QoS Routing with worst-case delay constraints: models, algorithms and performance analysis

In a network where weighted fair-queueing schedulers are used at each link, worst-case end-to-end delays can be inferred from per-link rate reservations. Therefore, it is also possible to compute resource-constrained paths that meet target delay constraints, and optimize some key performance metrics (e.g., minimize the overall reserved rate, maximize the remaining capacity at bottleneck links, etc.). Despite the large amount of literature on QoS routing appeared since the mid '90s, few papers so far have discussed solving such path computation problem at optimality in general settings. In this paper, we formulate and solve the optimal path computation and resource allocation problem assuming different types of weighted fair-queueing schedulers in the network. We show that, depending on the scheduling algorithm, routing a new flow may or may not affect the performance of existing flows; hence, explicit admission control constraints may be required to ensure that existing flows still meet their deadline afterwards. Yet, for the relevant schedulers proposed in the literature the problem can be formulated as a Mixed-Integer Second-Order Cone problem (MI-SOCP), and can be solved at optimality in split-second times even in fairly large networks