Andrew Kohlsmith wrote:
On Monday 24 April 2006 13:30, Michael Collins wrote:
IIRC, standard Ethernet uses pairs 1&2 and 3&6. The color scheme on
"568B" is 1&2 = white/orange pair, 3&6 = white/green pair
Most Ethernet cables then have the white/blue pair on 4&5, and
white/brown on 7&8.
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.
As far as T568A and T568B... I always went by the Canadians using T568A ("Tee
five six eight, eh?) and the rest of the world using T568B, which seems to be
pretty damn close to reality. Honestly I think 568A is for patch panels
terminating to one type of equipment (CPE) and 568B for inter-panel, but I'm
not sure. Essentially they're different in such a way as they'll act as an
ethernet crossover.
An RJ45 carrying a T1 is:
1 - RxA
2 - RxB
4 - TxA
5 - TxB
Assuming that you'd want RxA and TxA in the same twisted pair (ditto for
RxB and TxB) then a cable would look something like this at each end:
1&4 = white/orange pair
2&5 = white/blue pair
Careful. You're mixing up nomenclature. If you are referring to A and B as
"side A" and "side B" then you have the wiring mixed up. 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. :-)
Pair 1 is the blue/bluewhite pair. Pair 2 is the orange/orangewhite pair.
For a T1 crossover, the blue/bluewhite must go up the middle of one end and
on the lefthand side of the other, and the orange/orangewhite pair must be on
the lefthand side of one and up the middle of the other.
I don't know if there's an industry standard for T1 cabling to have a
certain color pair for A and another for the B pairs. Electrically,
though, the color is insignificant - as long as the correct pairs are
twisted together then all is well.
Very true, you don't want to split pairs. Causes all kinds of nasties. As
far as standards go: Yep; there are standards. And there are many to choose
from. :-) The telco standard is as follows:
I think I'm getting confused now.
A 'real' T1 cable would use a twisted pair for pins 1 & 2 and another
twisted pair for 4 & 5. Looks like a typical cat5 straight-through
cable uses twisted pairs straight across pins 1 through 8.
So, if my eyes are worth a damn (which they probably aren't), a cat5
cable uses one lead from a twisted pair for pin 4 (on the T1) and lead
from another twisted pair for pin 5. Not cool.
If that's correct, then a cat5 cable should not be used for a T1 run of
any significant length as the transmit leads (pins 4 & 5) would be
highly susceptible to induced noise.
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