Transmission Control Protocol (TCP) and Internet Protocol (IP) are the two most important lower-level protocols enabling Internet connectivity. IP is responsible for moving packets of data from one connection point to the next, while TCP verifies the integrity of data traveling between two endpoints. TCP and IP work together so much that the two protocols are commonly referred to as TCP/IP.
TCP/IP is the most widely implemented, non-vendor-specific Internet protocol suite in use today, according to networking giant Cisco Systems. The protocols were developed by the U.S. Department of Defense to connect a number of different computer networks designed by different vendors into one "network of networks," a concept which grew into what is known as the Internet.
The Defense Department realized a need to develop a "least common denominator" network protocol after the 1983 invasion of Grenada exposed the fact that Army, Navy and Air Force computers could not communicate with one another. A new network communications standard needed to be put in place, and TCP/IP filled that niche. Because of its military origin, TCP/IP was also purposefully designed to automatically compensate for the failure of a network node or phone line, such as might be caused by a communications center sustaining damage in battle.