NETWORK CONTROL APPARATUS, NETWORK CONTROL METHOD, AND STORAGE MEDIUM

A network control apparatus includes a memory that stores route information indicating a route of a path established in a network; and a processor coupled to the memory and configured to determine a target node of which signal output power is to be adjusted among a plurality of nodes on the route included in the route information, based on a signal quality between the plurality of nodes on the route; and instructs the determined target node to adjust the signal output power.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2017-74932, filed on Apr. 5, 2017, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a network control apparatus, a network control method, and a storage medium.

BACKGROUND

Regarding optical networks, long-distance and large-capacity optical transmission has been developed by the practical use of wavelength division multiplexing (WDM). In addition, optical network topologies have been expanded from linear configurations in which nodes are connected to each other in a point-to-point manner to ring configurations in which nodes are connected to each other in loop forms and mesh configurations in which nodes are connected to each other in mesh forms. As related art, Japanese Laid-open Patent Publication No. 2016-072834, Japanese Laid-open Patent Publication No. 2010-200059, and the like have been disclosed.

In optical paths established between nodes of an optical network, various transmission patterns (differences between transmission distances, types of signal modulation, and the like) of the optical paths exist. In the design of the optical network, optical output power is set for each of channels in such a manner that optical signal-to-noise ratios (OSNRs) are equal to each other in all the optical paths established between the nodes regardless of the channels in order to support these transmission patterns.

In the case where the optical output power is set in such a manner that the OSNRs are equal to each other, an optical path that does not satisfy a desirable OSNR exists. Thus, the desirable OSNR may be satisfied in this optical path by installing a regenerator in a node installed on the optical path.

In the design of this optical network, the number of nodes in which regenerators are to be installed may increase due to the expansion of the topology of the optical network. Due to an increase in the number of regenerators to be installed, the cost (network cost) of building the optical network increases. Under such circumstances, it is desirable to suppress the network cost.

SUMMARY

According to an aspect of the invention, a network control apparatus includes a memory that stores route information indicating a route of a path established in a network; and a processor coupled to the memory and configured to determine a target node of which signal output power is to be adjusted among a plurality of nodes on the route included in the route information, based on a signal quality between the plurality of nodes on the route; and instructs the determined target node to adjust the signal output power.

DESCRIPTION OF EMBODIMENTS

Embodiments are described with reference to the accompanying drawings.

First Embodiment

A first embodiment is described below.FIG. 1is a diagram illustrating an example of a configuration of a network control apparatus. A network control apparatus1includes a storage section1aand a controller1b. The storage section1astores routes of paths established in a network2.

The controller1bdetermines, based on a signal quality between nodes on a route, a target node that is among the nodes on the route and of which signal output power is to be adjusted. Then, the controller1binstructs the target node to adjust the signal output power.

The network2includes nodes N1, . . . , and N4connected to each other in a linear manner. The network control apparatus1is connected to one or more of the nodes N1, . . . , and N4. Upon receiving the adjustment instruction notified by the network control apparatus1, a node connected to the network control apparatus1transmits the adjustment instruction to the target node.

In the network2, a path P1ais established between the node N1and the node N4and extends from the node N1to the node N4, and a path P1bis established between the node N1and the node N3and extends from the node N1to the node N3. Route information of the paths is stored in the storage section1a.

In S1, the controller1bcalculates a subtracted value (hereinafter referred to as margin) obtained by subtracting a signal-to-noise ratio limit of the node N4from a signal-to-noise ratio of the node N4on the path P1aestablished in the network2. The controller1bcalculates a margin by subtracting a signal-to-noise ratio limit of the node N3from a signal-to-noise ratio of the node N3on the path P1aestablished in the network2.

Then, the controller1bextracts a path having a negative margin. This example assumes that the path P1ahas a negative margin. Specifically, this example assumes that the signal-to-noise ratio of the terminal node N4of the path P1ais lower than the signal-to-noise ratio limit of the node N4and that a signal level of the path P1ais insufficient.

The example assumes that the path P1bhas a positive margin (the signal-to-noise ratio of the terminal node N3of the path P1bis higher than the signal-to-noise ratio limit of the node N3).

In S2, the controller1bcalculates signal qualities (for example, signal-to-noise ratios) between the nodes of the path P1a. Specifically, the controller1bcalculates a signal quality IND1between the nodes N1and N2, a signal quality IND2between the nodes N2and N3, and a signal quality IND3between the nodes N3and N4.

The controller1bgives priorities to sections between the pairs of adjacent nodes in ascending order of signal quality value (or in descending order of the degree of reduction in signal quality). If the signal qualities have relationships of IND1<IND2<IND3, a priority given to a section between the nodes N1and N2is set to the highest priority, a priority given to a section between the nodes N2and N3is set to the next highest priority, and a priority given to a section between the nodes N3and N4is set to the lowest priority.

In S3, the controller1bincreases and adjusts signal output power in order from the highest priority. In this example, the controller1bselects the section that is located between nodes N1and N2and to which the highest priority has been given. Then, the controller1binstructs the start node N1among the nodes N1and N2to increase the output power of the signal to be transmitted in the path P1a.

In this case, when the margin of the path P1abecomes positive due to the increase in the signal output power of the node N1, the controller1bterminates the adjustment of the signal output power. Specifically, when the signal-to-noise ratio of the terminal node N4of the path P1aexceeds the signal-to-noise ratio limit of the node N4, the controller1bterminates the adjustment of the signal output power.

