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TCP Probe: A TCP with Built-in Path Capacity Estimation

TCP Probe: A TCP with Built-in Path Capacity Estimation. Anders Persson, Cesar Marcondes, Ling-Jyh Chen, Li Lao, M. Y. Sanadidi, Mario Gerla Computer Science Department University of California, Los Angeles. Motivation. Knowledge of “ narrow link capacity ” is important for:

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TCP Probe: A TCP with Built-in Path Capacity Estimation

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  1. TCP Probe: A TCP with Built-in Path Capacity Estimation Anders Persson, Cesar Marcondes, Ling-Jyh Chen, Li Lao, M. Y. Sanadidi, Mario Gerla Computer Science Department University of California, Los Angeles

  2. Motivation • Knowledge of “narrow link capacity” is important for: • Optimizing network utilization via better congestion control & adaptive streaming • Tracking dynamic changes in capacity due to Vertical Handoffs Global Internet 2005

  3. Bandwidth Estimation Techniques • Active • Send out-of-band packets into the network • CapProbe [SIGCOMM04] and Pathrate [INFOCOM01] • Passive • Use ongoing data packets without additional overhead to the network • TCP Probe – similar to CapProbe technique but uses only “actual” data packets Global Internet 2005

  4. CapProbe Recap • Packet pair technique • Compression & expansion due to cross traffic distorts Tb • Filter out distorted samples by using samples with minimum end-to-end delay sum • Fast and accurate estimation of bottleneck capacity Global Internet 2005

  5. TCP Probe • Idea: Use CapProbe technique but passively within TCP • Rely on dispersion of ACK pairs and filter distorted dispersion based on end-to-end delay sum • Have to ensure that data packet pairs & corresponding ACK pairs produce accurate capacity estimates Global Internet 2005

  6. Challenge • TCP implementations try to reduce network overhead by sending one ACK for two data packets, but: • We want an ACK for each data packet! Global Internet 2005

  7. Solution • Sender sends inverted data packets • Receiver replies a duplicate ACK and an incremental ACK Global Internet 2005

  8. Packet Size Issue • Probing packet size: • forward direction: TCP data 1500 bytes • reverse direction: TCP ACK 40 bytes • The newly developed AsymProbe [Networking05] has shown: • If , TCP Probe estimates the capacity of the forward direction link • If , TCP Probe estimates the capacity of the reverse direction link Global Internet 2005

  9. Implementation • Implemented in NS-2 and Linux 2.4 Network Stack • Approach: • Periodically mark data packet pairs • Sender timestamps the data packets and the corresponding ACKs (sec granularity) Global Internet 2005

  10. Simulation Scenario • NS-2 simulation • Compare TCP Probe capacity estimation with TCPW BE (bandwidth estimation) • TCPW BE is based on dispersion of ACK packets without filtering samples Global Internet 2005

  11. TCP Probe vs. TCPW • 20 flows of the same kind • TCP Probe: All flows estimate C=10 Mbps • TCPW: Flows estimate BE between 0 to 7 Mbps Capacity Estimation (Mbps) TCP Probe TCPW BE Global Internet 2005

  12. TCP Probe vs. TCPW • 1 TCP Probe and 5 TCP New Reno flows • 1 TCPW and 5 TCP New Reno flows Capacity Estimation (Mbps) TCP Probe TCPW BE Global Internet 2005

  13. Internet Measurement • Three different paths: • Los Angeles: 3 Mbps (cable modem) • China: 45 Mbps • Alabama: 100 Mbps Global Internet 2005

  14. Cable Modem (3 Mbps) Global Internet 2005

  15. China (45 Mbps) Global Internet 2005

  16. Alabama (100 Mbps) Global Internet 2005

  17. Statistical Analysis • 30 measurements to each destination Global Internet 2005

  18. Applications • TCP Probe in Vertical Handoff Scenario • A vertical handoff involves two different network interfaces • Usually represent different technologies and thus result in a drastic change in link capacity • How to get advantage of the extra capacity when we are in congestion avoidance? • Revised TCP Probe • Re-initiate the estimation every n samples (n=50) • Detect a huge increase in the capacity estimation • Trigger a new slow start phase (i.e. fast rate adaptation) Global Internet 2005

  19. Simulation Scenario • TCP Probe: 1 → 6 • Pareto flows: 7 → 10, 8 → 9, 11 → 14, 12 → 13 • Capacity between node 1 and 2 increases from 10Mbps to 100Mbps at 80 second Global Internet 2005

  20. Fast Rate Adaptation Global Internet 2005

  21. Conclusions • TCP Probe passively provides to a TCP flow sender an accurate estimate of path capacity • Estimated capacity can be used as an upper bound on TCP sender rate • Vertical Handoff applications can benefit from detecting capacity change • Work in progress • TCP Probe provides improved performance under high loss rate (5%) • Astart [INFOCOM04] can benefit from accurate capacity estimation Global Internet 2005

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