[Asterisk-Users] Poor pstn line quality

[Rich Adamson]

> I just installed a new asterisk box with a wctdm with 4 FXO modules.  The lines
> in the office have terrible static (using standard analog phones) and this
> static can obviously be heard through the asterisk box on the sipura sip phones
> we installed.  This by itself would not be a problem as the office is used to
> and doesn't mind (I don't know how) the static.
> 
> However it appears that this really bad line quality is causing the fxo ports to
> drop calls.  We tested all of the FXO ports in our office before we took the
> box to install it, and it worked just fine... Here are the problems we are
> seeing:
> 
> 1) Incoming calls, although immediate=no is set in zapata.conf the caller hears
> one ring, and then when asterisk starts the simple switch, the caller hears
> static and dead air, as if asterisk had done an "answer()".  The caller doesn't
> hear any more rings.  It takes asterisk about 3 seconds before it even rings
> the internal sip phone, and then while the sip phone is ringing, until it is
> answered the caller hears static and dead air. It seems as if the call has been
> disconnected, or at least it will be very confusing for the customers of this
> business, at any rate its unacceptable.
> 
> 2) Outgoing and incoming calls: call quality is bad because of the static, but
> randomly the zap channel that the call is on will hang up even though neither
> side has hung up.  It seems like the poor line quality is somehow simulating a
> "hangup" signal from the CO, and the fxo line is dropping the call.
> 
> has anyone seen poor line quality cause the digium fxo modules to have strange
> errors such as these?
> 
> Thanks in advance for any replies/ideas/solutions (besides obviously calling the
> phone company and telling them they suck)

>From your description, it sounds more like a shared interrupt problem
(cat /proc/interrupts) then it does a pstn line problem.

If it really is a pstn line problem, then plug the line into a ordinary
analog phone set and listen. If the pstn line is bad, you'll hear
the same noise on the analog set.