Route search device and route search method

Abstract

A route search device (1) is provided with: a route calculation unit (111) which stores information on a network for route search taking a transmission device as a node, and information on a network for signal noise calculation taking the transmission device and an amplifier as nodes; a route calculation unit (111) which searches for routes one hop at a time by using the network for route search; and a loss calculation unit (112) which calculates a signal-to-noise ratio indicating the transmission loss of the route by using the network for signal noise calculation. When the calculated signal-to-noise ratio falls below a threshold value of the signal-to-noise ratio, the route calculation unit (111) searches for a route assuming that reproduction relay processing is to be performed.

Description

Route search device and route search method

[0001] The present invention relates to a route search device and a route search method for searching for a route in an optical transmission network.

[0002] An optical transmission network realizes communication using optical signals and is a backbone network for IP (Internet Protocol) communication networks, etc. The optical transmission network is composed of multiple nodes and edges that connect the nodes.

[0003] In optical transmission networks, the cost of communication (distance between two points) has traditionally varied depending on the edge, requiring the selection of a transmission route that takes cost into consideration. A transmission route is the path of an optical signal from a source node to a destination node, and refers to the nodes and edges through which the optical signal passes between the source node and the destination node. Hereinafter, "transmission route" will also be simply referred to as "route." A commonly used route design method is, for example, the Dijkstra method, which finds the route from the source node to the destination node with the lowest cost (hereinafter also referred to as the "shortest route").

[0004] Furthermore, as a method for designing routes for multiple routes, for example, a method using the k-SPF algorithm has been proposed (see Non-Patent Document 1). In the method using the k-SPF algorithm, k routes that do not overlap with each other (overlapping nodes, edges, etc.) can be selected in order of lowest cost as pairs of active and backup routes that pass through specified nodes.

[0005] Hiroshi Matsuura and six others, "Redundant Route Configuration in Optical Networks Using the k-SPF Algorithm," Institute of Electronics, Information and Communication Engineers, 2022 Institute of Electronics, Information and Communication Engineers Society Conference, Proceedings of the 2022 Society Conference of the Institute of Electronics, Information and Communication Engineers, Communications Lecture Papers 2, B-12-2 (2022)

[0006] Meanwhile, recent repeated improvements in communication equipment functionality and facility expansion have led to a situation in which communication equipment with different processing capabilities coexist. The most expensive equipment cost in optical transmission is regenerative repeating using transponders. Regenerative repeating is the process of restoring a transmitted signal that has been attenuated and noisy to its original state before transmission. Specifically, regenerative repeating realizes the 3R functions of optical amplification (re-amplification), waveform shaping (re-shaping), and timing regeneration (re-timing). In optical transmission networks where multiple transmission equipment coexists, the "shortest route" calculated using conventional methods may not necessarily be the "route with the lowest equipment cost," i.e., the route with the fewest regenerative repeats.

[0007] Traditionally, it has been said that there is a rough correlation between distance and the number of regenerative repeats. However, this is not always the case when trying to find a precise solution. In transmission equipment, the transponders that perform the processing required for regenerative repeats to remove signal noise account for the largest proportion of costs. Therefore, by deriving a route with fewer regenerative repeats in route design, it is possible to reduce transmission equipment costs. For this reason, a route search algorithm with fewer regenerative repeats is needed.

[0008] However, until now, it has been difficult to precisely consider the number of regenerative repeats when searching for a route. This is because it is difficult to model the noise that causes regenerative repeats. In optical transmission networks, regenerative repeats occur due to a degradation of the signal-to-noise ratio. In particular, amplifier loss (ASE noise), which is noise caused by amplifiers, generates noise with different amplitudes depending on the intensity of the light incident on the amplifier. When considering route search, even routes arriving at the same node differ in the intensity of the incident light due to differences in the routes up to that point, and therefore the amplitude of the noise also differs. Therefore, when the amplitude of this noise is set as a weight in route search, it does not apply to conventional static searches, i.e., searches in which the distance between nodes can be preset as a cost (weight), and therefore the problem could not be solved.

[0009] The present invention has been made in view of the above points, and an object of the present invention is to search for a route in an optical transmission network with a reduced number of regenerative repeats.

[0010] A route search device according to the present invention is a route search device that searches for a route from a start node to an end node in an optical transmission network including a plurality of nodes connected by edges, the route search device comprising: a memory unit that stores a network information database that stores topology information including a plurality of transmission devices that are nodes included in the optical transmission network and the arrangement of amplifiers that can be installed between the transmission devices; and using the topology information, information on a route search network in which the transmission devices having a regenerative repeating function of an optical signal are nodes, and information on a signal noise calculation network in which the transmission devices and the amplifiers are nodes, is stored in the network information database; the route search device comprises: a route calculation unit that uses the route search network to perform a route search hop by hop from the start node; and a loss calculation unit that uses the signal noise calculation network to calculate a signal-to-noise ratio that indicates the transmission loss of the route searched hop by hop, the route calculation unit being characterized in that when the signal-to-noise ratio calculated by the loss calculation unit falls below a readable signal-to-noise ratio threshold set in the terminal node of the route searched, the route search device searches for a route assuming that regenerative repeating processing will be performed.

[0011] According to the present invention, it is possible to search for a route in an optical transmission network with a reduced number of regenerative repeats.

[0012] 1 is a diagram for explaining a problem to be solved by a route search device according to an embodiment of the present invention. FIG. 1 is a diagram for explaining a regenerative repeating function of a ROADM. FIG. 1 is a diagram for explaining a problem when noise magnitude is used as a cost in a conventional route search method. FIG. 2 is a diagram for explaining that regenerative repeating is not taken into consideration in a conventional transmission loss calculation method. FIG. 2 is a diagram showing a route search network and a signal noise calculation network used in a route search device according to an embodiment of the present invention. FIG. 3 is a diagram showing the overall configuration of a route search system including a route search device according to an embodiment of the present invention. FIG. 4 is a functional block diagram showing the configuration of a route search device according to an embodiment of the present invention. FIG. 5 is a diagram showing the timing of measuring GSNR in a ROADM. FIG. 6 is a flowchart showing the flow of processing by a route search device according to an embodiment of the present invention. FIG. 7 is a diagram showing initial values ​​of an execution example of a route search device according to an embodiment of the present invention. FIG. 8 is a diagram showing route search processing for the first hop by a route search device according to an embodiment of the present invention. FIG. 9 is a diagram showing route search processing for the second hop by a route search device according to an embodiment of the present invention. FIG. 10 is a diagram showing route search processing for the third hop by a route search device according to an embodiment of the present invention. FIG. 11 is a diagram showing route search processing for the fourth hop by a route search device according to an embodiment of the present invention. FIG. 12 is a diagram showing route search processing for the fifth hop by a route search device according to an embodiment of the present invention. FIG. 13 is a diagram showing the results of a route search by a route search device according to an embodiment of the present invention.

