Presentation and major design aspects of the CYCLADES computer network

Abstract

A computer network is being developed in France, under government sponsorship, to link about twenty heterogeneous computers located in universities, research and D.P. Centers. Goals are to set up a prototype network in order to foster experiment in various areas, such as: data communications, computer interaction, cooperative research, distributed data bases. The network is intended to be both, an object for research, and an operational tool. In order to speed up the implementation, standard equipment is used, and modifications to operating systems are minimized. Rather, the design effort bears on a carefully layered architecture, allowing for a gradual insertion of specialized protocols and services tailored to specific application and user classes. A particular objective, for which CYCLADES should be an operational tool, is to provide various departments of the French Administration with access to multiple data bases located in geographically distant areas. Host-host protocols, as well as error and flow control mechanisms are based on a simple message exchange procedure, on top of which various options may be built for the sake of efficiency, error recovery, or convenience. Depending on available computer resources, these options can be implemented as user software, system modules, or front end processor package. For each of them, network-wide interfaces are defined, to conserve consistency in human communications. CYCLADES uses a packet-switching sub-network, which is a transparent message carrier, completely independent of host-host conventions. While in many ways similar to ARPANET, it presents some distinctive differences in address and message handling, intended to facilitate interconnection with other networks. In particular, addresses can have variable formats, and messages are not delivered in sequence, so that they can flow out of the network through several gates toward an outside target. Terminal concentrators are mini-hosts, and implement whatever services users or applications require, such as sequencing, error recovery, code translation, buffering, etc. Some specialized hosts may be installed to cater for specialized services, such as mail, resource allocation, information retrieval, mass storage. A control center is also being installed and will be operated by the French PTT.