JP2017220777A - Optical communication system, optical communication unit, and communication line switching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a switching time of switching of a communication line from an in-operation line to a standby line.SOLUTION: An optical communication system 1 is configured to switch a communication line between an in-operation line and a standby line. A first pre-equalization optical transmitter receiver 10 has a first optical transmitting/receiving function part 14 for transmitting an optical signal including a redundancy code for detecting a code error, and a first control part 17 for adjusting a wavelength dispersion compensation value of the optical signal. A second pre-equalization optical transmitter receiver 20 has a second optical transmitting/receiving function part 24 for receiving the optical signal, and a second control part 27 for detecting a code error rate of the optical signal. When the communication line is switched, the first control part 17 increases a rate of the redundancy code of the optical signal, the second pre-equalization transmitter receiver 20 transmits information, based upon the code error rate of the optical signal having been increased in ratio of redundancy code, to the first pre-equalization optical transmitter receiver 10, and the first control part 17 adjusts the wavelength dispersion compensation value of the optical signal based upon the information received from the second pre-equalization optical transmitter receiver 20.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical communication system.

  2. Description of the Related Art In recent years, optical communication systems using optical communication devices have a transmission capacity of communication data from a range of 2.5 Gbps to 10 Gbps to a range of 40 Gbps to 100 Gbps on one line as communication data increases in capacity and speed. However, there is an increasing demand for transmission capacity. As the transmission capacity increases, it is important to secure a backup path (backup system line) and shorten the communication line switching time in a ring network and a mesh type (multi-way) network. When the communication line is switched, the chromatic dispersion value (hereinafter referred to as “dispersion value” or simply “dispersion”) changes in proportion to the length of the optical line (for example, fiber length). The optimum value of “compensation value”) changes. Therefore, it is necessary to optimize the dispersion compensation value every time the communication line is switched.

  Patent Document 1 discloses a chromatic dispersion compensation control that specifies a measurable range of BER (Bit Error Ratio) by changing a dispersion compensation value, and searches for a dispersion compensation value that minimizes the BER within the identified range. A system is disclosed.

JP 2011-205185 A

  However, since the system disclosed in Patent Document 1 needs to pass information for determining an optimum dispersion compensation value between the transmission-side transmission apparatus and the reception-side transmission apparatus, the dispersion compensation value is optimized. There is a problem that it takes time to complete.

  Therefore, an object of the present invention is to shorten the switching time when switching the communication line from the active line to the standby line.

  The optical communication system of the present invention is an optical communication system capable of switching a communication line between an operation line and a protection line, and includes a first optical communication device and the first line via the communication line. A second optical communication device that communicates with the first optical communication device, wherein the first optical communication device transmits an optical signal including a redundant code for detecting a code error; and A first control unit that adjusts a chromatic dispersion compensation value of the optical signal transmitted from the first optical communication device, and the second optical communication device is transmitted from the first optical communication device. A second interface unit that receives the optical signal; and a second control unit that detects a code error rate of the optical signal transmitted from the first optical communication device; When the operation line is switched to the protection line, the first control unit is configured to transmit the optical line. And the second optical communication device transmits information based on the code error rate of the optical signal with the increased redundant code rate to the first optical communication device. The first control unit adjusts a chromatic dispersion compensation value of the optical signal based on the information received from the second optical communication device.

  According to the present invention, when switching the communication line from the active path to the protection path, the adjustment time of the chromatic dispersion compensation value is shortened by increasing the ratio of the redundant code in the optical signal, thereby switching the communication line. Time can be shortened.

1 is a block diagram schematically showing a configuration of an optical communication system according to Embodiment 1 of the present invention. 10 is a flowchart illustrating an example of dispersion compensation setting processing performed in the optical communication system when a communication line is switched from an active system path to a backup system path. It is a figure which shows an example of the dispersion compensation value-BER characteristic of the main signal transmitted on the communication line of an optical communication system. It is a figure which shows an example of the limit value (limit BER and limit dispersion compensation value) in which the error correction before and behind the change of a FEC (Forward Error Correction) rate is possible. It is a flowchart which shows the search algorithm of the upper limit and lower limit in the search range of the dispersion compensation value for obtaining the optimum dispersion compensation value. It is a figure which shows an example of the dispersion compensation value-BER characteristic of the main signal transmitted on the communication line as a backup path. 10 is a flowchart illustrating a dispersion compensation setting process performed in the optical communication system when a communication line is switched from an active system path to a backup system path. 6 is a diagram showing an example of dispersion compensation value-BER characteristics of a main signal transmitted on a communication line of an optical communication system according to Embodiment 2. FIG. It is a block diagram which shows the structure of the control part of the pre-equalization optical transmitter-receiver in the optical communication system which concerns on a modification.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram schematically showing a configuration of an optical communication system 1 according to the first embodiment.
The optical communication system 1 includes a first pre-equalized optical transceiver 10 as a first optical communication device, a second pre-equalized optical transceiver 20 as a second optical communication device, and a first transmission. Side optical coupler 15 (optical coupler), second transmission side optical coupler 25 (optical coupler), first reception side optical switch 16 (optical switch), and second reception side optical switch 26 (optical switch) And have. The first pre-equalized optical transceiver 10 and the second pre-equalized optical transceiver 20 have an active system line (hereinafter referred to as “active system path”) and a standby system line (hereinafter referred to as “backup system path”). The communication line can be switched between. That is, the optical communication system 1 is a system capable of switching communication lines between an active system path and a backup system path.

