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Packet Capture UDP Experiments

Packet Capture UDP Experiments. Christopher Ware - TITR, University of Wollongong chris@titr.uow.edu.au Eryk Dutkiewicz - Motorola Australia Research Centre Eryk.Dutkiewicz@motorola.com. Overview.

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Packet Capture UDP Experiments

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  1. Packet Capture UDP Experiments Christopher Ware - TITR, University of Wollongong chris@titr.uow.edu.au Eryk Dutkiewicz - Motorola Australia Research Centre Eryk.Dutkiewicz@motorola.com C Ware - UoW, E Dutkiewicz - MARC

  2. Overview • Capture experiments using TCP over hidden terminal connections illustrate a strong signal strength dependence (11-01/058) • In all cases, the stronger connection is able to lock other connections out, capturing the channel • TCP backoff and timeout exacerbates this problem C Ware - UoW, E Dutkiewicz - MARC

  3. Overview • ‘Capture’ occurs at two levels • Packet capture where a frame is ‘captured’ by the receiver in the presence of noise/other interference • Channel capture where protocol timers interact to prevent stations from accessing the channel • Hidden terminal TCP experiments exhibit channel capture, but the signal strength dependence indicates there are additional factors effecting this behaviour C Ware - UoW, E Dutkiewicz - MARC

  4. Scenario • Repeat the previous experiments without TCP to remove the effect of retransmission timers and timeouts • Two hidden terminals are used, each sending traffic to a common receiver each node floods the channel with UDP packets • No retransmission, timeout, ACK’s etc • Perform experiments with NIC’s from 2 manufacturers • Use 802.11b 11Mbit/s PHY C Ware - UoW, E Dutkiewicz - MARC

  5. Experiment Setup • Nodes hidden from transmission range viewpoint • carrier sense may be available • 802.11b, RTS/CTS used, (500 byte thresh) • Send 10,000+ 512 byte UDP packets to host 2 • Trace each transfer with tcpdump C Ware - UoW, E Dutkiewicz - MARC

  6. Vendor A - Equal SNR SNR Con. A - 25dB Con. B - 25dB Connection A commences first C Ware - UoW, E Dutkiewicz - MARC

  7. Vendor B - Equal SNR SNR Con. A - 25dB Con. B - 25dB Connection B commences first C Ware - UoW, E Dutkiewicz - MARC

  8. Vendor A - Unequal SNR SNR Con. A - 25dB Con. B - 20dB Stronger Host commences first C Ware - UoW, E Dutkiewicz - MARC

  9. Vendor B - Unequal SNR SNR Con. A - 25dB Con. B - 20dB Stronger Host commences first C Ware - UoW, E Dutkiewicz - MARC

  10. Vendor A - Unequal SNR SNR Con. A - 25dB Con. B - 20dB Weaker host commences first C Ware - UoW, E Dutkiewicz - MARC

  11. Vendor B - Unequal SNR SNR Con. A - 25dB Con. B - 20dB Weaker host commences first C Ware - UoW, E Dutkiewicz - MARC

  12. Results Summary • In the equal case, sharing of the channel occurs • In the unequal cases, the stronger host obtains significantly greater throughput, less errors etc. • There is no channel capture due to transmission timers etc. • Remove TCP and unfairness still present C Ware - UoW, E Dutkiewicz - MARC

  13. Questions / Issues • Is it possible to address this issue within the current QoS draft? • Current simulation models do not show this behaviour • This is not a fundamental problem with the MAC • relative fairness with equal signal power • This manifestation of near/far effect greatly affects fairness properties, particularly when hidden terminals are present C Ware - UoW, E Dutkiewicz - MARC

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