What is a protocol?

Protocols are:

• how devices communicate on the Internet
• sets of rules for sending, receiving, and responding to messages

Definition of a network protocol:

A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event.

Protocols are essential for effective communication, whether among humans or in computer networking:

• people follow expected patterns (e.g., exchanging greetings) before proceeding with a conversation
• if the response to a greeting is negative or absent: the conversation usually doesn't continue

Successful communication requires all parties to follow the same protocol.