Bhatnagar, ShalabhFu, Michael C.Marcus, Steven I.Optimal multilevel control policies for rate based flow control in available bit rate (ABR) service in asynchronous transfer mode (ATM) networks are obtained in the presence of information and propagation delays, using a numerically efficient two timescale simultaneous perturbation stochastic approximation (SPSA) algorithm. Numerical experiments demonstrate fast convergence even in the presence of significant delays and a large number of parametrized parameter levels.en-USoptimal controldiscrete event dynamical systems DEDSflexible manufacturingmanufacturingoptimal multilevel feedback policyrate based ABR flow controltwo timescale SPSAIntelligent Control SystemsSystems Integration MethodologyTechnical Report