Core-Stateless Fair Queueing (CSFQ)

If the biggest objection to FQ is the per-flow state, the authors show how that state can be pushed to the edges of the network to allow core devices to function on individual packets while maintaining the nice properties of fair queueing. The actual exposition of their algorithm only takes a couple of pages, and the rest of the paper is an evaluation of the architecture and performance. In CSFQ, all per-flow state is maintained and ingress routers, which tag packets with a rate representing the rate of the flow. The use an exponential filter to estimate the arrival rate of packets for a particular flow which keeps the flow state to a few state variables. Write the fair rate into an MPLS-style tag at the head of the packet. What seems like it could be a crucial part of the algorithm is rewriting the rate estimates in the core, by reestimating the "fair rate" downward when packets are dropped.

The authors' simulation seems to show CSFQ working about as well as DRR (Deficit Route Robin), which seems to be the benchmark here since it has per-flow queue dicipline. The advantage of CSFQ is the careful state management. The other algorithms really do not perform well at all, for the same reasons the authors argued in Analysis and Simulation...

The authors mentions MPLS as one example of existing labeling and classification at the edge; there's a more recent modification (MPLS-TE for Traffic Engineering) that provides some administrative control over routes. However, I think that modern routers do implement forms of fair queueing. It may be the case that the amount of state to implement fair queueing at every router is no longer prohibitive; also, it seems that some routers implement fair queueing between administratively-defined traffic classes, which both reduces the state since N is now the number of classes and not the number of conversations, and accomplishes part of the intent of FQ.

I'm not sure I would include both this paper and the original FQ one.