WO2004077701A1

WO2004077701A1 - Method and device for switching between active and auxiliary circuits for optical transmission

Info

Publication number: WO2004077701A1
Application number: PCT/JP2003/002018
Authority: WO
Inventors: Michio Tanaka
Original assignee: Fujitsu Limited
Priority date: 2003-02-25
Filing date: 2003-02-25
Publication date: 2004-09-10

Abstract

A method comprising a step of providing an active circuit and an auxiliary circuit for respectively transmitting WDM signal lights generated by wavelength-division-multiplexing optical signals having different wavelengths, a step of assigning one of the optical signals as an optical monitoring channel, a step of allowing the optical monitoring channel to include a parameter for measuring the difference in optical path length between the active and auxiliary circuits, and a step of allowing the receiving side to compensate the optical length difference according to the parameter. The method enables high-speed switching between the active and auxiliary circuits of a wavelength-division multiplexing (WDM) transmission without converting the multiplexed optical signal (WDM signal light) into an electrical signal.

Description

Method and apparatus for switching between working and protection lines in optical transmission

The present invention generally relates to a method and apparatus for switching between a working and protection line in optical transmission, and more particularly to a method for switching a working and protection line suitable for WDM in which a plurality of optical signals having different wavelengths are wavelength-division multiplexed. The present invention relates to a switching method and a switching device. Background technology

In recent years, techniques for manufacturing and using silica-based optical fibers with low loss (for example, 0.2 dB / km) have been established, and optical communication systems using optical fibers as transmission lines have been put into practical use. Optical amplifiers for amplifying optical signals or signal light have been put to practical use in order to enable long-distance transmission by compensating for losses in optical fibers. It is known in the art that the optical amplification medium is supplied with the signal light to be amplified, and the optical amplification medium is pumped so as to provide a gain band including the wavelength of the signal light. This is an optical amplifier composed of a bombing unit.

For example, erupium-doped fiber amplifiers (EDFAs) have been developed to amplify signal light in the 1.55-μm wavelength band with low loss using silica-based fibers. The EDFA includes an erbium-doped fiber (EDF) as an optical amplification medium, and a pump light source for supplying a pump light having a predetermined wavelength to the EDF. By using pump light having a wavelength of 0.98 / im band or 1.48 / 1m band, a gain band including a wavelength of 1.55 / m can be obtained.

Wavelength division multiplexing (WDM) is a technology for increasing the transmission capacity of optical fibers. In a system to which WDM is applied, a plurality of optical carriers having different wavelengths are used. Multiple optical signals obtained by independently modulating each optical carrier are wavelength-division multiplexed by an optical multiplexer, and the resulting WDM signal light is transmitted to an optical fiber transmission line. On the receiving side, the received WDM signal light is separated into individual optical signals by an optical demultiplexer, and based on each optical signal, Thus, the transmission data is reproduced. Therefore, by applying WDM, the transmission capacity of one optical fiber can be increased in accordance with the number of multiplexing.

By the way, in optical transmission before WDM transmission, one optical signal having a single wavelength was transmitted on one line, that is, one optical fiber transmission line. In addition, a failure recovery function was provided to prepare the working line and the protection line, perform transmission and reception using the working line normally, and switch to the protection line when a failure occurs in the working line. These functions are called protection functions. This switching operation is called active standby switching. Such protection functions and active spare switching can be extended and applied to WDM systems as they are, but at present there is a problem that the form of application is not optimized. Disclosure of the invention

Therefore, an object of the present invention is to provide a method and an apparatus for switching between a working channel and a protection channel suitable for WDM.

Other objects of the present invention will become clear from the following description.

According to the present invention, providing a working line and a protection line for transmitting WDM signal light obtained by wavelength division multiplexing a plurality of optical signals having different wavelengths, and providing one of the plurality of optical signals Assigning one of the two as an optical supervisory channel, including a parameter for measuring the optical path length difference between the working line and the protection line in the optical supervisory channel, and determining the optical path length difference on the receiving side based on the parameter. And compensating the following.

According to this method, in wavelength division multiplexing (WDM) transmission, it is possible to quickly switch between the active and standby circuits without converting the multiplexed optical signal (WDM signal light) into an electrical signal. It becomes.

For example, the compensating step includes delaying the WDM signal light transmitted by at least one of the working line and the protection line so that the optical path length difference becomes substantially zero.

Preferably, the method comprises the steps of: measuring the intensity of the WDM signal light transmitted by the working line; and determining if the measured intensity does not reach a predetermined level. Switching the WDM signal light transmitted by the service line to the protection line.

