Scalable ethernet clos-switches

Scalability of Cluster-Computers utilizing Gigabit-Ethernet as an interconnect is limited by the unavailability of scalable switches that provide full bisectional bandwidth. Clos' idea of connecting small crossbar-switches to a large, non-blocking crossbar - wide-spread in the field of high-performance networks - is not applicable in a straightforward manner to Ethernet fabrics. This paper presents techniques necessary to implement such large crossbar-switches based on available Gigabit-Ethernet technology. We point out the ability to build Gigabit-Ethernet crossbar switches of up to 1152 ports providing full bisectional bandwidth. The cost of our configuration is at about EURO125 per port, with an observed latency of less than 10 mu sec. We were able to find a bidirectional point-to-point throughput of 210 MB/s using the ParaStation Cluster middle-ware[2].