NAS (Non-access stratum (a functional layer between the core network and the terminal that supports signaling))

Non-Access Stratum (NAS) is a functional layer that is located between the terminal and the core network in mobile communication systems such as GSM, UMTS, LTE, and 5G. The main purpose of the NAS layer is to provide signaling functions and control the mobile station (MS) when it is attached to the network. The NAS layer is responsible for several important functions such as authentication, security, mobility management, session management, and supplementary services.

In this article, we will discuss in detail the different functions of the NAS layer and their importance in mobile communication systems.

Authentication and Security Functions

Authentication and security are two important functions of the NAS layer. When a mobile station (MS) is attached to the network, the network needs to authenticate the MS to ensure that it is a valid user and not an imposter. Authentication is the process of verifying the identity of the MS. The NAS layer performs the authentication function by exchanging messages with the Authentication Center (AuC) in the core network.

The security function of the NAS layer is to protect the communication between the MS and the network from unauthorized access and eavesdropping. The security function is achieved through the use of encryption and decryption algorithms. The NAS layer is responsible for setting up and maintaining the security associations between the MS and the network.

Mobility Management Functions

Mobility management is another important function of the NAS layer. When a mobile station (MS) moves from one location to another, it needs to inform the network about its new location. This process is called location update. The NAS layer is responsible for managing the location update process. The NAS layer sends location update messages to the network to inform it about the new location of the MS.

In addition to location update, the NAS layer is also responsible for other mobility management functions such as registration, de-registration, paging, and handover. Registration is the process of registering the MS with the network. De-registration is the process of removing the MS from the network. Paging is the process of searching for the MS when it is in a dormant state. Handover is the process of transferring the ongoing call or session from one cell to another when the MS moves from one cell to another.

Session Management Functions

Session management is another important function of the NAS layer. A session is a logical connection between the MS and the network that is used to transmit data. The NAS layer is responsible for setting up and maintaining the session between the MS and the network. The NAS layer also performs functions such as session establishment, modification, and release.

Supplementary Services Functions

Supplementary services are additional services that are provided to the MS in addition to the basic voice and data services. The NAS layer is responsible for managing the supplementary services. Some examples of supplementary services include call forwarding, call waiting, call barring, and conference calling.

Conclusion

In conclusion, the Non-Access Stratum (NAS) is a functional layer that is located between the terminal and the core network in mobile communication systems such as GSM, UMTS, LTE, and 5G. The NAS layer is responsible for several important functions such as authentication, security, mobility management, session management, and supplementary services. These functions are critical for the proper functioning of mobile communication systems.