Anatomy of 20 ms G.729 audio packet shows the anatomy of a 20 ms G.729 audio packet, which is preferably used across limited bandwidth WAN links. Notice that two-thirds of the packet is consumed by overhead such as IP, UDP, and RTP and only one-thirds is used by the actual audio.

All 20-ms G.729 audio packets, regardless of the vendor, are constructed like this. Not only is the structure of the packet the same, but the method of encoding and decoding the audio itself is also the same. This similarity allows an Avaya IP telephone to communicate directly with a Cisco IP telephone or any other IP telephone when using matching codecs. The packets from the application perspective are identical.