A protocol would set the format and the order in which data would be transmitted on a network.

For example, a protocol may state ...

• what data should be placed in the header of a data packet
• how to format the data in the packet
• handshaking procedures
• what to do if errors are detected

Computers would not be able to communicate if there was no protocol as they would not be able to interpret the other's data.

There are a number of standards set down for protocols. The most common is TCP/IP.

TCP/IP
(Transmission Control Protocol / Internet Protocol) - the basic protocol used for transmitting any data over a network, and particularly, the Internet.

HTTP
(HyperText Transfer Protocol) -  used for transmitting web pages over the Internet.

FTP
(File Transfer Protocol) - a protocol for transmitting files over the Internet

POP3
(Post Office Protocol 3) -  a protocol for retrieving emails

SMTP
(Simple Mail Transfer Protocol) - a protocol for sending emails.