[0013] First, the details of the problem to be solved by the route search device 1 according to this embodiment (see FIG. 7 described later) and an overview of the processing of the route search device 1 will be described.

[0014] In an optical transmission network where multiple transmission devices are mixed, as described above, there are cases where the route with the shortest distance (shortest route) is not the route with the lowest transmission equipment cost (route with the fewest number of regenerative repeats).

[0015] Fig. 1 is a diagram for explaining a problem to be solved by a route search device according to this embodiment. A hypothetical model of an optical transmission network is indicated by the reference numeral 50 in Fig. 1. Here, buildings A, C, D, and E are buildings equipped with ROADMs (Reconfigurable Optical Add / Drop Multiplexers), which are transmission devices with regenerative repeating functions. Building B is a building equipped with an AMP (amplifier).

[0016] Here, ROADM is a system that adds / drops wavelengths to optical signals. As shown in Figure 2, ROADM 6 branches an optical path signal that requires regenerative repeating at WSS (wavelength selective switch) 62 via preamplifier 61, performs photoelectric conversion (optical signal → electrical signal) at transponder 63, and regenerates the signal at regenerator 64. ROADM 6 further performs photoelectric conversion (electrical signal → optical signal) at transponder 63, multiplexes the signal at WSS 62, and transmits it to the next node via booster amplifier 65. Therefore, regenerative repeating can only be performed in buildings equipped with ROADM 6, and cannot be performed in buildings that only use amplifiers for optical amplification.

[0017] Here, as shown by reference numeral 50 in Fig. 1, in the case where building A is the starting point and building D is the ending point, there are two routes: a first route via building A → building B → building C → building D, and a second route via building A → building E → building D. The first route has a short total distance between each building and a low cost based on distance, but low fiber capacity (here, there is a lot of degradation in the signal-to-noise ratio, etc.). On the other hand, the second route has a longer total distance between each building than the first route and a high cost based on distance, but high fiber capacity (here, there is little degradation in the signal-to-noise ratio, etc.).

[0018] In a conventional method using the shortest route for route design, the first route (Building A → Building B → Building C → Building D) with the shortest distance would be selected (reference numeral 51 in FIG. 1). In this case, regenerative repeating may be required due to low fiber capacity. In other words, there is a possibility that a route that does not require regenerative repeating may not be selected.

[0019] In route design by the route search device 1 according to this embodiment, a route with the lowest transmission equipment cost (a route with the fewest number of regenerative repeats) is searched for, and therefore, a second route is selected in consideration of fiber capacity (reference numeral 52 in FIG. 1 ). Although the second route is longer and more circuitous than the first route, it is possible to select a route that does not require regenerative repeats.

[0020] Here, similar to conventional path search methods that set distance as the cost (weight) required for communication on edges between nodes, a method can be considered that uses the magnitude of noise as the cost required for communication. However, amplifier loss (ASE noise), which is noise caused by amplifiers in particular, generates noise of different magnitudes depending on the intensity of light incident on the amplifier. Therefore, even if the noise magnitude is used as the cost and edge costs are set in advance, as shown in Figure 3, for example, if the route to node "V3" is different, the cost between node "V3" and node "D" will be different (symbol x in Figure 3). Specifically, when node "V3" is reached via the route from node "S" → "V2" → "V3," the cost of the noise magnitude between node "V3" and node "D" is "2." On the other hand, when node "V3" is reached via the route from node "S" → "V1" → "V3," the cost of the noise magnitude between node "V3" and node "D" is "3." Therefore, since the cost varies depending on the route, this problem could not be solved by the conventional route search method in which the cost is set in advance when searching for a route.

[0021] Furthermore, the conventional technology also has the following problems. GNPy is known as an open-source library that is commonly used as an evaluation tool for optical transmission. GNPy can calculate the GSNR (Generalized Signal to Noise Ratio), which is the transmission loss upon reaching the final point (Building H) for a path from Building A to Building B to Building C to Building D to Building E to Building F to Building G to Building H, as shown in FIG. 4 . Here, it is assumed that Buildings A, D, F, and H are equipped with ROADMs, and Buildings B, C, E, and G are equipped with AMPs (amplifiers). The GSNR calculates, as noise between nodes, nonlinear interference (NLI) that occurs over the distance a signal travels through an optical fiber, and noise (ASE noise) that is carried on the signal due to the influence of amplified spontaneous emission (ASE) that occurs when the signal strength is amplified by an amplifier.

[0022] That is, with GNPy, it is possible to calculate the GSNR at the time of arrival at the final point (Building H), which reflects the transmission loss along the path from Building A to Building H, and as shown by symbol a in Figure 4, it is possible to confirm that the GSNR falls below the GSNR threshold (the limit value of the signal-to-noise ratio at which an optical signal can be regenerated) when the signal reaches Building H. However, since GNPy does not take into account the processes of route search and regenerative repeating, it is not possible to evaluate which building equipped with a ROADM should perform regenerative repeating, how many times regenerative repeating is required (the number of regenerative repeats), etc.

[0023] In the example of Fig. 4, since the GSNR falls below the threshold upon arrival at building F (symbol b in Fig. 4), regenerative repeating is required in building D, the building equipped with a ROADM one building before on the route (symbol c in Fig. 4). Furthermore, after regenerative repeating and signal amplification in building D, the GSNR exceeds the threshold upon arrival at building H (symbol d in Fig. 4), so the number of regenerative repeats required for the entire route is "1". To obtain such information on the number of regenerative repeats, the GSNR needs to be calculated for each hop.

