Digium TE131, Руководство пользователя

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Chapter 1: Overview
Echo-Cancellation
Users connecting their TE130 Series cards to the PSTN or other devices
are likely to be placing calls that will result, at some point, in an
unbalanced 4­wire/2­wire hybrid. The result of this hybrid is the
reflection of a near­end echo to the calling party. Elimination of this echo
is the responsibility of echo cancellation.
If not explicitly disabled in chan_dahdi.conf, the integrated hardware
echo cancellation of the TE133 and TE134 models will automatically
operate and cancel all network echo within its tail range (1024 taps)
.
The
TE131 and TE132 models depend instead on software­based echo
cancellation and are best suited for environments or installations that do
not require hardware­based echo cancellation.
Digium, Inc. Page 15