Recently, packet networks are enabling the integration of heterogeneous traffic with a wide range of characteristics that extend from video traffic with stringent QoS requirements to best- effort traffic requiring no guarantees. QoS guarantees can be provided in packet networks by using the proper packet scheduling algorithms. In this book, we propose a new priority assignment scheduling algorithm, Hierarchical Diff-EDF, which can meet the real-time needs while continuing to provide best effort service over heterogeneous real- time network traffic. The Hierarchical Diff-EDF service meets the flow miss rate requirements through the combination of the single step hierarchal scheduling for the heterogeneous network flows and the admission control mechanism that detects the overload conditions to modify packets'' priorities. An Agent-based Simulator for Real-Time Schedulers (ASRTS) has been developed to evaluate this algorithm. Based on the selected performance measures, the evaluation clearly shows that the Hierarchical Diff-EDF achieves robustness results.