Delay bound Guarantees with WFQ-based CBQ discipline

Class Based Queueing (CBQ) is a packet scheduling discipline that enables hierarchical link-sharing. Compared to other algorithms, it is modular and intuitive in a first approach, and so is implemented and used nowadays. In this paper, we adapt the discipline to schedule critical real-time flows mixed with other kinds of traffic, as is necessary in a DiffServ environment This requires that some guarantees must be provided deterministically, particularly on queueing delay bounds. Yet theoretical delay bounds for CBQ were never expressed in a general case and with end-to-end derivation, because the nesting of mechanisms makes it hard to predict a worst case scenario. Here we study some cases where an analysis is possible, focusing on two variants of CBQ, and we use network calculus technique to set up a bound that seems realistic. We then show simulations to check the precision of our results.