End-to-End guaranteed network QoS is a requirement for predictable data transfers between geographically distant end-hosts. Existing QoS systems, however, do not have the capability/intelligence to decide what resources to reserve and which paths to choose when there are multiple and flexible resource reservation requests. In this paper, we design and implement an intelligent system that can guarantee end-to-end network QoS for multiple flexible reservation requests. At the heart of this system is a polynomial time algorithm called resource reservation and path construction (RRPC). The RRPC algorithm schedules multiple flexible end-to-end data transfer requests by jointly optimizing the path construction and bandwidth reservation along these paths. We show that constructing such schedules is NP-hard. We implement our intelligent QoS system, and present the results of deployment on real world production networks (ESnet and Internet2). Our implementation does not require modifications or new software to be deployed on the routers within network.