[0024] Therefore, in the route search device 1 according to this embodiment, the route search and the calculation of the signal-to-noise weight are separated, and the route search proceeds while calculating the noise (signal-to-noise ratio) generated by transmission for each hop in the route search. Specifically, as shown in FIG. 5 , a route search network 71 and a signal-to-noise calculation network 72 are prepared, and the route search proceeds while exchanging information between them. The signal-to-noise calculation network 72 regards the deterioration of signal quality (deterioration of the signal-to-noise ratio) as a weight in the route search, and performs the route search while taking into account the weight that dynamically changes during the route search. When the transmission loss ("GSNR loss" described later) becomes large, the transponder in the relay node cannot decode the signal. Therefore, when the signal-to-noise ratio falls below a readable threshold (GSNR threshold), a regenerative relay process is performed, and the route search proceeds while performing this process. Note that the regenerative relay process is performed at the previous relay node when the signal reaches a relay node (transmission device) that falls below the threshold.

[0025] Next, a route search system 1000 including a route search device 1 according to this embodiment will be described in detail. FIG. 6 is a diagram showing the overall configuration of the route search system 1000 including the route search device 1 according to this embodiment. The route search system 1000 includes an optical transmission network 100 including a plurality of nodes and edges (optical fibers) connecting the nodes, and a route search device 1 that searches for and designs transmission paths (routes) in the optical transmission network 100. The nodes included in the optical transmission network 100 are, as in conventional route searches, transmission devices such as optical cross connect (OXC) devices and ROADMs. However, in practice, one or more AMPs (amplifiers) may be provided between the transmission devices. In this embodiment, the route search network 71 regards the transmission devices as nodes. Meanwhile, the signal noise calculation network 72 regards the AMPs (amplifiers) as nodes in addition to the transmission devices, and performs signal noise calculation (see FIG. 5).

[0026] 7 is a functional block diagram showing the configuration of a route search device 1 according to this embodiment. As shown in FIG. 7, the route search device 1 includes a control unit 10, an input / output unit 11, and a storage unit 12.

[0027] The input / output unit 11 is composed of an input / output I / F (Interface), a communication I / F, etc. The input / output unit 11 receives topology information indicating connections between nodes (repeaters and amplifiers) and edges of the optical transmission network 100, and search conditions for performing a route search, from a management device (not shown) of the route search system 1000, etc. The search conditions include, for example, a start node and an end node, the number k of routes (k is an integer equal to or greater than 1) to be output as a result of the route search, and a readable signal-to-noise ratio threshold (here, "GSNR threshold") set in each node (transmission device).

[0028] The storage unit 12 is configured with a ROM (Read Only Memory), a RAM, an HDD (Hard Disk Drive), etc. The storage unit 12 stores a network information database (DB) 200 and a route information database (DB) 300.

[0029] The network information DB 200 stores topology information indicating the connections between nodes (transmission devices, amplifiers) and edges of the optical transmission network 100, obtained from a management device (not shown) of the route search system 1000, etc. In addition, using this topology information, information (topology information) of a route search network 71 in which nodes are transmission devices (relay devices) equipped with a regenerative repeating function for optical signals, and information (topology information) of a signal noise calculation network 72 in which nodes are transmission devices (relay devices) and amplifiers, are stored in the network information DB 200. The route information DB 300 stores a route list 310 in which information on route candidates created by the route calculation unit 111, information on the k routes ultimately searched, and information such as a readable signal-to-noise ratio threshold (GSNR threshold) set for each node are recorded (details will be described later).

[0030] The control unit 10 controls the entire route search device 1 and includes a route search unit 110. The route search unit 110 includes a route calculation unit 111 and a loss calculation unit 112.

[0031] In a network (route search network 71) in which transmission devices (relay nodes) such as ROADMs with regenerative relay functions are the targets of route search, the route search unit 110 (route calculation unit 111) selects, based on topology information, a route with the fewest number of regenerative relays and the highest GSNR as the selected route, starting from the source node. Specifically, the route calculation unit 111 first selects the route with the fewest number of regenerative relays, and then selects the route with the highest GSNR as the selected route. Next, the route calculation unit 111 creates route candidates by adding the next-hop node (adjacent node) at the terminal node of the selected route. The route calculation unit 111 then outputs the created route candidates to the loss calculation unit 112.

[0032] Furthermore, when the loss calculation unit 112 calculates the transmission loss for a route candidate (for example, a GSNR loss (GSNR loss) that can be calculated using GNPy), the route calculation unit 111 determines whether the signal-to-noise ratio (GSNR) upon arrival at an adjacent node is below a signal-to-noise ratio threshold (GSNR threshold) set for each node. If the GSNR is below the GSNR threshold, the route calculation unit 111 determines that regenerative relay processing is necessary, resets the GSNR of the terminal node of the selected route to its initial value, and adds "1" to the count of the number of regenerative relays. The route calculation unit 111 repeats the creation of route candidates by selecting this route and the process of determining the GSNR threshold. At this time, the route calculation unit 111 generates a route list 310 that indicates "route information" including the searched route information, GSNR, the number of regenerative relays, etc. for each terminal node, and stores the route list 310 in the route information DB 300. As a result, the route calculation unit 111 searches for k routes with a small number of regenerative relays.

[0033] The route search unit 110 (loss calculation unit 112) calculates the signal-to-noise ratio (GSNR) and transmission loss (GSNR loss) for the route candidate created by the route calculation unit 111. For example, the loss calculation unit 112 calculates the GSNR using GNPy, thereby calculating the transmission loss (GSNR loss) caused by NLI and ASE noise.

[0034] When calculating the GSNR loss using GNPy, the loss calculation unit 112 calculates the GSNR at a point where a signal output from an object representing the ROADM 6 (a main component of the ROADM) via a booster amplifier 65 passes through a preamplifier 61 and reaches the object representing the ROADM 6, as shown in Fig. 8. This eliminates the need to further break down and calculate GNPy in accordance with the internal configuration of the ROADM 6, thereby reducing the operation cost.

[0035] <Processing Flow> The processing flow of the route search device 1 will be described below with reference to a specific example. FIG. 9 is a flowchart showing the processing flow of the route search device 1 according to this embodiment. The route search unit 110 of the route search device 1 processes the route search network 71 and the signal noise calculation network 72 separately. In the route search network 71, ROADMs with regenerative repeating functions are treated as nodes. Amplifiers do not have a route switching function and therefore have no effect on route search. Therefore, amplifiers are not treated as nodes. On the other hand, in the signal noise calculation network 72, amplifiers as well as ROADMs are treated as nodes. The loss calculation unit 112 calculates loss using the GSNR calculated by GNPy.

