TCP/IP

in full Transmission Control Protocol/Internet Protocol

Standard Internet communications protocols that allow digital computers to communicate over long distances. The Internet is a packet-switched network, in which information is broken down into small packets, sent individually over many different routes at the same time, and then reassembled at the receiving end. TCP is the component that collects and reassembles the packets of data, while IP is responsible for making sure the packets are sent to the right destination. TCP/IP was developed in the 1970s and adopted as the protocol standard for ARPANET (the predecessor to the Internet) in 1983.

(Transmission Control Protocol/Internet Protocol) A communications protocol developed under contract from the U.S. Department of Defense to internetwork dissimilar systems. Invented by Vinton Cerf and Bob Kahn, this de facto Unix standard is the protocol of the Internet and the global standard for local area networks and wide area networks, the major exception being the traditional networks of the telephone companies. However, telephone companies that deploy voice over IP (VoIP) networks are, in fact, using TCP/IP as well (see VoIP).

Reliable and Unreliable
The TCP/IP suite provides two transport methods. TCP ensures that data arrive intact and complete, while UDP just sends out packets. TCP is used for everything that must arrive in perfect form, and UDP is used for streaming media, VoIP and videoconferencing, where there is no time to retransmit erroneous or dropped packets in real time.

IP Makes It Routable
TCP/IP is a routable protocol, and the IP "network" layer in TCP/IP provides this capability. The header prefixed to an IP packet contains not only source and destination addresses of the hosts, but source and destination addresses of the networks they reside in. Data transmitted using TCP/IP can be sent to multiple networks within an organization or around the globe via the Internet, the world's largest TCP/IP network. The terms "TCP/IP network" and "IP network" are synonymous.

The IP Identifies Everything
Every node in a TCP/IP network requires an IP address (an "IP") which is either permanently assigned or dynamically assigned at startup (see IP address). For an explanation of how the various layers in TCP/IP work, see TCP/IP abc's and OSI model. For a conceptual picture, see communications protocol. See protocol stack, TCP/IP port, DNS, DHCP and IP on Everything.

The TCP/IP Stack
The TCP or UDP transport layer 4 sends packets to IP network layer 3, which adds its own header and delivers a "datagram" to a data link layer 2 protocol such as Ethernet, ATM or SONET. See datagram.

(protocol)

TCP/IP - Transmission Control Protocol over Internet Protocol.

The de facto standard Ethernet protocols incorporated into 4.2BSD Unix. TCP/IP was developed by DARPA for internetworking and encompasses both network layer and transport layer protocols. While TCP and IP specify two protocols at specific protocol layers, TCP/IP is often used to refer to the entire DoD protocol suite based upon these, including telnet, FTP, UDP and RDP.

See also ICMP, SMTP, SNMP.