Optical subscriber network system

Details Optical subscriber network system Optical subscriber network system

1998-02-09

2001-09-11

Pascal, Leslie (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200

Reexamination Certificate

active

06288809

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light or optical subscriber network system, and in particular to an optical subscriber network system which is formed of a passive optical network.
2. Description of the Related Art
To subscribers requiring a high-speed and large capacity of communication, as shown in
FIG. 12
, has generally known a network system which accommodates optical subscribers #1-#n with optical network units generally designated by ONU through optical fibers generally designated by OF correspondingly constructed from an optical service unit (station unit) OSU in a station ST which is formed of the optical service unit OSU and a switchboard EX.
On the other hand, in recent years, a passive optical subscriber network system as shown in
FIG. 13
has been put into practice which accommodates optical subscribers which need a broad-band communication.
This passive optical subscriber network system has an optical star coupler SC which consists of passive elements between a station unit and the optical network units (subscriber units). A pair or two pairs for redundancy of optical fibers OF
1
are provided between the station ST and the star coupler SC. Optical fibers OF
2
, which are exclusive for each subscriber, are provided from the star coupler SC to the subscribers #1-#n.
In the star coupler SC, a down optical signal is distributed from the station ST to the respective optical subscribers #1-#n while up optical signals are united from the optical subscribers #1-#n to the station ST.
In such an optical subscriber network system as mentioned above, TCM (Time Compression Multiplexing) method has been used which adopts TDMA (Time Division Multiple Access) method enabling subscribers to access the station unit by allotting time slots to the up signal from the optical network unit ONU to the optical service unit OSU and TDM (Time Division Multiplexing) method used in the down signal from the optical service unit OSU to the optical network unit ONU when the outputs of the plural optical network units ONU are multiplexed to a single optical transmission line (optical fiber).
That is, as shown in
FIG. 14
, the down signal frame from the optical service unit OSU is provided for the optical subscribers e.g. #1 and #2 by the TDM method, and the up signal frame from the subscribers #1 and #2 to the optical service unit OSU is provided by the TDMA method.
In this TCM method, the construction cost of the system can be reduced by sharing both the optical transmission line and the optical service unit of the station, in comparison with the method of connecting the optical service unit OSU and the optical network unit ONU correspondingly. Moreover, the reliability of the system can be improved because passive elements are used for a star coupler, compared with the method of multiplexing/demultiplexing optical signals with an active unit.
In the passive optical subscriber network system shown in
FIG. 13
, it is considerably easy to form duplexed optical transmission lines for redundancy from the station to the star coupler.
However, the formation from the star coupler to the subscribers is not duplexed. Therefore, if a fault occurs in the optical transmission-reception portion (transceiver system) of the optical network unit ONU, the communication between the station and the faulted optical network unit ONU will be completely broken.
In the worst case, as shown in
FIGS. 15 and 16
, the optical transmission portion of the faulted optical network unit ONU
2
emits light abnormally at the time slot TS′ which is not the same as the time slot TS (shown by a dotted line) in which light should be emitted. The abnormal light emission may collide with the up frame in the optical network unit ONU
1
which is accommodated in the same star coupler. Eventually the communication can be obstructed and interrupted.
Moreover, the maintenance in the station is relatively easy while it is difficult to specify whether the faulted point resides in the transmission line or in the optical network unit because information of the optical network unit is not obtained at the side upon the fault. Therefore, fieldworks increase so that restoration time, material and human costs grow to remove the fault of the optical network unit.
As measures for these problems, another optical network system has been considered as shown in FIG.
17
. This system is formed of a star coupler SC, an optical fiber OF
2
, and an optical transmission-reception portion of an optical network unit ONU which are respectively duplexed. This system must follow a great cost increase.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide an optical subscriber network system which connects plural optical network units (subscriber units) to an optical service unit (station unit) through optical transmission lines with passive optical elements, in which the optical transmission system is duplexed with a lower cost.
In order to achieve the above-mentioned object, an optical subscriber network system according to the present invention is characterized in that the optical service unit and the optical network units each comprise a plurality of transmission-reception portions which transmit and receive signals the wavelengths of which are different from each other, an optical coupler installed between the transmission-reception portions and the optical transmission line, a system changer which switches over the transmission-reception portions and receives a main signal of one system, and a controller which monitors the reception state detected at the transmission-reception portions, and switches over the system changer to the system without a fault which the controller detects from the reception state.
Namely, in the present invention, the optical service unit and the optical network unit have transmission-reception portions of more than two systems with different wavelengths. The inputs and outputs of the transmission-reception portions are multiplexed with wavelengths into a single optical transmission line to form a pseudo redundant communication path between the optical service unit and the optical network units.
Furthermore, two kinds of communication systems are provided. One is an active system between the optical service unit and the optical network units with a certain wavelength while the other with a different wavelength is a standby system. When the active system has a fault, a switchover is made to the standby system, thereby improving faultiness between the optical service unit and the optical network units.
The above-mentioned system changer may separate the main signal into both of the transmission-reception portions.
The above-mentioned controller may drop or add a frame signal which has the subscriber overhead indicating the reception state, from the transmission-reception portions.
Namely, the information of communication state such as optical input, bit error rate (BER) between the optical service unit and the optical network units with respect to each wavelength and the system changer is transmitted from the optical network units to the optical service unit through the overhead. The optical service unit collects the communication states of the active system as well as the standby system with that information for a maintenance person. The maintenance person can find a fault of the standby system earlier, and specify the fault point, from that information.
Also, in the optical subscriber network system according to the present invention, the optical service unit and the optical network units each comprise plural combinations of; a plurality of transmission-reception portions which transmit and receive signals the wavelengths of which are different from each other, an optical coupler installed between the transmission-reception portions and the optical transmission line, and a system changer/multiplexing/demultiplexing portion which switches over the transmission-reception portions and re

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