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The CYCLADES packet switching network was a French research network created in the early 1970s. It was developed to explore alternatives to the ARPANET design and to support network research generally. It was extremely influential on the Internet's initial design.[1]

The CYCLADES network was the first to make the hosts responsible for the reliable delivery of data, rather than the network itself, using unreliable datagrams and associated end-to-end protocol mechanisms. These concepts were later used in the TCP/IP, the protocol of the Internet; CYCLADES was one of the predecessor systems with the greatest technical influence on the Internet.

The network was sponsored by the French government, through the Institut de Recherche d'lnformatique et d'Automatique (IRIA), the national research laboratory for computer science in France (now known as INRIA), which served as the co-ordinating agency. Several French computer manufacturers, research institutes and universities contributed to the effort. CYCLADES was designed and directed by Louis Pouzin.


Conception and deployment

CYCLADES was developed in France by Louis Pouzin. Having worked with the ARPANET in the US, Pouzin wanted to create a testbed for research on network protocols that would develop further uses of packet-switching and routing systems. It was named after an island group in the Greek Aegean Sea called the Cyclades as it was designed to "connect isolated 'islands' of computing" (Abbate 1999:125[2]).

Design and staffing started in 1972, and November 1973 saw the first demonstration, using three hosts and one packet switch. Deployment continued in 1974, with three packet switches installed by February, although at that point the network was only operational for three hours each day. By June the network was up to seven switches, and was available throughout the day for experimental use.

A terminal concentrator was also developed that year, since time-sharing was still a prevalent mode of computer use. In 1975, the network shrank slightly due to budgetary constraints, but the setback was only temporary. At that point, the network provided remote login, remote batch and file transfer user application services.

By 1976 the network was in full deployment, eventually numbering 20 nodes with connections to NPL in London, ESA in Rome, and to the European Informatics Network (EIN).

Technical details

CYCLADES used a layered architecture, as did the Internet. The basic packet transmission function, named CIGALE, was novel; however, it provided an unreliable datagram service (the word was coined by Louis Pouzin by combining data and telegram). Since the packet switches no longer had to ensure correct delivery of data, this greatly simplified their design.

The CIGALE network featured a distance vector routing protocol, and allowed experimentation with various metrics. it also included a time synchronization protocol in all the packet switches. CIGALE included early attempts at performing congestion control by dropping excess packets.

The name CIGALE—which is French for cicada—originates from the fact that the developers installed a speaker at each computer, so that "it went 'chirp chirp chirp' like cicadas" when a packet passed a computer (Gillies and Cailliau 2000:38[3]).

An end-to-end protocol built on top of that provided a reliable transport service, on top of which applications were built. It provided a reliable sequence of user-visible data units called letters, rather than the reliable byte stream of TCP. The transport protocol was able to deal with out-of-order and unreliable delivery of datagrams, using the now-standard mechanisms of end-end acknowledgments and timeouts; it also featured sliding windows and end-to-end flow control.


By 1976, the French PTT was developing Transpac, a packet network based on the emerging X.25 standard. The academic debates between datagram and virtual circuit raged for some time, but were eventually cut short by bureaucratic maneuvering.

Data transmission was a state monopoly in France at the time, and IRIA needed a special dispensation to run the CYCLADES network. The PTT did not see why the French government would fund a competitor to their Transpac network, and insisted that the permission and funding be rescinded. By 1981, Cyclades was forced to shut down.


As mentioned, the most important legacy of CYCLADES was in showing that moving the responsibility for reliability into the hosts was workable, and produced a well-functioning service network. It also showed that it greatly reduced the complexity of the packet switches. Today's Internet still uses these ideas.

It was also a fertile ground for experimentation, and allowed a generation of French computer scientists to experiment with networking concepts. Louis Pouzin and the CYCLADES alumni initiated a number of follow-on projects at IRIA to experiment with local area networks, satellite networks, the Unix operating system, and the message passing operating system Chorus.

Hubert Zimmerman used his experience in CYCLADES to influence the design of the OSI 7 layer model, which is still an extremely common pedagogical device.

CYCLADES alumni and researchers at IRIA/INRIA were also influential in spreading the Internet in France, eventually witnessing the success of the datagram-based Internet, and the demise of the X.25 and ATM virtual circuit networks.



  1. Bennett, Richard (2009), Designed for Change: End-to-End Arguments, Internet Innovation, and the Net Neutrality Debate, Information Technology and Innovation Foundation.
  2. Abbate, Janet (1999). Inventing the Internet. MIT Press. ISBN 0-262-01172-7. 
  3. Gillies, James and Robert Cailliau (2000). How the Web Was Born: The Story of the World Wide Web. Oxford University Press. ISBN 978-0-19-286207-5. 

Further reading

  • Louis Pouzin (editor), The Cyclades Computer Network: Toward Layered Network Architectures (North-Holland, Amsterdam, 1982)

External links

fr:Cyclades (réseau) pl:CYCLADES

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