JP4999759B2 - Optical path switching device - Google Patents

Description

  The present invention relates to an optical path switching device for switching an optical path in an optical network.

  A conventional optical path switching device in a ring-type optical network is described in Non-Patent Document 1 below. In this optical network, the optical couplers in the optical path switching device constituting the ring send the same signal to different transmission lines, and the opposite optical path switching device transmits the signals from the different transmission lines to 2: 1 light. The optical path can be switched by selecting with a switch. For example, in the situation where one transmission path is used as an active system, when a failure such as a cut occurs in the optical fiber of the transmission path, the optical path switching apparatus detects that the optical input is disconnected within the apparatus, and 2 1: Control the optical switch to switch the optical path to the other transmission path.

Optical Fiber Communication Conference, 2004 (OFC 2004) Volume 1, 23-27 Feb. 2004

  However, the optical path switching device described in Non-Patent Document 1 switches the transmission path only when it is detected that the optical signal is disconnected. Therefore, for example, in a case where the transmission quality does not satisfy a desired value because the optical SNR is deteriorated even if the light level is within a predetermined range, the transmission path is not switched. That is, there is a problem that when the quality of the transmission path is deteriorated, the optical path cannot be relieved.

  The present invention has been made in view of the above, and an object of the present invention is to obtain an optical path switching device that can relieve an optical path whose transmission quality has deteriorated.

  In order to solve the above-described problems and achieve the object, the present invention provides an optical network that transmits a wavelength-multiplexed optical signal via two transmission lines, one of which is an active transmission line and the other is a standby transmission line. An optical demultiplexer that transmits and receives and demultiplexes the received wavelength multiplexed optical signal and outputs a through wavelength signal and a drop wavelength signal, and combines the through wavelength signal and the add wavelength signal. And an optical multiplexer that outputs a wavelength-division multiplexed optical signal, wherein a drop wavelength signal from each of the optical demultiplexers is input and two systems of inputs are selected for different transmission paths. Optical switch means for outputting optically, and an input level monitoring means for monitoring the optical input level in each transmission line from which the optical switch means outputs a drop wavelength signal and outputting an optical input cutoff signal when an optical input cutoff is detected And a communication abnormality monitoring means for monitoring whether or not the transmission line condition further satisfies a standard in each of the transmission lines, and outputting a communication abnormality signal when a communication abnormality is detected, and based on a monitoring result of each of the monitoring means Switching control means for performing control for switching the output destination transmission path of the optical switch means, and the switching control means indicates a communication abnormality in the working transmission path among the two transmission paths. When a communication error signal is received, if the optical input interruption and communication error are not detected in the standby transmission line, it is determined that the standby transmission line is normal, and control is performed to switch between the active transmission line and the standby transmission line. It is characterized by performing.

  According to the present invention, in the active system, when the optical input level of the drop wavelength signal satisfies a predetermined standard but the transmission path state does not satisfy the standard due to degradation of the optical SNR, an abnormality is detected, There is an effect that the path can be switched.

  Embodiments of an optical path switching device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a ring network using the optical path switching apparatus according to the present embodiment. In FIG. 1, 1A, 1B, 1C, and 1D are optical path switching devices connected by an optical fiber 2. The optical path switching devices 1A, 1B, 1C, and 1D all have the same configuration, and FIG. 1 shows the configuration of the optical path switching device 1A.

  The optical path switching device includes: west side transmission lines 101w and 103w, east side transmission lines 101e and 103e, optical demultiplexers 102w and 102e, optical multiplexers 104w and 104e, optical coupler 105, and 2: 2 light. A switch 106, a switching control circuit 107, and a transponder 108 are provided. The transponder 108 includes an electro-optical conversion circuit 109, photoelectric conversion circuits 110 and 111, a transmission frame processing circuit 112, a photoelectric conversion circuit 113, an electro-optical conversion circuit 114, and a transmission frame monitor circuit 115. I have.

