Question: Under what condition does the Visitor Location Register (VLR) initiate the Non-EPS alert procedure by sending an SGsAP-ALERT-REQUEST message to the Mobility Management Entity (MME)?
Option 1: When a User Equipment (UE) initiates a voice call.
Option 2: Periodically, as part of routine network maintenance.
Option 3: When the VLR wants to be notified of further activity from a specific UE by the MME.
Option 4: Upon receiving a location update from a UE.
Explanation: This is correct because, according to the specification, the VLR sends an SGsAP-ALERT-REQUEST message to the MME when it wants to be informed about any further activity from a User Equipment (UE), thereby initiating the alert procedure for monitoring UE activity.