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Approximating the end-to-end delay using local measurements: A preliminary study based on conditional expectation

With Software-Defined Networking (SDN), computer networks will gain a better control and management on their physical resources and on flows requiring a specific type of QoS. To fulfil these objectives, networks must be able to characterize the end-to-end performance of flows, which are usually unknown and not directly measurable. Instead, networks have typically at their disposal only local measurements, collected at each node. In this paper, we propose a new method to evaluate the variance of the end-to-end delay based only on measurements collected on nodes. The core of our solution is to link samples of waiting times at different nodes in order to approximate the corresponding covariance terms, needed to refine the approximate value of the sought variance. We evaluate the accuracy of our solution using two different scenarios. The obtained results show that the method is generally good, with a relative error on the estimated standard deviation of the end-to-end delay usually close to 5%, though it may exceed 10% when the network is facing high levels of load and experiencing packet losses.