Standardized active measurements on a tier 1 IP backbone

Synthetic or active measurements are often used to characterize IP performance; however, it is rare to find them used to resolve problems in an operational setting. We show that the active monitoring system in the AT&T IP backbone provide\´s a comprehensive view of network performance that is complementary to traditional element level monitoring, making it an integral part of network management. This paper discusses the design and implementation of these active measurements in the network. We continuously monitor "path-level" performance metrics such as round-trip delay, loss, jitter, and reordering events to proactively detect impairments. Our system relies on the promotion of key metrics to the operational displays, while maintaining a rich set of statistics for analyzing rare and unforeseen events. This timely information enables us to react,quickly to performance degradation, avoiding any sustained effect on customer applications. The results also help us understand the network\´s ability to support time-sensitive application performance. Selected "interesting" events observed are presented, including detection of degradation caused by low-level bit errors on a physical link, detection of route changes on the network and their impact on real-time applications, and finally detection of reordering caused by forwarding loops.