The messages in this procedure are:
The identification procedure is used by the network to request a particular UE to provide specific identification parameters, e.g. the International Mobile Subscriber Identity (IMSI) or the International Mobile Equipment Identity (IMEI).
The network initiates the identification procedure by sending an IDENTITY REQUEST message to the UE and starting the timer T3470
The IE is “Identity type”.
Upon receipt of the IDENTITY REQUEST message the UE shall send an IDENTITY RESPONSE message to the network. The IDENTITY RESPONSE message shall contain the identification parameters as requested by the network.
The network shall, on the first expiry of the timer T3470, retransmit the IDENTITY REQUEST message and reset and restart the timer T3470. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3470, the network shall abort the identification procedure and any ongoing EMM procedure.
This message is sent by the UE to the network in response to an IDENTITY REQUEST message and provides the requested identity.
The UE will response in the IE “Mobile identity”.
If the UE cannot encode the requested identity in the IDENTITY RESPONSE message, e.g. because no valid USIM is available, then it shall encode the identity type as “no identity”.
Reference: 3GPP TS 24.301