Latency Budget — Sources of Delay in a VoIP Call
Learn about latency budget — sources of delay in a voip call
When someone says "this call feels laggy," they're experiencing latency — the time it takes for sound to travel from the speaker's mouth to the listener's ear. In the PSTN world, latency was mostly fixed and predictable (the speed of light through fiber, plus minimal switching delay). In VoIP, latency comes from a dozen different sources, each adding their own contribution. Understanding this latency budget is how you diagnose why a call feels wrong.
The ITU-T G.114 Guidelines
The ITU-T recommendation G.114 defines the thresholds:
| One-Way Delay | Quality Impact |
|---|---|
| < 150 ms | Excellent — conversational quality, no perceptible delay |
| 150–300 ms | Acceptable — slight delay noticeable, manageable |
| 300–450 ms | Poor — noticeable lag, conversation becomes difficult |
| > 450 ms | Unusable — severe delay, people talk over each other |
These are one-way delays. Round-trip time is double. At 200ms one-way, you're at 400ms round-trip — that's when people start unconsciously pausing and then talking over each other.
Dissecting the Delay Chain
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