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The information exchange among interconnected systems is generally managed by means of a protocol, which is set of formal rules describing how to transmit data, especially across a network. Low level protocols define the electrical and physical standards to be observed, bit- and byte-ordering and the transmission and error detection and correction of the bit stream. High level protocols deal with the data formatting, including the syntax of messages, the terminal to computer dialogue, character sets, sequencing of messages etc.
The International Standard Organization has defined a notorious seven-layer model of information exchange protocols among so-called open systems (ISO-OSI model). This model provides a formal specification of a reference network architecture in the form of a suite of protocols, so that systems implementing them are ``open'', in the sense that they can communicate despite the differences in their architectures, in the communication technologies, etc. The reference (or model) architecture is split between seven layers, and each layer uses the layer immediately below it and provides a service to the layer above.
Example protocols that can be cast in this model are Ethernet (physical and data-link layers), IP (Internet Protocol, network layer in the ISO-OSI model), TCP (Transmission Control Protocol, transport layer).