Preferably, the method further comprises the steps of: measuring the strength of the optical signal of the optical supervisory channel transmitted by the working line; and determining the strength of the optical signal when the measured strength does not reach a predetermined level. And a step of switching the transmitted WDM signal light to a protection line.

Preferably, the method further comprises the steps of: measuring a quality of an optical signal of an optical supervisory channel transmitted by the working line; and, if the measured quality does not reach a predetermined level, using the working line. And a step of switching the transmitted WDM signal light to a protection line.

According to another aspect of the present invention, one of the working line and the protection line for transmitting WDM signal light obtained by wavelength division multiplexing a plurality of optical signals having different wavelengths, and one of the plurality of optical signals As an optical monitoring channel, a means for supplying an optical monitoring signal including a parameter for measuring the optical path length difference between the working line and the protection line, and a means for compensating the optical path length difference on the receiving side based on the parameter An apparatus comprising: BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a block diagram of a conventional single-wavelength working standby switching device;

Figure 2 is a block diagram of a conventional WDM working standby switching device;

Fig. 3 is a block diagram of a conventional WDM active standby non-stop switching device due to delay; Fig. 4 is a block diagram of a conventional WDM active standby non-stop switching device using buffer memory;

Fig. 5 is a block diagram of a conventional WDM active standby non-stop switching device due to optical delay; Fig. 6 is a block diagram showing an example of a point-to-point network configuration in a conventional WDM active standby switching device (during normal operation). );

Figure 7 is a block diagram showing an example of a point-to-point network configuration in a conventional WDM active protection switching device (when a single failure occurs);

Fig. 8 is a block diagram showing an example of a point-to-point network configuration in a conventional WDM active / standby switching device (when a double failure occurs); Figure 9 is a block diagram to explain the switching configuration classification when switching with conventional single-wavelength signals;

Fig. 10 is a block diagram to explain the switching configuration and the classification of the device providing vendor when switching with the conventional single wavelength signal;

FIG. 11 is a block diagram showing an example of a point-to-point network configuration in a WDM active standby switching device to which the present invention is applied (during normal operation);

FIG. 12 is a block diagram showing an example of a point-to-point network configuration in a WDM active standby switching device to which the present invention is applied (when a single failure occurs);

FIG. 13 is a block diagram showing an example of a point-to-point network configuration in a WDM active standby switching device to which the present invention is applied (part 1 when a double failure occurs);

FIG. 14 is a block diagram showing an example of a point-to-point network configuration in the WDM active standby switching device to which the present invention is applied (part 2 when a double failure occurs);

FIG. 15 is a block diagram of the switching device at the transmission side according to the present invention;

FIG. 16 is a block diagram of a WDM active standby non-stop switching device using optical delay to which the present invention is applied;

FIG. 17 is a diagram showing an OSC signal frame format having optical delay control information; FIG. 18 is a block diagram of a WDM active spare non-stop switching device using a buffer memory to which the present invention is applied;

FIG. 19 is a diagram showing an OSC signal frame format having a buffer memory control information value. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to describing the embodiments of the present invention, a description will be given of a conventional technique which is considered useful for understanding the usefulness of the present invention.

In optical transmission before WDM transmission, one optical signal having a single wavelength was transmitted over one line, or one optical fiber transmission line. In addition, a provision was made for a working line and a protection line, and a failure recovery function was provided, which normally performs transmission and reception using the working line and switches to the protection line when a failure occurs in the working line. These functions are protected This switching operation is referred to as a “yone function”, and this switching operation is referred to as “active standby switching”.

Specifically, as shown in FIG. 1, a working line 1 and a protection line 2 are provided, and the transmitting node 1 0 and the E / O converters 1 1 1 1 and 1 1-2 respectively transmit the working lines 1 and Transmit the same signal to protection line 2. Here, the suffixes "1-1" and "1-2j" are added to distinguish between the working line 1 and the protection line 2, and may be abbreviated as far as possible.

In the receiving node unit 20, the optical signal is converted into an electric signal by the OZE conversion unit 21 and the signal state is detected by the detection unit 24. If there is no abnormality in the signal, the switching unit 23 normally uses the signal. Select line 1. If there is an error in the signal, the switching unit 23 switches to the spare line 2 according to the command from the control unit 25.

For example, when the detector 24-E-1 detects a failure in the working line 1, the detector 24-E-1 notifies the controller 25-E of the detection of the failure. Based on this, the control unit 25-E controls the switching unit 23, selects the protection line 2 instead of the working line 1, and recovers from the failure by switching to the protection line 2. Here, the suffix “E” is used to mean that it is related to an electric signal, and is distinguished from “0” that is related to an optical signal in the present invention described later.