On the other hand, if the controller1bincreases the signal output power of the node N1to an output upper limit, and the margin of the path P1adoes not become positive, the signal output power of the node N1is maintained at the output upper limit.

Then, the controller1bselects the section that is located between the nodes N2and N3and to which the second highest priority has been given. Then, the controller1binstructs the start node N2among the nodes N2and N3to increase the output power of the signal to be transmitted in the path P1a. In this manner, the controller1bsequentially adjusts the signal output power until the margin of the path1abecomes positive.

In S4, when the controller1bterminates the adjustment of the signal output power for the path P1a, the controller1bdetects a path having a positive margin and extending between nodes of the path P1a. Then, the controller1breduces and adjusts the signal output power in such a manner that a margin of the detected path does not become negative and that the signal output power does not become lower than a lower limit. In this case, the controller1breduces and adjusts the signal output power for a path including the section that is located between the nodes and to which the highest priority has been given in S3.

In this example, the section to which the highest priority has been given is located between the nodes N1and N2, and the path P1bextends through the section located between the nodes N1and N2. The path P1bhas the positive margin. Thus, the controller1binstructs the node N1to reduce and adjust the output power of the signal to be transmitted in the path P1b.

A node instructed by the network control apparatus1to adjust signal output power adjusts the signal output power by controlling an amplifier included in the node and configured to amplify a signal level, a variable attenuator (VAT) included in the node and configured to attenuate the signal level in a variable manner, or the like.

In this manner, the network control apparatus1determines, based on signal qualities between the nodes on the routes of the paths, a node of which signal output power is to be adjusted in the design of the network. Then, the network control apparatus1instructs the determined node to adjust the signal output power. Thus, the network cost may be suppressed.

The network control apparatus1reduces and adjusts the signal output power for a path having a positive margin in such a manner that the margin does not become negative and that the signal output power does not become lower than the lower limit. Thus, the signal output power is not set to a value equal to or higher than a predetermined value, and resources may be efficiently used. In addition, it may be possible to suppress the degradation, caused by excessively high signal output power, of transmission characteristics.

Second Embodiment

Next, a second embodiment is described. A network control apparatus according to the second embodiment determines, based on OSNRs of optical paths extending through sections between nodes in an optical network in which WDM optical transmission is executed, nodes of which optical output power is adjusted. The network control apparatus according to the second embodiment notifies the determined nodes of the adjustment of the optical output power. First, an example of the configuration of the optical network in which the WDM optical transmission is executed and examples of the expansion of the topology of the optical network are described with reference toFIGS. 2 and 3.

FIG. 2is a diagram illustrating the example of the configuration of the optical network. An optical network20is a multi-relay network in which WDM transmission is executed. The optical network20includes nodes n1and n2and inline amplifiers (ILAs) a1and a2.

At relay points between the nodes n1and n2, the inline amplifiers a1and a2that are liner optical relay devices are installed. The nodes n1and n2and the inline amplifiers a1and a2are connected to each other via an optical fiber L0in a linear manner (and the number of inline amplifiers is arbitrary). An optical receiver31aand an optical transmitter32aare connected to the node n1. An optical receiver31band an optical transmitter32bare connected to the node n2.

In the nodes n1and n2, reconfigurable optical add and drop multiplexing (ROADM) control is executed to add light with an arbitrary wavelength and drop light with an arbitrary wavelength.

Specifically, upon receiving a wavelength channel transmitted by the optical transmitter32a,the node n1adds the wavelength channel to WDM signal light having passed through the optical fiber L0and multiplexes and outputs the WDM signal light having the wavelength channel to the node n2located at the next stage.

The node n1receives the WDM signal light having passed through the optical fiber L0, separates the wavelength of the WDM signal light to drop a predetermined wavelength channel, and transmits the WDM signal light to the optical receiver31a.In the node n2, the same ROADM control is executed.

FIG. 3is a diagram illustrating the examples of the expansion of the topology of the optical network. An optical network2aincludes the nodes n1and n2. The optical network2ahas a linear configuration in which the nodes n1and n2are connected to each other in a point-to-point manner.

An optical network2bincludes nodes n1, . . . , and n4and has a ring configuration in which the nodes n1. . . , and n4are connected to each other in a loop form.

An optical network2cincludes node n1, . . . , and n8, while the nodes n3and n8have a hub line concentration function and connect two ring networks to each other. The optical network2chas a hub and mesh configuration in which the nodes n1. . . , and n8are connected to each other in a mesh form.

Next, optical paths established between nodes in an optical network are described.FIG. 4is a diagram illustrating an example of the establishment of the optical paths in the optical network. An optical network2dincludes nodes n1, . . . , and n7and inline amplifiers a1, . . . , and a9. In the optical network2d,11 optical paths p1, . . . , and p11are established.

The optical path p1is established between the nodes n1and n2. The optical path p2is established between the nodes n2and n3. The optical path p3is established between the nodes n3and n4. The optical path p4is established between the nodes n4and n5. The optical path p5is established between the nodes n5and n6. The optical path p6is established between the nodes n1and n6.

The optical path p7is established between the nodes n1and n7. The optical path p8is established between the nodes n2and n7. The optical path p9is established between the nodes n4and n7. The optical path p10is established between the nodes n2and n4. The optical path p11is established between the nodes n5and n7.

