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Evaluation and Design of High-Performance Network Topologies

Cherkasova, Ludmila; Kotov, Vadim; Rokicki, Tomas

HPL-95-69

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Abstract: The Fiber Channel standard provides a mechanism for interconnecting heterogeneous systems containing peripheral devices and computer systems through optical fiber media. In this paper, we consider how FC switches can be cascaded to form a Fiber Channel fabric. We begin with an analytical model of topology performance that provides a theoretical upper bound on fabric performance and a method for the practical evaluation of fabric topologies. This model does not depend on any specific characteristics of Fiber Channel and can be applied to ATM networks, Ethernet networks, and many other forms on networks. It allows us to calculate the approximate traffic throughput supported by a particular network graph, and thus easily compare different network topologies. Fiber Channel fabrics are particularly vulnerable to buffer-cycle deadlock. Only a small subset of topologies based on tree structure or complete graphs are innately free from deadlocks. Most optimal and high-performance fabric topologies will deadlock if not routed intelligently. A specific deadlock-free routing usually introduces imbalance in link utilization, so the traffic must be carefully assigned given a particular deadlock-free routing. We call the combination of traffic-balancing and our deadlock-free routing algorithm "Smart Routing"; for most networks, there exists a Smart Routing that is very close in throughput to that of the network ignoring the possibility of deadlock.

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