network. Instead, we transmit what we called as SUCI it is concealed because it is encrypted from the SUPI. so the hacker or the middleman will not understand because they don’t have decrypted key to decrypt it as it is in encrypted form.

iii) GUTI (Globally Unique Temporary Identifier)

When the device connects to the network. The AMF will allocate the temporary identifier to the device and this temporary identifier is used for further communication, so we don’t need to transmit the encrypted information often in the network the temporary identifier here is known as GUTI and it has two components GUAMI (Globally Unique AMF ID) and TMSI (Temporary Mobile Subscriber Identity).

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