[0036] The route search unit 110 performs the search while updating a route list 310 (details of which will be described later) that stores information on a readable signal-to-noise ratio threshold (here, "GSNR threshold") that is preset for each node (excluding the amplifier), GSNR information associated with the route to the node, and route information such as the number of regenerative relays. Furthermore, of the processes shown in Fig. 9, the processes enclosed by single lines are executed by the route calculation unit 111, and the processes enclosed by double lines are executed by the loss calculation unit 112.

[0037] First, the route search unit 110 (route calculation unit 111) of the route search device 1 selects a route with the smallest number of regenerative relays (3R count) and the largest GSNR (step S1). The route selected in step S1 is referred to as the "selected route." Here, the number of regenerative relays (3R count) has an initial value of "0," and the GSNR is set to, for example, "100," as the initial value before transmission loss.

[0038] Next, the route calculation unit 111 extracts adjacent nodes (hop destination nodes) directly connected to the terminal node of the selected route by edges, and creates route candidates by adding the adjacent nodes to the selected route (step S2). Note that if there are multiple adjacent nodes, multiple route candidates are created. The route calculation unit 111 outputs information about these route candidates to the loss calculation unit 112.

[0039] Next, upon receiving the information on the route candidate, the route search unit 110 (loss calculation unit 112) calculates the transmission loss of the route candidate (step S3). Specifically, the loss calculation unit 112 calculates the GSNR loss by calculating the GSNR between nodes (ROADMs) using, for example, GNPy.

[0040] The route calculation unit 111 then determines whether the signal-to-noise ratio (GSNR) of the route candidate when it reaches the adjacent node is below a readable signal-to-noise ratio threshold (GSNR threshold) set for each node (step S4). If the signal-to-noise ratio (GSNR) of the route candidate is not below the threshold (step S4 → No), that is, if it is equal to or greater than the threshold, the process proceeds to the next step S5.

[0041] In step S5, the route calculation unit 111 stores information (route information) about the route candidates and the like in the route list 310. Next, the route calculation unit 111 determines whether k routes are stored at the end node of the route list 310 (step S6). If k routes are stored (step S6 → Yes), the process ends. On the other hand, if k routes are not stored (step S6 → No), the process returns to step S1 and continues.

[0042] Also, in step S4, if the signal-to-noise ratio (GSNR) at the time of reaching the adjacent node in the route candidate is below the readable signal-to-noise ratio threshold (GSNR threshold) set for each node (step S4 → Yes), the route calculation unit 111 proceeds to the next step S7.

[0043] In step S7, the route calculation unit 111 resets the signal-to-noise ratio (GSNR) of the route information of the selected route to the initial value (100). That is, it is assumed that the signal has been regenerated by the regenerative relay processing of the ROADM and has returned to the initial value with no transmission loss.

[0044] Next, the route calculation unit 111 adds "1" to the number of regeneration relays (3Rcount) in the route information of the selected route (step S8).Then, the route calculation unit 111 outputs information on the route candidates that have been regeneration relayed at the end nodes of the selected route to the loss calculation unit 112.

[0045] Next, when the route search unit 110 (loss calculation unit 112) receives the information on the route candidate again, it calculates the transmission loss of the route candidate after regeneration and relaying (step S9). Specifically, the loss calculation unit 112 calculates the GSNR loss after regeneration and relaying by calculating the GSNR between nodes (ROADMs) using, for example, GNPy.

[0046] Then, the route calculation unit 111 determines whether the signal-to-noise ratio (GSNR) of the route candidate when it reaches the adjacent node after regenerative relay is below the readable signal-to-noise ratio threshold (GSNR threshold) set in each node (step S10). If the signal-to-noise ratio (GSNR) of the route candidate is not below the threshold (step S10 → No), that is, if it is above the threshold, proceed to next step S5, store information (route information) of the route candidate, etc. in the route list 310, and proceed with processing. On the other hand, if the transmission loss (GSNR) of the route candidate is below the threshold (step S10 → Yes), even with regenerative relay, it cannot exceed the readable signal-to-noise ratio threshold (GSNR threshold) at the adjacent node, so stop route search for this route (step S11: route discard). Then, return to step S1 to continue processing.

[0047] The processing flow of the route search device 1 will be described below with reference to a specific example. As a premise, the route search unit 110 of the route search device 1 performs route search and transmission loss calculation using two networks: a route search network 71 and a signal noise calculation network 72. In this case, ROADMs are used as nodes in the route search network 71. On the other hand, ROADMs and amplifiers (AMPs) are used as nodes in the signal noise calculation network 72. Furthermore, to show that a detour (longer distance) route may be able to reduce the number of regenerative relays, distance is also calculated as a weight in the following processing.

[0048] In the example shown below, the k-SPF algorithm is used as the route search algorithm. A GSNR threshold is used as the threshold for the readable signal-to-noise ratio, and an arbitrary value is set in advance for each node. The GSNR loss between ROADMs is NLI and ASE noise, and is calculated by the loss calculation unit 112 using, for example, GNPy. The initial value of GSNR is assumed to be "100." There is no node overlap in the route to be searched. Furthermore, the number of searches to be finally output is assumed to be k=2.

[0049] FIG. 10 is a diagram showing the initial values ​​of an execution example of the route search device 1 according to this embodiment. As shown in FIG. 10, the route search device 1 searches for a route with a small number of regenerative relays in the optical transmission network 100 (FIG. 6) to be searched, using information from the route search network 71 and the signal noise calculation network 72. In the route search network 71, weights based on the distance (length) between nodes are set in advance. In addition, in the signal noise calculation network 72, it is assumed that an AMP (amplifier) ​​is set between the nodes. Note that, since there is no amplifier between node S and node V1, no AMP noise occurs, and noise occurs due to NLI (symbol e in FIG. 10).

