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We examine a proportional-delay model for Internet differentiated services. Under this model, an ISP can control the waiting-time "spacings" between different classes of traffic. Specifically, the ISP tries to ensure that the average waiting time of class traffic relative to that of class 1 traffic is kept at a constant specified ratio. If the waiting-time ratio of class 1 to class is greater than one, the ISP can legitimately charge users of class traffic a higher tariff rate (compared to the rate for class 1 traffic), since class users consistently enjoy better performance than class 1 users. To realize such proportional-delay differentiated services, we use the time-dependent priority scheduling algorithm. We formally characterize the feasible regions in which given delay ratios can be achieved. Moreover, a set of control parameters for obtaining the desired delay ratios can be determined by an efficient iterative algorithm. We also use an adaptive control algorithm to maintain the correctness of these parameters in response to changing system load. Experiments are carried out to illustrate the short-term, medium-term and long-term relative waiting-time performances for different service classes under Poisson, Pareto, MMPP and mixed traffic workloads. We also carry out experiments to evaluate the achieved end-to-end accumulative waiting times for different classes of traffic which traverse multiple hops under our service model.

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