Next, a state in which a regenerator is installed in a node included in an optical network is described with reference toFIGS. 5 and 6. The regenerator (REG) converts received signal light to an electric signal, executes processes including waveform shaping and amplification on the electric signal, reconverts the electric signal after the processes to signal light, and outputs the signal light. In the following description, an illustration of optical transmitters connected to the nodes and optical receivers connected to the nodes is omitted.

FIG. 5is a diagram describing an example of the state in which the regenerator is installed. In each of graphs g1and g2, an abscissa indicates a wavelength channel ch, and an ordinate indicates an OSNR. An optical network21aincludes nodes n1, n2, and n3and inline amplifiers a1, . . . , and a6and executes WDM transmission that enables the wavelength multiplexing of 80 waves.

The inline amplifiers a1, a2, and a3are installed between the nodes n1and n2. The inline amplifiers a4, a5, and a6are installed between the nodes n2and n3. The nodes n1, n2, and n3and the inline amplifiers a4, a5, and a6are connected to the optical fiber L0in a linear manner.

In the optical path P11established between the nodes n1and n2, wavelength channels ch1to ch40are used for short-distance transmission. In the optical path P12established between the nodes n1and n3, wavelength channels ch41to ch80are used for long-distance transmission.

It is assumed that optical output power of all the nodes is set in such a manner that OSNRs of the optical paths included in the optical network21aare equal to each other. In this case, it is likely that, in the optical path P11in which the wavelength channels ch1to ch40are used for short-distance transmission, OSNRs become higher than an OSNR limit of an optical receiving section included in the node n2(or the optical path P11has a positive margin with respect to the OSNR limit), as indicated in the graph g1.

There is, however, a possibility that, in the optical path P12in which the wavelength channels ch41to ch80are used for long-distance transmission, the OSNRs become lower than an OSNR limit of an optical receiving section included in the node n3(or the optical path P12has a negative margin with respect to the OSNR limit), as indicated in the graph g1.

This is due to the fact that, in the case where the optical output power is set in such a manner that the OSNRs are equal to each other and the wavelength channels ch41to ch80are used, optical output power for long-distance transmission from the node n1through the node n2to the node n3is insufficient.

In order to normally transmit the wavelength channels ch41to ch80, a regenerator4may be installed in the node n2and suppress reductions in the OSNRs by executing regenerative relay on the wavelength channels ch41to ch80, for example.

FIG. 6is a diagram describing an example of the state in which the regenerator is installed. The configuration of an optical network21bis the same as that of the optical network21aillustrated inFIG. 5. In the optical network21b,WDM transmission is executed to transmit the wavelength channels ch1to ch80.

In the optical network21b,an optical path P13is established between the nodes n1and n2. In the optical path P13, quadrature phase shift keying (QPSK) of 100 Gb/s throughput is used for the modulation of the wavelength channels ch1to ch40for short wavelengths.

16 quadrature amplitude modulation (QAM) of 200 Gb/s throughput is used for the modulation of the wavelength channels ch41to ch80for long wavelengths.

It is assumed that optical output power of all the nodes established in the optical network21bis set in such a manner that OSNRs of the optical path established in the optical network21bare equal to each other for all the modulation. In this case, since the wavelength channels ch1to ch40for QPSK is used for short-distance transmission, it is likely that the OSNRs are higher than the OSNR limit of the optical receiving section included in the node n2for QPSK, as indicated in the graph g3.

However, even if the wavelength channels ch41to ch80for 16 QAM are used for short-distance transmission, the OSNRs may become lower than the OSNR limit of the optical receiving section included in the node n3for 16 QAM.

While the amount of information to be transmitted per unit of time in 16 QAM is larger than that in QPSK, an error rate of 16 QAM is larger than that of QPSK. Thus, in order to obtain the same error rate as that of QPSK, the OSNRs of the receiving node are to be increased by setting output levels in 16 QAM to be higher than those in QPSK. Thus, the OSNR limit in 16 QAM is higher than the OSNR limit in QPSK.

Thus, in the case where the optical output power is set in such a manner that the OSNRs are equal to each other and the wavelength channels ch41to ch80are used, the OSNRs may become lower than the OSNR limit of the optical receiving section included in the node n2for 16 QAM.

Thus, in order to normally transmit the wavelength channels ch41to ch80, the regenerator4may be installed in the node n2in the same manner as the case illustrated inFIG. 5and suppress reductions in the OSNRs by executing the regenerative relay on the wavelength channels ch41to ch80. This suppresses reductions in the OSNRs.

In the optical networks21aand21b,the optical paths of which transmission distances are different from each other exist or different types (100-Gb/s QPSK, 200-Gb/s 16 QAM, 300-Gb/s 64 QAM, and the like) of the signal modulation are used. Thus, in the case where the optical output power is set in such a manner that the OSNRs are equal to each other, an optical path that does not satisfy an OSNR limit may exist.

However, if the regenerator is installed in the node located on the aforementioned optical path to satisfy the OSNR limit, the number of nodes in which regenerators are to be installed may increase due to the expansion of an optical network topology or the like, and the network cost may increase.