[0050] Furthermore, the route search device 1 searches for a route from the start node "node S" to the end node "node D" while updating the route list 310 for each hop. As shown in FIG. 10 , the route list 310 stores GSNR threshold information associated with each node, and stores calculation results for each hop in the list items. The list items store route information in a predetermined format as shown below: "Route: GSNR, number of regeneration relays (, route length)" In the initial values ​​shown in FIG. 10 , the start node node S, the initial GSNR value "100", the number of regeneration relays "0", and the route length "0" are stored in the following format: "S: 100, 0 (, 0)" Note that the route information stores the calculation result of "route length" for comparison with conventional shortest route searches, but this is not essential in this embodiment. Below, the processing of the route search device 1 will be described with reference to the steps shown in FIG. 9. In this case, among the tables shown in Figures 11 to 15, tables surrounded by thin single lines indicate the results executed by the path calculation unit 111, and tables surrounded by double lines indicate the results executed by the loss calculation unit 112.

[0051] <First Hop> FIG. 11 is a diagram illustrating the route search process for the first hop by the route search device 1. First, the route search unit 110 (route calculation unit 111) of the route search device 1 selects a route with the smallest number of regenerative relays (3R count) and the largest GSNR (step S1). Here, since node S is stored as the route in the route information as the initial value, as shown in FIG. 10, node S is selected as the initial value of the "selected route." For ease of explanation, the route selected in step S1 (selected route) for each hop is marked with a star in the route list 310 shown in FIG. 11 and subsequent figures. Here, as shown in the route information for node S, the initial value of the number of regenerative relays is "0" and the initial value of the GSNR is "100." In addition, in the route list 310 of FIG. 11, the route information of the route selected as the selected route is indicated by a strikethrough, indicating that it will not be selected next time or later.

[0052] Next, the route calculation unit 111 extracts adjacent nodes (hop destination nodes) that are directly connected to the terminal node of the selected route by edges, and creates route candidates by adding the adjacent nodes to the selected route (step S2). Here, nodes V1 and V2 are extracted as adjacent nodes of node S, which is the selected route, and route candidates "S-V1" and "S-V2" are created (reference symbol A1 in FIG. 11). Then, the route calculation unit 111 outputs information about these route candidates to the loss calculation unit 112.

[0053] Next, upon receiving the information about the route candidate, the route search unit 110 (loss calculation unit 112) calculates the transmission loss of the route candidate (step S3). The loss calculation unit 112 calculates the GSNR between nodes S and V1 to be "95" using, for example, GNPy, and calculates the GSNR loss to be "-5" based on the difference from the initial value "100". The loss calculation unit 112 also calculates the GSNR between nodes S and V2 to be "75" and calculates the GSNR loss to be "-25" based on the difference from the initial value "100" (reference symbol A2 in FIG. 11).

[0054] The route calculation unit 111 then determines whether the signal-to-noise ratio (GSNR) of the route candidate when it reaches the adjacent node is below the readable signal-to-noise ratio threshold (GSNR threshold) set for each node (step S4). Here, the GSNR "95" of route S-V1 is equal to or greater than the GSNR threshold "70" set for node V1, and the GSNR "75" of route S-V2 is equal to or greater than the GSNR threshold "65" set for node V2. Therefore, it is determined that the GSNR is not below the GSNR threshold (reference A3 in FIG. 11: threshold determination "OK"). Therefore, the route calculation unit 111 stores the route information of routes S-V1 and S-V2 in the route list 310 (step S5, see FIG. 11). Here, "S-V1: 95, 0(, 3)" is stored as route information in the list for node V1 of route list 310, and "S-V2: 75, 0(, 5)" is stored as route information in the list for node V2 of route list 310. Note that the route length is calculated and stored by route calculation unit 111. For the following hops, route calculation unit 111 generates route information in a similar format.

[0055] Next, the route calculation unit 111 determines whether k routes are stored in the end node of the route list 310 (step S6). In this case, since the number of routes stored in node D, which is the end node of the route list 310, is 0 (step S6 → No), the process returns to step S1 and continues.

[0056] <Second Hop> FIG. 12 is a diagram showing the route search process for the second hop by the route search device 1. First, the route search unit 110 (route calculation unit 111) of the route search device 1 selects a route with the smallest number of regenerative relays (3R count) and the largest GSNR (step S1). Here, referring to the route list 310 at the first hop shown in FIG. 11, the route with the smallest number of regenerative relays and the largest GSNR is selected as the selected route from among the routes S-V1 and S-V2. The number of regenerative relays for both the routes S-V1 and S-V2 is "0." Furthermore, the GSNR of the route S-V1 is "95," and the GSNR of the route S-V2 is "75." Therefore, the route calculation unit 111 selects the route S-V1 with the largest GSNR as the selected route, as shown in the route list 310 in FIG. 12.

[0057] Next, the route calculation unit 111 extracts adjacent nodes (hop destination nodes) that are directly connected to the terminal node of the selected route by an edge, and creates a route candidate by adding the adjacent nodes to the selected route (step S2). Here, node V3 is extracted as an adjacent node of the terminal node (V1) of route S-V1, which is the selected route, and creates a route candidate "S-V1-V3" (symbol B1 in FIG. 12). Then, the route calculation unit 111 outputs information about this route candidate to the loss calculation unit 112.

[0058] Next, upon receiving the information about the route candidate, the route search unit 110 (loss calculation unit 112) calculates the transmission loss of the route candidate (step S3). The loss calculation unit 112 calculates the GSNR between nodes S-V1-V3 to be "40" using, for example, GNPy, and calculates the GSNR loss to be "-55" from the difference with the GSNR "95" between route S-V1 (symbol B2 in FIG. 12).

[0059] The route calculation unit 111 then determines whether the signal-to-noise ratio (GSNR) of the route candidate when it reaches the adjacent node is below a readable signal-to-noise ratio threshold (GSNR threshold) set for each node (step S4). Here, it is determined that the GSNR of the route S-V1-V3 is "40" below the GSNR threshold of "60" set for the node V3 (symbol B3 in FIG. 12: threshold determination "NG", step S4 → Yes).

[0060] Next, the route calculation unit 111 resets the signal-to-noise ratio (GSNR) of the route information of the selected route to its initial value (100) (step S7). Then, the route calculation unit 111 adds "1" to the number of regenerative relays (3Rcount) of the route information of the selected route (step S8). As a result, as shown by reference symbol B4 in FIG. 12, the route information of the selected route becomes "S-V1:100,1(,3)". Then, the route calculation unit 111 outputs information on the route candidate (route S-V1-V3) regenerated and relayed at the terminal node (V1) of the selected route to the loss calculation unit 112.

