ISDN Pinout Mapping

[dajo]

I need to compose an RJ45 to RJ11 ISDN cable for a customer site in order to bypass the make-shift wire job that was originally done. Most of the ISDN boxes I've seen have the RJ45 input, but this site has an RJ11 input on the ISDN box at the phone patch panel area.

I've found several links about ISDN wiring, and the most logical is "U-Loop" with pins 4 and 5 active on the RJ45.

Can I simply map these to pins 2 and 3 on the RJ11 terminator?

Do you think the U-Loop is the one for this site? It's a simple setup with two computers on the LAN.

 

[spidey07]

ISDN U interface uses pins 4 and 5 for tip and ring. I guess you could use RJ11 but I've never seen this before. What kind of device will terminate this ISDN circuit?

spidey

 

[dajo]

Well, these guys have suffered with timeouts connecting for a while, and now they cannot connect at all. It is a very old house.

I've never seen this before either, but I guess at some point the RJ45 does get translated into a "regular" phone line twisted pair.

The ISDN device terminates in a tan input box at the phone patch panel area as usual, but this box, which has the ISDN number on it, has an RJ11 input jack.

Pretty weird. I guess the phone company set it up that way. I don't know.

Currently, the RJ45 out of the router goes through some very strange and questionable configurations. The RJ45 cable is only three feet long, and it first plugs into this funky small box that has a switch for "tele" or "modem". Wires come out of that box which are have been stripped, twisted, and capped to connect to some other bared wires that then disappear under the floor. At the phone patch panel area, some wires come off the patch, turn into insulated wiring, and terminate into an RJll phone box just dangling in the air. There is then a regular phone cord, about a foot long, connecting that dangling box to the ISDN input box mounted on the wall. Pretty weird, huh? Far from optimal, I'd say.

The phone company says the ISDN line checks out okay in their tests, so I'm hoping that by composing a cable to run straight out of the router back to the ISDN phone box (RJ11 in this bizarre case) that I might be able to solve the problem.

I am really currious as to why the ISDN signal in this case seems to be sharing the patch panel with the rest of the house phone wiring. Again, I have never seen this happen.

Anyway, it sounds like I just need to map the two RJ45 4-5 pins to the two RJ11 2-3 pins, don't you think? Since there are only two permutations possible here for the RJ45 to RJ11 mappings I should be able to get it fairly quickly.

Thanks for responding. I appreciate it very much.

 

[spidey07]

You should be fine by taking the middle pair. (never hurts to try)

Quick tutorial on ISDN.

Runs over normal phone lines via a single pair. Is a digital service. This is called the U interface. No problem running it on the same panel as the phones lines. That was the promise of ISDN...work on existing phone lines. You have a basic rate interface (BRI - two 64kb B channels and one 16k D channel)

From the U interface you connect to an NT1. Sometimes the NT1 is external but nowadays most ISDN terminal equipment has a built in NT1. You can tell by looking at the description of the interface on the terminal equipment (router in this case)

Terminal equipment ports:
U - means one pair with built-in NT1 and you can plug directly into phone jack from provider
S/T - means two pair and you need an NT1

Some soho routers have both, check manual or look on router itself.

 

[dajo]

Thank you for your responses. I appreciate it.

The whole point of this is to figure out why they are timing out at that site. The phone company says the ISDN line is okay, and we've even had a phone tech out there who says the signal from the router to the ISDN line is good, although I find it hard to believe that he didn't comment on the weird wiring.

Could making the cable that goes straight from the router to the ISDN out box possibly solve our problem?

The router says that it detects the ISDN line, but 9 out of 10 times the loop back test fails, and when I call out it immediately says "LCP stopped" right after the "calling out" message along the lines of:

Call CONNECT speed<64000> chan<1> prot<1>
LCP stopped


Any ideas?

PS-Update:
The phone company finally found a problem in the &quot;interface box&quot;, which I assume is the SNI or NID or phonebox outside the house. We'll have someone run a direct router-to-ISDN box inside the house anyway, but the interface box problem is most likely the cause of the failure to connect.