Optical communications – Multiplex – Optical local area network
Reexamination Certificate
2000-05-24
2004-08-03
Pascal, Leslie (Department: 2733)
Optical communications
Multiplex
Optical local area network
C398S045000, C398S051000
Reexamination Certificate
active
06771907
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical ring system that is composed of multiple nodes connected in the form of a ring, and more particularly to, an optical ring system to process optical signal with multiple wavelengths.
BACKGROUND OF THE INVENTION
Owing to an increase in amount of communications caused by the popularization of the Internet etc. and the emergence of wideband data service, the enhancement of transfer capacity in backbone network has been desired increasingly. Some of Routers and ATM (asynchronous transfer mode) switches as a device for data service are already provided with a wideband interface at a transfer rate of Gbit/sec, and therefore it is difficult to connect such a device to an existing synchronous network. So, a technology to connect to the network while skipping “a device to do the time-division multiplexing of low-order group of signal into high-order group of signal”, an interface of the existing synchronous network, or a WDM (wavelength division multiplexing) technology having a transfer performance more than Gbit/sec to each wavelength has been required.
FIG. 1
shows a prior point-to-point wavelength multiplexing transmission system. First to N-th optical wavelength transmitters
11
1
,
11
2
, . . . ,
11
N
, respectively, convert first to N-th optical signal into optical signal of intrinsic wavelength &lgr;
1
to &lgr;
N
, and then output it to an optical wavelength multiplexer
12
. The optical wavelength multiplexer
12
multiplexes these optical signal and then outputs it to transmission line
13
connected on the output side. An optical amplifier
14
, suitably provided on the transmission line
13
, conducts the recovery of deteriorated light in optical signal with wavelength &lgr;
1
, to &lgr;
N
multiplexed.
An optical wavelength demultiplexer
15
is input optical signal multiplexed from transmission line
16
, and demultiplexes it into former optical signal of wavelength &lgr;
1
to &lgr;
N
, and then corresponding first to N-th optical wavelength receivers
16
1
,
16
2
, . . . ,
16
N
reproduces the original signal.
Such a point-to-point wavelength multiplexing transmission system as shown in
FIG. 1
is equipped with no protection function to protect the transmission of signal when it is subject to a failure such as disconnection of optical fiber to form the transmission lines
13
,
16
, and malfunction of the optical transmitter/receiver.
The simplest method to provide the optical wavelength multiplexing protection function is to detect a failure at each optical terminal node to provide the protection at multiplexing level of all wavelengths, i.e. in unit of one optical fiber.
FIG. 2
shows an example of optical ring system that employs such a protection method suggested so far. This optical ring system, which is disclosed in Japanese patent application laid-open No. 6-61986 (1994), comprises a four-fiber ring which is of four optical fibers
31
to
34
connected in the form of ring among a master station
21
and first to third slave stations
22
to
24
. Of the four fibers, two optical fibers
31
,
32
compose work line, i.e. actually-working line, and the remaining two optical fibers
33
,
34
compose protection line, i.e. backup line.
The optical ring system in
FIG. 2
is not subject to failure. In
FIG. 2
, master clock output from a clock-supplying device
25
, which is disposed in the master station
21
, is supplied sequentially from the first to third slave stations
22
to
24
.
FIG. 3
shows a case that the work line between the master station
21
and the first slave station
22
in the optical ring system is subject to a failure
41
. When the failure
41
occurs on the work line composed of the first and second optical fibers
31
1
,
32
1
, the transmission line is switched so that two optical fibers
33
1
,
34
1
to compose the protection line in this section can supply the master clock. Then, between the first slave station
22
and the master station
21
, the transmission line through the second slave station
23
and the third slave station
24
supplies the master clock like that in FIG.
2
.
FIG. 4
shows a case that, between the master station
21
and the first slave station
22
in this optical ring system, not only the work line but also the protection line is subject to a failure
42
. When the failure
42
occurs on both the work line composed of the first and second optical fibers
31
1
,
32
1
and the protection line composed of the third and fourth optical fibers
33
1
,
34
1
, the master clock is supplied through optical fiber
32
4
in the direction from the master station
21
to the third slave station
24
.
Although the transmission of master clock is explained in this example. the first to fourth optical fibers
31
to
34
respectively transmit multiplexing optical signal with multiple wavelengths &lgr;
1
to &lgr;
N
, and when optical signal with more than one of the wavelengths is subject to a failure, the switching of transmission line is conducted in like manner described above.
Thus, in the case that, as shown in
FIG. 1
, optical signal with multiple wavelengths &lgr;
1
to &lgr;
N
is multiplexed in one transmission line, even when the transmission line of partial wavelength is subject to a failure, the protection of signal transmission line is conducted by unit of one optical fiber. This means that due to failure of one wavelength, the transmission line of optical signal to the remaining wavelengths has to be switched.
In recent years, optical amplification technology and wavelength multiplexing technology have been developed abruptly. Along with this, the multiplexing number N of optical signal to be transmitted through one optical fiber has increased. Under this background, if even for a failure concerning one wavelength the switching of optical signal to all the remaining wavelengths must be conducted, then optical signal to the wavelengths operated normally may be influenced by an instantaneous shut-off by the switching operation to switch into the protection line. Also, due to the rerouting required when conducting the switching operation of transmission line, delay in transmission of signal occurs, and as a whole the efficiency in use of wavelength band lowers.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide an optical ring system that when a failure occurs as to only part of wavelengths in point-to-point wavelength multiplexing transmission system, the protection function is conducted to only a wavelength subject to the failure.
According to the invention, an optical ring system, comprises:
a wavelength demultiplexing means to which wavelength-multiplexed optical signal to be sent through an optical fiber from a previous node of multiple nodes composing a ring network is input and in which optical signal with each wavelength assigned to itself is demultiplexed;
an optical ring means which is provided in a predetermined node of the multiple nodes to the each wavelength assigned and which is composed of a failure existence judging means which terminates an overhead of each optical signal with a wavelength demultiplexed by the wavelength demultiplexing means and judges whether a failure occurs in regard to a wavelength in a previous section through which optical signal with the assigned wavelength is sent, and a switching means which, when the failure existence judging means determines the occurrence of failure, selects a path that allows optical signal with the wavelength to be transmitted to the previous node while avoiding the previous section incurring the failure; and
a wavelength multiplexing means which multiplexes optical signal to be output from the optical ring means and then outputs it to an optical fiber connected to a next node composing the ring network.
In this invention, the optical ring means is provided for each wavelength in each node, and after being demultiplexed by the wavelength demultiplexing means, optical signal with a wavelength assigned to the optical ring means is input. The optical ring m
Ando Naoki
Haga Tukasa
Henmi Naoya
Iida Shuichi
Kikuchi Hitoshi
NEC Corporation
Pascal Leslie
Tran Dzung
Young & Thompson
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