| After struggling with an ISDN system with a little (Thanks, Thomas!) help, I decided to put up this WU to help others out in case they decide to wire their casa with ISDN phone lines. This is just a simple description on how to wire the ISDN LAN.
The U-line
The POTS line you used with your old phones is dead to your dear old phones. Realize it and get on with your life. The 2-wire POTS line is now a U-line. The U-line is the line that carries multiple-bandwith data (Like ISDN and ADSL signals) to the phone central. A switch in the central makes your POTS line a U-line.
The NT box
No, not the nightmarish Microsoft OS, but a box that sit on your wall. This box takes the U-line signal, mixes it with AC power and produces the S/T-lines, or the actual phone lines. In short, it transforms the ISDN signals (Which can't travel very far) into the U-line signals. Actually, there are two NT boxes, but since the the other NT box is a part of your phone or ISDN TA (Modem), we'll just refer to this one as the NT box. The NT box is powered at all times. The AC power supplies the phones in the ISDN chain with enough power to operate, some phones can't function without the power from the NT box.
Usually, the NT box has two lights. The amber light indicates AC power, while the green light indicates an correctly installed U-line.
- Install your NT box in a nice discreet place, and run the U-line up to the box, or just place the box near your normal phone outlet.
- Connect your old phone outlet to the LINE or U-LINE input of the NT box. The green light should be lit if the central office has switched your line to ISDN function. If not, check you connections, if they are OK, call the phone company because they haven't made the switch in the central office.
- Connect the AC power, the amber light will light up. If not, something is seriously wrong. Check the AC outlet with a lamp or something, check you wiring. If this is OK, exchange the NT box.
The ISDN outlet
OK. The NT box is glowing like a cheap Christmas tree, and the ISDN phone is waiting... If you don't want to establish an ISDN network, just plug in the phone and you're set. You may have to program the phone; look up that in the phone manual.
The ISDN network
Making a ISDN network isn't as easy as ethernet. You want to have a CAT-5 cable and use two of the pairs. This network is called an S0 bus, don't be scared of the sci-fi-like name; it is easy to understand after some years...
All cool and old-school networks use termination. There are two ways to terminate an ISDN bus: - Using Arnold Schwarzenegger
- Using 50/100 Ohm resistors
Since Arnie is expensive to hire, we'll use resistors. I recommend buying ISDN outlets with resistors welded on the circuit board. If you're reading this manual to understand how to build the S0 net, that's your sign to buy those. The network (Ooh, your phones have suddenly become quite advanced!) need to be terminated at both ends. The NT box has DIP switches inside. When these are in the ON positions, the box is a terminated end. That means that you can strech the S0 line up to 100 meters to connect your phone. You need to remember that the other end has to be terminated as well. This is where the pre-terminated ISDN outlet comes in handy. Put up the cable and crimp on all wires on the RJ45 plug, even if only the two pairs in the middle are used. The RJ45 plug goes in the "ISDN out" jack on the NT box.
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This is what your crimped RJ45 plug looks like; the locking tab is on the reverse side. Make a note of what colours the 3, 4, 5 and 6 use.
Now:
Cable 4 from the plug goes to 5 on the outlet.
Cable 5 from the plug goes to 4 on the outlet.
Cable 3 from the plug goes to 6 on the outlet.
Cable 6 from the plug goes to 3 on the outlet.
BE CAREFUL TO NOT SHORT PAIRS 4/3 and 5/6!
That's it! Remember to turn on the termination on the LAST outlet, and activate the emergency power function on at least one phone in case of an AC power loss in your house.
/msg me any corrections... | 