Under such circumstances, according to the network control apparatus according to the second embodiment, a regenerator is not installed and the network cost is suppressed by the adjustment of optical output power for a wavelength channel that does not satisfy an OSNR limit. The network control apparatus according to the second embodiment adjusts the optical output power in such a manner that, even if OSNR limits are satisfied, output levels are not increased to a predetermined level or higher. The configuration and operations of the network control apparatus according to the second embodiment are described below in detail.

The configuration of a network control system in which the network control apparatus is connected to an optical network is described below.FIG. 7is a diagram illustrating an example of the configuration of the network control system. A network control system1-1includes an optical network21and a network control apparatus10.

The optical network21includes nodes n1, n2, and n3and inline amplifiers a1, . . . , and a6. The inline amplifiers a1, a2, and a3are installed between the nodes n1and n2. The inline amplifiers a4, a5, and a6are installed between the nodes n2and n3. The nodes n1, n2, and n3and the inline amplifiers a1, . . . , and a6are connected to each other via the optical fiber L0in a linear manner.

The network control apparatus10is connected to one or multiple nodes within the optical network21. The network control apparatus10transmits an instruction to adjust optical output power to a predetermined node within the optical network21. Then, the predetermined node adjusts the optical output power based on the received instruction to adjust the optical output power.

FIG. 7illustrates the example in which the network control apparatus10is connected to the optical network21having a linear configuration. The network control apparatus10, however, may be connected to an optical network that has a ring configuration, a mesh configuration, or the like or has one or more of various topologies.

Next, a hardware configuration of the network control apparatus10is described.FIG. 8is a diagram illustrating an example of the hardware configuration of the network control apparatus. The entire network control apparatus10is controlled by a processor100. The processor100functions as a controller of the network control apparatus10.

The processor100is connected to a memory101and multiple peripheral devices via a bus103. The processor100may be a multiprocessor. The processor100is, for example, a central processing unit (CPU), a micro processing unit (MPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), or a programmable logic device (PLD). Alternatively, the processor100may be a combination of two or more of a CPU, an MPU, a DSP, an ASIC, and a PLD.

The memory101is used as a main storage device of the network control apparatus10. In the memory101, a portion of a program of an operating system (OS) to be executed by the processor100and an application program is temporarily stored, or the program of the OS and the application program are temporarily stored. In addition, in the memory101, various types of data to be used for processes to be executed by the processor100are stored.

The memory101is used also as an auxiliary storage device of the network control apparatus10. In the memory101, the program of the OS, the application program, and the various types of data are stored. In the case where the memory101is used as the auxiliary storage device, the memory101may include a magnetic recording medium that is a semiconductor storage device such as a flash memory or an SSD, an HDD, or the like.

The peripheral devices connected to the bus103are an input and output interface102and a network interface104. The input and output interface102is connected to a monitor (for example, a light emitting diode (LED), a liquid crystal display (LCD), or the like) that functions as a display device that displays the state of the storage control apparatus10in accordance with a command from the processor100.

In addition, the input and output interface102may be connected to an information input device such as a keyboard or a mouse and transmits a signal transmitted by the information input device to the processor100.

Furthermore, the input and output interface102functions as a communication interface that connects the peripheral devices to each other. For example, the input and output interface102may be connected to an optical driving device that uses laser light or the like to read data recorded in an optical disc. The optical disc is a portable recording medium in which the data that is read by light reflection is recorded. Examples of the optical disc are a digital versatile disc, (DVD), a DVD random access memory (DVD-RAM), a compact disc read only memory (CD-ROM), a CD-Recordable (CD-R), and a CD-Rewritable (CD-RW).

The input and output interface102may be connected to a memory device or a memory reader or writer. The memory device is a recording medium that has a communication function of executing communication with the input and output interface102. The memory reader or writer is a device that writes a message to a memory card or reads a message from the memory card. The memory card is a card-type recording medium.

The network interface104may be a network interface card (NIC), a radio local area network (LAN), or the like, for example. A signal, data, and the like that are received by the network interface104are output to the processor100.

Processing functions of the network control apparatus10are achieved by the aforementioned hardware configuration. For example, the network control apparatus10controls and adjusts optical output power by causing the processor100to execute predetermined programs.

The network control apparatus10executes a program recorded in a computer-readable recording medium, thereby achieving the processing functions according to the second embodiment, for example. The program in which details of processing to be executed by the network control apparatus10are described may be recorded in various recording media.

For example, the program to be executed by the network control apparatus10may be stored in the auxiliary storage device. The processor100loads a portion of the program stored in the auxiliary storage device or the entire program into the main storage device and executes the loaded program. The program may be recorded in a portable recording medium such as an optical disc, a memory device, or a memory card. For example, the program stored in the portable recording medium may be installed in the auxiliary storage device and executed under control by the processor100. The processor100may read the program directly from the portable recording medium and execute the read program.

Next, functional blocks of the network control apparatus10are described.FIG. 9is a diagram illustrating an example of the functional blocks of the network control apparatus. The network control apparatus10includes a network controller11and a design information database12.

The network controller11includes a margin processing section11a,an optical output power increase adjuster11b,and an optical output power reduction adjuster11c.The network controller11achieves the functions of the controller1billustrated inFIG. 1, while the design information database12achieves the functions of the storage section1aillustrated inFIG. 1.

The margin processing section11acalculates margins of optical paths included in an optical network and gives priorities to sections between nodes of the optical network based on values of the margins. The optical output power11binstructs a node, which is to be adjusted, to increase and adjust optical output power for a path having a negative margin.

