OSI Model
- You are sitting behind your computer and want to download some pictures from facebook web server. You start up your web browser and type in the URL www.facebook.com and your computer will send a message to facebook web server requesting the web page. You are now using the HTTP protocol which lives on the application layer.
- The presentation layer will structure the information of the application in a certain format.
- The session layer will make sure to separate all the different sessions. You will not be the only one trying to access facebook webpage so the web server needs to maintain all the sessions.
- Depending on the application, you want a reliable (TCP) or unreliable (UDP) protocol to transfer data towards the web server. In this case, it’ll choose TCP since you want to make sure the webpage makes it to your computer. We’ll discuss TCP and UDP later.
- Your computer has a unique IP address 192.168.1.1 and it will build an IP packet. This IP packet will contain all the data of the application, presentation and session layer. It also specifies which transport protocol it’s using (TCP in this case) and the source IP address 192.168.1.1 and the destination (facebook web server’s IP address).
- The IP packet will be put into an Ethernet Frame. The Ethernet frame has a source MAC address (my computer) and the destination MAC address (my computer's default gateway)
- Finally, everything is converted into bits and sent down the cable using electric signals.