Hitachi, Ltd.

Hitachi Communication Technologies, Ltd.

Ryosuke Nishino

Tohru Kazawa

Kenichi Sakamoto

Yoshihiro Ashi

Masayuki Takase

Masahiko Mizutani

Masao Niibe

Takeshi Kiyose

An optical access system capable of avoiding cutoffs or interruption in the periodically transmitted signals that occur during the ranging time is provided. A first method to avoid signal cutoffs is to stop periodic transmit signals at the transmitter during the ranging period, and transmit all the periodic transmit signals together when the ranging ends, and buffer the signals at the receiver to prepare for ranging. A second method is to fix definite periods ahead of time for performing ranging, then cluster the multiple periodic transmit signals together in sets at the transmitter and send them, and then disassemble those sets back into signals at the receiver. The transmitting and receiving is then controlled so that the transmit periods do not overlap with the ranging periods. In this way an optical access system is provided that can send and receive signals requiring periodic transmissions without interruption even during ranging operation.

Optical access system

In a PON system with WDM, at the time of initial setting, each ONU negotiates with an OLT, and automatically acquires a wavelength which can be used by the ONU. One wavelength for negotiation of assigned wavelength is fixed as a default, and a newly connected ONU first uses the wavelength. The OLTincludes a plurality of light sources for downstream communication. The ONUincludes a wavelength variable filter selectively receiving one of wavelengths of downstream communication, and a wavelength variable light source selectively emitting light of one of plural wavelengths for upstream communication. The ONUuses a transmission wavelength (for example, &#x3bb;u) for negotiation and transmits a wavelength assignment requestto the OLT. The OLTselects a wavelength &#x3bb;uto be assigned from unused wavelengths, and transmits wavelength information to the ONU. The OLTand the ONUcommunicates using the notified wavelengths.

Passive optical network system and wavelength assignment method

In a GPON system conforming to ITU-T Recommendations G.984.3, an optical line terminal is provided which has an active bandwidth allocation function that preferentially puts small bandwidth signals in a particular segment of a frame, e.g., at a head of the frame, to prevent fragmentations that may occur particularly when allocating small bandwidths of about 100 kbits/s.

Optical line terminal capable of active bandwidth allocation for passive optical network system

In a passive optical network system in which signals from a master station to plural slave stations are time-division multiplexed and transmitted, the slave stations different in transmission speed are mixedly contained. The master station (OLU) performs ranging for each transmission speed, and grasps all the slave stations different in transmission speed for each transmission speed, and generates a frame including signals of a suitable transmission speed corresponding to each slave station. When the frame is generated, in a downstream signal in which signals of plural transmission speeds are mixed, a dummy signal is set at a place where the transmission speed is changed, and a time necessary to follow a change in level of a received signal due to a change in optical level caused when the transmission speed is changed is secured. Thereby, each ONU avoids a reception error occurring in the time necessary to follow.

Passive optical network system and optical line terminator

A station-side apparatus adapted for use in a passive optical network (PON) system is disclosed, which remotely collects inside information of optical network terminals (ONTs) even before completion of start-up of an optical network unit (ONU), permits an obstruction-detected ONU to send out an emergency notification message to the station-side apparatus, e.g., optical line terminal (OLP), and permits the OLT that received this message to interrupt the transmission of an upload signal toward another ONU after the elapse of a fixed length of time while at the same time receiving information from the obstruction-suffering ONU to thereby facilitate cut-and-divide or 'segmentation' of obstruction. A subscriber-side device for use in the PON system is also disclosed.

Growing community of inventors

Yokohama, Japan

Ryosuke Nishino