Optical amplifier placement method, optical amplifier placement support device, and repeater device

Abstract

Provided is an optical amplifier deployment method including: an acquisition step for obtaining transmission route information indicating a configuration of a network in which an optical signal is transmitted via multiple relay nodes and a transmission route of the optical signal transmitted through the network; and a determination step for using the transmission route information to group multiple optical fibers passing through the same one of the relay nodes and determine whether optical amplification is necessary at each of the relay nodes for each of the groups of the optical fibers, thereby determining the deployment of optical amplifiers in the network.

Description

[Technical field]

[0001] The present invention relates to an optical amplifier placement method, an optical amplifier placement support device, and a repeater device. [Background technology]

[0002] In an optical transmission system, an optical signal transmitted from a transmitter is attenuated during propagation due to the transmission loss characteristics of the optical fiber. If the signal strength of the optical signal entering the receiver is lower than the minimum receiving sensitivity, the bit error rate (BER) increases due to the effect of thermal noise generated in the receiver. Therefore, in transmissions with large transmission losses, such as long-distance transmissions, it is effective to use optical amplifiers to compensate for the decrease in signal strength.

[0003] Amplified spontaneous emission (ASE) emitted by optical amplifiers is optical noise and can degrade the reception characteristics of optical signals. For example, even if the signal strength of an optical signal entering a receiver is amplified to a high level by an optical amplifier, if the signal strength of the spontaneous emission is large relative to the signal light, that is, if the optical signal to noise ratio (OSNR) is low, the bit error rate increases. In order to avoid such an increase in bit error rate, it is important to keep the signal strength of the optical signal entering the optical amplifier relatively high compared to the level of the spontaneous emission emitted by the optical amplifier during optical amplification.

[0004] Fig. 20 is a diagram for explaining the change in signal strength with respect to transmission distance (level diagram). The upper part of Fig. 20 shows a transmitting terminal 81 (Tx: Transmitter), which is a user terminal on the transmitting side, a receiving terminal 82 (Rx: Receiver), which is a user terminal on the receiving side, and three relay nodes 83. These three relay nodes 83 relay the transmission of an optical signal from the transmitting terminal 81 (Tx) to the receiving terminal 82 (Rx). Each of the three relay nodes 83 is equipped with an optical amplifier 84. The lower part of Fig. 20 shows the transition of the signal strength of the optical signal due to attenuation due to the transmission loss characteristics of the optical fiber and amplification by the optical amplifier 84.

[0005] Here, the threshold value of the signal strength at which an increase in the bit error rate occurs due to a decrease in the optical signal-to-noise ratio is denoted as Pmin. As shown in Fig. 20, by arranging the optical amplifier 84 so that the signal strength is higher than Pmin in all sections of the transmission line, it is possible to avoid the deterioration of the receiving characteristics caused by spontaneous emission.

[0006] As described above, in order to avoid the influence of spontaneous emission, it is important to keep the signal strength in the transmission path relatively high. However, on the other hand, even if the signal strength is excessively high, waveform degradation occurs due to nonlinear optical effects, and the bit error rate increases (see Non-Patent Document 1). Here, the threshold value of the signal strength at which the bit error rate increases due to the influence of nonlinear optical effects is defined as Pmax. Generally, in order to perform error-free transmission in a system in which optical signals are amplified at relay nodes, it is important to design the transmission path so that the value of the signal strength in the transmission section is maintained between Pmax, which is an upper limit, and Pmin, which is a lower limit.

[0007] Also, Fig. 20 shows an example in which all relay nodes 83 are provided with optical amplifiers 84. However, in order to reduce costs, it is important to reduce the number of optical amplifiers 84. Fig. 21 is a diagram for explaining the change in signal strength with respect to transmission distance (level diagram). As in Fig. 20, the upper part of Fig. 21 shows a transmitting terminal 81 (Tx), which is a user terminal on the transmitting side, a receiving terminal 82 (Rx), which is a user terminal on the receiving side, and three relay nodes 83. These three relay nodes 83 relay the transmission of an optical signal from the transmitting terminal 81 (Tx) to the receiving terminal 82 (Rx).

[0008] Also, while in Fig. 20 optical amplifiers 84 are provided in all relay nodes 83, in Fig. 21 optical amplifiers 84 are provided only in some of the relay nodes 83. Specifically, in Fig. 21, the optical amplifier 84 in the second relay node 83 from the transmitting terminal 81 (Tx) side is thinned out compared to Fig. 20. In the following explanation, "thinning out optical amplifiers 84" means "not placing an optical amplifier 84 (in that relay node 83)".

[0009] Also, similar to Fig. 20, the lower part of Fig. 21 shows the transition of the signal strength of the optical signal due to attenuation due to the transmission loss characteristics of the optical fiber and amplification by the optical amplifiers 84. As shown in Fig. 21, even if some of the optical amplifiers 84 are thinned out, error-free transmission is possible as long as the transmission loss between the multiple relay nodes 83 is small and the signal strength transitions between Pmax and Pmin. Therefore, it is possible to thin out some of the optical amplifiers 84 within the range where the signal strength transitions between Pmax and Pmin.

[0010] In recent years, studies on all-optical networks have been progressing in order to further reduce latency and power consumption (see, for example, Non-Patent Document 2). An all-optical network is a network in which all forwarding functions are processed in the optical domain. FIG. 22 is a diagram showing an example of the configuration of an optical transmission system using an all-optical network. FIG. 22 shows a transmitting terminal 81 (Tx) which is a user terminal on the transmitting side, a receiving terminal 82 (Rx) which is a user terminal on the receiving side, multiple relay nodes 83, and a concentrator 85. Note that the concentrator 85 also functions as a relay node. Some of the relay nodes 83 are equipped with optical amplifiers 84, which may or may not be shown in the figure.

[0011] Also, in Fig. 22, the transmission path of an optical signal from a transmitting terminal 81 (Tx) to a receiving terminal 82 (Rx) is indicated by a dashed arrow. As shown in Fig. 22, the transmission path is a transmission path from the transmitting terminal 81 (Tx) to the receiving terminal 82 (Rx) via a relay node 83 not equipped with an optical amplifier 84, a relay node 83 equipped with an optical amplifier 84 (relay node marked with the symbol B in Fig. 22), a relay node 83 which is also a concentrator (relay node marked with the symbol A in Fig. 22), and a relay node 83 equipped with an optical amplifier 84 (relay node marked with the symbol C in Fig. 22).

[0012] In an all-optical network, optical switches are used at relay nodes. This eliminates the need to convert optical signals to electrical signals at relay nodes before retransmitting the optical signals, as in conventional networks, and allows direct connections between user terminals using only optical signal transmission paths. In addition, when the transmission loss between user terminals is large, optical amplifiers are placed at each relay node to compensate for the transmission loss.

[0013] The network shown in Fig. 22 can be regarded as a network configured with a tree topology consisting of a four-layer tree as shown in Fig. 23. Fig. 23 is a diagram showing an example of the configuration of an optical transmission system using an all-optical network. Below, a case where the network is configured with a tree topology will be described as an example.

[0014] Hereinafter, a network configured with a tree topology consisting of a four-layer tree as shown in FIG. 24 is assumed. FIG. 24 is a diagram showing an example of the configuration of an optical transmission system using an all-optical network. Here, a case is considered in which an optical signal is transmitted in the following order: lower layer (layers 3 and 4), relay node 83 (B in FIG. 24), relay node 83 (A in FIG. 24), relay node 83 (C in FIG. 24), and lower layer (layers 3 and 4). In FIG. 24, a dashed arrow indicates a transmission path (01) of an optical signal from a transmitting terminal 81 (Tx1) which is a user terminal on the transmitting side to a receiving terminal 82 (Rx1) which is a user terminal on the receiving side. In addition, in FIG. 24, a dashed arrow indicates a transmission path (02) of an optical signal from a transmitting terminal 81 (Tx2) which is a user terminal on the transmitting side to a receiving terminal 82 (Rx2) which is a user terminal on the receiving side.

