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

[Andrew Kohlsmith]

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:

Pair 1: Blue
Pair 2: Orange
Pair 3: Green
Pair 4: Brown
Pair 5: Slate

Then you have the "group" colours:
Group 1: White
Group 2: Red
Group 3: Black
Group 4: Yellow
Group 5: Violet

5 pairs with 5 groups gets you 25 pairs of wire.  Hey, that sounds like a 
standard trunk!  :-)  Then you can get into bundle groups (which follow the 
pair wiring), and a grouping larger than that whose name escapes me that 
follows the group colouring...  All in all you can get 625 pairs in a single 
trunk with only these ten colours.

Google's got plenty of resources on this. "Telephone wiring color code" or 
somesuch.

-A.