Call Manager and echo

My company has been rolling out Cisco VOIP phone systems to remote offices, and we've had a hard time with echo.  I was wondering if anyone could shed some light on it.

We've done 3 sites so far, and each site needs alot of tweaking to remove the echo (changing the attenuation and gain).  Each site is using a PRI to the telco, and an MPLS (pip) to headquarters.  They have a cisco 3850, and end up on 7940 handsets.

Cisco seems to act like echo is rare, but 3 of the 3 sites we've done have needed significant back and forth to try and remove the echo.  We've gotten rid of it in one site, but the other two are still being tweaked.
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terrymasonAsked:
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shepimportCommented:
willing to simplify it? look at converged access's solution for passive qos... i have done testing on it... it worked in our labs very well and had an easy setup... if not... echo is caused by the delay of packets... so setting your router to a lower buffer and to drop packets may work... but, than you need to implement diff serv or simular layer 3 qos

also... what is your ping on the MPLS to your hq... ?

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terrymasonAuthor Commented:
Thanks for the help.  It turns out that we were making things worse instead of better.

Out of the box, echo cancelation is set at -3, 3 (we though it was 0,0).

We then increased (in our minds) the echo cancelation to -1,1, and then to -2,2

We've gotten it straight now.
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