I had a problem... and now a solution

But first some background.

In my noder flat we have a small network set up. We've got an ADSL connection coming in to the flat. That passes through a Linux server (which also hosts our domains and mail) and on to the rest of the network. Behind the server we've got a 100mbs switch and six computers. We've strung Cat-5 to all the bedrooms in the flat and the server, switch and modem all live in our lounge. I wanted to move my second computer from the lounge where it was happily living next to the server in to my room where it could live happily with my laptop. But there was a small problem - I didn't have enough cable left to run a second line to my room, which is about 20 cable-meters from the switch. So what to do?

So there I was - staring at the length of Cat-5 that was already running into my room, when it struck me. I realized that only two pairs out of the four were being used... so could I run another connection down the other two? I did the first thing that I always did when thinking of these ideas - I went and googled on it. Hmmmm.... no info there. I did however get a few hits that discussed how susceptible Cat-5 is to interference. I also came across a few hits that discussed using the extra pairs to carry telephone signals, but most of them said that it would most likely cause undue interference that would screw the connections up.

Undeterred I decided to follow through my idea anyway. Since my wiring follows the 568B standard it looks like this:

W/O  1 
O    2
W/G  3
B    4
W/B  5
G    6
W/Br 7
Br   8

As the Green and Brown pairs aren't used I decided to run my second connection down them.

So here's how to do it:

Items needed: Cat-5, RJ-45's, knife, wire stripers, electrical tape, soldering iron, solder.

  1. Decide where you want your connections to split off to go to their respective network sockets.
  2. Strip the outer layer of the cable away at those two points. Be very careful not to damage the wires underneath the plastic sheath.
  3. Cut the Green and Brown pairs at the side nearest the RJ-45 plug. Be careful no to damage or cut the other pairs.
  4. Pull the cut pairs up and use electrical tape to recover the connected pairs to protect them.
  5. Take your new piece of Cat-5 and solder the following wires together: (New Cable->Old Cable) White/Orange -> White/Brown, Orange -> Brown. White/Blue -> White/Green, Blue -> Green.
  6. Use some more electrical tape to secure all the wires and to make a nice Y-Joint so you don't strain the soldered wires too much.
  7. Repeat at the other end of the cable
  8. If necessary then crimp some RJ-45s to the new cables
  9. Plug everything in and watch it work!

I didn't want a hub - they cost money, and I've got a good (read expensive) 16 port fast ethernet hub already.
And this is currently running at 100megabit/second at the moment - no problems.

That's all there is to it. I found that this works perfectly. I can't detect any packet loss down the connection, and I use it pretty hard for streaming movies from one computer to the other. Bear in mind though that I'm only doing down 20 cable-meters of Cat-5 so YMMV.

Notable Quotes:

"That ain't never going to work man" - Arieh
"Please get out of the way of the TV" - The Debutante, while I was moving my computer.
The Heschelian merely gave me an odd look....

At Iowa State University, the Ethernet links to dorm rooms are wired up this way. They have small splitter boxes that plug into the wall and provide the two ports. Of course, since these are not real hubs, they can't be chained together, as we found out the hard way. If anyone wants to pick some up, last I knew they were available at the ISU surplus sale. The connections were plenty fast; I'm not sure if they were fully 100-megabit.

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