Designing a new BitTorrent Client Improving BitTorrent Designing a new BitTorrent Client 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Overview How BitTorrent Works Experimental Analyses Modeling: Gittins’ Indices Our New Algorithms Proposed Evaluation HELP! 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science File Organization File 1 2 3 4 Piece 256KB Block 16KB Incomplete Piece 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Initialization HTTP GET MYFILE.torrent http://mytracker.com:6969/ S3F5YHG6FEB FG5467HGF367 F456JI9N5FF4E … MYFILE.torrent webserver “register” ID1 169.237.234.1:6881 ID2 190.50.34.6:5692 ID3 34.275.89.143:4545 … ID50 231.456.31.95:6882 list of peers user tracker Peer 40 … Peer 1 Peer 2 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science “On the Wire” Protocol (Over TCP) Non-keepalive messages: 0 – choke 1 – unchoke 2 – interested 3 – not interested 4 – have 5 – bitfield 6 – request 7 – piece 8 – cancel 1 ID/Infohash Handshake BitField BitField Remote Peer Local Peer Interested = 0 choked = 1 Interested = 0 choked = 1 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Piece Selection Pipelining (5 requests) Strict Priority 3 stages: Random first piece Rarest First Endgame mode 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Peer Selection Focus on Rate Upload to at most 4 peers Random Unchoke Global rate cap only 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Analyses N. Liogkas et al., “Exploiting BitTorrent For Fun (But Not Profit)”, IPTPS 2006. A. Legout et al., “Rarest First and Choke Algorithms Are Enough”, June 2006 A. R. Bharambe et al. “Analyzing and Improving BitTorrent Performance”, Feb 2005. 11/16/2018 Dimitri DeFigueiredo – Computer Science

Exploitation – Liogkas et al. PlanetLab & Real Torrent Exploits: Download only from seeds Median improvement of 7-20% Download only from fastest peers Contradictory results: good in PlanetLab (+22%) bad in the wild(-1 to -30%) Advertise false pieces 22% better download rates 11/16/2018 Dimitri DeFigueiredo – Computer Science

Piece Selection – Legout et al. 11/16/2018 Dimitri DeFigueiredo – Computer Science

Piece Selection – Legout et al. a = local peer interested in remote peer b = time peers are connected c = remote peer interested in local peer 11/16/2018 Dimitri DeFigueiredo – Computer Science

Piece Selection – Legout et al. Limitations: In 25% of the torrents the local peer is not interested. Who is interested in me? 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Gittins Indices The Two-armed bandit problem Same prize Unknown winning probabilities Known discount factor Limitation: Infinitely discounted or fixed horizon Projects remain dormant One project at a time P. Whittle 1988 Restless bandits m projects “on average” Asymptotically optimal for large m and n 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Piece Selection Key ideas: We don’t care about piece selection Keep download pipes full Peer Queues Assume: We receive pieces at a rate of 1 per second 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Piece Selection 5 6 7 1 2 3 4 – 1 2 3 4 5 6 7 Remote Peer Local Peer 1 2 3 4 5 6 7 1 3 6 5 6 7 1 2 3 4 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Piece Selection 3 1 Q1 Peer 1 1 3 6 Q2 Remote Peer Peer 2 Local Peer 4 Q3 Peer 3 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Piece Selection Cost of empty queue = Ci per unit time Discount factor d <1 Piece consumption rate li (Poison Process) Queue has length li(t) 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Piece Selection Minimize: where We can Solve this with Gittins’ Indices! 11/16/2018 Dimitri DeFigueiredo – Computer Science

Piece Selection Algorithm (alpha version) Calculate Gittins’ Index for each queue: Feed the queue with the highest index. Two Problems: 1 piece goes into many queues it takes a while to get the pieces 11/16/2018 Dimitri DeFigueiredo – Computer Science

Piece Selection Algorithm (beta version) Calculate Gittins’ Index for each queue: Calculate Gittins’ index for each piece. n(piece) = SA Get piece with highest index possible. 11/16/2018 Dimitri DeFigueiredo – Computer Science

Piece Selection Algorithm highest index 7 Peer 1 7 5 2 Peer 2 2 lowest index 5 Peer 3 time 11/16/2018 Dimitri DeFigueiredo – Computer Science

Piece Selection Algorithm (Final Release) Calculate Gittins’ Index for each queue. Calculate “Gittins’ index” for each piece. Extrapolate piece download finishing time. Order finishing times (earliest first). Order pieces (highest index first). Match best piece with earliest finishing time. 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Peer Selection Key Ideas: upload rate is a perishable good Throttle each connection individually Do not limit number of downloaders to 4 11/16/2018 Dimitri DeFigueiredo – Computer Science

Peer Selection – Our Model Series of rounds E[download rate] = f(upload rate) Estimate download rates with “have”. 11/16/2018 Dimitri DeFigueiredo – Computer Science

Peer Selection Algorithm Keep clients with best ratios. Throttle to estimated safe bound. Solve Knapsack problem: Total upload bandwidth = max weight Item value = download rate we are getting Item weight = estimated upload bound If download/upload rate ratio is < 1 Random unchoke 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Evaluation Simultaneously Identical machines and network. Repeat experiment and swap clients. Different torrents vs. 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science HELP! What we need: An awesome python programmer ;0) What’s in it for you: We are cool! ;0) Publications Open Source Real Estate… 11/16/2018 Dimitri DeFigueiredo – Computer Science

Dimitri DeFigueiredo – Computer Science Thank you! defigued@cs.ucdavis.edu 11/16/2018 Dimitri DeFigueiredo – Computer Science