Realistic Media Streaming over BitTorrent George Xylomenos Mobile Multimedia Laboratory Greece Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory.
Download ReportTranscript Realistic Media Streaming over BitTorrent George Xylomenos Mobile Multimedia Laboratory Greece Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory.
Realistic Media Streaming over BitTorrent George Xylomenos Mobile Multimedia Laboratory Greece Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory Outline • • • • • • • • • Context Motivation Advantages Streaming over BitTorrent Experimental setup Number of stall periods Average stall duration Download and seeding time Conclusion Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory Context • The ICT PURSUIT Project – The Internet mostly disseminates data – Publish-Subscribe Internet Technology – Clean slate approach to Future Internet • What does that have to do with BitTorrent? – PURSUIT was motivated by content distribution – BitTorrent is the perfect benchmark for this! – Now if we only had a good BitTorrent simulator… Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory Motivation • Why a BitTorrent simulator? – BitTorrent swarms exhibit very complex behavior • Many mechanisms and strategies are at play – Traces are hard to gather and understand • Fully distributed systems are hard to monitor – Performance predictions are simply guesses • What happens when we modify a strategy? – Existing simulators were not detailed enough • Some omit large parts of the protocol • Others only work over abstract networks • Most are custom-built and hard to extend Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory Advantages • Why bother with our simulator? – It operates over the OMNeT++ platform • You can use it with everything available for OMNeT++ • Example: OMNeT++ supports two types of network – InetUnderlay: hosts with full TCP/IP stacks – SimpleUnderlay: simple and fast abstract hosts – It incorporates nearly all BitTorrent details • All policies and options are present and tunable • If something is missing, feel free to add it! – Extra features that simplify simulations • Asymmetric links, churn model, GT-ITM topologies – To probe further – K. Katsaros, V. Kemerlis, C. Stais, and G. Xylomenos, A BitTorrent module for the OMNeT++ simulator, IEEE MASCOTS, 2009 Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory Streaming over BitTorrent • A case in point: Streaming over BitTorrent – A download window favors “sequential” downloads – Window moves on playback or piece download • If a piece is not available for playback, the player stalls – Three different proposals exist, but… • Undocumented simulation setups • Different evaluation metrics • Retransmissions and congestion are ignored – This paper avoids all these problems • Realistic simulations with the same assumptions – To probe further – C. Stais, G. Xylomenos, and A. Archontovasilis, A comparison of streaming extensions to BitTorrent, IEEE ISCC, 2011 Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory Streaming over BitTorrent • Fixed-Size Window (FSW) – Fixed sliding window from first non-available piece – Rarest-first only within the window • High-Priority Set (HPS) – Fixed size window of non-downloaded pieces – Download outside the window with probability 1-p • Stretching Window (SW) – Also uses an HPS but only downloads inside it – Bounded distance between first and last piece Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory Streaming over BitTorrent Player Begin OK OK D 1 2 3 End OK OK 5 6 4 7 8 FSW Player Begin OK OK D 1 2 3 HPS 4 3478 End OK OK 5 6 7 8 HPS Player Begin OK OK D 1 2 3 HPS 4 347 End OK OK 5 6 7 8 SW Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory Experimental setup • Main parameters – Video: 200 MB @ 256 kbps (106 min) • 112 KB pieces (1 GOP = 3.5 seconds) – 4 core / 192 access routers – ADSL access links: Uplink 1-2 Mbps, Download 4-24 Mbps – 1 seeder and 120 peers, incremental joins • 50% of peers stay in the swarm until playback completes – Prefetch 1 or 5 pieces before playback – Window size 2% or 8% of file (36 or 147 pieces) – HPS probability 80% – SW limit 50 or 200 pieces – Two player modes • B1: the player stalls until the next piece completes • B2: the player stalls until the next three pieces complete Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory Number of stall periods 4.50 3.50 HPS: 1p & 2% 4.00 HPS: 5p & 2% 3.50 HPS: 1p & 2% 3.00 HPS: 5p & 2% HPS: 1p & 8% HPS: 5p & 8% 3.00 HPS: 1p & 8% 2.50 HPS: 5p & 8% FSW: 1p & 2% 2.50 FSW: 5p & 2% 2.00 FSW: 1p & 8% FSW: 1p & 2% 2.00 FSW: 5p & 2% FSW: 1p & 8% 1.50 FSW: 5p & 8% 1.50 SW: 1p & 2% 1.00 SW: 5p & 2% 0.50 SW: 1p & 8% FSW: 5p & 8% SW: 1p & 2% 1.00 SW: 5p & 2% 0.50 SW: 1p & 8% SW: 5p & 8% 0.00 SW: 5p & 8% 0.00 • How many times will a user experience a stall? – 30% more when we stall only for a single piece (left) – In all cases, very few stalls for 100+ minutes – HPS is the worst performer, despite its complexity Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory Average stall duration 300.00 400.00 HPS: 1p & 2% HPS: 5p & 2% 250.00 HPS: 1p & 8% HPS: 1p & 2% 350.00 HPS: 5p & 2% 300.00 HPS: 1p & 8% HPS: 5p & 8% 200.00 FSW: 1p & 2% FSW: 5p & 2% 150.00 FSW: 1p & 8% FSW: 5p & 8% 100.00 HPS: 5p & 8% 250.00 FSW: 1p & 2% FSW: 5p & 2% 200.00 FSW: 1p & 8% 150.00 FSW: 5p & 8% SW: 1p & 2% SW: 5p & 2% 50.00 SW: 1p & 8% SW: 1p & 2% 100.00 SW: 5p & 2% SW: 1p & 8% 50.00 SW: 5p & 8% 0.00 SW: 5p & 8% 0.00 • How long does each stall last? – 30% more when we stall for three pieces (right) – Stall durations vary from noticeable to quite long – HPS is the worst by far with a larger window Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory Download and seeding time 4000.00 3000.00 HPS: 1p & 2% 3500.00 HPS: 5p & 2% 3000.00 HPS: 1p & 8% HPS: 5p & 8% 2500.00 HPS: 1p & 2% HPS: 5p & 2% 2500.00 HPS: 1p & 8% HPS: 5p & 8% 2000.00 FSW: 1p & 2% FSW: 5p & 2% 2000.00 FSW: 1p & 2% FSW: 5p & 2% 1500.00 FSW: 1p & 8% 1500.00 FSW: 5p & 8% SW: 1p & 2% 1000.00 FSW: 1p & 8% FSW: 5p & 8% 1000.00 SW: 1p & 2% SW: 5p & 2% SW: 1p & 8% 500.00 SW: 5p & 2% 500.00 SW: 1p & 8% SW: 5p & 8% 0.00 SW: 5p & 8% 0.00 • Download time: same for B1 and B2 – Better with HPS, but always lower than the video duration • Seeding time: same for B1 and B2 – Also better with HPS, as the download finishes earlier Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory Conclusion • Which scheme is best? – HPS leads to visibly worse user experience • More stalls with longer durations – FSW and SW are acceptable and very close • SW is not worth the extra complexity over FSW – FSW leads to 1-2.5 stalls of 40-60 seconds for 100+ minutes – The two buffering modes offer the expected tradeoff • Either fewer or longer stall periods • Future work – Explore additional parameters and tricks – Study individual peer performance Session 8b, 5th July 2012 Future Network & MobileSummit 2012 Copyright 2012 Mobile Multimedia Laboratory