The working protection switching in WDM transmission is basically performed in the same manner as in the case of single wavelength transmission. That is, a detection unit 24 is provided for each wavelength, a fault is detected for each wavelength signal, and a signal of the wavelength at which the fault is detected is switched to the protection line 2.

If a failure occurs only in a single wavelength of one working line 1 (for example, when a transmission circuit fails), only the signal of that wavelength is switched to the protection line 2.

For example, if a failure occurs in the signal of wavelength 1 in FIG. 2, the receiving node unit 20 converts the optical signal into an electric signal in the OZE conversion unit 21 and detects the failure in the detection unit 24. Switch the signal of wavelength 1 to protection line 2. Also, if a failure such as disconnection occurs in the working line 1, a failure occurs in all wavelength signals transmitted to the line, so that all wavelength signals are switched to the protection line 2.

Reference numerals 12-1 and 12-2 denote optical wavelength multiplexing units (optical multiplexers) for obtaining a WDM signal light by wavelength division multiplexing a plurality of optical signals, and reference numerals 22-1 and 22-2. 2 is an optical wavelength demultiplexing unit (optical demultiplexer) for dividing WDM signal light into a plurality of original optical signals. Lexa).

Next, a conventional hitless switching method will be described. As described above, in optical transmission, it is possible to automatically recover from a failure by switching. However, there is a problem that a momentary interruption of about several tens of ms occurs during this switching operation. Therefore, the following methods have been considered to realize instantaneous switching in optical transmission.

(1) Use optical delay after converting optical signal to electrical signal

(2) Use buffer memory after converting optical signals to electrical signals

(3) Use optical delay

These methods are equally applicable to WDM transmission.

In the case of WDM transmission, the procedure is as follows.

(1) Convert single-wavelength optical signals before optical wavelength multiplexing to electrical signals and use electrical delay

(2) Convert the single-wavelength optical signal before optical wavelength multiplexing into an electrical signal and use the buffer memory

(3) Use optical delay in single wavelength optical signal before optical wavelength multiplexing

Hereinafter, each method will be described in order.

First, a method of converting a single-wavelength optical signal before optical wavelength multiplexing into an electrical signal and then using an electrical delay will be described. In FIG. 3, each WDM signal of the working protection is transmitted from the working line 1 and the protection line 2 to the receiving node unit 20. The working WDM signal is transmitted to the wavelength demultiplexing unit 22-1, and the backup WDM signal is transmitted to the wavelength demultiplexing unit 22-2, where it is separated into optical signals of each wavelength.

Here, an optical signal of wavelength 1 is taken as an example. This optical signal is converted into an electric signal by the OZE conversion unit 21 together with the working spare, and the signal state is detected by the detection units 24-E-1 and 24-E-2. The detected signal is notified to the control unit 251-1E.

Here, the signal flowing through the protection line is given a constant or variable electrical delay by the delay unit 26_E. The delay unit 26-E is controlled by the control unit 25-E.

When a failure occurs in the working line 1, the switching to the protection line 2 is performed by the switching unit 23 by the command of the control unit 25-E. Since the protection line 2 has a delay compared to the working line 1, there is no momentary interruption due to the switching operation, and switching can be performed without interruption. Figure 4 uses a buffer memory 27-E instead of the delay unit 26-E. The operation when buffer memory 27-E is used is basically the same as the delay method.

Next, a method is described in which the optical signal of each wavelength before optical wavelength multiplexing is not converted into an electrical signal, and instantaneous interruption switching is performed without changing the optical signal.

In the receiving node 20 of FIG. 5, the working WDM signal light is transmitted to the wavelength demultiplexing unit 22-1, and the protection WDM signal light is transmitted to the wavelength demultiplexing unit 22-2, and separated into optical signals of each wavelength. Is done. Here, an optical signal of wavelength 1 is taken as an example. The signal states of the working optical signal and the standby optical signal are detected by the respective detectors 24-O-1 and 24-O-2. The detected signal is notified to the control unit 25-E. Here, the optical signal flowing through the protection line is given a constant or variable optical delay by the optical delay unit 26_O. The optical delay unit 26-O is controlled by the control unit 25-E.

When a failure occurs in the working line 1, the switching to the protection line 2 is performed by the switching unit 23 to O by the command of the control unit 25-E. Since the protection line 2 is given a delay compared to the working line 1, there is no momentary interruption due to the switching operation, and switching can be performed without interruption. The advantage of the method of performing instantaneous interruption switching without changing the optical signal is that since the electrical signal conversion processing is not performed, low-speed electrical circuit processing is not required and switching can be performed while maintaining the original high speed of the optical signal. can give.

The conventional method applies a switching method before WDM transmission to WDM transmission, and may not always be optimal. Also, no instantaneous interruption switching with WDM signals is not realized.

