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SWiFT Status Report

SWiFT Status Report. Dan Berger <dberger@cs.ucr.edu> 060203. Outline. Split TCP: The Aftermath False Link Failures: ns-2, The Revenge Current Work: 802.11 Rendezvous Conclusion. Split TCP: The Aftermath. Recall my last update:

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SWiFT Status Report

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  1. SWiFT Status Report Dan Berger <dberger@cs.ucr.edu> 060203

  2. Outline • Split TCP: The Aftermath • False Link Failures: ns-2, The Revenge • Current Work: 802.11 Rendezvous • Conclusion

  3. Split TCP: The Aftermath • Recall my last update: • SplitTCP, while intuitively attractive; did not perform as expected when modeled accurately. • Since then a handful of additional experiments were performed to strengthen understanding. • This work is now indefinitely on hold.

  4. False Link Failures • Subsequent discussions focused attention on false link failures. • Incorrect link abandonment due to congestion. • Extensive simulations were performed: • Static string of various lengths > 3* • Looking at the number and distribution of false link failures * This becomes important – stay tuned

  5. ns-2, The Revenge • Just when you thought it was safe to run a simulation… • Analysis of the simulation results revealed surprising patterns. • FLF’s were occurring with almost predictable periodicity. Theories abounded: • Long range dependence? • Invaders from Planet X?

  6. A Mystery Solved • A simulation of a three node provided a key insight: • FLF’s shouldn’t occur – but were. • Something was rotten in Denmark. • After consultation with Vikram, we isolated the problem to a recent (2/03) change to the NS 802.11 code.

  7. Nothing to see here, move along… • A fix was developed and tested – once we were satisfied it was submitted to the ns-2 maintainers. • Unfortunately they still haven’t applied it to the official sources. • It’s available on my cs web page.

  8. Back to your regularly scheduled programming • Attention was returned to False Link Failures. • They’re not, as far as we can tell, periodic • But they are hugely destabilizing. • Eliminating* FLF’s saw a 100% improvement in goodput. *Via a static topology, simulation-only hack

  9. Current Work: Rendezvous • During discussion, Prasun suggested modifying the MAC to exchange packets in an effort to reduce channel contention. • Total data transmission time is bounded. • An initial implementation has been done, and showed positive results (30% improvement @ 20 hops).

  10. Rendezvous 802.11 802.11 Rendezvous* RTS RTS CTS CTS Data Data(1) ACK ACK Data(2) ACK

  11. Rendezvous: Current State • Similar results were published in ACM Mobile Networks & Applications in 2000. • We’re assessing the appropriate reaction. • The model has been iterated on once, and has (at least) one more iteration before it’s general.

  12. Conclusion • This, and similar work by Frank is being targeted for an Infocomm paper. • Questions?

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