ISDN RJ11 to RJ45 FREE cabling and networking Helpdesk
 Question by Jack Shugart posted 15 Aug 2006
 ISDN RJ11 to RJ45
I just got ISDN 128k service installed to my house, now I have to run the cable to the ISDN modem.

The phone company box has a RJ11 jack for the ISDN, but the incoming port on the ISDN Modem is a RJ45.

Can someone tell me the correct pinout for the jacks?
 Answer by Dmitri Abaimov posted 15 Aug 2006
Dear Jack,

If you are in US or Canada, chances are you are getting an ISDN-U variety of service from the phone company which works over a single pair. The pair used is the two central conductors in both RJ11 and RJ45 interfaces. Actually, I believe that by RJ45 you mean simply an 8 pin 8 conductor plug/jack interface that is commonly referred to as RJ45. Actually RJ45 stands for a particular pin payout.

In any case you should be able to get away with simply plugging an RJ11-RJ11 cord into both devices. It should fit nicely inside the 8 pin jack as well.

Dmitri Abaimov, RCDD

Click here to see the expert's profile
Back to the current page of questions | Back to all the questions
Back to HELPDESK | Ask your question
Residential Cabling Guide

Home Cabling Guide

Finally, an instantly downloadable book that saves you thousands in home improvement dollars! Enjoy living in 21st century technology-advanced home while increasing its selling value and competitive advantage on the real estate market. Whether your cabling is for home office or high-tech leisure, you can wire your home yourself or learn "wirish" to speak with your cabling contractors in their language!

Learn more ...