In the conventional technique, switching is performed in units of each wavelength signal. As a result, the lines passing through each wavelength signal differed, and a situation occurred in which one wavelength passed through the working line and another through the protection line at the same time. As a result, both lines became the working line at the same time, which sometimes became a problem in fault management.

Fig. 6 to Fig. 8 show examples of the conventional network configuration between WDM active and standby switching points for each wavelength signal unit. Here, there are WDM devices (see the transmitting node 10 and the receiving node 20 shown in Fig. 5) at points A, B, and C, respectively. It is assumed that four optical signals are multiplexed and transmitted to points B and C. Optical signals of wavelengths 1 and 2 are transmitted between points A and B, and optical signals of wavelengths 3 and 4 are transmitted between points A and C.

A protection function is provided for optical signals of each wavelength, and switching between active and standby is performed for each wavelength. In the figure, the solid line is the working line, and the dotted line is the protection line. In the following, an optical signal passing through the line with a dash attached to the line is indicated by a dotted line, which means that the signal is disconnected due to the occurrence of a fault.

FIG. 7 shows a state in which the working WDM line 1 between points A and B in this network has a fault such as a broken fiber. At this time, the optical signals of all wavelengths are switched to the spare WDM line 2. By this switching, all signals are restored. Therefore, this network operates normally without being affected by the failure.

However, as shown in Fig. 8, if a fault S 'also occurs in the backup WDM line 2 between points B and C at the same time, the optical signals of wavelengths 3 and 4 transmitted to the backup WDM line 2 are in a normal state. It is not possible to switch to the working WDM circuit 1, which is in a state, and the signal is lost without reaching point C.

Other problems of switching in wavelength units are shown in FIGS. 9 and 10.

FIG. 9 is a diagram for simply explaining a conventional switching configuration in wavelength units. Signal transmission / reception devices 18—1 to 18—4 are classified into four types of configurations.

The configuration related to the transmission / reception device 18-1 and 18-2 consists of four parts: a signal transmission / reception device, a switching unit, an O / E Ζθ wavelength conversion unit, and an optical wavelength multiplexing unit. The protection function is switched. 'In the department. The switching unit monitors the quality of the electrical signal of the O / E / O wavelength conversion unit, and normally selects the working line, and switches to the protection line if the working line deteriorates to a quality below the reference value due to a failure or the like. .

The configuration related to the transmission / reception device 18-3 is composed of three parts: a signal transmission / reception device, a Ο / ΕΖΟ wavelength converter, and an optical wavelength multiplexing unit. The protection function is in the signal transmission / reception device. The signal transmitter / receiver monitors the quality of the electrical signal of the Ο / ΕΖΟ wavelength converter, and normally selects the working line, and switches to the protection line if the working line is deteriorated to a level below the reference value due to a failure or the like.

As a configuration similar to this, there is also a signal transmission / reception device that includes a wavelength conversion unit. In this case, the switching operation is the same as described above. The configuration related to the transmission / reception device 18-4 is composed of four parts: a signal transmission / reception device, an OZE / O wavelength conversion unit, a switching unit, and an optical wavelength multiplexing unit. The protection function is provided in the switching unit. The difference from the transmission / reception devices 18-1 and 18-2 is that the switching unit is located closer to the optical wavelength multiplexing unit than the O / E / O wavelength conversion unit. The switching unit monitors the quality of the single-wavelength optical signal branched from the wavelength multiplexing unit, and normally selects the working line.If the working line is deteriorated to a quality below the reference value due to a failure or the like, it is switched to the protection line. Perform switching.

In the configuration of the normal transmission / reception device 18-1, 18-2 and 18-4, the Ο / Ε, Ο wavelength conversion unit and switching unit are combined as a single set from a single equipment vendor to the customer. Provided and it was possible to take into account the protection functions. For this reason, even if a signal transceiver without protection function is connected to each wavelength signal,

(4) The wavelength conversion unit and the switching unit provided a protection function. Therefore, switching of the wavelength signal unit in the above configuration was not a problem.

However, as shown in Fig. 10, when using a signal transmission / reception device, switching unit, or ΟΖΕ / 0 wavelength conversion unit from another vendor, the configuration may not be protected. I will. Here, it is assumed that the hatched portion is provided by another vendor.

The configuration related to the transceiver 191-1 is the same as the configuration related to the transceiver 18-1, but the signal transceiver is provided by a different device pendant. In this configuration, there is no problem because the protection function can be realized by the wavelength conversion unit and the switching unit.

