Question: Upon rejecting a location update, what actions does the Visitor Location Register (VLR) take regarding the Mobility Management Entity (MME) and the SGs association?
Option 1: Sends an SGsAP-LOCATION-UPDATE-ACCEPT message with a warning cause to the MME and maintains the current SGs association state.
Option 2: Moves the SGs association to SGs-ACTIVE without sending any message to the MME regarding the location update rejection.
Option 3: Sends an SGsAP-LOCATION-UPDATE-REJECT message with an appropriate reject cause to the MME, indicating the received Location Area Identifier, and then moves the SGs association to SGs-NULL.
Option 4: Requests additional information from the MME before deciding on the next step for the location update rejection.
Explanation: This correct answer reflects the precise protocol behavior for a location update rejection scenario. The VLR informs the MME of the update failure via an SGsAP-LOCATION-UPDATE-REJECT message with the appropriate reject cause and Location Area Identifier, then moves the SGs association to SGs-NULL, maintaining protocol consistency and network resource management.