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Packet Video 2003
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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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Packet Video 2003
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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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Packet Video 2003
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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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Packet Video 2003
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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?