  BitTorrent, one of the most widespread used P2P application for file-sharing,
recently got rid of TCP by introducing an application-level congestion control
protocol named uTP. The aim of this new protocol is to efficiently use the
available link capacity, while minimizing its interference with the rest of
user traffic (e.g., Web, VoIP and gaming) sharing the same access bottleneck.
In this paper we perform an experimental study of the impact of uTP on the
torrent completion time, the metric that better captures the user experience.
We run BitTorrent applications in a flash crowd scenario over a dedicated
cluster platform, under both homogeneous and heterogeneous swarm population.
Experiments show that an all-uTP swarms have shorter torrent download time with
respect to all-TCP swarms. Interestingly, at the same time, we observe that
even shorter completion times can be achieved under careful mixtures of TCP and
uTP traffic.
