Résumé des résultats (Abstract)
(Anglais)
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The design of algorithms is a fundamental part of information science where the 'network' concept plays today one of principal roles. This concept led to the concept of communication and as a result a new body of algorithms, based on the exchange of messages between activities has been developed. Communication is a basic tool in the design of parallel algorithms.in the field of networks such parallel algorithms are called protocols; they provide the services of information transfer and activity control in a set of processes, executing on physically distinct sites and linked by communication channels, that co-operate to perform some specified application. This co-operation between processes gives rise to specific problems whose solution requires new approaches, based on sophisticated algorithmic techniques.
The objective of this project is to improve the existing networking technologies and to design novel approximation and randomized algorithms. The collaboration exploits the different skills and capabilities of the six research partners. Research subjetcs include optical network, radio network and satellite systems.
Satellite communication has played a major role in the development of telecommunication networks. Today, satellite systems are becoming deeply involved in the internet, particularly in the areas of providing broadband access, content distribution and multicast applications, all of which can benefit from the inherent capabilities of satellite solutions.
In internet, the reliable file transfer such as ftp or e-mails are based on tcp/ip congestion control protocol. However, the performance of tcp is often degraded when the end-to-end path includes a satellite link. Among the factors that can adversely affect tcp performances over satellite links, we give the so-called: bit error rate (ber), round-trip time (rtt), bandwidth-delay product (bdp), variable round-trip time.
In our research, we focus on the problems due to the long rtts. The most challenging problem is the tcp fairness. Tcp's congestion avoidance algorithm leads to unfair bandwidth allocations when multiple connections with different rtts share a bottleneck link. The long rtt connections (such as satellite connections) obtain only a small fraction of their fair share of the bandwidth. This problem has been observed by several researchers but a viable solution has not been proposed. We proposed a new congestion avoidance algorithm which we refer to canit (congestion avoidance with normalized interval of time). We also studied the performance of canit algorithm taking into account the satellite environment and the related problems.
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