Sign in Subscribe

Non Access Stratum – NAS

Last updated on 
5G & 6G Prime Membership Telecom


Non-Access Stratum (NAS) is a protocol stack layer in mobile communication networks that plays a crucial role in handling signaling between user equipment (UE) and the core network. NAS operates above the radio interface protocols (Access Stratum) and is responsible for tasks related to the control and support of the mobile device. I'll explain NAS in the context of LTE (Long-Term Evolution) and 5G networks.

Functions and Components of Non-Access Stratum (NAS):

  1. Mobility Management (MM):
    • Registration Management: The UE registers and deregisters with the network, informing it about its presence and location updates.
    • Location Management: Deals with tracking the UE's location and managing handovers between cells and different Tracking Areas (TA).
  2. Session Management (SM):
    • PDP Context Activation/Deactivation: In 4G LTE and earlier technologies, the Packet Data Protocol (PDP) context activation is used for setting up and releasing IP-based data sessions.
    • Bearer Management: In 4G and 5G, the term "bearer" is used to represent a communication channel, and NAS handles the establishment, modification, and release of bearers.
  3. Security Functions:
    • Authentication and Key Agreement (AKA): NAS handles authentication procedures where the UE and the network authenticate each other and establish shared security keys for communication.
    • Ciphering and Integrity Protection: Once authentication is successful, NAS ensures the confidentiality and integrity of user data by applying encryption and integrity protection algorithms.
  4. Connection Management:
    • Idle Mode Control: Manages the UE's state when it is not actively communicating, optimizing power consumption and network resources.
    • Establishment, Maintenance, and Release of Radio Bearers: Controls the establishment, maintenance, and release of radio bearers used for communication.
  5. Session Management for IP Multimedia Services:
    • IMS (IP Multimedia Subsystem) Registration: NAS supports the registration and deregistration of the UE with the IMS network for multimedia services.
  6. SM (Short Message) over NAS:
    • Short Message Services: Provides support for SMS (Short Message Service) over the NAS layer.
  7. Emergency Services:
    • Emergency Call Handling: Supports procedures related to emergency calls, ensuring prioritized access to the network.

NAS Procedures:

  1. Attach and Detach Procedures:
    • Attach: The UE connects to the network, and NAS performs authentication, security setup, and registration procedures.
    • Detach: The UE informs the network that it is disconnecting, and NAS ensures that the UE is properly deregistered.
  2. Routing Area Update (RAU):
    • Tracking Area Update (TAU) in LTE/RA Update in 5G: NAS handles the UE's movement between tracking areas, updating the network about the new location.
  3. Service Request and Paging:
    • Service Request: The UE may request specific services, triggering corresponding procedures in NAS.
    • Paging: The network may page the UE to initiate a service request.
  4. PDN Connectivity Procedures:
    • Activate/Deactivate EPS Bearer Context: NAS initiates the establishment and release of IP-based bearers for data communication.
  5. Security Mode Control:
    • Security Mode Command and Complete: NAS manages the establishment and completion of security procedures, ensuring secure communication.

NAS Security:

  1. Protection Against Attacks:
    • NAS includes mechanisms to protect against various security threats, including eavesdropping, impersonation, and man-in-the-middle attacks.
  2. Key Derivation and Management:
    • NAS handles the derivation and management of keys used for encryption and integrity protection during communication.
  3. Authentication Challenges:
    • NAS supports mutual authentication between the UE and the network using challenge-response mechanisms.

In summary, Non-Access Stratum (NAS) in mobile communication networks manages signaling procedures between the user equipment (UE) and the core network. It handles mobility management, session management, security functions, and various procedures necessary for the establishment, maintenance, and release of connections. The specific functionalities and procedures can vary between different generations of mobile networks, such as LTE and 5G.