IEEE802.11 wireless LAN systems are being widely used and multiple wireless LAN coexistence systems like 802.11b/g are available at the same time. However, in such environments, network performance is likely to degrade because the CAMA/CA mechanism does not always work well. Especially in the 802.11b/g systems, issues on performance degradation caused by the CTSprotection mechanism come to surface. To manage and maintain the QoS in such environments, it is required to detect and estimate the QoS degradation effectively. We found that the so-called retry ratio (i.e., the retry ratio of the numbers of transmitted packets to retransmitted ones) is strongly correlated with IPpacket quality metrics through our IP packet experiments. It is thus considered that retry ratio is applicable to managing the quality of some applications over wireless LAN.

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