[0061] Next, when the route search unit 110 (loss calculation unit 112) receives the route candidate information again, it calculates the transmission loss of the route candidate after regenerative relay (step S9). The loss calculation unit 112 calculates the GSNR between nodes S-V1-V3 as "55" using GNPy, and calculates the GSNR loss as "-45" from the difference from the initial value "100" (symbol B5 in FIG. 12).

[0062] Then, the route calculation unit 111 determines whether the signal-to-noise ratio (GSNR) of the route candidate when it reaches the adjacent node after regenerative relay is below the readable signal-to-noise ratio threshold (GSNR threshold) set for each node (step S10). Here, it is determined that the GSNR "55" of the route S-V1-V3 after regenerative relay is below the GSNR threshold "60" set for node V3 (symbol B6 in FIG. 12: threshold determination "NG", step S10 → Yes). In this case, even with regenerative relay, the signal-to-noise ratio cannot exceed the readable signal-to-noise ratio threshold (GSNR threshold) at the adjacent node, so the route search for this route is stopped (symbol f in FIG. 12, step S11: route discard). Then, the process returns to step S1 and continues.

[0063] <Third Hop> Fig. 13 is a diagram showing the route search process for the third hop by the route search device 1. First, the route search unit 110 (route calculation unit 111) of the route search device 1 selects a route with the smallest number of regenerative relays (3Rcount) and the largest GSNR (step S1). Here, referring to the route list 310 at the second hop shown in Fig. 12, route S-V2 is selected as the selected route, which has the smallest number of regenerative relays and the largest GSNR (see route list 310 in Fig. 13).

[0064] Next, the route calculation unit 111 extracts adjacent nodes (hop destination nodes) that are directly connected to the terminal node of the selected route by an edge, and creates route candidates by adding the adjacent nodes to the selected route (step S2). Here, nodes V3 and V4 are extracted as adjacent nodes of the terminal node (V2) of route S-V2, which is the selected route, and route candidates "S-V2-V3" and "S-V2-V4" are created (reference symbol C1 in FIG. 13). Then, the route calculation unit 111 outputs information about these route candidates to the loss calculation unit 112.

[0065] Next, upon receiving the information about the route candidates, the route search unit 110 (loss calculation unit 112) calculates the transmission loss of the route candidates (step S3). Using, for example, GNPy, the loss calculation unit 112 calculates the GSNR between nodes S-V2-V3 to be "62," and calculates the GSNR loss to be "-13" based on the difference from the GSNR of "75" between route S-V2. The loss calculation unit 112 also calculates the GSNR between nodes S-V2-V4 to be "55," and calculates the GSNR loss to be "-20" based on the difference from the GSNR of "75" between route S-V2 (reference symbol C2 in FIG. 13 ).

[0066] The route calculation unit 111 then determines whether the signal-to-noise ratio (GSNR) of the route candidate when it reaches the adjacent node is below the readable signal-to-noise ratio threshold (GSNR threshold) set for each node (step S4). Here, the GSNR "62" of the route S-V2-V3 is equal to or greater than the GSNR threshold "60" set for node V3, so it is determined that it is not below the GSNR threshold (reference symbol C3 in FIG. 13: threshold determination "OK", step S4 → No). On the other hand, it is determined that the GSNR "55" of the route S-V2-V4 is below the GSNR threshold "60" set for node V4 (reference symbol C3 in FIG. 13: threshold determination "NG", step S4 → Yes). Therefore, the route calculation unit 111 stores the route information of the route S-V2-V3 in the route list 310, as shown in the route list 310 in FIG. 13 (step S5). Next, the route calculation unit 111 determines whether k routes are stored in the end node of the route list 310 (step S6). In this case, since the number of routes stored in node D, which is the end node of the route list 310, is 0 (step S6 → No), the process returns to step S1 and continues.

[0067] On the other hand, since the path S-V2-V4 is below the threshold (step S4 → Yes), the path calculation unit 111 resets the signal-to-noise ratio (GSNR) of the path information of the selected path (path S-V2) to the initial value (100) (step S7). Then, the path calculation unit 111 adds "1" to the number of regenerative relays (3Rcount) of the path information of the selected path (step S8). As a result, as shown by reference symbol C4 in FIG. 13, the path information of the selected path becomes "S-V2: 100, 1 (, 5)." Then, the path calculation unit 111 outputs information on the path candidate (path S-V2-V4) regenerated and relayed at the terminal node (V2) of the selected path to the loss calculation unit 112.

[0068] Next, when the route search unit 110 (loss calculation unit 112) receives the route candidate information again, it calculates the transmission loss of the route candidate after regenerative relay (step S9). The loss calculation unit 112 calculates the GSNR between nodes S-V2-V4 as "85" using GNPy, and calculates the GSNR loss as "-15" from the difference from the initial value "100" (reference symbol C5 in FIG. 13).

[0069] Then, the route calculation unit 111 determines whether the signal-to-noise ratio (GSNR) of the route candidate at the time of arrival at the adjacent node after regeneration relay is below the readable signal-to-noise ratio threshold (GSNR threshold) set for each node (step S10). Here, the GNSR "85" of the route S-V2-V4 after regeneration relay is equal to or greater than the GNSR threshold "60" set for node V4, so it is determined that the GSNR is not below the GSNR threshold (reference C6 in FIG. 13: threshold determination "OK", step S10 → No). Therefore, the route calculation unit 111 stores the route information of the route S-V2-V4 in the route list 310 as shown in the route list 310 in FIG. 13 (step S5). Next, the route calculation unit 111 determines whether k routes are stored at the end node of the route list 310 (step S6). Here, since there are no routes stored in node D, which is the end node of the route list 310 (step S6→No), the process returns to step S1 and continues.

[0070] <Fourth Hop> Figure 14 is a diagram showing the route search process for the fourth hop by the route search device 1. First, the route search unit 110 (route calculation unit 111) of the route search device 1 selects the route with the smallest number of regenerative relays (3R count) and the largest GSNR (step S1). Here, by referring to the route list 310 at the third hop shown in Figure 13, the route with the smallest number of regenerative relays and the largest GSNR is selected as the selected route from among the routes S-V2-V3 and S-V2-V4. Here, since the number of regenerative relays for the route S-V2-V3 is "0" and the number of regenerative relays for the route S-V2-V4 is "1", the route S-V2-V3 with the smallest number of regenerative relays is selected as the selected route (see the route list 310 in Figure 14).

