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TCP-LP: A Distributed Algorithm for Low
Priority Data Transfer
Aleksandar Kuzmanovic, Edward W. Knightly
Department of Electrical and Computer Engineering
Rice UniversityIEEE INFOCOM 2003
Presented by Ryan
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Introduction
Service prioritization among different traffic classes E.g. better than best-effort (real-time service) Not easy to deploy in the current Internet
TCP-LP (Low Priority) An end-point protocol achieving two-class service
prioritization without any support from the network
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Introduction
Objective of TCP-LP Utilizing available bandwidth in a TCP transparent
fashion Fair sharing the excess bandwidth among
multiple TCP-LP flows (TCP-like fair share)
Application of TCP-LP Background file transfer Probing available bandwidth
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Reference Model
Two class hierarchical scheduling model High-priority VS Low-priority class Strict priority service
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TCP-LP Protocol
An end-point congestion control algorithm Early Congestion Indication Congestion Avoidance Policy
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TCP-LPEarly Congestion Indication
One-way packet delays as early indicators Smoothed one-way delay (weighted moving average)
Early congestion indication condition
d – measured one-way delay, γ- delay smoothing parameter, δ- delay threshold
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TCP-LPCongestion Avoidance Policy
Receipt of first early congestion indication halving the congestion window entering an inference phase
During the inference phase Without increasing the congestion window If receiving another indication
setting the congestion window to 1
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TCP-LPCongestion Avoidance Policy
After the expiration of the inference phase increasing the congestion window by 1 per
RTT (like TCP)
Early Congestion Induction
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Parameter Settings
Delay Smoothing, γ= 1/8 (typical value for computing the smoothed RTT for TCP)
Delay Threshold, δ= 0.15
Inference Phase Time-out, itt = 3*RTT
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Simulation
Run on NS2 (each run lasts 1000s)
Topology Bottleneck link – 1.5Mb/s or 10Mb/s with delay
20ms Other access links – 100Mb/s with delay 2ms
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Simulation Results
FTP and Reverse Background Traffic
First Row (excess capacity not available) 2 simultaneous FTP downloads
Second Row (excess capacity available) 2 simultaneous FTP downloads 10 TCP flows in the reverse direction
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Simulation Results
Square-wave Background Traffic 1 TCP/TCP-LP flow
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Simulation Results
10 TCP/TCP-LP flows
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Simulation Results
HTTP Background Traffic Web traffic between Node 0 and 1 FTP connection in the same direction
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Simulation
Multiple Bottlenecks Topology 1 Links 0-1, 1-2 and 2-3 with capacity of 1.5Mb/s Others with capacity of 100Mb/s
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Simulation Results
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Simulation
Multiple Bottleneck Topology 2 Links capacity – same as Topology 1
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Simulation Results
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Conclusion
TCP-LP achieves low-priority service without the support of the network
Simulations results support its functions Experiments on the Internet should be
performed to validate its performance