NAS (Non-Access Stratum (a functional layer between the core network and the terminal that supports signaling and user data transfer).)
Non-Access Stratum (NAS) is a functional layer in the 3GPP (3rd Generation Partnership Project) mobile network architecture that is situated between the core network and the user equipment (UE). The purpose of NAS is to provide support for signaling and user data transfer functions in the mobile network. NAS is responsible for handling the signaling messages between the UE and the core network, as well as for the control of the UE's mobility and security.
The Non-Access Stratum consists of several functional entities, which are responsible for different tasks in the mobile network. These functional entities are:
- Mobility Management Entity (MME)
- Serving Gateway (S-GW)
- Packet Data Network Gateway (P-GW)
- Home Subscriber Server (HSS)
- Authentication Center (AuC)
Each of these functional entities performs a specific task in the mobile network. Let's discuss each of these entities in detail.
Mobility Management Entity (MME)
The Mobility Management Entity (MME) is responsible for managing the UE's mobility in the mobile network. The MME is responsible for the following functions:
a. Authentication and Authorization - The MME is responsible for authenticating the UE and authorizing it to access the mobile network. The MME communicates with the HSS to authenticate and authorize the UE.
b. Paging and Tracking - The MME is responsible for paging the UE and tracking its location in the network. The MME communicates with the S-GW to locate the UE.
c. Mobility Management - The MME is responsible for managing the UE's mobility in the network. The MME communicates with the UE and the S-GW to manage the UE's mobility.
Serving Gateway (S-GW)
The Serving Gateway (S-GW) is responsible for routing and forwarding user data packets between the UE and the Packet Data Network (PDN). The S-GW is responsible for the following functions:
a. Routing - The S-GW routes user data packets between the UE and the PDN. The S-GW communicates with the MME and the P-GW to route user data packets.
b. Mobility Management - The S-GW is responsible for managing the UE's mobility in the network. The S-GW communicates with the MME to manage the UE's mobility.
Packet Data Network Gateway (P-GW)
The Packet Data Network Gateway (P-GW) is responsible for connecting the UE to the PDN. The P-GW is responsible for the following functions:
a. Packet Filtering - The P-GW filters user data packets based on the UE's subscribed services. The P-GW communicates with the HSS to determine the UE's subscribed services.
b. Charging - The P-GW is responsible for collecting charging information for the UE's data usage. The P-GW communicates with the Charging Gateway Function (CGF) to collect charging information.
c. Policy and Charging Control - The P-GW is responsible for enforcing policy and charging rules for the UE's data usage. The P-GW communicates with the Policy and Charging Rules Function (PCRF) to enforce policy and charging rules.
Home Subscriber Server (HSS)
The Home Subscriber Server (HSS) is responsible for storing and managing subscriber data in the mobile network. The HSS is responsible for the following functions:
a. Authentication and Authorization - The HSS is responsible for authenticating and authorizing the UE to access the network. The HSS communicates with the MME to authenticate and authorize the UE.
b. Subscriber Data Management - The HSS is responsible for storing and managing subscriber data in the network. The HSS communicates with the P-GW to determine the UE's subscribed services.
Authentication Center (AuC)
The Authentication Center (AuC) is responsible for providing authentication and security services in the mobile network. The AuC is responsible for the following functions:
a. Authentication - The AuC is responsible for providing authentication services for the UE in the network. The AuC communicates with the HSS to provide authentication services.
b. Security Management - The AuC is responsible for managing the UE's security keys in the network. The AuC communicates with the UE and the MME to manage the security keys.
Now that we have discussed the different functional entities in the Non-Access Stratum, let's discuss the different procedures that take place in the NAS.
Attach Procedure
The Attach Procedure is used by the UE to attach to the mobile network. The Attach Procedure consists of the following steps:
a. Authentication - The UE sends an authentication request to the MME. The MME communicates with the HSS to authenticate the UE.
b. Location Update - The UE sends a location update request to the MME. The MME communicates with the S-GW to locate the UE.
c. Default Bearer Activation - The MME sends a default bearer activation request to the S-GW. The S-GW communicates with the P-GW to activate the default bearer.
Detach Procedure
The Detach Procedure is used by the UE to detach from the mobile network. The Detach Procedure consists of the following steps:
a. UE Initiated Detach - The UE sends a detach request to the MME. The MME communicates with the S-GW to release the UE's resources.
b. Network Initiated Detach - The MME sends a detach request to the UE. The UE releases its resources and detaches from the network.
Service Request Procedure
The Service Request Procedure is used by the UE to request a specific service from the mobile network. The Service Request Procedure consists of the following steps:
a. Authentication - The UE sends an authentication request to the MME. The MME communicates with the HSS to authenticate the UE.
b. Service Request - The UE sends a service request to the MME. The MME communicates with the S-GW to establish a dedicated bearer for the service.
Security Mode Control Procedure
The Security Mode Control Procedure is used by the UE and the network to establish and maintain security keys for secure communication. The Security Mode Control Procedure consists of the following steps:
a. Authentication - The UE sends an authentication request to the MME. The MME communicates with the HSS to authenticate the UE.
b. Security Mode Command - The MME sends a Security Mode Command to the UE. The UE uses the security keys to encrypt and decrypt the data packets.
In conclusion, the Non-Access Stratum (NAS) is a functional layer in the 3GPP mobile network architecture that is responsible for providing support for signaling and user data transfer functions in the mobile network. The NAS consists of several functional entities, which are responsible for different tasks in the mobile network, including Mobility Management, Serving Gateway, Packet Data Network Gateway, Home Subscriber Server, and Authentication Center. The different procedures that take place in the NAS include the Attach Procedure, Detach Procedure, Service Request Procedure, and Security Mode Control Procedure. By understanding the different functional entities and procedures in the NAS, we can better understand the functioning of the mobile network.