a distributed measurement technique for an operating ethernet network (abstract only)  the objective of the research is to design and implement a monitoring system for an operating ethernet network. several existing monitoring techniques have been examined and contrasted. this examination led to the development of a master/slave monitoring system. the proposed technique counters the drawbacks of existing hybrid techniques by relocating the interface between the node and monitor and establishing a master/slave relationship among the monitors.  a monitor observes the network, collects data, and presents results in a usable form. monitors can provide traces or profiles of network transactions. although useful for debugging purposes, traces, or complete records of network traffic, impose excessive storage and processing requirements on a monitor. thus, a profile made up of certain statistics about network traffic is often more practical. these statistics are collected by both the slave and master monitors with the final data reduction occurring in the master monitor.  the slave monitor is a passive device that collects information at a node by directly monitoring the transceiver cable, processes the information, and transfers statistical data to the master monitor over a dedicated inter- monitor bus. by using the passive tap the slave monitors provide distributed measurement without introducing changes in the network nodes or the software running on the nodes. the slave monitors communicate with the master monitor via an economical multidrop twisted pair network. this network provides sufficient bandwidth without the overhead and cost associated with a standard network. the overhead produced by using the network under evaluation as the master to slave communication facility is also eliminated. the slave monitors consist of a small number of off the self components and derive power from the transceiver cable. these monitors process the data locally and only send the processed results to the master monitor. the slave monitors can be reconfigured by the master monitor to provide maximum flexibility.  the master monitor functions as a data collector, data analyzer, and traffic generator, and supports an intelligent user interface. the master monitor can generate traffic with time stamps and can measure several system parameters. the master monitor also can use the information obtained from the slave monitors to provide detailed traffic information for each node. this node by node traffic information will provide an accurate profile of the network and of network performance. the master monitor consists of a standard multibus ethernet controller board with an on- board cpu and memory. the software for the master monitor will replace the standard ethernet driver software for the board. the monitor will also contain a standard multibus cpu for additional processing and to provide the user interface. in addition the master monitor will provide and interface to a personal computer for additional data processing and storage.  the monitoring system can support very large networks consisting of multiple networks and bridges. the monitors can be configured in a hierarchical topology with multiple master monitors connected together. each master monitor is responsible for a portion of the total network. these sub-master monitors will communicate with a center master monitor that provides the user interface and central control.  this monitoring system is under development at iowa state university and will be tested on a 15 node network that supports a wide variety of traffic. once the monitor system is developed it can be used for both teaching and research and will help in the development of a distribute file system based on a large collection of unix machines connected via ethernet.  d. w. jacobson