What is the Open Systems Interconnection Model?

Abdullah Baghuth
3 min readNov 15, 2020


The OSI Model

If you read what I wrote before you will see that I spooked a lot about layer three or layer two, but what is these layer, these all correspond with what is called OSI model, Now if you ever in network interview or you have talked with somebody has experience in networking will hear a lot of these layers especially from people who have been in the filed for some time may just say layer two instead of switching or layer three inside of routing, so will discuss the OSI model very quickly, give you how to remember all these layers, and some of the concepts within it.

7- Application -HTTP, SMTP

6- Presentation — WMV, JPEG, MOV

5- Session — Session management

4- Transport — TCP/UDP

3- Network — IP addresses, routing

2- Datalink — Switching and MAC addresses

1- Physical — Data cables, cat6

A mnemonic can be used to remember the seven layers: Please Do Not Throw Sausage Pizza Away.

again why are these important, if I say my home route is layer two, three that means it does routing and switching.

coming to the troubleshooting :
you may ask to troubleshoot, so actually, when we receive data we receive it from down through the physical layer all aways up to the application layer, and when we transmit data will go from the application layer down to the physical layer.
When we troubleshooting this always better to start from the physical layer and go up to the application layer, take this scenario you work at the help desk and someone called you saying my internet is not working, so help me.
Do you will ask him the application layer question probably not. you may say hi can you look at the back of the computer, Do you see the cable plugged in, oh the cable is plugged in ok will Do you see where the cable plugged in is there a blink light green by chance, if it ok will check the IP address and so on.
This important also as pentester because you will sit in a table with networks engineers these people how are very very smart about this stuff and will through all these lingoes to you, so if you know that it really benefits to you or else you going to sit there and you don't know what they are talking about.
again remember Please Do Not Throw Sausage Pizza Away this is the easiest way to remember the seven later of the OSI model, I hope this helps you all. Stay Safe. By