  Communication lines Pa1 and Pb1 as communication paths (transmission paths) are active paths, and communication lines Pa2 and Pb2 as communication paths are backup paths. Each of the communication lines Pa1, Pb1, Pa2, and Pb2 is an optical line realized by an optical fiber, for example.

  The main signal that is an optical signal used for communication in the optical communication system 1 includes a redundant code (FEC (Forward Error Correction) data) for detecting a code error. Specifically, the main signal includes an overhead area, a payload area, and an FEC redundant area in which redundant codes are stored.

  The first pre-equalized optical transceiver 10 communicates with the second pre-equalized optical transceiver 20 using the main signal (at least one of transmission and reception of the main signal). The first pre-equalized optical transceiver 10 includes a first optical transmission / reception function unit 14 as a first interface unit and a first control unit 17. The first control unit 17 includes a first automatic dispersion compensation function unit 11, a first BER (Bit Error Ratio) information acquisition function unit 12, and a first FEC function unit 13. The first control unit 17 includes, for example, a processor and a memory.

  The first pre-equalized optical transceiver 10 communicates with the second pre-equalized optical transceiver 20 which is another optical communication device using the main signal. Specifically, the first pre-equalized optical transceiver 10 transmits the main signal to the second pre-equalized optical transceiver 20 via the communication line Pa1 or Pa2, and via the communication line Pb1 or Pb2. A main signal is received from the second pre-equalized optical transceiver 20. When the first pre-equalization optical transceiver 10 transmits a main signal, the first optical transmission / reception function unit 14 transmits the main signal, and the main signal transmitted from the first pre-equalization optical transceiver 10 is The first transmission side optical coupler 15 branches to either of the communication lines Pa1 and Pa2. When the second pre-equalized optical transceiver 20 transmits the main signal, the first optical transmission / reception function unit 14 receives the main signal transmitted from the second pre-equalized optical transceiver 20 as the first reception. Receive via the side light switch 16.

  The first control unit 17 (for example, the first automatic dispersion compensation function unit 11) detects the main signal transmitted from the first pre-equalized optical transceiver 10 by the second pre-equalized optical transceiver 20. The code error rate (hereinafter referred to as “BER”) is adjusted. In the present embodiment, the first automatic dispersion compensation function unit 11 executes chromatic dispersion compensation control for compensating the chromatic dispersion of the main signal. Specifically, the first automatic dispersion compensation function unit 11 adjusts the dispersion compensation value for the main signal to perform the second pre-equalization of the main signal transmitted from the first pre-equalization optical transceiver 10. The BER detected by the optical transceiver 20 is adjusted.

  Furthermore, the first control unit 17 (for example, the first BER information acquisition function unit 12) can detect the BER of the main signal transmitted from the second pre-equalized optical transceiver 20. In addition, the first BER information acquisition function unit 12 transmits the BER of the main signal transmitted from the first pre-equalized optical transceiver 10 and received by the second pre-equalized optical transceiver 20 and information based on the BER. (For example, information (state information) indicating whether or not the LOF (frame synchronization loss) state) can be acquired.

  Further, the first control unit 17 (for example, the first FEC function unit 13) is configured to transmit a redundant code ratio (hereinafter referred to as “FEC rate”) of the main signal transmitted from the first pre-equalization optical transceiver 10. Can also be changed (increase and decrease). In the present embodiment, the first FEC function unit 13 can adjust the error correction capability for the code error of the main signal by changing the FEC rate.

