# Communication protocol | | A **Communication protocol** is a system of rules that allows two or more entities of a communications system to transmit information via any variation of a physical quantity. The protocol defines the rules, syntax, semantics, and synchronization of communication and possible error recovery methods. Protocols may be implemented by hardware, software, or a combination of both. | |-|-| | | wikipedia:: [Communication protocol](https://en.wikipedia.org/wiki/Communication_protocol) | Ossification [[XMPP]] [[Email]]