  The west-side transmission lines 101w and 103w are connected to the west-side optical fiber 2 and transmit wavelength multiplexed optical signals. The east-side transmission lines 101e and 103e are connected to the east-side optical fiber 2 and transmit wavelength multiplexed optical signals. The optical demultiplexer 102w demultiplexes the wavelength multiplexed optical signal from the west-side transmission path 101w, outputs the drop wavelength signal to the 2: 2 optical switch 106, and outputs the through wavelength signal to the optical multiplexer 104e. On the other hand, the optical demultiplexer 102e demultiplexes the wavelength multiplexed optical signal from the east-side transmission path 101e, outputs the drop wavelength signal to the 2: 2 optical switch 106, and outputs the through wavelength signal to the optical multiplexer 104w. To do. The optical multiplexer 104e combines the through wavelength signal from the optical demultiplexer 102w and the add wavelength signal from the optical coupler 105 to generate a wavelength multiplexed optical signal, and outputs it to the east-side transmission path 103e. On the other hand, the optical multiplexer 104w combines the through wavelength signal from the optical demultiplexer 102e and the add wavelength signal from the optical coupler 105 to generate a wavelength multiplexed optical signal, and outputs it to the west-side transmission path 103w.

  The optical coupler 105 divides the optical signal from the transponder 108 (described later) into two, and outputs the optical signal to the optical multiplexers 104w and 104e as added wavelength signals. Based on the control from the switching control circuit 107, the 2: 2 optical switch 106 outputs the wavelength signal dropped from the optical demultiplexers 102w and 102e to either the photoelectric conversion circuit 110 or 111, respectively. The switching control circuit 107 switches the 2: 2 optical switch 106 based on the light input interruption signal from the photoelectric conversion circuits 110 and 111 or the communication abnormality signal from the transmission frame processing circuit 112 and the transmission frame monitor circuit 115. The transponder 108 converts the optical signal to / from an external device (not shown) into a wavelength to be added to the wavelength multiplexed optical signal, and the wavelength signal dropped from the optical demultiplexers 102w and 102e to the external device. And processing for converting to the wavelength of the optical signal between.

  The electro-optical conversion circuit 109 in the transponder 108 performs electro-optical conversion on the transmission frame signal from the transmission frame processing circuit 112 and outputs an add wavelength signal to the optical coupler 105. When the photoelectric conversion circuit 110 performs photoelectric conversion on the drop wavelength signal from the 2: 2 optical switch 106 and outputs it to the transmission frame processing circuit 112, monitors the optical input level, and determines that it is below a predetermined level. In this case, the optical input cutoff signal is output to the switching control circuit 107. When the photoelectric conversion circuit 111 photoelectrically converts the drop wavelength signal from the 2: 2 optical switch 106 and outputs it to the transmission frame monitor circuit 115, monitors the optical input level, and determines that it is below a predetermined level In this case, the optical input cutoff signal is output to the switching control circuit 107. The transmission frame processing circuit 112 generates an add wavelength signal transmission frame for the signal from the photoelectric conversion circuit 113 and outputs the transmission frame to the electrical / optical conversion circuit 109. Further, the transmission frame processing circuit 112 determines whether or not the transmission frame signal from the photoelectric conversion circuit 110 corresponds to a communication abnormality, and if a communication abnormality is detected, the communication frame signal is sent to the switching control circuit 107. Output. The photoelectric conversion circuit 113 converts an optical signal from an external device into an electric signal and outputs it to the transmission frame processing circuit 112. The electro-optical conversion circuit 114 performs electro-optical conversion on the signal from the transmission frame processing circuit 112 and outputs the signal to an external device. The transmission frame monitor circuit 115 determines whether or not the transmission frame signal from the photoelectric conversion circuit 111 corresponds to a communication abnormality, and outputs a communication abnormality signal to the switching control circuit 107 when a communication abnormality is detected. .

