Analysis of Anomalies on a Virtualized Network Testbed

To clarify useful parameters for avoiding unstable conditions in network experiments on a virtualized testbed, we used PlanetLab as the virtualized testbed and measured network throughput using a combination of probe and data transfers. Although PlanetLab has been widely used as a testbed for overlay networks, distributed systems, and network measurement, it is provided as a virtualized environment to users. A set of these environments on different nodes is called as `slice´, and multiple slices run simultaneously on each node. We found that network throughput was occasionally decreased even though the network condition was stable. The cause of the throughput decrease was an unintended large packet spacing. The unintended large packet spacing is an anomaly. Although the cause of the anomaly is known to be unstable CPU scheduling latency, no clear conditions for anomaly avoidance had previously been given. We investigated throughput measurement with resource monitoring to clarify anomaly avoidance conditions. When the CPUs at a node are shared by many slices, slices are frequently scheduled off the CPUs, and the anomaly occurs. If network throughput is decreased by the anomaly, the measurement results should be discarded.