Abstract: A three level network microprocessor based nodal architecture for a fiber optic local area network communication system is disclosed in which the processing responsibility for establishing a voice, video or data communication link between an initiating I/O device and a recipient I/O device and for subsequent two way data exchange between the initiating and recipient devices are shared between three levels of digital processing capability in such manner as to demand the least amount of time from the highest, most intelligent processing level common to all devices thereby making more efficient use of its processing capability as an overall supervisory processor. Each I/O device whether it be a digital terminal, computer or telephone set interfaces with a nodal system through a middle level of processor. An initial communication request from any device at the middle level generates an interrupt command to the highest supervisory processing level which responds to the interrupt, resulting in the identification of the desired recipient station by recalling from storage, associated with the highest level processor, routing information required in establishing a communication link with the desired recipient device. That information is provided to the processor at the middle level associated with the initiating device. That processor completes the link if the recipient is local to it. Otherwise the addresse or recipient device identifying codes are communicated from the middle level to a third level processor responsible for effecting the actual routing of the communication.