While on a VoIP call, one user is unable to understand the other because the...

High latency is what best describes what is occurring on a VoIP call when one user is unable to understand the other because the audio is breaking up. Latency is the delay between sending and receiving data over a network, and high latency can cause poor quality or interruptions in VoIP calls. External interference, no connectivity, or port flapping are not likely to cause audio breaking up, but rather complete loss of signal or connection.