Optical communications – Diagnostic testing – Determination of communication parameter
Reexamination Certificate
2000-04-28
2004-10-05
Chan, Jason (Department: 2733)
Optical communications
Diagnostic testing
Determination of communication parameter
C398S181000, C398S177000
Reexamination Certificate
active
06801720
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical communication system, and more particularly to an optical signal quality supervisory device that supervises the quality of a light wave network.
BACKGROUND ART
In an optical communication system, the quality supervision of an optical signal is very important for the operation of a network. In a light amplification relay transmission system, the degradation of an optical SNR (Signal-to-Noise Ratio) caused by the degradation of a light amplifier is a factor in the degradation of the quality of an optical signal. A demand for supervising this optical signal with high accuracy has been increased. Also, in a wavelength multiplex system, because a plurality of wavelength channels interfere with each other, the supervision of the optical signal quality with higher precision has been demanded.
In addition, in a coming light wave network, because a plurality of optical network elements (ONEs) constitute a transparent network, if one of those ONEs generates an optical noise, the optical transmission line quality of the entire network is degraded. Thus, a quality supervision high in level is required.
FIG. 16
is a conceptual block diagram showing a light wave network constituted by four ONEs as the optical communication system.
In
FIG. 16
, reference numeral
90
denotes an optical fiber cable, and
91
to
94
denote optical network elements (ONEs), and each of those ONEs is made up of an optical add-drop multiplexer, an optical cross-correct, an optical line terminal and so on. Reference numeral
95
denotes a main signal transmitter (LINE OS),
96
is a main signal receiver (LINE OR),
97
is a main signal,
98
is an optical supervisory channel transmitter,
99
is an optical supervisory channel receiver that constitutes an optical signal quality supervisory device in association with the supervisory signal optical transmitter
98
, and
100
is an optical supervisory channel that is transmitted from the optical supervisory channel transmitter
98
and received by the optical supervisory channel receiver
99
.
It is assumed that a trouble such as an increase in the loss of optical parts or a failure of the optical amplifier occurs, for example, in the ONE
92
in FIG.
16
.
When the ONE
92
transmits the optical supervisory channel
100
, the quality of the optical supervisory channel
100
is degraded by the trouble. The optical supervisory channel receiver
99
, upon receiving the optical supervisory channel, detects the degradation of quality and notifies all the ONEs of the trouble through a built-in network management system (NMS).
Incidentally, the conventional optical supervisory channel
100
is made up of a bit interleaved parity (hereinafter referred to as “BIP”) byte provided in a section over head (SOH) of a synchronous digital hierarchy (SDH). The BIP byte is made up of a B1 byte (BIP-
8
) or a B2 byte (BIPN×24) and counts code errors between the respective relays, between the relay and the line terminal device, or between the respective line terminal devices. The details are disclosed in “Error Rate Degradation Detecting Method in SDH” Spring Conference of The Institute of Electronics, Information and Communication Engineers, B-762, 1990, written by Fujime et al.
The inner structure of the conventional optical supervisory channel receiver
99
that supervises the quality of transmission line by using the BIP byte is shown in FIG.
17
.
In
FIG. 17
, reference numeral
101
denotes an optical fiber;
102
, a photo diode (hereinafter referred to as “PD”);
103
, a pre-amplifier;
104
, a post-amplifier;
105
, an equivalent filter;
106
, a clock extraction circuit;
107
, a discriminator;
108
, a serial-parallel conversion circuit;
109
, a frame synchronizing circuit;
110
, a descrambler circuit;
111
, a BIP error detection circuit;
112
, a signal degradation (SD) alarm;
113
, a section over head (SOH) termination circuit; and
114
, a system alarm transfer byte (APS byte).
Subsequently, the operation of the conventional optical supervisory channel receiver
99
will be described.
The optical signal inputted from the optical fiber
101
is photoelectrically converted by the PD
102
and thereafter amplified by the pre-amplifier
103
and the post-amplifier
104
. The amplified received signal is subjected to band limit and waveform shaping by the equivalent filter
105
. The equivalent filter
105
is normally formed of a quaternary vessel Tomson filter. The equalized signal is branched into two signals, and one of those signals is inputted to the clock extraction circuit
106
from which a clock signal is extracted. The other signal is inputted to the discriminator
107
, and then discriminated and reproduced by the extracted clock signal.
The signal discriminated and reproduced by the discriminator
107
is normally developed into
8
parallel signals by the serial-parallel conversion circuit
108
, passes through the frame synchronizing circuit
109
and then is descrambled by the descramble circuit
110
. Thereafter, the BIP error detection circuit
111
detects an error from the BIP byte separated by the BIP error detection circuit. If the detected error exceeds a preset threshold value, the SD alarm
112
is issued. Also, the APS byte
114
that receives and transmits the supervisory signal between the different ONEs is extracted from the SOH termination circuit
113
.
It is assumed that the main signal is, for example, of STM-16 (2.48832 Gbit/s). In this case, the PD
102
, the pre-amplifier
103
, the post-amplifier
104
, the discriminator
107
and the serial-parallel conversion circuit
108
are formed of high-speed semiconductors having a frequency band of 2 GHz or higher. On the other hand, the equivalent filter
105
is set to about 0.7 times the normal bit rate, that is, a frequency band of 1.7 GHz.
However, in the above-described conventional optical signal quality supervisory device, particularly in the optical supervisory channel receiver
99
, as the bit rate is higher in speed, it becomes more difficult to constitute the circuit shown in FIG.
17
. In particular, the high-speed semiconductor integrated circuit technique is demanded for the clock extraction circuit
106
, the discriminator
107
and the serial-parallel conversion circuit
108
, accompanied by high costs and increased power consumption. Also, the frame synchronizing circuit
109
, the descramble circuit
110
and the BIP error detection circuit
111
increase in circuit scale, and a volume for installing the circuit increases, thereby leading to enlargement of the entire device.
The present invention has been made in order to solve the above-described problems, and therefore an object of the present invention is to provide an optical signal quality supervisory device that is capable of supervising the quality of an optical signal simply, efficiently and with high accuracy without inviting an increase in circuit scale, high costs and an increase in power consumption.
DISCLOSURE OF THE INVENTION
In order to achieve the above object, an optical signal quality supervisory device according to the present invention comprises: optical supervisory channel transmitting means that transmits an optical supervisory channel for supervising the transmission line quality of an optical communication system to a main optical channel receiving means which receives a main optical channel transmitted over the optical communication system, and an optical supervisory channel receiving means that receives the optical supervisory channel transmitted through the optical communication system to supervise the quality of the transmission line, and is characterized in that the bit rate of the optical supervisory channel is made lower than the bit rate of the main optical channel, and in that there are provided, as the optical supervisory channel receiving means, reception discriminating means that receives the signal transmitted through the optical communication system to discriminate and reproduce the optical supervisory channel from the r
Ichibangase Hiroshi
Kabashima Takatomi
Kitayama Tadayoshi
Kobayashi Naoki
Matsushita Kiwami
Birch & Stewart Kolasch & Birch, LLP
Chan Jason
Payne David C.
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