[Asterisk-Users] Poor pstn line quality

Rich Adamson radamson at routers.com
Sun Mar 27 06:08:40 MST 2005


> Thanks for your help Rich,
> I think it was a combination of poor line quality and shared IRQs and a couple
> setup mistakes (oops), we set busydetect=no in zapata.conf (it wasn't there
> before), and that seemed to clear up the 1 ring problem, then we got the fxo
> card on its own IRQ, and that cleared up the dropped call problem, the call
> quality is still lacking, (lots of static as I said thats just on the line) but
> we fixed the drop call problems, and the funny incoming call problem.. So they
> now have a working system that sounds the same as their old analog phone
> solution, so good job on your diagnosis!  I had heard of the shared IRQs
> causing bad quality (popping, etc), but not dropped calls as I saw here.
> Thanks again!

I would kind of doubt the shared irqs are actually behind the dropped
calls. Possible, but not as likely as other things.

If I were on site, I'd put a milliameter in series with the pstn line
and watch for variations in line current during a call. If you see 
any flucuations, the pstn line (and any non-asterisk hardware involved 
with the line) is flacky.

If you're going to be seriously involved with selling and supporting *
systems, I'd also suggest a rather inexpensive transmission test set.
Something that can measure noise, audio levels, line current, etc.
If you have such a test set, then use it to dial into the telco's
quite termination and milliwatt generator to diagnose/quantify the 
pstn problem.

One last item, the tdm-fxo cards are rather sensitive to line current
changes and the chipset on the card has the capability of sensing when
parallel analog telephone sets are off hook, etc. Asterisk drivers 
don't make use of a lot of those chipset functions. At one time (and
I think its still true), if you interrupted the pstn line (unplug and
replug) the card/line would oftentimes end up in some unknown state.
So, cleaning up the pstn line problems will likely result in a much
more stable * system.





More information about the asterisk-users mailing list