4.8.2 Installation Summary

		backplane bandwidths between 20 and 40Gbps are available with moderate per port costs. The Caltech Naegling Beowulf employs a Lucent Technologies Cajun P550 switch to integrate up to 160 processors in a single system. This switch has a 45 Gbps backplane bisection bandwidth and 22 Gbps switched throughput. Several manufacturers including 3Com and Summit are competing in this market, and we expect prices to fall and performance to increase.

		Auto-Negotiation The use of smart active switches provides new opportunity for data transfer between Beowulf node NICs and the switch input ports. Autonegotiation is a machine to machine language that allows the devices at the two ends of an interconnecting line to determine the best mode of operation. It permits full duplex operation in which a Beowulf node can both transmit and receive packets at the same time, doubling the effective bandwidth. Another feature of autonegotiation is that mixed mode systems can be created and legacy hardware can be integrated. Systems with 10 base-T, 100 base-T, and Gigabit Ethernet can be co-resident in the same system. Autonegotiation sometimes fails, and the symptom is very poor performance due to mismatched duplex assumptions. It is always possible to disable autonegotiation and manually set switches and NICs to a common configuration.

		5.1.5 Gigabit Ethernet

		The success of 100 base-T Fast Ethernet and the growing demands imposed on networks by high resolution image data, real-time data browsing, and Beowulf-class distributed applications has driven the industry to establish a new set of standards for Ethernet technology capable of 1 Gbps. Referred to as ''Gigabit Ethernet." a backward compatible network infrastructure has been devised and early products are available from various vendors. A number of changes were required to Fast Ethernet including the physical layer and much of the data exchange protocols. However, to maintain compatibility with 100 base-T systems, means for mixed mode operation has been provided. Gigabit Ethernet is not cost effective for Beowulf-class computing yet. The early market for Gigabit Ethernet was expected to be for backbone service rather than direct terminal connections so the demand for NICs was assumed to be low and a large market has not yet emerged to amortize development costs. Both switches and NICs are substantially more expensive than 100 base-T systems.

		Several factors will motivate the migration of next generation of Gigabit Ethernet into the role of SANs for Beowulf-class systems. While Fast Ethernet served well for 200 MHz Intel Pentium Pro processor based Beowulf nodes, Intel Pentium