[0015] Hereinafter, we will consider reducing the number of optical amplifiers 84, focusing on a group of user terminals (Tx1 and Rx1) communicating on transmission path (01) and a group of user terminals (Tx2 and Rx2) communicating on transmission path (02). For simplicity of explanation, we will assume that all optical amplifiers 84 are "constant output control" optical amplifiers that output signals at a constant level of signal strength. We will also assume that the signal strength of signals output from all optical amplifiers 84 is equal to the signal strength of signals output from transmitting terminals 81 (Tx1 and Tx2). We will also assume that the transmission loss between adjacent relay nodes 83 is constant at all points.

[0016] A level diagram in the above case is shown in Fig. 25. Fig. 25 is a diagram for explaining the change (level diagram) in signal strength with respect to the conventional arrangement of optical amplifiers. The upper part of Fig. 25 shows a transmitting terminal 81 (Tx1-1 to 3 and Tx2-1 to 3) which is a transmitting user terminal, a receiving terminal 82 (Rx1-1 to 3 and Rx2-1 to 3) which is a receiving user terminal, and five relay nodes 83. These five relay nodes 83 relay the transmission of optical signals from the transmitting terminals 81 (Tx1-1 to 3 and Tx2-1 to 3) to the receiving terminals 82 (Rx1-1 to 3 and Rx2-1 to 3). Each of the five relay nodes 83 is provided with an optical amplifier 84. The lower part of Fig. 25 shows the transition of the signal strength of the optical signal due to attenuation due to the transmission loss characteristics of the optical fiber and amplification by the optical amplifier 84.

[0017] Here, assuming that communication is performed using three optical fibers in each of the transmission paths (01) and (02), six optical amplifiers 84 are required in each relay node 83 (for example, A to C in FIG. 25) as shown in Fig. 25. Below, a configuration in which these optical amplifiers 84 are thinned out to reduce the number of optical amplifiers 84 will be considered. Here, a case where optimization is performed on an optical fiber basis will be described.

[0018] Hereinafter, a case where optimization is performed for each of the six optical fibers in total, the transmission path (01) and the transmission path (02), will be considered. FIG. 26 shows a configuration in which the optical amplifiers 84 of the relay nodes 83 located at odd positions counting from the transmitting terminal 81 (Tx1-1 to 3 and Tx2-1 to 3) side in FIG. 25 are thinned out. FIG. 26 is a diagram for explaining the change in signal intensity (level diagram) with respect to the arrangement of conventional optical amplifiers. The upper part of FIG. 26 shows transmitting terminals 81 (Tx1-1 to 3 and Tx2-1 to 3) which are transmitting user terminals, receiving terminals 82 (Rx1-1 to 3 and Rx2-1 to 3) which are receiving user terminals, and five relay nodes 83. These five relay nodes 83 relay the transmission of optical signals from the transmitting terminals 81 (Tx1-1 to 3 and Tx2-1 to 3) to the receiving terminals 82 (Rx1-1 to 3 and Rx2-1 to 3).

[0019] Also, in Fig. 25, all relay nodes 83 are provided with optical amplifiers 84, whereas in Fig. 26, only some of the relay nodes 83 are provided with optical amplifiers 84. Specifically, in Fig. 26, unlike Fig. 25, the optical amplifiers 84 of odd-numbered relay nodes 83 counting from the transmitting terminal 81 (Tx1-1 to 3 and Tx2-1 to 3) are thinned out.

[0020] Also, the bottom of Fig. 26 shows the transition of the signal strength of the optical signal due to attenuation due to the transmission loss characteristics of the optical fiber and amplification by the optical amplifier 84. As shown in Fig. 26, if the transmission loss between the relay nodes 83 is small relative to the output level from the optical amplifier 84 and the signal light strength input to the next-stage optical amplifier 84 does not fall below Pmin, error-free transmission is possible even if the optical amplifiers 84 are thinned out. Therefore, it is possible to thin out some of the optical amplifiers 84 within the range where the signal strength transitions between Pmax and Pmin.

[0021] In Fig. 26, each transmission path in the same transmission path group has the same configuration. The transmission paths in the same transmission path group here are, for example, the transmission path from Tx1-1 to Rx1-1, the transmission path from Tx1-2 to Rx1-2, and the transmission path from Tx1-3 to Rx1-3 in the transmission path group of transmission path (01). Here, when the optical amplifiers 84 to be thinned out are selected by the same algorithm, optical amplifiers 84 of the same relay node 83 are selected between the transmission paths. Therefore, in this case, the optical amplifiers 84 are concentrated in a specific relay node 83.

[0022] For example, as shown in Fig. 26, if odd-numbered optical amplifiers 84 (1, 3, and 5 in Fig. 26) counting from a transmitting terminal 81 (Tx1-1 to 3 and Tx2-1 to 3) are thinned out, the optical amplifiers 84 are concentrated in the relay node 83 marked with the symbol B and the relay node 83 marked with the symbol C in Fig. 24. Then, as shown in Fig. 26, six optical amplifiers 84 are required in each of the relay node 83 marked with the symbol B and the relay node 83 marked with the symbol C.

[0023] In an all-optical network, paths are flexibly switched in response to user requests. Hereinafter, a case will be considered in which the state of the network transmission paths shown in FIG. 24 changes over time to the state of the network transmission paths shown in FIG. 27. FIG. 27 is a diagram showing another example of the configuration of an optical transmission system using an all-optical network. In contrast to FIG. 24 described above, in FIG. 27, the transmitting terminal 81 (Tx1-1 to 3 and Tx2-1 to 3) has moved from the third layer position to the fourth layer position of the tree topology. As a result, the transmission path (01) shown in FIG. 24 changes to the transmission path (03) in FIG. 27, and the transmission path (02) shown in FIG. 24 changes to the transmission path (04) in FIG. 27.

[0024] FIG. 28 shows a configuration in which odd-numbered optical amplifiers 84 counted from the transmitting terminal 81 (Tx1-1 to 3 and Tx2-1 to 3) side are thinned out in such transmission paths (03) and (04). FIG. 28 is a diagram for explaining a change in signal intensity (level diagram) with respect to the conventional arrangement of optical amplifiers. The upper part of FIG. 28 shows transmitting terminals 81 (Tx1-1 to 3 and Tx2-1 to 3) which are transmitting user terminals, receiving terminals 82 (Rx1-1 to 3 and Rx2-1 to 3) which are receiving user terminals, and six relay nodes 83. These six relay nodes 83 relay the transmission of optical signals from the transmitting terminals 81 (Tx1-1 to 3 and Tx2-1 to 3) to the receiving terminals 82 (Rx1-1 to 3 and Rx2-1 to 3).

[0025] As described above, the transmission paths in the same transmission path group have the same transmission path configuration. Here, when the optical amplifiers 84 to be thinned out are selected based on the same algorithm, the optical amplifiers 84 of the same relay node 83 are selected between the transmission paths. For example, as shown in FIG. 28, when the optical amplifiers 84 of the odd-numbered relay nodes 83 (1, 3, 5 in FIG. 28) counting from the transmitting terminal 81 (Tx1-1 to 3 and Tx2-1 to 3) side are thinned out, the optical amplifiers 84 are concentrated in the relay node 83 marked with the symbol A in FIG. 27. And, as shown in FIG. 28, six optical amplifiers 84 are required in the relay node 83 marked with the symbol A. [Prior art documents] [Non-patent literature]

[0026] [Non-Patent Document 1] Ruben S. Luis et al., "Analytical Characterization of SPM Impact on XPM-Induced Degradation in Dispersion-Compensated WDM Systems", Journal of Lightwave Technology, Vol.23, No.3, pp.1503-1513, March 2005. [Non-Patent Document 2] H. Kawahara et al., "Optical Full-mesh Network Technologies Supporting the All-Photonics Network", NTT Technical Review, Vol. 18, No.5, pp. 24-29, May 2020. Summary of the Invention [Problem to be solved by the invention]

[0027] As described above, when the number of optical amplifiers 84 is reduced by thinning out the optical amplifiers 84 independently for each optical fiber, the positions of the relay nodes 83 where the optical amplifiers 84 are thinned out will also be the same within the same transmission path group. This results in the occurrence of relay nodes 83 where optical amplifiers 84 are concentrated. In a network in which the positions of the transmitting terminal 81 and the receiving terminal 82 change over time and the transmission paths are switched over time, such as an all-optical network, the positions of the relay nodes 83 where the optical amplifiers 84 are concentrated also change over time.

