Performance evaluation of a picture archiving and communication network using stochastic activity networks

A fiber-optic star-based picture archiving and communication system (PACS) network that is based on a multiplexed passive star local area network with wavelength-division multiplexing (WDM) to provide separate logical channels for transfer of control and image data is discussed. The system consists of an image network (INET), for image transfer at a rate of 140 Mb/s, and a control network (CNET), operating at 10 Mb/s, for mediating the flow of image transfers. INET is a circuit switched network devoted solely to image transfer, while CNET employs the CSMA/CD protocol for bus arbitration. Stochastic activity networks were used to develop a detailed model of the command and image channels. The performance of the system was then evaluated under realistic workload conditions. In particular, a number of important performance variables, including the image response time, command channel delay, and queue length at each type of node and the network supervisor, are estimated. The results (1) show that stochastic activity networks are an appropriate model type for evaluating picture archiving and communication systems, (2) delineate the workload conditions under which PACS may effectively operate, and (3) show that even when these conditions are exceeded, the command channel load remains extremely light.