Measuring Congestion Responsiveness of Windows Streaming Media

1
Measuring Congestion Responsiveness of Windows
Streaming Media
James Nichols
Advisors Prof. Mark Claypool Prof. Bob
Kinicki Reader Prof. David Finkel
Thesis Presentation PEDS - 12/8/03
2
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.

3
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

4
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

5
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.

6
Outline

• Introduction
• Related Work ?
• Methodology
• Results Analysis
• Conclusions
• Future Work

7
Related Work

• Some research has been done in the general area
  of Streaming Media
• Traffic characterization studies VAM02, 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

8
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

9
Outline

• Introduction
• Related Work
• Methodology ?
• Results Analysis
• Conclusions
• Future Work

10
Methodology

• Construct testbed
• Create/adapt tools
• Encode content
• Systematic control

• Examine SBR clip
• Range of SBR clips
• MBR clips
• Vary loss and latency

11
Results and Analysis

• Single Bitrate Clip

12
Experiments

• Single bitrate (SBR) clip in detail ?
• Range of SBR clips
• Multiple bitrate (MBR) clips
• Additional experiments performed but not
  discussed here

13
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

14
340 Kbps Clip - Bottleneck Capacity 725 Kbps
TCP- Friendly?
lt 0.001 packet loss After 15 seconds
15
548 Kbps Clip - Bottleneck Capacity 725 Kbps
Not TCP- Friendly!
0.003 packet loss for WSM 0.006 packet loss
for TCP after 15 seconds
16
1128 Kbps Clip - Bottleneck Capacity 725 Kbps
Responsive!
17
Network Topology
18
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

19
Experiments

• SBR clip in detail
• Range of SBR clips ?
• MBR clips

20
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

21
SBR Clips - Bottleneck Capacity 725
KbpsBuffering Period
22
SBR Clips - Bottleneck Capacity 725 KbpsPlayout
Period
23
Results and Analysis

• Multiple Bitrate Clips

24
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

25
Multiple Bitrate Content

• First set of clips (adding lower)
• 1128 Kbps
• 1128-764 Kbps
• 1128-764-548 Kbps
• 1128-764-548-340-282-148-109-58-43-28 Kbps

• Second set of clips (adding higher)
• 28 Kbps
• 28-43 Kbps
• 28-43-56 Kbps
• 28-43-58-109-148-282-340-548-764-1128 Kbps

26
Adding lower bitrates to clip - 250 Kbps
Bottleneck Capacity - Buffering Period
27
Adding lower bitrates to clip - 250 Kbps
Bottleneck Capacity - Playout Period
28
Adding lower bitrates to clip - 725 Kbps
Bottleneck Capacity
Buffering
Playout
29
Adding higher bitrates to clip - 725 Kbps
Bottleneck Capacity
Buffering
Playout
30
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

31
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)

32
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 isnt encoded in
  clip
• However, the chosen bitrate probably isnt fair
  to TCP

33
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

34
Questions