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Balia ( Ba lanced li nked a daptation) A new MPTCP congestion control algorithm

Balia ( Ba lanced li nked a daptation) A new MPTCP congestion control algorithm. Qiuyu Peng Steven Low. Anwar Walid Jaehyun Hwang. July 2014. MPTCP Congestion Control. How to control congestion over multiple paths?

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Balia ( Ba lanced li nked a daptation) A new MPTCP congestion control algorithm

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  1. Balia (Balanced linked adaptation) A new MPTCP congestion control algorithm QiuyuPeng Steven Low Anwar Walid Jaehyun Hwang July 2014

  2. MPTCP Congestion Control How to control congestion over multiple paths? Desirable Control Properties: Increase throughput and robustness to link failure while remaining • TCP friendly • Responsive (IETF RFC 6824)

  3. Key message Tradeoff between friendliness (to single path TCP) & responsiveness (to network changes) • is inevitable, but • can be systematically balanced New Algorithm Balia explicitly balances this tradeoff • based on a new design framework

  4. Prior Proposals • EWTCP • [Iyengar’ 06] [Honda’ 09] • Coupled MPTCP • [Kelly’ 05] [Han 06] • Semi-coupled MPTCP • [Wischik’ 11] • LIA (RFC6356) MPTCP • [Wischik’ 11] • OLIA MPTCP • [Khalili’ 12]

  5. Desirable properties Increase throughput and robustness to link failure while remaining • TCP friendly • Responsive Unfortunately … there is provably an inevitable tradeoff EWTCP Semi. LIA Coupled Responsiveness Friendliness

  6. Two questions • Have prior algorithms achieved the best tradeoff possible? • Bad news: No ! EWTCP Semi. LIA Coupled … but significant improvement is possible Responsiveness Friendliness

  7. Two questions • Can we systematically design this inevitable tradeoff ? • Good news: Yes ! EWTCP Semi. LIA Coupled … a new framework to better understand & design Responsiveness Friendliness

  8. First question first … … let’s first understand some problems with LIA and OLIA … and then look at a solution

  9. Problem with LIA (RFC6356) LIA can be • unfriendly to single path TCP (SPTCP)

  10. LIA can be unfriendly to SPTCP • … even when its own throughput is max’ed out ! SPTCP is worse off than optimal • by 26% • by 50% [Source: Khaliliiccrg presentation on OLIA]

  11. We have confirmed Khalili’s discovery with our own testbed Router1 10Mbps Type 1 flows 10Mbps Type 2 flows Router2 Router3 Type 2 flows are SPTCP.

  12. When all flows are SPTCP, they achieve capacity on each path aggregate throughput N1=5 N2=5 N1=15 N2=5 C1=C2=10Mbps

  13. When type 1 users are MPTCP, LIA starves SPTCP • … even when LIA throughput is max’ed out ! SPTCP’s are worse off N1=5 N2=5 • by 19% N1=15 N2=5 • by 25% C1=C2=10Mbps

  14. Two better designs • OLIA • Balia N1=5 N2=5 N1=15 N2=5 C1=C2=10Mbps

  15. Let’s now examine OLIA in more detail • Is OLIA responsive to network changes?

  16. OLIA can be unresponsive to network changes LIA OLIA Coupled 20Mbps, 10ms 1 MP-TCP flow: 0-200s 5 SP-TCP flows: 40-80s 20Mbps, 10ms

  17. Balia is responsive to network changes Balia LIA OLIA 20Mbps, 10ms 1 MP-TCP flow: 0-200s 5 SP-TCP flows: 40-80s 20Mbps, 10ms

  18. So LIA can be unfriendly, while OLIA can be unresponsive Second question now … … what is the nature of this inevitable tradeoff … how does Balia design this tradeoff

  19. Balia Generalized MPTCP algorithm that strikes a good balance • Friendly • Responsive EWTCP Semi. LIA Balia Responsiveness Coupled Friendliness Balia: Balanced linked adaptation

  20. Balia Generalized MPTCP algorithm that strikes a good balance • Friendly • Responsive … designed based on a new theoretical framework … that allows better understanding of this tradeoff

  21. Balia • ForeachACKonpathr, increment window by: • ForeachLossonpathr, decrement window by: is the round trip time On a single path, ar=1 and Balia reduces to Reno

  22. Key message Tradeoff between friendliness & responsiveness • is inevitable, but • can be systematically balanced Balia explicitly balances this tradeoff • based on a new design framework

  23. Current status • Linux implementation • Working on approval to make our code part of the UCLouvain’s MPTCP implementation • Documents • Paper: “Multipath TCP: Analysis, Design and Implementation” (http://arxiv.org/abs/1308.3119v2) • To be submitted: draft-walid-mptcp-congestion-control-00 • Experiment plans • NorNet: Multi-homed research testbed • Small-scale data center testbed • Mobile testbed with WiFi/3G/LTE

  24. Back up slides Theoretical Framework for Design - “Multipath TCP: Analysis, Design and Implementation,” Peng, Walid, Hwang and Low (http://arxiv.org/abs/1308.3119v2). Earlier version appeared in ACM Sigmetrics, 2013.

  25. Unified MPTCP model • Dynamics of throughput on path r: Congestion price Algorithm Different designs: different • TCP Reno (Jacobson 1988) • EWTCP (Honda et al 2009) • Coupled MPTCP (Kelly & Voice 2005, Han et al 2004) • Semicoupled MPTCP (Wischik et al 20011) • LIA MPTCP (Wischik et al 2011) • Balia (Peng et al 2013)

  26. Provable properties Theorem Balia has a unique equilibrium point Theorem (Almost) all MPTCP algorithms face an inevitable tradeoff between • TCP friendliness • Responsiveness Theorem The unique equilibrium point is asymptotically stable

  27. Design of the tradeoff • Explicitly parameterize friendliness and responsiveness EWTCP Semi. Max more friendly: small b more responsive: large b, h Coupled Responsiveness Friendliness

  28. Design of the tradeoff • Choose parameters judiciously balanced tradeoff more responsive LIA: Balia: more friendly

  29. Asymmetric paths 8Mbps, 10ms 1 MP-TCP flow: 0-300s 5 SP-TCP flows: 40-80s 2Mbps, 100ms

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