Tcp/Ip | Research & Encyclopedia Articles

Tcp/Ip

TCP/IP, which stands for Transmission Control Protocol/Internet Protocol, is a suite of protocols built into the Unix operating system and is the standard used to connect computers over the Internet. The term TCP/IP actually refers to a whole family of protocols, of which TCP and IP are just two. TCP and IP were first developed in the 1970s in connection with a United States Department of Defense (DoD) research project to connect numerous separate networks designed by different companies into a network of networks, the ARPAnet, named for the DoD's Advanced Research Projects Agency (ARPA).

Tracing the history of TCP/IP therefore leads back to the inception of the Internet. TCP as a suite of communications protocols providing end-to-end network communication was first proposed and implemented in 1974 throughout the ARPAnet, which formed the core of the modern Internet. The emergence of packet-switching technology at the time ensured that ARPAnet was designed (in 1968) to be a packet switching network with a proposed line speed of 50 Kbps. Packet switching, still the fundamental technology driving the Internet, comprises a data network in which all components (i.e., hosts and switches) operate independently. Data is transmitted in a series of discrete packets (containing both data and header information) across complex networks and can be switched dynamically across nodes. This results in fast, economical networks.

ARPAnet started with four University nodes in 1969, spanned the continental U.S. by 1971, and had connections to Europe by 1973. In 1974, following a trail of other protocols, TCP, offering a new and robust suite of end-to-end protocols, was introduced for use throughout the ARPAnet. However, since an end-to-end protocol was widely seen as unnecessary for the gateways (known as routers today) at intermediary points in the network, a new design came into use in 1978, splitting responsibilities between a pair of protocols: the new Internet Protocol (IP) was intended for intermediate data routing and host-to-gateway or gateway-to-gateway communication; and TCP was intended for reliable end-to-end host communication. Since TCP and IP were originally intended to function as a single protocol, the protocol suite, which actually refers to a large collection of protocols and applications, is referred to simply as TCP/IP. Original versions of TCP and IP in common use today were written in September 1981, although both have undergone several modifications. In addition, the IP version 6, or IPv6, specification was released in December 1995.

TCP/IP's usage profile has undergone a few transformations. In 1983, the DoD mandated the use of the TCP/IP protocol suite for all long-distance communications. TCP/IP became the protocol suite of choice for the evolving Internet, and it developed during the late 1980s as the Internet grew. Meanwhile the OSI (Open Systems Interconnect) protocols also came into prominence, and in 1988 the DoD and most of the U.S. Government chose to adopt OSI protocols, since OSI products were believed to be only a couple of years away. TCP/IP then ran only on limited platforms. The DoD mandated that all computer communications products would use OSI protocols by August 1990 and use of TCP/IP would be phased out. Subsequently the U.S. Government OSI Profile (GOSIP) excluded TCP/IP when defining the set of protocols to be supported in products sold to the federal government.

Despite this mandate, TCP/IP development continued in an open environment at ARPA/NSF (National Science Foundation) sites. OSI products were still a couple of years away, and TCP/IP became the de facto open systems interconnection protocol suite. In 1990 the DoD created an environment to allow OSI applications to operate over TCP/IP. Meanwhile the Internet and OSI communities worked together to combine TCP/IP and OSI; many TCP and IP features started to migrate into OSI protocols. The National Institute for Standards and Technology (NIST) suggested in 1994 that GOSIP incorporate TCP/IP and drop the "OSI-only" requirement. Interestingly it is often noted that OSI represents the ultimate sliding window since OSI protocols have been "two years away" since about 1986.

The IP portion of TCP/IP is the most fundamental protocol on the Internet, responsible for both the transmitting of data packets from one system to another, and for the system of numeric IP addresses, which determines destination points for data on a network. IP operates on gateway machines that move data internally from departments to enterprise networks and then externally to regional networks and finally across the world on the global Internet. The associating of natural language host names with IP addresses established the domain name system (DNS), a distributed database of IP addresses and their host names.

TCP is the protocol that ensures correct delivery of data from client to server. Since data can be lost or delayed across networks, TCP provides support to detect errors or lost data and to initiate retransmission until the data is correctly and completely received. This design allows the construction of large decentralized networks. The TCP protocol provides both a virtual connection between two systems (over the base network of physical connections), as well as connection guarantees like retransmission of dropped packets, sequential receipt of packets (though each packet may take a different route to reach its address), and integrity of data content. Designed initially by the Department of Defense to withstand battlefield damage to communications networks, TCP/IP is built to be robust and to recover automatically from phone line or node failure.

A protocol often substituted for TCP by applications requiring speedy transmission and high performance (as opposed to reliability and integrity) is UDP, or User Datagram Protocol. UDP sends data one chunk at a time in a "datagram" and does not provide a virtual connection or make the guarantees TCP does. Datagrams can be lost, arrive out of sequence, or be dropped if corrupted. Despite these drawbacks, UDP, being lighter and faster, is useful for some bulky applications like audio/video streaming, and Internet phone applications. TCP, though more reliable, is slower because of all the extra information required by its guarantees.