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Cheapernet versus Broken String
Dec. 6th, 2020 09:21 pm[Repurposed from a Reddit comment]
Ethernet is not just a kind of cable. It's also the electronic signals carried over that cable, and the format of the data packets that are sent over it.
Token Ring is a totally different kind of network, with totally different signals. You can't just convert one to the other.
If you write a sentence of Chinese in Roman characters, you've still got Chinese. It's not magically become Latin. "你吃了吗？" becomes "Nǐ chīle ma?" but it hasn't been translated -- it's still Chinese and unless you speak Chinese you cannot understand it.
This is not Token Ring converted to Ethernet -- it's Token Ring over unshielded twisted-pair cabling (UTP), the kind that some forms of Ethernet (10base-T, 100base-T, 1000base-T) happen to run over too. UTP comes in different categories – low grades are enough for voice phone calls but not for data. The minimum standard for 10base-T was Category 3, and 100base-T (called Fast Ethernet) used 2 higher: Cat5.
The connectors are a separate standard -- 8 position 8 contact (8P8C). However that doesn't tell you which wire is connected to which connector. Those are standardized as Registered Jack standards. The one that was used 10base-T was adapted from telephony standard #45 – RJ45.
The defining feature of Ethernet is that them medium is a straight line, A to B, and all computers share it. Everyone tries to talk at once, and if someone else is talking to, you hear it, shut up, wait a random time and then try again. This is called Collision Sensing Multiple Access with Collision Detection: CSMA/CD.
Dead simple to implement, therefore easy to implement, therefore cheap. But it doesn't scale. If too many people talk at once, they can't make themselves heard. 20-30 computers works OK; 200-300 and performance falls off a cliff.
Token Ring doesn't work like that. In a TR network, the wiring is a electronically a loop: no "ends". (Actually that's really fragile in real life, so the loop has long fingers reaching out from a central box, the Medium Access Unit – MAU – to each computer and back -- physically it's a star.) There is one magic golden ticket that means "I can use the network!" It goes round and round. If you need to talk, you grab it, send your message, then send it on its way. The next machine that needs to talk waits for the ticket, grabs it, talks, then lets it go. A single Token going round and round the ring.
This is complicated, so it's expensive, but because access to the medium is controlled, it scales really well, so it was worth it for big networks that had to perform even under heavy load.
Token Ring worked at 2 speeds: 4Mb/s and later 16Mb/s.
On top of the electronic signalling system, you can put whatever data you want. Normally, some kind of network protocol -- IBM used SNA and DLC, but also later NetBEUI in DOS and OS/2; Novell used IPX/SPX; Apple used AppleTalk; and those weird super-expensive UNIX computers in universities and reseach labs used their own weird thing called TCP/IP.
This isn't Token Ring over Ethernet. This is plain pure Token Ring, but using media converters to run it over cheap Cat5 UTP cabling with 8P8C connectors wired up as RJ45.
But hang on, you say, Ethernet cabling isn't one line. It's a star too.
Well, yes, it is now, because UTP is point-to-point. Older Ethernet standards such as 10base-5 (orginally called just Ethernet) and the later, thinner, cheaper 10base-2 ("CheaperNet", later renamed Thin Ethernet and the older stuff was retconned as Thick Ethernet) are a single long wire, up to a bit under 200 metres (600 feet), with special caps on the end called terminators. But if it breaks at any point, the whole network fails – and to add a new computer, you have to break the cable. Accidentally introduce a branch or fork and it fails. So, cheap but flawed.
So someone came up with a way to run it over UTP, adapted phone wiring really. Each machine has its own cable and they all meet in the middle in a box called a hub. But electronically, it's a line -- the ends aren't connected. You can just plug in new machines while the others keep talking. You need a lot more cables, dozens of them, but it's good, it works, and it's cheap.
You need a lot more cables and you need either a big hub -- but remember, Ethernet maxed out at under 50 machines or so. (Very hand-wavy number: the "everyone shout at once" model depends on what you're doing, obviously.)
It was difficult but you could interconnect hubs. But then you double the size of your network, and it doesn't scale.
So if you put a mini router in each hub, and it only passes traffic destined for the other hub, it scales better – but only to a 4-5 hubs or it gets too complex.
But once you're making cheap mini router chips, you can make a hub that listens to the traffic and only connects machines when they're talking. It's like a little telephone exchange, instead of lots of people on one line all talking at once. It switches circuits. Normally, client computers all talk to a server, not to each other, so it's quite scalable.
Now your hub has smarts. It doesn't act like a dumb everyone-to-everyone hub any more. It's a mini call-centre, routing calls from machine to machine: a switch. So normally only 2 machines are ever connected at once, and that scales really well, to hundreds and hundreds of machines with no drop in performance. No token required, just smarter, faster electronics. And all at 100Mb/s.
