Patent ID: 7738790
Filing Date: 2010-06-15
Classification: H04J

Abstract:
1. A WDM (Wavelength Division Multiplexing) type PON (Passive Optical Network) system in which a central office side apparatus OLT (Optical Line terminal) and a plurality of subscriber connection apparatuses ONUs (Optical Network Units) are connected by a passive optical network and each of said ONUs communicates data with said OLT, using its specific upstream and downstream optical signal wavelengths that are not used by the other ONUs, said passive optical network comprising an optical fiber connected to said OLT, a plurality of branch optical fibers each connected to one of said ONUs, and a splitter for distributing to said branch optical fibers a wavelength multiplexed downstream optical signal transmitted from said OLT and combining upstream optical signals transmitted from said ONUs into a wavelength multiplexed signal which is transferred along the optical fiber to said OLT, each of said ONUs comprising an optical transmitter variable its transmitting wavelength for upstream optical signals, an optical signal receiving filter variable its receiving wavelength, and a control unit for controlling the transmitting wavelength of the optical transmitter and the receiving wavelength of the optical signal receiving filter, said OLT comprising a wavelength management table having a plurality of entries each indicating an identifier of a pair of wavelengths available in said passive optical network and a current use state of the wavelengths, and a control unit for searching the wavelength management table for an identifier of idle state wavelengths in response to a wavelength allocation request from each of said ONUs, and allocating a pair of a transmitting wavelength and a receiving wavelength corresponding to the searched identifier to the requester ONU by transmitting a wavelength allocation response indicating the pair of the transmitting wavelength and the receiving wavelength to the requester ONU, wherein the control unit of each of said ONUs transmits the wavelength allocation request to said OLT, in the state where the transmitting wavelength of the optical transmitter and the receiving wavelength of the optical signal receiving filter are set at predetermined wavelengths common for all ONUs, and wherein the control unit of said ONU switches the transmitting wavelength of the optical transmitter and the receiving wavelength of the optical signal receiving filter to specific wavelengths allocated from said OLT, in response to said wavelength allocation response message, thereby performing data transmission and reception by continuously occupying the specific wavelengths as dedicated wavelengths while the ONU is in an operating state.