Ethernet-ISDN splitter

2016-11-01

Two devices, one network outlet. That's were a splitter can help. I needed one for a computer and a phone, and decided to build it. The phone uses the ISDN protocol and the computer Ethernet. From my research, it looked like it is a rather unusual combination for a splitter. That comforted me into building my own pair.

Gigabit Ethernet over copper wiring (1000BASE-T) uses the 8 wires in the cable but if you only provide some 4 wires, it will usually downgrade to Fast Ethernet (typically 100BASE-TX) with a maximum bandwidth of 100 Mbps. That's a tradeoff I had to accept because there was no easy way to install a second cable in the wall. ISDN, on the other hand, only requires four wires, which was fine in this case.

If you want to build your own pair of splitters, I recommend you have a look at the Ethernet splitter guide on www.instructables.com. Just make sure you use the following Ethernet-ISDN wiring on both sides instead of the Ethernet-Ethernet one shown in the guide:

                shared

           1 2 3 4 5 6 7 8
          / / /  | | |  \ \
         / / /   | \/   | |
        / / /    | /\   | |
       / / /     \/  \  | |
      / / /      /\   \ | |
     / / /     _/  \_  \|_|
    / / /     /      \  | |\
   / / /     /        \ \ \ \
  / / / x x / x x  x x \ \ \ \ x x
 / / / / / / / /    \ \ \ \ \ \ \ \
1 2 3 4 5 6 7 8      1 2 3 4 5 6 7 8

   Ethernet               ISDN