Communication network

A high-speed fiber optic star configuration network uses a processor at the network hub to monitor and control network activity. The hub and the individual nodes of the network cooperate to calibrate node transmitter power levels and node receiver sensitivities. A token passing protocol is used to allocate network access. The token passing is monitored at the hub to detect lost tokens or a babbling bus. The hub processor has the capability to initiate tokens or restore lost tokens and to shut off the transmitter of a node which remains connected to the bus for an excessive period of time. In one embodiment, the circuit elements of the hub are duplicated to provide two separate paths through the hub.