Question: In an IP Multimedia Subsystem (IMS), what is the primary purpose of a Signalling Gateway Function (S-GW) when interworking with the PSTN/CS domain?
Option 1: To manage media streams between different network domains
Option 2: To convert signalling transport protocols between SCTP/IP and SS7 networks
Option 3: To authenticate User Equipment (UE) across heterogeneous networks
Option 4: To optimize session routing for Quality of Service (QoS) enhancement
Explanation: The Signalling Gateway Function (S-GW) plays a crucial role in interworking between different signalling networks, specifically to facilitate communication between SCTP/IP-based signalling networks and SS7 signalling networks. This is essential for seamless interaction with the PSTN/CS domain, enabling compatible signalling transport protocols.