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Collaboration, Voice & AV · Intermediate

Voice Activity Detection (VAD)

A codec feature that stops sending packets during silence to save bandwidth, also called silence suppression.

Definition

VAD detects when a speaker is silent and suppresses voice packets, which can save roughly 30 to 35 percent of bandwidth in a typical conversation. Because complete silence sounds like a dropped call, it is paired with comfort noise generation at the far end. Cisco recommends designing bandwidth without counting on VAD savings, and VAD can clip the first syllables of speech.

Example

G.729b includes VAD and comfort noise, while G.729a does not.

Exam tip

Never size links assuming VAD savings; plan for full-rate voice streams.

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