An Accuracy Study of Emulation Daemons for IEEE 802.11 Networks

Irreproducibility and external influences are common in wireless experiments. In addition, setups with multiple, possibly moving nodes are expensive to create for testing purposes. To address these issues, several wireless emulators and simulators are available. Wireless medium emulators are of particular interest because they allow the use of software designed for real wireless environments without adaptation. In this paper we evaluate the accuracy of the wireless medium emulators hwsim, wmediumd, and yawmd. We compare throughput and round-trip time with results from actual wireless transmissions in a shielded environment. We found large differences between real hardware and these emulators: hwsim throughput results are more than an order of magnitude higher than actual wireless transmissions and measured round-trip times are much lower than expected. wmediumd adds wireless logic such as data rates and media access to the emulation. However, we measured data rates well below one-fifth of the actual data rate available in wireless environments. The RTT under load with wmediumd and yawmd experiments are much higher than in real wireless transmissions and tend to vary widely. yawmd is more accurate in terms of performance but comes with more inaccurate RTTs than wmediumd with TCP traffic.