Published on February 26th, 2012 | by Kieran


ISDN Crossover Cable Pinout

Quite often when connecting a fax board or media gateway to an ISDN line, a crossover cable is required to make a successful connection. Usually this is the case when an ISDN line is provided from a Phone System.

Do not use an Ethernet or Network crossover cable as these are different to an ISDN crossover cable. Should you need to make one of these cables up, please use the diagram below as a reference.

The above diagram shows an Ethernet crossover cable pin out for reference.

  • Basic Rate Crossover /Basic Rate ISDN Crossover / BRI Crossover
  • Primary Rate Crossover /Primary Rate ISDN Crossover / PRI Crossover

[message_box title=”Update: 19th October 2012″ color=”green”]Many thanks to the very clever people that noticed I had a mistake in the E1/T1 diagram, and commented below. I’ve updated the diagram so it should now be correct.[/message_box]

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About the Author

has worked with computers and technology for nearly 20 years. Based in the United Kingdom, he works throughout EMEA as a Solution Consultant, specialising in Fax & Document Distribution technologies. Predominantly blogging on he can also be found on Twitter @KieranLane, and Flickr.

7 Responses to ISDN Crossover Cable Pinout

  1. Cyril Gilly says:

    I’m sorry but ithink there ‘s a an error on the third scheme, it should be :
    1 -> 5 and 5-> 1
    2 -> 4 and 2-> 4
    3 -> 3

  2. turok says:

    The E1/T1 crossover is not correct. It should be 1 – 4, 2 – 5 for both pairs. You’re showing 1 – 4, 2 – 5 then 4 – 2, 5 – 1.


  3. Chandrasen says:


    thanks a lot. For me it works for the ISDN PRA.



  4. Cory says:

    Thanks for this info. We are taking 4 ISDN BRI lines from Cox Business. I was told for a video conferencing application to wire each BRI on pins 4 and 5 (standard wt/blue Ethernet pins) on a RJ-45. I was told I could use 1 Cat-3 cable for all 4 ISDN BRI lines. This does not appear to be true compared to what you show here. Thanks.

  5. scott House says:

    You are correct, you cannot use one cat3 cable for more than 2 ISDN lines! But I personally would recommend cat5E or cat6. But ISDN requires 2 pair and a cat3 station cable is only 4 pair allowing for two. That being said I don’t recommend that for fear of crosstalk. If I can help let me know!? Thanks.

  6. scott House says:

    Let me clarify myself, it does depend on the application you are using. It can be done but I don’t recommend it!

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