  Next, an optical path switching operation in a ring network using the optical path switching apparatus configured as described above will be described. In FIG. 1, the optical coupler 105 of the optical path switching device branches the add wavelength signal output from the transponder 108 into two, and adds them to the east side and west side transmission lines, respectively. The optical signal added to the east-side and west-side transmission lines in this way is input to another optical switching device that is an optical path connection destination. The optical path switching device connects the drop wavelength signal input from the active transmission line of the east-side transmission line or the west-side transmission line to the photoelectric conversion circuit 110 via the 2: 2 optical switch 106. On the other hand, the drop wavelength signal input from the standby transmission line is connected to the photoelectric conversion circuit 111 via the 2: 2 optical switch 106.

  When a drop wavelength signal from the active transmission line is input, the transmission frame processing circuit 112 first performs known frame synchronization determination, error detection, and the like for the transmission frame corresponding to the wavelength signal. Then, the transmission frame is converted into a signal format for exchanging with the external connection device, and is output to the electro-optical conversion circuit 114. The electro-optical conversion circuit 114 converts the signal format into an optical signal and outputs it to an external device.

  When a drop wavelength signal from the standby transmission line is input, the transmission frame monitor circuit 115 performs well-known frame synchronization determination, error detection, and the like, similar to the transmission frame processing circuit 112. When an abnormality is detected in these processes, the transmission frame monitor circuit 115 outputs a communication abnormality signal to the switching control circuit 107.

  For example, it is assumed that the east-side transmission line is an active system as an initial state. In this state, when the transmission frame processing circuit 112 detects a communication abnormality due to some failure in the east-side transmission path, the transmission frame processing circuit 112 indicates that the switching control circuit 107 has an abnormality in the active system. A communication abnormality signal indicating is output. At this time, when the optical input interruption signal from the photoelectric conversion circuit 111 or the communication abnormality signal from the transmission frame monitor circuit 115 is not detected, the switching control circuit 107 indicates that the west side transmission line (standby system) is normal. It is determined that there is, and control for switching the 2: 2 optical switch 106 is performed. Specifically, the drop wavelength signal from the west side is connected to the photoelectric conversion circuit 110, and the drop wavelength signal from the east side is connected to the photoelectric conversion circuit 111.

  On the other hand, when an optical input interruption signal from the photoelectric conversion circuit 111 or a communication abnormality signal from the transmission frame monitor circuit 115 is detected, the switching control circuit 107 is abnormal also on the west side transmission line (standby system). It is determined that there is, and control for switching the 2: 2 optical switch 106 is not performed.

  In the above, the communication abnormality detected by the transmission frame processing circuit 112 and the transmission frame monitor circuit 115 includes failure such as loss of frame synchronization, transmission line error deterioration when a bit error exceeds a predetermined threshold, and the like. There is. FIG. 2 is a diagram illustrating an example of a transmission frame used in the ring network of FIG. FIG. 709 is a transmission frame. In this transmission frame, the signal from the external device is stored in the “payload”, and “overhead byte” and “FEC redundant area” are added in the transmission frame processing circuit 112. The overhead byte stores a frame alignment byte for frame synchronization and a parity byte for detecting a bit error. The receiving device can detect a loss of frame synchronization by examining the frame alignment byte, and can detect a bit error by examining the parity byte.

  As described above, the present embodiment is configured to include the 2: 2 optical switch for switching the redundant optical path and the transmission frame monitor for detecting a communication abnormality. As a result, for the active system, when the optical input level of the drop wavelength signal satisfies a predetermined standard, but the transmission line condition is deteriorated due to optical SNR degradation or the like (not satisfying the standard), an abnormality is detected. Thus, the optical path can be switched. Further, since the standby system abnormality is also taken into consideration when switching the optical path, unnecessary switching can be avoided. As a result, the redundant optical path can be relieved, and a highly reliable optical path can be provided.

  In the present embodiment, the transponder 108 is provided in the optical path switching device and connected to an external device (not shown) via the photoelectric conversion circuit 113 and the photoelectric conversion circuit 114. Instead, a regenerative repeater transponder may be provided. FIG. 3 is a diagram illustrating an example of an optical path switching apparatus using the regenerative repeater transponder 116.

