The procedures for the Non Access Stratum, especially power management procedures are substantially similar to UMTS. Main change is that the UMTS EPS allows concatenation certain procedures to allow faster creation of connection and media.
Create MME UE context, when the UE is on and attaches to the network. Assign a unique ID called SAE short temporary Mobile Subscriber Identity Temporary (S-TMSI) which identifies the context of the UE MME. This context the UE has user subscription information downloaded from HSS.
Local storage of data in the MME subscription allows faster execution of the procedures, such as setting the carrier because it eliminates the need to consult HSS every time. In addition, the UE context has also dynamic information such as the list of carriers that are set and terminal capabilities. To reduce overhead in E-UTRAN and processing in the UE, all UE-related information in the access network, including wireless carriers, may be released during long periods of inactivity data.
This is the state-ECM IDLE.MME kept in the UE context and information about carriers established in those periods of inactivity. To enable the network to contact an ECM IDLE UE, network updates as UE the new location whenever it comes out of the current track (TA) This is called an update tracking area.MME domain is responsible for tracking the location user, while the UE is in ECM-IDLE.
When there is a need to provide data downlink at UE ECM-IDLE, MME sends a paging message to all current eNodeBs its TA and UE eNodeBs page radio interface. Upon receiving a paging message, the UE makes a call for service, leading to the displacement UE ECM connected state. Such UE-related information is created in E-UTRAN and radio bearers are restabilite.MME is responsible for restoring and updating radio bearers UE context eNodeB.
This transition between the UE is called a transition-inactive to active. To speed-inactive to active transition and establishing carrier EPS support concatenation of NAS and Access Stratum (AS) bearer activation procedures.
Some relations between the NAS and AS protocol is used intentionally to allow the procedure to run simultaneously rather than sequentially, as in the UMTS. For example, the procedure for determining the carrier can be carried by the network without waiting for the conclusion of safety.
Security features are the responsibility of the MME for both signaling and user data. When a UE attaches to the network, mutual authentication is done between the EU network and MME / HSS. This authentication feature sets also security keys are used to encrypt carriers.
How Non-Access Stratum Procedures Work in LTE
In LTE, the Non-Access Stratum (NAS) refers to the layer responsible for communication between the User Equipment (UE) and the Evolved Packet Core (EPC), excluding the radio access network (RAN). The NAS is responsible for handling signaling and procedures related to user mobility, session management, and security. Unlike the Access Stratum, which manages radio resources, the NAS handles more high-level tasks such as connection establishment and management.
Key NAS Procedures in LTE:
- Attach Procedure: When a UE first connects to the LTE network, it performs the attach procedure. This involves authentication, authorization, and setting up of a default bearer for data transfer. The procedure includes communication between the UE, MME (Mobility Management Entity), and HSS (Home Subscriber Server) to verify the user’s identity and subscription details.
- Detachment Procedure: When the UE disconnects from the network, either voluntarily or due to a network failure, the detachment procedure is initiated. This involves signaling between the UE and MME to release the bearers and clean up the user’s session data. It ensures that the user is properly disconnected and that network resources are freed up.
- Attach Reject and Authentication Failure: If there are issues during the attach procedure, such as authentication failure or subscription issues, the MME can send an attach reject message. This ensures that only authorized users can connect to the network. If the authentication fails, the network rejects the UE’s connection attempt.
- Mobility Management: The NAS procedures also handle UE mobility. When the UE moves between different eNodeBs or even across different networks (Inter-RAT mobility), the MME communicates with the HSS and other network elements to ensure seamless handovers and re-establishment of services.
- Bearer Resource Command: NAS is responsible for initiating and modifying bearers for user data. This ensures that different types of traffic (e.g., voice, video, data) are given the appropriate Quality of Service (QoS) based on the user’s needs and network policies.
Security Procedures: The NAS also plays a role in ensuring the security of data transfer. This includes the encryption of signaling messages between the UE and the core network and the establishment of secure keys for authentication and communication. It ensures the confidentiality and integrity of user data and signaling during their interaction with the network.
Overall, NAS procedures are essential for managing user sessions, ensuring mobility, enforcing security, and providing access to the core network. They operate independently of the physical layer and are focused on ensuring smooth, secure, and efficient user experiences in LTE networks.