May 2001 doc IEEE 802 11 00xxx Packet
- Slides: 13
May 2001 doc. : IEEE 802. 11 -00/xxx 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 Submission 1 C Ware - Uo. W, E Dutkiewicz - MARC
May 2001 doc. : IEEE 802. 11 -00/xxx 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 Submission 2 C Ware - Uo. W, E Dutkiewicz - MARC
May 2001 doc. : IEEE 802. 11 -00/xxx 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 additional factors effecting this behaviour Submission 3 C Ware - Uo. W, E Dutkiewicz - MARC
May 2001 doc. : IEEE 802. 11 -00/xxx 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. 11 b 11 Mbit/s PHY Submission 4 C Ware - Uo. W, E Dutkiewicz - MARC
May 2001 doc. : IEEE 802. 11 -00/xxx Experiment Setup • Nodes hidden from transmission range viewpoint – carrier sense may be available • 802. 11 b, RTS/CTS used, (500 byte thresh) • Send 10, 000+ 512 byte UDP packets to host 2 • Trace each transfer with tcpdump Submission 5 C Ware - Uo. W, E Dutkiewicz - MARC
May 2001 doc. : IEEE 802. 11 -00/xxx Vendor A - Equal SNR Con. A - 25 d. B Con. B - 25 d. B Connection A commences first Submission 6 C Ware - Uo. W, E Dutkiewicz - MARC
May 2001 doc. : IEEE 802. 11 -00/xxx Vendor B - Equal SNR Con. A - 25 d. B Con. B - 25 d. B Connection B commences first Submission 7 C Ware - Uo. W, E Dutkiewicz - MARC
May 2001 doc. : IEEE 802. 11 -00/xxx Vendor A - Unequal SNR Con. A - 25 d. B Con. B - 20 d. B Stronger Host commences first Submission 8 C Ware - Uo. W, E Dutkiewicz - MARC
May 2001 doc. : IEEE 802. 11 -00/xxx Vendor B - Unequal SNR Con. A - 25 d. B Con. B - 20 d. B Stronger Host commences first Submission 9 C Ware - Uo. W, E Dutkiewicz - MARC
May 2001 doc. : IEEE 802. 11 -00/xxx Vendor A - Unequal SNR Con. A - 25 d. B Con. B - 20 d. B Weaker host commences first Submission 10 C Ware - Uo. W, E Dutkiewicz - MARC
May 2001 doc. : IEEE 802. 11 -00/xxx Vendor B - Unequal SNR Con. A - 25 d. B Con. B - 20 d. B Weaker host commences first Submission 11 C Ware - Uo. W, E Dutkiewicz - MARC
May 2001 doc. : IEEE 802. 11 -00/xxx 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 Submission 12 C Ware - Uo. W, E Dutkiewicz - MARC
May 2001 doc. : IEEE 802. 11 -00/xxx Questions / Issues • Is it possible to address this issue within the current Qo. S 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 Submission 13 C Ware - Uo. W, E Dutkiewicz - MARC
