My company has begun leasing new office space, and our modem was installed in a room without ethernet, a little ways from the router.

There is a bundle of unused telephone lines (RJ-11) which run from the modem room to the router room. I propose to splice an ethernet connector onto the ends of these phone lines, and use them to connect the modem and router. To provide enough pins, I may even need to combine two separate cables.

Would this be detrimental to performance? I would not expect gigabit or higher speeds from such a line, however the modem is only a 45 Mbps DSL modem. It doesn't need the maximum speed. If this hack performed at 50% of the speed of a regular cable, it would be sufficient.

Is that correct? Or am I missing something? Thanks! :)

  • so you have a modem connected to a phone line... and then some unused phone line... and at the end of that is where you want to have Ethernet? Just move the modem to the router room, then connect the spare phone line to the live one that the modem is currently connected to, then connect the modem to the router end of the spare phone line. Aug 27, 2016 at 4:27
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer.
    – Ron Maupin
    Jan 5, 2021 at 19:18

1 Answer 1


Category-3 cable, is used for 10BASE-T ethernet (10 Mbps), but it can't branch or have a bunch of connections, and you aren't allowed to splice. If you need anything faster, you need to use Category-5E, installed to specification.

You would be better off using the Category-3 cable to extend from the DMARC to where you can place the modem close to the router.

  • Are you recommending that I use a standard ethernet connector, but only use one phone cable, which provides only 4 wires? You mention that Cat3 cable can deliver up to 10 Mbps, but my modem is 45 Mbps. This would slow things down? I would have to shoot for something more ambitious. Mar 22, 2016 at 17:44
  • 1
    I recommend moving the modem to where the router is. You can extend the DSL line with the Category-3 phone cable since DSL uses phone cabling. Then the modem and router can use a Category-5E cable for the ethernet connection between the two. Basically, use the correct cable for the connection type.
    – Ron Maupin
    Mar 22, 2016 at 17:48

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