Domain 4 Overview and The OSI Reference Model

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Time
15 hours 43 minutes
Difficulty
Advanced
CEU/CPE
16
Video Transcription
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>> All right folks, here we are at domain 4.
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We only have eight domains to go through.
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We're getting towards the point
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where we're going to be halfway through.
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Domain 4 is a great chapter because it
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covers network communications and network security.
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I think that's one area that it
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should go without saying that's big on the exam.
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We have to understand the basic concepts
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of networking and then look at
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those elements in terms of security and consider how
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we implement the appropriate risk mitigation
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from more of a technical focus.
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Now word to the wise.
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[NOISE] If you're not a network person,
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you don't have to be to do well on this exam.
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You do not have to be a technical person.
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But if you're not,
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domain 4 is going to require
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a little bit more work on your part.
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You're going to have to do a little bit more research
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on network security,
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and you're going to have to work a little
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harder to understand the concepts.
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Just to prepare you for that idea,
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because in a lot of ways,
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this is almost like a Network Plus class
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that's normally a five-day class,
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boiled down into three hours
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or so of the most significant concepts.
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Let's get started. What are we going to
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talk about in this chapter?
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We're going to start off by focusing
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on the OSI reference model.
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The OSI model stands for Open Systems Interconnect.
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If you haven't heard about the OSI model,
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you probably haven't sat through
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network security or networking classes because
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almost every class includes
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a discussion on the OSI model.
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We're going to talk about what the various layers,
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the seven layers of the OSI model.
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We're going to try to put that in context of
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what does it mean and why do we use it?
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Then we're going to talk about
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the TCP/IP model and
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review that up against the OSI model,
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and we're going to compare and contrast the two.
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The next elements we're going to look at are going to
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be security zones and firewalls,
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we'll look at remote access protocols so
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that we can connect to
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systems from alternative locations,
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we'll talk about tunneling that
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we usually associate VPNs,
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and then we'll talk also
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about wireless networking as well.
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We'll talk about some way and
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strategies in their wide area network strategies.
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That's the direction we're going with Chapter 4.
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Let's start out by talking about
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>> the OSI reference model.
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>> As I mentioned before,
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OSI stands for Open Systems Interconnect
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and it comes to
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us from the International Organization of Standard.
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We're going to talk about the fact that this is
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to promote standards and interoperability.
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We'll talk about this idea of
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encapsulation, which means wrapping.
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Then we'll also look at a term
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called the protocol data unit.
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When we talk about why,
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I always like to start with why,
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because I can't just memorize facts.
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I have to know why they're relevant to me.
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When I started with computing back in the '90s,
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you would go into an organization and they
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might be running Novell on their back-end servers,
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so they used a protocol called IPX/SPX.
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Then you had Macs systems
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using Apple Talk for their protocol,
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Microsoft systems might be using NET LUIS,
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Linux systems, Unix systems might be using TCP/IP.
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Everybody was doing their own thing.
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Everybody was trying to make it by being proprietary.
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Well, the problem with proprietaryism,
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>> if that's a word.
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>> Today it's a word, proprietaryism.
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The problem with being proprietary is that you're
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locking your customers in to
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using your services and only your services,
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which at first sounds good, right?
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Oh they'll just come and spend all their money with me.
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But customers, as a general rule, want choice.
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I want to be able to run.
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If we're all in this room connected to
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a switch and that switch fails,
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I want to be able to run down to
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Best Buy and be able to use
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a Cisco switch or
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a Belkin switch or a Linksys or NETGEAR.
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I don't want to be tied in to the same vendor.
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We like standards-based because
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that gives us more freedom and more choice.
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At this period of time when
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every vendor was doing something proprietary,
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the International Organization of Standard said,
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"Hey, let's focus on standardization."
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They came out with this idea of
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the OSI model that says, okay,
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if you're going to build a standards-based device,
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there are certain functions your device
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has to adhere to in order to meet the standard.
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Network functionality was divided up into seven layers.
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The idea is that,
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to get data from one computer to another,
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it's actually very complex process.
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A lot of things have to happen.
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There's no one device,
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there's no one protocol that's going to do it all.
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The International Organization of Standard
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broke down networking into
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seven categories of function
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called the layers of the OSI model.
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If I was going to build a Layer 2 device,
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there was a standard for
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Layer 2 devices and I had to meet that standard.
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If I met that standard,
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then a switch,
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for instance, is Layer 2.
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If I built a Layer 2 switch
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according to Layer 2 standards,
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then I could count on my component
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being interoperable with other
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>> standards-based equipment,
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>> so customers prefer standards.
