Question: In a GSM PLMN, when a Short Message Service (SMS) is sent via a circuit-switched service in S1 mode, what entity is used to tunnel the messages, based on network configuration and UE subscription data?
Option 1: Mobility Management Entity (MME)
Option 2: Serving GPRS Support Node (SGSN)
Option 3: Service Centre
Option 4: Mobile Switching Centre (MSC)
Explanation: In the context of SMS support in a GSM PLMN, when circuit-switched service is utilized instead of packet-switched service for CS/PS services in S1 mode (as determined by network configuration and UE subscription data), the messages are specifically tunneled through the Mobility Management Entity (MME). This highlights the MME's role in managing and routing SMS traffic under specific network conditions, ensuring seamless communication.