The optical output power reduction adjuster11cinstructs a node, which is to be adjusted, to reduce and adjust optical output power for a path having a positive margin and extending through a portion of the path having the negative margin. The optical output power is adjusted or controlled upon the design of the optical network or upon a change in the topology of the optical network. Detailed operations of the network controller11are described later with reference toFIG. 12and later.

In the design information database12, design information (for example, information to be used to calculate and manage signal qualities of the optical paths) to be used for the design of the optical network is stored. Parameters of the design information include, for example, losses in the transmission paths, the distances of the transmission paths, the types of the transmission paths, input power for the transmission paths, noise figures (NFs) of optical amplifiers, gains of the optical amplifiers, gain tilts of the optical amplifiers, and nonlinear penalties.

In addition, the parameters of the design information include polarization mode dispersion (PMD) and polarization dependent loss (PDL) penalties, OSNR tolerance of optical receivers, and the like. These parameters may be manually calculated or may be monitor values obtained by monitoring the optical network. Various types of table information described later are stored in the design information database12.

Next, a configuration of each of nodes forming the optical network is described.FIG. 10is a diagram illustrating an example of a configuration of a node. A node50includes an optical pre-amplifier51, an optical post-amplifier52, route selectors53aand53b,a dropping section54, and an adding section55(or a configuration per path is illustrated). The node50is connected to an optical receiver31and an optical transmitter32.

The optical pre-amplifier51receives WDM signal light having passed through the optical fiber L0and amplifies the WDM signal light. The route selector53aincludes a wavelength switch sa-1, while the route selector53bincludes a wavelength switch sb-1. As the wavelength switches, wavelength selective switches (WSSs) are used, for example.

The route selector53aseparates the wavelength of the received WDM signal light and selects a wavelength channel. The route selector53breceives the wavelength channel output from the route selector53aand executes wavelength multiplexing on the wavelength channel. The optical post-amplifier52amplifies light output from the route selector53band outputs the amplified light from the optical fiber L0.

The dropping section54receives the wavelength channel output from the route selector53aand transmits a predetermined wavelength channel to the optical receiver31. The adding section55multiplexes wavelength channels transmitted by the optical transmitter32and transmits the multiplexed wavelength channels to the route selector53b.

Although not illustrated, a variable optical attenuator (VOA) is installed between the route selector53aand the route selector53bfor each of the wavelength channels, for example. Upon receiving an instruction to adjust optical output power from the network control apparatus10, the node50variably controls output of the VOA included in the node50, thereby adjusting the optical output power for each of the wavelength channels. Alternatively, the node50may use VOA functions included in the WSSs to variably control the output of the VOA included in the node50and adjust the optical output power for each of the wavelength channels.

FIG. 11is a diagram illustrating an example of the adjustment of the optical output power.FIG. 11illustrates the example in which the optical output power of the nodes n1and n2included in the optical network21is adjusted by the network control apparatus10for each of the wavelength channels.

In each of graphs g11, . . . , and g14, an abscissa indicates a wavelength channel. In each of the graphs g11and g13, an ordinate indicates optical output power. In each of the graphs g12and g14, an ordinate indicates an OSNR.

The node n1transmits WDM signal light including the wavelength channels ch1to ch80to the node n2. Upon receiving the WDM signal light transmitted by the node n1, the node n2drops the wavelength channels ch1to ch40to a tributary.

New wavelength channels ch1to ch40are added to the node n2from the tributary. The node n2multiplexes the added new wavelength channels ch1to ch40and the wavelength channels ch41to ch80transmitted by the node n1to transmit the WDM signal light including the wavelength channels ch1to ch80to the node n3. Upon receiving the WDM signal light transmitted by the node n2, the node n3drops the wavelength channels ch1to ch80to the tributary.

In this case, the wavelength channels ch1to ch40are transmitted between the nodes n1and n2or between the nodes n2and n3and are wavelength channels for short-distance transmission. The wavelength channels ch41to ch80are transmitted between the n1and n3via the node n2and are wavelength channels for long-distance transmission.

In all the nodes forming the optical network, a standard value of optical output power for transmission of WDM signal light including all wavelengths is set. In the example illustrated inFIG. 11, in the nodes n1and n2that transmit WDM signal light including all the wavelengths of the wavelength channels ch1to ch80, a standard value r1of optical output power is set, as indicated in the graphs g11and g13.

The standard value r1is an optical output power value, set in advance upon the design of the optical network, of the WDM signal light including all the wavelength channels and to be wavelength-multiplexed in the optical network.

When the WDM signal light is to be transmitted by the node n1, the node n1sets optical output power of the wavelength channels ch1to ch40in such a manner that OSNRs are higher than an OSNR limit of the optical receiving section included in the node n2(refer to the graph g12).

In this case, if the wavelength channels ch1to ch40are set and transmitted in such a manner that the optical output power is lower than the standard value r1, and the OSNRs are higher than the OSNR limit, the node n1sets the optical output power of the wavelength channels ch1to ch40to be lower than the standard value r1.

Thus, optical amplifier resources for the wavelength channels ch1to ch40of which the optical output power is lower by a negative margin than the standard value r1may be assigned to the transmission of the wavelength channels ch41to ch80, and the efficiency of assigning the resources may be improved.

