Experiences with a wide area gigabit network

The Blanca gigabit testbed is one of the national, high speed networking testbeds coordinated by the Corporation for National Research Initiative. After two years of continuous development, the Blanca high speed trunk now consists of two local-area HIPPI networks bridged by a wide-area OC-12 ATM link. Because there are many elements involved in the proper operation of the experimental network, application level testing often requires the coordination of multiple parties at different sites to monitor the hardware and systems software involved. In short, gathering application level performance data has been a real challenge. We describe and analyze the application level performance data gathered from the Blanca gigabit network. We have developed a high-speed networking library and a distributed image server application to help us understand the behavior of high speed network. Our measurements over Blanca showed that large TCP window sizes are crucial to achieving high bandwidth utilization. In addition, the host operating system idiosyncrasies significantly affect the networking performance. Using a variety of optimization techniques, we were able to improve the throughput by as much as 65 percent. The techniques described should prove useful to application developers who wish to exploit the bandwidth of high speed networks.