1. Packet Capture UDP Experiments
May 2001
Packet Capture UDP Experiments
Christopher Ware - TITR, University of Wollongong
Eryk Dutkiewicz - Motorola Australia Research Centre
C Ware - UoW, E Dutkiewicz - MARC

2. Month 2000
doc.: IEEE /xxx
May 2001
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
John Doe, His Company

3. Overview ‘Capture’ occurs at two levels
May 2001
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. May 2001
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 b 11Mbit/s PHY
C Ware - UoW, E Dutkiewicz - MARC

5. Experiment Setup Nodes hidden from transmission range viewpoint
May 2001
Experiment Setup
Nodes hidden from transmission range viewpoint
carrier sense may be available
802.11b, RTS/CTS used, (500 byte thresh)
Send 10, 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
May 2001
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
May 2001
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
May 2001
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
May 2001
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
May 2001
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
May 2001
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
Month 2000
doc.: IEEE /xxx
May 2001
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
John Doe, His Company

13. May 2001
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