Latency

Latency is the delay between when someone speaks and when the other person hears it. On a phone call, audio has to travel from your device, across the network, and to the far end, and every hop along the way adds a little time. We measure it in milliseconds. A small amount is invisible; too much and conversations turn awkward, with people talking over each other because the gap throws off the natural rhythm of speech.

In a VoIP call the audio packets ride on RTP, and latency is mostly a function of distance and network congestion between the agent, the server, and the carrier. Under about 150 milliseconds one way, most people never notice. Past roughly 300 milliseconds, the delay becomes a real drag on the conversation and agents start interrupting callers without meaning to.

Latency is not the same as its two close relatives. Jitter is the variation in delay from packet to packet, and Packet loss is packets that never arrive at all. All three drag down the MOS (mean opinion score), the overall score people use to grade call quality. When agents complain about laggy or talk-over calls, latency is usually the culprit, and the fix is almost always about the network path — moving the server closer to agents, or clearing congestion — rather than anything inside VICIdial.