One of the more important networking concepts is the protocol . Protocols usually exist in two forms. First, they exist in a textual form for humans to understand. Second, they exist as programming code for computers to understand. Both forms should ultimately specify the precise interpretation of every bit of every message exchanged across a network.
Protocols exist at every point where logical program flow crosses between hosts.
In other words, we need protocols every time we want to do something on another computer. Every time we want to print something on a network printer we need protocols. Every time we want to download a file we need protocols. Every time we want to save our work on disk, we don't need protocols - unless the disk is on a network file server. Usually multiple protocols will be in use simultaneously.