Transcript ppt

Measuring Congestion
Responsiveness of Windows
Streaming Media
James Nichols
Thesis Presentation
PEDS - 12/8/03
Advisors:
Prof. Mark Claypool
Prof. Bob Kinicki
Reader:
Prof. David Finkel
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Network Impact of Streaming Media
• Unlike file transfer or Web browsing,
Streaming Media has specific bitrate
and timing requirements.
• Typically, UDP is the default network
transport protocol for delivering
Streaming Media.
• UDP does not have any end-to-end
congestion control mechanisms.
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The Dangers of Unresponsiveness
• Flows in the network which are
unresponsive to congestion can cause
several undesirable situations:
• Unfairness when competing with responsive
flows for limited resources
• Unresponsive flows can contribute to
congestion collapse
• Some Streaming Media applications use
UDP, but rely on the application layer to
provide adaptability to available capacity
• Performance of these application layer
mechanisms is unknown
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Intelligent Streaming
• Application layer mechanism of Windows
Streaming Media (WSM) to adapt to network
conditions
• Can “thin” streams by sending fewer frames
• If the content producer has encoded multiple
bitrates into the stream, IS can choose an
appropriate one
• Chung et al. suggests that technologies like IS
may provide responsiveness to congestion,
even TCP-friendliness
• Performance of Intelligent Streaming is
unknown
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Research Goals
• No measurement studies have been
completed where researchers had total
control over:
• The streaming server
• Content-encoding parameters
• Network conditions at or close to the server
• We seek to characterize the bitrate response
function of Windows Streaming Media in
response to congestion in the network.
• Want to precisely quantify relationship
between content encoding rate and
performance.
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Outline
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Introduction
Related Work 
Methodology
Results & Analysis
Conclusions
Future Work
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Related Work
• Some research has been done in the
general area of Streaming Media:
• Traffic characterization studies [VAM+02, dMSK02]
performed through log analysis
• Empirical studies using custom tools [CCZ03,
WCZ01, LCK02]
• Characterization of streaming content available
on the Web [MediaCrawler]
• None had control of the server, client, and
network conditions
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Need control over the server
• Not having server limits possible data
set of content to study
• For example, [LCK02], measured IP
packet fragmentation when streaming
WSM clips but packet size can be
tuned server-side
• Other research [CCZ03] had to stream
over the public Internet while
measuring network performance
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Outline
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Introduction
Related Work
Methodology

Results & Analysis
Conclusions
Future Work
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Methodology
•Construct testbed
•Examine SBR clip
•Create/adapt tools
•Range of SBR clips
•Encode content
•MBR clips
•Systematic control
•Vary loss and latency
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Results and Analysis
Single Bitrate Clip
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Experiments
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Single bitrate (SBR) clip in detail
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Range of SBR clips
Multiple bitrate (MBR) clips
Additional experiments performed but
not discussed here
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Single Bitrate Clip Experiment
• Hypothesis: SBR clips are unresponsive
to congestion
• Latency: 45 ms
• Induced loss: 0%
• Bottleneck capacity: 725 Kbps
• Start a TCP flow through the link
• 10 Seconds later stream a WSM clip
• Measure achieved bitrates and loss rates
for each flow
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340 Kbps Clip - Bottleneck Capacity 725 Kbps
TCPFriendly?
< 0.001 packet loss
After 15 seconds
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548 Kbps Clip - Bottleneck Capacity 725 Kbps
Not
TCPFriendly!
~ 0.003 packet loss for WSM
~ 0.006 packet loss for TCP
after 15 seconds
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1128 Kbps Clip - Bottleneck Capacity 725 Kbps
Responsive!
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Network Topology
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Measuring Buffering Performance
• Parse packet capture for
RTSP PLAY message
• Examine MediaTracker
output and measure how
long it took from the start
of streaming to when the
buffer is reported to be
full
• PLAY + interval =
buffering period
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Experiments
• SBR clip in detail
• Range of SBR clips
• MBR clips

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Comparison of Single Bitrate Clips
• Want to precisely quantify relationship
between content encoding rate and
performance
• Repeat the previous experiment, but for a
range of single bitrate clips:
• 28, 43, 58, 109, 148, 282, 340, 548, 764, 1128 Kbps
• Vary network capacity: 250, 750, 1500
Kbps
• Measure performance during and after
buffering
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SBR Clips - Bottleneck Capacity 725 Kbps
Buffering Period
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SBR Clips - Bottleneck Capacity 725 Kbps
Playout Period
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Results and Analysis
Multiple Bitrate Clips
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Multiple Bitrate Clips
• Hypothesis: Multiple Bitrates make WSM
more responsive to congestion
• Same experiment as before, but with
different encoded content
• Vary network capacity: 250, 725, 1500
Kbps
• Created two sets of 10 multiple bitrate
clips
• Experiments with lots of other MBR clips
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Multiple Bitrate Content
• First set of clips
(adding lower):
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1128 Kbps
1128-764 Kbps
1128-764-548 Kbps
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1128-764-548-340282-148-109-58-4328 Kbps
• Second set of clips
(adding higher):
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28 Kbps
28-43 Kbps
28-43-56 Kbps
…
28-43-58-109-148282-340-548-7641128 Kbps
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Adding lower bitrates to clip - 250 Kbps
Bottleneck Capacity - Buffering Period
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Adding lower bitrates to clip - 250 Kbps
Bottleneck Capacity - Playout Period
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Adding lower bitrates to clip - 725
Kbps Bottleneck Capacity
Buffering
Playout
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Adding higher bitrates to clip 725 Kbps Bottleneck Capacity
Buffering
Playout
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Additional experiments
• Not enough time to discuss all the results
• Different bottleneck capacities
• Carefully choose 2 or 3 bitrates to include
in MBR clips
• Vary loss rate
• Vary latencies
• Also look at other network level metrics:
interarrival times, burst lengths, and IP
fragmentation
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Conclusions
• Prominent buffering period means WSM
cannot be modeled as a simple CBR flow
• WSM single bitrate clips:
• During buffering WSM responds to capacity
only when the encoding rate is less than
capacity
• Otherwise, high loss rates are induced
• During playout WSM responds to available
capacity
• Thin if necessary
• If rate is less then capacity, will still be responsive to
high loss rates (5%)
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Conclusions
• WSM multiple bitrate clips:
• During buffering WSM responds to capacity
only when content contains a suitable bitrate to
choose
• Chosen bitrate is largest that capacity allows
• Otherwise, still tries to fit the smallest available,
again resulting in high amounts of loss
• During playout WSM is responsive to available
capacity
• Either because it chose the proper rate, or because it
thins if proper rate isn’t encoded in clip
• However, the chosen bitrate probably isn’t fair to
TCP
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Future Work
• Run the same experiments with other
streaming technologies: RealVideo
and Quicktime
• Examine the effects of different
content types
• Build NS simulation model of
streaming media for use in future
research
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Questions
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