  The first optical transmission / reception function unit 14 bundles main signals from a client (for example, a communication device on the upstream side of the first pre-equalization optical transmitter / receiver 10) and WDM (Wavelength Division Multiplex) section (communication line). The main signal can be transmitted and received.

  The second pre-equalized optical transceiver 20 communicates with the first pre-equalized optical transceiver 10 using the main signal (at least one of transmission and reception of the main signal). The second pre-equalized optical transceiver 20 includes a second optical transmission / reception function unit 24 as a second interface unit, and a second control unit 27. The second control unit 27 includes a second automatic dispersion compensation function unit 21, a second BER information acquisition function unit 22, and a second FEC function unit 23. The second control unit 27 includes, for example, a processor and a memory.

  The second pre-equalized optical transceiver 20 communicates with the first pre-equalized optical transceiver 10 which is another optical communication device using the main signal. Specifically, the second pre-equalized optical transceiver 20 transmits the main signal to the first pre-equalized optical transceiver 10 via the communication line Pb1 or Pb2, and via the communication line Pa1 or Pa2. A main signal is received from the first pre-equalized optical transceiver 10. When the second pre-equalized optical transceiver 20 transmits the main signal, the second optical transmission / reception function unit 24 transmits the main signal, and the main signal transmitted from the second pre-equalized optical transceiver 20 is The second transmission side optical coupler 25 branches to either of the communication lines Pb1 and Pb2. When the first pre-equalized optical transceiver 10 transmits a main signal, the second optical transmission / reception functional unit 24 receives the main signal transmitted from the first pre-equalized optical transceiver 10 as a second reception. Reception is performed via the side light switch 26.

  The second control unit 27 (for example, the second BER information acquisition function unit 22) detects the BER of the main signal transmitted from the first pre-equalized optical transceiver 10. Further, the second BER information acquisition function unit 22 transmits the second pre-equalized optical transceiver 20 and receives the BER of the main signal received by the first pre-equalized optical transceiver 10 and information based on the BER. (For example, information indicating whether or not the LOF state is present).

  Further, the second control unit 27 (for example, the second automatic dispersion compensation function unit 21) is configured to transmit the first pre-equalized optical transceiver 10 of the main signal transmitted from the second pre-equalized optical transceiver 20. It is possible to adjust the detected BER. For example, the second automatic dispersion compensation function unit 21 can execute chromatic dispersion compensation control. Specifically, the second automatic dispersion compensation function unit 21 adjusts the dispersion compensation value for the main signal, thereby first pre-equalizing the main signal transmitted from the second pre-equalization optical transceiver 20. The BER detected by the optical transceiver 10 can be adjusted.

  Further, the second control unit 27 (for example, the second FEC function unit 23) changes (increases and decreases) the ratio of the redundant code in the main signal transmitted from the second pre-equalization optical transceiver 20. ). For example, the second FEC function unit 23 can adjust the error correction capability for the code error of the main signal by changing the FEC rate.

  The second optical transmission / reception function unit 24 can send and receive the main signal to the WDM section (communication line) by bundling the client signals.

  The first transmission-side optical coupler 15 and the second transmission-side optical coupler 25 make the communication path between the first pre-equalized optical transceiver 10 and the second pre-equalized optical transceiver 20 redundant. .

  The first reception side optical switch 16 performs line switching between the communication line Pb1 and the communication line Pb2 in cooperation with the second transmission side optical coupler 25. Similarly, the second reception-side optical switch 26 performs line switching between the communication lines Pa1 and Pa2 in cooperation with the first transmission-side optical coupler 15.

  The main signal transmitted from the first pre-equalized optical transceiver 10 is transmitted to the second pre-equalized optical transceiver 20 via the communication line Pa1 or the communication line Pa2. The main signal transmitted from the second pre-equalized optical transceiver 20 is transmitted to the first pre-equalized optical transceiver 10 via the communication line Pb1 or the communication line Pb2. When a failure occurs in the communication line, the communication line is switched from one to the other. For example, the first transmission-side optical coupler 15 and the second reception-side optical switch 26 can be used to switch the communication line from the communication line Pa1 as the active path to the communication line Pa2 as the backup path. Similarly, using the second transmission-side optical coupler 25 and the first reception-side optical switch 16, the communication line can be switched from the communication line Pb1 as the active path to the communication line Pb2 as the backup path. Thereby, the redundancy of the communication path in the optical communication system 1 is realized.

