Non Access Stratum (NAS) Protocols
The Non-Access Stratum (NAS) protocols form the highest stratum of the control plane between the user equipment (UE) and MME. NAS protocols support the mobility of the UE and the session management procedures to establish and maintain IP connectivity between the UE and a PDN GW. They define the rules for a mapping between parameters during inter-system mobility with 3G networks or non-3GPP access networks. They also provide the NAS security by integrity protection and ciphering of NAS signaling messages. EPS provides the subscriber with a "ready-to-use" IP connectivity and an "always-on" experience by linking between mobility management and session management procedures during the UE attach procedure.
Complete NAS transactions consist of specific sequences of elementary procedures with EPS Mobility Management (EMM) and EPS Session Management (ESM) protocols.
Read more about this topic: System Architecture Evolution
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