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TCP-LP: A Distributed Algorithm for Low Priority Data Transfer

TCP-LP is an end-point protocol enabling two-class service prioritization without network support, ensuring fair bandwidth sharing & congestion control. Explore its concepts and simulation results for effective low-priority data transfer.

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TCP-LP: A Distributed Algorithm for Low Priority Data Transfer

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  1. TCP-LP: A Distributed Algorithm for Low Priority Data Transfer Aleksandar Kuzmanovic, Edward W. Knightly Department of Electrical and Computer Engineering Rice University IEEE INFOCOM 2003 Presented by Ryan

  2. 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

  3. 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

  4. Reference Model • Two class hierarchical scheduling model • High-priority VS Low-priority class • Strict priority service

  5. TCP-LP Protocol • An end-point congestion control algorithm • Early Congestion Indication • Congestion Avoidance Policy

  6. 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

  7. 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

  8. TCP-LPCongestion Avoidance Policy • After the expiration of the inference phase •  increasing the congestion window by 1 per RTT (like TCP) Early Congestion Induction

  9. 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

  10. 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

  11. 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

  12. Simulation Results • Square-wave Background Traffic • 1 TCP/TCP-LP flow

  13. Simulation Results • 10 TCP/TCP-LP flows

  14. Simulation Results • HTTP Background Traffic • Web traffic between Node 0 and 1 • FTP connection in the same direction

  15. 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

  16. Simulation Results

  17. Simulation • Multiple Bottleneck Topology 2 • Links capacity – same as Topology 1

  18. Simulation Results

  19. 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

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