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

[Vasyl Rublyov]

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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