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Internet Streaming Media Delivery:

Lei Guo1, Enhua Tan1, Songqing Chen2, Zhen Xiao3, Oliver Spatchcheck4, and Xiaodong Zhang1

Delving into

A Quality and Resource Utilization Perspective

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Multimedia on the Internet

• Internet video traffic is doubling every 3 to 4 months (IBLNEWS, comScore)– Youtube nearly doubled its traffic in May– 100 million video streams were served per day in July, 2006

by Alexa Internet

X 400% from May to Oct

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Pseudo Streaming

HTTP

Web server

X 1 hours

Flash based

Short video: 3min

High cost: 1-1.5 million$ a month

RTMP: streaming flash video

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Streaming Media

Akamai, LimeLight Networks

Streaming serverCDN

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Streaming Media

• Merits– Thousands of concurrent streams– Flexible response to network congestion– Efficient bandwidth utilization– High quality to end users

• Challenges– Lack of QoS on the Internet– Diverse network connection of users

• Research and techniques– Effective utilization of server and Internet resources– Protocol rollover, Fast Streaming, MBR and rate adaptation

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Limits of Existing Measurements

• Few studies on the quality and mechanism of streaming media delivery– Coarse granularity studies on access pattern and user behaviors– Small scaled experiments in lab environment– Unknown on the state of the art of Internet streaming delivery– Unknown on the resource utilization of modern streaming services

• Challenge of streaming quality studies– Server logs are not enough– Packet level analysis is difficult: reconstruct TCP flow to get

streaming protocol header

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Our Objective and Methodology

• Understand modern streaming techniques– 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 (Gigascope)– RTSP, RTP/RTCP, MMS, RDT packet headers instead of server lo

gs

• Analyze commonly used streaming techniques– Protocol rollover– 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 users in a cable network– Business users hosted by a big ISP– Have different access patterns

• Media hosting services– Self-hosting– Third-party hosting

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Which is more popular: audio or video?

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 songs(3-5 min)music

Previews(30 sec)

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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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Media hosting services

Self-hosting: yahoo.com, aol.com, wbr.com

Third-party hosting: akamai.com. LimeLight Networks, fplive.net

CDN/MDN are widely used

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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

X

X

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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

Content provider: use URL modifier to specify protocol in the meta file rtspt://xxx.xxx.com:/xxx.wmv (TCP) >70% rtspu://xxx.xxx.com:/xxx.wmv (UDP) rarely

TCP will be used even UDP is supported

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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: fill the initial buffer– Fast cache: optional– Fast recovery– Fast reconnect

• Always TCP-based

Back

40%60%

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Media objects delivered with Fast Cache

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 streaming

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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

Early termination: most streaming sessions only request the initial part of a media object

Fast Cache: > 55% oversupplied

Normal TCP: < 5% oversupplied

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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

handshake

20 ms

> 40%

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Server Load

Windows media load simulator

Windows Server 2003 Win XP

Server log

…

Ethernet

1 X 4 X

Some CDNs/MDNs do not support Fast Cache at all

Link

Bandwidth CPU

1 X 4 X

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Effectiveness of resource over-utilization

• Fast Cache is TCP-based– Only feasible when bandwidth is large enough– Less possibility of congestion in this case

Encoding rate: 200 – 320 K bpsBandwidth: > 500 Kbps

Fast Cache: not resource-efficient

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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

Windows: Intelligent streamingRealNetworks: SureStream

Stream thinning: deliver key frame only

Video cancellation: play audio only

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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 encodedMaximum streams in a video: 20

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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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Fast Cache and stream switch

Do not work with each other: stream switch is disabled in Fast Cache

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 due to the longer playback time

>100 sec

88%

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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

high rate stream

low rate stream

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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

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Thank you!Thank you!

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Traffic Overview

• Different access patterns in user communities– Not due to the business related media traffic: both are

news and entertainment sites– Working environment affects access pattern

• Media hosting services– Self-hosting– Third-party hosting

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Streaming quality summary

The quality of media streaming on the Internet leaves much to be improved

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Stream thinning (play key frames only)

30 sec

70%

+Stream thinning duration

Thinning intervalSmooth play

Key frame play