[comp.dcom.telecom] Let's Get This Straight

Lars Aronsson <aronsson@lage.lysator.liu.se> (04/06/91)

This is a size 6/6 modular plug:

	                  |           |
	                 ||           |
	                 ||   Cord    |
	                 ||           |
	                +---------------+
	               /| Strain relief |
	              + |               |
	              | |    P i n s    |
	              | |  6 5 4 3 2 1  |
	              | +---------------+
	              |/               /
	              +----/     /----+
	                  +-----+

This is one wiring scheme for an extension cord: 1-1, 2-2, 3-3, 4-4,
5-5, 6-6. Let's call it Scheme A.

This is another wiring scheme: 1-6, 2-5, 3-4, 4-3, 5-2, 6-1. Let's
call that Scheme B.

If you're using your cords for telephones, then Scheme A and Scheme B
cords are interchangable. For some other purposes, that might not be
the case.

I would like to call Scheme A cords "straight", since every pin is
connected to a pin with the same number. Scheme B cords I would like
to call "cross-connected". The Swedish subsidary of Inmac agrees with
me.

However, a local vendor uses exactly the opposite terminology, calling
Scheme B cords "straight". The explanation is that when you look at a
jack-to-jack (female-to-female) joint, Scheme A makes the wires
physically cross while Scheme B has physically parallel (straight)
wires.

Scheme A is like shaking hands (right hand to right hand) with a
person. If you face the person, your arms physically cross your
eye-to-eye line (unless one of you is standing on her head!).

(Along the same lines, your right hand is the one where the thumb
points to the left.)

This all makes me so confused. Please tell me who is wrong and who is
right (!). We Europeans are not that familiar yet with modular jacks
and plugs. Is there any standard that defines "straight" and
"cross-connected" in this context? Or do you have a de-facto standard?
Or is there equal confusion on both sides of the Atlantic? Do you even
use the words "straight" and "cross-connected"?


Lars Aronsson, Lysator computer club, Linkoping University, Sweden
     Aronsson@Lysator.LiU.SE    Voice phone at home +46-13-17 2143