This section describes the OSI model and protocols used in internetworking. As an introduction, imagine that you are in Toronto and you want to send an e-mail to your friend in San Francisco. Successfully sending and receiving e-mail involves doing many things, including the following:
■ You must type the message in your e-mail application.
■ You must address the message in your e-mail application.
■ You must click the Send button in your e-mail application to start sending the message.
■ You must use the correct type of connections and wires to connect your PC to your local network.
■ Your PC must be able to connect to the Internet, and you must provide any necessary login information.
■ Network devices must find the best path through the Internet so that the e-mail is received by the right person.
The following section introduces the OSI model, a model that describes all these communication functions and their relationships with each other.
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