Enable fair queueing with decoupled bandwidth-delay guarantees by relaxing the packet service order

This paper addresses the well-known, intrinsic limitation of weighted fair queueing (WFQ or PGPS), i.e., the delay bounds provided by WFQ schedulers are coupled with the guaranteed bandwidths, or more specifically, the delay bound of a flow is inversely proportional to its guaranteed bandwidth. This paper argues that this limitation is caused by the constrained packet service order under WFQ. Based on the ideal generalized processor sharing (GPS) fluid model, a new scheduling algorithm, relaxed-order fair queueing (R_Δ-FQ), is proposed. R_Δ-FQ still provides the guaranteed bandwidths and fairness, however, it does not constrain the packet service order. This enables fair queueing algorithms to remove the intrinsic limitation of WFQ. Based on R_Δ-FQ, another scheduling algorithm, priority-order fair queueing (P_Δ-FQ), is developed to simultaneously support guaranteed bandwidth services, fairness and priority.