Abstract: We propose a network-based endpoint admission control system for scalable QoS guaranteed real-time communication services. This system is based on a sink tree-based resource management strategy, and is particularly well suited for differentiated-services based architectures. By performing the admission decision at the endpoints, the flow setup latency and the signaling over-head are kept to a minimum. In addition, the proposed system integrates routing and resource reservation along the routes, and therefore displays higher admission probability and better link resource utilization. This approach achieves low overall admission control overhead because much of the delay computation is done during system configuration, and so resources can effectively be pre-allocated before run time. We investigate a number of resource sharing approaches that allow resources to be efficiently re-allocated at run time with minimized additional overhead. We provide simulation experiments that illustrate the benefits of using sink tree-based resource management for resource pre-allocation and for routing, both with and without resource sharing.