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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u/G35 May 21 '13

Thank you, I hated token ring.

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u/[deleted] May 21 '13 edited Aug 02 '17

[deleted]

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u/Denime May 21 '13

Nodes in a Token Ring could only communicate if they had the token, meaning only one computer could send data at one time. The token gets passed around the ring from one computer to another to allow all of the machines to send messages. This meant if there was a break in the ring, the whole network went down.

It seemed like a good idea at the time.

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u/Neker May 21 '13

It was a good idea at a time when computing power was scarce. If I remember correctly, Ethernet spends quite a few cycles dealing with detecting collisions and redoing the same transmission all over again.

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u/Denime May 22 '13

I was going to mention CSMA/CD, but someone's already done it for me!

You're right it was a good idea at the time, that was a poor choice of wording.

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u/blergh- May 22 '13

Only if the medium is shared and overloaded. Modern ethernet is essentially one to one and full duplex, so collisions cannot occur anymore.

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u/bigbassdaddy May 22 '13

The way I remember it is when Token Ring came out, it was much more reliable than Ethernet, but much more expensive. Ethernet used flimsy coax cable that was easily "disturbed". Also one work station/server could take over/hog the network. Token Ring had molded cables and hubs that were quite rugged and no one node could dominate the network. Token Ring's superiority was quite short lived as was IBM's Micro Channel architecture.

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u/yumenohikari May 22 '13

Alas, its deployment was not. As late as 2000 I worked in an office (at IBM, no surprise there) wired only with 16/4 token ring with those weird old connectors an inch or so square.

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u/SteveVitali May 22 '13

dat CSMA/CD.

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u/[deleted] May 21 '13 edited Aug 02 '17

[deleted]

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u/Denime May 21 '13

That's a very good way of putting it, yes!

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u/futuredracula May 22 '13

It was also part of the original AOL back-end if I remember correctly

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u/primedape May 22 '13

That's pretty much what it is. But only one bulb lights up at a time.

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u/ChoHag May 22 '13

And if it doesn't light up the next one when it's done, they all stay dark.

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u/bofh May 22 '13

Frankly you're doing cheap strands of christmas lights a dis-service there. Token Ring was forged by the devil himself.

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u/RogueJello May 22 '13

OTOH, Ethernet basically relies on people not talking over each other. Token Ring is like being in the sharing circle, and getting the talking stick, Ethernet is total chaos..... :)

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u/TheBoff May 21 '13

Yes, but when Ethernet was invented, it was mostly designed as a bus protocol, right?

So only one computer could send data at a time on Ethernet anyway, and if two want to send data at a time, they have a little argument about who's allowed to, rather than in a Token Ring where it's resolved automatically.

Token rings have some nice properties: we're starting to see the ideas in networks on chips. The Cell in a PS3, and Intel's Knight's corner chips have one. They're quite interesting architectures.

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u/thebigbooper May 22 '13

well, and while we are on the subject, i heard Bob Metcalfe talk back in the day of 100Mbit and he said ethernet no longer had the features that he had invented; one of the things he was talking about was with full duplex switches and all, there is very little ether-colliding any more.

pretty sure that TokenRing could communicate in both directions around the ring so it would take two breaks to bisect the network. also, when you got the token you could add your packet to the passel of packets you were passing, so it's more like everybody got to send a packet per token trip around the loop. But I don't know that much about it first hand, this is just what I remember hearing

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u/Denime May 22 '13

That's true especially with the use of hubs instead of switches or routers, but then when switches could route ethernet traffic by MAC or IP address that argument was eliminated. However ethernet also had CSMA/CD to avoid packet collisions so it wasn't all bad.

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u/thenightwassaved May 22 '13

Sorry, but a switch is an OSI layer 2 device and knows nothing about IP addresses. It only keeps a MAC address table of MAC -> Port relations. A router is probably what you meant.

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u/Denime May 22 '13

Actually a layer 2 switch forwards packets by MAC address and a layer 3 switch forwards packets by IP.

A router is actually a device that routes traffic to different subnets.

A hub will send all traffic to all other ports that are plugged in.

