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Passive assessment of QoS in a WLAN for Sudden Onset Disasters (SODs)

Real-time voice and video streaming applications require a certain Quality of Service (QoS) level for providing user satisfaction. As Wireless Local Area Networks (WLAN's) are not designed for such applications, assessing the communication's QoS level is a challenging task. Sudden Onset Disasters (SODs) poses even a greater challenge as the QoS level must be assessed without generating traffic or consuming any other network resources that the response forces needs for communicating among themselves. As such, passive measurement is the only viable approach, but it lacks suitable metrics for doing so. In this paper, we briefly review the main QoS parameters and later, we propose two new possible measurements. These measures are an extension of the retry-ratio measurements such as the Frame Retry Ratio (FRR) which reflects the effort-efficiency to communicate through the ratio of the extra effort (retries) to the overall effort. Data Retry-Ratio (DRR) is the ratio of extra data transmitted to the overall transmitted data in a period of time. Airtime Retry-Ratio (ARR) is the ratio of the extra airtime cost to the overall used airtime cost. For exploring the performances of these measures, we have developed and designed a special portable testbed which among other things includes a stratum-1 NTP time server. We used this testbed to explore the relations between active measurements: such as one-way delay, throughput and jitter to passive measurements: one-way throughput, one-way FRR, DDR and ARR. The results of a large field-test reveal that passive measurements can reflect the QoS parameters such as the average throughput and can indicate an asymmetric link similar to one-way delay.