As the demand for real-time IP media transport over multi-point delivery environments increases, it is essential to monitor the time-varying status of both network metrics (i.e., delay, jitter, and loss) and system metrics (i.e., CPU and memory utilization). In this paper, we propose and implement a new monitoring system for the high-quality real-time media delivery over multicast-enabled network. It monitors the time-varying conditions of both the multicast network and the node system. When the media performance degrades, the proposed monitoring system attempts to pinpoint the cause of performance degradation to improve the end-to-end performance. The experimental results show that we can effectively infer the cause of performance degradation using the implemented prototype of the proposed monitoring system.