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.
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