User manual

Digium, Inc. Page 16
Chapter 1: Overview
Echo-Cancellation
Users connecting their 800 Series cards to the PSTN or other devices are
likely to be placing calls that will result, at some point, in an unbalanced
4-wire/2-wire hybrid. The result of this hybrid is the reflection of a near-
end echo to the calling party. Elimination of this echo is the responsibility
of echo cancellation.
The 800 Series cards, unless otherwise equipped, utilize Asterisk to
perform software-based echo cancellation. Asterisk maintains a number
of open source echo cancelers. These open source echo cancelers provide
a moderate level of echo cancellation, but are not capable of dealing with
higher levels of, or more advanced, echoes.
Digium recommends that those users concerned about echo cancellation
purchase the VPMADT032 hardware echo cancellation module. The
VPMADT032 may be combined with both the TDM800P and AEX800.
The VPMADT032 is designed to handle up to 128ms of echo cancellation
across all channels and provides a G.168 echo cancellation solution.