METHOD FOR COMPENSATING ROUND TRIP DELAY IN TRANSMITTING ETHERNET FRAME THROUGH PASSIVE OPTICAL NETWORK AND DOWNSTREAM GRANT SIGNAL FRAME FORMAT

摘要

PURPOSE: A method for compensating RTD(Round Trip Delay) in transmitting an Ethernet frame through a PON(Passive Optical Network) and a downstream grant signal frame format are provided to efficiently receive Ethernet traffics in a PON system and exactly adjust the clock synchronization between an OLT(Optical Line Transmission) and an ONU(Optical Network Unit). CONSTITUTION: An OLT sends a gate message at To with its own clock. The OLT writes a value of To+RTT(i) and Ts, time to receive a slot to allocate, at the time stamp field and slot start field of the gate message respectively. An ONU(i), receiving the gate message, adjusts its own local clock count to the time recorded at the time stamp field of the gate message. The ONU(i) sends a report message at Ts on the basis of its own local clock. On the assumption that the synchronization of two clocks is well adjusted and there is no clock drift, the OLT receives the report message at Ts on the basis of its own clock.