Speaker A
Hello again. As you know, I'm Eli the Computer Guy over here for Everyman IT. Today's class is the OSI model, this demystified.
Eli the Computer Guy demystifies the OSI model, explaining its seven layers and how it aids in network troubleshooting and understanding.
Ask about this video. Answers come from its transcript only — with the timestamp, so you can check them.
Generated from the transcript and can be wrong — check the timestamp.
Key Takeaways
- Understanding the OSI model simplifies troubleshooting network issues by isolating problems to specific layers.
- Each layer has distinct functions and hardware or software components associated with it.
- The OSI model is a valuable tool for IT professionals, especially for diagnosing and fixing network problems.
- Programmers may use the OSI model differently, focusing on building network communication rather than troubleshooting.
- The model helps conceptualize complex network interactions in a structured, manageable way.
What the video covers
- The OSI model is a logical framework for how network systems communicate with each other.
- It consists of seven layers, each representing different components of network communication.
- The layers range from the Application Layer (closest to the user) down to the Physical Layer (actual hardware connections).
- The Physical Layer involves wiring and physical connections like Cat 5 cables.
- The Data Link Layer is where switches operate and MAC addresses reside.
- The Network Layer is the domain of routers and IP addressing.
- The Transport Layer manages data transport, including windowing and data block sizes.
- The Session Layer creates and manages communication sessions between computers.
- The Presentation Layer generally involves the operating system and data formatting.
- The Application Layer is what the user interacts with, such as browsers and email clients.
Chapters
- 00:00Introduction to the OSI Model
- 01:00Common Misconceptions About the OSI Model
- 01:58What is the OSI Model?
- 03:03Physical Layer Overview
- 04:19OSI Model Layers and Troubleshooting
- 05:33Programmers and the OSI Model
- 06:44Focus on IT Troubleshooting
- 07:41Detailed Explanation of OSI Layers
- 09:51Application Layer Explained
- 10:53Session and Transport Layers
Full Transcript — Download SRT & Markdown
Speaker A
have heard of The OSI model and almost everybody hates the OSI model for some reason they they hear of the OSI model and they all they think is that they're just going to have to do a lot of
Speaker A
Now, if you've done networking for any length of time or if you plan to do networking, you probably have heard of the OSI model.
Speaker A
easier for you uh to understand all the OSI model is is it's just a logical model for how Network systems are supposed to communicate to each other so basically all the model does is break down the different components of network
Speaker A
Almost everybody hates the OSI model for some reason. They hear of the OSI model and all they think is that they're just going to have to do a lot of memorization and it's going to be a big pain in the butt.
Speaker A
this is the layer where where switching occurs so all those switches that that you plug your computers into all all of what they do resides on on on Layer Two so basically the OSI model is seven logical layers that allows you to think
Speaker A
Honestly, as a technologist who's been doing this for a long time, the OSI model is an incredibly useful tool. If you take the time to learn the OSI model, it makes life easier for you to understand.
Speaker A
and then fix it uh programmers uh they they do it the opposite way instead of fixing things uh they use the OSI model to to to narrow in and figure out exactly what they have to build for um
Speaker A
All the OSI model is, is just a logical model for how network systems are supposed to communicate with each other.
Speaker A
you're a programmer well I don't know take a programming class uh we're not going to deal with it here basically I'm going to to explain to you the OSI model the way that I actually use it and show
Speaker A
Basically, all the model does is break down the different components of network communication and kind of slot them into layers.
Speaker A
model okay so the OSI model this is just oi model OKAY The OSI model is made up of seven layers the layers from top to bottom are for what is closest to the end user so what the user is interacting with all
Speaker A
So you may hear of the physical layer. The physical layer is all the wiring, all the physical stuff that connects computers together.
Speaker A
or Internet Explorer if you're going onto a a website the application layer uh for that whole communication with the website is Firefox Internet exp Explorer Safari Chrome Etc the this is the layer that that the the user is actually
Speaker A
You then have Layer Two, the data link layer. This is the layer where switching occurs. So all those switches that you plug your computers into, all of what they do resides on Layer Two.
