Introduction
Here we are going to explain in detail how data travels through the OSI model. You must keep in mind that the OSI model is a guideline. It tells the computer what it's supposed to do when data needs to be sent or when data is received.
Our Study Case
We are going to analyse an example in order to try and understand how data encapsulation and decapsulation works. This should make it easier for most people.Try to see it this way :
When a car is built in a factory, one person doesn't do all the jobs, rather it's put into a production line and as the car moves through, each person will add different parts to it so when it comes to the end of the production line, it's complete and ready to be sent out to the dealer.
The same story applies for any data which needs to be sent from one computer to another. The OSI model which was created by the IEEE committee is to ensure that everyone follows these guidelines (just like the production line above) and therefore each computer will be able to communicate with every other computer, regardless of whether one computer is a Macintosh and the other is a PC.
One important piece of information to keep in mind is that data flows 2 ways in the OSI model, DOWN (data encapsulation) and UP (data decapsulation).
The picture below is an example of a simple data transfer between 2 computers and shows how the data is encapsulated and decapsulated:
