Networking Wiring – oh the joys of needing a cable and not having one with you or the length that you need.  I figured I would post up some info  on how to make Ethernet cables, Cross-over Ethernet cables, T1/E1 cables, and cross-over T1/E1 cables.
Here is a quick image of a RJ45 head with the pins numbered.

 
When it comes to Ethernet cabling there are two common types – 568A and 568B – of wiring.  The more commonly found one is 568B, but on occasion you will find 568A cabling in some older sites.  The reason I want to mention both is because they come into play in a cross-over cable.

To make a TIA/EIA-568A cable, the color coding is Green White / Green / Orange White / Blue / Blue White / Orange / Brown White / Brown.

To make a TIA/EIA-568B cable, the color coding similar, just that the green and orange pairs are reversed.  So it is Orange White / Orange / Green White / Blue / Blue White / Green / Brown White / Brown.

Now, for a cross-over you make one end of the cable 568A and the other end 568B. This swaps the transmit and receive pair in order to make the cross over cable.  So one side will be 568A – Green White / Green / Orange White / Blue / Blue White / Orange / Brown White / Brown and the other will be 568B Orange White / Orange / Green White / Blue / Blue White / Green / Brown White / Brown.

 
If you need to make a console cable that would be a roll cable – Orange White – Orange – Green White – Green – Blue White – Blue – Brown White – Brown on one end and Brown – Brown White – Blue- Blue White – Green – Green White – Orange – Orange White on the other end (Pins 1-8 and then 8-1)

 
Now T1 cables are something that we do come across quite often in our day to day jobs, and occasionally we need a cable or need to extend a cable.  So below are the pin-outs for a T1/E1 cable and cross, as well as a loopback plug.
 
For a straight T1 cable, its Orange White – Orange – Space – Blue – Blue White – Space – Space – Space.  for the spaces you can just insert any cable as those pins are not used. I typically just do the green – green white – brown white – brown routine.
 

For a T1 cross-over, we need to swap 1 and 2 with 4 and 5.  So the color code would be Orange White – Orange – Space – Blue – Blue White on one end and Blue – Blue White – Space – Orange White – Orange on the other end of the cable.

 
A T1 loopback plug can quickly clear your side of the network.  If you put in a T1 loopback plug in a smartjack and the carrier does not see the loop, the problem is on their side of the network.  Below are is the pin out for a loopback plug using Orange and Orange White.  Basically you are connecting Pin 1 to 4 and Pin 2 to 5.


Hope this helps!