Speaker A
you interact with the application layer that sends information down to the presentation layer which is generally the like I say the the layer that the operating system works on underneath the presentation layer you have What's called the session
Speaker A
Basically, the OSI model is seven logical layers that allow you to think about a networking problem and then figure out how to try to fix the problem.
Speaker A
trying to access to get data from so that's what the session layer does the session layer actually creates the session between your computer and the computer you're trying to get information from underneath that is called the transport layer the transport layer uh this layer
Speaker A
If you understand how these layers work, it's much easier to focus in on what the individual problem is in a network system and then fix it.
Speaker A
information will be communicated back this deals with the transport of of the data back and forth you then have the network layer the network layer is the layer that routers operate at so you know your your router uh that you have at home or
Speaker A
Programmers do it the opposite way. Instead of fixing things, they use the OSI model to narrow in and figure out exactly what they have to build for.
Speaker A
layer the data link layer is the layer that switches operate on uh so again you know all the computers on a network get plugged into a switch so that they can talk to each other that happens that that layer is
Speaker A
Like I say, it's not that hard. It's not that complicated. This will be a short and sweet, simple little class.
Speaker A
so basically if if if your computer isn't actually connected to the network if you don't have a patch cable running from your computer uh to the network then it's a layer one problem your your your your network cable isn't connected
Speaker A
This class on the OSI model is focused from the IT technologist standpoint, so for troubleshooting and such.
Speaker A
seven layers you've got the application layer you've got the presentation layer you've got the session layer you've got the transport layer you've got the network layer you've got the data link layer and then you have the physical layer so again how how this works out
Speaker A
If you're a programmer, well, I don't know, take a programming class. We're not going to deal with it here.
Speaker A
problem um there's really no there's no there's no fancy configurations here there's no Doss prompts there's no Linux prompts there's no fancy stuff basically this is this is cable this is Cat 5 cable that's what the physical layer is
Speaker A
Basically, I'm going to explain to you the OSI model the way that I actually use it and show you how it helps you troubleshoot problems and zero in on what the problem you're having is.
Speaker A
this the data link layer this is where switches uh reside so we're going to have a class on switches to explain how all of this works better but basically the data link layer this is where things called Mac address uh addresses reside
Speaker A
So give me a second and I'll get the whiteboard over here and we'll dig into this OSI model.
Speaker A
called arp arp address resolution protocol this this is again how switches work how they actually operate we will have a full class on things like AR just understand everything about how a switch operates uh resides on the data link lay
Speaker A
Okay, so the OSI model, this is just the OSI model.
Speaker A
do with the TCP IP protocol with IP addresses all of that happens at the network layer so uh if if you put in the wrong IP address and then you can't get to wherever you want to get to uh that
Speaker A
The OSI model is made up of seven layers. The layers from top to bottom are for what is closest to the end user, so what the user is interacting with, all the way down to actually shooting the information out on the network.
Speaker A
called windowing so uh windowing is a process where where where computers uh send information back and forth we'll have another class on that one but basically the transport level again it decides uh how large a block of information should be sent how long
Speaker A
The first layer, the top layer, Layer Seven, is called the Application Layer.
Speaker A
or doesn't work for us Above This is the session level again every time a computer communicates with another computer they have to open up a session they have to be you know communicating with each other so uh again if you're if
Speaker A
Now, the Application Layer is the layer that the user is actually interacting with, so things like Firefox or Internet Explorer.
Speaker A
session layer now above the session layer is again the presentation layer basically the presentation layer all this you should really think about is basically the operating system so it's it's a lot of configurable information but it's not generally what the user is is actually
Speaker A
If you're going onto a website, the Application Layer for that whole communication with the website is Firefox, Internet Explorer, Safari, Chrome, etc.
Speaker A
interacting with uh to send information back and forth so again this might be Skype it might be Chrome it might be whatever now like I say in in the real world what what most of us deal with with the it level is uh you know you
Speaker A
This is the layer that the user is actually interacting with the information on.
Speaker A
it's corrupted well that's an application layer problem uh then you have the presentation layer problems uh generally this is device drivers are messed up uh something within the operating system isn't allowing the user uh to go onto the internet uh so maybe
Speaker A
So if you're doing email, this would be the actual Outlook application.
