[Asterisk-Users] Echo on a PRI

[Steven Critchfield]

On Mon, 2004-07-19 at 19:12, David Goldfein wrote:
> Hi,
> I recently set up the following in a production system (2.8 GHZ Xeon, 1 Gig
> Memory, Dell 2650).
> 
> Telco - PRI - Asterisk - T1 - PBX
> 
> I am getting an occasional noticeable echo on some of the phone lines
> (random inbound and outbound).  Everyone I ask keeps telling me that I can't
> be having echo since I am on a PRI, which is a digital circuit.  Ok, so I
> can't be having echo, but I am!  Does anyone have any ideas of what might be
> causing the echo in this situation?  

Your PRI and the T1 itself cannot introduce echo on their own. What you
may see though is that you are introducing a delay as you traverse the
asterisk link. Asterisk will buffer 8 bits per channel from the PRI
before it send it down the T1 line to the PBX. This is a new delay that
is now added on to the latency your PBX introduces. 

A guess is that you also get the 2 machines fighting against each other
on the echo. I doubt you can turn off echo cancel in the PBX so you
should try turning it off in asterisk. It should help reduce some
latency in asterisk and let the PBX handle the rest of the echo cancel
on it's own.
-- 
Steven Critchfield <critch at basesys.com>