1、Incentives Build Robustness in BitTorrent?Analysis on Bit Torrent Client performanceBy Jimmy Wong1Agenda Introduction BitTorrent Basics Bit Tyrant:A strategic client Bit Thief:A free-riding client Other Tricks of BT Client Real World Experiments Avoiding of Tricks Conclusion2Introduction BitTorrent
2、core incentive Upload More,Download More Problem Definition I am a selfish user Can I gain without pay/pay less?3BitTorrent Basics Step 0 Publishing Content Create Torrent file Tracker URL SHA-1 Hash Checksum Assign a Tracker Distribute Torrent to users through Web Site,Newsgroup or Forum4BitTorrent
3、 Basics Step 1 Joining Peers get the Torrent Connect to Tracker Look for available peers DHT(Distributed Hash Table)Create connection with other peers Start with Others Optimistic Unchoking Look for better peers Let other peers join the swarm5BitTorrent Basics Step 2 to N-1 Pipelining Exchange bitma
4、p about which chunks are available Pay more,get more To build incentive for peers to upload Reciprocal Rarest first To preserve File completeness among the swarm To build up peers reputation6BitTorrent Basics Choking Send data to only few good peers Contribute data to you Have pieces that you wants
5、A resourceful peers It will be nice if I can pay minimal cost to be un-choke!7BitTorrent Basics Optimistic Un-choking Allow new peers to get some pieces for exchange Allow discovery of better exchanging partners Most peers are so friendly I can gain without contribute!8BitTorrent Basics Ending Phase
6、 Toward the end of download Request for missing pieces Search for available peers 20-30 pieces left9Bit Tyrant:A strategic client Incentive 100KB/s 15KB/s 1%drop 15KB/s 10KB/s 40%drop About 1.9Mbps World Wide Bandwidth http:/ Why do I still need to give u so much?10Bit Tyrant:A strategic client Reso
7、urce Management Bandwidth fixed#Conn x Speed=Constant Current Official BT Protocol(#of Leecher Even better Gain from both methodology17Other Tricks of BT Client Client Discrimination Higher priority for Similar Client Delibrately choke other client Pretend to be Local Neighbor Fake tracker with wron
8、g upload rate Retrieve from Seed Rapid Disconnect and Reconnect Hope to gain from optimistic unchoking Remove from black-list Multiple Connection to the same client For high speed BB Gain the most from the same client18Experiment with BT Client Testing Environment Athlon 64 2800+1GB Ram 120GB 7200 r
9、pm HDD Windows XP SP2 w/TCP Conn Crack BT Software Utorrent/Mainline Bit Comet Bit Tryant iCable internet Connection19Experiment with BT Client Gentoo AMD 64 Minimal ISO 54.4MB 34 Seeders,0 Leechers Ubuntu 7.10 i386 Desktop ISO 695MB 928 Seeders/78 Leechers NBA Match 921MB 120 Seeders,714 Leechers20
10、Experiment with BT ClientGentooUploadTimeAvg SpeedKB/sConn PeerSeed/LeechBit Comet018:4050.6510/0uTorrent017:0155.6212/0Bit Tyrant015:0462.7516/021Experiment with BT ClientUbuntuUploadTimeAvg SpeedKB/sConn PeerSeed/LeechBit Comet32MB15:20773.5775/70uTorrent112KB69:13171.3736/1Bit Tyrant100KB26:28448
11、.1640/122Experiment with BT ClientNBAUploadTimeAvg SpeedKB/sConn PeerSeed/LeechBit Comet1070MB52:3229911/53uTorrent1035MB1:42:501527/29Bit Tyrant540MB1:20:1019610/2223Experiment with BT Client Bit Thief Achieve a high download rate(150KB/s)for Ubuntu and NBA Suck at 25%24Avoiding Tricks Target Stop
12、Fake Information Identify Free-riding Difficulties Bit Torrent is so wide spread Too many implementations Incentive driven works again!Co-operative identify bad client Block bad peers,Share with good peers25Avoiding Tricks Sharing with Peers Search for local optimal best peers Search for potential b
13、ad peers Broadcast of bad peers(In a majority basics)It will fail if more than half of clients are in-honest26Conclusion BT Robustness Most peers are friendly Ways to Crack Gain from cracking the protocol Bit Tyrant:Download Upload Bit Thief:Free Riding Proposed Solution Decentralized Client Solution27Reference Incentives Build Robustness in BitTorrent http:/www.bittorrent.org/bittorrentecon.pdf Do incentives build robustness in BitTorrent?http:/www.cs.washington.edu/homes/piatek/papers/BitTyrant.pdf Free Riding in BitTorrent is Cheap http:/dcg.ethz.ch/publications/hotnets06.pdf28
