Below are a diffrent types of Codecs that Asterisk can handle
|Codec||Speed||Simultaneous Calls over T1 (1.5 Mbps)||Notes|
|u-law||64 Kbps||24||US Standard|
|a-law||64 Kbps||24||European standard|
|G.729||8 Kbps||192||Requires license|
|Speex||2.15 – 44.2 Kbps||714 – 34||Open Codec|
With higher compression you can squeeze more calls through the same connection pipe, however, the savings of bandwidth does not come without a cost. The hight the compression the lower the voice quality of the call.