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

[Rich Adamson]

Michael Collins wrote:
>> 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?

Use a twisted pair for pins 1 & 2 and another twisted pair for pins 4 & 
5. Which pair and which color is not of any concern.

Or, just use a straight-through cat5 cable. Your choice since you're 
only talking about a patch cable.