CYCLADES

Hosts instead of network

CYCLADES was an innovative packet-switching research network created in France in 1972. It introduced a number of new concepts that had a major technical influence on the development of the Internet, especially on the design of Internet protocols on which the modern Internet now runs. It was the first network that made the hosts responsible for the reliable delivery of data, rather than the network itself.

Technical design

CYCLADES was designed and directed by Louis Pouzin, who used the ARPANET as a reference model. Like the ARPANET, CYCLADES used packed-switching, meaning information would be broken down into packets, before travelling across the wire. ARPANET required a path across the network to be created for each communications between two computers. The hosts had to wait for the acknowledgement of each packet before sending the next one. The new transmission function invented with CYCLADES, CIGALE, used howewer an unreliable datagram¹ service, because the user only had to provide the destination address and received no guarantee of delivery. This connection for packet-switching reduced the need for sophisticated and costly equipment to establish predetermined routes for the packets to take.

Other influences

The network also gave the opportunity to a whole generation of French computer scientists to experiment with different networking approaches. Louis Pouzin and the CYCLADES alumni, infact, started to experiment with concepts like local area networks and satellite networks. Hubert Zimmermann used his experience in CYCLADES to influence the design of the OSI model, which is still a common pedagogical tool.