[0071] Next, the route calculation unit 111 extracts adjacent nodes (hop destination nodes) that are directly connected by edges to the terminal node of the selected route, and creates a route candidate by adding the adjacent nodes to the selected route (step S2). Here, node D, which is the end node, is extracted as an adjacent node to the terminal node (V3) of route S-V2-V3, which is the selected route, and creates a route candidate "S-V2-V3-D" (reference symbol D1 in FIG. 14). Then, the route calculation unit 111 outputs information about this route candidate to the loss calculation unit 112.

[0072] Next, upon receiving the information about the route candidate, the route search unit 110 (loss calculation unit 112) calculates the transmission loss of the route candidate (step S3). The loss calculation unit 112 calculates the GSNR between nodes S-V2-V3-D to be "51" using, for example, GNPy, and calculates the GSNR loss to be "-11" from the difference with the GSNR "62" between route S-V2-V3 (reference symbol D2 in FIG. 14).

[0073] Then, the route calculation unit 111 determines whether the signal-to-noise ratio (GSNR) of the route candidate when it reaches the adjacent node is below a readable signal-to-noise ratio threshold (GSNR threshold) set for each node (step S4). In this case, the GSNR "51" of the route S-V2-V3-D is equal to or greater than the GSNR threshold "50" set for node D, so it is determined that the GSNR is not below the GSNR threshold (reference symbol D3 in FIG. 14: threshold determination "OK", step S4 → No). Therefore, the route calculation unit 111 stores the route information of the route S-V2-V3-D in the route list 310 as shown in FIG. 14 (step S5).

[0074] Next, the route calculation unit 111 determines whether k routes are stored in the end node (node ​​D) of the route list 310 (step S6). In this case, since one route is stored in node D, which is the end node of the route list 310 (step S6 → No), the process returns to step S1 and continues.

[0075] <Fifth Hop> Fig. 15 is a diagram showing the route search process for the fifth hop by the route search device 1. First, the route search unit 110 (route calculation unit 111) of the route search device 1 selects a route with the smallest number of regenerative relays (3Rcount) and the largest GSNR (step S1). Here, referring to the route list 310 at the fourth hop shown in Fig. 14, the route S-V2-V4 is selected as the selected route, which has the smallest number of regenerative relays and the largest GSNR (see route list 310 in Fig. 15).

[0076] Next, the route calculation unit 111 extracts adjacent nodes (hop destination nodes) that are directly connected to the terminal node of the selected route by edges, and creates a route candidate by adding the adjacent nodes to the selected route (step S2). Here, node D, which is the end node, is extracted as an adjacent node to the terminal node (V4) of route S-V2-V4, which is the selected route, and creates a route candidate "S-V2-V4-D" (reference symbol E1 in FIG. 15). Then, the route calculation unit 111 outputs information about this route candidate to the loss calculation unit 112.

[0077] Next, upon receiving the information about the route candidate, the route search unit 110 (loss calculation unit 112) calculates the transmission loss of the route candidate (step S3). The loss calculation unit 112 calculates the GSNR between nodes S-V2-V4-D to be "64" using, for example, GNPy, and calculates the GSNR loss to be "-21" from the difference with the GSNR "85" between the route S-V2-V4 (reference symbol E2 in FIG. 15).

[0078] The route calculation unit 111 then determines whether the signal-to-noise ratio (GSNR) of the route candidate when it reaches the adjacent node is below a readable signal-to-noise ratio threshold (GSNR threshold) set for each node (step S4). Here, the GSNR of route S-V2-V4-D is "64," which is equal to or greater than the GSNR threshold "50" set for node D, so it is determined that the GSNR is not below the GSNR threshold (reference E3 in FIG. 15: threshold determination "OK," step S4 → No). Therefore, the route calculation unit 111 stores the route information of route S-V2-V4-D in the route list 310, as shown in FIG. 15 (step S5).

[0079] Next, the route calculation unit 111 determines whether k routes are stored in the end node (node ​​D) of the route list 310 (step S6). In this case, the number of routes stored in node D, which is the end node of the route list 310, is two (=k) (step S6 → Yes), so the process ends.

[0080] 16 is a diagram showing the results of a route search performed by the route search device 1. As shown in the route list 310 in FIG. 16, two routes from the start node S to the end node D are searched for. S-V2-V3-D: 51, 0(, 18) S-V2-V4-D: 64, 1(, 16)

[0081] The route S-V2-V3-D has a total distance-based route cost of "18." On the other hand, the route S-V2-V4-D has a total distance-based route cost of "16." However, the number of replays for route S-V2-V3-D is "0," and the number of replays for route S-V2-V4-D is "1." Therefore, route S-V2-V4-D has a short distance but a large number of replays (symbol g in FIG. 16). On the other hand, route S-V2-V3-D has a long distance but a small number of replays (symbol h in FIG. 16). In other words, according to the route search device 1, unlike conventional search results that use distance as cost, it is possible to prioritize the selection of routes with a small number of replays even if the distance is long.

[0082] <Hardware Configuration> The route search device 1 according to this embodiment is realized by, for example, a computer 900 as shown in Fig. 17. Fig. 17 is a hardware configuration diagram showing an example of the computer 900 that realizes the functions of the route search device 1 according to this embodiment. The computer 900 has a CPU (Central Processing Unit) 901, a ROM (Read Only Memory) 902, a RAM 903, an HDD (Hard Disk Drive) 904, an input / output I / F (Interface) 905, a communication I / F 906, and a media I / F 907.

[0083] The CPU 901 operates based on a program (route search program) stored in the ROM 902 or HDD 904, and performs control by the control unit 10 of the route search device 1 shown in Fig. 7. The ROM 902 stores a boot program executed by the CPU 901 when the computer 900 is started up, programs related to the hardware of the computer 900, and the like.

[0084] The CPU 901 controls an input device 910 such as a mouse or keyboard, and an output device 911 such as a display, via an input / output I / F 905. The CPU 901 acquires data from the input device 910 via the input / output I / F 905, and outputs generated data to the output device 911. Note that a GPU (Graphics Processing Unit) or the like may be used as a processor together with the CPU 901.

[0085] The HDD 904 stores programs executed by the CPU 901 and data used by the programs. The communication I / F 906 receives data from other devices such as a management device (not shown) via a communication network (e.g., NW (Network) 920) and outputs the data to the CPU 901, and also transmits data generated by the CPU 901 to other devices via the communication network.

