We introduce ImSystem, a distributed system that infers real-time information concerning the available bandwidth of all of the paths in the overlay networks, using a technique called inline network measurement. The key concept in ImSystem is that, when the overlap hosts transmit overlay traffic, they deploy the traffic to perform inline network measurements and exchange results with each other. ImSystem performs supplemental active measurements only when overlay traffic is insufficient for inline measurements, and therefore injects very little probe traffic onto the network. In addition, we enhance the system to ImSysiemPlus, in which conflicts of the supplemental active measurements are greatly reduced, providing that the IP network topology is known. The simulation results show that the proposed systems have the same accuracy as that when all paths are measured by active measurements, while using only a small amount of probe traffic.