Question: Under what condition is the "Explicit IMSI Detach from EPS Services" procedure **not** applicable for a UE, according to the Mobility Management Entity (MME) - Visitor Location Register (VLR) SGs interface specification?
Option 1: When the UE initiates an EPS detach.
Option 2: When the network initiates an EPS detach as specified in NAS protocol for EPS.
Option 3: When the UE is in the SGs-NULL state at the MME.
Option 4: During a successful combined tracking area update procedure.
Explanation: The correct answer is Option 3 because, according to the specification, this procedure "only applies to UEs which are not in the SGs-NULL state at the MME", implying that if a UE is in the SGs-NULL state, the procedure is not applicable. This highlights an important nuance in the management of UE states and their implications for EPS services detachment procedures in telecom networks.