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INFOCOM 2003
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A Receiver-Driven Bandwidth Sharing System (BWSS) for TCP
Puneet Mehra, Avideh ZakhorUC Berkeley, USA
Christophe De VleeschouwerUniversité Catholique de Louvain,
Belgium
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Talk Outline
Motivation & Goals BWSS Overview NS-2 Simulations Internet Experiments Related Work Conclusion
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Motivation
Most traffic on Internet is TCP HTTP, FTP, P2P,…
In many cases access links are bottleneck Limited Bandwidth (B/W) eg: DSL/Cable < 1.5Mbps User run many apps that compete for B/W
Problem: TCP shares bottleneck B/W according to RTT Not fair to flows w/ large RTT Doesn’t consider application needs or user prefs!
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Example Situation
Internet
User’s PC
FTP
P2PVIDEO
BottleneckAccess
Link
=
High RTT
Med. RTT
Low RTT
Congestion
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Goal & Approach Goal: Let user control application B/W
allocations User preferences dictate bandwidth allocation
Approach: limit throughput of low-priority flows to provide additional B/W for high-priority ones
Ensure full utilization of access link
Don’t change TCP/senders or routers easily deployable!
INFOCOM 2003
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Talk Outline
Motivation & Goals BWSS Overview NS-2 Simulations Internet Experiments Related Work Conclusion
INFOCOM 2003
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BWSS Overview
FCS1
Flow ControlSystem
FCSn
Flow ControlSystem
TRASTRAS
TargetRate
AllocationSub-
System
TargetRate
AllocationSub-
System
CalculationSub-System
Internet
BWSSBandwidth Sharing System
UserPreferences Receiver
Tn
T1
R1
R1
Rn
Rn
W1 & d1
Sender1
Sendern
For the receiver: = system target bit-rate
For the n th connection:W n = Advertised Windowdn = Delay in ACK packetsTn = Target RateRn = Measured Rate
Wn & dn
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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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BWSS Overview
FCS1
Flow ControlSystem
FCSn
Flow ControlSystem
TRASTRAS
TargetRate
AllocationSub-
System
TargetRate
AllocationSub-
System
CalculationSub-System
Internet
BWSSBandwidth Sharing System
UserPreferences Receiver
Tn
T1
R1
R1
Rn
Rn
W1 & d1
Sender1
Sendern
For the receiver: = system target bit-rate
For the n th connection:W n = Advertised Windowdn = Delay in ACK packetsTn = Target RateRn = Measured Rate
Wn & dn
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Flow Control System (FCS)
MeasureBit-rate and RTT
CalculateTarget Rate
- Measured Rate
AdaptReceiver Window
ACK Delay
W i
Ri
Ti
Wi = Advertised Windowdi = Delay in ACK packetsTi = Target RateRi = Measured Rate
FCS
di
dRTT
MSSwR
w – TCP window
d – delay in ACKs
RTT – Flow RTT
MSS – TCP MSS
wR
RTw
anddRTT
MSS
w
R
/
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BWSS Overview
FCS1
Flow ControlSystem
FCSn
Flow ControlSystem
TRASTRAS
TargetRate
AllocationSub-
System
TargetRate
AllocationSub-
System
CalculationSub-System
Internet
BWSSBandwidth Sharing System
UserPreferences Receiver
Tn
T1
R1
R1
Rn
Rn
W1 & d1
Sender1
Sendern
For the receiver: = system target bit-rate
For the n th connection:W n = Advertised Windowdn = Delay in ACK packetsTn = Target RateRn = Measured Rate
Wn & dn
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σ – Calculation Subsystem
Goal: Choose σ to maximize link utilization. U = Σi Ri (σ)
Approach: Iteratively increase/decrease σ and measure the impact on utilization
R1
RN
σ
T1 = R1
σ UW2W1
Link Capacity
T2 = R2
T1 = R1
T2 != R2
T2 = R2
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BWSS Overview
FCS1
Flow ControlSystem
FCSn
Flow ControlSystem
TRASTRAS
TargetRate
AllocationSub-
System
TargetRate
AllocationSub-
System
CalculationSub-System
Internet
BWSSBandwidth Sharing System
UserPreferences Receiver
Tn
T1
R1
R1
Rn
Rn
W1 & d1
Sender1
Sendern
For the receiver: = system target bit-rate
For the n th connection:W n = Advertised Windowdn = Delay in ACK packetsTn = Target RateRn = Measured Rate
Wn & dn
INFOCOM 2003
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Talk Outline
Motivation & Goals BWSS Overview NS-2 Simulations Internet Experiments Related Work Conclusion
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Example of User Preferences
Time 0: Min. Rate = 0 Kb/sweights = 1,2,3 for S0-S2Priority -> S0 (max), S2(min)
Time 300: Min Rate = 600 Kb/s
TCP BWSS
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Network-Congestion Example
Priorities: increasing from S0-S2Min Rate:S0,S2 – 600Kb/sS1 – 100 Kb/s
Time 400s to 1200s700Kb/s Interfering TCP trafficS2 limited to 300Kb/s
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Multimedia Streaming Example
• S0 – Ftp traffic. Low Priority• Min Rate = 700Kb/s
• S1 – Streaming at 450Kb/s• High Priority
• 300Kb/s UDP flow (400s-1000s)
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Talk Outline
Motivation & Goals BWSS Overview NS-2 Simulations Internet Experiments Related Work Conclusion
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BWSS Implementation
Internet
User’s PC
ETH0
BWSSUser-space shared
librarysetsockopt()
No Kernel Mods!
APP_1 APP_nAPP_2
Invisible to Apps
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Experimental Setup
Internet
ftp14.freebsd.org
ftp12.freebsd.org
ftp13.freebsd.org
Host PC running Linux 2.4.8 kernel
AT&T Cable modem connection
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Experiment 1 – User Preferences
BWSS allows flexible allocation of B/W
Standard TCP
Weighted Fair SharingRatios: 3,2,1
Minimum Rate of 100Kb/sPriorities: Blue, green, red
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Related Work Network-Modifying Solutions
Router Scheduling Policies WFQ, W2FQ: allow B/W allocation Require infrastructure changes little deployment
Network Appliances – PacketShaper Placed at network ingress does traffic
management
Not easy to manage individual preferences
End-Host solution Modify receiver’s window [Spring et al, 2000]
Prioritize short-lived flows over longer ones Focus: reduce queuing delay for interactive apps
(telnet)
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Conclusions
BWSS allows user to allocate link B/W Flexible B/W allocation model Adapts to changing network conditions No changes to TCP/senders/routers Implemented as shared library easily deployable
Enables efficient video streaming over TCP Simulations show better performance than standard
TCP Additional Internet experiments validate
[TCP Based Video Streaming using Receiver-Driven Bandwidth Sharing, Packet Video 2003, To appear]