Quantifying the Overhead Due to Routing Probes in Multi-Rate WMNs

The selection of high-throughput routes is a key element towards improving the performance of wireless multihop networks. While several routing metrics have been proposed in the literature, it has been shown that link-quality aware metrics can provide significantly higher end-to-end throughput. To date, the online computation of such metrics requires the periodic transmission of probe packets at all available transmission rates. However, our link level measurement study on two different 802.11 testbeds demonstrates that: (a) multi-rate probe transmissions increase the number of collisions and enforce nodes to reside in the back-off state for prolonged time periods, and (b) the extent of performance degradation depends on the network density; a network-wide throughput reduction of the order of 400% is possible. In addition, our measurements show that the impact of probing in terms of end-to-end performance can be devastating. In particular, the probing functionality can pose a significant degradation in the end-to-end throughput of a single flow, by at least 35% and as high as 90%, depending on the probing frequency and network density. Finally, we discuss different alternatives to multi-rate probing for the online computation of such metrics.