[0086] The media I / F 907 reads a program or data stored in the recording medium 912 and outputs it to the CPU 901 via the RAM 903. The CPU 901 loads a program related to a target process from the recording medium 912 onto the RAM 903 via the media I / F 907, and executes the loaded program. The recording medium 912 is an optical recording medium such as a DVD (Digital Versatile Disc) or a PD (Phase Change Rewritable Disc), a magneto-optical recording medium such as an MO (Magneto Optical Disc), a magnetic recording medium, a conductive memory tape medium, a semiconductor memory, or the like.

[0087] For example, when the computer 900 functions as the route search device 1 according to this embodiment, the CPU 901 of the computer 900 executes a program loaded onto the RAM 903 to realize the functions of the route search device 1. Furthermore, the HDD 904 stores data in the RAM 903. The CPU 901 reads and executes a program related to a target process from the recording medium 912. Alternatively, the CPU 901 may read a program related to a target process from another device via a communication network (NW 920).

[0088] <Effects> The effects of the route search device 1 according to the present invention will be described below. The route search device 1 according to the present invention is a route search device 1 that searches for a route from a start node to an end node in an optical transmission network 100 including a plurality of nodes connected by edges, and the route search device 1 includes a storage unit 12 that stores a network information database 200 that stores topology information including the arrangement of a plurality of transmission devices (ROADMs) that are nodes included in the optical transmission network 100 and amplifiers (AMPs) that can be installed between the transmission devices, and uses the topology information to search for information on a route search network 71 in which nodes are transmission devices that have a function of regenerating and repeating optical signals, and the arrangement of the transmission devices and amplifiers. The network information database 200 stores information about a signal noise calculation network 72 having nodes, and includes a route calculation unit 111 that uses the route search network 71 to search for a route hop by hop from a start node, and a loss calculation unit 112 that uses the signal noise calculation network 72 to calculate a signal-to-noise ratio that indicates the transmission loss of the route searched for hop by hop, and the route calculation unit 111 searches for a route by assuming that regenerative relay processing will be performed when the signal-to-noise ratio calculated by the loss calculation unit 112 falls below a readable signal-to-noise ratio threshold set at the terminal node of the route searched for.

[0089] In this way, the route search device 1 prepares a route search network 71 and a signal noise calculation network 72, and performs route search hop by hop using the route search network 71, while taking into account deterioration of the signal-to-noise ratio when performing route search using the signal noise calculation network 72. The route search device 1 performs regenerative repeat processing when the signal-to-noise ratio falls below a readable threshold at the terminal node of a route searched using the route search network 71. This allows the route search device 1 to search for a route in the optical transmission network 100 with a reduced number of regenerative repeats.

[0090] In addition, in the route search device 1, the route calculation unit 111 stores the number of times regenerative relay processing has been performed, and when searching for a route hop by hop, it selects the route with the smallest number of regenerative relays and the largest signal-to-noise ratio calculated by the loss calculation unit as the route to be searched.

[0091] This allows the route search device 1 to search for a route in the optical transmission network 100 that minimizes the number of regenerative relays.

[0092] Furthermore, the route search device 1 is characterized in that the route calculation unit 111 performs regenerative relay processing at a transmission device that is the previous node on the route of a node whose signal-to-noise ratio has fallen below the threshold value for readability.

[0093] This allows the route search device 1 to reduce the number of times the regenerative relay process is performed, compared to performing the regenerative relay process at a node located further ahead on the route than the node immediately before the node that has fallen below the threshold.

[0094] The present invention is not limited to the above-described embodiments, and many modifications can be made by a person having ordinary skill in the art within the technical concept of the present invention.

[0095] REFERENCE SIGNS LIST 1 Route search device 10 Control unit 11 Input / output unit 12 Storage unit 71 Route search network 72 Signal noise calculation network 100 Optical transmission network 110 Route search unit 111 Route calculation unit 112 Loss calculation unit 200 Network information database (DB) 300 Route information database (DB) 310 Route list 1000 Route search system

Claims

1. A route search device that searches for a route from a start node to an end node in an optical transmission network including a plurality of nodes connected by edges, the route search device comprising: a storage unit that stores a network information database containing topology information including a plurality of transmission devices that are nodes of the optical transmission network and the arrangement of amplifiers that can be installed between the transmission devices; using the topology information, information on a route search network in which the transmission devices having an optical signal regenerative repeating function are nodes, and information on a signal noise calculation network in which the transmission devices and the amplifiers are nodes, is stored in the network information database; the route search device comprises: a route calculation unit that uses the route search network to search for a route hop by hop from the start node; and a loss calculation unit that uses the signal noise calculation network to calculate a signal-to-noise ratio that indicates the transmission loss of the route searched for hop by hop, the route calculation unit searches for a route assuming that regenerative repeating processing will be performed when the signal-to-noise ratio calculated by the loss calculation unit falls below a readable signal-to-noise ratio threshold set at the end node of the route searched for.

2. The route search device according to claim 1, characterized in that the route calculation unit stores the number of times the regenerative relay process has been performed, and when searching for a route hop by hop, selects the route with the smallest number of regenerative relays and the largest signal-to-noise ratio calculated by the loss calculation unit as the route to be searched.

3. The route search device according to claim 1, characterized in that the route calculation unit performs the regenerative relay processing at a transmission device that is the node immediately preceding the node on the route from the node whose readable signal-to-noise ratio has fallen below the threshold.

4. A route searching method of a route searching device that searches for a route from a start node to an end node in an optical transmission network including a plurality of nodes connected by edges, wherein the route searching device has a memory unit that stores a network information database that stores topology information including a plurality of transmission devices that are nodes of the optical transmission network and the arrangement of amplifiers that can be installed between the transmission devices, and uses the topology information to store information on a route searching network in which the transmission devices having an optical signal regenerative repeating function are nodes, and information on a signal noise calculation network in which the transmission devices and the amplifiers are nodes, and executes the steps of: using the route searching network to search for a route hop by hop from the start node; and using the signal noise calculation network to calculate a signal-to-noise ratio that indicates the transmission loss of the route found hop by hop; and when the calculated signal-to-noise ratio falls below a readable signal-to-noise ratio threshold set in the terminal node of the route found, performing the route searching hop by hop.

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