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Trafics bidirectionnels et asymétrie : mécanismes pour optimiser les performances et maximiser l'utilisation des liens de l'Internet

Fatma Louati 1
1 PLANETE - Protocols and applications for the Internet
Inria Grenoble - Rhône-Alpes, CRISAM - Inria Sophia Antipolis - Méditerranée
Abstract : Asymmetric networks are networks that do not have the same capacity in term of bandwidth available in their forward and reverse directions. Typical examples are asymmetric satellite networks and ADSL lines. If these kinds of networks are crossed by two-way TCP traffic, we are in a situation where data packets and acknowledgments (ACK) share the same scarce resource in the upload direction. This sharing implies lot of problems to the TCP protocol. In order to alleviate these problems, many solutions have been proposed in the literature. However, all these solutions try to improve performances of one traffic at the expense of the opposite. For this reason, we propose in this thesis two solutions, that differ by their approach, and that have another objective: satisfy the user of a two-way traffic by considering at the same its upload and download traffic. This satisfaction is obtained by maximizing the utilisation of both links.
Our first solution is called Adaptive Class-based Queuing mechanism ACQ and aims to handle two-way TCP traffic over links that exhibit bandwidth asymmetry. ACQ runs at the entry of the slow link and relies on two separate classes, one for Ack packets and one for Data. ACQ proposes to adapt the weights of both classes according to the crossing traffic. We present also VAQ - for Virtual Ack based Queuing -, our second solution that uses a fine-grained approach at the packet level to schedule data and ACKs at the entry of the slow reverse link of the asymmetric access network. VAQ uses two parallel queues: one for ACK packets and one for data packets. It grants a credit for the data packets queue, and proposes to adapt this credit by monitoring the ACKs of the download traffic.
We show by simulations that our mechanisms are able to reach a good utilization of the available resources, managing then to maximize the satisfaction of the user. ACQ and VAQ are also robust when changing the network conditions.
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Submitted on : Friday, July 31, 2009 - 2:33:33 PM
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Fatma Louati. Trafics bidirectionnels et asymétrie : mécanismes pour optimiser les performances et maximiser l'utilisation des liens de l'Internet. Réseaux et télécommunications [cs.NI]. Université de Nice Sophia Antipolis, 2004. Français. ⟨tel-00408683⟩



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