A novel algorithm for buffer management and rate allocation is presented for providing loss and delay differentiation for traffic classes at a network router. The algorithm, called JoBS, provides delay and loss differentiation independently at each node, without assuming admission control or policing. Contrary to most existing algorithms, scheduling and buffer management decisions are performed in a single step. Both relative and (whenever possible) absolute QoS requirements of classes are supported. Simulation examples, including results for a heuristic approximation, are presented to illustrate the effectiveness of the approach, to compare the new algorithm to existing methods for loss and delay differentiation. 1 Key Words: Buffer Management, Scheduling, Service Curves, Quality-of-Service, Service Differentiation. This work is supported in part by the National Science Foundation through grants NCR-9624106 (CAREER), ANI-9730103, and ANI-0085955. 1 An earlier version of this paper w...