Hierarchically Aggregated Fair Queueing (HAFQ) for Per-Flow Fair Bandwidth Allocation

Because of the development of recent broadband access technologies, fair service among users is becoming more important goal. The most promising router mechanisms for providing fair service is per–flow traffic management. However, it is difficult to implement in high–speed core routers because per– flow state management is prohibitively expensive; thus, a large number of flows are aggregated into a small number of queues. This is not an acceptable situation because fairness degrades as the number of flows so aggregated increases. In this paper, we propose a new traffic management scheme called Hierarchically Aggregated Fair Queueing (HAFQ) to provide per–flow fair service. Our scheme can adjust flow aggregation levels according to the queue handling capability of various routers. This means the proposed scheme scales well in high–speed networks. HAFQ improves the fairness among aggregated flows by estimating the number of flows aggregated in a queue and allocating bandwidth to the queue proportionally. In addition, since HAFQ can identify flows having higher arrival rates simultaneously while estimating the number of flows, it enhances the fairness by preferentially dropping their packets. We show that our scheme can provide per–flow fair service through extensive simulation and experiments using a network processor. Since the currently available network processors (Intel IXP1200 in our case) are not high capacity, we also give extensive discussions on the applicability of our scheme to the high–speed core routers. key words: Fairness, Packet Scheduler, Scalability, Network Processor