When WDM signal light is transmitted at a predetermined output level or higher regardless of short-distance transmission, nonlinear waveform distortion may noticeably occur and result in an increase in the degradation of the quality of the transmission due to a nonlinear effect (cross phase modulation (XPM) or the like) of the optical fiber transmission. Thus, an effect of suppressing the degradation of the quality of transmission may be obtained by transmitting the wavelength channels ch1to ch40in such a manner that the optical output power is lower than the standard value r1.

Since the wavelength channels ch41to ch80are used for long-distance transmission, the node n1sets the optical output power of the wavelength channels ch41to ch80to be higher than the standard value r1.

Thus, the node n1sets the optical output power of the wavelength channels ch1to ch40to be lower than the standard value r1, sets the optical output power of the wavelength channels ch41to ch80to be higher than the standard value r1, and transmits the WDM signal light including the wavelength channels ch1to ch80, as indicated in the graph g11.

The optical output power of the wavelength channels ch1to ch40and the optical output power of the wavelength channels ch41to ch80are set by the node n1based on an instruction, received from the network control apparatus10, to adjust the optical output power.

The node n2adjusts the optical output power in the same manner as the node n1for the transmission of the WDM signal light by the node n2. Specifically, the node n2sets the optical output power of the wavelength channels ch1to ch40added from the tributary to be lower than the standard value r1and sets the optical output power of the wavelength channels ch41to ch80to be higher than the standard value r1, as indicated in the graph g13. Then, the node n2transmits the WDM signal light including the wavelength channels ch1to ch80.

The optical output power of the wavelength channels ch1to ch40and the optical output power of the wavelength channels ch41to ch80are set by the node n2based on an instruction, received from the network control apparatus10, to adjust the optical output power.

As described above, since the nodes n1and n2set the optical output power of the wavelength channels, the OSNRs of all the wavelength channels ch1to ch80that have reached the node3are higher than the OSNR limit of the optical receiving section included in the node3(refer to the graph g14). Thus, the WDM transmission of all the wavelength channels ch1to ch80is executed without a regenerator.

Since the optical transmission is executed in such a manner that the OSNR limit is satisfied due to the adjustment of the optical output power by the network control apparatus10, a regenerator is not installed in the nodes and the network cost may be suppressed.

Next, operations of the network control apparatus10are described with reference toFIGS. 12 and 13.FIGS. 12 and 13are flowcharts of an example of the operations of the network control apparatus. S10to S13are operations of the margin processing section11a.S14to S19are operations of the optical output power increase adjuster11b.S20to S25are operations of the optical output power reduction adjuster11c.

In all the nodes forming the optical network, the standard value of the optical output power that is used for the transmission of WDM signal light including all the wavelengths is set. Optical paths are established between predetermined nodes based on the standard value (in a state that is hereinafter referred to as initially designed state). InFIGS. 12 and 13, M_Path_xx indicates a path having a negative margin, and P_Path_xx indicates a path having a positive margin.

In S10, the margin processing section11acalculates margins of all optical paths established in the optical network in the initially designed state. Specifically, the margin processing section11acalculates, as the margins, differences between OSNRs of terminal nodes of the optical paths and OSNR limits of the terminal nodes.

In S11, the margin processing section11adetermines whether or not one or more negative margins (margins when OSNRs of one or more optical paths are lower than an OSNR limit) exist among the margins of all the optical paths. If the one or more negative margins do not exist among the margins of all the optical paths, a process is terminated. If the one or more negative margins exist among the margins of all the optical paths, the process proceeds to S12.

In S12, the margin processing section11aextracts the one or more optical paths having the one or more negative margins.

In S13, the margin processing section11agives ranks to the optical paths having the negative margins in descending order of absolute negative margin value and lists the optical paths having the negative margins.

In S14, the optical output power increase adjuster11btreats the optical paths listed in S13as optical paths (M_Path_xx) for which optical output power is to be increased. Then, the optical output power increase adjuster11bcalculates OSNRs (OSNRn) of the optical paths and transmitting penalties (TPs) (TPn), calculates section indices (SCTN_INDn) by adding the OSNRs OSNRn to the TPs TPn, and holds the section indices SCTN_INDn. The section indices are used as indices for signal qualities.

In S15, the optical output power increase adjuster11bgives priorities to the calculated section indices SCTN_INDn in such a manner that, as the value of a calculated section index is smaller, a higher priority is given to the section index, and the optical output power increase adjuster11bgenerates a list of the section indices SCTN_INDn.

In S16, the optical output power increase adjuster11bselects a section index SCTN_INDn having the highest priority from among the section indices included in the list generated in S15and increases optical output power for an optical path (M_Path_xx) having the selected SCTN_INDn d section index. In this case, for example, the optical output power increase adjuster11bincreases the optical output power by a predetermined amount in a stepwise manner (refer toFIG. 21described later).

In S17, the optical output power increase adjuster11bdetermines whether or not the optical output power exceeds the output upper limit. If the optical output power exceeds the output upper limit, the process proceeds to S17a.If the optical output power does not exceed the output upper limit, the process proceeds to S18.

In S17a,the optical output power increase adjuster11bsets the optical output power for the optical path having the section index SCTN_INDn to the output upper limit. Then, the optical output power increase adjuster11bselects an optical path having a section index SCTN_IND(n+1) having the next highest priority, causes the process to return to S16, and increases and adjusts optical output power for the selected optical path.

