Part 2 - Communication over the Internet: The OSI Reference Model

Communication over networks and the Internet works in much the same way. For example, when you send a message from an email client (a program that sends and receives emails), the data must pass through many different layers. It must be temporarily stored on your computer, and then passed to your network card, which sends it to your local network and along the path to your final destination. Figure 2 shows the OSI Reference Model that specifies the layers of communication over networks. Notice that there are seven layers. When you send a message, it must go down through each of these layers to the physical layer, where it is sent to the destination. The data must then be transferred back up to layer seven for your friend to be able to open and read the email in his client.


Figure 2-1: The OSI Reference Model

Parts of this figure taken from www.cs.vu.nl/~sbhulai/ ecr/et.html.


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