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Internet Streaming Media Delivery:
Zhen Xiao
Joint work with Lei Guo, Enhua Tan, Songqing Chen, Oliver Spatchcheck, and Xiaodong Zhang
Delving into
A quality and Resource Utilization Perspective
ACM SIGCOMM Internet Measurement Conference (IMC'06), October 2006
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Multimedia on the Internet
• Education and research
• News media
• Entertainment and gaming
• Advertisement
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Streaming Media
CDN/MDN
Streaming server
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Pseudo Streaming
HTTP
http://www.YouTube.com/http://video.google.com/
meta file
Web server
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Streaming Media
• Thousands of concurrent streams
• Flexible response to network congestion
• Efficient bandwidth utilization
• High quality to end users
• Challenges and techniques
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Existing Measurements
• Access pattern and user behaviors– A bunch of measurement studies– Server clusters, media proxies
• Streaming mechanism and delivery quality– Few studies
• Traffic volume …– Downloading > pseudo streaming > streaming
(WWW’05, cookie talk 2005)– P2P >> all other media delivery systems
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Our Measurement
• Investigate modern streaming services– The delivery quality and resource utilization
• Collect a large streaming media workload – From thousands of home users and business users– Hosted by a large ISP– Packet level instead of server logs
• Analyze commonly used streaming techniques– Automatic protocol switch– Fast Streaming– MBR encoding and rate adaptation
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Outline
• Traffic overview
• Protocol rollover
• Fast Streaming
• Rate adaptation
• Conclusion
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Traffic Overview
• User communities– Home user– Business user
• Media hosting services– Self-hosting– Third-party hosting
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Number of requests
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
Home user Busi ness user
audi ovi deo
Business users access more audio than home users
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On-demand media: File length
Business users tend to access longer audio/video files
Audio Video
pop songsmusic previews
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On-demand media: Playback duration
Business users tend to play audio/video longer
Audio Video
pop songs
music previews
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Live media: Playback duration
Business users tend to access live audio/video longer
Audio Video
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Traffic Overview
• User communities– Home user– Business user– Working environment affects access pattern
• Media hosting services– Self-hosting– Third-party hosting
News and entertainment sites
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Traffic Overview
• User communities– Business users tend to access streaming
media longer than home users– Working environment affects access pattern
• Media hosting services– Self-hosting– Third-party hosting
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Media hosting services
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Outline
• Traffic overview
• Protocol rollover
• Fast Streaming
• Rate adaptation
• Conclusion
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Protocol RolloverStreaming server
RTSP/UDP
RTSP/TCP
HTTP/TCP Embed RTSP commands in HTTP packets
Media player
Traffic volume:
UDP: 23%
TCP: 77%
HTTP: rare
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Protocol rollover time
Windows media service RealNetworks media service
Protocol rollover increases user startup time significantly
Startup latency = protocol rollover time + transport setup time + startup buffering time
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Protocol selection and rollover avoidance
• Most streaming traffic are TCP-based– The usage of NAT?– MMS clients report private IP address in clear text
• Home user: 98.3% report 192.168.*.*• Business user: 89.5% report 192.168.*.*
• Protocol rollover sessions are minor– Home user: 7.37%– Business user: 7.95%
• Most streaming sessions use TCP directly– Why?
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Protocol selection and rollover avoidance
• Windows media service– Specify the protocol in the media meta file
Use URL modifiers to avoid protocol rollover
Ex: rtspt://xxx.xxx.com:/xxx.wmv– More than 70%
• RealNetworks media service– NAT transversal techniques
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Outline
• Traffic overview
• Protocol rollover
• Fast Streaming
• Rate adaptation
• Conclusion
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Fast Streaming
• Fast Streaming: deliver media data “faster” than its encoding rate– Fast start– Fast cache– Fast recovery– Fast reconnect
• Always TCP-based
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Media objects delivered with Fast Cache(VoD home user workload)
File length Encoding rate
Fast Cache is more widely used for media files with longer length and higher encoding rate.
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Bandwidth Utilization
PLAY RTSP/1.0Bandwidth: 1.12 MbpsSpeed: 20.5
RTSP /1.0 200 OKSpeed: 5
Fast Cache Normal TCP
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Fast Cache smooth bandwidth fluctuation
Rebuffer ratio = rebuffer time / play time
Fast Cache
Normal TCP
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Fast Cache produces extra traffic
Most streaming sessions only request the initial part of a media object
Over supplied dataFast Cache: 55%
Normal TCP: 5%
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Server response time
Third party media service Self-hosting media service
DESCRIBE foo.wmv RTSP/1.0
RTSP /1.0 200 OKSDP
RTT
SRT
sniffer
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Server Load
Windows media load simulator
Windows Server 2003 Win XP
Server log
…
Ethernet
1 X 4 XSome CDNs/MDNs do not support Fast Cache at all
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Outline
• Traffic overview
• Protocol rollover
• Fast Streaming
• Rate adaptation
• Conclusion
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Rate Adaptation
96Kbps128Kbps320Kbps
… 1.128Mbps
Multiple-bit-rate encoding
Stream switch
WM: Intelligent streaming RM: SureStream
Stream thinning: deliver key frame only
Video cancellation
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MBR encoding
on-demand audio
live audio
audio stream in video objects
video stream in video objects
42% on-demand video are MBR encoded
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Stream switch
30 sec
60%
Streaming switch latency Low quality duration
3 sec
40%
Play-out buffer
Stream switch is often not smooth
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Stream thinning
30 sec
70%
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Fast Cache and stream switch
Do not work with each other: fewer stream switches than MBR encoded objects
playing buffering playing buffering bufferingplaying
5 sec
When network congestion occurs …
Like pseudo streaming
When rebuffer occurs
time
fill play-out buffer
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Streaming quality and playback duration
Home user business user
Longer duration sessions have higher prob. of quality degradation
Business user workload has more quality degradation
>100 sec
88%
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Streaming quality summary
The quality of media streaming on the Internet leaves much to be improved
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Coordinating caching and rate adaptation
• Fast Cache: aggressively buffer data in advance– Over-utilize CPU and bandwidth resources– Neither performance effective nor cost-efficient
• Rate adaptation: conservatively switch to lower bit rate stream– Switch handoff latency
• Coordinated Streaming
Upper boundPrevent aggressive buffering
Lower boundPrevent switch latency
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Coordinated Streaming
Rebuffering ratio Over-supplied data Switch latency
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Conclusion
• Quality of Internet streaming– Often unsatisfactory– Need to improve
• Modern streaming media services– Over-utilize CPU and bandwidth resources– Not a desirable way to improve quality
• Coordinated Streaming– Combine merits of both caching and rate adaptation– Simple but effective