When switches got cheap, that was it for Token Ring.
Ethernet is not just a kind of cable. It's also the electronic signals carried over that cable, and the format of the data packets that are sent over it.
Token Ring is a totally different kind of network, with totally different signals. You can't just convert one to the other.
If you write a sentence of Chinese in Roman characters, you've still got Chinese. It's not magically become Latin. "你吃了吗？" becomes "Nǐ chīle ma?" but it hasn't been translated -- it's still Chinese and unless you speak Chinese you cannot understand it.
This is not Token Ring converted to Ethernet -- it's Token Ring over unshielded twisted-pair cabling (UTP), the kind that some forms of Ethernet (10base-T, 100base-T, 1000base-T) happen to run over too. UTP comes in different categories – low grades are enough for voice phone calls but not for data. The minimum standard for 10base-T was Category 3, and 100base-T (called Fast Ethernet) used 2 higher: Cat5.
The connectors are a separate standard -- 8 position 8 contact (8P8C). However that doesn't tell you which wire is connected to which connector. Those are standardized as Registered Jack standards. The one that was used 10base-T was adapted from telephony standard #45 – RJ45.
The defining feature of Ethernet is that them medium is a straight line, A to B, and all computers share it. Everyone tries to talk at once, and if someone else is talking to, you hear it, shut up, wait a random time and then try again. This is called Collision Sensing Multiple Access with Collision Detection: CSMA/CD.
Dead simple to implement, therefore easy to implement, therefore cheap. But it doesn't scale. If too many people talk at once, they can't make themselves heard. 20-30 computers works OK; 200-300 and performance falls off a cliff.
Token Ring doesn't work like that. In a TR network, the wiring is a electronically a loop: no "ends". (Actually that's really fragile in real life, so the loop has long fingers reaching out from a central box, the Medium Access Unit – MAU – to each computer and back -- physically it's a star.) There is one magic golden ticket that means "I can use the network!" It goes round and round. If you need to talk, you grab it, send your message, then send it on its way. The next machine that needs to talk waits for the ticket, grabs it, talks, then lets it go. A single Token going round and round the ring.
This is complicated, so it's expensive, but because access to the medium is controlled, it scales really well, so it was worth it for big networks that had to perform even under heavy load.
Token Ring worked at 2 speeds: 4Mb/s and later 16Mb/s.
On top of the electronic signalling system, you can put whatever data you want. Normally, some kind of network protocol -- IBM used SNA and DLC, but also later NetBEUI in DOS and OS/2; Novell used IPX/SPX; Apple used AppleTalk; and those weird super-expensive UNIX computers in universities and reseach labs used their own weird thing called TCP/IP.
This isn't Token Ring over Ethernet. This is plain pure Token Ring, but using media converters to run it over cheap Cat5 UTP cabling with 8P8C connectors wired up as RJ45.
But hang on, you say, Ethernet cabling isn't one line. It's a star too.
Well, yes, it is now, because UTP is point-to-point. Older Ethernet standards such as 10base-5 (orginally called just Ethernet) and the later, thinner, cheaper 10base-2 ("CheaperNet", later renamed Thin Ethernet and the older stuff was retconned as Thick Ethernet) are a single long wire, up to a bit under 200 metres (600 feet), with special caps on the end called terminators. But if it breaks at any point, the whole network fails – and to add a new computer, you have to break the cable. Accidentally introduce a branch or fork and it fails. So, cheap but flawed.
So someone came up with a way to run it over UTP, adapted phone wiring really. Each machine has its own cable and they all meet in the middle in a box called a hub. But electronically, it's a line -- the ends aren't connected. You can just plug in new machines while the others keep talking. You need a lot more cables, dozens of them, but it's good, it works, and it's cheap.
You need a lot more cables and you need either a big hub -- but remember, Ethernet maxed out at under 50 machines or so. (Very hand-wavy number: the "everyone shout at once" model depends on what you're doing, obviously.)
It was difficult but you could interconnect hubs. But then you double the size of your network, and it doesn't scale.
So if you put a mini router in each hub, and it only passes traffic destined for the other hub, it scales better – but only to a 4-5 hubs or it gets too complex.
But once you're making cheap mini router chips, you can make a hub that listens to the traffic and only connects machines when they're talking. It's like a little telephone exchange, instead of lots of people on one line all talking at once. It switches circuits. Normally, client computers all talk to a server, not to each other, so it's quite scalable.
Now your hub has smarts. It doesn't act like a dumb everyone-to-everyone hub any more. It's a mini call-centre, routing calls from machine to machine: a switch. So normally only 2 machines are ever connected at once, and that scales really well, to hundreds and hundreds of machines with no drop in performance. No token required, just smarter, faster electronics. And all at 100Mb/s.
When switches got cheap, that was it for Token Ring.
