Handling Two-Way TCP Traffic in Bandwidth Asymmetric Networks
Résumé
The TCP congestion control protocol assumes bandwidth symmetric paths. As two-way asymmetric connections will probably become common case in the future with the widespread use of ADSL and satellites technologies, it will be important to assure that congestion is properly handled in these environments. A lot of researches were done to find way to do this, but most of them are ad hoc solutions unable to go very far in solving the general problem.In this context, we propose two new approaches for handling two-way traffic over links that exhibit bandwidth asymmetry: an Adaptive Class-based Queuing mechanism called ACQ and a Virtual Ack-based Queuing mechanism called VAQ. Both mechanisms runs at the entry of the slow link. ACQ relies on two separate classes, one for Ack packets and one for Data and proposes to adapt the weights of both classes according to the crossing traffic and to an utility function defined by the user or the network operator. VAQ relies on two virtual classes, one for Ack packets and one for Data. It grants a credit to the Data class and adapts this credit according to the crossing traffic through a WFQ scheduling scheme.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 of such asymmetric connections. We also demonstrate by simulations the robustness of ACQ and VAQ when confronted to different network settings.