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Because of the development of recent broadband access technologies, fair services among users are becoming more important criteria. The most promising scheme of router mechanisms for providing fair service is per-flow traffic management. However, it is difficult to be implemented in high speed core routers because per-flow state management is prohibitive; thus, a large number of flows are aggregated into a small number of queues. This is not a preferable situation because the more number of flows aggregated into a queue increases, the worse fairness tends to become. In this paper, we propose a new traffic management scheme called hierarchically aggregated fair queueing (HAFQ) to provide per-flow fair service. Our proposed scheme can adjust flow aggregation levels according to the queue handling capability of various routers. That means the proposed scheme is scalably used 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 in estimating the number of flows, it enhances the fairness by preferentially dropping their packets. We show that our proposed scheme can provide per-flow fair service through extensive simulation and experimental studies 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.