The configuration related to the transmission / reception device 191-2 is the same as the configuration related to the transmission / reception device 18-2, but the signal transmission / reception device and the switching unit are provided by different device vendors. That is, the optical wavelength multiplexing unit and the wavelength conversion unit are provided by a device vendor, and the signal transmitting / receiving device and the switching unit are provided by another device ender. In this configuration, the switching unit monitors the quality of the electrical signal of the OZEZO wavelength conversion unit and performs switching. Therefore, it is necessary that the switching unit can monitor the quality of the electrical signal of the wavelength conversion unit of another device vendor. This is a condition for realizing the function. Therefore, there is a problem that the protection function cannot be realized for equipment vendors who cannot monitor the quality. The configuration related to the transmission / reception device 19-13 is the same as the configuration related to the transmission / reception device 18-3, and the signal transmission / reception device is provided by a different device vendor. In this configuration, there is no problem because the protection function can be realized by the signal transmitting / receiving device. The configuration related to the transmission / reception device 19-14 is the same as the configuration related to the transmission / reception device 18-4, and the signal transmission / reception device and the O / E / O wavelength converter are provided by different device vendors. The switching unit is provided by the same equipment vendor or a different pendant as the optical multiplexing unit. In this configuration, the protection unit monitors the quality of the single-wavelength optical signal branched from the wavelength division multiplexing unit and performs the switching. Therefore, the switching unit can monitor the quality of the optical signal of another device vendor. This is a condition for realizing the protection function. Therefore, there is a problem that the protection function cannot be realized in the case of a device pendant that cannot monitor the quality.

The configuration related to the transmitting / receiving device 1915 includes two parts, a signal transmitting / receiving device and an optical wavelength multiplexing unit. The signal transmitting / receiving device does not have the protection function, and in this configuration, there is a problem that the protection function cannot be realized regardless of the device vendor that provides the signal transmitting / receiving device.

As can be seen from the above, in the case of switching in wavelength units, there are two types of switching: those that can achieve the protection function and those that cannot.

In addition, the conventional switching method generally performs processing after converting an optical signal of each wavelength into an electric signal. Since this electric signal processing requires low-speed electric circuit processing, the high-speed optical signal transmission is reduced. There was a problem of losing it.

Further, the working standby switching operation time of the transmission device is about several tens of ms, and a momentary interruption for this switching operation time has occurred. The instantaneous interruption caused data loss, and the quality of the service provided by the communication line service provider deteriorated. In particular, in the WDM service, a signal of several hundred Gbps to several Tbps is transmitted on one line, and data loss due to instantaneous interruption increases, which is a problem.

In the present invention, switching is performed with the wavelength-multiplexed optical signal (WDM signal) as it is, and all wavelengths are simultaneously switched from working to standby, so that only one line becomes the working line.

This solves the problem that both lines simultaneously become the working lines.

To realize WDM signal switching, one of the following three methods using optical characteristics Or a combination of two or more of the three.

In the first method, the OSC (light monitoring channel) detector that detects the light intensity level at the receiving node measures the OSC signal light intensity, and the OSC signal light intensity flowing through the working line reaches a certain level. Otherwise, the switching unit switches to the protection line according to the instruction from the detection unit.

The second method uses an optical spectrum analyzer for the optical signal detector, analyzes the optical SNR (optical signal-to-noise ratio), chromatic dispersion, and other qualities of the OSC signal. The switching unit switches to the protection line according to the instruction of the detection unit.

The third method is to measure the signal light intensity of the WDM signal instead of the OSC, and when the signal level does not reach a certain level, the switching unit switches to the protection line according to the instruction of the detection unit.

According to such a switching method, optical signal processing can be performed without conversion to an electric signal, and high speed can be maintained.

In addition, the switching by the WDM signal can solve the problem of multiple failures caused by the switching in the wavelength unit illustrated in FIGS. 6 to 8 described above.

FIGS. 11 to 14 illustrate switching by the WDM signal. As in the above example, it is assumed that the optical signals of wavelengths 1 and 2 are transmitted between points A and B, and the optical signals of wavelengths 3 and 4 are transmitted between points A and C. The protection function is performed for each WDM signal, not for each wavelength. In the figure, the solid line is the working line, and the dotted line is the protection line. If a signal is marked on the line and the wavelength signal passing through the line is indicated by a dotted line, it means that the signal has been interrupted due to the occurrence of a fault.

The transmission from point A to point B in Fig. 11 is as follows. At point A, the optical signal of each wavelength is wavelength-division multiplexed by the optical wavelength multiplexing unit 12 and then branched into the working and standby WDM signal lights at the branching unit BS, and passed through the switching unit SS at point B. After that, the wavelength is demultiplexed by the optical wavelength demultiplexing unit 22 to return to an optical signal of each wavelength. Points B-C operate in a similar manner.

