Qualitative investigation of cost optimization strategies for industrial-based fiber optic local area networks

The inherent properties of optical fibers such as small size and weight, EMI/RFI immunity, low attenuation, and large bandwidth provide many advantages over wire conductors that make fiber well-suited for communications. Fiber optic local area networks are particularly suited for use in electrically noisy and space sensitive industrial environments.

The diversity of communication requirements that exist in a typical factory situation can be accommodated by the use of a hierarchical communications structure consisting of multiple tiers of fiber optic networks. The lowest tier of this structure would be inexpensive feeder networks used to connect devices such as sensors, actuators, PLCs, robots, and small computers on a factory floor. The emphasis at this level is low cost, but while providing interconnection to higher tiers.

An approach which satisfies the lowest tier requirements is a non-shared medium scheme which is link based, consisting of an active star architecture using a roll-call polling access method. The centralized intelligence structure of a master/slave access method allows one to concentrate on the cost optimization of the optical data links. The use of low-cost optical components such as LEDs, PIN diodes, and plastic fiber as well as the potential for a significant amount of common hub equipment provides considerable economies.