In the case where the main signal from the client is transmitted from the first pre-equalized optical transceiver 10 (transmission side apparatus) to the second pre-equalized optical transceiver 20 (reception side apparatus), the dispersion compensation setting is made as an example. An example of processing (communication line switching method) will be described below.
FIG. 2 is a flowchart showing an example of dispersion compensation setting processing (communication line switching method) performed in the optical communication system 1 when the communication line is switched from the active path to the protection path.
FIG. 3 is a diagram illustrating an example of the dispersion compensation value-BER characteristic of the main signal transmitted on the communication line of the optical communication system 1.

  In the optical communication system 1, when a line failure occurs in the communication line Pa1 as the active path, the communication line switching process from the communication line Pa1 to the communication line Pa2 as the backup path is started (step S11). .

  When the communication line is switched from the communication line Pa1 to the communication line Pa2, since the optimum dispersion compensation value (optimum chromatic dispersion compensation value) in the communication line Pa2 is not set, the main signal is not properly transmitted to the communication line Pa2. State.

Therefore, in step S12, when the communication line is switched from the active path to the backup path, the first FEC function unit 13 temporarily increases the error correction capability by temporarily increasing the FEC rate of the main signal. To improve. As a result, as shown in FIG. 3, the limit value of the error-correctable BER increases, and the dispersion width of the main signal transmitted from the first pre-equalized optical transceiver 10-the width of the curve of the BER characteristic ( Since the difference between the upper limit value and the lower limit value of the dispersion compensation value for restoring the LOF is widened, it is possible to widen the range of dispersion compensation values for which error correction (code error correction) for the main signal can be performed. In the example shown in FIG. 3, the range of dispersion compensation values that can be corrected for the main signal extends from the range of dispersion compensation values σ ₁ ′ to σ ₂ ′ to the range of dispersion compensation values σ ₁ to σ ₂ .

A specific example of the process in step S12 will be described below.
In the processing in step S12, the first pre-equalized optical transceiver 10 (specifically, the first FEC function unit 13), which is a transmission side device, reduces the payload area without changing the transmission rate. As the payload area is reduced, the FEC redundant area is expanded (that is, the FEC rate is increased).

FIG. 4 is a diagram illustrating an example of limit values (limit BER and limit dispersion compensation value) that allow error correction before and after the change of the FEC rate.
For example, in the example shown in FIG. 4, by increasing the FEC rate in one frame of the main signal from 10% (before change) to 50%, the dispersion compensation value capable of error correction is about 50 ps / nm in the positive direction. Can be increased. Similarly, by increasing the FEC rate in the main signal from 10% to 50%, the dispersion compensation value capable of error correction can be increased by about 50 ps / nm in the minus direction. Therefore, in the example shown in FIG. 4, by increasing the FEC rate from 10% to 50%, the range of dispersion compensation values capable of error correction as a whole (positive direction and negative direction) is increased by about 100 ps / nm. be able to.

  For example, when the range of dispersion compensation values capable of error correction (difference between the upper limit value and the lower limit value) is 300 ps / nm before the change of the FEC rate, the FEC rate is increased from 10% to 50%. As a result, the range of dispersion compensation values capable of error correction can be expanded to about 400 ps / nm.

In step S13, the second control unit 27 (for example, the second BER information acquisition function unit 22) detects the BER of the main signal and determines whether or not the LOF state is set. The second pre-equalized optical transmitter / receiver 20 which is the receiving side device is the transmitting side device through the communication line Pb1, for example, the information based on the BER, that is, the information including whether or not the LOF state is determined as described above. It can be transmitted to the first pre-equalized optical transceiver 10. Thereby, the 1st control part 17 of the 1st pre-equalization optical transceiver 10 acquires information (information which shows whether it is a LOF state) based on BER, and changes the 1st based on the change of the state. Two dispersion compensation values for obtaining the optimum chromatic dispersion compensation value (optimum dispersion compensation value σ ₀ in the backup path) set in the pre-equalized optical transceiver 10 are searched. The two dispersion compensation values searched in step S13 are the lower limit value σ ₁ (first limit value) and the upper limit value σ ₂ ( _second ) in the dispersion compensation value search range for obtaining the optimum dispersion compensation value σ ₀ . Limit value). By the processing in step S13, the upper limit value and lower limit value of the dispersion compensation value that does not become LOF (frame synchronization loss) (can be corrected) can be found relatively quickly. A specific example of the process in step S13 will be described later with reference to FIG.

  In step S14, the first automatic dispersion compensation function unit 11 of the first pre-equalized optical transceiver 10 obtains 2 obtained in step S13 based on the information received from the second pre-equalized optical transceiver 20. Two values are set as the upper limit value and the lower limit value in the search range of the dispersion compensation value for obtaining the optimum dispersion compensation value. For example, the difference (range of dispersion compensation value) between the upper limit value and the lower limit value is 300 ps / nm.

