Why can't a single Ethernet cable carry 2 independent connection?

Question

A Ethernet cable has 4 pairs of data lines. In normal conditions only two pairs are used, one as a Tx pair and another as Rx pair. So two pairs are left unused. Is it possible to make use of these 2 pairs to carry another independent connection?

Of course I am expecting some obstacles. Maybe it will lead to a lot of noise and subsequent signal degradation. Can this be avoided by using a different color code?

It should be noted that I am not using Gigabit hardware. I just have 10 Mbps. So if I give this a try, will my connection speed be further reduced?

Another reason why this solution will be great is because I have only one power outlet in my room.

Sure it can. If you're willing to restrict yourself to fast ethernet speeds (or worse), there's devices that would split up an ethernet connection into 2 pairs for you. I've even seen stock cables that only have 4 connectors, and there was a little wierdness with it. However, modern gigabit ethernet needs all 4 pairs. — Journeyman Geek, Oct 04 '15 at 08:50
Cause you need 4 pairs for gigabit (so you'll be running at fast ethernet speeds), and as per my answer for the second question I referenced, empirically some gigabit ethernet cards or switches drop down to 10mbps when you do this. A switch would really be the intelligent way to multiplex a ethernet cable. — Journeyman Geek, Oct 04 '15 at 08:56
@JourneymanGeek My existing connecting is not gigabit. (University Network) Will I have any difference then? — daltonfury42, Oct 04 '15 at 08:57
@Linef4ult why go for a switch($10) if I can get the same result my spending less than $1? The only question is weather it is reliable. — daltonfury42, Oct 04 '15 at 08:59
@daltonfury42: Well that's exactly the thing, it's not the same result. We've had such "creative" wiring in some places here at $WORK, and ... it isn't exactly fast nor reliable. — u1686_grawity, Oct 04 '15 at 09:01
@daltonfury42 but it wont work. If its your house you can split the CAT5/6 at either end into two jacks and make 2x connections from 1 cable. But you can only split one end. You'll just kill the link. — Linef4ult, Oct 04 '15 at 10:03
@Linef4ult They provide a switch at each floor of our hostel and I know the LAN admin ;-). — daltonfury42, Oct 04 '15 at 10:06

score 3 · Answer 1 · edited Mar 20 '17 at 10:16

3

Sure it can. If you're willing to restrict yourself to fast ethernet speeds (or worse), there's devices that would split up an ethernet connection into 2 pairs for you. However, modern gigabit ethernet needs all 4 pairs.

I've even seen stock cables that only have 4 connectors, and there was a little wierdness with it.

However you'd need to split the cable on both ends for your scheme to work, based off the comments, and its a pretty horrid way to get another 'drop' between two ends of a ethernet cable.

What you want to do won't work, unless you're trying to turn one connection -------- into something like this >--------<. On a university connection, the best you can do is >------- and that essentially just throws half the wiring away for no gain.

Assuming you do this correctly, and don't have wierd slowdowns and other issues like the 4 stranded cable I mentioned. You'd also need to buy unusual hardware (no one really users splitters much) or additional gear you'd use once (ethernet crimping gear!), and a switch makes much more sense here. Its unlikely to be reliable, may fail in strange ways, and might not even work.

edited Mar 20 '17 at 10:16

Community

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answered Oct 04 '15 at 08:50

Journeyman Geek

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Splitting an ethernet connection tends to result in regrets... – u1686_grawity Oct 04 '15 at 09:00
Thank you for taking time to answer my question. I am sorry for not being more descriptive in the question. I've added more information to the end of the question. Since my existing network is not gigabit, will my speed be further reduced? Also in my case, I have a crimping tool at my disposal. Also it will look geeky when my friends notice it. ;-) – daltonfury42 Oct 04 '15 at 09:13
Well honestly, reading into the whole question, I suspect it would end badly. If you must, its a better bet to get a proper splitter. You'd also need to split the other end, and it needs to plug in somewhere. A multisocket, and cheap switch is the logical choice here. – Journeyman Geek Oct 04 '15 at 09:15
I understand that. But still you are not answering my question. Since my existing network is not gigabit, will my speed be further reduced? And why? – daltonfury42 Oct 04 '15 at 09:27
Possibly 2. It may not work at all the way you want it to. 3. The issue is more with the NICs on either end and you might unpredictably get dumped down to 10mbps if one of the NICs decides the cable is faulty.4. You need to do this on both ends and have a second port on the other end, And I suspect your university would not be very happy about even one end getting modified like that.

Journeyman Geek

Oct 04 '15 at 09:29

Why can't a single Ethernet cable carry 2 independent connection?

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