OSI and DoD Models

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Hey, guys. Welcome to another episode of the S S C P Exam prep.

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I'm your host, Peter. Simple of this is going to be the sixth domain Lesson one, and it's all about networking.

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So in this lesson, our first thing that will take a look at are the O S I and D o d models. These models are the ones that are best described, um, for how to describe a network. These are the ones that will be used to understand how to transmit

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and send data from one host to the other.

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Let's get started.

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This is the OS I model, the open system interconnect model.

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This model is that describes the process off sending information over network from one host to the other.

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Now this is sometimes considered a really complex, but it's the most widely accepted way to describe networking.

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So how it works is

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one user

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sends data

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from their computer and it travels

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down every single layer of the OS I model

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across the physical link to that's like the Ethernet cord or anything like that,

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and then back up every single layer off the OS I model till reaches thesis unde person's computer.

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Now there are seven layers of the OS eyeball. They are the application layer,

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the presentation wire, recession layer,

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the transport layer network, layer, the data link layer and the physical layer.

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Let's look at all of these in a little bit more detail.

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Fire one is the physical layer.

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Networked apologies, which we'll get a little bit later. This lesson are defined here.

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Most visible devices are also at this level.

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This level is very simple, very straightforward. It is simply just

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bits on a wire. This is where the signal and binary transmission happens. She goes across the wire in the physical link,

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now the leg above it.

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The layer above it is the data link layer.

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This receives the packets. It gives fromthe wire and formats, then for the network.

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The data link layer has two main functions. They have the Logical Link Control,

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which manages connections between two piers.

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And it has the media access control, which transmits and receives frames from peers,

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hardware addresses or defined at this layer. That's where you hear the phrase the Mac address. That's just the media access control. These two functions maintained that the bits are put on the wire when transmitting,

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and that they are pulled off the wire and formed into packets when they're being received.

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Liar three is the network layer.

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This liar moves information between two hosts. Uses logical address ING and the Internet protocols.

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There are two main functions of the network. Leg.

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Worst is addressing. This used the destination I P addresses

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to send packets.

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Ah, the second is fragmentation, so this sub divides packets if its size is greater than the maximum size allowed

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on a network.

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Routers work at this level, and they send packets from place to place based on the I P address.

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Now, writers work by tables.

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There are static routing tables and dynamic routing tables. Thes ratting tables are used to tell the packet where they should go to get to the next place on their way to getting to the destination.

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Now, with static routing tables, they're updated manually. This has to be done by hand by a person

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through ads in the information on how to send packets to where they go. There's also dynamic ratting tables. Everyone sit awhile. Routers were share information and say an address that where they can send packets to on a network. They can talk about

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what they see their network pictures like.

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And that's how the writing tables get updated

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network routing protocols. There are two main ones. There is the I. C N P Internet Control Message protocol and the Eye GMP Internet group Management Protocol.

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Now that I see MP does things like managed network errors,

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congestion and trouble shoots any problems on the network. So if packets are being congested, it will find a way around them. If packets are getting lost or taking too long or if they're packing their timing out, then the ICMP will send messages. The letter. You know what has happened?

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I GMP really just manages multicasting groups.

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There are several layer three protocols that work here. You have the IBD four and I P V six.

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You have the D. V M or P,

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I, P, sec,

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IBX,

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GDP and SPB.

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Layer four is the transport layer. This creates an end end connection between two hosts.

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Two major protocols that work of this player are TCP,

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which is the transmission control protocol on the UDP,

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which is the user data graham control protocol.

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So these air to protocol True protocols that are used to send data from the network up to the host.

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So there are several layers.

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Uh, Blair four protocols at work here There is the f c p r d p

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s c T p as p X

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on the SST

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by your five is the session later.

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The goal of this layer is to provide a consistent connection between two hosts. This layer

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deals with setting up maintaining a connection and then at the end, tearing down. There are three different types of sessions which can be created at this layer. There is the full duplex or both. Host can pass information at the same time, back and forth to each other.

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There is the half duplex where both hosts can pass information, but only one at a time.

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And then there is the simplex were on Lee Won Ho's consent information to appear in one direction only.

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Other protocols that work at theseventies layer include h 0.245 I s s

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P a p

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p p t p

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rpc

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arti c p and S N a P P.

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Liar six is the presentation Liar This layer provides service is to ensure that all the applications use a common format to represent data. So if the data coming from a host is not in the proper format, that application can read

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that the presentation layer

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will convert that format into a readable format.

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So, for example, if an application can only read askyou values

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and receives Unicode data, then the presentation liar will convert it to ask

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application Liar. This is the applications portal to network based service is this is where it all starts. So this is where the data, when it gets sent to start from here and goes down into the wire. And also when data is being received, it comes all the way back up

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and ends there in the application layer

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where it is then shown to the user.

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There are many protocols that work in this layer, and these are the most popular once you have D H c p,

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you have d N s. You have http.

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I'm at

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El Bab,

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SMTP

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and FTP.

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We'll be going over many of these protocols later in the lesson.

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So now that we've taken a look at the O S I model, we will look at the T c P i p model. This is also known as the D O D Department of Defense model or the TCP I P model. It really doesn't matter. This model on Lee has

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four layers in 77 so it has the network in her face the intern that layer, the transport layer and the application layer. Now some of these layers are

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combined together, so, such as the session layer, the presentational layer and the application layer in the OS I model

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are all combined just into the application layer in the TCP I p model.

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In today's lecture, we discussed the O S I and the T C T I P model

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TCP and UDP protocols are associated with which OS I model

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a special player

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be network layer

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sea transport layer or D presentation wire.

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If you said c transport layer that you are correct, remember TCP and UDP our protocols which set up the information to pass through from the network to the application.