To address the challenges brought about by wireless broadband technologies and keep the leading position of 3GPP network, the 3GPP launched the Long Term Evolution (LTE) in 2004. The LTE defines a new architecture of mobile communications network, namely, evolved packet system (EPS).
Many services of carriers operate in the circuit switched (CS) domain in the GPRS/UMTS, and a method is developed to connect the EPS to the CS core network to reuse the existing CS services in the EPS, namely, CS fallback (CSFB). The registration process of the CSFB is as follows: A UE transmits an Attach Request to a mobile management entity (MME). After receiving the Attach Request, the MME performs the Attach operation. In a standard Attach process, after receiving a subscription data insertion process from a home subscriber server (HSS), the MME initiates the Location Update (LU) process to the Mobile Switching Center/Visitor Location Register (MSC/VLR) to register the UE. After receiving the Location Update Request, the MSC/VLR stores information (e.g., address information) about the MME, and connects to the MME through an SGs interface, and then performs a standard CS domain LU process. When the LU process is complete, the MSC/VLR notifies the MME that the LU process ends. After that, the MME notifies the UE that the Attach process ends. Now, the UE successfully creates a context and registers it in the EPS and CS networks.
However, the prior art offers no solution in detaching the UE from the EPS.