About NAS (Non-Access Stratum)

The non-access stratum (NAS)forms the highest stratum of the control plane between UE and MME at the radio interface ("LTE-Uu interface")

Main functions of the protocols that are part of the NAS are:

• the support of mobility of the user equipment (UE).
• the support of session management procedures to establish and maintain IP connectivity between the UE and a packet data network gateway (PDN GW).

NAS security is an additional function of the NAS providing services to the NAS protocols, e.g. integrity protection and ciphering of NAS signalling messages.

For the support of the above functions, the following procedures are supplied within 3GPP 24301 specification:

• elementary procedures for EPS mobility management
• elementary procedures for EPS session management.