A hands-on assessment of transport protocols with lower than best effort priority

Last year, the official BitTorrent client switched to LEDBAT, a new congestion control algorithm targeting a lower-than Best Effort transport service. In this paper, we study this new protocol through packet-level simulations, with a special focus on a performance comparison with other lower-than Best Effort protocols such as TCP-LP and TCP-NICE: our aim is indeed to quantify and relatively weight the level of Low-priority provided by such protocols. Our results show that LEDBAT transport generally achieves the lowest possible level of priority, with the default configurations of TCP-NICE and TCP-LP representing increasing levels of aggressiveness. In addition, we perform a careful sensitivity analysis of LEDBAT performance, by tuning its main parameters in both an inter-protocol (against TCP) and intra-protocol (against LEDBAT itself) scenarios. In the inter-protocol case, even in case of misconfiguration LEDBAT competes as aggressively as TCP, but we show that it is not possible to achieve an arbitrary level of low-priority by merely tuning its parameters. In the intra-protocol case, we show that coexistence of legacy flows with slightly dissimilar settings, or experiencing different network conditions, can result in significant unfairness.

[1]  Mikel Izal,et al.  Dissecting BitTorrent: Five Months in a Torrent's Lifetime , 2004, PAM.

[2]  Balázs Sonkoly,et al.  A comprehensive TCP fairness analysis in high speed networks , 2009, Comput. Commun..

[3]  Robert Shorten,et al.  Experimental Evaluation of TCP Protocols for High-Speed Networks , 2007, IEEE/ACM Transactions on Networking.

[4]  Dario Rossi,et al.  Yes, We LEDBAT: Playing with the New BitTorrent Congestion Control Algorithm , 2010, PAM.

[5]  Janardhan R. Iyengar,et al.  Low Extra Delay Background Transport (LEDBAT) , 2012, RFC.

[6]  R. Srikant,et al.  Modeling and performance analysis of BitTorrent-like peer-to-peer networks , 2004, SIGCOMM '04.

[7]  B. J. Prabhu,et al.  Fairness in MIMD Congestion Control Algorithms , 2005, Telecommun. Syst..

[8]  Arun Venkataramani,et al.  Proceedings of the 5th Symposium on Operating Systems Design and Implementation Tcp Nice: a Mechanism for Background Transfers , 2022 .

[9]  Larry L. Peterson,et al.  TCP Vegas: new techniques for congestion detection and avoidance , 1994 .

[10]  Shao Liu,et al.  4 CP : Competitive and Considerate Congestion Control Protocol , 2006 .

[11]  Dario Rossi,et al.  The Quest for LEDBAT Fairness , 2010, 2010 IEEE Global Telecommunications Conference GLOBECOM 2010.

[12]  Venkata N. Padmanabhan,et al.  Analyzing and Improving a BitTorrent Networks Performance Mechanisms , 2006, Proceedings IEEE INFOCOM 2006. 25TH IEEE International Conference on Computer Communications.

[13]  Van Jacobson,et al.  Congestion avoidance and control , 1988, SIGCOMM '88.

[14]  Dario Rossi,et al.  LEDBAT: The New BitTorrent Congestion Control Protocol , 2010, 2010 Proceedings of 19th International Conference on Computer Communications and Networks.

[15]  E.W. Knightly,et al.  TCP-LP: low-priority service via end-point congestion control , 2006, IEEE/ACM Transactions on Networking.

[16]  Eitan Altman,et al.  c ○ 2005 Springer Science + Business Media, Inc. Manufactured in The Netherlands. Fairness in MIMD Congestion Control Algorithms , 2022 .

[17]  Dario Rossi,et al.  News from the Internet congestion control world , 2009, ArXiv.

[18]  William Chan,et al.  Improving Traffic Locality in BitTorrent via Biased Neighbor Selection , 2006, 26th IEEE International Conference on Distributed Computing Systems (ICDCS'06).