Getting the most for your Megabit

Abstract

The Gigabit Study Group at the University of Illinois is developing a tool that will permit analysis of the network from the application point of view, providing input into the network engineering process and predicting application performance. Phases in this development include the measurement of existing networks, the profiling of application input/output activity, and the integration of the information derived from these into a simulation tool.Maximum throughput ratings on networks continue to rise but our measurements show that the throughput realized by an application is closely tied to the sizes of data ( buffer sizes ) used by the application over the network and the number of buffers that are sent consecutively. Our preliminary study indicates that, while there are applications are specifically designed to take advantage of large network packets, most interactive TCP/IP applications use small (4 bytes to 8k bytes) buffers and do not send large numbers of buffers in a row. For this type of traffic, a 1 Gbps UltraNet provides about the same performance as a 10 Mbps Ethernet. For large volume traffic (32k bytes to 256k bytes), either generated by large packets or sequences of small packets, the UltraNet provides quite satisfactory throughput to the application. The study described herein examines the throughput of four networks as a function of buffer size for sequences of 4 buffers and 128 buffers.Because the maximum rated throughput of a network can be a poor indicator of the throughput that network provides to an application, we believe that a tool that takes into account the characteristics of the application set is needed.