internet streaming media delivery:

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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