  In the present embodiment, an example in which the optical path switching device is applied to a ring network is shown. However, the present invention is not limited to this, and the optical path switching device of the present embodiment is applied to a mesh network or a point-to-point network. Even when applied, the same effects as described above can be obtained.

Embodiment 2. FIG.
In the first embodiment, the switching operation when an abnormality occurs in the working transmission line has been described. In the present embodiment, a case will be described in which the working system is switched to the protection system when both the working system transmission line and the protection system transmission line are normal.

  For example, in a ring network, when an apparatus is added to a working transmission line, the working system may be added after switching the working system to a standby system by setting from a device management system or the like.

  In such a case, both the active system and the standby system are forcibly switched in a normal state, but at the time of switching, the output of the 2: 2 optical switch 106 in the optical path switching device of FIG. I refuse. For this reason, there is a possibility that unnecessary switching may occur due to the detection of the light input interruption in the active system and the standby system and the variation in release time.

  4A and 4B are timing charts showing generation patterns of unnecessary switching due to output interruption of the optical switch. FIG. 4A shows a state in which switching occurs when an abnormality in the working transmission line (light input interruption) is detected earlier than an abnormality in the standby transmission line (light input interruption). This shows the situation when unnecessary switching is avoided. In FIG. 4A, when the output light level of the 2: 2 optical switch 106 decreases (disconnects), first, an optical input disconnection is detected by the photoelectric conversion circuit 110 as an abnormality in the working transmission line, and then the standby transmission line. As a result, the photoelectric conversion circuit 111 detects a light input interruption. At this time, the switching control circuit 107 determines that the standby system is normal because it has not received the optical input cutoff signal from the standby system at the timing of receiving the optical input cutoff signal from the active system. As a result, a switching instruction signal from the active system to the standby system is output, so unnecessary switching is performed.

  FIG. 5A shows a state in which switching occurs when an abnormality in the standby transmission line is detected earlier than an abnormality in the active transmission line, and FIG. 5B shows a case in which unnecessary switching is avoided. The state of is shown. In FIG. 5A, when the output light level of the 2: 2 optical switch 106 decreases (disconnects), first, an abnormality in the standby transmission line is detected, and then an abnormality in the active transmission line is detected. At this time, since the switching control circuit 107 has already received the optical input cutoff signal from the standby system at the timing of receiving the optical input cutoff signal from the active system, it determines that both the active system and the standby system are abnormal. And do not switch. On the other hand, when the output light level of the 2: 2 optical switch 106 recovers, at the timing when the abnormality of the standby system is canceled (becomes normal), the abnormality is still continuing in the active system. As a result, a switching instruction signal from the active system to the standby system is output, so unnecessary switching is performed.

  As described above, in both the patterns of FIGS. 4A and 5B, an unnecessary switching request is generated, and predetermined switching cannot be performed. Therefore, in the present embodiment, as shown in FIGS. 4-2 and 5-2, the switching time of the 2: 2 optical switch 106 is made shorter than the abnormality detection time. In FIGS. 4-2 and 5-2, after the output light level of the 2: 2 optical switch 106 is lowered (disconnected), the timing at which an abnormality in the active transmission line (or the standby transmission line) is detected is as follows. The timing at which the output light level recovers is earlier. Thus, unnecessary switching can be avoided when the transmission path is forcibly switched in a normal state in both the active system and the standby system.

  As described above, in this embodiment, the switching time of the 2: 2 optical switch is made shorter than the abnormality detection time of the transmission line. Thereby, unnecessary switching of the transmission path can be avoided, and highly reliable switching of the optical path can be realized even when communication is normal.

  In this embodiment, the switching time of the 2: 2 optical switch is made shorter than the abnormality detection time of the transmission path, thereby avoiding unnecessary switching of the transmission path. A switching request protection time may be provided for detection and release. The switching request protection time is a time provided to absorb a shift in abnormality detection timing between transmission paths. For example, when an abnormality or normality of one transmission line is detected, the optical path switching device also detects the abnormality detected above for the other transmission line until the switching request protection time elapses from that timing. / Consider that the condition is the same as normal.

