What is the role of ICE in NAT traversal for VoIP?

• A. Coordinates the gathered candidates for connectivity.
• B. Discards unusable candidates.
• C. Routes media through a single fixed path.
• D. Estimates network bandwidth.

Answer: (A)

ICE (Interactive Connectivity Establishment) helps VoIP work across NATs by coordinating how endpoints discover and test all possible ways to reach each other. It first gathers all potential network addresses—host candidates from the local interface, server-reflexive candidates discovered via STUN, and optionally relay candidates via TURN. Then it runs connectivity checks between local and remote candidates to see which pair can actually communicate. This coordination of the gathered candidates for connectivity is what makes ICE effective for NAT traversal: it identifies a working path (or paths) for media between the two endpoints.

The other options don’t fit because ICE isn’t about discarding unusable candidates as its main job, nor does it lock media to a single fixed path by default—ICE may test multiple candidate pairs and select the best working path. It also doesn’t estimate network bandwidth; bandwidth estimation is handled by separate mechanisms and not by ICE.