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How many layers are there in networking.
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Do we have a four layer TPP model or perhaps a five layer TPP IP model.
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Or do we have a seven layer oversight model.
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How many layers are there.
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Why do we actually care.
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Now in the previous version of the CCMA we were taught the over side model which consists of seven layers
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starting at the top.
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It's inverted.
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So from layer seven to layer one all people slipping through networking don't POS Well that's not actually
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what it is.
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It's actually application presentation session transport network data link and physical layer.
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Now that caused a lot of confusion a lot of people have debated how relevant the OSA model is in today's
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networks.
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Have a look here on Twitter.
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Rob tweeted I've got three hours to kill in an airport lounge and I'm going to discuss the OSA model.
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There's no such thing.
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What they taught you was a lie and they knew it but they didn't care.
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And that's interesting.
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People in the real world are saying that the OSA model is rubbish.
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Other people are saying well that's not true.
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The OSA model is required.
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Now Ivan is someone that I recommend that you follow on Twitter or go to his website and sign up for
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his free courses.
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Ivan is someone who doesn't mess around.
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As in he speaks what he thinks he will tell you what is true and what is not true.
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I highly recommend that you follow Ivan and perhaps you know take some of these free courses if nothing
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else.
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Follow him on Twitter and read his blog posts.
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Now if you'd really need to networking you may not understand everything that he talks about.
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Don't worry most of us struggle with some of the concepts.
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Ivan is really intelligent has years and years of experience.
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But if you want to learn from someone who has got lots of experience and can help you in your networking
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career follow him on Twitter are basically in his response.
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Ivan is saying that we do need the OSA model and if people have followed the US model life would be
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a lot simpler today.
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Now I don't want to muddy the waters just as you starting with the OSA model and the TTP IP model.
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Again I'll tell you what you need to know for the exam.
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But just note that nothing in life is as simple as it seems sometimes there are gray areas in the OSA
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model and the TCB IP model they taking what's called a protocol stack.
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In other words different protocols that do different things and they try and put it into neat layers.
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Now that's not always clear cut and it's not always possible to take protocols and put them neatly into
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individual layers because some developers have programmed the applications to do things that supposedly
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they shouldn't be doing.
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We are told in the CCN course that specific layers should talk to specific layers but that doesn't always
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happen that way.
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So moral of the story is for the real world.
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Things get more complicated and people get into these rants or discussions if you like about the OSA
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model is rubbish or we shouldn't be learning the OSA model.
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We shouldn't be learning the TTP IP model and then people code stuff from various CCN a box showing
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an original TTP IP model and an updated TTP IP model.
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And just to further complicate it here's a whole range of different models.
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Now the original model comes from RC eleven 22.
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This is a four layer model.
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We have what's called an application layer transport layer Internet layer and link layer.
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The Cisco Academy talks about Internet model being application transport into network and network interface.
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But then on wikipedia here they start quoting different books and what you'll notice we have a five
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layer TTP IP model and then a four plus one layer and then right at the end we have a seven layer over
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assigned model.
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Now the OS model once again is what was taught in previous versions of the CCMA in this version of the
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CCMA.
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They are teaching the so-called five layer TPP model which is a combination of the original RF C 11
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22 TTP IP model and the OSA models.
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So basically it's a hybrid of multiple models.
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Now the reason we have a model is we taking a complex problem and we breaking it up into smaller components
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or smaller pieces.
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This has been done for many many years.
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The Romans had a divide and conquer policy so we divide a problem into smaller parts and then we conquer
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smaller parts rather than trying to do everything in one go.
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Models are used in many places as an example if you're building a house you typically have a blueprint
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or a model of what the House is going to look like.
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So before you even dig the foundations a model is created or a blueprint is created of what the House
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is going to look like.
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It makes a lot more sense to create a blueprint of a house and then have specific people work on specific
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parts of the building and do what they are good at.
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So as an example a plumber will work on the plumbing an electrician will concentrate on the electricity
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a bricklayer will concentrate on laying the bricks.
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But they all work together to correct to the end result which is the house that you want built.
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It's going to be much easier to have a blueprint or a model that everyone works towards to build something
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rather than them just arriving on site and then saying let's bulldoze house but they don't actually
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know what the house looks like.
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You have an electrician working on the plumbing or a plumber working on bricklaying.
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That's not going to scale very well.
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So we have a model of a network and then we have specific layers or specific components or subunits
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if you like that people specialize in and concentrate on that layer.
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So manufacturer of fiber cables concentrates on building this to a specification.
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If you're a application developer you don't worry so much about the physical layer or how data is transmitted
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from let's say the US to Europe across the Atlantic using light under the ocean.
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You concentrate on building your application.
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So we have different layers in the oversight model and different people concentrate on different layers.
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Now the layers that we as networking people concentrate on are the lower four layers which in the OSA
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model are called transport network data link and physical.
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In the new version of the CCMA they are using this hybrid model where they've taken parts of the oversized
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model and added it to the TTP IP model.
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So rather than the original model of just a link layer or network interface layer we actually have what's
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called the data link layer which is called Layer 2 and the physical layer which is layer one we accounting
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upwards through the layers from layer 1 being the physical layer so ignoring all the debates and all
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the wars if you like on Twitter about which model is important and why we care about models.
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This is what you need to know.
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You need to know both the OS model and TTP IP model but concentrate on the TTP IP model.
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The OSA model which consists of the seven layers physical layer data link layer network layer transport
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layer session layer presentation layer and application layer isn't as important as the TTP IP hybrid
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model if you like.
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So a five layer TTP IP model which is more real world which has a physical layer data link layer network
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layer transport layer and a combined application layer.
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But notice we talk about Layer 7 applications because of the history of the OSA model being used.
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So notice we have layer one layer to layer three layer for those are the layers that we concentrate
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on as a networking person.
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And then we have a combined layer 5 2 Layer 7 called the application layer but we still referred to
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it as application layer.
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Now I'm gonna show you this practically using Packet Tracer but I want you to download this yourself
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and try it.
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So don't just follow me do this yourself and see if you can answer some of these questions yourself
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and see if you can understand the various layers in Packet Tracer they still have the seven layers of
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the OSA model but what you'll notice is layer five and layer six are basically ignored for for the most
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part we concentrate on the lower four layers and then layer seven the application layer.
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