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Abstract-To support the Internet's explosive growth and expansion into a true integrated services network, there is a need for cost-effective switching technologies that can simultaneously provide high capacity switching and advanced QoS. Unfortunately, these two goals are largely believed to be contradictory in nature. To support QoS, sophisticated packet scheduling algorithms, such as Fair Queueing, are needed to manage queueing points. However, the bulk of current research in packet scheduling algorithms assumes an output buffered switch architecture, whereas most high performance switches (both commercial and research) are input buffered. While output buffered systems may have the desired quality of service, they lack the necessary scalability. Input buffered systems, while scalable, lack the necessary quality of service features. In this paper, we propose the construction of switching systems that are both input and output buffered, with the scalability of input buffered switches and the robust quality of service of output buffered switches. We call the resulting architecture Distributed Packet Fair Queueing (D-PFQ) as it enables physically dispersed line cards to provide service that closely approximates an output-buffered switch with Fair Queueing. By equalizing the growth of the virtual time functions across the switch system, most of the PFQ algorithms in the literature can be properly defined for distributed operation. We present our system using a crossbar for the switch core, as they are widely used in commercial products and enable the clearest presentation of our architecture. Buffering techniques are used to enhance the system's latency tolerance, which enables the use of pipelining and variable packet sizes internally. Our system is truly distributed in that there is neither a central arbiter nor any global synchronization. Simulation results are presented to evaluate the delay and bandwidth sharing properties of the proposed D-PFQ system.

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