@article {DR:COMNET-14a,
	title = {Delay-based congestion control: Flow vs. BitTorrent swarm perspectives},
	journal = {Elsevier Computer Networks},
	volume = {60},
	year = {2014},
	month = {02/2014},
	chapter = {115 -- 128},
	abstract = {<p>BitTorrent, one of the most widespread file-sharing P2P applications, recently introduced LEDBAT, a novel congestion control protocol aiming at (i) limiting the additional delay due to queuing, to reduce interference with the rest of user traffic (e.g., Web, VoIP and gaming) sharing the same access bottleneck, and (ii) efficiently using the available link capacity, to provide users with good BitTorrent performance at the same time. In this work, we adopt two complementary perspectives: namely, a flow viewpoint to assess the Quality of Service (QoS) as in classic congestion control studies, and a BitTorrent swarm viewpoint to assess peer-to-peer users Quality of Experience (QoE). We additionally point out that congestion control literature is rich of protocols, such as VEGAS, LP, and NICE sharing similarities with LEDBAT, that is therefore mandatory to consider in the analysis. Hence, adopting the above viewpoints we both (i) contrast LEDBAT to the other protocols and (ii) provide deep understanding of the novel protocol and its implication on QoS and QoE. Our simulation based investigation yields several insights. At flow-level, we gather LEDBAT to be lowest priority among all protocols, which follows from its design that strives to explicitly bound the queuing delay at the bottleneck link to a maximum target value. At the same time, we see that this very same protocol parameter can be exploited by adversaries, that can set a higher target to gain an unfair advantage over competitors. Interestingly, swarm-level performance exhibit an opposite trade-off, with smaller targets being more advantageous for QoE of BitTorrent users. This can be explained with the fact that larger delay targets slow down BitTorrent signaling task, with possibly negative effect on the swarming protocol efficiency. Additionally, we see that for the above reason, in heterogeneous swarms, any delay-based protocol (i.e., not only LEDBAT but also VEGAS or NICE) can yield a competitive QoE advantage over loss-based TCP. Overall this tension between swarm and flow-levels suggests that, at least in current ADSL/cable access bottleneck scenarios, a safe LEDBAT operational point may be used in practice. At the same time, our results also point out that benefits similar to LEDBAT can also be gathered with other delay-based protocols such as VEGAS or NICE.</p>},
	url = {http://www.enst.fr/~drossi/paper/rossi14comnet-a.pdf},
	author = {Claudio Testa and Dario Rossi}
}
@article {DR:COMNET-14b,
	title = {{Fighting the bufferbloat: on the coexistence of AQM and low priority congestion control (extended version)}},
	journal = {Elsevier Computer Networks},
	volume = {60},
	year = {2014},
	chapter = {115--128},
	abstract = {<p>Nowadays, due to excessive queuing, delays on the Internet can grow longer than the round trip time between the Moon and the Earth {\textendash} for which the {\textquoteleft}{\textquoteleft}bufferbloa t{\textquoteright}{\textquoteright} term was recently coined. Some point to active queue management (AQM) as the solution. Others propose end-to-end low-priority congestion control techniques (LPCC). Under both approaches, promising advances have been made in recent times: notable examples are CoDel for AQM, and LEDBAT for LPCC. In this paper, we warn of a potentially fateful interaction when AQM and LPCC techniques are combined: namely, AQM resets the relative level of priority between best-effort and low-priority congestion control protocols. We validate the generality of our findings by an extended set of experiments with packet-level ns2 simulation, considering 5 AQM techniques and 3 LPCC protocols, and carry on a thorough sensitivity analysis varying several parameters of the networking scenario. We complete the simulation via an experimental campaign conducted on both controlled testbeds and on the Internet, confirming the reprioritization issue to hold in the real world at least under all combination of AQM policies and LPCC protocols available in the Linux kernel. To promote cross-comparison, we make our scripts and dataset available to the research community.</p>},
	url = {http://www.enst.fr/~drossi/paper/rossi14comnet-b.pdf},
	author = {YiXi Gong and Dario Rossi and Claudio Testa and Silvio Valenti and Dave Taht}
}
