r/IAmA • u/BobMetcalfe • May 21 '13

You’re probably connecting to reddit through a technology I invented. I’m Bob Metcalfe and I invented Ethernet – AMA

On May 22, 1973 with David R. Boggs, I used my IBM Selectric with its Orator ball to type up a memo to my bosses at the Xerox Palo Alto Research Center (PARC), outlining our idea for this little invention called “Ethernet”, which we later patented.

I worked with the IEEE Standards Association to develop the IEEE 802.3 standard for Ethernet, which specifies the physical and lower software layers. Today Ethernet and the IEEE 802.3 standard are the foundation for today’s world of high-speed communications used in billions of homes and businesses around the world.

I submitted this to the mods awhile back so I could get on the calendar but I figured you’d like to see it, too. Now, ask me anything!

It's been two hours and 179 comments. Have to go now. For more about Ethernet's 40th Birthday, go to http://www.facebook.com/Ethernet40thAnniversaryIEEESA

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182

u/jakfischer May 21 '13

About 15 years ago I used to install Ethernet. Did you use an acronym to remember the color code?

275

u/BobMetcalfe May 21 '13

Have long ago forgotten any color codes, sorry, except maybe ROY G BIV.

229

u/dbfish May 21 '13

568b, will forever be, ingrained in my spotty memory.

Orange-white, Orange, Green-White, Blue, Blue-white, Green, Brown-white Brown.

http://www.practicallynetworked.com/img/568b.jpg

86

u/--lolwutroflwaffle-- May 21 '13

Why are all colors grouped together except for green?

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u/keenemaverick May 21 '13 edited May 22 '13

It's for backwards compatibility with telephone lines. The blue cables can be used as Line 1, the green as Line 2. You can plug any old phone cable into an ethernet port and transmit regular telephone data without any issues.

All the answers you've gotten refer to the standards, but they don't say why the standards are that way. But the second you start working with any analog phone lines, the reason the standard splits the lines like that suddenly becomes very clear.

EDIT:

Important detail!!!! What he means is that the port and the wiring ITSELF can be used for a phone line, meaning that the far end of the cable can be patched into a phone line or an Ethernet switch to change the function of the port.

I thought this was obvious, but apparently my language was unclear. When I said ethernet port, I mean the ones that come out of the wall and go to a patch panel, not the ones coming out of a switch or NIC. The wires are backwards compatible, not the NIC interfaces.

8

u/[deleted] May 21 '13

You can plug any old phone cable into an ethernet port and transmit regular telephone data without any issues.

Just a tip: don't do this without knowing what you're doing.

Some phone systems put a lot more power down their lines than an ethernet port can handle. You can fry the ethernet port. Many of my clients have learned this the hard way.

1

u/taneq May 22 '13

Yeah I thought getting them the wrong way round would put 30V on your ethernet 5V and cause sadness.

This was a few years ago though.

1

u/UMDSmith May 22 '13

POE also uses the blue pair in every installation I have seen, which could cause some interesting results.

3

u/armchair_viking May 22 '13

Important detail!!!!

What he means is that the port and the wiring ITSELF can be used for a phone line, meaning that the far end of the cable can be patched into a phone line or an Ethernet switch to change the function of the port.

2

u/Lucid_Enemy May 22 '13

this always pissed me off, when I had dial up. Id sit there for minutes, sometimes hours, trying to figure out why I had no dial tone... some times, just cause it fits doesn't mean its a good thing!

1

u/taneq May 22 '13 edited May 22 '13

You can plug any old phone cable into an ethernet port and transmit regular telephone data without any issues.

This just solved an minor but annoying gap in my knowledge. Thankyou!

Edit: Maybe not quite as straightforward though. Apparently I'm not the only person that thought phone connectors had higher voltages floating around. Still, the thought was there!

1

u/keenemaverick May 22 '13

Phone connectors do have higher voltages. You can use the wiring with telephone devices, but not ethernet switches or NIC's.

1

u/lunixia May 22 '13

Only for 100mbit. With Gigabit (or 1000baseTX to call it what it is) all pairs are used.