In step S <b> 15, the first control unit 17 adjusts the dispersion compensation value of the main signal based on the information received from the second pre-equalized optical transceiver 20. Specifically, the first automatic dispersion compensation function unit 11 obtains the dispersion compensation value σ ₀ that is the median value of the two dispersion compensation values (upper limit value and lower limit value) obtained in step S13. The dispersion compensation value (median value) is set as the optimum dispersion compensation value (optimum chromatic dispersion compensation value) in the backup path. Thereby, the BER detected by the second pre-equalized optical transceiver 20 of the main signal transmitted from the first pre-equalized optical transceiver 10 after switching the communication line is appropriately adjusted.

  In step S16, the first FEC function unit 13 returns the FEC rate to the ratio before the change in step S12 (the FEC rate before the change).

  With the above processing, the dispersion compensation value (optimum chromatic dispersion compensation value) setting (BER adjustment) is completed, and the main signal is appropriately transmitted on the communication line Pa2 as the backup path (step S17).

FIG. 5 is a flowchart showing a search algorithm (search process) for an upper limit value and a lower limit value in a search range of dispersion compensation values for obtaining an optimum dispersion compensation value. The processing from step S21 to step S28 shown in FIG. 5 is a specific example of the processing in step S13 shown in FIG.
FIG. 6 is a diagram illustrating an example of the dispersion compensation value-BER characteristic of the main signal transmitted on the communication line Pa2 as the backup path. The curve shown in FIG. 6 is the same as the curve shown in FIG.

In step S21, the first pre-equalized optical transceiver 10 searches for the lower limit value σ ₁ (first limit value) in the search range of the dispersion compensation value for obtaining the optimum dispersion compensation value σ ₀ . A dispersion value σ (dispersion compensation value) as a first initial setting value is set in the first automatic dispersion compensation function unit 11 on the main signal transmission side. Similarly, in order to search for the upper limit value σ ₂ (second limit value), in the first pre-equalization optical transceiver 10, the dispersion value σ ′ (dispersion compensation value) as the second initial setting value is It is set in the first automatic dispersion compensation function unit 11 on the main signal transmission side. The dispersion values σ and σ ′ are set to arbitrary values. In the present embodiment, the dispersion values σ and σ ′ are set to values that are in the LOF state (dispersion compensation values that cannot be corrected for errors).

Hereinafter, processing for searching for the lower limit value σ ₁ will be described. In each processing shown in FIG. 5, processing for searching for the upper limit value σ ₂ based on the variance value σ ′ is similarly performed.

  In step S <b> 22, in the first pre-equalized optical transceiver 10 that is the transmission side device, the first BER information acquisition function unit 12 performs information based on the BER acquired from the second pre-equalized optical transceiver 20 ( Whether or not there is a change in the LOF state (whether error correction is possible) for the transmission signal transmitted through the backup path (communication line Pa2) with the dispersion value σ based on the information indicating whether or not the LOF state is present To do.

If there is no change in the state of LOF (No in step S22), the first automatic dispersion compensation function unit 11 uses the predetermined dispersion value σ _step (dispersion compensation amount) as the dispersion value σ set in step S21. _Prev (= dispersion value σ) is added (step S23), and the process returns to step S21. In step S21 after step S23, the dispersion value (σ _prev + σ _step ) obtained in step S23 is set.

On the other hand, if there is a change in the state of LOF (Yes in step S22), the first automatic dispersion compensation function unit 11 determines whether or not the dispersion value σ _step is equal to a predetermined minimum value (step S24).

When the dispersion value σ _step does not reach the predetermined minimum value (No in step S24), the first automatic dispersion compensation function unit 11 sets the dispersion value σ _step by a predetermined amount (absolute value). Updating is performed so as to decrease, and the sign of the updated variance value σ _step is inverted (step S25).

  After step S25, step S23 is performed.

When the variance value σ _step reaches the predetermined minimum value in Step S24 (Yes in Step S24), the first BER information acquisition function unit 12 determines whether or not the transmission signal is in the LOF state (Step S26). . If it is in the LOF state (Yes in step S26), the search for the lower limit σ ₁ is terminated. The dispersion value σ at this time is set as the lower limit value σ ₁ in the search range of the dispersion compensation value for obtaining the optimum dispersion compensation value.

