[Asterisk-Users] Upgrading 1.0.9 to 1.2 beta

[Rich Adamson]

> > I'm contemplating upgrading a client's asterisk system from 1.0.9  
> > to 1.2
> > beta to take advantage of some of the new echo cancellers in the later
> > zaptel packages. Problem is, I'll be doing it without physical  
> > access to the
> > box and without being able to personally test the new echo  
> > cancellation for
> > them, so I'll be relying on information they provide me with.
> >
> > Their setup involves a Rev. I TDM400 card with 3 FXO modules  
> > connected to
> > standard BT analogue lines. They've been complaining about echo for  
> > some
> > time, despite the multitude of options I've tried in zapata.conf to  
> > limit
> > the echo problem.
> >
> > Here are the current zapata.conf settings:
> > echocancel=yes
> > echocancelwhenbridged=yes
> > echotraining=800
> > rxgain=12.0
> > txgain=8.0
> >
> > (rxgain and txgain calculated by running ztmonitor on a number of  
> > different
> > calls over a period of a few days, aiming to keep the levels in the  
> > middle)
> 
> Chris,
> 
> Before you upgrade to 1.2 and potentially break a lot of things, have  
> you followed the instructions available at <http://www.voip-info.org/ 
> wiki/view/Asterisk+zapata+gain+adjustment> to adjust the rxgain and  
> txgain? I can't say without testing the machine, but those levels  
> look extremely high to me , and might be exacerbating, if not causing  
> the echo problem. Try to adjust the gains quantitatively using  
> milliwatt lines first before you go the upgrade route.
 
Based on my extensive professional experience and applying that
experience to the TDM card, I'd have to agree. The TDM card will
certainly generate echo with those gains.

Incrementally reduce those gains by 2db per day and listen to your
customer's feedback relative to echo. Don't bother using milliwatt
generators and ztmonitor. (Those tools are okay to find a starting
point if you have no other transmission test sets, but will not
help even one little tiny bit after that.)

You _will_ reach a point where the echo is minimal, but you will also
begin to hear complaints about 'low audio volume'. Your goal is to
find those gain values where you are trading off minimal echo with
low audio.

The TDM card does a pretty good job for those asterisk systems that are
fairly close to the central office (maybe something within about 5db
or so of pstn loss). It does a fairly poor job of balancing echo with 
proper audio levels the further one is from the CO past about 5db.

It's my opinion (and nothing more then that) that part of the problem
relates to the fairly narrow operating range of the existing echo
cancellers.  The new KB1 canceller is much better, but still no where
near commercial cancellers. About the same is true with the MG2 when
used with the TDM card. Comparing the MG2 canceller to KB1, I've seen
about another 1 db of improvement in audio levels during my early
tests of MG2. (I've stayed with the KB1 canceller for now.)

Before upgrading your customer's system to any newer version, make
sure you research "changes" to asterisk, and have a valid backout plan
in case your research misses items of importance to your customer's
operation.