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What Is a Protocol?

What Is a Communication Protocol?

Preview: Learn more about communication protocols and how they enable different devices to exchange information reliably.

A protocol is a set of agreed rules that governs how information is exchanged between communicating devices. Just as people must share a common language and follow conversational conventions to communicate effectively, computers, communication equipment, and networks require protocols to ensure that information is transmitted, interpreted, and processed correctly. Every modern communication system, from the Internet and mobile telephone networks to satellite communications and industrial control systems, relies on protocols.

A communication protocol specifies many aspects of data exchange, including how a connection is established, how information is formatted, how errors are detected and corrected, how devices identify one another, and how the communication session is terminated. By following the same protocol, equipment manufactured by different vendors can communicate reliably despite differences in hardware and software.

Protocols generally define several key functions. They specify the syntax of the transmitted information (its format and structure), the semantics (the meaning of each field), and the timing (when messages are transmitted and how quickly responses are expected). Many protocols also define procedures for acknowledging successful reception, retransmitting lost data, controlling the flow of information, and maintaining security.

A useful analogy is the rules governing a telephone conversation. One person speaks while the other listens, greetings are exchanged at the beginning, questions are answered in an expected manner, and the conversation ends with a recognised closing. Without these conventions, communication would quickly become confusing. A communication protocol provides similar rules for electronic devices.

Modern communication systems employ many different protocols operating together in layers. For example, when accessing a web page, the physical network may use Ethernet or Wi-Fi, data transport may use the Internet Protocol (IP) and the Transmission Control Protocol (TCP), while the web page itself is transferred using the Hypertext Transfer Protocol (HTTP) or its secure version, HTTPS. Each protocol performs a specific function while working with the others to provide reliable end-to-end communication.

Protocols may be either connection-oriented or connectionless. Connection-oriented protocols, such as TCP, establish a logical connection before exchanging data and provide mechanisms for reliable delivery. Connectionless protocols, such as the User Datagram Protocol (UDP), transmit data without first establishing a connection, offering lower delay but without guaranteeing delivery.

Standardisation is one of the principal advantages of communication protocols. International standards organisations, including the International Telecommunication Union (ITU), the Institute of Electrical and Electronics Engineers (IEEE), and the Internet Engineering Task Force (IETF), publish protocol specifications that allow equipment from different manufacturers to interoperate. This standardisation has been fundamental to the growth of the Internet and global communications.

It is important to distinguish a protocol from a communication standard. A standard is a broader specification that may include electrical characteristics, radio frequencies, modulation methods, connectors, and testing requirements in addition to one or more protocols. A protocol, by contrast, defines the rules governing the exchange of information between communicating devices.

Today, thousands of communication protocols are used throughout digital communications. Whether sending an email, making a Voice over IP (VoIP) call, streaming a video, browsing the web, or communicating with a satellite, numerous protocols work together behind the scenes to ensure that information is exchanged accurately, efficiently, and securely. They form the common language that enables the world's communication networks to function as a single interconnected system.