[Asterisk-Users] analog FXO debug suggestions

[Samudra E. Haque]

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> On Tue, 2004-12-07 at 09:34 -0600, asterisk-users-
> > request at lists.digium.com wrote:
> > > I've been struggling with a test * install for a couple months now in
a
> > > small office and am just about ready to give up on it.  It's not that
the
> > > system itself is a problem.  I've got everything (attendant,
voicemail,
> > > FXS extensions, Cisco and Polycom hard-IP phones, and 2 VOIP carriers)
> > > working except for the frigging analog FXO interfaces.  These things
are
> > > driving me completely mad.  Since this is obvioiusly a deal breaker,
I'm
> > > looking for any more suggestions on how I might fet these things
working.


Hi,

some quick suggestions may get you results.

a) make an appointment with the most helpful person in that local telco
switch (anybody!) who has the expertise to help you with analog telephone
"OUTSIDE CABLE PLANT" problems. Tell him you suspect "cross talk, noise,
grounding or mis-wire of the pairs".

b) announce system maintenance time if your main trunks are all analog, if
not, simply disable those extensions by RENUMBERING them from your
exten.conf, so that regular users don't have access to them. ONLY YOU AND
YOUR TEST ENGINEER FROM THE CO should test these lines.

c) Please have your hearing checked (you will need this feature) or get a
good telephone butt test set, so that you can "hear" the audio quality
clearly and I want to say that you must be able to determine if you are
getting cross-talk "from another line", which normally you would not hear
when you are talking to someone. If you are getting noise / cross-talk,
mis-wiring (A1+B2 and A2+B1 of two telephone pairs, A, B) you will get mixed
results.

d) If you can, physically uproot and disconnect the main lines from your
incoming demarc and temporarily replace those wires with a long spool of
normal cat-5 cables (the UTP Ethernet kind..) doesn't matter, but make sure
the wires are SECURELY fastened at the joints so you have no loose
connections. What I mean is if you had...

d.1) [diagram] telco -- demarc/wall junction box/internal wiring/asterisk
change it to
d.2) [diagram] telco -- demarc/wall junction box/very long spool of
wire/RJ-11 block/asterisk

e) Note that on your Asterisk FXO ports, typically there is RJ-45, instead
of RJ-11 connectors, so you will have to fashion a RJ-45 plug with only the
MIDDLE two wires connected and then terminate the other end of the "flat"
cable with a RJ-11 cable. It doesn't hurt to make this cable very long, as
long as you don't trip over it.

f) Please make sure you study up and understand the implications of TXGAIN
and RXGAIN and how to use it, I recently screwed up my system by INCREASING
the gain, and obviously increasing the analog noise channel, so you may want
to DECREASE gain by adjusting the RX parameter. Don't play with the TX
parameter just yet, only test ONE at a time. Have the external engineer call
from various places, inside your office (from you), outside your office (to
asterisk) and make sure you see the console real time messages in highly
verbose mode so you can "trap" the error if it happens. WHAT IS THE ERROR
MESSAGE from Zaptel if any ?

g) Hook up a test set IN PARALLEL to the incoming line at the demarc, and
THEN SEPARATELY at the asterisk location.Make a habit of when the engineer
from outside (it could actually be one of your colleagues!!) calls in, you
SPY and MONITOR the "audio" level / quality of your connection, and if you
suspect a problem, (it should sound CRYSTAL CLEAR and the SAME LEVEL) you
can divert the incoming line into your test set and then have them call you,
and you be the judge of what the level is.

h) If you are aware of any humidity problems now is the time to speak up, as
if a telephone pair wire is near a humid / wet
location/pipe/gutter/roof/floor, it will provide the equivalent of
audio-limited-bandwidth service, and most of your DTMF signals and audio
conversations will be affected.

i) If you can, please use TWISTED pair wires for the internal connections
(in-house) and also consider strongly testing the whole setup in reverse
direction by CALLING OUT and asking the other side "how do you hear me ?"

j) Also please note that you need to ask your engineers what average DC
voltages you should be expecting for off-hook conditions (use a DC 48Volts
meter and the excellent guide available on the Wiki page), and also
http://www.teracomtraining.com/tutorials/teracom-tutorial-PSTN.htm, and also
the expected ring voltage when CO rings the FXO port. Please make sure you
know the "names" of the points at which you are testing, so that you can be
"knowledgeable" and provide that input to the engineer who will then treat
you quite well. If you can tell them to test the line upto your asterisk
premise, they may accomodate you just this once, and that will help you
incredibly.


k) If you did get satisified, they would get revenue, OR THEY WILL LOSE YOU,
that is their motiviation.

Finally, analog telephone lines are simpler to fix than digital, only
because they can be diagnosed within the range of human listening. You don't
need expensive test sets.... but here is a trick, if you can find a software
audio spectrum analyser (ref. WINSCOPE.EXE) which is simple, stupid and
works, it would listen to a microphone audio input (or perhaps the audio
from a compatible telephone set headphone connection) and show you in
realtime what the quality of the audio signals you receive on that line are,
and if you use the wide-band display function, you can easily see unwanted
audio signals where you should have none (if you don't speak, the line
should be CLEAR). Search for WINSCOPE on google, it should be available many
places.



-samudra haque
dhaka, bangladesh


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