Question: What is the primary function of an MC (Mission Critical) Gateway Server in interconnecting two MC systems from different trust domains?
Option 1: To directly expose MC Service Servers of one domain to another for simplified management
Option 2: To handle only media transfer between MC Service Servers, offloading signaling control
Option 3: To act as a proxy for MC Service Servers in a partner system, providing topology hiding and relaying both signaling control messages and media
Option 4: To merge the trust domains of the two interconnected MC systems for unified security management
Explanation: The correct answer is Option 3 because the MC Gateway Server's primary role is to facilitate secure interconnection between MC systems from different trust domains. This is achieved by acting as a proxy, which hides the topology of one domain from another (topology hiding), and by relaying both signaling control messages (for management and coordination) and media (actual communication content) between the MC Service Servers in the interconnected systems. This approach ensures security and integrity of each trust domain while enabling necessary communications.