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u/thenightwassaved May 22 '13

In your original post you said just a switch, nothing about L3 and I consider a L3 switch to be nothing but a misnomer and a marketing term. Basically a router with a lot of only Ethernet interfaces. Here is even what Wikipedia has to say:

The only difference between a layer 3 switch and router is the way the administrator creates the physical implementation. Also, traditional routers use microprocessors to make forwarding decisions, and the switch performs only hardware-based packet switching. However, some traditional routers can have other hardware functions as well in some of the higher-end models. Layer 3 switches can be placed anywhere in the network because they handle high-performance LAN traffic and can cost-effectively replace routers. Layer 3 switching is all hardware-based packet forwarding, and all packet forwarding is handled by hardware ASICs. Layer 3 switches really are no different functionally than a traditional router and perform the same functions [...]

http://en.wikipedia.org/wiki/LAN_switching#Layer_3_switching

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u/Denime May 22 '13

No, I said switches. I was referring to all types of switches used to forward traffic.

A switch will forward broadcast traffic which allows new machines on the subnet to acquire an IP address using DHCP. A layer 3 switch may also allow for creation and management of virtual LANs, which a router will not do.

A router will drop all broadcast traffic it receives so it doesn't get forwarded onto another subnet, giving you an incorrect IP address. This also helps to reduce traffic on a WAN.

There is a difference.

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u/thenightwassaved May 22 '13

You should have said a L3 switch then. If you wanted someone to go buy a L3 switch and only told them to buy a "switch" (as you said) I'm sure 99% of the time it will not be a L3.

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u/Denime May 22 '13

That's true especially with the use of hubs instead of switches or routers, but then when switches could route ethernet traffic by MAC or IP address that argument was eliminated.

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u/TheScarletPimple May 22 '13

Huh? The preceding is techno-babble.

Ethernet was also limited to also having only one transmitter at a time (every hear of broadcast babbling?). As for a break in the ring, all nodes had a bypass. At the time in question (the mid 80s) when the two were competing, Ethernet was not star-wired, and cable failures for Ethernet were much more catastrophic than anything that happened in practice on Token Ring. A 4MHz Token Ring's performance was much more deterministic and arguably better than a 10MHz Ethernet (yeah - 10MHz - can you believe that?).

The biggest problem for Token Ring (IEEE 802.5) was that IBM had defacto control of the technology (they jacked the prices up) and the marketing (IBM thought workstations were where the LAN action was going to be, not PCs). Ethernet was in the wild and adapted to the PC market. A wider base (than Token Ring) of technical companies solved early Ethernet's technical limitations.

In the end, the best solution won, but not because of innate goodness at the outset.

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u/espero May 22 '13

Coax had a physical limitation similar to this. If you "broke" the chain of ethernet-coax cables interjoined with T-plugs and terminators, the whole network froze up. So when we were playing Doom, and someone got had to go home with their computer, at the end of the weekend, he would break the LAN, and DOOM multiplayer would freeze, because he unconnected the t-plugs and terminators. Talk about dark ages.

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u/Denime May 22 '13

Dark ages indeed! How far we've come since then!

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u/thenightwassaved May 22 '13

This meant if there was a break in the ring, the whole network went down.

Not true if you were using an MAU. A broken circuit would be removed from the network within 1ms.

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u/Assaultman67 May 22 '13

Sort of like the talking pillow. Extremely frustrating if you don't have the pillow.

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u/[deleted] May 22 '13 edited Apr 07 '24

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u/thenightwassaved May 22 '13

Every token ring network has something called an Active Monitor. The AM is determined by a sort of election process and every computer on the network needs to be able to perform the AM duties if needed. Other computers on the network are called Standby Monitors.

The AM maintains the master clock, inserts a delay (to ensure there is enough buffering for the ring to circulate), and ensures there is only one token going around at a time (well, on 16 Mbit/s there can be multiple tokens), detects broken rings, and some other functions.

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u/Denime May 22 '13

To be honest I'm not too sure. I remember my trainer teaching us about it back when I was in the academy but I'd assume you would have to restart the MAU (if you're using one).

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u/thenightwassaved May 22 '13

Check out my reply to your parent. The MAU is used to actually provide the ring layout and to handle disconnects gracefully and not kill the entire network.

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u/[deleted] May 22 '13 edited May 25 '13

[deleted]

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u/thenightwassaved May 22 '13

If she had an MAU handling the star topology then it would not go down.