[Asterisk-Users] PRI echo issues: solvable?

[canuck15]

I think there is a negligible difference btw 14844 and 14500 so it was
rounded down to 14500.  When you do the test you will understand why. 

I am still not sure if those numbers are correct though as they are full
scale so that would make them 0dbm?  To achieve -3dbm I believe you would
want to shoot for half that which would be 7250 assuming it's linear (which
I have no clue).

Anyone know for sure what to do because I am getting confused a bit myself?

> -----Original Message-----
> From: Andrew Kohlsmith [mailto:akohlsmith-asterisk at benshaw.com] 
> Sent: Tuesday, October 11, 2005 9:31 AM
> To: asterisk-users at lists.digium.com
> Subject: Re: [Asterisk-Users] PRI echo issues: solvable?
> 
> On Tuesday 11 October 2005 11:49, alan wrote:
> > After solving the other "low hanging fruit" audio issues in our 
> > Asterisk PBX, we are left with occasional cases of severe 
> echo which 
> > we have not found a solution for yet.
> 
> > Our system:
> > - Asterisk 1.2.0-beta1
> > - TE110P on a PRI
> > - TDM04 and TDM40, but these are unrelated to current echo issues
> > - Fedora core 3
> > - Echo canceller KB1
> 
> Add to the mix
> Asterisk CVS HEAD (always within a couple of weeks of today) 
> Slackware 10.1
> TE405 and TE406 (with and without VPM support) Tried with 
> various motherboards and chipsets (all P4)
> 
> > Most calls have minimal, acceptable echo levels. But 
> occasionally, we 
> > get a call where the echo is delayed by a substantial amount 
> > (sometimes around 250ms), and sounds as loud as the remote party.
> 
> Yup.
> 
> > One example: when one number (local to the same CO as our 
> PRI) calls 
> > us, the echo on our end is unbearably bad. When we call 
> them, No Problem.
> 
> I've never seen that, it's always when we call out.  Certain 
> numbers will always trigger it.  888-737-4787 (IPC Resistors, 
> it dumps into an IVR so it's safe to call) is one such 
> number, but we have local numbers that hit other COs which 
> exhibit this problem as well so it's not a specific CO or 
> switch problem.
> 
> I have just verified today with the 888 # mentioned above 
> that zaptel is NOT disabling its echo canceller.  dmesg shows 
> no "disabling echo canceller due to tone" message and "zap 
> show channel [affectedchannel] shows that the echo canceller 
> is configured correctly (128 taps for us) and is ON.
> 
> I hope to do further testing as I am made more aware of the 
> numbers causing the issues.
> 
> > - Gain tuning: Is the ztmonitor quantitative target value 14500 or
> >   14844?  These two sources conflict on this point:
> >   http://www.voip-info.org/wiki/view/Asterisk+zapata+gain+adjustment
> 
> I think you want to achieve an effective value of -2 to 
> -3dBm.  I'm unsure what "value" this is in ztmonitor -v.  I 
> know this should not be needed at all on a PRI or other 
> digital connection.
> 
> -A.
> 
>