OSI Model Layers 5, 6, 7 and OSI Summary

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after the network and the transport layer coming up the SC model. We're now at Layer five, which is the session layer.

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The session layer is all about the setup, maintenance and tear down of the connection.

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Quite honestly, it's about the setup, maintenance and tear down of a session that seems a little redundant.

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So when I say session is about when your Web browser or client system uses a Web browser to connect to a Web server,

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that's an application to application session.

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You communicate throughout that session, you close out the session, you connect again 10 minutes later and you have a new session.

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So that session layer is the setup, maintenance and tear down of the session between one application and another. It is a client peace and server piece.

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There are a couple of protocols that work there.

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RPC is referred to as remote procedure Call

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when you're performing an operation that's actually happening on another system that's a remote procedure. Call

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sip stands for a session initiation protocol.

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This is used with VoIP, and as a matter of fact, it's this protocol that makes the VoIP phones ring.

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If it makes sense, you dial a number, and that session has to be set up.

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Receiving end has to have that ringing to say, Okay, we're connecting.

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So that's it.

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SQL, which is database language, but it's also is a protocol. It's Layer five base from the database client to the database server.

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And as we continue to head them up when we go to Layer six, which is the presentation layer, three big things happen at the presentation layer

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formatting, compression and encryption.

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When we talk about formatting, we're talking about presenting the data and a universal format.

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That's why you can sit at Mac and I can be in a Windows PC, and you send me a message that I can read perfectly.

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That's because at some point in time, that message has to be translated to a universal format that regardless of where the message is going, it will present correctly when it arrives.

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So formatting happens here at Layer six.

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What compression does is remove redundancy from files

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that allows the file to be smaller as it's being transported across the network so it doesn't take as long. It doesn't take as much space in order to transmit

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and then of course we have encryption.

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I'll mention encryption happens in many places on the OSI model.

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At Layer one, there's hardware based encryption.

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At Layer three, we have I P SEC, which secures I P. Traffic, in which we can use encryption

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at later four through seven. We have SSL and TLS, which we haven't talked about yet, but that secures Web traffic

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here at Layer six. The encryption that happens at this level is within the filing system.

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So if you're using F s and you're going to send a file that's encrypted, that happens at this layer.

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Or if you're going to store the file encrypted format summer within the filing system. That also happens here

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for multimedia formatting, whether you have a Jeff J. P. G or an MP four or really any type of multimedia that formatting happens at this layer.

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Interestingly enough, this is the only layer the entire OSI model that has no protocols.

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So that's probably worth a look from a test taking perspective,

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man. If you want to get to the layer where you get the most intelligence, it's here,

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Remember, down at Layer one, we said that those were the devices that don't really know much. They don't know what data is traversing. A cable doesn't know what data is going across it, and a cable doesn't care.

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But if you really want intelligence with your devices and go all the way up to the top, which is the application layer Layer seven.

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Mhm.

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These are the protocols that drive the applications users are using.

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So these protocols have to be really smart because they have direct access to your data

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when we're thinking about things that we can do it later. Seven. This is where you'll see certificate services.

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To tell you the truth, a lot of these things we haven't talked about, so what I'm going to encourage you to do is later on. Come back and review this session on the OSI model after we've talked about what a Web application firewall is, what certificate services are

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for now, we're just going to suffice to say that certificate services happen at this layer.

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Certificates are used in order to provide authentication for individuals or for systems, so that's going to be important.

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Proxy servers, which are high and deep packet inspection devices, give us a really good understanding and inspection of the content of traffic and other information.

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A Web application firewall is specific to Web traffic

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but provides a good degree of protection, specifically focusing in on http and https.

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So when it comes to any attacks that are specifically geared towards Web servers, a waf is a really good defensive mechanism.

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Your email applications are going to use digital signatures.

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Digital signing happens up at layer seven. So there's a lot of really good, very important stuff that happens here and just a ton of protocols

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S and m p Simple network management protocol ftp t f T p By the way, let me just mention you. See FTP and T f T P mentioned here.

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Most people have heard of files transfer protocol,

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but there's also a trivial fire away transfer protocol

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the only difference between the two. If you remember earlier we talked about TCP and UDP and that upper layers services piggyback

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ftp piggybacks on TCP

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TFT be piggybacks on UDP.

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So which one do you think is going to provide better performance?

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T f d P. Because UDP is fast.

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FTP is going to provide more reliable delivery.

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Okay,

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what are a key takeaways from the OSI model?

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Well,

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Oh, yes, I models Conceptual model that was brought to us from the International Organization for Standardization.

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It essentially breaks down networking into seven categories called layers, and you see the layers in front of us here.

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This is a really good chart, and I would certainly recommend screen shotting it and printing it out because this hits the gist of what is going on with the S. I model

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gives you a look at network processes to the application layer seven data representation into host communication and to end path. Determination

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down layer by layer gives you a quick view of what happens at each layer.

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It also gives you some of the more important protocols, but you can go back and add to this.

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You know that cable is at layer one. Switches and Mac addresses are at Layer two.

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At Layer three. We have routers and layer three switches,

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so if there's anything missing, you can go back and fill us in.