How does LTE handle UEs that initiate the detach procedure to exit the network?

When a User Equipment (UE) initiates the Detach procedure in LTE to exit the network, it involves a series of signaling messages and processes to inform the network about the UE's departure. The Detach procedure allows the UE to detach either temporarily or permanently. Here is a detailed technical explanation of how LTE handles UEs that initiate the Detach procedure to exit the network:

1. UE-Initiated Detach Request:
   • The UE initiates the Detach procedure by sending a Detach Request message to the network. This message includes information indicating the type of detachment (temporary or permanent) and may also include additional details, such as the reason for detachment.
2. Detach Request Transmission:
   • The UE transmits the Detach Request message to the Evolved NodeB (eNB), which is the base station in LTE. The eNB is responsible for managing radio resources and communication with the UE.
3. Processing at the eNB:
   • Upon receiving the Detach Request message, the eNB processes the request and may perform actions such as releasing radio bearers and signaling connections associated with the UE. The eNB prepares to forward the Detach Request to the Mobility Management Entity (MME) in the core network.
4. Detach Request Forwarded to MME:
   • The eNB forwards the Detach Request message to the MME, which is responsible for mobility management and tracking the location of the UE within the network.
5. Detach Accept Message:
   • The MME processes the Detach Request and responds with a Detach Accept message. This message acknowledges the UE's detachment and may include additional information related to the detachment process. If the detachment is temporary, the MME maintains some UE-related information for a period, anticipating the UE's return.
6. Release of Resources:
   • The MME instructs the eNB to release resources associated with the UE. This involves releasing radio bearers, signaling connections, and other resources allocated for the UE's communication with the network.
7. Update to Home Subscriber Server (HSS):
   • The MME may update the Home Subscriber Server (HSS) with information about the UE's detachment. The HSS is a central database that stores subscriber-related information, including subscription profiles and authentication data.
8. Paging Optimization:
   • Once the Detach procedure is completed, the network is aware that the UE is not reachable. This optimization reduces unnecessary paging attempts for the detached UE, minimizing signaling overhead in the network.
9. Temporary Detach Considerations:
   • If the Detach Request indicates a temporary detachment, the UE may plan to reattach to the network in the future. The network keeps certain UE-related information to facilitate a smoother reattachment when the UE returns.
10. User Privacy and Security:
    • The Detach procedure provides a mechanism for users to control their network attachment, contributing to privacy and security. Users can choose to detach when they want to exit the network temporarily or permanently.

In summary, when a UE initiates the Detach procedure to exit the LTE network, the procedure involves communication between the UE, eNB, MME, and potentially the HSS. The network acknowledges the detachment, releases resources, and updates relevant databases. The Detach procedure is a fundamental part of LTE's mobility management and allows UEs to control their network attachment status based on user preferences or specific scenarios.