the Non-Access Stratum (NAS) layer serves as a critical bridge between the User Equipment (UE) and the Core Network (CN). It acts as the control plane for user equipment, handling procedures that don’t directly involve data transmission over the air interface. Here are its key responsibilities:

1. Mobility Management: NAS establishes, maintains, and terminates connections between the UE and the network, including procedures for cell registration, roaming, and handover.
2. Security Management: NAS plays a crucial role in network security by handling user authentication, key management, and ciphering to protect signaling messages.
3. Service Activation and Deactivation: NAS activates and deactivates various services for the UE, such as voice calls, data services, and emergency calls.
4. QoS Management (Optional): In some configurations, NAS participates in Quality of Service (QoS) management by negotiating and controlling the level of service provided to the UE based on network conditions and user subscriptions.
5. Signaling Procedures: NAS handles various signaling procedures that don’t involve user plane data transmission, such as paging (alerting the UE for incoming calls), location updates, and network measurements.