[Asterisk-Users] Analog FXO Woes Continue

[Rich Adamson]

> > Don't have any real answers, but might check the following...
> > at least to rule them out.
> > 
> > Telco folks _always_ check lines from their demarc (which in
> > some cases is the protector box on the outside of the
> > building). Most will not come inside to measure anything from
> > the customer equipment jack. If that's true in your case,
> > then you have to question the cabling inside the building (to
> > asterisk). That cabling is most often simple inside wire that
> > can easily pick up noise (eg, induction from florescent lights,
> > motors, wall-wart transformers, some desk lamps). If you
> > don't know where the inside wire is run, might try to find
> > out or bypass it with cabling laying on the floor for at
> > least an elementary test.
> 
> Testing from the demarcation point is essential, and poor inside cabling
> can contribute to the problem, but if the cable is Cat 3 or better, it
> is unlikely that it will be succeptible to induced noise; that's why
> twisted pair is twisted - to protect it from induced noise.

"Inside wire" in the US is NOT twisted pair. That _was_ the point.
Doubtful it is in canada either. Check any of the cable specs for
the 4-wire el-cheapo inside wire that's been in use for years.
Inside wire has been known to create issues for well over twenty years
_if_ the cable is located anywhere near noise-generating electrical
devices.

> > If you did not _see_ a telco person on site doing the
> > transmission checks, you have to assume that someone did them
> > from the central office (most common approach). That's okay
> > in many cases, but its not okay in other more serious cases.
> > The majority of the telco people that would be dispatched for
> > testing only know enough to follow printed procedures using
> > whatever testset they've been given;
> > they don't have the skills to actually interpret the readings
> > for cases they've never seen or been trained to recognize.
> > 
> > Its not hard to plug an ordinary phone into the same rj11 jack
> > used by asterisk. Do it and listen close. Given the problems
> > that you've stated, it should not be difficult to hear noise, hum,
> > low volume, etc, if it is in fact bad lines. Also, compare
> > lines; it is not very often four of four lines go bad in
> > exactly the same way. Can you hear any difference between lines?
> 
> This is not a bad idea, but is not always conclusive. I've done numerous
> tests on circuits where it sounded great on a butt set, but was
> nevertheless out of spec. Also, if the problem is due to loss, it is
> quite reasonable to expect all the lines to have the exact same problem,
> because they will all be exactly the same distance from the C.O.

The point was the poster is suggesting some very serious line
deficiencies, and if those deficiencies are truly the result of bad
lines, he should be able to detect at least _some_ issues by using
at least some of his five senses.

> > Bridge an ordinary phone on the same pstn line as asterisk.
> > Place some calls from asterisk and listen to what's going on
> > via the analog phone. (Example: some central offices don't
> > like dtmf tones within xxx milliseconds after going off-hook. You'll
> > get wrong numbers, etc. Insert the 'w' option in your Dial statement
> > to delay those dtmf tones a little bit.) To be a little sneaky,
> > unscrew and remove the mouthpiece from the analog phone and
> > you can monitor calls all day long without impacting
> > asterisk's ability to handle calls. 
> 
> Say WHAT?!?!
> 
> OK look, I'm sorry, but this is just plain wrong. Disconnecting the
> transmitter in your handset will not alter the fact that you have
> introduced a device in the loop that is in an off-hook condition.

Better try it before you knock it (but use a real analog set, not the
el-cheapo electronic ones). Disconnecting the mic is exactly the same
thing as the old multi-party phones with the little switch on its side.
(In fact, playing with the mic use to be one way to bypass coin operated
requirements. :)
 
> To do what you are suggesting, one needs a butt set; which is equipped
> to passively monitor the line without affecting it.

Better take your butt set apart, draw the schematic, and do the same for
what is stated above. 

> > If asterisk is having an
> > echo issue (as an example) and you don't hear it with the
> > bridged phone, you at least know where to look.
> 
> That isn't really true. Since the analogue phone will not have a
> transcoding delay, the echo might still be there, just ocurring at the
> same time as the sidetone.

If you actually think about what you just said, you'll probably
want to take that statement back. Think real hard though! (Oh well,
let me give you a clue: near-end verses far-end.)
 
> > The telco's have a telephone number for a "quiet
> > termination" and another one for their "milliwatt generator".
> > Get those numbers and use the test set to measure noise
> > (quiet termination) and loss (milliwatt generator). If those
> > results are reaonable, then you've got an asterisk
> > configuration problem (and/or digium card problem).
> 
> Yes. And test the lines from the demarcation point, with all Customer
> Premise Equipment (CPE) REMOVED from the circuit (if you leave your
> inside wiring connected, you are not isolating the telco circuit from
> CPE). After testing from the demarc, test from the final termination
> (i.e. the cord you've plugged into your FXO). Any difference is your
> responsibility.

The above statement certainly tells us which part of the telco you
work(ed) in. :)

> The spec for loss on a circuit is -8.5dB. Nominal is -3dB to -6db.

Actually, the spec is rated in terms of xx db loss per 1,000 feet
from the CO per gauge of copper actually used, but your training 
department translated that into something that doesn't require a 
calculator.