See also: crossover T1 cable
Two devices with PRI interfaces can be connected together with a PRI crossover or null-modem cable.
It should be emphasized that while a common ethernet patch cord can by used just fine for a PRI patch cord (they are both 4 pair RJ45 straight thru’s), the different signal assigments suddenly matter when building a crossover. Therefore the “Ethernet Crossover Cable” can NOT be used as a substitute for a “PRI crossover”.
What’s more, the PRI crossover cable seems to be a pretty rare item. Most places you ask for it will hear the words “crossover cable” and ask a few times if you want an ethernet x-o. Just say no! You will probably just end up rolling your own.
I avoid crimping my own cables and being left doubting their integrity, so I use regular patch cords but built an F/F crossover box using a 2 port RJ45 housing. IMHO, jacks in a box are easier to handle, see, label, verify, correct and change. It also allows for easier cable swapping for diagnosis and for length and colour changes.
For those using a 586A wall type box, here is a picture of a working one wired for a T1 crossover:
WARNING, I believe this image is incorrect, this image is 1,6 2,5 6,1 5,2 …
all other documentation states 1,4 2,5 5,1 5,2
April 7, 2023
Phone System 