On the forwarding capability of mobile handhelds for video streaming over MANETs

Despite the importance of real-world experiments, nearly all ongoing research activities addressing video streaming over MANETs are based on simulation studies. Earlier research shows that the limited resources of mobile handhelds, which are not modeled in most network simulators, can be a severe bottleneck. We study the capability of a modern handheld to perform one core task, which is the forwarding of video streams. We present end-to-end video quality and network measurements, along with an analysis of resource consumption. Our studies of the recent handheld Nokia N900 show that it can forward up to 3.70 Mbps. However, subjective video quality is compromised already at 3.35 Mbps, due to excessive delay. Our analysis unveils that direct memory access (DMA) relieves the CPU of forwarding overhead and that, due to the digital signal processor (DSP) support, additional coding overhead does not decrease the forwarding capacity. Finally, we find that power management impacts results considerably. It is possible to increase the forwarding capacity up to 27.4% by increasing the frequency of internal buses. Hence, our results demonstrate that the forwarding capacity is highly dependent on the internal state and activity of the device.