Optical subscriber line terminal unit and a state transition control method

An optical subscriber line terminal unit connected to an optical subscriber system for performing optical burst transmission, comprising:

• state information storing means for storing state information about the unit;
• startup preparatory state shifting means for causing a shift to a startup preparatory state at startup;
• flag setting means for setting an emergency stop state flag during a period of the startup preparatory state if it is judged based on the state information that a state before the startup is an emergency stop state;
• and
• state transition control means for causing a shift from the startup preparatory state to the emergency stop state if the emergency stop state flag is set, and causing a shift from the startup preparatory state to an initial state if the emergency stop state flag is not set,
• the startup preparatory state being distinct from the emergency stop state, the emergency stop state flag having at any time one of only two values of ON when the emergency stop state flag is set and OFF when the emergency stop state flag is not set, the initial state being a single state.