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Confused, Timid and Unstable: Picking a Video Rate is Hard

Confused, Timid and Unstable: Picking a Video Rate is Hard. Te-Yuan (TY) Huang Stanford University Nov 15 th , 2012 Joint work with Nikhil Handigol , Brandon Heller, Nick McKeown , Ramesh Johari. Video is the BIG thing on the Internet. Video is more than 50% of peak traffic in the US

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Confused, Timid and Unstable: Picking a Video Rate is Hard

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  1. Confused, Timid and Unstable:Picking a Video Rate is Hard Te-Yuan (TY) Huang Stanford University Nov 15th, 2012 Joint work with Nikhil Handigol, Brandon Heller, Nick McKeown, RameshJohari

  2. Video is the BIG thing on the Internet • Video is more than 50% of peak traffic in the US • Trend: Streaming over HTTP • Content Distribution Networks (CDNs) • Well-provisioned HTTP servers at the edge of the Internet • Cheap (2-3 cents per GB in 2011) • Firewall friendliness Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  3. Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  4. Before download started Afterdownload started Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  5. What happened? • Both the download and video are over HTTP • TCP shares my home link equally among all flows What is the problem? Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  6. Experiment Setup CDN 1 The Internet CDN 2 CDN 3 Bandwidth Controller Content Distribution Networks Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  7. Video Ratein the Presence of a Competing Flow Video Flow Throughput Competing Flow Throughout Fair share Steps down all the way to the lowest quality Video Rate Available Video Rates Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  8. What If We Manually Select a Video Rate? Video Flow Throughput Video keeps playing without any problem Video Rate Available Video Rates Manually select 1750kb/s Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  9. What If We Manually Select a Video Rate? Competing Flow Throughput Competing flow throughput is brought down Video Flow Throughput Video Rate Available Video Rates Manually select 1750kb/s Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  10. Not Just One Service’s Problem • This happens in all the services we measured • Hulu, Netflix, Vudu Video Rate Video Rate Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  11. The Problem Video client ends up with much less throughput than its fair share It picks a video rate that is much too low Why? Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  12. Outline • How does rate selection over HTTP work? • The rate selection process • Where does it go wrong? • The complete story • Conclusion Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  13. How Does Rate Selection over HTTP Work? 1750 1750 File 1: 1050 1050 1050 Get File 1 (1750kb/s) File 2: The Internet CDN 3 PlayoutBuffer Client Rate selection logic resides at client side Standard, commoditized HTTP Servers Serve the video with quality 1750kb/s Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  14. The Rate Selection Process Bandwidthestimation Initial video rate Download& measure Pick a rate Video rate for the next video segment What goes wrong? Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  15. The Rate Selection Process Bandwidthestimation Initial video rate Download& measure Pick a rate Video rate for the next video segment Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  16. TCP Throughput of the Video Flow Playout Buffer is Full TCP Throughput OFF Period: 1-2 seconds Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  17. Impact of OFF period on TCP • TCP sender resets its congestion window • When idle more than one RTO (200ms) • Slow-start restart, RFC 2581/5681 • Linux 3.x (tcp_output.c, line 163) • Throughput will be affected • Worse with a competing flow • Experience packet loss during slow start 50% of the segments get < 1.8Mb/s (Fair Share is 2.5Mb/s) Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  18. The Rate Selection Process Bandwidthestimation Initial video rate Underestimation Download& measure Pick a rate Video rate for the next video segment If perceived 1.8 Mb/s, which video rate would it pick? Even lower? 1750 kb/s? 1400 kb/s? Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  19. Conservative Rate Selection Available BW If 1.8Mb/s BW is perceived,the client switches down to1050kb/s video rate Video Rate Te-Yuan (TY) Huang @ ACM IMC'12, Boston 19

  20. The Rate Selection Process Bandwidthestimation Initial video rate Underestimation Download& measure Pick a rate Conservatively Video rate for the next video segment Is there any consequence of being conservative? Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  21. Smaller Segment Size for Lower Video Rate When requesting a smaller segment size, lower probability of obtaining fair share. Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  22. Lower video rate leads to further bandwidth underestimation Lowest Video Rate Highest Video Rate Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  23. The Rate Selection Process Further Bandwidthestimation Initial video rate Underestimation Download& measure Pick a rate Conservatively Video rate for the next video segment Request for a smaller segment Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  24. The Complete Story Bandwidth Underestimation Video Quality Conservatism Further Underestimation Te-Yuan (TY) Huang @ ACM IMC'12, Boston

  25. Conclusion • The problem: Video flow gets a much lower throughput than its fair share • Problem occurred in all the services we measured • The reason: Video client tries to do TCP’s job • It is afraid of causing network congestion • It becomes timid • It tries to figure out its available bandwidth • Without seeing the interaction between the playout buffer, segment sizes and TCP dynamics • It is easily confused and becomes unstable • One service provider changed its algorithm because of this work Te-Yuan (TY) Huang @ ACM IMC'12, Boston

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