NAS

The non-access stratum (NAS) is highest stratum of the control plane between UE and MME at the radio interface. Main functions of the protocols that are part of the NAS are the support of mobility of the user equipment (UE) and the support of session management procedures to establish and maintain IP connectivity between the UE and a packet data network gateway (PDN GW).

 

NAS control protocol performs followings:
 

• EPS bearer management;
   
  

• Authentication;
    
  

• ECM-IDLE mobility handling;
    
  

• Paging origination in ECM-IDLE;
    
  

• Security control.

http://4g5gworld.com/specification/non-access-stratum-nas-protocol

http://www.3gpp.org/ftp/Specs/html-info/24301.htm

Hope this can help you

Non-access stratum (NAS) is a functional layer in the UMTS and LTE wireless telecom protocol stacks between the core network and user equipment.

This layer is used to manage the establishment of communication sessions and for maintaining continuous communications with the user equipment as it moves. The NAS is defined in contrast to the Access Stratum which is responsible for carrying information over the wireless portion of the network. A further description of NAS is that it is a protocol for messages passed between the User Equipment, also known as mobiles, and Core Nodes (e.g. Mobile Switching Center, Serving GPRS Support Node, or Mobility Management Entity) that is passed transparently through the radio network. Examples of NAS messages include Update or Attach messages, Authentication Messages, Service Requests and so forth. Once the User Equipment (UE) establishes a radio connection, the UE uses the radio connection to communicate with the core nodes to coordinate service. The distinction is that the Access Stratum is for dialogue explicitly between the mobile equipment and the radio network and the NAS is for dialogue between the mobile equipment and core network nodes. For LTE, the Technical Standard for NAS is 3GPP TS 24.301.

BR

Non-access stratum (NAS) is a functional layer in the UMTS and LTE wireless telecom protocol stacks between the core network and user equipment. This layer is used to manage the establishment of communication sessions and for maintaining continuous communications with the user equipment as it moves. The NAS is defined in contrast to the Access Stratum which is responsible for carrying information over the wireless portion of the network.
The following functions exist in the non-access stratum:

  - Mobility management: maintaining connectivity and active sessions with user equipment as the user moves
  - Call control management
  - Session management: establishing, maintaining and terminating communication links
  - Identity management