Confused, Timid, and Unstable: Picking a Video Streaming Rate is - PowerPoint PPT Presentation

Confused, Timid, and Unstable: Picking a Video Streaming Rate is Hard Five students from Stanford • Published in 2012 • ACM’s Internet Measurement Conference (IMC) • 23 citations • Ahmad Tahir 1/26

o Problem o Background Knowledge o Research Motivation o Experimental Setup o First Results The streaming video quality deteriorates when another competing flow for a o Downward Spiral limited bandwidth starts. o Intervention Maintaining a careful balance between: o Before, After  not wanting to cause a re-buffer  not wanting to deliver unnecessarily low quality 2/26

o Problem Typical HTTP streaming setup o Background Knowledge Client must pick what to request • o Research Motivation o Experimental Setup Careful balance for user satisfaction • o First Results o Downward Spiral o Intervention o Before, After 3/26

 Problem How well do they pick what to request?  Background Knowledge o Research Motivation o Experimental Setup o First Results o Downward Spiral o Intervention o Before, After 4/26

It’s bad Maximum:5 Mb/s Fair Share: 2.5 Mb/s Optimal: 1.75 Mb/s Used: 235 kb/s What makes this so difficult? 5/26

 Problem Services are similar - not identical  Background Knowledge  Research Motivation Ways to stream HTTP video: o Experimental Setup Web browser vs. PS3 • o First Results o Downward Spiral Single connection vs. many • o Intervention Entire file vs. chunks • o Before, After 6/26

Implementation Details 7/26

Network Parameter Controls NetFPGA rate limiter: 5 MB/s Competing flow: same file, same CDN, simple TCP file download 8/26

 Problem No surprises - they’re terrible  •  Background Knowledge Repeated 76 times over four days •  Research Motivation  Experimental Setup 91% of cases failed predictably • o First Results o Downward Spiral o Intervention o Before, After 9/26

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Sanity Check? 11/26

 Problem Follow the spiral down  Background Knowledge  Research Motivation Monitor everything:  Experimental Setup TCP throughput  First Results • o Downward Spiral Buffer size • o Intervention Request interval • o Before, After Congestion window • Where do these algorithms go wrong? 12/26

Client Network Behavior 13/26

TCP Congestion Window • Times out in 4s OFF period • Reset to initial value of 10 packets, every time • Single persistent connection • Ramp up from slow start for each segment anyway • No competing flow? No problem 14/26

Completely Squashed 15/26

Rational Behavior 16/26

A More Complete Picture • Playback buffer fills – starts periodic ON-OFF • During OFF period: • Video stream congestion window idle resets • Competing flow is still going, filling the routers buffer • ON period starts: • Very high initial packet loss • Estimate artificially low bandwidth • Lower playback rate 17/26

The “Spiral” Part • ON period starts: • Very high initial packet loss • Estimate artificially low bandwidth • Lower playback rate – which means shorter segments • Each estimate is ever lower than the previous • Spiral down until you can’t play lower quality 18/26

Another Thing - Timing 19/26

 Problem Mimic Service A  Background Knowledge  Research Motivation  Experimental Setup  First Results  Downward Spiral o Intervention o Before, After 20/26

Less Conservative • Service A ~40% • Try out 10% 21/26

Better Filtering • Service A: ten sample moving average • Try: 80 th percentile 22/26

Finally: Bigger Segments 23/26

 Problem  Background Knowledge  Research Motivation  Experimental Setup  First Results  Downward Spiral  Intervention o Before, After 24/26

To Conclude • On the one hand, there are changes to how the client estimates bandwidth which can improve its interplay with TCPs congestion control • A more radical solution: • Don’t attempt to estimate bandwidth at all • Competing goals: highest bitrate, and no underruns • Goal is NOT “keep the buffer full” • Goal is “don’t let the buffer get empty” • Increase the playback bitrate when the buffer is high • Decrease the playback bitrate when the buffer is low • Perfect layer of separation: • TCP responsible for delivering fair share bandwidth • Video player responsible for showing the highest rate it can 25/26

Questions Thank you for listening 26/26