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If I want to build a standards-based component,
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I can look to the OSI model to determine
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what elements of performance and
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what elements of function need to be included.
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It's also a good way to learn
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networking because there's so much that has to happen,
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as I mentioned, to get data from
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computer A to computer B.
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We can't look at it all at once.
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We have to break it down and look at each element.
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We'll talk about components at
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each element that satisfy
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that particular layers standards.
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Then the last thing that we learned from
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the OSI model is we learn
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about the process of encapsulation.
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Encapsulation is packaging. For instance,
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if all I have is data,
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that data is not going to know
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where to go, how to get there,
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how to determine if there
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>> was a reliable delivery or not.
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>> We have to add addressing information.
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We have to add formatting information.
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We have to add a means of
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determining if the data was received.
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We have to add
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network addressing and physical addressing and then
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data's got to go across the cable and it's got to know
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how to turn these electronic signals into,
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or these ones and zeros,
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these digital bits into electronic signal.
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Ultimately, what happens is we
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start out with data at the top of
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the OSI model and as it
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conceptually travels down the OSI model,
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additional headers are added.
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We start out with data up at the top,
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as we go down to presentation,
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headers added down the session,
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down to transport and so on and so forth,
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so that by the time the
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data's ready to go across the network,
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it has all of this packaging that's been
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added to make sure the data gets to the right system,
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in the right way,
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in the right format,
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in a means that is
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consistent with what the
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>> receiving computer is expecting.
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>> When we talk about this process of encapsulation,
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we start by looking at a PDU,
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a protocol data unit.
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All that means is data,
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regardless of its packaging,
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is called a PDU.
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Whether data is at the application layer,
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or the session,
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or the data link or network,
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it can be called a PDU.
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Now, more specifically,
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when the PDU is at the transport layer,
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we call it a segment.
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When the PDU is at the network layer,
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we call it a packet.
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When data is at the data link layer,
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we call it a frame,
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and when data's at the physical layer,
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we just refer to it as bits.
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Depending on what packaging is added,
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the PDU has different names at different layers.
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Transport, it's called the segment.
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Network, it's called the packet.
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Data link, it's a frame
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and bits are at the physical layer.
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I remember some people fear birthdays.
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Segment, packet, frame, bits, SPFB.
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That'll help you remember that based on
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the heading and the information
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>> that's in those headers,
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>> how we can better describe the protocol data unit.
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This is something I've included just
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because I think it might make a good screenshot,
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because I think that once we
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understand and once we
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>> go through and get the OSI model,
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>> then we get to the point of,
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okay, what do I need to know for the test?
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What I've included here,
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I think this is about
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as in-depth as you need to go for the test.
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We want to talk about it in
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>> more depth for understanding.
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>> But as far as what to memorize,
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I think this is a good overview.
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I might take a screenshot of it and make
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maybe some flashcards on the front.
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I might put hub on the back physical layer.
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I might put flow control on
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the front and on the back put transport layer.
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You do need to know the layers by number and name.
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Seven is at the top,
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all the way down to one at the bottom.
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But also application is Layer 7,
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presentation, session,
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transport, network, data link, and physical.
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Find some mnemonic trick
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to help you remember these layers in order.
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I do not recommend that you go out to
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the Internet and Google mnemonic tricks
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to remember the OSI model.
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There are some things you cannot
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unsee and people on
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the Internet have questionable judgment.
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Now what I've probably just done is
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guaranteed 400,000 people right
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now are googling mnemonic tricks
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to remember the OSI model.
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I am not responsible for that.
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I'm just saying be prepared for what
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you get because not very appropriate or some of these.
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But find a way. One way from the top down,
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all people seem to need data processing.
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From the bottom up,
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please do not throw sausage pizza away.
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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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I firmly believe that and will stand by it.
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But whatever your trick is,
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find a way to memorize the OSI model.
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Make sure you know the layers,
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and make sure that you know
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the names of each layer as well.
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Just wrapping up.
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I want you to know the purpose of
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the OSI model from this section and
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know it's all about promoting
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>> standards between vendors.
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>> Making sure we have an environment where
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devices are compatible and interoperable.
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Then I also want you to know
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that each layer of the OSI model provides
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packaging that helps the data get from
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point A to point B in the right format,
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with the right security,
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with the right acknowledgments and so on.
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Depending on, well, we'll say
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data regardless of its headers is called the PDU,
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and depending on where
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that protocol data unit lies on the OSI model.
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At the transport layer,
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it's referred to as a segment.
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Network layer, it's a packet.
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Data link layer, it's a frame,
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and down at the physical layer, it is bits.
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