Robust Distributed Monitoring of Traffic Flows
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Scalable monitoring of traffic flows faces challenges posed by unrelenting traffic growth, device heterogeneity, and load unevenness. We explore an approach that tackles these challenges by shifting a portion of the monitoring-task execution from an overloaded network element to another element that has spare resources. Moving the entire execution of the task to a lightly loaded element might be infeasible because execution on multiple elements is inherent in the task or requires at least partial participation by the particular overloaded element (e.g., flow-size computation at the ingress element for billing purposes). Distributed execution of a stateful traffic-monitoring task has to be robust against packet reordering or loss, i.e., network noise. This paper designs robust traffic monitoring where the goal is to determine a flow metric for each flow exactly in spite of network noise. We follow the open-loop paradigm that does not add any control packets, communicates flow state in-band by appending few (on the order of 2 or 4) control bits to packets of the monitored flows, and keeps latency low. We consider the task of flow-size computation, analytically derive conditions assuring correct operation of the designed algorithms, and evaluate the algorithms on realistic traffic traces. The algorithms successfully distribute the monitoring-task load without imposing significant computation or storage overhead.