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Glossary · Voice technology

What is Latency?

  • Also called: delay, one way delay, voice latency

Reviewed by Sujan ThapaliyaLast updated

Definition

Latency is the delay between someone speaking and the other person hearing it. Under about 150 milliseconds one way it is imperceptible; past roughly 300 milliseconds people start talking over each other, because the natural turn-taking of conversation breaks down.
The three STIR/SHAKEN attestation levels, which underpin how latency behaves in practice: A asserts both that the carrier knows the customer and that the customer may use the calling number, B asserts the customer only, and C asserts neither. A shared number pool can reach B at best, which is why number ownership keeps recurring in these definitions.
Attestation is the backdrop to most caller-ID and deliverability terms, latency included.

In practice

How latency actually works

Latency does not damage audio quality — every word arrives intact — which is why it is often misdiagnosed. The symptom is not distortion but collision: both parties pausing, then both speaking.

It accumulates along the path: encoding, network transit, jitter buffering, decoding. A jitter buffer stretching to smooth an unstable connection is a common hidden contributor.

International routes carry unavoidable transit delay, which is why a call across the world can feel slower even on excellent connections.

Latency is also cumulative across a call path in a way that surprises people building distributed teams. An agent in one region, a platform in another and a customer in a third can each add a hundred milliseconds that nobody owns, and the result is a conversation that feels off with no single component at fault.

Latency does not damage audio quality — every word arrives. It damages turn-taking.
One-way latencyConversation feelsCause
Under 150 msNormalNothing to fix
150–300 msSlightly stiltedJitter buffering, long routes
300–500 msBoth parties talk over each otherTranscoding, bad routing
Over 500 msHalf-duplex, like a radioSatellite or a badly hairpinned media path

Worked example

At 400 milliseconds one way, both parties leave a polite pause, both conclude the other has finished, and both start talking. The audio is perfect; the conversation is not.

Latency: common questions

What causes people to talk over each other on VoIP calls?
Latency. Past roughly 300 milliseconds one way, the pause each speaker leaves for the other is longer than it seems, and both start again at once.
Is latency the same as jitter?
No. Latency is how long audio takes to arrive; jitter is how much that time varies. Jitter is fixed by buffering, which adds latency — which is why over-correcting one worsens the other.
What latency should I aim for?
Under 150 milliseconds one way for a call that feels normal. Between 150 and 300 is workable; beyond that conversation becomes stilted regardless of audio quality.

Sources

  1. Combating Spoofed Robocalls with Caller ID Authentication — Federal Communications CommissionThe STIR/SHAKEN framework, the attestation levels carriers sign calls with, and the mandate requiring providers to authenticate caller ID.
  2. 47 U.S.C. § 227 — Restrictions on the use of telephone equipment — Cornell Legal Information InstituteThe Telephone Consumer Protection Act itself — the consent requirements, calling-hours limits, and private right of action.
  3. ITU-T Recommendation E.164 — The international public telecommunication numbering plan — International Telecommunication UnionThe international number format, the 15-digit maximum, and how country codes and national numbers compose.

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