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A protocol (also called communications protocol) is

a standard agreed upon by groups of users to insure interoperability on a network. It is a detailed process the sender and receiver agree upon for exchanging data.
[a] set of rules (i.e., formats and procedures) to implement and control some type of association (e.g., communication) between systems.[1]
a set of digital rules for data exchange within or between computer systems. Protocols are valuable assets for the Internet infrastructure because they allow meaningful communication between different computer systems.[2]

A protocol is


"Protocols allow data to be taken apart for faster transmission, transmitted, and then reassembled at the destination in the correct order. The protocol used determines the way errors are checked, the type of compression, the way the sender indicates the end of the transmission, and the way the receiver indicates that the message has been received. Protocols can describe low-level details of machine-to-machine interfaces (e.g., the order in which bits and bytes are sent across a wire) or high-level exchanges between allocation programs (e.g., the way in which two programs transfer a file across the Internet)."[5]

The Internet largely uses formats built upon the Transmission Control Protocol/Internet Protocol (TCP/IP). "[T]he Hypertext Transfer Protocol ('HTTP') is used in web pages to transfer data over the internet from computer to computer, the Internet Protocol ('IP') is a building block in allowing data to use interconnected networks, and the Transmission Control Protocol ('TCP') is used to deliver information across the internet. These protocols are the methods by which data transfer is possible over nationwide and global networks."[6]

Other protocols include the Open Systems Interconnection (OSI) set.

The protocol of one system does not necessarily work with another system, and there is an effort to standardize or translate the various protocols so that computers can all talk easily with one another. To make this possible, some protocols may have to be abandoned, while others may be modified or translated when necessary.

Two sets of protocols — the Domain Name System (DNS) and the Border Gateway Protocol (BGP) — are essential for ensuring the uniqueness of each e-mail and website address and for facilitating the routing of data packets between autonomous systems, respectively.


  1. NIST Special Publication 800-82, at B-6.
  2. Threat Landscape and Good Practice Guide for Internet Infrastructure, at 6.
  3. Department of the Army, Supervisory Control and Data Acquisition (SCADA) Systems for Command, Control, Communications, Computer, Intelligence, Surveillance, and Reconnaissance (C4ISR) Facilities, at B-4 (Jan. 21, 2006) (full-text).
  4. US-CERT,"Security of the Internet" (full-text).
  5. Privacy Impact Assessment EINSTEIN Program: Collecting, Analyzing, and Sharing Computer Security Information Across the Federal Civilian Government, at 7.
  6. Centripetal Networks, Inc. v. Cisco Sys., Inc., 2020 WL 5887916, at *5 (E.D. Va. Oct. 5, 2020).

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