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Accurate link quality estimation is an important building block in quality aware routing. In an inherently lossy, unreliable and dynamic medium such as wireless, the task of accurate estimation becomes very challenging. Over the years ETX has been widely used as a reliable link quality estimation metric. However, more recently it has been established that under heavy traffic loads ETX performance gets significantly worse [4, 18, 19]. Contributions made in this paper are twofold. Firstly, we examine the ETX metric's behavior in detail with respect to the MAC layer and UDP data; and identify the causes of its unreliability. Secondly, we present the design and implementation of the xDDR link quality measurement metric - a variation of ETX - motivated by the observations made in our analysis. Our experiments show that xDDR substantially outperforms minimum hop count, ETX and HETX in packet delivery ratio. |
