TRIO: Measuring asymmetric capacity with three minimum round-trip times

Measuring network path capacity is an important capability to many Internet applications. But despite over ten years of effort, the capacity measurement problem is far from being completely solved. This paper addresses the problem of measuring network paths of asymmetric capacity without requiring the remote node's control or overwhelming the bottleneck link. We first show through analysis and measurement that the current packet-dispersion methods, due to the packet size limitations, can only measure up to a certain degree of capacity asymmetry. Second, we propose TRIO that removes the limitation by using round-trip times (RTTs). TRIO cleverly exploits two types of probes to obtain three minimum RTTs to compute bothforward and reverse capacities, and another minimum RTT for measurement validation. We validate TRIO's accuracy and versatility on a testbed and the Internet, and develop a system to measure path capacity from the server or user side.