[0028] In order to accommodate such changes, it is not possible to reduce the number of optical amplifiers 84 that must be prepared in advance at each relay node 83, and so there has traditionally been a problem in that it has been difficult to reduce equipment costs and save space.

[0029] In view of the above circumstances, an object of the present invention is to provide a technique capable of reducing the number of optical amplifiers to be installed in a relay node. [Means for solving the problem]

[0030] One aspect of the present invention is an optical amplifier placement method comprising: an acquisition step of acquiring transmission route information indicating the configuration of a network that transmits an optical signal via a plurality of relay nodes and the transmission route of the optical signal transmitted by the network; and a determination step of determining the placement of optical amplifiers in the network by grouping a plurality of optical fibers that pass through the same relay node based on the transmission route information and determining the need for optical amplification at each of the relay nodes on a group-by-group basis of the optical fibers.

[0031] Another aspect of the present invention is an optical amplifier placement assistance device that includes an acquisition unit that acquires transmission route information indicating the configuration of a network that transmits an optical signal via a plurality of relay nodes and the transmission route of the optical signal transmitted by the network, and a determination unit that determines the placement of optical amplifiers in the network by grouping a plurality of optical fibers that pass through the same relay node based on the transmission route information and determining the need for optical amplification at each of the relay nodes on a group-by-group basis of the optical fibers.

[0032] Moreover, one aspect of the present invention is a relay device comprising: an acquisition unit that acquires transmission route information indicating the configuration of a network in which an optical signal is transmitted through a plurality of relay devices and the transmission route of the optical signal transmitted by the network; and a determination unit that determines the placement of optical amplifiers in the network by grouping a plurality of optical fibers passing through the device itself or a plurality of optical fibers passing through the same relay device other than the device itself based on the transmission route information, and determining the need for optical amplification at each of the relay nodes on a group-by-group basis of the optical fibers. Effect of the Invention

[0033] According to the present invention, it is possible to reduce the number of optical amplifiers to be installed in a relay node. [Brief description of the drawings]

[0034] [Figure 1] 1 is an overall configuration diagram of an optical transmission system using an all-optical network in a first embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram illustrating an example of a configuration of a relay node of the optical transmission system according to the first embodiment of the present invention. [Diagram 3] 3 is another overall configuration diagram of the optical transmission system using the all-optical network in the first embodiment of the present invention. FIG. [Figure 4] FIG. 4 is a diagram illustrating another example of the configuration of a relay node in the optical transmission system according to the first embodiment of the present invention. [Diagram 5]3 is another overall configuration diagram of the optical transmission system using the all-optical network in the first embodiment of the present invention. FIG. [Figure 6] FIG. 2 is a diagram illustrating an example of an arrangement of optical amplifiers in an optical transmission system according to the first embodiment of the present invention. [Figure 7] 3 is another overall configuration diagram of the optical transmission system using the all-optical network in the first embodiment of the present invention. FIG. [Figure 8] FIG. 2 is a diagram illustrating an example of an arrangement of optical amplifiers in an optical transmission system according to the first embodiment of the present invention. [Figure 9] FIG. 2 is a diagram illustrating an example of an arrangement of optical amplifiers in an optical transmission system according to the first embodiment of the present invention. [Figure 10] 5 is a flowchart showing an operation of a relay node 13 in the first embodiment of the present invention. [Figure 11] FIG. 11 is an overall configuration diagram of an optical transmission system using an all-optical network in a second embodiment of the present invention. [Figure 12] FIG. 1 is a diagram illustrating an example of an arrangement of optical amplifiers in a conventional optical transmission system. [Figure 13] FIG. 11 is another overall configuration diagram of the optical transmission system using the all-optical network in the second embodiment of the present invention. [Figure 14] FIG. 11 is a diagram illustrating an example of an arrangement of optical amplifiers in an optical transmission system according to a second embodiment of the present invention. [Figure 15] FIG. 11 is a diagram illustrating an example of an arrangement of optical amplifiers in an optical transmission system according to a second embodiment of the present invention. [Figure 16] FIG. 11 is a diagram illustrating an example of an arrangement of optical amplifiers in an optical transmission system according to a second embodiment of the present invention. [Figure 17] 11A and 11B are diagrams for explaining other arrangement methods of optical amplifiers in the optical transmission system according to each embodiment of the present invention. [Figure 18] 11A and 11B are diagrams for explaining other arrangement methods of optical amplifiers in the optical transmission system according to each embodiment of the present invention. [Figure 19]11A and 11B are diagrams for explaining other arrangement methods of optical amplifiers in the optical transmission system according to each embodiment of the present invention. [Figure 20] FIG. 2 is a diagram for explaining changes in signal intensity (level diagram) with respect to the arrangement of optical amplifiers. [Figure 21] FIG. 2 is a diagram for explaining changes in signal intensity (level diagram) with respect to the arrangement of optical amplifiers. [Figure 22] FIG. 1 illustrates an example of a configuration of an optical transmission system using a conventional all-optical network. [Figure 23] FIG. 1 illustrates an example of a configuration of an optical transmission system using a conventional all-optical network. [Figure 24] FIG. 11 is a diagram illustrating another example of the configuration of an optical transmission system using a conventional all-optical network. [Diagram 25] FIG. 1 is a diagram for explaining changes in signal strength (level diagram) with respect to the arrangement of conventional optical amplifiers. [Figure 26] FIG. 1 is a diagram for explaining changes in signal strength (level diagram) with respect to the arrangement of conventional optical amplifiers. [Figure 27] FIG. 11 is a diagram illustrating another example of the configuration of an optical transmission system using a conventional all-optical network. [Figure 28] FIG. 1 is a diagram for explaining changes in signal strength (level diagram) with respect to the arrangement of conventional optical amplifiers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0036] <First embodiment> A first embodiment of the present invention will now be described. Fig. 1 is a diagram showing the overall configuration of an optical transmission system 1 using an all-optical network in the first embodiment of the present invention.

[0037] The all-optical network used in the optical transmission system 1 of the first embodiment is a tree-type topology network having a three-layer tree structure. Fig. 1 shows the arrangement of a plurality of relay nodes 13 and a concentrator 15 constituting the optical transmission system 1. The concentrator 15 also functions as a relay node. Fig. 1 also shows two transmitting / receiving terminals 10 (TRx), which are user terminals that communicate with each other.

[0038] Some of the relay nodes 13 are equipped with optical amplifiers 14 (not shown). In Fig. 1, the relay nodes 13 are assigned symbols A to G so that they can be distinguished from one another in the following description. Hereinafter, for example, the relay node 13 assigned symbol A may be referred to as "relay node A," and the relay node 13 assigned symbol B may be referred to as "relay node B."

[0039] 1, one transmitting / receiving terminal 10 (TRx) is connected to a relay node E, and the other transmitting / receiving terminal 10 (TRx) is connected to a relay node G. Below, as an example, a case will be described in which the transmitting / receiving terminal 10 (TRx) connected to the relay node E and the transmitting / receiving terminal 10 (TRx) connected to the relay node G communicate with each other. Also, below, the configuration of the relay node 13 will be described taking the case of the relay node B as an example.

