In 5G, the Non-Access Stratum (NAS) plays a crucial role in network signaling and control functions. It is divided into two main components: Access Stratum (AS) and Non-Access Stratum (NAS). Here, we will delve into the specifics of 5G NAS, focusing on its Non-Access Stratum aspect.
1. Definition of NAS:
- Non-Access Stratum (NAS): NAS represents the signaling and control plane functions in 5G that are independent of the radio access network. It handles procedures related to the establishment, modification, and release of the UE (User Equipment) connection with the 5G core network.
2. Key Components of NAS (Non-Access Stratum):
- Mobility Management (MM):
- Registration and Connection Management: NAS is responsible for procedures related to UE registration and connection to the network, ensuring the network is aware of the UE’s location and availability.
- Authentication and Security: NAS handles authentication procedures to ensure secure access and communication between the UE and the 5G core network.
- Session Management (SM):
- UE Session Establishment: NAS manages the establishment, modification, and release of user sessions, facilitating the connection of the UE to various services in the core network.
- PDU Session Establishment: For services like Enhanced Mobile Broadband (eMBB) and Ultra-Reliable Low Latency Communications (URLLC), NAS is involved in establishing Packet Data Unit (PDU) sessions.
- EMM (EPS Mobility Management):
- Idle Mode Mobility Handling: When the UE is in an idle state, NAS handles mobility procedures, ensuring smooth transitions between different states and locations.
- Connection Mode Mobility Handling: During an active connection, NAS manages mobility procedures to support seamless handovers and session continuity.
- ESM (EPS Session Management):
- Bearer Handling: ESM within NAS manages the establishment, modification, and release of bearers to support different services and Quality of Service (QoS) requirements.
- QoS Negotiation: NAS negotiates QoS parameters between the UE and the core network to ensure the desired service quality.
- SMS (Short Message Service):
- Handling of SMS Procedures: NAS oversees the signaling procedures related to Short Message Service (SMS) in 5G.
- UE Reachability Management:
- UE Paging and Notification Handling: NAS is involved in handling procedures related to paging and notifying the UE of incoming data or signaling.
3. Signaling Flows in NAS:
- Initial Registration and Attach: When a UE initially connects to the 5G network or reattaches, NAS manages the registration and attach procedures, ensuring the UE is authenticated and authorized for network access.
- Handover Procedures: During handovers, NAS plays a crucial role in signaling to ensure seamless mobility of the UE between different cells and radio access technologies.
- UE Identity Handling: NAS manages the handling and updating of UE identity information within the network.
- Service Request and Release: For services like SMS or specific data sessions, NAS handles the initiation, modification, and release of these services based on UE and network requirements.
4. Security Aspects of NAS:
- Authentication and Key Agreement (AKA): NAS is responsible for initiating the AKA procedures to authenticate the UE and establish secure key material for encrypted communication.
- Integrity Protection and Ciphering: NAS ensures the integrity and confidentiality of signaling messages by applying integrity protection and ciphering mechanisms.
- Security Context Management: NAS manages the security context for the UE, maintaining the information required for secure communication with the network.
5. Interactions with Access Stratum (AS):
- Control Plane Separation: NAS and AS operate independently but are closely coordinated. AS handles radio-specific functions, while NAS manages core network-related signaling and procedures.
- AS-NAS Interface: The AS-NAS interface facilitates communication and coordination between the Access Stratum and Non-Access Stratum components.
6. Evolution from Previous Generations:
- Enhancements in 5G NAS: 5G NAS introduces enhancements compared to previous generations, supporting new services, improved security mechanisms, and optimized signaling procedures.
7. Evolution to Support New Services:
- URLLC and mMTC Support: NAS in 5G is designed to support the unique requirements of services like Ultra-Reliable Low Latency Communications (URLLC) and Massive Machine-Type Communications (mMTC).
8. Interactions with Core Network Functions:
- Integration with 5G Core Functions: NAS interfaces with various functions within the 5G core network, including the AMF (Access and Mobility Management Function), SMF (Session Management Function), and UDM (Unified Data Management).
In summary, 5G NAS (Non-Access Stratum) is a critical component of the 5G architecture, handling signaling and control plane functions that are independent of the radio access network. It plays a key role in managing UE registration, mobility, session establishment, and security procedures, ensuring the efficient and secure operation of 5G networks.