The current generation of network carriers competes intensely to satisfy the diverse wide-area connectivity requirements of customers. At the same time, the carriers inherently wish to maximize the usage efficiency of their network infrastructure. Much of the research in network resource management has been devoted to providing bandwidth guarantees and preventing network congestion. However, the rapid growth in number and diversity of real-time network applications has made it imperative to consider the impact of end-to-end delay of traffic requirements on network resource provisioning. We present an efficient network resource provisioning algorithm, called link criticality based routing (LCBR), which relies on the guiding theme that load balancing leads to higher resource utilization efficiency. LCBR applies a simple but very effective notion of link criticality to achieve networkwide load balance while simultaneously meeting the QoS requirements of bandwidth and end-to-end delay. In addition, LCBR can simultaneously provision both primary and backup routes to support fast recovery from node or link failures. This article reviews the state of the art in network resource provisioning with QoS guarantees, introduces the LCBR algorithm, and identifies future research challenges.