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Collaboration, Voice & AV · Intermediate

Packetization Delay

The time a codec waits to collect enough audio samples to fill one voice packet, typically 20 ms.

Definition

Packetization delay equals the amount of audio in each packet, also called the packetization period or ptime. Cisco IP phones default to 20 ms, producing 50 packets per second; larger values such as 30 or 40 ms reduce header overhead but add delay and make each lost packet more noticeable. It is a fixed component of the one-way delay budget along with codec algorithmic delay, serialization and jitter buffer delay.

Example

Changing G.729 from 20 ms to 30 ms packets drops the rate from 50 to about 33 packets per second and lowers bandwidth.

Exam tip

Smaller packets mean more packets per second and higher header overhead; larger packets mean more delay and worse impact from loss.

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