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Application, Network, and Link Layer

Measurements of Streaming Video

over a Wireless Campus Network

Group Members:

Berk BerkerEmrah BayraktarogluS. Tuncer ErdoganMustafa Omer KilavuzErkan Okuyan

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

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?

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

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

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

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

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.

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)

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

II. Methodology (Experiment)Campus Network Map:

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

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

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.

Categorization

• There is a “cliff” between signal strengths -70 and -80 dBm

Categorization

• From now on, experiments are categorized in one of the regions: “Good”, “Edge” or “Bad”

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.

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)

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


• 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




• 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




• 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.



• TCP may have longer play out than the UDP for the same length of video

• Because in TCP, retransmissions take a lot of time


The Challenges of Streaming over Wireless

TCP-Friendly Capacity

• s = packet size• R = round-trip time• p = packet drop rate

• trto = TCP retransmission timeout

Average Application Encoding Rate versus Wireless Capacity for TCP and UDP Streams

Average Application Encoding Rate versus TCP-Friendly Capacity for TCP and UDP Streams

Average Application Encoding Rate versus Wireless Capacity for Multiple and Single Level Stream

Average Application Encoding Rate versus TCP-Friendly Capacity for Multiple and Single Level Stream

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

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.

End of Presentation

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