[Asterisk-Users] Re: Shielding of T1/E1 cables WAS RE: PinoutsforT1/E1 crossover

[Michael Collins]

> Close.  10/100mbps Ethernet uses wires 1,2,3,6 but that is pair 2 & 3.
> Pair
> one is the pair up the dead center (pins 4&5), pair 2 is pins 1&2,
pair 3
> is
> 3&6 and pair 4 is 7&8.  A T1 uses pairs 1&2, which is why you can't
use a
> regular crossover cable for a T1 crossover, but you can use a regular
> ethernet patch cable as a T1 patch cable.

Correct.  I mixed up "pair 1" with "the pair of wires connected to pins
1 and 2."  T1 uses "Pair 1" and "Pair 2," which was what I was trying to
say and what you *did* say! :)

> > An RJ45 carrying a T1 is:
> > 1 - RxA
> > 2 - RxB
> > 4 - TxA
> > 5 - TxB
> If you are referring to A and B as the differential signal components
then you're right about the wiring.  In either case you're wrong with
respect to the pairing.  :-)

Sorry, I am used to the way NEC documents their PBXs and this is what
they call it.  The Zytrax website documents it like this:
Pin:	Signal:
1	Rx1
2	Rx2
4	Tx1
5	Tx2
(http://www.zytrax.com/tech/layer_1/cables/tech_rs232.htm - bottom of
page)

So my question about a "real" T1 cable isn't specifically about a
crossover cable, although the principle will still apply.  I was talking
about using Cat5/5e 4-pair cable (*not* a pre-made Ethernet patch cable,
just Cat5 cable in general) to carry a T1 signal between the
NIU/SmartJack to the CPE.  (I could crimp my own or buy them, depending
upon my specific needs.  For a short jump I'd probably just fabricate my
own.)

So the question is really this: which pairs need to be twisted together
in a "real" T1 patch cable?  Since the two receive wires are on pair 2,
and the two transmit wires are on pair 1, it *seems* logical enough to
say that Rx1 and Rx2 should be on the same twisted pair, ditto for Tx1
and Tx2.  Is that correct?

-MC