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2 Ethernet Connections Down 1 Rj45 Wire ? Here's How ..


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#1 RBJTech

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Posted 09 March 2007 - 10:02 AM

I've been asked a couple of times from my 'Live/Ethernet LED' tutorial in the hardware section (+FAQ) how do you run two ethernet connections down a single RJ45 cable..

This is extremly useful is you have taken the time to run a long RJ45 cable around your house, only to discover that you now should have run two cables as you need another one ... doh!

The 10/100 Mbit/spec only actually uses 4 of the 8 available wires as so :-

1. White/Orange (used - Tx Pair 1)
2. Orange/White (used - Rx Pair 1)
3. White/Green (used - Tx Pair 2)
4. Blue/White - not used.
5. White/Blue - not used.
6. Green/White - (used - Rx Pair 2)
7. White/Brown - not used.
8. Brown/White - not used.

So all we need to do is wire the 2 unused pairs (4 wires) into the same connections as you would have done normally in the 2nd RJ45 plug at both ends of the RJ45 wire - ie

(was 5 now 1) White/Blue (now used, Tx Pair 3)
(was 4 now 2) Blue/White (now used, Rx Pair 3)
(was 7 now 3) White/Brown (now used, Tx Pair 4)
(was 8 now 6) Brown/White (now used, Rx Pair 4)

There you have it, 2 Ethernet connections down a single RJ45 wire. smile.gif

There are a few different ways to practically implement this

A.) Use a RJ45 faceplates, where you can simply wire the 'fixed' cabling as above, keeping the RJ flyleads the same. You'll need to buy 2 x RJ45 dual faceplates but it will look much more professional ...
B.) Buy some RJ45 plugs and an RJ45 crimper - not the most cost effective option if you are just doing a couple of connections though ...
C.) Lastly, cut the ends off existing RJ45 patch cables and connect the wires together. It's important to try and keep the 'twists' going, especially for longer runs of cable. Ideally solder the wires together and use heat shrink, but if you're really on a budget, then electrical tape and twisted wires should work ok .. wink.gif

Last couple of points -

1. This will NOT work for Gigabit Ethernet - that uses all 4 pairs.
2. Make sure you identify the pins correctly, the colour codes I've given 'may' not be valid for your cables (there are two different standards.. sad.gif )

Look here to check the RJ45 Pinout (courtesy datalinkcom.net)

Enjoy ...

Edited by RBJTech, 09 March 2007 - 10:04 AM.


#2 tgm4883

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Posted 09 March 2007 - 03:52 PM

Why wouldn't you just get a switch? Seems like it would be easier and its about $20

#3 Reaper527

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Posted 09 March 2007 - 05:47 PM

because you've already gone through the trouble to wire up the wall, and this looks SO much nicer wink.gif also you don't have to hog up a power outlet with a switch if you do it this way.

#4 RBJTech

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Posted 09 March 2007 - 08:56 PM

QUOTE(Reaper527 @ Mar 9 2007, 04:54 PM) View Post

because you've already gone through the trouble to wire up the wall, and this looks SO much nicer wink.gif also you don't have to hog up a power outlet with a switch if you do it this way.


Absolutely ..

Here's a quick diagram too for those that follow diagrams better than my explanation ...

IPB Image




#5 StrictPuppet

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Posted 10 March 2007 - 06:57 AM

Very helpful, RBJTech. Thank you for posting that.

#6 DuBob4432

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Posted 16 March 2007 - 03:33 PM

just out of curiosity, does this mess with the 100M spec? or could one still use a 100M piece of ca5e/cat6 and not have any issues?

also, what about GbE? i have one piece of cat5e running into the master bedroom where my 360 is and obviously 10/100 is fine for the 360, but i also have a laptop, and i move a lot of data around the condo, so GbE is kind of a must if i am going to use a wired connection, otherwise i would just the laptopls 802.11g connection.

thanks in advance for this and also your lan activity mod - one i am going to do since i plan on getting a new faceplace anyway in case i mess it up, but i have always been curious with lan activity, any chance for a hdd activity led??

thanks again for your hard work and knowledge smile.gif

#7 tgm4883

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Posted 17 March 2007 - 05:14 AM

QUOTE(DuBob4432 @ Mar 16 2007, 08:40 AM) View Post

just out of curiosity, does this mess with the 100M spec? or could one still use a 100M piece of ca5e/cat6 and not have any issues?

