Description of Fasnet - A Unidirectional Local-Area Communications Network

Local computer networks operating at 1 to 10 Mb/s are being commercially offered and appear to adequately meet current demands for computer communications within the office environment. However, future needs stimulated by both a broader range of services than is now available and changes in system architecture (e.g., the trend towards distributed processing) could increase significantly the demand for digital capacity. For example, one would like to be able to handle video information, voice traffic, and facsimile, as well as computer traffic, in a single digital system. The availability of a cheap, high-capacity communication conduit between computers will itself stimulate increased traffic. For example, processing time can be traded for communication capacity; rather than transmitting a text file and * Department of Electrical Engineering and Computer Science, University of California at Berkeley. 1413 formatting it at a remote location, one may choose to transmit a formatted version or even a bit map. Thus, while today 10 Mb/s may be regarded as an extremely generous bit rate for a local computer network, 200 Mb/s may become limiting for an integrated communications network. Carrier-sense multiple access with collision detection (CSMA/CD) is reliable and reasonably efficient even under heavy load for most conditions.1 Shoch and Hupp2 show that measurements of channel utilization of an Ethernet* yield results that are close to calculations made by Metcalf and Boggs, using a simplified model and assuming that active stations have data continuously queued for transmission.