  FIG. 6A is a timing chart when a switching request protection time is provided for the abnormality detection pattern shown in FIG. 4A. FIG. 6B is a timing chart for the abnormality detection pattern shown in FIG. It is a timing chart at the time of providing switching request protection time. For example, in FIG. 6A, the standby transmission line is also considered abnormal from the timing when the abnormality of the active transmission line is detected until the switching request protection time elapses. In FIG. 6B, it is considered that the active system is also normal from the timing when the abnormality (normal) of the protection transmission line is detected until the switching request protection time elapses. In these cases, since no switching is performed, unnecessary switching can be avoided.

  As described above, the optical path switching apparatus according to the present invention is useful for an optical communication network, and is particularly suitable when it is desired to provide a highly reliable optical path.

It is a figure which shows the structural example of the ring network using the optical path switching apparatus of this Embodiment. It is a figure which shows an example of the transmission frame used in the ring network of FIG. It is a figure which shows the example of the optical path switching apparatus using a regenerative repeater transponder. It is a timing chart which shows the generation | occurrence | production pattern of the unnecessary switching by the output disconnection of an optical switch. It is a figure which shows the mode in the case of avoiding unnecessary switching. It is a timing chart which shows the generation | occurrence | production pattern of the unnecessary switching by the output disconnection of an optical switch. It is a figure which shows the mode in the case of avoiding unnecessary switching. FIG. 4 is a timing chart in a case where a switching request protection time is provided for the abnormality detection pattern shown in FIG. FIG. 5 is a timing chart when a switching request protection time is provided for the abnormality detection pattern shown in FIG.

Explanation of symbols

1A, 1B, 1C, 1D Optical path switching device 101w, 103w West side transmission path 101e, 103e East side transmission path 102w, 102e Optical demultiplexer 104w, 104e Optical multiplexer 105 Optical coupler 106 2: 2 optical switch 107 Switching control Circuit 108 Transponder 109 Electro-optical conversion circuit 110, 111 Photo-electric conversion circuit 112 Transmission frame processing circuit 113 Photo-electric conversion circuit 114 Electro-optical conversion circuit 115 Transmission frame monitor circuit 116 Regenerative repeater transponder

Claims (4)

In an optical network, wavelength-multiplexed optical signals are transmitted and received through two transmission lines, one of which is a working transmission line and the other is a standby transmission line. And an optical demultiplexer that outputs a through wavelength signal and a drop wavelength signal, and an optical multiplexer that outputs a wavelength multiplexed optical signal obtained by multiplexing the through wavelength signal and the add wavelength signal. A switching device,
An optical switch means for receiving a drop wavelength signal from each of the optical demultiplexers, and selectively outputting two systems of input to different transmission paths;
Input level monitoring means for monitoring the optical input level in each transmission line for outputting a drop wavelength signal by the optical switch means, and outputting an optical input cutoff signal when detecting an optical input cutoff;
Monitoring whether or not the transmission line condition further satisfies the standard in each transmission line, and communication abnormality monitoring means for outputting a communication abnormality signal when a communication abnormality is detected,
Based on the monitoring result of each of the monitoring means, switching control means for performing control for switching the output destination transmission path of the optical switch means,
With
When the switching control means receives a communication abnormality signal indicating a communication abnormality of the working transmission line of the two transmission lines, the switching control means is in a standby state if no optical input interruption or communication abnormality is detected in the standby transmission line. An optical path switching device characterized by determining that the system transmission line is normal and performing control to switch between the active transmission line and the standby transmission line.   2. The optical path switching according to claim 1, wherein the communication abnormality monitoring unit outputs a communication abnormality signal when detecting at least one of transmission frame loss of synchronization and bit error rate deterioration. apparatus.   3. The optical path switching device according to claim 1, wherein a time required for switching the transmission path by the optical switch means is shorter than a time required from detection of an optical input interruption to detection. Provide a protection time that is a time to absorb the deviation of the light input interruption detection timing between the transmission lines,
3. The optical path switching device according to claim 1, wherein the switching control means reserves transmission path switching control during a protection time.

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