[0040] 2 is a diagram showing an example of the configuration of a relay node B (relay node 13) of the optical transmission system 1 in the first embodiment of the present invention. As shown in FIG. 2, the relay node B includes three input / output ports (input / output port 130-1, input / output port 130-2, input / output port 130-3), three circulators 131, four optical switches 132, a transmission path information acquisition unit 135, an optical amplifier necessity determination unit 136, an optical switch control unit 137, and six optical amplifiers 14.

[0041] 1. The input / output port 130-1 is connected to the relay node D shown in FIG. 1, the input / output port 130-2 is connected to the relay node E shown in FIG. 1, and the input / output port 130-3 is connected to the relay node A shown in FIG.

[0042] An optical signal transmitted from relay node A enters relay node B from input / output port 130-3. The optical signal that enters relay node B is separated into optical signals according to the traveling direction by circulator 131. The separated optical signals enter optical switch 132, which has a two-stage configuration. As shown in Fig. 2, optical amplifiers 14 are installed in some of the multiple communication paths between the two optical switches 132.

[0043] The optical switch 132 is configured to be able to select whether or not to pass an optical signal through the optical amplifier 14, and from which input / output port (input / output port 130-1 or input / output port 130-2) the optical signal is to be output, by changing the selection of these communication paths. The optical switch 132 outputs the optical signal from the selected input / output port.

[0044] An optical signal transmitted from relay node D enters relay node B from input / output port 130-1. The optical signal that entered relay node B is separated by circulator 131 according to the traveling direction of the optical signal. The separated optical signals enter optical switch 132, which has a two-stage configuration. An optical amplifier 14 is installed in part of the multiple communication paths between the two optical switches 132. The optical switch 132 is configured to be able to select whether or not to pass an optical signal through the optical amplifier 14 by changing the selection of these communication paths. The optical switch 132 outputs the optical signal from input / output port 130-3.

[0045] An optical signal transmitted from relay node E enters relay node B from input / output port 130-2. The optical signal that entered relay node B is separated into optical signals according to the traveling direction by circulator 131. The separated optical signals enter optical switch 132, which has a two-stage configuration. As described above, optical switch 132 is configured to be able to select whether or not to pass an optical signal to optical amplifier 14 by changing the selection of the transmission path. Optical switch 132 outputs the optical signal from input / output port 130-3.

[0046] 2, the case where an optical signal transmitted from relay node A enters relay node B from input / output port 130-3, is separated by circulator 131 into each traveling direction of the optical signal, and is output from input / output port 130-2 toward relay node E via a communication path that passes through optical amplifier 14 due to switching of the communication path by optical switch 132 is shown by a dashed arrow. Also, in FIG. 2, the case where an optical signal transmitted from relay node E enters relay node B from input / output port 130-2, is separated by circulator 131 into each traveling direction of the optical signal, and is output from input / output port 130-3 toward relay node A via a communication path that passes through optical amplifier 14 due to switching of the communication path by optical switch 132 is shown by a dashed arrow.

[0047] The transmission path information acquisition unit 135 calculates a transmission path for connecting two transmitting / receiving terminals 10 (TRx) with each other using a predetermined algorithm. The transmission path here is, for example, a transmission path in the order of transmitting / receiving terminal 10 (TRx), relay node G, relay node C, relay node A, relay node B, relay node E, and transmitting / receiving terminal 10 (TRx) in Fig. 1. The transmission path information acquisition unit 135 outputs transmission path information indicating the configuration of the all-optical network and the calculated transmission path to the optical amplifier necessity determination unit 136 and the optical switch control unit 137, respectively.

[0048] The optical amplifier necessity determining unit 136 acquires the transmission path information output from the transmission path information acquiring unit 135. The optical amplifier necessity determining unit 136 judges whether the optical amplifier 14 is required in the relay node 13 (relay node B in this case) by a predetermined algorithm based on the resource status of the entire optical transmission system 1 indicated by the acquired transmission path information. The optical amplifier necessity determining unit 136 outputs optical amplifier necessity information indicating the result of the judgment to the optical switch control unit 137.

[0049] The optical switch control unit 137 receives the transmission path information output from the transmission path information acquisition unit 135. and the optical amplifier necessity information output from the optical amplifier necessity determining unit 136. The optical switch control unit 137 controls the setting of a transmission path by the optical switch 132 based on the optical amplifier necessity information notified from the optical amplifier necessity determining unit 136.

[0050] 2 and 4 described later, the transmission path information acquisition unit 135 and the optical amplifier necessity determination unit 136 are shown to be provided in the relay node 13 (relay device), but the present invention is not limited to such a configuration. The transmission path information acquisition unit 135 and the optical amplifier necessity determination unit 136 may be provided in a device other than the relay node 13 (relay device), for example.

[0051] Hereinafter, as an example, a case will be described in which the input / output port 130-1 and the input / output port 130-3 are connected to each other in the relay node B, and the optical amplifier 14 is thinned out.

[0052] In this case, the transmission path in the all-optical network of the optical transmission system 1 is, for example, the transmission path indicated by the dashed arrow in Fig. 3. Fig. 3 is another overall configuration diagram of the optical transmission system 1 using the all-optical network in the first embodiment of the present invention. As shown in Fig. 3, the transmission path is a transmission path in the order of the transmitting / receiving terminal 10 (TRx), relay node D, relay node B, relay node A (concentrator 15), relay node C, relay node G, and transmitting / receiving terminal 10 (TRx), or a transmission path in the reverse order.

[0053] In this case, the transmission path in the relay node B is, for example, the transmission path indicated by the dashed arrow in Fig. 4. Fig. 4 is a diagram showing another example of the configuration of the relay node 13 in the optical transmission system 1 in the first embodiment of the present invention.

[0054] 4, the case where an optical signal transmitted from relay node A enters relay node B from input / output port 130-3, is separated by circulator 131 into the optical signal traveling direction, and is output from input / output port 130-2 toward relay node E via a communication path that does not pass through optical amplifier 14 due to switching of the communication path by optical switch 132 is shown with a dashed arrow. Also, in FIG. 4, the case where an optical signal transmitted from relay node D enters relay node B from input / output port 130-1, is separated by circulator 131 into the optical signal traveling direction, and is output from input / output port 130-3 toward relay node A via a communication path that does not pass through optical amplifier 14 due to switching of the communication path by optical switch 132 is shown with a dashed arrow.

[0055] Hereinafter, an algorithm used by the optical amplifier necessity determining unit 136 shown in, for example, FIGS. 2 and 4 to determine the relay node 13 in which the optical amplifier 14 is to be thinned out will be described with reference to FIGS.

[0056] First, with reference to Fig. 5, a method of thinning out and reducing the number of optical amplifiers 14 will be considered when transmitting terminals 11 (Tx1 and Tx2) are located at the third layer of the tree topology of the all-optical network. Fig. 5 is another overall configuration diagram of an optical transmission system using an all-optical network in the first embodiment of the present invention.

[0057] 5 shows a transmission path (1) indicated by a dashed arrow connecting the transmitting terminal 11 (Tx1) to the receiving terminal 12 (Rx1), and a transmission path (2) indicated by a dashed arrow connecting the transmitting terminal 11 (Tx2) to the receiving terminal 12 (Rx2). As shown in FIG. 5, the transmission path (1) is a transmission path in the order of the transmitting terminal 11 (Tx1), relay node 13, relay node B, relay node A (concentrator 15), relay node C, relay node 13, and receiving terminal 12 (Rx1). Also, as shown in FIG. 5, the transmission path (2) is a transmission path in the order of the transmitting terminal 11 (Tx2), relay node 13, relay node B, relay node A (concentrator 15), relay node C, relay node 13, and receiving terminal 12 (Rx2).

[0058] Here, in each of the transmission paths (1) and (2), M optical fibers are grouped into one group. In each group, the upper limit of the number of optical amplifiers 14 available for each relay node 13 is set to N. Under these conditions, an example of a state in which the optical amplifiers 14 are thinned out is shown in FIG. 6.

