[Asterisk-Users] zaptel and low ring voltage

[Rich Adamson]

Inline...

> > Several months ago we built an * box with a quad-FXO tdm400p
> > (REV e/f).
> >> From the get-go, there has been a problem where occasionally
> > (2-3 times
> > a week) zaptel/* will not detect the ringing on a line.  (The
> > call will ring through to telco voicemail).
> > 
> > The problem is not specific to a single line or FXO port on the
> > tdm400p. 
> > 
> > I have 2 theories:
> > 
> > #1 - the ring voltage for some calls is below acceptable levels
> 
> Possible, but also possible that there is too much loss on the circuit.
> 
> You can test the ringing voltage with a meter, it needs to be between
> 90V and 110V.
> 
> Beyond that you may need to use a transmission test set (such as a
> Wilcom T136B). I got mine for $20 bucks on eBay. Using a butt set and
> the test set you'll need to call a 1004Hz source from TELUS and then
> check that you're within the following specs:
> Loop mA:		23 or better (too hot is no good either, but I
> doubt that's your problem)
> Circuit loss:	between 0 and -8dB. 0 is really too hot, -3 to -6 is
> nominal, -8.5 is pushing it, but still within spec.
 
Not likely the above is the root-cause as that implies the pstn line
is 'changing' characteristics on almost a daily basis (highly
unlikely). Also, the spec's for the 3050 chip (on the tdm fxo module) 
indicates it will detect ringing voltage down to 40v (or lower on some 
some specific configurations).
 
> > #2 - the tdm400p card is bad
> > 
> > Assuming #1, can the zaptel driver be tweaked to be more sensitive to
> > ringing? 
> > 
> > Any other ideas or experiences?
> > 
> > Running asterisk/zaptel v1.0.2

If you search through the archives you'll see others have also had
issues with the tdm using fxo modules. Lots of references relative
to stop/restart asterisk, unload/reload wctdm & zaptel, reboots, 
hear nothing but white noise, can only reload zaptel so many times
before a machine reboot is necessary, etc. Seems there has been
(maybe still are) issues that are driver related, kernel related,
and/or possibly distro related.

Some folks seem to have the same issues more frequently then others,
which would suggest there is some sensitivity to call volumes or
something like that. Several use the word monthly, others weekly,
etc.

The downside of this is there are very few developers that actually
use the tdm-fxo card in their systems, and only a subset of those 
seem to have the skills to diagnose wctdm/zaptel driver issues.