One-way delay measurement based on flow data: Quantification and compensation of errors by exporter profiling

摘要

One-way delay (OWD) is an important measurand for network management. It can indicate routing problems, network congestion, and is useful for tracking down application problems to network effects. While active measurements deliver high accuracy, measuring OWD actively on all paths of large networks results in high effort. Thus, passive measurements are attractive. Our approach for measuring OWD is based on flow data, which is often exported from flow capturing enabled routers (exporters) for traffic accounting and reporting. Thus, this approach does not require additional network components and often comes at almost no additional cost. It is well-known that flow data is often inaccurate and incomplete due to record loss. However, only little information is available on timestamp accuracy of flow data. Therefore, we investigated timestamp errors and developed a method for quantifying them in order to improve the accuracy of flow capturing based OWD measurements. Our contribution is threefold: First, we analyze clock resolution effects based on a reference model for flow record creation. Second, we develop methods for exporter profiling, i.e., extracting errors introduced by exporters from flow data. Third, we present results obtained from data collected in a global enterprise network. We conclude that precision of flow data based OWD calculation heavily depends on the capturing devices, especially on timestamp resolution. Standard deviations observed range from 2.07 ms to 34.02 ms.