Comparing the results from various performance models of IEEE 802.11g DCF

  • Authors:

  • P. S. Kritzinger;Henry Msiska;Tino Mundangepfupfu;Paolo Pileggi;Andrew Symington

  • Affiliations:

  • Data Network Architectures Group, Computer Science Department, University of Cape Town, South Africa;Data Network Architectures Group, Computer Science Department, University of Cape Town, South Africa;Data Network Architectures Group, Computer Science Department, University of Cape Town, South Africa;Data Network Architectures Group, Computer Science Department, University of Cape Town, South Africa;Computing Laboratory, Oxford University, England, UK

  • Venue:
  • Computer Networks: The International Journal of Computer and Telecommunications Networking
  • Year:
  • 2010

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Abstract

IEEE 802.11 DCF is the most widely-used CSMA/CA access control mechanism. Recent analytic performance models for DCF have received acclaim for both their simplicity and reported accuracy. Most of these models share the assumptions of full single-hop connectivity among all stations, that DCF back-off may be modeled as a Markov process and that the network is saturated with traffic. In order to verify the accuracy of existing analytic models we developed a discrete-event simulator to record the performance of the DCF protocol and ensure that every detail of the standard is represented. Simultaneously we set up a hardware test bed to measure the same performance metrics in an environment that makes none of the simplifying assumptions of either the analytic models or the simulation. In the test bed, as in the simulator, we used the same physical parameter settings prescribed by the standard. As is the case for the analytic models we used, we subjected the simulator and the test bed to the same saturated workload for both basic and RTS/CTS access modes. Finally, we also implemented a non-saturating Markov Modulated Arrival Process (MMAP) workload model for our simulator to test the performance of DCF subject to more realistic internet traffic conditions. We describe both the simulator and the test bed in some detail in order to testify to the accuracy and detail of our results. The results show that the analytic models are mostly pessimistic for small numbers of nodes and optimistic for larger numbers of nodes. The performance measurements from the test bed, in turn, indicate that the simulation results are similarly optimistic when large numbers of nodes are concerned. Since the test bed uses an error-prone wireless channel, this latter result is, in principle, not surprising. The rate of deterioration in the actual performance is however something that is not widely known and is much more rapid than analytic models would suggest.