[Asterisk-Users] How to wire Asterisk to stations?

[trixter aka Bret McDanel]

On Fri, 2005-10-21 at 15:39 -0500, Larry Alkoff wrote:
> I've just finished the O-Reilly book on Asterisk and setup a separate 
> computer with Asterisk at Home.
> 
> The book has a lot of good information but for some reason does not 
> discuss the physical wiring that goes to stations (FXS) and FXOs.
> 
> I understand that cat5 type wire would be used.
> What commonly used standards, if any, are used on the various colored 
> wires?  What signals and voltages to they carry?

This is tough to answer becuase it varies based on country.  I will
assume that you are in America and give you that info ...

A pots line uses 2 wires.  Ring and tip (designations from back when
they were plugs, like a headphone plug).  Ring is negative voltage and
tip is positive.  Tip is switched, the reason they switch the positive
voltage side is to prevent corrosion on the poles.  When the phone is
onhook (hung up) ring has -48VDC normally.  When you pick up the phone
(offhook) its about 7vdc.  When the phone rings its 90-110vac @ 20Hz.
The reason it goes AC for ring is due to the old mechanical bells that
were in use way back when.  This would cause the electromagnet to fire
then release which causes the hammer to strike the bell and make noise.
Now that everything is more sophisticated this backwards compatibility
has to be preserved.

As for wiring, when using regular phone wire (internal) it will usually
be 2 pair to be connected to a RJ-11 or RJ-12 connector.  Red is the
primary ring, green primary tip.  Yellow and black are used for the 2nd
line.  The reality is that it doesnt matter what color goes where,
inductance is usually not a problem for analog lines so twisting often
doesnt occur in phone lines.  Just make sure that you get it the same on
both ends (which largely doesnt matter as much anymore either, but with
some equipment it still does).

On a RJ-11 or RJ-12 connector it will be the center two for the line.
Any other wires are only used if its a dualline device.  When it comes
to FXO/FXS stuff normally they are single line ports so you only need 1
pair per connection.  


-- 
Trixter http://www.0xdecafbad.com     Bret McDanel
UK +44 870 340 4605   Germany +49 801 777 555 3402
US +1 360 207 0479 or +1 516 687 5200
FreeWorldDialup: 635378
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