In this paper, a lightweight enhanced monitoring (LEMON) algorithm based on packet sampling, is proposed. It targets a preassigned accuracy on bitrate estimates, for each monitored flow at a router interface. To this end, LEMON takes into account some basic properties of the flows, which can be easily inferred from a sampled stream, and it exploits them to dynamically adapt the monitoring time ... [Show full abstract] window on a per-flow basis. Its effectiveness has been tested using real packet traces. Experimental results show that LEMON is able to finely tune, in real time, the monitoring window associated to each flow, and, compared with a classic fixed scale monitoring approach, it is able to better satisfy the accuracy requirements of bitrate estimates. Moreover, its communication overhead can be kept low enough by choosing an appropriate aggregation policy in the message exporting process. Finally, LEMON produces a low processing overhead, which can be easily sustained by currently deployed routers. Copyright © 2013 John Wiley & Sons, Ltd.