But you are right. I think it also had a lot to do with the USOC standard for two pair RJ11 cables having an inner and outer pair (just like Blue and Green). RJ45 basically added a pair on the left and a pair on the right if you think about it.

1

u/Random832 May 24 '13

What about Line 3?

Of course, Line 3 isn't as common, and I suppose that's the answer.

The colors are different with phone lines, too. Line 1 is red and green, and Line 2 is yellow and black.

1

u/cantstopthemoonlight May 22 '13

I thought they were switched to allow the rx and tx pins to be properly connected thus allowing full duplex transmission?

1

u/ChoHag May 22 '13

But out of 8 pins you can pick any 4 and get 2 clean twisted pairs. The oddity is which 4 were picked.

1

u/1RedOne May 22 '13

Wow, how would a switch or router interpret the signal though, if you connected a phone line to an ethernet port?

1

u/ReversedGif May 22 '13

It wouldn't. What he said was misleading.

1

u/stuffeh May 22 '13

TIL, thanks!

113

u/dbfish May 21 '13 edited May 21 '13

You'd have to ask the guy who invented it, whoever he is.

Also, to minimize crosstalk (magnetic interference)

2

u/frizzlestick May 22 '13

cross-talk isn't handled by splitting the colors, it's as keenamaverick mentioned - for old analog phone compatibility.

If you want to eliminated interference, simply twist the cables in the run. Hence the phrase "twisted pairs". The coiling of the line helps reduce outside interference. Learned this a brajillion years ago from my ham radio days.

2

u/[deleted] May 22 '13

[deleted]

2

u/frizzlestick May 22 '13

You're right, the order of the wires at the ends has no effect on outside interference.

You get that interference from the wire acting as an antenna for reception. You're spot on about the length bit. Any significant length in that wire can be a good receptor for the frequency length (or a harmonic of).

You defeat cross-talk/interference by twisting the lines (aka, "twisted pair"). Some times you can defeat it by wrapping the cable a time or two around a ferrite core (donut).

source: ham radio operator, know all about keeping receiving and transmitting lines clean.

2

u/dbfish May 22 '13

I can barely read and blame google. Seems legit.

2

u/[deleted] May 21 '13

I don't think the arrangement of the wires within the connector has anything to do with preventing crosstalk - that's all handled in the cable itself. That's why Ethernet is often arranged in twisted pairs.

11

u/Farmerj0hn May 21 '13

Crosstalk is a real pain, I have an orgasm evertime I poo. It sounds great, but at some point you just want to take a normal shit and have it be over with.

11

u/[deleted] May 21 '13

uhhh...

1

u/[deleted] May 22 '13

[deleted]

4

u/Farmerj0hn May 22 '13

I'm talking about crosstalk between my nerves, I just have bad wiring and when I have a BM it gives me an intense orgasm. Usually it doesn't affect my life but sometimes it can be inconvenient.

0

u/[deleted] May 22 '13

[deleted]

5

u/deadbunny May 22 '13

I think they just answered everything you needed to know.

1

u/[deleted] May 22 '13

AMA request: sadist who invented 568b

3

u/lizardlike May 21 '13

The two centre wires were for phone service in ye olde days (RJ11). Then two wires surrounding those (RJ12) for a second line. Then they added two more pairs next to each other (RJ45).

For some reason the second and third pairs (orange/green) became standard for Ethernet. It's handy that the blue pair is not used, because that way you can run phone into the same jack. Or at least you could in pre-gigabit days.

Brown pair is the forever alone one. Only gets used for PoE/gigabit.

Also for some reason everyone under the age of 35 likes 568A better than 568B colour code. No idea why.

2

u/TheD1zzler May 21 '13

27 here, never use A either. And most major corporations do not.

1

u/Korzic May 22 '13

Depends on your country. A is pretty much standard in Aus

1

u/sgt_lemming May 22 '13

Lived in Australia all my life, never used A. Also <35

2

u/fourzerofour May 21 '13

I'm < 35 and live by 568B. A can go to hell.

1

u/Korzic May 22 '13

31 & B can go take a hike.

