Join Mike Meyers for an in-depth discussion in this video Introduction to Ethernet, part of CompTIA Network+ (N10-006) Cert Prep: 2 The Physical Network.
- One of the many many things that cracks me up by being a network technician is that normal people, just regular users, throw around a lot of high-tech terminology without really understanding what it's all about. And we hear people throw around terms like TCPIP or wi-fi, and they may or may not really understand it, but they like to throw it out anyway. The one term that drives me absolutely bonkers, that I hear people use all the time, is Ethernet. You'll hear folks say things like, "Oh here I got an Ethernet cable" or "Oooh look at my little SOHO Ethernet switch" or "Oh look! Ethernet fiber optic." On the back of just about every computer around is a network connection, and people go, "Oh that's my Ethernet connection." Well, that's one of those terms that's kinda right but really basically wrong.
So, what I want to do right now is clarify the term "Ethernet." If you wanna understand Ethernet, you need to understand that a long time ago, way back in 1980, a bunch of people got together with the IEEE, this is the big U.S. Standards Board, and they came together and they created a standard called IEEE 802.3. Now, IEEE 802.3, which we call Ethernet, is a book, and inside this book is everything you need to know to make a network called Ethernet.
Inside here is what kind of cables to use. Inside here is how fast does it run? Inside here is what type of frame is it going to use? Inside here is how do you sense it? How do you communicate together? I mean, everything you need to know to make a network is in this one book. Now, this was developed way back in February of 1980, 802, so the 802.3 standard has gone through a lot of changes since way back then. We have things like, oh I don't know, 802.3a 802.3b and 802.3i and they actually ran out of letters of the alphabet, and they had to start at the beginning.
So they have things like 802.3ae, and I mean, if I wanted to show you all of the addendums to the 802.3 standard, this thing would stack up probably about 100 yards over my head, so I don't want to do that. For right now, what we need to appreciate (notebooks hitting ground) is that Ethernet, at least in terms of one piece, never really changes. And that's right here in the frame. The Ethernet frame has stayed the same since pretty much from the beginning.
Now, there's gonna be some nerd out there who's like, "Well wait. There were earlier versions of Ethernet." But they haven't been around since, I don't know, since I was listening to Wham!. So, we ignore those people, and if they ever say that to you, punch them. So, the bottom line is that we have this little Ethernet frame. Now, we've talked about frames earlier. So what I want to add at this point is that Ethernet lives on MAC addresses. So it has the MAC address To and the MAC address From. There's gonna be some amount of data, and there's a CRC. But when we're talking about Ethernet we call this the frame check sequence or FCS.
So, this is the base frame. Now, in later episodes, we're gonna add a lot to this. This frame normally will never be more than 1500 bytes. So this can get a lot bigger, well at least in terms of ones and zeros. But the bottom line is that unless you're doing something weird, it's never gonna go over 1500 bytes. Okay. Now if you understand that the frame doesn't change, then some cool things can be thought about. For example, in the Ethernet world it's trivial for us to take a very modern network card and make it easily backward compatible with older equipment.
All we have to do is slow down the card because the frame never changes. Or if you have an Ethernet network that uses fiberoptic, it's not that big of a deal to connect it to a unshielded twisted pair just by using little media converters. Because the frame never changes. And that's a big deal. Now, given that the frame doesn't change, you do appreciate that Ethernet has gone through a lot of changes over the years since 1980. It started out with big thick wire and now it's down to unshielded twisted pair or fiberoptic.
It started out at ten megabits per second, and now it's going ten gigabits per second. So, when we talk about these different types of Ethernet, we have a standard nomenclature, and I wanna show that to you right now. So, if you take a look, here is an example of a standard nomenclature for one of those versions of 802.3. And this one says 10Base5, so let's break this down. On the far left hand side, what we're looking at is the speed in megabits per second. So this can be 10, this can be 100, this could be 1000.
It could be more than that, but let's stick with those three for right now. In the center, that value is either going to be Base or Broad. Broadband is Ethernet that runs kinda like cable television, where you have channels. And so you have one piece of cable that's running lots and lots of different conversations at once. But the more, vastly more common version is Base. And when you see the word Base, that means that the entire bandwidth, however you wanna look at it. There's only one channel. Everything that's being used is to send one conversation at a time.
So, let's go ahead and set this to something. I don't know, how about 10Base? There we go. So, the last value, this one's a little bit weird. Back in the old days of Ethernet, before we had switches laying around, what we would do is we would just have this big long cable, and you would hook into this cable. We actually have to know this for Network+ And the length of that cable was that last value. So if you saw a 5, that stood for 500 meters. And that's a little bit old but still on Net+.
Today, pretty much the only value you're gonna see there is T. So if we see something like 10BaseT, what we're talking about is that it runs at 10 megabits per second, it's Base band, and it uses unshielded twisted pair with a switch in the middle. So, for the exam, make sure that you're comfortable with these different types of nomenclatures, because you're gonna be seeing them all over the place.
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