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1、Incentives Build Robustness in BitTorrent?,Analysis on Bit Torrent Client performanceBy Jimmy Wong,1,Incentives Build Robustness in,Agenda,IntroductionBitTorrent BasicsBit Tyrant: A strategic clientBit Thief: A free-riding clientOther Tricks of BT ClientReal World ExperimentsAvoiding of TricksConclu
2、sion,2,AgendaIntroduction2,Introduction,BitTorrent core incentiveUpload More, Download MoreProblem DefinitionI am a selfish userCan I gain without pay / pay less?,3,IntroductionBitTorrent core in,BitTorrent Basics,Step 0 Publishing ContentCreate Torrent fileTracker URLSHA-1 Hash ChecksumAssign a Tra
3、ckerDistribute Torrent to users through Web Site, Newsgroup or Forum,4,BitTorrent BasicsStep 0 Publ,BitTorrent Basics,Step 1 JoiningPeers get the TorrentConnect to TrackerLook for available peersDHT (Distributed Hash Table)Create connection with other peersStart with Others Optimistic UnchokingLook
4、for better peersLet other peers join the swarm,5,BitTorrent BasicsStep 1 Join,BitTorrent Basics,Step 2 to N-1 PipeliningExchange bitmap about which chunks are availablePay more, get moreTo build incentive for peers to uploadReciprocalRarest firstTo preserve File completeness among the swarmTo build
5、up peers reputation,6,BitTorrent BasicsStep 2 to N-1,BitTorrent Basics,ChokingSend data to only few good peersContribute data to youHave pieces that you wantsA resourceful peersIt will be nice if I can pay minimal cost to be un-choke!,7,BitTorrent BasicsChoking7,BitTorrent Basics,Optimistic Un-choki
6、ngAllow new peers to get some pieces for exchangeAllow discovery of better exchanging partnersMost peers are so friendlyI can gain without contribute!,8,BitTorrent BasicsOptimistic Un,BitTorrent Basics,Ending PhaseToward the end of downloadRequest for missing piecesSearch for available peers20-30 pi
7、eces left,9,BitTorrent BasicsEnding Phase9,Bit Tyrant: A strategic client,Incentive100KB/s 15KB/s1% drop15KB/s 10KB/s40% drop About 1.9Mbps World Wide Bandwidthhttp:/ do I still need to give u so much?,10,Bit Tyrant: A strategic client,Bit Tyrant: A strategic client,Resource ManagementBandwidth fixe
8、d# Conn x Speed = ConstantCurrent Official BT Protocol (=5.0)4 un-choking peers1 optimistic un-chokingA Optimization Problem!,11,Bit Tyrant: A strategic client,Bit Tyrant: A strategic client,Bit Tyrant Un-chocking algorithmMark Dp be download rate of conn pMark Up be upload rate of conn pFor each ro
9、undCalculate performance metric Dp / UpUn-choking the conn with the highest metricAt the end of each roundIf peer doesnt un-choking us Up (1+delta)UpIf peer un-choking us Dp = downlod rateIf peer has un-choked us for r round Up (1-lamda)Up,12,Bit Tyrant: A strategic client,Bit Tyrant: A strategic cl
10、ient,Very simple algorithmNet EffectSelect friendly peersFilter out unfriendly peersGain from peers most of the time,13,Bit Tyrant: A strategic client,Bit Tyrant: A strategic client,Dynamic sizing of active setServing the best peers firstThe 2nd best next and so on Until upload rate is exhaustedLoca
11、l Optimal tradingNot global, because only concern your local peers group,14,Bit Tyrant: A strategic client,BitThief : A free-riding client,Download onlyNo copy right issue (Only Contributor is sued)Conserve ResourceUse to spoil the communityBasic IdeaGain from optimistic un-chokingGain from free sha
12、ring of Seeder,15,BitThief : A free-riding clien,BitThief : A free-riding client,Gain From Optimistic Un-chokingRequest for as many clients as possibleMay be block by the TrackerSIMD like query to TrackerConnect to all client available Higher Chance of being un-chokingAlways pretend to be a new come
13、rA bitmap with no available pieceTry to download whatever availableMost Clients are so nice,16,BitThief : A free-riding clien,BitThief : A free-riding client,Gain From Free Sharing of SeederSeeder select peers in two waysThe Highest Bandwidth (from tracker)Round Robin Bit Thief report high upload ra
14、te# of Seeder # of Leecher Even betterGain from both methodology,17,BitThief : A free-riding clien,Other Tricks of BT Client,Client DiscriminationHigher priority for Similar ClientDelibrately choke other clientPretend to be Local NeighborFake tracker with wrong upload rateRetrieve from Seed,Rapid Di
15、sconnect and ReconnectHope to gain from optimistic unchokingRemove from black-listMultiple Connection to the same clientFor high speed BBGain the most from the same client,18,Other Tricks of BT ClientClien,Experiment with BT Client,Testing EnvironmentAthlon 64 2800+1GB Ram120GB 7200 rpm HDDWindows X
16、P SP2 w/ TCP Conn CrackBT SoftwareUtorrent / MainlineBit CometBit TryantiCable internet Connection,19,Experiment with BT ClientTesti,Experiment with BT Client,Gentoo AMD 64 Minimal ISO 54.4MB34 Seeders, 0 LeechersUbuntu 7.10 i386 Desktop ISO695MB928 Seeders / 78 LeechersNBA Match921MB120 Seeders, 71
17、4 Leechers,20,Experiment with BT ClientGento,Experiment with BT Client,21,Experiment with BT ClientGento,Experiment with BT Client,22,Experiment with BT ClientUbunt,Experiment with BT Client,23,Experiment with BT ClientNBAUp,Experiment with BT Client,Bit Thief Achieve a high download rate (150KB/s)
18、for Ubuntu and NBASuck at 25%,24,Experiment with BT ClientBit T,Avoiding Tricks,TargetStop Fake InformationIdentify Free-ridingDifficultiesBit Torrent is so wide spreadToo many implementationsIncentive driven works again!Co-operative identify bad clientBlock bad peers, Share with good peers,25,Avoid
19、ing TricksTarget25,Avoiding Tricks,Sharing with PeersSearch for local optimal best peersSearch for potential bad peersBroadcast of bad peers (In a majority basics)It will fail if more than half of clients are in-honest,26,Avoiding TricksSharing with Pe,Conclusion,BT RobustnessMost peers are friendly
20、Ways to CrackGain from cracking the protocolBit Tyrant: Download UploadBit Thief: Free RidingProposed SolutionDecentralized Client Solution,27,ConclusionBT Robustness27,Reference,Incentives Build Robustness in BitTorrent http:/www.bittorrent.org/bittorrentecon.pdfDo incentives build robustness in BitTorrent? http:/www.cs.washington.edu/homes/piatek/papers/BitTyrant.pdfFree Riding in BitTorrent is Cheap http:/dcg.ethz.ch/publications/hotnets06.pdf,28,ReferenceIncentives Build Robu,