Figure 12 shows a situation in which a failure such as a fiber disconnection has occurred in the working WDM line 1 between points A and B. In this case, the data is transmitted to the protection WDM line 2 at the switching unit SS at the point B. By selecting the WDM signal light that has been turned on, switching to the standby WDM line 2 is performed. By this switching, the optical signal of each wavelength is recovered from the failure.

Next, as shown in Fig. 13, the operation in the double failure state in which a failure has occurred in the working WDM circuit 1 between points B and C at the same time is seen. The WDM signal light transmitted to the working WDM line 1 is switched to the backup WDM line 2 in a normal state, and the optical signals of wavelengths 3 and 4 reach the point C without signal interruption.

Figure 14 shows a different double failure condition than Figure 13. The working WDM line 1 at points A and B and the protection WDM line 2 at points B and C have failed simultaneously. At this time, the WDM signal light passes through the protection WDM circuit 2 at points A and B and the working WDM circuit 1 at points B and C, and the optical signal of each wavelength is not affected by the failure.

As described above, in switching in units of WDM signal light, if one of the working protection lines between two points is normal on the transmission line connecting multiple points, even if multiple simultaneous failures including double failures occur, Optical signals can be transmitted normally. This is an advantage compared to switching in wavelength units that does not have fault tolerance to multiple faults.

For the problem that the protection function cannot be realized by connecting to a device from a different device vendor, which occurs when switching in wavelength units as shown in Figs. Is shown in FIG. Here, a switching unit SS that performs switching on a WDM signal light unit basis is provided downstream of the optical wavelength multiplexing unit 12.

In switching with WDM signal light, protection is guaranteed regardless of the switching configuration. The equipment connected to the optical signal of each wavelength can realize the protection function even if it is freely selected, regardless of the presence or absence of the protection function and the equipment vendor.Freely regardless of the existing equipment when setting the wavelength You can choose the connection device.

In the switching configuration using WDM signal light, the number of switching units can be reduced to one. In the case of the conventional switching configuration, as shown in FIG. 10, N switching units are required for N wavelengths, but in the present invention, one switching unit SS is sufficient regardless of the number of wavelengths. However, the simplification of the system becomes possible, which is advantageous in terms of the cost of the apparatus.

Further, in the present invention, non-instantaneous switching is realized by providing a protection line with an optical delay compared to the working line, or storing a WDM signal in a WDM signal buffer memory, thereby reducing data loss due to an instantaneous interruption. It can be prevented (details will be described later). The OSC (optical monitoring channel) is a wavelength used for maintenance and control purposes in WDM transmission separately from the main signal transmission, and is mainly used for remote site alarm reporting, fault location notification, order wire function, etc. Used for The signal frame format of the OSC signal flowing through the OSC is determined independently by each vendor, and the regulations regarding the OSC are described in the international telecommunication standard ITU_TG.692. Next, some embodiments for realizing instantaneous interruption switching will be described.

In FIG. 16, optical signals of wavelength 1, wavelength 2,..., And wavelength n are input to the optical wavelength multiplexing unit 12 and wavelength division multiplexed. The WDM signal light obtained thereby is transmitted to the optical branching unit 13 and branched to the working WDM line 1 and the protection WDM line 2. The split WDM signal light is transmitted through the working line 1 and the protection line 2.

Since the working line 1 and the protection line 2 pass through different routes, the optical path lengths from the transmitting node 10 to the receiving node 20 are different. Due to this optical path length difference, the WDM signal light simultaneously transmitted to the working node and the standby node at the transmitting node 10 arrives at the receiving node 20 with a time lag. The following method is used to eliminate the difference between the working and standby reception times.

First, the optical path length of each of the working and protection lines 1 and 2 is measured by the OSC signal having the optical path length adjustment information. Specifically, in FIG. 16, first, the transmitting node 10 transmits an OSC signal to the working node 1 and the protection channel 1 to the receiving node 20. In the receiving node unit 20, the OSC signal transmitted on the working line 1 is detected by the optical signal detection unit 24—O—1, and the OSC signal transmitted on the protection line 2 is detected by the optical signal detection unit 24—O — Detect with 2.

Here, an example of the frame format of the OSC signal is shown in FIG. The frame includes, for example, alarm control information, order wire information, fault information, optical delay control information, and optical path length adjustment information.

