Optical subscriber network system and fault supervising...

Details Optical subscriber network system and fault supervising... Optical subscriber network system and fault supervising...

1998-03-24

2001-09-11

Chan, Jason (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200

Reexamination Certificate

active

06288806

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical subscriber network system suitable for use with a passive optical network system and a fault supervising method for an optical subscriber network system.
2. Description of the Related Art
FIG. 12
schematically shows a construction of an ordinary station subscriber network. In the construction of the ordinary station subscriber network shown in
FIG. 12
, for optincal network units (ONU)
1
′ to N′ (N′ is a natural number) which require high speed communication of a large capacity, optical fibers are usually laid in a one by one corresponding relationship from a station apparatus
100
′ to accommodate the optincal network units (ONU)
1
′ to N′ in the station.
In recent years, as a system which economically accommodates subscribers who require broad-band communication, such a passive optical network (PON) system as shown in
FIG. 13
has been proposed taking the economy and so forth into consideration.
In the passive optical network (PON) system shown in
FIG. 13
, an optical distributor-coupler (star coupler)
50
′ formed from a passive element is interposed between a station apparatus
100
″ and optical network units (ONU)
1
″ to N″ (N″ is a natural number), and one pair of optical fibers or, for the object of redundancy, two pairs of optical fibers, are laid between the station apparatus
100
′ and the optical distributor-coupler
50
′. The optical distributor-coupler
50
′ distributes downstream optical signals from the station apparatus
100
′ to the optical network units (ONU)
1
″ to N″. On the other hand, optical signals from the optical network units (ONU)
1
″ to N″ are transmitted in upstream frames only for times of time slots allocated thereto and then coupled by the optical distributor-coupler
50
′, whereafter they are transmitted to the station apparatus
100
″.
Here, for upstream communication from the optical network units (ONU)
1
″ to N″ to the station apparatus
100
″. TDMA (Time Division Multiple Access) is used, and for downstream communication, TCM (Time Compression Multiplexing) which is a combination of TDM (Time Division Multiplexing) is used.
A construction of a frame of the TDM/TDMA described above is illustrated in FIG.
14
.
Accordingly, with the passive optical network (PON) system, since the optical transmission lines and the subscriber optical transmission lines of the station apparatus
100
″ are used commonly, the cost required for construction of the system can be reduced comparing with the station subscriber network construction shown in
FIG. 12
wherein the station apparatus
100
′ and the optincal network units (ONU)
1
′ to N′ are connected in a one by one corresponding relationship to each other.
Further, since a passive element is used as an optical distributor-coupler, improvement in reliability of the system can be anticipated comparing with another system wherein optical signals are multiplexed and demultiplexed using an active apparatus.
However, with the construction of the passive optical network (PON) shown in
FIG. 13
, while dual construction of the transmission line from the station apparatus
100
″ to the optical distributor-coupler
50
′ can be achieved readily, if it is tried to construct the transmission lines on the subscribers side with respect to the optical distributor-coupler
50
′ in dual construction, then optical transmission/reception sections of the optical network units (ONU)
1
″ to N″ must all be constructed in dual construction, and a significant increase in cost cannot be avoided.
Further, if a fault such as a physical damage to an optical transmission line or a failure of an optical reception circuit of an optical network unit (ONU) occurs, then since an upstream optical signal must be transmitted based on a timing of a downstream signal, resultantly an upstream signal cannot be transmitted irrespective of the point of the fault, and there is no available method of discriminating the point of the fault from the station side.
Further, since a small number of optical transmission lines are used commonly by the plurality of optical network units (ONU)
1
″ to N″, if a certain optical network unit (ONU) transmits upstream data at an irregular timing to the station apparatus
100
″ because of a fault of the certain optical network unit (ONU), then it may possibly interfere with communication between station subscribers of those optical network units (ONU) which are operating regularly.
FIG. 15
illustrates an example of communication interference between station subscribers of the optical network unit (ONU)
1
″ which is operating regularly. As seen from
FIG. 15
, since, in the passive optical network (PON) system, a small number of optical transmission lines are used commonly by the plurality of optical network units (ONU)
1
″ to N″, if upstream data to the station apparatus
100
″ is transmitted at an irregular timing, then there is the possibility that a problem that the upstream data interferes with communication between station subscribers which are operating regularly may occur.
In other words, if, for example, the optical network unit (ONU)
2
″ transmits an upstream frame at a timing different from the timing at which it should originally be transmitted, then it may interfere with communication of the optical network unit (ONU)
1
″.
FIG. 16
illustrates an influence of a fault of an optical network unit when the optical network unit transmits an irregular upstream frame. Referring to
FIG. 16
, by an influence of an upstream frame transmitted from the optical network unit (ONU)
2
″ with which a fault has occurred, an upstream frame transmitted from the optical network unit (ONU)
1
″ suffers from frame collision, resulting in failure in communication.
Accordingly, there is a subject to be solved in that it is desirable to secure dual construction of optical transmission/reception sections and so forth of optical network units, specification of a failure fault point in optical transmission lines and optical network units and regular timing transmission of upstream data.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical subscriber network (PON) system which secures dual construction of optical transmission/reception sections and so forth of optical network units, specification of a failure fault point in optical transmission lines and optical network units and regular timing transmission of upstream data and a fault supervising method for an optical subscriber network system.
In order to attain the object described above, according to an aspect of the present invention, there is provided an optical subscriber network system of a passive optical network construction wherein a plurality of network units are accommodated in a station apparatus through an optical transmission line using a passive optical element, comprising bypass transmission lines for mutual supervision control between the network units, each of the network units including transmission/reception means for transmitting and receiving a network unit mutual supervision control signal to and from another one of the network units through an available one of the bypass transmission lines, and means for transmitting received network unit mutual supervision control information to the station apparatus through the optical transmission line, the station apparatus including means for supervising a fault from the network unit mutual supervision control information.
With the optical subscriber network system, it is possible to transmit information regarding each of the network units (unit information and so forth; a reception condition of an optical signal from the station apparatus, an optical signal transmission condition and so forth) to the station apparatu

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