Passive optical star bus with collision detection for CSMA/CD-based local-area networks

A prototype 16-terminal passive star bus suitable for carrier sense multiple access with collision detection (CSMA/CD)-based fiber-optic local-area network is described. Operation is at 16 Mbit/s over optical path lengths of 600 m. The optical wavelength is 830 nm. A novel and simple collision detection method based on listening onto the bus is incorporated within the system. In addition, data is scrambled instead of Manchester encoded. The effect that scrambling has on the collision detection method, as well as on the detection of both the bus idle state and the beginning and end of data packets is examined in detail. The network efficiency is calculated taking into account the operation of the scrambler as well as the collision detection method.