Evaluation of DEC's GIGAswitch for distributed parallel computing.

摘要

One of Sandia's research efforts is to reduce the end-to-end communication delay in a parallel-distributed computing environment. GIGAswitch is DEC's implementation of a gigabit local area network based on switched FDDI technology. Using the GIGAswitch, the authors intend to minimize the medium access latency suffered by shared-medium FDDI technology. Experimental results show that the GIGAswitch adds 16.5 microseconds of switching and bridging delay to an end-to-end communication. Although the added latency causes a 1.8% throughput degradation and a 5% line efficiency degradation, the availability of dedicated bandwidth is much more than what is available to a workstation on a shared medium. For example, ten directly connected workstations each would have a dedicated bandwidth of 95 Mbps, but if they were sharing the FDDI bandwidth, each would have 10% of the total bandwidth, i.e., less than 10 Mbps. In addition, they have found that when there is no output port contention, the switch's aggregate bandwidth will scale up to multiples of its port bandwidth. However, with output port contention, the throughput and latency performance suffered significantly. Their mathematical and simulation models indicate that the GIGAswitch line efficiency could be as low as 63% when there are nine input ports contending for the same output port. The data indicate that the delay introduced by contention at the server workstation is 50 times that introduced by the GIGAswitch. The authors conclude that the GIGAswitch meets the performance requirements of today's high-end workstations and that the switched FDDI technology provides an alternative that utilizes existing workstation interfaces while increasing the aggregate bandwidth. However, because the speed of workstations is increasing by a factor of 2 every 1.5 years, the switched FDDI technology is only good as an interim solution.