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CYCLADES was a French pilot project led by Louis Pouzin , the aim of which was to create a global telecommunications network based on the exchange of data packets. The project was in 1971 and launched in 1978 because of changes in priorities for France's national budget and, above all because they had seen the danger for the state telecom monopoly in favor of Transpac (X.25) , the backbone of Minitel , abandoned. Some of the developments of the CYCLADES project represent key technologies that have made today's Internet possible.


In 1970 , following a visit by a French delegation to BBN Technologies in the USA, the ARPANET project , one of the forerunners of the Internet, became known in France. This aroused interest in the concept of a decentralized network . At the same time, France only had dedicated data networks reserved for individual organizations. As a result, the CYCLADES project was born.


CIGALE and the datagram

At CYCLADES, as with earlier technical approaches (e.g. ARPANET), the decision was made to split the data for transmission into packets and then reassemble them at the destination. At that time, the ARPANET was using virtual connections ( Virtual Circuit , VC ). In contrast, CYCLADES was the first to use the so-called datagram ( French:  “ datagrams ”, analogous to “ télégramme ” - a “data telegram”) - a connectionless technology.

Virtual connections are logical channels that are created by dividing bit streams into packets in order to be able to send several of these bit streams - quasi simultaneously - over a common physical message connection . So that the recipient can correctly assign the individual packets to the bit streams, they are provided with a connection identifier. So nothing else happens than that several physical communication links are simulated in order to save lines.

CIGALE (French for cicada ), the CYCLADES layer that is responsible for packet switching , has now gone one step further. Instead of establishing virtual connections, the data packets are provided with the respective source and destination address. Every single packet of a bit stream can now freely and independently of the other packets find its way through the network. This method was the model for the protocol suite TCP / IP , which was developed for the ARPANET from 1973 and replaced the Network Control Program (NCP) used up until then on January 1, 1983 - from a technology point of view, the beginning of today's Internet.

Significance for today's internet

The scientists who were involved in the development of CYCLADES and ARPANET maintained an exchange of knowledge and in some cases even participated in both projects. This led to a significant technology transfer in both directions.

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