When the LOF is not set in step S26 (No in step S26), the variance value σ _step is obtained by subtracting the variance value σ _step from the currently set variance value σ _prev (the variance value set in step S21). (Step S27).

In step S28, the dispersion value σ obtained in step S27 is set as the lower limit value σ ₁ in the search range of the dispersion compensation value for obtaining the optimum dispersion compensation value.

Similarly, the dispersion value σ obtained based on the dispersion value σ ′ as the second initial setting value is set as the upper limit value σ ₂ . After the step S21 has completed the search for lower limit sigma ₁ by the processing in step S28, it may be searched upper limit sigma ₂ performs processing in step S28 from step S21 again. When searching for the upper limit value σ ₂ in the same step, the sign of the variance value σ _step starts from minus.

Through the above steps, the lower limit value σ ₁ and the upper limit value σ ₂ in the search range of the dispersion compensation value for obtaining the optimum dispersion compensation value are obtained.

In the conventional chromatic dispersion compensation control method, the range of dispersion compensation values (the difference between the upper limit value and the lower limit value for restoring the LOF) in which code error correction is possible is about 200 ps / nm. In order to search for this range (upper limit value and lower limit value), it is necessary to set the _step size of the dispersion value (dispersion value σ _step ) to about 150 ps / nm. For example, when the dispersion of the communication line (optical fiber) is positive and the search range of the dispersion compensation value is changed from 0 ps / nm to -1000 ps / nm, the dispersion compensation value is changed (set) seven times with a step size of 150 ps / nm. )Is required. If the time taken to detect the BER by changing the dispersion compensation value is 15 seconds, the time for completing the search is about 105 seconds. Furthermore, it is possible to search for a more accurate upper limit value and lower limit value by reducing the step size, but the time until search completion is increased.

According to the present embodiment, when the communication line is switched from the active path to the backup path, the dispersion compensation value that enables error correction can be increased by temporarily increasing the FEC rate in the main signal that is an optical signal. The range can be expanded. For example, the range of dispersion compensation values capable of code error correction (difference between the upper limit value and the lower limit value for restoring the LOF) can be expanded to about 300 ps / nm. As a result, the step size of the dispersion value (dispersion value σ _step ) for searching for the lower limit value and the upper limit value can be coarsened to, for example, about 220 ps / nm. It is possible to shorten the search time for the range (upper limit value and lower limit value) of dispersion compensation values that can be reduced. As a result, when the communication line is switched from the active path to the backup path, it is possible to shorten the time required to set the optimum dispersion compensation value. That is, according to the present embodiment, it is possible to reduce the communication line switching time when a line failure occurs in the active path.

  For example, if the search range of the dispersion compensation value is from 0 ps / nm to -1000 ps / nm, the search is completed by changing (setting) the dispersion compensation value five times at a step size of 220 ps / nm. In this case, if the time required to detect the BER by changing the dispersion compensation value is 15 seconds, the time for completing the search is about 75 seconds, which is required for completing the search compared to the conventional method described above. Time can be shortened by about 30 seconds.

Embodiment 2. FIG.
FIG. 7 is a flowchart showing a dispersion compensation setting process performed in the optical communication system according to the second embodiment when the communication line is switched from the active path to the backup path.
In the optical communication system according to the second embodiment, the optimum wavelength dispersion compensation value adjustment process (step S36 in FIG. 7) is different from the process (step S16 in FIG. 2) in the optical communication system 1 according to the first embodiment. The other points are the same. Therefore, in the second embodiment, the same or corresponding elements and steps as those described in the first embodiment will be described using the same reference numerals as those in the first embodiment.

  Hereinafter, differences between the configuration and operation of the optical communication system according to Embodiment 2 from the configuration and operation of the optical communication system 1 according to Embodiment 1 will be mainly described. The processing from step S11 to step S15 and step S17 shown in FIG. 7 is the same as the processing from step S11 to step S15 and step S17 shown in FIG. 2 described in the first embodiment.

FIG. 8 is a diagram illustrating an example of the dispersion compensation value-BER characteristic of the main signal transmitted on the communication line of the optical communication system according to the second embodiment.
When the FEC rate is large, the flat portion (error-free region shown in FIG. 8) of the dispersion compensation value-BER characteristic curve becomes large like the curve shown in FIG. 8, and fine adjustment of the dispersion compensation value becomes difficult. There is a case.

  In step S36, the first FEC function unit 13 before changing the FEC rate stepwise in step S12 so that the flat portion of the dispersion compensation value-BER characteristic curve (the value of the error-free BER) becomes small. Change to approach the ratio (FEC rate before change). That is, the FEC rate is decreased stepwise. As a result, as shown in FIG. 8, the error-free BER value decreases and the flat portion changes.

