Proportional differentiated services, part II: loss rate differentiation and packet dropping

The proportional differentiation model was proposed in Dovrolis et al. (1999), as a target for controllable and predictable relative differentiated services. Only the delay differentiation aspect of the model was considered, and focused on packet scheduling mechanisms. In this paper, we extend the proportional differentiation model in the direction of loss rate differentiation. Several previous mechanisms for buffer management and packet dropping, such as complete buffer partitioning, partial buffer sharing, or multi-class RED, are not suitable for relative differentiated services. We propose and evaluate two dropping mechanisms that closely approximate the proportional loss rate differentiation model. The two droppers, PLR(/spl infin/) and PLR(M), differ in the time interval over which the loss rates are measured and proportionally adjusted. This difference results in several trade-offs, in terms of implementation complexity, accuracy, and ability to deal with nonstationary traffic loads. We also re-evaluate the delay differentiation that the waiting time priorities (WTP) scheduler, of Dovrolis et al., can achieve in the presence of finite buffers and packet losses; this study extends their results providing further insight into the behavior of WTP in heavy load conditions. Finally, we examine the coupled effect of delay and loss rate proportional differentiation on the throughput of bulk-transfer TCP connections.