[0059] Fig. 6 is a diagram showing an example of the arrangement of optical amplifiers 14 in the optical transmission system 1 in the first embodiment of the present invention. Fig. 6 shows a transmitting terminal 11 (Tx1 and Tx2) which is a transmitting user terminal, a receiving terminal 12 (Rx1 and Rx2) which is a receiving user terminal, and five relay nodes 83. These five relay nodes 83 relay the transmission of an optical signal from a transmitting terminal 81 (Tx1 and Tx2) to a receiving terminal 82 (Rx1 and Rx2).

[0060] Fig. 6 illustrates an example in which M = 3 and N = 2. Fig. 6 shows a first group in which three optical fibers included in the transmission path from the transmitting terminal 11 (Tx1) to the receiving terminal 12 (Rx1) are grouped, and a second group in which three optical fibers included in the transmission path from the transmitting terminal 11 (Tx2) to the receiving terminal 12 (Rx2) are grouped.

[0061] In this case, since the upper limit of the number of optical amplifiers 14 available for each relay node 13 in each group is N as described above, the number of optical amplifiers 14 arranged in the relay nodes 13 of the first group and the number of optical amplifiers 14 arranged in the relay nodes 13 of the second group are always less than or equal to N. For example, as shown in Fig. 6, relay nodes B and C require one optical amplifier 14 for each group, and relay node A requires two optical amplifiers 14 for each group.

[0062] Next, with reference to Fig. 7, a method of reducing the number of optical amplifiers 14 by thinning them out will be considered when transmitting terminal 11 (Tx1 and Tx2) is located at the fourth layer of the tree topology of the all-optical network. That is, consider the case where transmitting terminal 11 (Tx1 and Tx2) located at the third layer of the tree topology shown in Fig. 5 has been moved to the fourth layer of the tree topology shown in Fig. 7. Fig. 7 is another overall configuration diagram of an optical transmission system using an all-optical network in the first embodiment of the present invention.

[0063] 7 shows a transmission path (3) indicated by a dashed arrow connecting the transmitting terminal 11 (Tx1) to the receiving terminal 12 (Rx1), and a transmission path (4) indicated by a dashed arrow connecting the transmitting terminal 11 (Tx2) to the receiving terminal 12 (Rx2). As shown in FIG. 7, the transmission path (3) is a transmission path in the order of the transmitting terminal 11 (Tx1), relay node 13, relay node 13, relay node B, relay node A (concentrator 15), relay node C, relay node 13, and receiving terminal 12 (Rx1). Also, as shown in FIG. 7, the transmission path (2) is a transmission path in the order of the transmitting terminal 11 (Tx2), relay node 13, relay node 13, relay node B, relay node A (concentrator 15), relay node C, relay node 13, and receiving terminal 12 (Rx2).

[0064] Here, similarly to the above, M optical fibers are grouped into one group in each of the transmission paths (3) and (4). In each group, the upper limit of the number of optical amplifiers 14 available for each relay node 13 is set to N. Under such conditions, an example of a state in which the optical amplifiers 14 are thinned out is shown in FIG.

[0065] Fig. 8 is a diagram showing an example of the arrangement of optical amplifiers 14 in the optical transmission system 1 in the first embodiment of the present invention. Fig. 8 shows a transmitting terminal 11 (Tx1 and Tx2) which is a transmitting user terminal, a receiving terminal 12 (Rx1 and Rx2) which is a receiving user terminal, and six relay nodes 83. These six relay nodes 83 relay the transmission of an optical signal from a transmitting terminal 81 (Tx1 and Tx2) to a receiving terminal 82 (Rx1 and Rx2).

[0066] Fig. 8 illustrates an example in which M = 3 and N = 2. Fig. 8 shows a first group in which three optical fibers included in the transmission path from the transmitting terminal 11 (Tx1) to the receiving terminal 12 (Rx1) are grouped, and a second group in which three optical fibers included in the transmission path from the transmitting terminal 11 (Tx2) to the receiving terminal 12 (Rx2) are grouped.

[0067] In this case, since the upper limit of the number of optical amplifiers 14 available for each relay node 13 in each group is N as described above, the number of optical amplifiers 14 arranged in the relay nodes 13 of the first group and the number of optical amplifiers 14 arranged in the relay nodes 13 of the second group are always less than or equal to N. For example, as shown in Fig. 8, two optical amplifiers 14 are required for each group at relay node B and relay node C, and one optical amplifier 14 is required for each group at relay node A.

[0068] In this way, the optical transmission system 1 in the first embodiment of the present invention can prevent the optical amplifiers 14 from concentrating at a specific relay node 13 even when the transmission path is switched, by distributing the optical amplifiers 14 in multiple optical fibers, and can reduce the number of optical amplifiers 14 provided at the relay node 13 to N or less.

[0069] Although the case of M=3 and N=2 has been exemplified here, the numbers of optical fibers and optical amplifiers 14 are not limited to these. In other words, the values ​​of M and N are arbitrary as long as the condition that "M optical fibers are grouped into one group in each transmission path, and the upper limit of the number of optical amplifiers 14 available for each relay node in each group is N" is satisfied.

[0070] Hereinafter, a method for calculating a specific arrangement of optical amplifiers 14 will be described with reference to Fig. 9. Fig. 9 is a diagram showing an example of an arrangement of optical amplifiers in an optical transmission system in the first embodiment of the present invention. Fig. 9 shows a transmitting terminal 11 (Tx) which is a user terminal on the transmitting side, a receiving terminal 12 (Rx) which is a user terminal on the receiving side, and four relay nodes 83. These four relay nodes 83 relay the transmission of an optical signal from a transmitting terminal 81 (Tx) to a receiving terminal 82 (Rx).

[0071] Below, as an example, consider the case where M = 3 and N = 2. In Fig. 9, three optical fibers constituting one group are shown as a first optical fiber, a second optical fiber, and a third optical fiber.

[0072] Here, in a certain relay node 13, the case where an optical amplifier 14 is provided for a certain optical fiber is represented as 1, and the case where the optical amplifier 14 is thinned out is represented as 0. For example, in a certain relay node 13, a state in which optical amplifiers 14 are provided for the first and second optical fibers and the optical amplifiers 14 are thinned out for the third optical fiber is represented as (1,1,0). In this case, since N=2 as described above, there are three possible arrangement patterns of the optical amplifiers 14 in a certain relay node 13: (1,1,0), (1,0,1,) and (0,1,1).

[0073] For example, as shown in FIG. 9, when the number of relay nodes 13 through which each optical fiber passes in a certain transmission path is X and X=4, the possible combinations of the arrangement of the optical amplifiers 14 in a certain transmission path are as follows: X =3 4 = 81 (patterns). Then, by calculating the bit error rate at the receiving terminal 12 (Rx) for all these patterns in a brute-force manner, for example by a transmission simulation using a computer, it is possible to identify the combination of the arrangement of the optical amplifiers 14 that enables error-free transmission.

[0074] If the calculation result indicates that none of the combinations enables error-free transmission, the value of N, which is the upper limit of the number of optical amplifiers 14 that can be used for each relay node 13 in each group, may be increased, and calculations such as a transmission simulation may be performed again. Although changing the conditions in this way increases the number of optical amplifiers 14 required, it is possible to increase the possibility of identifying a configuration that enables error-free transmission. Also, from the viewpoint of reducing the number of active optical amplifiers 14, calculations may be performed under the condition that the number of optical amplifiers 14 for each relay node 13 is N or less, rather than N.

[0075] The following describes an example of the operation of the relay node 13. Fig. 10 is a flowchart showing the operation of the relay node 13 in the first embodiment of the present invention.

[0076] First, the transmission path information acquisition unit 135 (acquisition unit) of the relay node 13 calculates a transmission path for connecting two transmitting / receiving terminals 10 (TRx) with each other by a predetermined algorithm (step S01). The transmission path information acquisition unit 135 outputs information on the configuration of the optical network and transmission path information indicating the calculated transmission path to the optical amplifier necessity determination unit 136 and the optical switch control unit 137, respectively.

