LTE NAS Layer Interview Questions And Answers 11-15

Q11. Define EPS Mobility Management?

Ans. EPS (Evolved Packet System) Mobility Management (EMM) in LTE refers to the set of procedures and protocols used to manage the mobility of UE within network. It involves tracking the location of UEs, handling UE mobility between different cells, and ensuring uninterrupted connectivity during handovers.
The primary features and components of EPS Mobility Management in LTE include:
1. Tracking Area (TA): LTE divides the network coverage area into TAs, which consist of multiple cells. TAs are used for tracking the location of UEs when they are in idle mode.
2. Tracking Area Update (TAU): When a UE moves from one TA to another, it performs a TAU procedure to inform the network about its new location. This procedure involves updating the UE's registration with the network, including its current TA and serving cell information.
3. Mobility Management Entity (MME): The MME is a key network element responsible for managing mobility in LTE. It handles UE tracking, authentication, security, and initiates the procedures for handovers.
4. Handover: Handover is the process of transferring an ongoing communication session from one cell to another as the UE moves. There are various types of handovers, such as intra-LTE handover (between LTE cells) and inter-RAT handover (between LTE and other radio access technologies).
5. Paging: Paging is used to locate and wake up UEs in idle mode when there is an incoming call or data session for them. The network initiates a paging procedure to inform the UE to establish a connection.

Q12. EMM Common Procedure?

Ans. EMM (EPS Mobility Management) Common Procedures are a set of standardized procedures defined in LTE networks to manage mobility and signaling between the UE and the network. Some important EMM Common Procedures include:
1. Attach: The UE initiates an attach procedure to establish initial access to the network. It includes authentication, security setup, and registration with the network.

2. Detach: The UE can initiate a detach procedure to release its connection and detach from the network. This may occur during power-off, when moving out of network coverage, or upon user request.
3. Tracking Area Update (TAU): The TAU procedure is performed by the UE to inform the network about its current location when it moves from one tracking area to another. It includes updating the registration information and location information of the UE.
4. Service Request: The UE can send a service request to the network to request specific services or establish a new session. This procedure is typically used when the UE is in idle mode and wants to initiate a new data session or voice call.

5. Authentication and Security: These procedures ensure the secure authentication of the UE and establish secure communication channels between the UE and the network.
6. Paging: The network initiates a paging procedure to locate and notify the UE that there is an incoming call or data session. This procedure involves broadcasting paging messages to specific tracking areas or cells where the UE may be located.
7. Identity Check: The network may request an identity check procedure to verify the UE's identity during certain operations or when additional security measures are needed.

Q13. EMM Specific Procedure?

Ans. 1. Extended Service Request: This procedure is used by the UE to request specific services or establish a new session while it is in connected mode.
2. Authentication and Security Mode Control: These procedures are used to authenticate the UE and establish secure communication channels between the UE and the network during the initial attach or subsequent reattach procedures.
3. Tracking Area Update (TAU) Accept: The network sends a TAU Accept message in response to the TAU procedure initiated by the UE. It indicates that the network has accepted the UE's location update and provides updated network parameters if necessary.
4. Tracking Area Update (TAU) Reject: If the network cannot accept the TAU request from the UE, it sends a TAU Reject message, specifying the reason for rejection. The UE may need to take corrective actions and retry the TAU procedure.
5. Service Reject: If the network cannot provide the requested service or establish a new session, it sends a Service Reject message to the UE, indicating the reason for rejection.
6. Combined Attach: In certain cases, the attach and TAU procedures are combined into a single Combined Attach procedure to reduce signaling overhead.
7. Security Mode Command and Complete: These procedures are used to establish or update the security mode between the UE and the network during connected mode operation.
8. EMM Status: The network can send an EMM Status message to the UE to provide specific status information or instructions related to EMM procedures.

Q14. EMM Connection Management Procedure?

Ans. 1. Attach Procedure: The attach procedure is used to establish initial access and connection between the UE and the network. It includes authentication, security setup, and registration of the UE with the network.
2. Detach Procedure: The detach procedure is initiated by the UE to release its connection and detach from the network. It may occur during power-off, when moving out of network coverage, or upon user request.
3. Tracking Area Update (TAU) Procedure: The TAU procedure is performed by the UE to update its location information when it moves from one tracking area to another. It ensures that the network can route incoming data and signaling messages to the UE correctly.
4. Service Request Procedure: The service request procedure is used by the UE to request specific services or establish a new session while in connected mode. It allows the UE to initiate a new data session or voice call.
5. Connection Re-establishment Procedure: This procedure is used when a radio connection is lost due to factors such as coverage issues or radio link failure. The UE attempts to re-establish the connection with the network.
6. Radio Resource Control (RRC) Connection Setup and Release: The RRC connection setup procedure is used to establish the radio link between the UE and the network. The RRC connection release procedure is used to release the established connection.
7. Handover Procedure: The handover procedure facilitates the seamless transfer of an ongoing communication session from one cell to another as the UE moves within the network. It ensures uninterrupted connectivity and optimizes the use of network resources.
These EMM Connection Management Procedures play a vital role in establishing, maintaining, and releasing the radio connection between the UE and the LTE network, enabling reliable and efficient communication for mobile devices.

Q15. EMM Sublayer States?

Ans. 1. EMM-Deregistered: This is the initial state when the UE is not registered with the network. The UE is either powered off or has not performed an initial attach procedure.
2. EMM-Registered Initiated: In this state, the UE has initiated the attach procedure and is in the process of registering with the network. It is awaiting a response from the network.
3. EMM-Registered: Once the network accepts the attach request and authenticates the UE, the UE transitions to the EMM-Registered state. It is now successfully registered with the network and can receive services.
4. EMM-Registered Normal Service: In this state, the UE is registered with the network and can access all the available services and functionalities.
5. EMM-Registered Limited Service: If the UE experiences certain limitations or restrictions in service availability or network coverage, it transitions to the EMM-Registered Limited Service state. The UE may have limited access to specific services or operate in a restricted capacity.
6. EMM-Deregistered Initiated: When the UE initiates the detach procedure or experiences a failure in the registration process, it transitions to the EMM-Deregistered Initiated state. The UE is in the process of deregistering from the network.
7. EMM-Deregistered Normal Service: This state occurs when the UE has successfully completed the detach procedure and is no longer registered with the network. The UE is not connected to the network and cannot access services.