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.
@cite_24: BitTorrent, one of the most widespread file sharing P2P applications, recently introduced uTP, an application-level congestion control protocol which aims to efficiently use the available link capacity, while avoiding to interfere with the rest of user traffic (e.g., Web, VoIP and gaming) sharing the same access bottleneck. Research on uTP has so far focused on the investigation of the congestion control behavior on rather simple settings (i.e., single bottleneck, few backlogged flows, etc.), that are fairly far from the P2P settings in which the protocol is deployed. Moreover, prior work typically addressed questions, such as fairness and efficiency, that are natural from a congestion control context perspective, but are not directly related with the performance of the overall P2P system. In this work, we refine the understanding of uTP, by gauging its impact on the primary BitTorrent user-centric metric, namely the torrent download time, by means of packet level simulation. Results of our initial investigations show that: (i) in case uTP clients fully substitute TCP clients, no performance difference arise; (ii) in case of heterogeneous swarms, comprising peers using uTP and TCP congestion control, completion time of uTP peers can possibly benefit of lower uplink queuing delays, as signaling traffic (e.g., chunk requests) are not slowed down by long waits in the ADSL buffers.
The only previous work addressing the impact of uTP on BitTorrent completion time is our own recent work @cite_24 , that however employs ns2 simulations unlike in this work. Interestingly, some of the observations of this study are in agreement with @cite_24 , e.g., showing a larger completion time for increasing buffer occupancy on the data plane. Yet, we point out that @cite_24 does not consider an hardcoded preference for uTP, nor bidirectional uTP connections: hence, an interesting difference with respect to the current work is that @cite_24 forecasted heterogeneous performance for heterogeneous swarms (i.e., larger completion time for TCP peers) that we have shown not to hold on practice.