[0077] In addition, information regarding the configuration of the entire optical network of the optical transmission system 1 used to calculate the transmission path (e.g., the arrangement and hierarchy of the relay nodes 13, information indicating the relay nodes 13 to which the two transmitting / receiving terminals 10 (TRx) are connected, etc.) may be configured to be stored in advance in the relay nodes 13, for example, or may be configured to be appropriately transmitted via the network, for example.

[0078] Next, the optical amplifier necessity determination unit 136 (decision unit) acquires the transmission path information output from the transmission path information acquisition unit 135. The optical amplifier necessity determination unit 136 determines whether the optical amplifier 14 is required in the relay node 13 using a predetermined algorithm based on the resource status of the entire optical network indicated by the acquired transmission path information (step S02). The optical amplifier necessity determination unit 136 outputs optical amplifier necessity information indicating the result of the determination to the optical switch control unit 137.

[0079] Next, the optical switch control unit 137 acquires the transmission path information output from the transmission path information acquisition unit 135 and the optical amplifier necessity information output from the optical amplifier necessity determination unit 136. The optical switch control unit 137 controls the setting of the transmission path by the optical switch 132 based on the optical amplifier necessity information notified from the optical amplifier necessity determination unit 136 (step S03). With this, the operation of the relay node 13 shown in the flowchart of FIG. 10 is completed.

[0080] The details of the operation of the optical amplifier necessity determining unit 136 in the above step S02 are as follows, for example: The optical amplifier necessity determining unit 136 groups a plurality of optical fibers passing through the same relay node 13 based on the transmission route information, and determines the necessity of optical amplification at each relay node 13 for each group of the optical fibers, thereby determining the placement of the optical amplifiers 14 in the all-optical network.

[0081] For example, when the number of optical fibers grouped in the relay node 13 is M and the number of optical amplifiers 14 per relay node 13 in each group is N, the optical amplifier necessity determination unit 136 simulates the transmission of optical signals for possible patterns of combinations of the values ​​of M and N, and determines the placement of the optical amplifiers 14 based on the results of the simulation. For example, the optical amplifier necessity determination unit 136 calculates the bit error rate at the receiving terminal 12 (Rx) that receives the optical signal for each pattern by simulation, and determines the placement of the optical amplifiers 14 based on the calculated bit error rate.

[0082] Here, for example, the optical amplifier necessity determination unit 136 determines the placement of the optical amplifier 14 so that the signal strength of the optical signal passing through the relay node 13 transitions between the signal strength (Pmax above) at which the signal strength is affected by the nonlinear optical effect and the signal strength (Pmin above) at which an increase in the bit error rate occurs due to a decrease in the optical signal-to-noise ratio (OSNR).

[0083] As described above, the optical transmission system 1 in the first embodiment of the present invention can appropriately thin out the optical amplifiers 14 in a network in which the positions of user terminals and transmission paths change over time.

[0084] In conventional optical transmission systems, optical amplifiers are used to compensate for the decrease in signal light power in order to achieve long-distance transmission. Since installing optical amplifiers at all nodes in an optical transmission system increases costs, error-free transmission is possible by arranging optical amplifiers so that the signal light power remains between Pmax (the signal power affected by nonlinear optical effects) and Pmin (the signal power at which an increase in bit error rate occurs due to a decrease in the optical signal-to-noise ratio (OSNR)) even if some of the optical amplifiers are thinned out.

[0085] However, when minimizing the number of optical amplifiers independently for each fiber, in a network in which the transmission path switches over time (e.g., an all-optical network), the nodes where optical amplifiers are concentrated move over time, so there is a problem that the number of optical amplifiers to be prepared at each node cannot be reduced.

[0086] In contrast, the optical transmission system 1 in the first embodiment groups a plurality of adjacent optical fibers passing through the same relay node into one, and determines the placement of the optical amplifiers 14 on a group-by-group basis, not on an optical fiber-by-optical fiber basis. In this way, the optical transmission system 1 distributes the optical amplifiers 14 provided in the relay nodes 13 for each group, thereby preventing the optical amplifiers 14 from concentrating at a specific relay node 13.

[0087] Then, the optical transmission system 1 determines the arrangement of the optical amplifiers 14 so that the number of optical amplifiers 14 per relay node 13 is, for example, N or less. The optical transmission system 1 sets the number of optical fibers to be grouped to M, and the upper limit of the number of optical amplifiers 14 per relay node 13 in each group to N, and performs calculations such as transmission simulations on a brute-force basis for all patterns that can arise from the values ​​of M and N.

[0088] As a result, the optical transmission system 1 can derive a combination of installation positions of the optical amplifiers 14 that can achieve error-free operation and that reduces the number of optical amplifiers 14. Therefore, the optical transmission system 1 in the first embodiment of the present invention can reduce the number of optical amplifiers 14 to be installed in the relay nodes 13.

[0089] <Second embodiment> A second embodiment of the present invention will be described below. In the above-mentioned first embodiment, a case where an all-optical network used in an optical transmission system is a tree topology network has been described. In the second embodiment described below, a case where an all-optical network used in an optical transmission system is a ring topology network has been described.

[0090] Fig. 11 is an overall configuration diagram of an optical transmission system using an all-optical network in a second embodiment of the present invention. The all-optical network used in the optical transmission system of the second embodiment is a ring topology network. Fig. 11 shows the arrangement of multiple relay nodes 13 that constitute the optical transmission system. Fig. 11 also shows two pairs of user terminals that communicate with each other: a transmitting terminal 11 (Tx1) and a receiving terminal 12 (Rx1), and a transmitting terminal 11 (Tx2) and a receiving terminal 12 (Rx2).

[0091] Some of the relay nodes 13 are equipped with optical amplifiers 14 (not shown). In Fig. 11, the relay nodes 13 are assigned symbols A to G so that they can be distinguished from one another in the following description. Hereinafter, for example, the relay node 13 assigned symbol A may be referred to as "relay node A," and the relay node 13 assigned symbol B may be referred to as "relay node B."

[0092] In Fig. 11, as an example, at a certain time (time 1), a transmission path (5) is indicated by a dashed arrow, and a transmission path (6) is indicated by a dashed arrow. As shown in Fig. 11, the transmission path (5) is a transmission path in the order of the transmitting terminal 11 (Tx1), relay node A, relay node B, relay node C, and receiving terminal 12 (Rx1). Also, as shown in Fig. 11, the transmission path (6) is a transmission path in the order of the transmitting terminal 11 (Tx2), relay node C, relay node B, relay node A, and receiving terminal 12 (Rx2).

[0093] When optical amplifiers 14 are installed so as to reduce the number of units per optical fiber as in the past, the number of required optical amplifiers 14 is concentrated at relay node B, as shown in FIG. 12, for example, and three optical amplifiers 14 are required for each transmission path. FIG. 12 is a diagram showing an example of the arrangement of optical amplifiers in a conventional optical transmission system. FIG. 12 shows a transmitting terminal 11 (Tx1-1 to 3 and Tx2-1 to 3) which is a transmitting user terminal, a receiving terminal 12 (Rx1-1 to 3 and Rx2-1 to 3) which is a receiving user terminal, and three relay nodes 83. These three relay nodes 83 relay the transmission of optical signals from a transmitting terminal 81 (Tx1-1 to 3 and Tx2-1 to 3) to a receiving terminal 82 (Rx1-1 to 3 and Rx2-1 to 3). In such a case, consider the case where time has passed from time 1 shown in FIG. 11 to time 2 shown in FIG. 13.

