An end user reports that when making B2B calls, the calls are connecting, however, no audio or video is being received by either party. Local calls work fine. Which two areas must be investigated?…

The VCS traversal zone is responsible for both signaling and media, but because calls are successfully connecting, the traversal zone signaling path is already functioning - the fault is isolated to media flow, not zone configuration.

The endpoint traversal mode determines how the endpoint handles media routing through the VCS Expressway path. If this mode is misconfigured or disabled, signaling can succeed while RTP/RTCP media streams fail to traverse correctly, causing silent or black-screen calls.

Far end camera control (FECC) is a supplementary feature for remotely adjusting a remote endpoint's camera pan/tilt/zoom and has no effect on whether audio or video media is received.

Firewalls must allow the RTP/RTCP media ports used by video endpoints in addition to signaling ports. Because calls are connecting (signaling is intact), a firewall blocking media ports is the most common cause of no audio or video in B2B scenarios.

DNS resolves hostnames needed to establish a call connection. Because B2B calls are connecting successfully, DNS is resolving correctly and is not contributing to the media failure.