OSI Model Intro and Encapsulataion

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our next topic is going to be the OSI reference model.

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The OSI reference model provides us a framework so that we can understand the different elements of networking and how they work together.

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There are a couple of purposes with the OSI reference model to cover first,

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and then we'll get into exactly what it is and how it works.

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It's the idea of inter proper ability between vendors.

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What we want is an environment where different components from different vendors all work together.

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So we don't want to have to buy everything on our network from a single vendor.

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We don't want vendors to have a monopoly of services because they can then charge whatever they want. And we're locked into that specific vendor,

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whereas if instead we have a variety of components and I'm connected to a Netgear switch and that fails, I can go out and buy a Linksys switch that makes my life easier.

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We prefer standardization.

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Usually when we have vendors that have proprietary equipment, it may take additional training in order to work with those devices.

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There's usually additional costs and sometimes additional complexity.

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The OSI model promotes standardization,

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so ultimately what we have is seven layers of the OSI model and standards at each layer.

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So if I have a layer to device and I built it to the standard of an OSI layer to device, then it will be interoperable and a standard space environment.

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That's great for me as a vendor, because standardization cells,

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that doesn't mean proprietary stuff doesn't sell. But standardization really is what most network administrators are looking for.

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There might be times when we purchase a proprietary device or component, but for the most part, we like standardization.

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Each layer of the OSI model is going to give us a description of certain services based on the standard.

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What we're also going to see with the OSI model is an idea of encapsulation.

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When we talk about encapsulation, it is packaging.

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It's placing headers around data or it's putting a protocol in a protocol.

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The best example I can offer is this.

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Let's say my Uncle Steve in Seattle has an anniversary,

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and in order to help him celebrate, I'm going to send him some champagne glasses.

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Technically, I could write his name on the champagne glasses and say Happy anniversary Uncle Steve and put a stamp on them and put them in the mailbox.

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But of course, as soon as I do that, I'll hear clink, clink, clink.

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So what I'm going to do instead is wrapped the champagne glasses in bubble wrap,

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put them in a small box and put bubble wrap around that box.

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I'm going to give drop the box and write Happy Anniversary or best wishes on the box.

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I do want to point out that when I write best wishes Uncle Steve that the Uncle Steve pieces in addressing element.

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It's not worldwide addressing, but when the package finds Steve's house, he's going to see that it's for him.

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So some of what we're doing is for protection and padding,

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and some of it is for addressing.

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Ultimately, we start out with a very small payload, the champagne glasses

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and as we package and add addressing and protection all those things.

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By the time we're ready to pass this off to FedEx, we wind up with a much more sizable package.

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We continue to add. We put in a FedEx box, we get a FedEx label we handed off to the FedEx carrier.

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That's encapsulation.

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It's not the same as encryption, though sometimes people make that mistake.

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I never encrypted the champagne glasses. I didn't magically turn them into coffee mugs. They're still champagne glasses. They're just all wrapped up.

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That's our goal with encapsulation.

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Of course, the only piece that I missed in the instructions is that if you have pets

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at some point in time, I can guarantee you there will be a cat in the packing peanuts or perhaps a pug wrapped up in bubble wrap.

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So if you need to shock the animals, you can add those steps in here.

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I do want to mention no animals were harmed during the making of this video,

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so this encapsulation ideas illustrated here on the right.

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At the top, we have seven layers application down a presentation session, transport network, data link and finally, physical.

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The idea here is data conceptually travels down through the OSI model.

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When I say that, what I mean is that the sending computer starts with an application layer protocol,

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so application layer protocols are those protocols that drive user applications.

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If you think about a Web browser, you got http.

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If you think about Male, you've got pop three or IMAP or some of those other mail protocols.

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So data starts at the very top of the OSI model, and as it conceptually travels down, headers are added

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so you can see we start with the data alone at the application layer.

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But as we moved on to presentation, we get a presentation hunter, a session header next, a transport header than network header data link header all the way down to the point where we have the conversion in the bits that relay electronic signal on the network.

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At each layer, something is added that will help the data gets where it needs to go

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all the way to the destination hosts.

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There's formatting. There's perhaps receipt of Acknowledgments. There's I p addressing. There's Mac addressing and all these things we'll talk about as we move on.

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But I just want you to have this idea that at each layer something gets added until the computer is ready to put that data out on the network.

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Now, I would definitely recommend that you know, the OSI model top down.

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I know it by number and by name.

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All people seem to need Domino's pizza is a good little trick that a lot of folks use from the top down.

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All people seem to need Domino's pizza. That will help you remember

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my personal favorite from the bottom up.

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People don't need to see Paula Abdul

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changed my mind. I'm standing by that.

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But anyway, you find some little trick.

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I do not recommend that you go out and Google harmonic tricks for the OSI reference model.

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There are some things you cannot unsee and there are people of questionable intent on the Internet. That's all I'm gonna say about that.

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What I probably just done is guaranteed that 2200 people go on the Internet and Google you demonic tricks for the OSC model.

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But at any rate, find some trick that helps you remember it and go with that.

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Okay?

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The other thing I ask you to think about is that each layer of the OSI model we refer to data a little bit differently based on the headers.

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When data is at the application presentation session layer, we still refer to it as data.

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But once it comes down to the transport layer, we have a segment down to the network layer.

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We have a pocket down to the data link layer. We have a frame, and at the physical layer

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it's converted in a bit.

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So segment pocket frame bits.

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Sometimes you'll hear these terms used interchangeably, and that's okay.

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But I just want you to know that, really, these terms should vary based on the headers that have been added to the data,

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So

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a pack it has more headers than a segment.

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A frame has more headers than a packet and so specifically at the transport layer, their specific transport information that's added to the hunter.

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Next at the network Claire, specific information is added.

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Then, at the data link layer, specific information is added.

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This kind of gives you an idea of the broad purpose of the OSI model.

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Just keep in mind. It's a seven layer model. It's designed to promote interoperability among vendors. There are standards at each of the layers,

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and really, what it does is it helps us describe the process of encapsulation