[0094] Fig. 13 is an overall configuration diagram of an optical transmission system using an all-optical network in a second embodiment of the present invention. As in Fig. 11, the all-optical network of the optical transmission system shown in Fig. 13 is a ring topology network. Fig. 11 shows the arrangement of multiple relay nodes 13 that constitute the optical transmission system. Fig. 11 also shows two pairs of user terminals that communicate with each other: a transmitting terminal 11 (Tx1) and a receiving terminal 12 (Rx1), and a transmitting terminal 11 (Tx2) and a receiving terminal 12 (Rx2).

[0095] In Fig. 13, as an example, at a certain time (time 2), a transmission path (7) is indicated by a dashed arrow, and a transmission path (8) is indicated by a dashed arrow. As shown in Fig. 13, the transmission path (7) is a transmission path in the order of the transmitting terminal 11 (Tx1), relay node F, relay node A, relay node B, relay node C, and receiving terminal 12 (Rx1). Also, as shown in Fig. 13, the transmission path (8) is a transmission path in the order of the transmitting terminal 11 (Tx2), relay node D, relay node C, relay node B, relay node A, and receiving terminal 12 (Rx2).

[0096] As can be seen by comparing Figure 11 and Figure 13, the transmitting terminal 11 (Tx1) and the transmitting terminal 11 (Tx2) move between the state at time 1 shown in Figure 11 and the state at time 2 shown in Figure 13. Specifically, the transmitting terminal 11 (Tx1) moves from a position connected to relay node A to a position connected to relay node F, and the transmitting terminal 11 (Tx2) moves from a position connected to relay node C to a position connected to relay node D.

[0097] When optical amplifiers 14 are installed so as to reduce the number of units per optical fiber as in the past, the number of required optical amplifiers 14 is concentrated at relay nodes A and C, as shown in FIG. 14, for example, and three optical amplifiers 14 are required for each transmission path. FIG. 14 is a diagram showing an example of the arrangement of optical amplifiers in a conventional optical transmission system. FIG. 14 shows a transmitting terminal 11 (Tx1-1 to 3 and Tx2-1 to 3) which is a transmitting user terminal, a receiving terminal 12 (Rx1-1 to 3 and Rx2-1 to 3) which is a receiving user terminal, and five relay nodes 83 (relay nodes A to D, F). These five relay nodes 83 relay the transmission of optical signals from transmitting terminals 81 (Tx1-1 to 3 and Tx2-1 to 3) to receiving terminals 82 (Rx1-1 to 3 and Rx2-1 to 3).

[0098] In this way, when attempting to install optical amplifiers 14 so as to reduce the number per optical fiber, in a network in which the transmission paths change over time, the positions of relay nodes 13 where the optical amplifiers 14 are concentrated also change over time. Therefore, it is not possible to reduce the number of optical amplifiers 14 that should be prepared in advance at each relay node 13, making it difficult to reduce equipment costs and save space.

[0099] In contrast, a case where optimization is performed on a group basis, rather than on an optical fiber basis, as in the first embodiment, will be described. As in the first embodiment, M optical fibers are grouped into one group in each of the transmission paths (5) and (6) shown in Fig. 11. Also, in each group, the upper limit of the number of optical amplifiers 14 available for each relay node 13 is set to N. Under such conditions, an example of a state in which the optical amplifiers 14 are thinned out is shown in Fig. 15.

[0100] Fig. 15 is a diagram showing an example of the arrangement of optical amplifiers 14 in an optical transmission system 1 in the second embodiment of the present invention. Fig. 15 shows a transmitting terminal 11 (Tx1-1 to 3 and Tx2-1 to 3) which is a transmitting user terminal, a receiving terminal 12 (Rx1-1 to 3 and Rx2-1 to 3) which is a receiving user terminal, and three relay nodes 83. These three relay nodes 83 relay the transmission of optical signals from the transmitting terminals 81 (Tx1-1 to 3 and Tx2-1 to 3) to the receiving terminals 82 (Rx1-1 to 3 and Rx2-1 to 3).

[0101] Fig. 15 illustrates an example in which M = 3 and N = 2. Fig. 15 shows a first group in which three optical fibers included in the transmission path from the transmitting terminal 11 (Tx1) to the receiving terminal 12 (Rx1) are grouped, and a second group in which three optical fibers included in the transmission path from the transmitting terminal 11 (Tx2) to the receiving terminal 12 (Rx2) are grouped.

[0102] In this case, the number of optical amplifiers 14 arranged in the relay nodes 13 of the first group and the number of optical amplifiers 14 arranged in the relay nodes 13 of the second group are always equal to or less than N. For example, as shown in Fig. 15, two optical amplifiers 14 are required for each group in relay nodes A and C, and one optical amplifier 14 is required for each group in relay node B.

[0103] Similarly to the above, M optical fibers are grouped into one group in each of the transmission paths (7) and (8) shown in Fig. 13. In each group, the upper limit of the number of optical amplifiers 14 available for each relay node 13 is set to N. Under these conditions, an example of a state in which the optical amplifiers 14 are thinned out is shown in Fig. 16.

[0104] Fig. 16 is a diagram showing an example of the arrangement of optical amplifiers 14 in an optical transmission system 1 in the second embodiment of the present invention. Fig. 16 shows a transmitting terminal 11 (Tx1-1 to 3 and Tx2-1 to 3) which is a transmitting user terminal, a receiving terminal 12 (Rx1-1 to 3 and Rx2-1 to 3) which is a receiving user terminal, and six relay nodes 83 (relay nodes A to D, F). These three relay nodes 83 relay the transmission of optical signals from the transmitting terminals 81 (Tx1-1 to 3 and Tx2-1 to 3) to the receiving terminals 82 (Rx1-1 to 3 and Rx2-1 to 3).

[0105] Fig. 16 illustrates an example in which M = 3 and N = 2. Fig. 16 shows a first group in which three optical fibers included in the transmission path from the transmitting terminal 11 (Tx1) to the receiving terminal 12 (Rx1) are grouped, and a second group in which three optical fibers included in the transmission path from the transmitting terminal 11 (Tx2) to the receiving terminal 12 (Rx2) are grouped.

[0106] In this case, since the upper limit of the number of optical amplifiers 14 available for each relay node 13 in each group is N as described above, the number of optical amplifiers 14 arranged in the relay nodes 13 of the first group and the number of optical amplifiers 14 arranged in the relay nodes 13 of the second group are always less than or equal to N. For example, as shown in Fig. 16, two optical amplifiers 14 are required for each group at relay nodes B, D, and F, and one optical amplifier 14 is required for each group at relay nodes A and C.

[0107] In this way, according to the second embodiment, by distributing the optical amplifiers 14 across multiple optical fibers, the optical amplifiers 14 can be prevented from concentrating at a specific relay node 13 when switching the transmission path, and the number of optical amplifiers 14 provided at the relay node 13 can be reduced to N or less.

[0108] Although the case where M=3 and N=2 is illustrated here, the present invention is not limited to this configuration. Also, as long as the condition that "M optical fibers are grouped in each transmission path, and the upper limit of the number m of optical amplifiers 14 available for each relay node in each group is set to N," is satisfied, the arrangement of relay nodes 13 equipped with optical amplifiers 14 is not limited to the above example.

[0109] As described above, the optical transmission system in the second embodiment of the present invention can appropriately thin out the optical amplifiers 14 in a network in which the positions of user terminals and transmission paths change over time. The optical transmission system groups adjacent optical fibers passing through the same relay node 13 into one group, and determines the placement of the optical amplifiers 14 on a group basis, not on an optical fiber basis. In this way, the optical transmission system distributes the optical amplifiers 14 provided in the relay nodes 13 for each group, thereby avoiding concentration of the optical amplifiers 14 at a specific relay node 13.

[0110] The optical transmission system in the second embodiment determines the placement of the optical amplifiers 14 so that the number of optical amplifiers 14 per relay node 13 is, for example, N or less. The optical transmission system sets the number of optical fibers to be grouped to M, and the upper limit of the number of optical amplifiers 14 per relay node 13 in each group to N, and performs calculations such as transmission simulations on a brute-force basis for all patterns that can arise from the values ​​of M and N.