For example, in step S36, the first control unit 17 (for example, the first FEC function unit 13 and the first automatic dispersion compensation function unit 11) decreases the FEC rate stepwise, and the dispersion compensation value σ ₀ ( The BER of the main signal is adjusted by further adjusting (increasing or decreasing) the median value obtained in step S15. The second control unit 27 (for example, the second BER information acquisition function unit 22) transmits information based on the BER detected at any time to the first pre-equalized optical transceiver 10. The first controller 17 finely adjusts the dispersion compensation value based on the information received from the second pre-equalized optical transceiver 20. By repeating this process, the first control unit 17 (for example, the first BER information acquisition function unit 12) can acquire the optimum dispersion compensation value σ ₀ that minimizes the BER.

In step S17, the first control unit 17 (for example, the first automatic dispersion compensation function unit 11) obtains the optimum dispersion compensation value σ ₀ that minimizes the acquired BER as the optimum dispersion compensation value in the backup path. Set as (optimal chromatic dispersion compensation value). Thereby, the BER of the main signal transmitted from the first pre-equalized optical transceiver 10 after switching the communication line is appropriately set.

According to the optical communication system according to the second embodiment, as compared with the optical communication system 1 in the first embodiment, the optimal dispersion compensation value σ ₀ with higher accuracy is obtained by using the first pre-equalized optical transceiver 10. Can be set to

  The contents described in the first and second embodiments are that the main signal from the client is transmitted from the second pre-equalized optical transceiver 20 (transmitting side apparatus) to the first pre-equalized optical transceiver 10 (receiving side apparatus). It can also be applied to the case of being transmitted to. That is, the contents described in the first and second embodiments can be applied to the case where the communication line is switched from the communication line Pb1 as the active path to the communication line Pb2 as the backup path. In this case, the operation performed by the first pre-equalized optical transceiver 10 described in the first and second embodiments is performed by the second pre-equalized optical transceiver 20 and the second described in the first and second embodiments. The operation performed by the pre-equalized optical transceiver 20 is performed by the first pre-equalized optical transceiver 10. Thus, even when the main signal from the client is transmitted from the second pre-equalized optical transceiver 20 (transmission side apparatus) to the first pre-equalized optical transceiver 10 (reception side apparatus), the implementation is performed. The effects described in the first and second embodiments can be obtained.

Modified example.
FIG. 9 is a block diagram illustrating a configuration of the control unit 30 of the pre-equalized optical transceiver in the optical communication system according to the modification. The control unit 30 can be applied to the first control unit 17 of the first pre-equalized optical transceiver 10 in the optical communication system 1 according to the first embodiment. Similarly, the control unit 30 can be applied to the second control unit 27 of the second pre-equalized optical transceiver 20 in the optical communication system 1 according to the first embodiment.

  The control unit 30 includes a processor 30a such as a CPU (Central Processing Unit), a ROM (Read Only Memory) 30b, and a RAM (Random Access Memory) 30c. The ROM 30b stores a program for controlling components in the pre-equalized optical transceiver. The RAM 30c is used as a storage area for loading a program or the like stored in the ROM 30b. The processor 30a implements the function of the control unit 30 by, for example, loading a program into the RAM 30c and executing the program. For example, the functions of the first automatic dispersion compensation function unit 11, the first BER information acquisition function unit 12, and the first FEC function unit 13 described in the first embodiment are stored in the ROM 30b by the processor 30a. This is realized by executing the program. Similarly, when the control unit 30 is applied to the second control unit 27 of the second pre-equalized optical transceiver 20, the second automatic dispersion compensation function unit 21 described in the first embodiment, the second The functions of the BER information acquisition function unit 22 and the second FEC function unit 23 are realized by the processor 30a executing a program stored in the ROM 30b.

  In each of the above-described embodiments (including modifications), the method for adjusting the BER of the main signal has been described as an example of the method for adjusting the dispersion compensation value, which is one of the transmission conditions of the main signal. The method is not limited to adjusting the dispersion compensation value. For example, the optical output power from the first pre-equalized optical transceiver 10 and the second pre-equalized optical transceiver 20, the PMD (for example, the second pre-equalized optical transceiver 20) (Polarization mode dispersion) compensation amount, center wavelength, transmission optical spectrum width, modulator input signal timing, modulation amplitude, and at least one transmission condition of nonlinear compensation for compensating for waveform deterioration due to nonlinear effects in the transmission path The BER of the main signal may be adjusted by adjusting. That is, even when searching for the optimum condition so that the BER is minimized by adjusting at least one of these transmission conditions, the above-described embodiments (including modifications) are applied. Can do.

