OSI - Open Systems Interconnection Model

OSI model is just that how network systems communicate to each other, so basically what this model does is it breaks down different components of network communications and kind of slots them into layers.

So you may hear of the physical layer, physical layer is all the wiring, the physical stuffs that connect computers together.

You to have the layer two the data link layer, its where all the switching occurs, the switches you plug your computers into relies on layer two.

So basically OSI model is seven logical layers that allow you to think about the networking problems and figure out how to try & fix the problem.

If you understand how this layers works it is much easier to focus on what the individual problem is in a network system.

It’s not that hard or complicated.

OSI Model

So the OSI Model is made up of seven layers.

Layer 7 Application layer:

This is the layer where user is actually interacting. Like Firefox, Edge or Chrome .This is the layer where user is actually interacting with the information. So if you are using facebook   than this layer is the application.

Layer 6 Presentation Layer

This layer is the layer where the OS is up and works on. You interact with the application layer that sends information down to the presentation layer.

Layer 5 Session Layer

This layer deals with the communication, creates the session between the two computers. So you are going to a website, your computer at the session layer has to create a session with the web server that you are trying to access data from so that what the session layer does.

Layer 4 Transport Layer

This layer is what decides like how much information should sent at one time. So when you are communicating with a website, this is the layer that decides how much information you will communicate with the website and how much information we communicated back. This deals with the transport of data back & forth.

Layer 3 Network Layer

Network layer is the layer where routers operate at. So your IP address is at the network level.

Layer 2 Data Link Layer

Data link layer is the layer where switches operate on. So all the computers in the network get plugged into the switch so they can talk to each other. So that layer is called data link layer.

Layer 1 Physical Layer

Physical layer is literally all the physical stuffs that connects the computers together, includes cable etc. So say your cable is not connected for cut it’s the layer 1 or physical layer problem.95% problems are the layer 1 problems.

So it’s quite simple till here right. You have seven layers and that’s it.

Layer 1

You deal with all wiring and cabling. Say someone unplug the cable that’s a layer 1 problem.

Layer 2

Deals with MAC address. Every networking device in the earth has a MAC address assigned to it. That is all part of data link layer. You have ARP; this is how switches work and how it operates. When the network is slow that may be a switching problem.

Layer 3

This is the layer where IP addresses reside. Anything you do with the TCP/IP with IP addresses, all of that happens at the network layer. So if you put in the wrong IP address and then you can’t get to wherever you want to get to, so that is the network layer problem. If your router dies that’s the network layer problem, so anything that involves your IP address will be the network layer problem.

Layer 4

This has to do with something called windowing. Windowing is the process where a computer sends information back & fourth. So basically the transport layer decides how large a block of information should be sent, how long should the computer wait before it receive an acknowledgement that information was sent or received. Problems with IPs, Subnet Mask, DNS etc.

Layer 5

Every time a computer connects with another computer they have opened up a session, they have to be communicating with each other. Say you are into Flipkart to track your order, so when you go to Flipkart you create a session between your computer to their computer. All of that happens in the session layer. Say to have php config problem it a layer 5 problem.

Layer 6

It’s basically the OS, its alot of configurable information. If device drivers are messed up. Its the layer 6 problems.

Layer 7

There is where the user is where they are using Facebook or Flipkart or Twitter or Instagram or any other browser. It’s the actual application users are interacting to send & receive information.

If Firefox is corrupted it’s a layer 7 problem.