In S18, the optical output power increase adjuster11bdetermines whether or not the margin of the optical path (M_Path_xx) is positive. If the margin of the optical path (M_Path_xx) is not positive, the process returns to S16. If the margin of the optical path (M_Path_xx) is positive, the process proceeds to S19.

In S19, the optical output power increase adjuster11bdetermines whether or not another optical path having a negative margin exists. If the optical hath having the negative margin exists, the process returns to S14. If the optical hath having the negative margin does not exist, the process proceeds to S20.

In S20, the optical output power reduction adjuster11cdetects an optical path having a positive margin (margin when an OSNR of the optical path is higher than an OSNR limit) and established between nodes through which the optical path (M_Path_xx) for which the optical output power has been increased extends.

In S21, the optical output power reduction adjuster11creduces the optical output power for the optical path (P_Path_xx). In this case, for example, the optical output power reduction adjuster11creduces the optical output power by a predetermined amount in a stepwise manner (refer toFIG. 22described later).

In S22, the optical output power reduction adjuster11cdetermines whether or not the margin of the optical path (P_Path_xx) is positive. If the margin of the optical path (P_Path_xx) is not positive, the process proceeds to S22a.If the margin of the optical path (P_Path_xx) is positive, the process proceeds to S23.

In S22a,the optical output power reduction adjuster11cdetects that the optical output power for the optical path (P_Path_xx) has been excessively reduced, and the optical output power reduction adjuster11cchanges the optical output power by restoring the optical output power to a value before the reduction in the optical output power by the predetermined amount until the margin becomes positive again. Then, the process proceeds to S25.

In S23, the optical output power reduction adjuster11cdetermines whether or not the optical output power is lower than the output lower limit. If the optical output power is lower than the output lower limit, the process proceeds to S24. If the optical output power is not lower than the output lower limit, the process returns to S21.

In S24, the optical output power reduction adjuster11csets the optical output power for the optical path (P_Path_xx) to the output lower limit.

In S25, the optical output power reduction adjuster11cdetermines whether or not another optical path (P_Path_xx) exists. If the other optical path (P_Path_xx) exists, the process returns to S21. If the other optical path (P_Path_xx) does not exist, the process is terminated.

Next, a specific example of the adjustment of the optical output power is described with reference toFIGS. 14 to 20.FIG. 14is a diagram illustrating an example of the configuration of an optical network. An optical network22includes nodes n1, . . . , and n13and inline amplifiers a1, . . . , and a22. In the optical network22,9optical paths P1to P9are established.

FIG. 15is a diagram illustrating an example of a route table. A route table T1includes an optical path number item and a nodes item indicating nodes on the optical paths. In this example, the nodes of the optical paths P1, . . . , and P9of the optical network22illustrated inFIG. 22are registered.

For example, as nodes of the optical path P1, the nodes n1, n2, n3, n4, n5, n6, and n7are registered. The route table T1is stored in the design information database12.

FIG. 16is a diagram illustrating an example of a margin management table. A margin management table T2includes an optical path number item, a margin (dB) item, and a symbol name item and is generated by the margin processing section11a.In the symbol name item, M_Path_xx indicates an optical path having a negative margin, and P_Path_xx indicates an optical path having a positive margin. The margin management table T2is stored in the design information database12.

FIG. 17is a diagram illustrating an example of a negative margin extraction table. A negative margin extraction table T3includes a ranking item, an optical path number item, a negative margin (dB) item, and a symbol name item.

The margin processing section11agenerates the negative margin extraction table T3by extracting optical paths having negative margins from the margin management table T2.

As indicated in the margin management table T2illustrated inFIG. 16, the optical paths P1and P8have negative margins. The negative margin of the optical path P1is −0.5 dB, while the negative margin of the optical path P8is −0.2 dB. The absolute value of the negative margin of the optical path P1is larger than the absolute value of the negative margin of the optical path P8.

Thus, the negative margin extraction table T3is generated in such a manner that the optical path P1is ranked higher than the optical path P8(or the optical output power for the optical path P1is adjusted earlier than the adjustment of the optical output power for the optical path P8), as illustrated inFIG. 17. The negative margin extraction table T3is stored in the design information database12.

FIG. 18is a diagram illustrating an example of sections of the optical network.FIG. 18illustrates the route of the optical path P1having the negative margin whose absolute value is the maximum among the optical paths included in the optical network22. The optical path P1includes the sections sec1, . . . , and sec6.

The section sec1exists between the nodes n1and n2. The section sec2exists between the nodes n2and n3. The section sec3exists between the nodes n3and n4. The section sec4exists between the nodes n4and n5. The section sec5exists between the nodes n5and n6. The section sec6exists between the nodes n6and n7.

FIG. 19is a diagram illustrating an example of a section index management table. A section index management table T4includes a section number item, a name item, an OSNR item, a TP item, an SCTN_IND item (indicating values of section indices), and a priority item and is generated by the optical output power increase adjuster11b.

For example, regarding the section between the nodes n1and n2, a section number is sec1, a name is SCTN_IND1, an OSNR is 24.1 (=23.7+0.4), a TP is 0.4, and a priority is 4 (that is the fourth smallest value among 6 section indices SCTN_IND and indicates that optical output power is the fourth to be increased and adjusted). The section index management table T4is stored in the design information database12.

