What is the Non-Access Stratum in LTE?
Today, let’s dive into an important concept in LTE, the Non-Access Stratum (NAS). If you’ve been following our previous discussions on LTE architecture, you may already know that the system is designed to manage both the access and non-access aspects of mobile networks. The NAS is a key part of the overall system, and it plays a significant role in ensuring that users remain connected to the network in a seamless manner.
The Non-Access Stratum (NAS) is part of the LTE network that deals with the communication and control functions between the User Equipment (UE) and the Core Network (CN). Unlike the Access Stratum (AS), which is responsible for managing the radio interface between the UE and the eNodeB (base station), the NAS handles the signaling between the UE and the EPC (Evolved Packet Core) for functions like mobility management, session management, and security.
To better understand NAS, let’s break down its key components and functions:
- Mobility Management (MM): This involves handling tasks such as tracking the location of the UE, managing its state (e.g., idle or active), and ensuring it can move between cells and eNodeBs without losing connection.
- Session Management (SM): This function is responsible for managing the establishment, modification, and release of data sessions for the UE. It ensures that data flows properly between the UE and the EPC.
- Security: NAS also handles security procedures, including encryption and authentication of the UE to protect against unauthorized access to the network.
- Attach and Detach Procedures: When a UE connects to the network for the first time, or when it disconnects, NAS handles the attach and detach procedures to ensure proper registration and de-registration with the core network.
NAS is essential for managing the user’s connection at a higher level. For instance, when you turn on your mobile phone and it connects to the LTE network, the NAS handles the initial attachment process. It communicates with the EPC, verifies your identity, and ensures that you can start using services like voice calls and data transmission.
In addition, the NAS is responsible for ensuring that users can roam between different networks without interruption. This is particularly important when moving between different areas covered by LTE and legacy networks like 3G or 2G. By managing mobility and security, NAS ensures that your experience remains seamless, even if you move between different network types.
Let’s also touch on how NAS works in tandem with the Access Stratum (AS). While AS is concerned with the radio link and maintaining communication over the air interface, NAS manages the signaling between the UE and the core network. These two strata work together to ensure efficient and secure communication, with NAS handling the user’s higher-level network functions, and AS taking care of the radio-side communication.
As we’ve seen in earlier articles, LTE brings significant advancements in mobile technology, providing faster data speeds and better connectivity. The NAS plays a crucial role in these advancements, managing the core network interactions to keep users connected and ensure smooth service transitions. It’s essential for handling things like session continuity, security, and mobility management, especially in a world where users are always on the move between different network types.