NAS : Registration / Reject / Reject Cause
In the context of telecommunications, NAS stands for Non-Access Stratum. It is a layer in the LTE (Long-Term Evolution) and 5G (Fifth Generation) wireless communication systems that deals with the signaling between the User Equipment (UE) or device and the core network. NAS handles procedures such as registration, authentication, and connection management.
Let's break down the technical details of NAS Registration, Reject, and Reject Cause:
1. NAS Registration:
- Purpose:
- NAS Registration is the process through which a User Equipment (UE) informs the network about its presence and initiates the establishment of a connection. Registration is required when the UE first attaches to the network, moves to a new location, or is re-establishing a connection after a period of dormancy.
- Types of Registration:
- There are two types of NAS Registration: Initial Registration and Periodic Registration. Initial Registration occurs when the UE first attaches to the network, while Periodic Registration happens at regular intervals to update the network about the UE's presence.
- Messages:
- NAS Registration involves the exchange of NAS messages between the UE and the core network. These messages carry information such as the UE's identity, location, and capabilities.
2. NAS Reject:
- Purpose:
- NAS Reject occurs when the network refuses to accept the registration request from the UE. This rejection can happen for various reasons, such as lack of resources, authentication failure, or other network-related issues.
- Causes for NAS Reject:
- There are different reasons or causes for NAS Reject, and each rejection is associated with a specific cause. Some common causes include:
- Roaming Not Allowed (Cause #2): The UE is trying to attach to a network where roaming is not allowed.
- PLMN Not Allowed (Cause #6): The Public Land Mobile Network (PLMN) is not allowed for the UE.
- Authentication Failure (Cause #28): The UE failed to authenticate with the network.
- No Suitable Cells (Cause #58): There are no suitable cells available for the UE to attach.
- There are different reasons or causes for NAS Reject, and each rejection is associated with a specific cause. Some common causes include:
- Message Exchange:
- When a NAS Reject occurs, the network sends a NAS Reject message to the UE, indicating the specific cause for the rejection. The UE may then take appropriate actions based on the cause received.
3. NAS Reject Cause:
- Cause Values:
- NAS Reject Cause values are standardized codes that provide information about why the NAS registration was rejected. These cause values are part of the NAS Reject message and help the UE understand the reason for the rejection.
- Interpretation:
- Each NAS Reject Cause value has a specific interpretation, allowing network operators and device manufacturers to identify and address the issues leading to the rejection. For example, Cause #3 might indicate that the network is temporarily not reachable.
- Handling:
- The UE needs to interpret the NAS Reject Cause and take appropriate actions, such as attempting registration again or notifying the user about the issue.
In summary, NAS Registration involves the UE informing the network about its presence, while NAS Reject is the network's refusal to accept the registration request. NAS Reject Cause provides specific information about the reason for the rejection, enabling the UE to respond appropriately.