Speaker A
actually opens up the session uh between the two computers uh now if you're dealing with a website if you administer a website you may have settings within your web server uh that are causing problems with a session layer um things
Speaker A
Underneath that is what's called the Presentation Layer. This layer is basically the layer that the operating system is on.
Speaker A
can open up whatever web page is on that server but when the script runs to open open a session let's say to to look at their their their bank account information for some reason that isn't working properly so that that would be
Speaker A
So you interact with the Application Layer that sends information down to the Presentation Layer, which is generally the layer that the operating system works on.
Speaker A
forth yeah you don't use it a lot the network layer again is a huge one though this is where routers reside so when you're dealing with like I say IP addresses default gateways subnet masks DNS all that crap that resides on the
Speaker A
Underneath the Presentation Layer, you have what's called the Session Layer.
Speaker A
bunch of stuff that can happen with switches but again you know anything you you plug into the switch the switch isn't working properly information isn't being sent properly sometimes the network is slow that can be a switching problem again uh address resolution
Speaker A
The Session Layer is the layer that deals with the communication, creating a session between the two computers.
Speaker A
they cabling properly uh that is the physical layer again all this is all this is is seven layers all all it's trying to do is is what I want you to understand like I say as a professional Tech you know I I've done this a lot in
Speaker A
So if you are going to a website, basically your computer at the Session Layer has to create a session with the web server that you're trying to access to get data from.
Speaker A
just a model for for for how to think about the problem so you walk in an entire server room is down or uh or nobody can get on to the internet or you know any of the hundreds of problems
Speaker A
That's what the Session Layer does. The Session Layer actually creates the session between your computer and the computer you're trying to get information from.
Speaker A
a web server that that they need to get to information is not being sent properly and when you walk into that situation it could be any of a thousand problems you know even after you've done this for a long time when you walk into
Speaker A
Underneath that is called the Transport Layer.
Speaker A
reasons could be uh and then and then go about fixing it so if you understand and this it allows you like I said just to give you a beginning point and then give you a place to start troubleshooting
Speaker A
The Transport Layer is the layer that decides how much information should be sent at one time.
Speaker A
connection connecting light uh is lit if that's lit that means you probably don't have a physical layer problem you know you go through it that way like I say uh this is something that it'll take you a little bit to get used to but but it
Speaker A
So when you're communicating with a website, this is the layer that decides how much information you will communicate to the website and how much information will be communicated back.
Speaker A
session layer the connection between the two computers transport layer deals with all the the transport how big packets are and that kind of stuff Network layer this is where your IP addresses resolve you have Network layer problem uh it's
Speaker A
This deals with the transport of the data back and forth.
Speaker A
just a it's a logical model to allow you to think about problems and and try to decide where where the problem may be um like I say is you may you may not know which specific route is the problem uh
Speaker A
You then have the Network Layer. The Network Layer is the layer that routers operate at.
Speaker A
on the back of the computer you may not know where the wiring got cut but you know if there's no connector light the wiring got cut uh somewhere you know with the application layer if everybody's screaming because you know
Speaker A
So your router that you have at home, or if you've been doing networking technology, you know routers operate at the Network Layer.
Speaker A
know the specific problem but you have a better idea of of where the problem is basically using this process uh to to divide everything down again the OSI model um is not a huge issue I know a lot of people pull their hair out uh
Speaker A
Your IP address is at the Network Layer.
Speaker A
of the day I mean it really is useful I like I say as as a 12year technician I use this this is something that allows me to break down uh where the where the problem is uh that I'm looking at again
Speaker A
Underneath this, make sure you're still on the screen, you have the Data Link Layer.
Speaker A
useful very very very very very very useful uh as you know I'm Eli the computer guy over here for every man it as always I hope you understood this this class again important class very very useful uh I look forward to seeing
Speaker A
The Data Link Layer is the layer that switches operate on.
Topics:OSI modelnetworkingnetwork layersnetwork troubleshootingEli the Computer GuyData Link LayerPhysical LayerNetwork LayerTransport LayerSession Layer
