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Application, Network, and Link Layer
Measurements of Streaming Video
over a Wireless Campus Network
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Group Members:
Berk BerkerEmrah BayraktarogluS. Tuncer ErdoganMustafa Omer KilavuzErkan Okuyan
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I. Introduction (The Reason)The Reason for the Expectations about
Streaming Video:• Decrease in price of W-LAN AP’s• Increase in wireless link capabilities up to
54 Mbps
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I. Introduction (The Problem)The problem is all about:• RealNetworks & Windows Streaming Media
make decisions, but it is unclear that:– Frame Lost Rate?– Signal Strength?– Link Layer Bitrate?
are more important?
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I. Introduction (4 Hypothesis)This measurements study considers:i. W-LANs make it difficult for streaming
video to gracefully adapt when network conditions degrade.
ii. Multiple level encoding can stream better than videos encoded with only a single level when W-LAN conditions are poor.
iii. TCP is more effective than UDP.
iv. Current available estimation techniques for capacity are inadequate for W-LAN
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II. Methodology (Tools)1. Application Layer:• Media Tracker collects application layer
data specific to streaming video including:– Encoding data rate– Playout bitrate– Time spend buffering– Video frame rate– Video frames lost– Video frames skipped– Packets lost– Packets recovered
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II. Methodology (Tools)2. Network Layer:• UDP Ping measures:– Round-Trip time (?)– Packet loss rate along the stream flow
path
by providing:
– Constant ping rates– Configurable ping intervals in
milliseconds– Configurable ping packet sizes
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II. Methodology (Tools)3. Wireless Data Link Layer:• WRAPI library was enhanced to collect
information about:– Signal strength– Frame retransmission counts and
failures– The specific W-AP that handles the
wireless last hop to the client
• Typeperf collects:– Processor utilization– Various network data
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II. Methodology (Experiment)Experiments are done with hardware:• Windows Media Server• Windows Media Service v9.0• Dell laptop (Centrino Mobile CPU, Windows
XP SP1, IEEE 802.11g Wireless Network Adapter)
• Airspace APs, providing IEEE 802.11a/b/g wireless service.
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II. Methodology (Experiment)Experiments are done with videos of:• Two Video Clips: Coast Guard & Paris (Both
352x288 resolution & 30 frames per second, two minutes long)– Coast Guard: High Motion (5.4% skipped macro
blocks)– Paris: Low Motion (41.2% skipped macro blocks)
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II. Methodology (Experiment)Experiments are done with:• Single-Level version of videos encoded at
2.5 Mbps to stress the wireless link• Multiple-Level version including 11
encoding layers• Streamed using TCP & UDP for comparison
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II. Methodology (Experiment)Campus Network Map:
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II. Methodology (Design)Experiments done:• Downloading a large file with wget
– To estimate the effective throughput of a TCP bulk transfer
• 2 clips x 2 versions x 2 transport protocols• A final bulk download• UDP pings to determine round-trip time and
package lost– 200 milliseconds apart– 1350-byte packets for single level video– 978-byte packets for multiple level video
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II. Methodology (Design)Experiments done:• Five times x Three distinct locations x
Three floors in the CS department
= 45 experimental results
= 360 video streams
• Locations: Three laptop in good, fair, and bad reception locations
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III. RESULTS• Collected data is:
• No significant statistical difference between the high-motion and the low-motion video.
• High-motion and low-motion does not have a significant effect on wireless network performance.
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Categorization
• There is a “cliff” between signal strengths -70 and -80 dBm
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Categorization
• From now on, experiments are categorized in one of the regions: “Good”, “Edge” or “Bad”
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First Analysis: Single-Level vs. Multi-Level Encoding
• Multi-Level or Single-Level Encoded
• Streaming of single and multi-level encoded videos are compared according to their average frame rate in “Good” and “Bad” locations.
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Single-Level vs. Multi-Level
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Single-Level vs. Multi-Level
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Single-Level vs. Multi-Level
• In a Good location, number of encoded levels have a very little effect, since the stream does not have to be scaled to a lower bitrate.
• In a Bad location, for the 2/3 of the time, multiple level stream has a higher frame rate than the single level one. (22 fps to 11 fps on average)
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TCP Streaming Over UDP Streaming
• In good wireless locations, TCP streaming and UDP streaming have almost the same performance
• In bad wireless locations choosing one of them has significant impact on performance
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TCP Streaming Over UDP Streaming
• In bad wireless locations choosing TCP Streaming(24fps) provides better frame rate than the UDP(15fps) streaming
• TCP Streaming also have lower coefficient of variation of frame rate than the UDP Streaming
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TCP Streaming Over UDP Streaming
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TCP Streaming Over UDP Streaming
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TCP Streaming Over UDP Streaming
• TCP Streaming has better frame rates because TCP retransmits the data
• But, Without Built-in retransmissions,UDP does not recover the lost data, so loss rates occur
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TCP Streaming Over UDP Streaming
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TCP Streaming Over UDP Streaming
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TCP Streaming Over UDP Streaming
• UDP uses a high data rate to fill the playout buffer
• AP queue grows long and AP cannot drain the queue, because wireless layer capacity is limited.
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TCP Streaming Over UDP Streaming
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TCP Streaming Over UDP Streaming
• TCP may have longer play out than the UDP for the same length of video
• Because in TCP, retransmissions take a lot of time
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TCP Streaming Over UDP Streaming
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The Challenges of Streaming over Wireless
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TCP-Friendly Capacity
• s = packet size• R = round-trip time• p = packet drop rate
• trto = TCP retransmission timeout
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Average Application Encoding Rate versus Wireless Capacity for TCP and UDP Streams
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Average Application Encoding Rate versus TCP-Friendly Capacity for TCP and UDP Streams
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Average Application Encoding Rate versus Wireless Capacity for Multiple and Single Level Stream
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Average Application Encoding Rate versus TCP-Friendly Capacity for Multiple and Single Level Stream
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Conclusion (4 Hypothesis) Revisited This measurements study considers:i. W-LANs make it difficult for streaming
video to gracefully adapt when network conditions degrade.
ii. Multiple level encoding can stream better than videos encoded with only a single level when W-LAN conditions are poor.
iii. TCP is more effective than UDP.
iv. Current available estimation techniques for capacity are inadequate for W-LAN
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Improvement Areas1. Identifying and adapting to
challenging wireless transmission situations.
2. Understanding packet and frame burst loss behavior.
3. Effective media scaling
4. Real Media and Quick Time researches.
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End of Presentation
Questions?