Question: When a Visitor Location Register (VLR) needs to send a Non-Access Stratum (NAS) message to a User Equipment (UE), what condition must be met for the VLR to proceed with sending the message via the SGs interface?
Option 1: The state of the SGs association for the UE is SGs-ASSOCIATED and LA-UPDATE-PRESENT.
Option 2: The UE is currently engaged in a voice call.
Option 3: The VLR has an active connection to the Serving Gateway (S-GW).
Option 4: The MME has explicitly requested the NAS message transmission.
Explanation: This option is correct because, for the VLR to send a NAS message to the UE via the SGs interface, it must first verify that the state of the SGs association for the UE is indeed SGs-ASSOCIATED and LA-UPDATE-PRESENT. This ensures a valid connection exists for the message transmission. The other options are not relevant to the condition required for sending NAS messages via the SGs interface as described in the context of VLR procedures.