[0111] This makes it possible to derive a combination of installation positions of optical amplifiers 14 that can achieve error-free operation in the optical transmission system and that reduces the number of optical amplifiers 14. Therefore, the optical transmission system in the second embodiment of the present invention can reduce the number of optical amplifiers 14 to be installed in relay nodes 13.

[0112] In the above-described first and second embodiments, attention is paid to all relay nodes 13 between the transmitting terminal 11 (Tx) and the receiving terminal 12 (Rx), but attention may be paid to only some of the relay nodes 13 in the transmission path. Fig. 17 is a diagram for explaining another method of arranging optical amplifiers in the optical transmission system in each embodiment of the present invention.

[0113] Specifically, for example, as shown in Fig. 17, it is assumed that the optical amplifiers 14 are thinned out in relay node A, and that relay node B adjacent to relay node A is equipped with optical amplifiers 14. It is also assumed that the transition of the signal strength in this case is between Pmax and Pmin, as shown in the lower part of Fig. 17, for example, and that an error-free optical signal transmission is possible.

[0114] For example, in the configuration shown in Fig. 17, the relay node 13 equipped with the optical amplifier 14 is changed from relay node B to relay node A as shown in Fig. 18. Fig. 18 is a diagram for explaining another method of arranging optical amplifiers in the optical transmission system in each embodiment of the present invention. The transition of the signal intensity in this case is also within the range between Pmax and Pmin as shown in the lower part of Fig. 18, for example, and an error-free optical signal transmission is possible.

[0115] In this way, if error-free transmission is possible even if the relay nodes 13 in which the optical amplifiers 14 are arranged are swapped, such swapping can prevent the optical amplifiers 14 from concentrating at a specific relay node 13. Figure 19 is a diagram for explaining another method of arranging optical amplifiers in the optical transmission system in each embodiment of the present invention. For example, as shown in Figure 19, by changing the relay node 13 in which the optical amplifiers 14 are arranged from relay node B to relay node A for only one optical fiber (the second optical fiber in Figure 19), it becomes possible to prevent the optical amplifiers 14 from concentrating at a specific relay node 13 (for example, relay node B).

[0116] According to the above-described embodiment, the optical amplifier placement support device includes an acquisition unit and a determination unit. For example, the optical amplifier placement support device is the relay node 13 in the embodiment or a device other than the relay node 13, the acquisition unit is the transmission path information acquisition unit 135 in the embodiment, and the determination unit is the optical amplifier necessity determination unit 136.

[0117] The acquisition step acquires transmission route information indicating the configuration of a network that transmits an optical signal via a plurality of relay nodes and the transmission route of the optical signal transmitted by the network. For example, the relay node is relay node 13 in the embodiment, and the network is an all-optical network in the embodiment. The determination unit groups a plurality of optical fibers passing through the same relay node based on the transmission route information, and determines the necessity of optical amplification at each relay node for each group of optical fibers, thereby determining the placement of optical amplifiers in the network. For example, the groups are the first group and the second group in the embodiment, and the optical amplifier is optical amplifier 14 in the embodiment.

[0118] In addition, when the number of optical fibers grouped at a relay node is M and the number of optical amplifiers per relay node in each group is N, the above-mentioned determination unit may perform a simulation of optical signal transmission for possible combinations of the values ​​of M and N, and determine the placement of the optical amplifiers based on the results of the simulation.

[0119] The above-mentioned determination unit may calculate the bit error rate at the receiver receiving the optical signal for each pattern by simulation, and determine the placement of the optical amplifiers based on the calculated bit error rate. For example, the receiver is the receiving terminal 12 (Rx) and the transmitting / receiving terminal 10 (TRx) in the embodiment.

[0120] In addition, the above-mentioned determination unit may determine the placement of the optical amplifiers so that the signal strength value of the optical signal passing through the relay node is equal to or greater than the signal strength value at which an increase in bit error rate occurs due to a decrease in the optical signal-to-noise ratio (OSNR).

[0121] The determination unit may determine the placement of the optical amplifiers so that the signal strength of an optical signal passing through a relay node is equal to or less than the signal strength affected by the nonlinear optical effect.

[0122] A part of the optical transmission system in each of the above-mentioned embodiments may be realized by a computer. In that case, a program for realizing this function may be recorded in a computer-readable recording medium, and the program recorded in the recording medium may be read into a computer system and executed to realize the function. The term "computer system" as used herein includes hardware such as an OS and peripheral devices. The term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into a computer system. The term "computer-readable recording medium" may also include a medium that dynamically holds a program for a short period of time, such as a communication line when a program is transmitted via a network such as the Internet or a communication line such as a telephone line, and a medium that holds a program for a certain period of time, such as a volatile memory inside a computer system that is a server or client in that case. The above-mentioned program may be a program for realizing a part of the above-mentioned function, or may be a program that can realize the above-mentioned function in combination with a program already recorded in the computer system, or may be a program that is realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0123] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and designs that do not deviate from the gist of the present invention are also included. [Explanation of symbols]

[0124] 1...optical transmission system, 10...transmitting / receiving terminal, 11...transmitting terminal, 12...receiving terminal, 13...relay node, 14...optical amplifier, 15...concentrator, 81...transmitting terminal, 82...receiving terminal, 83...relay node, 84...optical amplifier, 85...concentrator, 130-1 to 3...input / output port, 131...circulator, 132...optical switch, 135...transmission path information acquisition unit, 136...optical amplifier necessity determination unit, 137...optical switch control unit

Claims

1. an acquisition step of acquiring transmission route information indicating a configuration of a network that transmits an optical signal via a plurality of relay nodes and a transmission route of the optical signal transmitted by the network; a determining step of grouping a plurality of optical fibers passing through the same relay node based on the transmission path information, and determining the necessity of optical amplification at each of the relay nodes for each group of the optical fibers, thereby determining the placement of optical amplifiers in the network; An optical amplifier arrangement method comprising:

2. In the determining step, when the number of the optical fibers grouped at the relay node is M and the number of the optical amplifiers per relay node in each group is N, a simulation of the transmission of the optical signal is performed for possible combinations of the values ​​of M and N, and the arrangement of the optical amplifiers is determined based on the results of the simulation.

2. The optical amplifier arrangement method according to claim 1.

3. In the determining step, a bit error rate at a receiver that receives the optical signal is calculated for each of the patterns by the simulation, and an arrangement of the optical amplifiers is determined based on the calculated bit error rate.

3. The optical amplifier arrangement method according to claim 2.

4. In the determining step, the arrangement of the optical amplifiers is determined so that the signal strength value of the optical signal passing through the relay node is equal to or greater than the signal strength value at which an increase in the bit error rate occurs due to a decrease in the optical signal-to-noise ratio.

4. The optical amplifier arrangement method according to claim 3.

5. In the determining step, the arrangement of the optical amplifiers is determined so that the signal strength value of the optical signal passing through the relay node is equal to or less than the signal strength value affected by the nonlinear optical effect.

5. The optical amplifier arrangement method according to claim 3 or 4.

6. an acquisition unit that acquires a configuration of a network that transmits an optical signal via a plurality of relay nodes and transmission path information that indicates a transmission path of the optical signal transmitted by the network; a determination unit that determines an arrangement of optical amplifiers in the network by grouping a plurality of optical fibers passing through the same relay node based on the transmission path information and determining whether optical amplification is required at each of the relay nodes for each group of the optical fibers; An optical amplifier placement support device comprising:

7. an acquisition unit that acquires a configuration of a network in which an optical signal is transmitted via a plurality of relay devices and transmission path information indicating a transmission path of the optical signal transmitted by the network; a determination unit that groups a plurality of optical fibers passing through the own device or a plurality of optical fibers passing through the same relay device other than the own device based on the transmission path information, and determines whether optical amplification is required in each of the relay devices for each group of the optical fibers, thereby determining the placement of optical amplifiers in the network; A relay device comprising:

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