The optical output power increase adjuster11bincreases and adjusts optical output power in order from the smallest value among the section indices SCTN_IND registered in the section index management table T4(or in order from the highest priority).

In this example, the section sec2has the highest priority, or the priority of the section sec2is 1. Thus, the optical output power increase adjuster11bincreases and adjusts optical output power of the start node n2of the section sec2and terminates the adjustment of the increase in the optical output power when the margin of the optical P1becomes positive in this adjustment.

If the optical output power reaches the output upper limit, and the margin does not become positive, the optical output power increase adjuster11bsets the optical output power of the node n2to the output upper limit and increases and adjusts the optical output power for the section sec3having the second highest priority. Specifically, since the start node of the section sec3is the node n3, the optical output power increase adjuster11bincreases and adjusts the optical output power of the node n3.

In this manner, the optical output power increase adjuster11bsequentially increases and adjusts optical output power based on the priorities until the margin becomes positive. In this example, when the adjustment of the increase in the optical output power of the optical path P1is completed, the optical output power for the optical path P8is increased and adjusted in the same manner as described above.

Next, the optical output power reduction adjuster11cdetects a path having a positive margin and including a section located between nodes and having the highest priority (and the smallest section index).

FIG. 20is a diagram illustrating an example of a reduction target path management table. In a reduction target path management table T5, optical paths for which optical output power is to be reduced and adjusted by the optical output power reduction adjuster11care registered. The reduction target path management table T5includes an optical path number item, a margin (dB) item, and a symbol name item.

The reduction target path management table T5is stored in the design information database12. Each of numbers indicated in the symbol name item is given in such a manner that, as a margin of an optical path having a symbol name with the number is smaller, the number is smaller. Thus, symbol names illustrated inFIG. 20are different from symbol names illustrated inFIG. 16.

A priority given to the section sec2of the optical path P1is the highest. Thus, paths that include the nodes of the section sec2and have positive margins are detected as the optical paths P2, P3, and P4and are registered in the reduction target path management table T5.

Then, the optical output power reduction adjuster11creduces and adjusts optical output power for the optical paths registered in the reduction target path management table T5. Specifically, the optical output power reduction adjuster11creduces and adjusts, for the start node n1of the optical path P2, optical output power of WDM signal light to be transmitted in the optical path P2in such a manner that the margin of the optical path P2is maintained at a positive level and that the optical output power is equal to or higher than the output lower limit.

Similarly, the optical output power reduction adjuster11creduces and adjusts, for the start node n2of the optical path P3, optical output power of WDM signal light to be transmitted in the optical path P3in such a manner that the margin of the optical path P3is maintained at a positive level and that the optical output power is equal to or higher than the output lower limit.

In addition, the optical output power reduction adjuster11creduces and adjusts, for the start node n2of the optical path P4, optical output power of WDM signal light to be transmitted in the optical path P4in such a manner that the margin of the optical path P4is maintained at a positive level and that the optical output power is equal to or higher than the output lower limit.

FIG. 21is a diagram illustrating an example of the amount of an increase in optical output power. InFIG. 21, an ordinate indicates optical output power (dBm/ch) and an abscissa indicates the number of times when the optical output power is increased. When the optical output power is to be increased and adjusted, the optical output power increase adjuster11bincreases the optical output power by a predetermined amount in a stepwise manner. For example, the optical output power increase adjuster11bincreases optical output power by levels of 0.5 dB in a stepwise manner.

FIG. 22is a diagram illustrating an example of the amount of a reduction in optical output power. InFIG. 22, an ordinate indicates optical output power (dBm/ch) and an abscissa indicates the number of times when the optical output power is reduced. When the optical output power is to be reduced and adjusted, the optical output power reduction adjuster11creduces the optical output power by a predetermined amount in a stepwise manner. For example, the optical output power increase adjuster11breduces optical output power by 0.5 dB in a stepwise manner.

The processing functions of the network control apparatuses1and10described in the first and second embodiments may be achieved by a computer. In this case, the program in which details of processing to be executed by the functions of the storage control apparatus1and in which the details of the processing to be executed by the functions of the storage control apparatus10are described is provided. When the computer executes the program, the aforementioned processing functions are achieved in the computer.

The program in which the details of the processing are described may be recorded in a computer-readable recording medium. Examples of the computer-readable recording medium are a magnetic storage device, an optical disc, a magneto optical recording medium, and a semiconductor memory. Examples of the magnetic storage device are a hard disk device (HDD), a flexible disk (FD), and a magnetic tape. Examples of the optical disc are a DVD, a DVD-RAM, a CD-ROM, and a CD-RW. An example of the magneto optical recording medium is a magneto optical (MO) disk.

In the case where the program is distributed, a portable recording medium in which the program is recorded and that is a DVD, a CD-ROM, or the like may be on sale. In addition, the program may be stored in a storage device of a server computer and transferred from the server computer to another computer via a network.

The computer that is configured to execute the program may store, in a storage device of the computer, the program recorded in the portable recording medium or transferred from the server computer. Then, the computer reads the program from the storage device of the computer and executes the processes in accordance with the program. The computer may read the program directly from the portable recording medium and execute the processes in accordance with the program.

Every time the program is transferred from the server computer connected to the computer via the network, the computer may sequentially execute the processes in accordance with the received program. In addition, a part or all of the aforementioned processing functions may be achieved by an electronic circuit such as a DSP, an ASIC, or a PLD.