The function of the optical path length adjustment information in the frame format will be described. The optical path length adjustment information includes a transmission time when the OSC signal is transmitted from the transmitting node 10. After the OSC signal is detected by the optical signal detection unit of the receiving node unit 20, the optical path length adjustment information is read by the optical signal control unit 25-O. The optical signal control unit 2510 has a timer in the circuit, receives the transmission time in the optical path length adjustment information, and compares it with the reception time. The transmission time from the transmission unit to the reception unit is determined by. The optical path length is calculated from this transmission time. Further, the control unit 25-O calculates an optical path length difference based on the OSC signal received from the working line 1 and the OSC signal received from the protection line 2, Next, referring to this optical path length difference, the variable optical delay unit 26-1, and 26-2, which have an optical delay function that can arbitrarily adjust the delay time, adjusts the timing of the WDM signal light. By doing so, adjust so that the working and protection reception times are equal. By this adjustment, the switching unit 23 simultaneously receives the same signal from each of the working and the standby.

The switching unit 23 normally selects the current WDM signal light, and the selected WDM signal light is transmitted to the optical wavelength separation unit 22. The WDM signal light is separated by the wavelength separation unit 22 into optical signals of wavelength 1, wavelength 2,..., And wavelength n.

Here, switching between the active and the standby will be described.

The conventional technique of switching between active and standby in WDM has already been described as being performed at the electrical level for each wavelength before wavelength division multiplexing.

In the present invention, switching is realized with the WDM signal light as it is, using the OSC signal light intensity, the WDM signal light intensity, and the OSC signal quality such as waveform, noise, and dispersion.

First, the procedure of the switching method based on the OSC signal light intensity will be described below. The device on the receiving side has light-receiving allowance and cannot read light signals with weak light intensity that does not reach the light-receiving allowance. Therefore, in the present invention, the OSC signal light intensity is measured by the optical signal detection unit 24 -O, and when the OSC signal light intensity flowing through the working line does not reach a certain level, the optical signal detection unit 24 -O switches the optical signal control unit to the optical signal control unit. 25 51 The detection result is transmitted to O. The control unit 25-O issues a switching instruction to the protection line 2 to the switching unit 23. The switching unit 23 switches the WDM signal light flowing through the working line 1 to the protection line 2.

Next, the procedure of the switching method using the WDM signal light intensity instead of the OSC signal will be described. The optical signal detector 2 4—O measures the WDM signal light intensity, and if the intensity of the WDM signal light flowing through the working line 1 does not reach a certain level, the optical signal detector 24 1 O to the optical signal controller 25 1 O The detection result is transmitted to. The control unit 25-10 issues a switching instruction to the protection line 2 to the switching unit 23. The switching unit 23 switches the WDM signal light flowing through the working line 1 to the protection line 2. ' As another method, a procedure of a switching method using an optical spectrum analyzer function for measuring the quality of an optical signal is described below. The optical signal detector 24 with optical spectrum analyzer function analyzes the optical signal quality such as optical SNR (optical signal-to-noise ratio) and chromatic dispersion of the OSC signal flowing through the working protection line using O-O, and If the quality does not reach a certain level, the detection result is transmitted from the optical signal detector 24 -O to the optical signal controller 25 -O. The control unit 25_0 issues a switching instruction to the protection line 2 to the switching unit 23. The switching unit 23 switches the WDM signal light flowing through the working line 1 to the protection line 2.

The switching method using the OSC signal light intensity, the WDM signal light intensity, and the OSC signal quality individually has been described above. As an application of the above method, when two or more of the OSC signal light intensity, WDM signal light intensity, and OSC signal quality are analyzed simultaneously, and one or more of them does not reach a certain level The method of switching the WDM signal light flowing through the working line 1 to the protection line 2 can be realized by basically the same procedure.

With the above operation, switching of the WDM signal light becomes possible. However, a short interruption occurs during this switch, which results in data loss. Therefore, instantaneous interruption switching is realized by the method described below, and switching without data loss is performed.

Fig. 16 shows a method that uses optical delay as one of the methods to realize instantaneous interruption switching. The optical delay unit 26 6 _ 2, which gives a delay to the protection line 2, gives the protection line 2 a predetermined delay in comparison with the working line 1. For example, if it takes 50 ms to switch the working protection line, the optical delay unit 26-2 is provided with a delay of 50 ms in advance, enabling instantaneous interruption switching. I do.

As another method using optical delay, a description will be given of instantaneous interruption switching by a variable optical delay module that can arbitrarily adjust the delay time. A variable optical delay module is used as the optical delay unit 26-2 shown in Fig. 16.

As described with reference to FIG. 2, the 0SC frame includes optical delay control information for delay control. In the optical signal control unit 25-O, the delay time can be arbitrarily set by manipulating the value of the optical delay control information. Thereby, the optical delay unit 26-2 can adjust the delay time based on the obtained delay time.

