How did these disparate data communications system become united into the global network that know as the internet? While some connections between networks were established in the 1970s, design incompatibilities generally limited their services to the exchange of mail and news. The technologies that allow the full range of network services to be shared seamlessly across systems were initially created for the ARPANET.
DARPA’s exploration in internetworking stemmed from its desire to connect the ARPANET with two new networks it had built, which extended packet switching techniques to radio and satellite communications. Since these media did not have the same technical characteristics as telephone lines-radio links were unreliable; satellites introduced delays-existing techniques such as X.25 or the original ARPANET protocols were not suitable for such a diverse interconnected system. In the early 1970s, therefore DARPA started an internet program to develop a more comprehensive solution.
Another technical development that helped drive the demand for internetworking was local area networks. Ethernet, the most influential of these, was invented in 1973 by Robert Metcalfe, drawing on an earlier network called Alohanet that was created by Norman Abramson, Frank Kuo, and Richard Binder (Metcalfe 1996; Abramson 1970). Ethernet and Alohanet pioneered a technique called random access that allowed many users to share a communication channel without the need for complex routing procedures.
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The simplicity of the random access design helped make LANs affordable for a broad range of users. Ethernet became formally standardized and commercially available in the early 1980s and was widely adopted by universities, businesses, and other organizations. Another popular LAN system, token ring, was invented by IBN researchers in Zurich and commercialized in 1985. The popularity of LANs would create many new networks that potentially could be interconnected; but, like the packet radio network, these random access systems could not guarantee a reliable connection, and therefore would not work well with existing wide-area network protocols. A new system was needed.
The internet program was led by Vinton Cerf and Robert Kahn, with the collaboration of computer scientists from around the world. In addition to US researchers at DARFA, Stanford, the University of Southern California, the University Hawaii, BBN, and Xerox PARC, Cerf and Kahn consulted networking experts from University College London, the NPL and CYCLADES group, and the International Network Working Group (Cerf 1990). The INWG had been founded in 1972 and included representatives from many national PTTs that were planning to build packet-switching networks. By sharing concerns and pooling ideas, this inclusive team was able to design a system that could serve users with diverse infrastructural resources and networking needs.
The internet architecture had two main elements. The first was a set of protocol called TCP/IP, or Transmission Control Protocol and Internet Protocol (Cerf and Kahn 1974(2) TCP was an example of a host protocol, whose function is to set up and manage a connection between two computers (hosts) across a network. The insight behind TCP was that host protocol could guarantee a reliable connection between hosts even if they were connected by an unreliable network, such as a packet radio or Ethernet system. By lowering the requirement for reliability in the network, the use of TCP opened the Internet to many more network, than it might otherwise have accommodated.
To ensure dependable connections, TCP was designed to verify the safe arrival of packet, using confirmation messages called acknowledgments; compensate for errors by retransmitting lost or damaged packets; and control the rate of date flow between the hosts by limiting the number of packets in transit. In contrast, the internet Protocol performed a much simpler set of tasks that allowed packets to be passed from machine to machine as they made their way through the network.
