[asterisk-users] HPEC > VPM ?

[John Novack]

Noah Miller wrote:
>>> Next question: does anybody know how to handle extremely long tail
>>> echo that a VPM module cannot?
>>>       
>> How long is 'long' in this case? The VPMs and HPEC (and OSLEC) can
>> handle 128ms echo tails, which is pretty darn long. It's rare to see an
>> echo tail longer than that except on very high latency connections, or
>> when the echo is actually acoustically generated by the far end and not
>> by network effects.
>>     
>
> I haven't done any real measurement on it, but I believe it's actually
> longer than 128ms.  As I go higher and higher with echocancel values,
> the echo does get better, but is never totally eliminated.  At
> echocancel=1024, there is still rather pronounced echo on calls in the
> "local" exchanges.  The calls are also more or less half-duplex at
> that point because the vpm is filtering out so much of the signal as
> echo.
>
> I may just tell the client to look at a partial PRI.  All this echo
> chasing is getting costly for them.
>
>
> Thanks!
> Noah
>   
In cases of really short loops, a loading network has really helped. 
Artificial cable  networks can be designed and inserted in 1/4 mile 
increments.
We have quite a few users using Asterisk directly connected to station 
lines or incoming selectors with effective loop lengths of a few feet 
have used artificial cable networks of 1 to 3 miles with great results.
Needless to say, this requires an understanding of basic telephony, some 
electrical engineering and use of stable capacitors and inductors which 
may be beyond the ability of many.
Country and existing loop length, type of cable loading, if any, are all 
variables to take into consideration, as well as the specific card involved.
the condition certainly can be improved, even with the old X100 card!

John Novack

-- 
Dog is my co-pilot