Applying the Concept of a Virtual Competitive Window to Determine the Qualitative Performance of a Wireless Network of the 802.11 Standard

Abstract

The article presents the results of the application of the concept of a virtual competitive window to determine such qualitative indicators as the bandwidth of the wireless network Wi-Fi, delay transmission of the data packet through the wireless channel, the probability of loss of data packet, jitter. Practical calculations was made for a network operating on the 802.11a specification in RST / CST mode, taking into account the collisions occurring on networks with a large number of active stations. The article considers the ideal network. That is, the one that was neglected by the effects of interference and interference occurring in the real wireless network. The paper examines processes in a wireless network with saturated load as quasi-stationary processes. On the basis of such a concept, the parameter named Virtual Competitive Window was introduced. Our research has allowed us to obtain the calculated relations, which establish the unequivocal connection between the system parameters of the network and the stochastic parameters of the network operation process. The results of the research are useful for improving the settlement ratios for determining the parameters of the quality of the 802.11 wireless network in the mode of competitive access. The above calculations do not take into account the effects of interference and interference occurring in the real wireless network. The calculation takes into account the time spent on transmitting the headings and checking blocks provided by the mentioned protocols, as well as the costs associated with the use of the SNAP protocol. The calculation is made for frames with different loads, namely: 64, 128, 256, 512, 1024, 1500 bytes, for networks in which the number of active stations varies from 2 to 14. To calculate the parameters of the network operation, which are provided for signal speed, are used. 24 Mbps (maximum required speed of the 802.11a specification). The calculations are made for cases where the data is transmitted using the protocols TCP and UDP. Chart of network operation in RTS / CTS mode is presented in the article. Thus, the results of the research are graphical dependencies for maximum bandwidth of the 802.11a wireless network in RTS / CTS mode, 802.11a wireless network bandwidth in RTS / CTS mode with allowance for collisions, the dependence of the average latency of data transmission on the 802.11a network in RTS / CTS mode and jitter change curve in a network with a different number of stations in the payload mode of all frames of 64 bytes. Determined that the transmission delay of the data frame depending on the type of multimedia information (small volumes for voice traffic and large for the transmission of digital data) can vary in very wide ranges from 450 to 1300 microseconds, and jitter from 600 to almost 4000 microseconds (for example, files from payload of 64 bytes). The research is relevant because, under ideal transmission conditions, without taking into account signal processing delays by hardware, the maximum bandwidth of the 802.11a network channel in RTS / CTS mode may vary several times compared to the declared 24 Mbps rate. Ref. 4, fig. 5.