[Asterisk-Users] DSP-based echo cancellation (T1).

[C F]

On 12/6/05, Ken D'Ambrosio <ken at jots.org> wrote:
> I've implemented several analog Asterisk installs, and echo has always
> given me grief.  I'm now looking at doing my first T1-based install, and
> I'd really like to go with a card that has DSP-based echo cancellation
> built in.  However, all T1 cards I see with echo cancellation are
> quad-spans.  So:
>
> 1) Are there any single-span T1 cards with DSP-based echo cancellation?

Not that I'm aware off. If you find one please let me know.

> 2) Does said echo cancellation actually *work* well?
>
> I'm certainly willing to pay the quad-span premium if it means that I
> can pretty much kiss echo goodbye... but I'd prefer not to spend the
> money if I didn't have to.

Well, I have a quad span card with on board echo can from digium, I
have changed the computer it's in, replaced the card, and I still have
a terrible echo. I have tried everything with this setup, spoke to
Digium (they were very helpfull, and arranged for crossshiping to
change the card), had the telco test the PRI, and still I have that
blasting echo. My next step is an external echo can made my tellabs.
To tell the truth, I have done several successfull installs without
onbaord echo can (just the software ones) and I was able to to
eliminate the echo completely, so I don't realy blame Digium or
anybody else, I think that it's like black jack, pure luck. I know
technicaly its something else (like a huge tail, and the most Zaptel
can handle AFAIK is 256 tabs which is 0.125 * 256=32ms, so if I have a
tail longer then 32ms Zaptel echo cans wont help) but basicly what you
should know as an installer is that the echo canceling is like black
jack, what works for you might or might not work for someone else.

>
> Suggestions?

I would suggest: use a single span T1 card, use the software echo can,
if you still have echo, then get an external echo can like the tellabs
one. That will save you lots of money, and will work in almost all
cases.

>
> Thanks!
>
> -Ken D'Ambrosio
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