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We present Data acceleration and reduction technology (DART), a new rate based congestion control and scheduling mechanism with integrated data compression. DART has been implemented in the 7-ip satellite gateway products and is based on SCPS-TP framework. We evaluate the performance of this scheme on two live commercially available satellite systems, IPSTAR and Inmarsat BGAN and compare it to the performance of a number of TCP flavors previously proposed for use on satellite links. We show that on congested satellite links the proposed scheme outperforms the established techniques. We additionally highlight the benefits of data compression when fully integrated within the transport protocol. Finally, we demonstrate fairness of the proposed scheme to other flows.

We present a novel mechanism for adjusting the combination of the number of simultaneous VoIP calls and voice quality, based on the monitored WiMax link parameters. We have implemented this mechanism which combines call admission control and setting of variable voice codec rate (and corresponding quality) dynamically in the Asterix PBX using the Speex voice codec. The mechanism includes dynamic parameter adjustments of currently active VoIP calls, with the capability to change quality on a per voice frame basis. It additionally limits acceptance of new calls until there is sufficient capacity to maintain a pre-defined minimum quality for the existing calls. We have also implemented the wireless link capacity estimator, which, based on the parameters measured in the receiver, estimates the data rate currently available on the wireless link. Our implementation is for a pre-WiMax service offered by UNWIRED in Australia. We show that the proposed cross layer optimisation enables a larger number of calls with improved voice quality, compared to a fixed scheme. We are currently working with a certified WiMax equipment supplier and we plan to extend the scheme to full WiMax implementation.