  The features in the embodiments described above and the features in the modified examples can be combined as appropriate.

  DESCRIPTION OF SYMBOLS 1 Optical communication system, 10 1st pre-equalization optical transmitter / receiver (1st optical communication device), 11 1st automatic dispersion compensation function part, 12 1st BER information acquisition function part, 13 1st FEC function 14, first optical transmission / reception function unit (first interface unit), 15 first transmission side optical coupler, 16 first reception side optical switch, 17 first control unit, 20 second pre-equalization Optical transceiver (second optical communication device), 21 second automatic dispersion compensation function unit, 22 second BER information acquisition function unit, 23 second FEC function unit, 24 second optical transmission / reception function unit (first 2 interface section), 25 second transmission side optical coupler, 26 second reception side optical switch, 27 second control section.

Claims (10)

An optical communication system capable of switching a communication line between an active line and a standby line,
A first optical communication device;
A second optical communication device that communicates with the first optical communication device via the communication line;
The first optical communication device is:
A first interface unit for transmitting an optical signal including a redundant code for detecting a code error;
A first control unit that adjusts a chromatic dispersion compensation value of the optical signal transmitted from the first optical communication device;
The second optical communication device is:
A second interface unit for receiving the optical signal transmitted from the first optical communication device;
A second control unit for detecting a code error rate of the optical signal transmitted from the first optical communication device,
When the communication line is switched from the active line to the protection line, the first control unit increases the ratio of the redundant code in the optical signal,
The second optical communication device transmits information based on the code error rate of the optical signal in which the ratio of the redundant code is increased to the first optical communication device,
The first control unit adjusts a chromatic dispersion compensation value of the optical signal based on the information received from the second optical communication device.   The first control unit adjusts a code error rate of the optical signal transmitted from the first optical communication device by adjusting a chromatic dispersion compensation value for the optical signal. An optical communication system according to claim 1.   The first controller is configured to obtain two chromatic dispersion compensation values for obtaining an optimum chromatic dispersion compensation value set in the first optical communication device based on the information received from the second optical communication device. The optical communication system according to claim 1, wherein the optical communication system is acquired.   4. The optical communication system according to claim 3, wherein the information includes information indicating whether or not a frame synchronization loss state based on the code error rate.   The first control unit sets a median value of the two chromatic dispersion compensation values as the optimum chromatic dispersion compensation value, thereby chromatic dispersion compensation of the optical signal transmitted from the first optical communication device. The optical communication system according to claim 3 or 4, wherein the value is adjusted.   The first control unit adjusts a chromatic dispersion compensation value of the optical signal transmitted from the first optical communication device by setting the optimum chromatic dispersion compensation value, and then performs the redundancy in the optical signal. 6. The optical communication system according to claim 5, wherein the ratio of the code is returned to the ratio before the change.   The first controller, after obtaining the information from the second optical communication device, gradually decreases the redundant code ratio in the optical signal and adjusts the median value of the two chromatic dispersion compensation values. 5. The optical communication system according to claim 3, wherein a chromatic dispersion compensation value of the optical signal is adjusted.   The first control unit sets, as the optimum chromatic dispersion compensation value, a chromatic dispersion compensation value that minimizes a code error rate of the optical signal based on the information received from the second optical communication device. The optical communication system according to claim 7, wherein a code error rate of the optical signal transmitted from the first optical communication device is set. The communication line can be switched between the active line and the standby line, and is an optical communication device that communicates with another optical communication device via the communication line,
An interface unit for transmitting an optical signal including a redundant code for detecting a code error;
A controller for adjusting a chromatic dispersion compensation value of the optical signal,
When the communication line is switched from the active line to the protection line, the control unit increases the ratio of the redundant code in the optical signal,
The said control part adjusts the chromatic dispersion compensation value of the said optical signal based on the information received from the said other optical communication device. The optical communication device characterized by the above-mentioned. A communication line switching method in an optical communication system in which communication is performed using an optical signal including a redundant code for detecting a code error and the communication line can be switched between a working line and a protection line. ,
Increasing the ratio of the redundant code in the optical signal when the communication line is switched from the active line to the standby line;
Obtaining information based on the code error rate of the optical signal in which the ratio of the redundant code is increased;
Adjusting the chromatic dispersion compensation value of the optical signal based on the information. A communication line switching method comprising:

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