Internet protocol suite

The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and the Internet Protocol (IP). Early versions of this networking model were known as the Department of Defense (DoD) Internet Architecture Model because the research and development were funded by the Defense Advanced Research Projects Agency (DARPA) of the United States Department of Defense. The Internet protocol suite provides end-to-end data communication specifying how data should be packetized, addressed, transmitted, routed, and received. This functionality is organized into four abstraction layers, which classify all related protocols according to each protocol's scope of networking. An implementation of the layers for a particular application forms a protocol stack. From lowest to highest, the layers are the link layer, containing communication methods for data that remains within a single network segment (link); the internet layer, providing internetworking between independent networks; the transport layer, handling host-to-host communication; and the application layer, providing process-to-process data exchange for applications. The technical standards underlying the Internet protocol suite and its constituent protocols are maintained by the Internet Engineering Task Force (IETF). The Internet protocol suite predates the OSI model, a more comprehensive reference framework for general networking systems.

History

Early research

The Internet protocol suite has its roots in research and development into computer networks sponsored by the Defense Advanced Research Projects Agency (DARPA) in the late 1960s. In August 1968, BBN was selected by ARPA to build the Interface Message Processors (IMPs) for the ARPANET, the precursor to the modern Internet. The IMPs were the very first generation of gateways, known today as routers. Under the leadership of Frank Heart and Bob Kahn, four IMPs were produced for nearly US$1 million from September to December 1969. The first IMP was shipped to the University of California, Los Angeles in September 1969 and the second to the Stanford Research Institute a month later. The first message between the two IMPs was "LO" — phonetically, "Hello" — but the SRI host crashed before the UCLA researcher could complete typing the "LOGIN" command. After DARPA initiated the pioneering ARPANET in 1969, Steve Crocker established a "Network Working Group" which developed a host-host protocol, the Network Control Program (NCP). In the early 1970s, DARPA started work on several other data transmission technologies, including mobile packet radio, packet satellite service, local area networks, and other data networks in the public and private domains. In 1972, Bob Kahn joined the DARPA Information Processing Technology Office, where he worked on both satellite packet networks and ground-based radio packet networks, and recognized the value of being able to communicate across both. In the spring of 1973, Vinton Cerf, at Stanford University, began collaborating with Kahn on the goal of designing the next protocol generation for the ARPANET to enable internetworking. They drew on the experience the international research community, through the International Network Working Group (INWG), chaired by Cerf, which included researchers from the ARPANET community, Xerox PARC, the United Kingdom and France. During the summer of 1973, Kahn and Cerf worked out a fundamental reformulation, in which the differences between local network protocols were hidden by using a common internetwork protocol, and, instead of the network being responsible for reliability, as in the existing ARPANET protocols, this function was delegated to the hosts. Cerf and Kahn credit several members of INWG with important influences on this design, which was published in May 1974. The first specification of this Transmission Control Program was written in December 1974 by Cerf, Yogen Dalal and Carl Sunshine at Stanford University. DARPA contracted with BBN Technologies, Stanford University, and University College London to begin developing operational versions of the protocol on several hardware platforms in 1975. Several versions were developed through discussion via the Internet Experiment Note (IEN) series. Initially, the Transmission Control Program, the precursor to the later protocol suite, provided only a reliable byte stream service, not datagrams. As experience with the protocol grew, collaborators recommended division of functionality into layers of distinct protocols, providing direct access to datagram service. Advocates included Bob Metcalfe, Yogen Dalal and John Shoch at Xerox PARC; Danny Cohen, who needed it for his packet voice work; and Jonathan Postel of the University of Southern California's Information Sciences Institute, who edited the Request for Comments (RFCs), the technical and strategic document series that has both documented and catalyzed Internet development. Postel stated, "We are screwing up in our design of Internet protocols by violating the principle of layering." Encapsulation of different mechanisms was intended to create an environment where the upper layers could access only what was needed from the lower layers. A monolithic design would be inflexible and lead to scalability issues. In version 4, written in 1978, Postel split the Transmission Control Program into two distinct protocols, the Internet Protocol (IP) as a connectionless layer and the Transmission Control Protocol (TCP) as a reliable connection-oriented service.

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