Passive optical network system and sleep time determination method

A passive optical network system comprising at least one optical line terminal and a plurality of optical network units,

• the optical line terminal comprising:
• a first interface for communications with an upper network at a first link speed;
• a first queue buffer for holding downstream data for each of the destination optical network units;
• an electro-optical converter for communications with the optical network units;
• and
• a first controller for applying sleep control to the optical network units;
• each of the optical network units comprising:
• a second interface for communications with a communication terminal at a second link speed;
• a second queue buffer for holding upstream data bound for the optical line terminal;
• an electro-optical converter for communications with the optical line terminal;
• and
• a second controller for applying sleep control to the local optical network unit;
• wherein:
• the first controller of the optical line terminal calculating a first sleep time candidate based on a capacity of an unused area of the first queue buffer and the first link speed;
• the second controller of each of the optical network units calculating a second sleep time candidate based on a capacity of an unused area of the second queue buffer and the second link speed;
• either the first controller or the second controller comparing the first sleep time candidate and the second sleep time candidate for at least one of the optical network units and determining the smaller thereof as an actual sleep time;
• and
• the at least one of the optical network units being changed to a sleep mode during the determined actual sleep time.