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Packet Video 2003 1 TCP Video Streaming to Bandwidth-Limited Access Links Puneet Mehra and Avideh Zakhor Video and Image Processing Lab University of California, Berkeley

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Page 1: PV Powerpoint

Packet Video 2003

1

TCP Video Streaming to Bandwidth-Limited Access Links

Puneet Mehra and Avideh ZakhorVideo and Image Processing LabUniversity of California, Berkeley

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Packet Video 2003

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Talk Outline

Goals & Motivation Our Approach Experimental Results Related Work Conclusion

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Packet Video 2003

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Goal

Efficient video streaming using TCP to bandwidth-limited receivers

Key Assumptions: Receivers have limited-bandwidth last mile

connections to Internet … and run multiple concurrent TCP networking apps

Constraints: Should not modify senders or network infrastructure

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Motivation

Increasingly access links are the net. Bottleneck! Limited Bandwidth (B/W) Less than 1.5MBps Users run concurrent apps compete for limited B/W

Most Traffic on Internet is TCP [HTTP, P2P, FTP] TCP handles recovery of lost packets TCP has congestion control UDP Streaming difficult w/ firewalls

Problem: TCP shares bottleneck B/W according to RTT

May Not provide enough B/W for streaming apps

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Example Situation

Internet

User’s PC

FTP

P2PVIDEO

BottleneckAccess

Link

=

High RTT

Med. RTT

Low RTT

Congestion

Most Bandwidth!

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Talk Outline

Motivation & Goals Our Approach Experimental Results Related Work Conclusion

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Our Approach

We developed a receiver-based bandwidth sharing system (BWSS) for TCP [INFOCOM 2003]

Key Idea: Break fairness among TCP flows to allow user-specified B/W allocation

Approach: Limit throughput of low-priority connections to provide B/W for high-priority ones

Ensures full utilization of access link Doesn’t require changes to TCP/senders or infrastructure

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BWSS Overview

FCS1

Flow ControlSystem

FCSn

TargetRate

AllocationSub-

System

CalculationSub-System

Internet

BWSSBandwidth Sharing System

UserPreferences Receiver

Tn

T1

R1

R1

Rn

Rn

Wn

W1

Sender1

Sendern

For the receiver: = system target bit-rate

For the nth connection:Wn = Advertised WindowTn = Target RateRn = Measured Rate

Flow ControlSystem

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Target Rate Allocation Subsystem

Some apps need minimum guaranteed rate(video), others don’t (ftp)

User assigns each flow: Priority, minimum rate and weight

Bandwidth allocation algorithm: Satisfy minimum rate in decreasing order of priority Remaining B/W shared according to weight

T1

User Prefs.

σ

Tn

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Flow Control System (FCS)

Wi = Advertised WindowTi = Target RateRi = Measured Rate

FCS

TiWi

Ri

AdaptReceiver Window

CalculateTarget Rate

- Measured Rate

MeasureBit-rate and RTT

RTT

MSSwR

w – TCP window

RTT – Flow RTT

MSS – TCP MSS

wR

RTw

and

RTT

MSS

w

R

/

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σ – Calculation Subsystem

Goal: Choose σ to maximize link utilization. U = Σi Ri (σ)

Approach: Use increase/decrease in measured throughput to guide increase/decrease of σ

R1

RN

σ = Σi Ti

T1 = R1

σ UW2W1

Link Capacity

T2 = R2

T1 = R1

T2 ≠ R2

T2 = R2

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Talk Outline

Motivation & Goals Our Approach Experimental Results Related Work Conclusion

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Experimental Setup

Internet

Cross-TrafficSourceVIDEO

SOURCE

ftp12.freebsd.org

Vonnegut

ftp13.freebsd.org

EECS DomainEECS Domain

EECS Domain

RUDE

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Experimental Details

Internet

User’s PC

ETH0

NIST NET EmulatorBW = 960 Kbps Delay = 30 ms

BWSS – Shared Library

APP_1 APP_nAPP_2

Invisible to Apps

User Level App easy to deploy

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TCP vs BWSS Internet Experiments

Video streamed at 496Kbps Congestion on access link from 30s to 60s Standard TCP not good enough during

congestion

TCP BWSS

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BWSS Reduces Required Pre-Buffering

BWSS provides 4X reduction in pre-buffering over standard TCP

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SureStreamTM Experimental Setup

Internet

Cross-TrafficSourceVIDEO

SOURCE

ftp12.freebsd.org

Vonnegut

ftp13.freebsd.org

EECS DomainEECS Domain

EECS Domain

RUDE

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RealVideo SureStreamTM Internet Experiments

Takeaway: standard TCP not good enough for streaming

TCPTCP w/ BWSS

Video encoded at 450Kbps, 350Kbps, 260Kbps & 64Kbps Congestion on access link from 60s to 100s (320Kbps)

Despite congestion, video streams at steady rate.

Poor streaming

quality

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RealVideo SureStreamTM Internet Experiments

UDP TCP w/ BWSS

Takeaway: BWSS can break fairness among flows locally, and provide additional B/W for video apps.

UDP SureStream unable to stream

at 450KBps till after congestionConstant streaming at 450Kbps

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Related Work – TCP Streaming

Network-Based Approaches Receiver-based Delay Control (RDC) [NOSSDAV

2001] receivers delay ACK packets based on router feedback Mimic a CBR connection

End-Host Approaches Time-lined TCP (T-TCP) [ICNP 2002] TCP Real-Time Mode (TCP-RTM) [ICNP 2002] Must modify both sender & receiver to allow

skipping “late” packets

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Conclusions

BWSS allows flexible allocation of link B/W Breaks fairness among TCP flows “locally” in

manner unavailable to TCP-Friendly UDP protocols

BWSS enables efficient video streaming over TCP to bandwidth-limited receivers

Better performance than standard TCP In some cases, better performance than

congestion-aware UDP

Future Work: Incorporating UDP flows

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Questions?