Delving into
Internet Streaming Media Delivery:
A quality and Resource Utilization Perspective
Zhen Xiao
Joint work with Lei Guo, Enhua Tan, Songqing Chen, Oliver Spatchcheck, and
Xiaodong Zhang
ACM SIGCOMM Internet Measurement Conference (IMC'06), October 2006
1
Multimedia on the Internet
• Education and research
• News media
• Entertainment and gaming
• Advertisement
2
Streaming Media
Streaming server
CDN/MDN
3
Pseudo Streaming
Web server
http://www.YouTube.com/
http://video.google.com/
HTTP
meta file
4
Streaming Media
• Thousands of concurrent streams
• Flexible response to network congestion
• Efficient bandwidth utilization
• High quality to end users
• Challenges and techniques
5
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
6
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
7
Outline
• Traffic overview
• Protocol rollover
• Fast Streaming
• Rate adaptation
• Conclusion
8
Traffic Overview
• User communities
– Home user
– Business user
• Media hosting services
– Self-hosting
– Third-party hosting
9
Number of requests
70.00%
60.00%
50.00%
40.00%
audio
video
30.00%
20.00%
10.00%
0.00%
Home user
Business user
Business users access more audio than home users
10
On-demand media: File length
Audio
music
previews
Video
pop songs
Business users tend to access longer audio/video files
11
On-demand media: Playback duration
Audio
Video
pop
songs
music
previews
Business users tend to play audio/video longer
12
Live media: Playback duration
Audio
Video
Business users tend to access live audio/video longer
13
Traffic Overview
• User communities
– Home user
News and entertainment sites
– Business user
– Working environment affects access pattern
• Media hosting services
– Self-hosting
– Third-party hosting
14
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
15
Media hosting services
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Outline
• Traffic overview
• Protocol rollover
• Fast Streaming
• Rate adaptation
• Conclusion
17
Protocol Rollover
Streaming server
Media player
RTSP/UDP
RTSP/TCP
HTTP/TCP
Embed RTSP commands in
HTTP packets
Traffic volume:
UDP: 23%
TCP: 77%
HTTP: rare
18
Protocol rollover time
Startup latency = protocol rollover time + transport setup time + startup buffering time
Windows media service
RealNetworks media service
Protocol rollover increases user startup time significantly
19
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
22
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/1.0
Bandwidth: 1.12 Mbps
Speed: 20.5
RTSP /1.0 200 OK
Speed: 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
Fast Cache: 55%
Over supplied data
Normal TCP: 5%
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Server response time
DESCRIBE foo.wmv RTSP/1.0
SRT
RTT
RTSP /1.0 200 OK
SDP
Third party media service
sniffer
Self-hosting media service
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Server Load
Windows Server 2003
Win XP
Windows media
load simulator
Ethernet
…
Server log
1X
4X
Some 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
Multiple-bit-rate encoding
96Kbps
128Kbps
320Kbps
…
1.128Mbps
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
32
Stream switch
Play-out buffer
Streaming switch latency
40%
Low quality duration
30 sec
60%
3 sec
Stream switch is often not smooth
33
Stream thinning
30 sec
70%
34
Fast Cache and stream switch
Do not work with each other: fewer stream switches than MBR encoded objects
When network congestion occurs …
fill play-out buffer
playing
buffering
playing
buffering
5 sec
playing
buffering
time
Like pseudo streaming
When rebuffer occurs
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Streaming quality and playback duration
Home user
business user
>100 sec
88%
Longer duration sessions have higher prob. of quality degradation
Business user workload has more quality degradation
36
Streaming quality summary
The quality of media streaming on the Internet leaves much to be improved
37
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
Lower bound
Prevent switch latency
Upper bound
Prevent aggressive buffering
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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
40