A protocol is a mutually agreed-upon format for doing something. With regard to computers, it most commonly refers a set of rules (i.e., a standard) that enables computers to connect and transmit data to one another; this is also called a communications protocol.
A protocol can be implemented by hardware, software, or a combination of the two. At the very least, it must define the rate of transmission (e.g., in bits per second), whether transmission is to be synchronous or asynchronous, and whether data is to be transmitted in half-duplex or full-duplex mode.
Protocols define issues such as data representation (i.e., how data is stored), error control (i.e., error detection and recovery), data compression methods, signaling, authentication, how the sending device will indicate that it has finished, and how the receiving device will indicate it has received the message.
Low-level protocols define the electrical and physical characteristics. High-level protocols deal with the formatting of data. TCP (transmission control protocol) and IP (Internet protocol) are examples of high-level network protocols. The main protocol for transmitting web pages is HTML (hypertext markup language), and the main protocol for transmitting e-mail is SMTP (simple mail transfer protocol).
The Internet protocol suite is the set of protocols that implement the protocol stack on which the Internet runs. A protocol stack is a layered set of protocols which work together to provide a set of network functions. In a protocol stack, each layer solves a set of problems involving the transmission of data and provides a well-defined service to the higher layers.
The Internet protocol suite is sometimes called the TCP/IP protocol suite, after the two most important protocols in it: the transmission control protocol (TCP) and the Internet protocol (IP). These were also the first two protocols in the suite to be developed.
There are other types of computer-related protocols. For example, security protocols, or cryptographic protocols, perform security-related functions and apply cryptographic methods.
The word protocol comes from the Greek word protocollon, meaning first glue. It referred to a leaf glued to a manuscript which described its contents.
Created October 14, 2005.