FREE online courses on Internet Network of Networks - What is a Protocol

 

A  protocol is a formal description of the message formats and the rules, two or more machines must follow to exchange those messages.

Protocols usually exist in two forms. First, they exist in a textual form for humans to understand. Second, they exist as programming codes for computers to understand. Both forms  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 the hosts. In other words, protocols are required 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. If 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. Therefore, most protocols support multi-tasking. Also, one operation can involve several protocols. For example, consider the NFS (Network File System) protocol. A write to a file is done with an NFS operation, that uses another protocol (RPC) to perform a function call on a remote host, that uses another protocol (UDP) to deliver a datagram to a port on a remote host, that uses another protocol to deliver a datagram on an Ethernet, and so on. Along the way we may need to lookup the host names (using the DNS protocol), convert data to a network standard form (using the XDR protocol), find a routing path to the host (using one or many of the numerous protocols) etc.