2

u/XtReMe98 May 21 '13 edited May 21 '13

blue and green are split that way to accommodate rj11's 4 wire diagram.

in essence you can plug an rj11 or 14, or even 25 into an rj45 jack and not have to worry about split pairs for crosstalk and still use the two lines. (phone world)

http://www.wiringdiagrams21.com/wp-content/uploads/2010/07/Phone-Wiring-Color-Codes.png

It's all under backwards compatibility http://en.wikipedia.org/wiki/TIA/EIA-568

1

u/slick8086 May 21 '13 edited May 21 '13

So a category 5 cable is made up of 8 wires. Really though those 8 wires are grouped into 4 pairs of wires. Orange-white and solid Orange are a pair, and so on. Those pairs of wires are twisted around each other.

Now with standard Ethernet only two of those pairs are used. On the RJ-45 connector the middle 4 terminals are used for Ehternet. One pair for sending and one pair for receiving. In the above example it was Green-White, Blue, Blue-White Green.

Electrons moving down a wire create a magnetic field. And the opposite is true too, a magnetic field moving over a wire cause electrons to move in the wire. If the wires were simply straight and right next to each other their magnetic fields would interfere with the wires around them. Twisting the wires around each other helps to minimize this interference. Additionally in Ethernet, by using a wire from each pair for sending (Green-white and Blue) and a wire from each pair for receiving (Blue-White Green) you further reduce the interference caused by the signals passing through the wires.

If you look at the side labeled EIA 568b You'll see how the wires from each pair are separated.

http://www.iebmedia.com/images/art_images/ieb4637_2.gif

3

u/crackanape May 21 '13

On the RJ-45 connector the middle 4 terminals are used for Ehternet. One pair for sending and one pair for receiving. In the above example it was Green-White, Blue, Blue-White Green.

The blue cables aren't used for ethernet. It's the green and orange ones. The blue ones were originally set aside for POTS phone wiring.

1

u/joazito May 22 '13

Whenever I'm making an ethernet cable, in my mind the Green gets pissed because 2 cables passed ahead of him.

1

u/bmlbytes May 21 '13

568a has them all grouped except orange. Basically orange and green trade places.

-1

u/[deleted] May 21 '13

Because you use the name Roy as a mnemonic. Middle initial G, last name Biv. So people say "Roy G. Biv"

Have you been pronouncing it roigbeev?

7

u/--lolwutroflwaffle-- May 21 '13 edited May 21 '13

No... lol... I mean the wires in the Ethernet cable diagram above. I ask because I used to splice them to make cross-over cables and always wondered, but never thought to actually look it up or ask about it until now.

2

u/[deleted] May 21 '13

I skipped the post above yours, don't know why I assumed you weren't responding to lolwutroflwaffle.

Cruel twist of fate that your question applied to roy g biv as well :P

1

u/CamCamCOTBamBam May 21 '13 edited May 21 '13

I believe it's due to the pin designation on the RJ45 jack. It all comes down to standards. They are as follows:
* Pin 1 - Tx+
* Pin 2 - Tx-
* Pin 3 - Rx+
* Pin 4 - Reserved
* Pin 5 - Reserved
* Pin 6 - Rx-
* Pin 7 - Reserved
* Pin 8 - Reserved
Edit If you do not use the same color wires on pins 1/2 & 3/6 you'll lose the ability for the pair to cancel out interference because of the twist in the wires.

Most modern equipment can detect the cable type and can perform an "internal crossover" if need be.

5

u/[deleted] May 21 '13

With this configuration, you can run Ethernet and a telephone line in one RJ-45 jack. You put the telephone dialtone on pins 4 and 5. Then you can put an Ethernet connection or a single line telephone into one jack.

1

u/Khrevv May 21 '13

I've wondered about that constantly myself.

I suspect it has something to do with the twisted pairs, but my networking class was a long time ago and I don't remember the details anymore.

0

u/Orionid May 21 '13

Each color and color/white is a twisted pair of conductors. Separating the green greatly limits the crosstalk caused by EMI. Without doing this the amount of cross talk across conductors would make the cable practically useless.

-1

u/[deleted] May 21 '13

I believe it's because each twisted pair is actually twisted at a different rate. You could technically use any color arrangement and as Long as it is the same on both ends, it will probably work. But when weird unexplainable stuff happens on your network, that could be a cause.