Routers in AT&Ts IP backbone compile summary statistics on each flow of traffic that passes through them, and exports them as flow records to a collector. These statistics are invaluable for network engineering, allowing us to see in detail how the network is used. Smart sampling is a technique to get a reliable estimate of detailed usage from only a subset of flow record. It exploits the fact that a large fraction of usage is contained in a small fraction of flows. By preferentially sampling larger flows over small ones, we can control the volume of statistics while simultaneously controlling the variance of statistical estimates derived from them Smart Sampling is deployed in the AT&T IP measurement infrastructure and underpins AT&Ts Traffic Analysis Service. | 
