The attachment procedure is described in Figure 2.1.
The attachment procedure is initiated by the mobile in the EMM-DEREGISTRERED state, by sending the EMM ATTACH REQUEST message to the Mobility Management Entity (MME).
This message contains the Globally Unique Temporary Identity (GUTI) or the International Mobile Subscriber Identity (IMSI).
On receipt of this message, the MME entity starts the authentication procedures and the security of Non-Access Stratum (NAS) messages.
If successful, the MME entity responds with the EMM ATTACH ACCEPT message containing a new GUTI identity.
The mobile switches to the EMM-REGISTERED state and responds with the EMM ATTACH COMPLETE message to acknowledge the previous message.
If the procedure fails, the MME entity responds with the EMM ATTACH REJECT message, causing the detachment of the mobile.
Detachment can be triggered by the mobile or the MME entity by sending the EMM DETACH REQUEST message.
The EMM DETACH ACCEPT response concludes the detachment process. The response is not transmitted by the MME entity when the detachment initialized by the mobile indicates a switch-off.
The mutual authentication procedure is initiated by the MME entity by sending the EMM AUTHENTICATION REQUEST message containing a random number (RAND) and the Authentication Network (AUTN) ...