Next, a method of using the buffer memory 27 for the WDM signal light will be described with reference to FIG. Buffer memory capable of storing WDM signal light data for a fixed time 2 7 By combining the operation of the optical signal control unit 25-O with the protection line 2, the non-instantaneous interruption switching is realized by giving the fixed line memory time in advance to the protection line 2 compared to the working line 1.

For example, if it takes 50 ms to switch between the active and protection lines 1 and 2, the buffer memory time is set to 50 ms in advance, so that instantaneous interruption is switched.

As another method of using the buffer memory 27, a description will be given of instantaneous interruption switching using a variable WDM signal light buffer memory capable of arbitrarily adjusting the buffer memory time. Here, a variable WDM signal light buffer memory 27 is used as the buffer memory 27 shown in FIG.

FIG. 19 shows the OSC signal frame format in this case. This OSC frame format has buffer memory control information for controlling the buffer memory 27. The value of the buffer memory control information is operated by the optical signal control unit 25-O.

In the optical signal control unit 25-0, the delay time can be arbitrarily set by manipulating the buffer memory control information value. The OSC signal having buffer memory time information in the buffer memory control information is supplied from the optical signal control unit 25-O to the buffer memory 27. Then, the buffer memory 27 adjusts the buffer memory time based on the OSC signal information. Industrial applicability

As described above in detail, according to the present invention, in wavelength division multiplexing (WDM) transmission, a multiplexed optical signal (WDM signal light) is not converted into an electric signal as it is, and is used at high speed and without interruption. It is also possible to switch the protection line. In addition, since a stronger fault recovery (protection) function is realized with a simpler configuration than the conventional WDM device, it greatly contributes to the development of the field of optical fiber communication.

Claims

The scope of the claims

1. Providing a working line and a protection line for respectively transmitting WDM signal light obtained by wavelength division multiplexing a plurality of optical signals having different wavelengths;

Allocating one of the plurality of optical signals as an optical monitoring channel, and including a parameter for measuring an optical path length difference between the working line and the protection line in the optical monitoring channel. ,

Compensating the optical path difference at the receiving end based on the parameters.

2. The step of compensating includes a step of delaying a WDM signal light transmitted by at least one of the working line and the protection line so that the optical path length difference becomes substantially zero. The method of claim 1.

3. A step of measuring the intensity of the WDM signal light transmitted by the working line, and the step of measuring the intensity of the WDM signal light transmitted by the working line when the measured intensity does not reach a predetermined level. Switching to the protection line. 4. The method according to claim 1, further comprising:

4. measuring the optical signal strength of the optical supervisory channel transmitted by the working line;

2. The method according to claim 1, further comprising the step of: switching the WDM signal light transmitted by the working line to the protection line when the measured intensity does not reach a predetermined level.

5. measuring the quality of the optical signal on the optical supervisory channel transmitted by the working line;

2. The method according to claim 1, further comprising the step of: switching the WDM signal light transmitted by the working line to the protection line when the measured quality does not reach a predetermined level.

6. The method according to claim 2, wherein said delaying step includes a step of delaying said WDM signal light by a time required for switching from said working line to said protection line.

7. The method according to claim 2, further comprising the step of storing the WDM signal light in a buffer memory for a time required for switching from the working line to the protection line.

8. A working line and a protection line for transmitting WDM signal light obtained by wavelength division multiplexing a plurality of optical signals having different wavelengths,

Means for providing one of the plurality of optical signals as an optical supervisory channel and supplying an optical supervisory signal including a parameter for measuring an optical path length difference between the working line and the spare line;

Means for compensating the optical path length difference on the receiving side based on the parameter.

9. The means for compensating includes means for delaying the WDM signal light transmitted by at least one of the working line and the protection line so that the optical path length difference becomes substantially zero. 9. The device according to claim 8, wherein:

10. A means for measuring the intensity of the WDM signal light transmitted by the working line, and a WDM signal transmitted by the working line when the measured intensity does not reach a predetermined level. 9. The apparatus according to claim 8, further comprising: means for switching light to said protection line.

11. A means for measuring the intensity of an optical signal of an optical supervisory channel transmitted by the working line;

9. The apparatus according to claim 8, further comprising: means for switching the WDM signal light transmitted by the working line to the protection line when the measured intensity does not reach a predetermined level.

12. A means for measuring the quality of an optical signal of an optical supervisory channel transmitted by the working line;

9. The apparatus according to claim 8, further comprising: means for switching the WDM signal light transmitted by the working line to the protection line when the measured quality does not reach a predetermined level.

13. The apparatus according to claim 9, wherein said delaying means includes means for delaying said WDM signal light by a time required for switching from said working line to said protection line.

10. The apparatus according to claim 9, further comprising a buffer memory for storing said WDM signal light for a time required for switching from said working line to said protection line.