[Asterisk-Users] Channelized T1, SIP phones, HW Echo Canceller

Vasyl Rublyov vasyl.rublyov at ionidea.com
Fri May 28 13:22:15 MST 2004


Steve,

Do you know buy any chance some info for HW Echo Cancellers which can be 
applied on the top of T1 PRI, E1 PRI... as well as to regular analog 
(FXO/FXS) trunks/lines?

Thanks,
   Vasyl

Steve Creel wrote:

>I have a channelized T1 coming in from our telco, terminated onto a TE405.
>There are three channelbanks serving internal analog extensions, and about
>10 Cisco 7960s.
>
>I have no reports of echo on the analog extensions (as expected).  The
>7960 users complain of occasional echo (seems like 1 in 5 calls).  Only
>the SIP user hears the echo, not the caller.
>
>I have echocancel=yes, echotraining=yes, echocancelwhenbridged=yes.
>Changes in the taps of echotraining have made things worse, so I have left
>it alone.
>
>I have backed the txgain down, as audio going out on the telco T1 is
>really hot.  Even at -6dB gain, it is still notably louder from outside
>than other audio (comparing the ring generated by the telco when calling
>into asterisk with the ring generated by asterisk calling a station from
>the auto-attendant).  If I drop gain to anything less that -6, I lose all
>audio.
>
>Would a hardware echo canceller deal with this type of echo?  My
>understanding is that it is a result of sip being non-realtime and
>introducing latency (the latency being half the difference from the
>original utterance and the echo).  Is this correct, or do I have it all
>wrong?
>
>From my studying of the list archives on this subject, it seems that there
>is no answer for "Why is it so intermittent", other than to say that the
>problem originates somewhere in the two-wire system of the remote party.
>Is that correct?
>
>Has anyone heard of any kind of contraption to use just a single Tellabs
>card outside of the chassis?  If possible, I'd like to avoid the cabling
>mess of a full tellabs chassis just to use one card.  I have looked for a
>single-card chassis, but with no luck.  Any pointers?
>
>
>Many thanks,
>
>Steve
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