also, what about GbE? i have one piece of cat5e running into the master bedroom where my 360 is and obviously 10/100 is fine for the 360, but i also have a laptop, and i move a lot of data around the condo, so GbE is kind of a must if i am going to use a wired connection, otherwise i would just the laptopls 802.11g connection.

thanks in advance for this and also your lan activity mod - one i am going to do since i plan on getting a new faceplace anyway in case i mess it up, but i have always been curious with lan activity, any chance for a hdd activity led??

thanks again for your hard work and knowledge smile.gif


QUOTE(RBJTech @ Mar 9 2007, 03:09 AM) View Post


Last couple of points -

1. This will NOT work for Gigabit Ethernet - that uses all 4 pairs.
2. Make sure you identify the pins correctly, the colour codes I've given 'may' not be valid for your cables (there are two different standards.. sad.gif )




#8 DuBob4432

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Posted 17 March 2007 - 04:27 PM

thanks, skimmed right over that..... blink.gif huh.gif uhh.gif

#9 magic_man185

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Posted 20 April 2007 - 08:03 PM

QUOTE(RBJTech @ Mar 9 2007, 05:09 AM) View Post


1. White/Orange (used - Tx Pair 1)
2. Orange/White (used - Rx Pair 1)
3. White/Green (used - Tx Pair 2)
4. Blue/White - not used.
5. White/Blue - not used.
6. Green/White - (used - Rx Pair 2)
7. White/Brown - not used.
8. Brown/White - not used.




Just a minor correction, pins 1 and 2 are both used for transmit, pin 1 for +, pin 2 for -, and the same for pins 3 and 6 as receive.



#10 ChadH

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Posted 19 May 2007 - 10:59 PM

Just one thing to bear in mind with this! From memory Cat5e is rated at about 125Mbps, whereas Cat6 is rated at about 350Mbps.

What this means with Cat5e is that you can't run two 100Mbps links down the same wire as it will exceed the specification, and result in a lot of lost data packets - which in turn means very slow network speeds. When I've done this in the past, I've always ensured that one of the links runs at 100Mbps, and the other at 10Mbps.

If you're using Cat6 then you can run two links at 100Mbps.

It's worth checking that your cable is Cat5e, and not Cat5 - Cat5 is only rated at 100Mbps, and therefore you can only really get away with both links running at 10Mbps.

#11 tcrandal

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Posted 24 May 2007 - 01:57 AM

I have no idea why this was made a sticky, however as mentioned, while it certainly can be done, you'll be very likely to experience crosstalk. We used to run voice and data on the same category 5 cable, and again, while it can be done, you'll be losing performance on the link.

Do yourself a favor and buy a switch. I build data centers for a living, and if it was a recommended way of doing things, cable costs for new sites would have been reduced by 50%.

Take off the sticky, it's not worthy.

#12 RBJTech

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Posted 15 June 2007 - 10:44 AM

First off - I never asked for it to be made a sticky... It's just useful info.

Secondly, I have never had ANY packet loss issues running two 100 Mbit connections down a single RJ45 cable (cat 5e). As long as you maintain the twists and keep to the correct pairs then this is actually no different whatsoever from a packed bundle of UTP RJ45 cables - I also build data centres ... wink.gif

Thirdly - we are not talking data centre grade communications here - I'd be very much surpised if both channels will be anywhere near maxed out at the same time in a typical home environment. I would not do it in a commercial implementation but for home use it's perfectly acceptable IMO.

Lastly - the 100Mbit or even 10Mbit/Sec speed is not the bottleneck on most peoples broadband/Xbox Live connection - it's the broadband itself, so speed is not really the issue here, it's practicality ...

If you don't want to do it fine - but I assure you it works fine for 99.9% of the people on this board ...

Edited by RBJTech, 15 June 2007 - 10:46 AM.


#13 AfternoonLemon

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Posted 19 June 2007 - 09:02 PM

I've done this for years, although it is a halved for a PC and XBox - they both won't be maxing out their bandwidth at the same time. I don't think there is any problems of interference - the 4 pairs are twisted for the full length of the cable, and seperated at the double wall socket at either end. Just the same as gigabit ethernet uses, except the data is not combined into one line.

#14 Vatamin R

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Posted 17 November 2007 - 02:09 AM

great tut. thanks

#15 Millerboy3

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Posted 28 November 2008 - 04:36 AM

awesome tut. worked great. thankx!!




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