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

[Rich Adamson]

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.