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Enhancing Video Over Mobile – Predicting the Future is Key

Trying to conduct a videoconference over a cellular network in a moving car “wasn’t working very well” for Keith Winstein, so he started trying to find a solution to the problem. The result was a new transport protocol called “Sprout” and the paper he and his co-authors wrote earned Winstein the second Applied Networking Research Prize for 2014.

Winstein won the 2014 ANRP for designing a transport protocol for interactive applications that desire high throughput and low delay. In their paper, “Stochastic Forecasts Achieve High Throughput and Low Delay over Cellular Networks” (Proc. 10th USENIX Symposium on Networked Systems Design and Implementation (NSDI), Lombard, IL, USA, April 2013.), Keith and his co-authors Anirudh Sivaraman and Hari Balakrishnan describe Sprout, a transport protocol that works well over cellular wireless networks, where link speeds change dramatically with time, and current protocols build up multi-second queues in network gateways.

Motivated by his sub-par videoconferencing experience, Keith and his team developed a novel end-to-end transport protocol that tries to maximise throughput whilst simultaneously bounding the risk of delay by modelling the variation in link speed based on observations of packet arrival times. The model is then used to predict the future link speed.

The results are compelling: experiments conducted on traces from four commercial cellular networks show many-fold reductions in delay, and increases in throughput, over Skype, Facetime, and Hangout, as well as over Cubic, Compound TCP, Vegas, and LEDBAT. Although Sprout is an end-to-end scheme, in this setting it matched or exceeded the performance of Cubic-over-CoDel, which requires modifications to network infrastructure to be deployed.

Keith received his award at the recent Internet Research Task Force open meeting at IETF 89 in London, where he also presented his results. Keith’s slides are available and audio from the presentation is also available (starting at 01:22:35).

The next ANRP nomination period for prizes to be awarded in 2015 will start later this year – stay tuned for more information on the nomination process.