This is a read-only gauge, in milliseconds, reporting the measured round-trip delay of voice packets between the local system and the remote system over the IP backbone during this active call. An admin monitors this as a key real-time indicator of call quality, since high round-trip delay directly causes noticeable conversational lag for the people on the call. For example, an admin fielding a complaint about awkward talk-over during a call would check this delay value to see if excessive network latency is the culprit.