Network architecture with variable-granularity optical routing

Abstract

An optical transport network (OTN) node (100) comprising a plurality of optical circuit switches (OCS) (102, 104), each OCS being a respective direction of the OTN node, at least two of the OCSs including an input port (112) configured to be connected to a respective optical transmission fiber (101) outside the OTN node, at least one first output port (114) connected to a first switching layer (120), and at least one second output port (116) connected to a second switching layer (130), the first switching layer (120) and the second switching layer (130) having different levels of granularity, such as, but not limited to, a wavelength-switched layer, a band-switched layer, or a fiber-switched layer.

Description

Background Art

[0001] An optical transport network (OTN) provides a widely adopted framework for routing optical signals over a fiber optic network using a combination of transmission, multiplexing, and switching elements. Current systems are compatible with wavelength switched architectures that control optical path routing at the wavelength level. For example, colorless / directionless (CD) systems and colorless / directionless / contentionless (CDC) systems rely heavily on wavelength selective switches (WSSs) that can be programmed to route optical signals through nodes based on the respective frequencies or wavelengths of the signals.

[0002] The increasing amount of traffic carried on optical transport networks already exceeds the progress of fiber optic capacity and is expected to accelerate further. Therefore, it is inevitable that fiber optics will be increasingly focused on to meet the growing demand. The more the number of deployed fiber paths increases, which is substantially correlated with the increase in capacity of each path, the more likely it is that the wavelength switched architecture will be replaced by a fiber switched architecture to ensure cost efficiency and scalability.

[0003] However, the current wavelength switched architecture presents several challenges for the transition from wavelength switched architecture to fiber switched architecture. First, the number of ports of the WSS module in the wavelength switched architecture is limited. Generally, a maximum of 16 transmission fibers can be connected to one WSS, and the industry is currently focusing on improving the cost efficiency of WSS through repackaging and multi-way integration. Second, in the case of CD systems and CDC systems, the optical loss generated in a reconfigurable optical add / drop multiplexer (ROADM) node that uses modules for inserting and branching optical signals, such as a multicast switch (MCS) module for signal insertion / branching, varies with the number of paths existing in that node. The number of paths that can be included at a certain point, where additional amplification is required to avoid performance degradation due to extremely large optical loss, is limited. Third, the WSS module is one of the most expensive components of the ROADM node. Summary of the Invention Means for Solving the Problems

[0004] Brief Summary The present disclosure provides an alternative switching architecture that can flexibly accommodate both wavelength switched domains and fiber switched domains as well as switching elements at other granularity levels.

[0005] One aspect of the present disclosure is directed to an optical transport network (OTN) node comprising a plurality of optical circuit switches (OCSs), each OCS being a respective path of the OTN node, at least two OCSs being configured to be connected to respective optical transmission fibers outside the OTN node, and each OCS including an input port, at least one first output port connected to a first switching layer having a first granularity level, and at least one second output port connected to a second switching layer having a second granularity level different from the first granularity level.

[0006] In some examples, the first switching layer may be one of a wavelength switched layer, a band switched layer, or a fiber switched layer, and the second switching layer may be a different one of a wavelength switched layer, a band switched layer, or a fiber switched layer.

[0007] In some examples, the OTN node may further include a plurality of bidirectional node line amplifiers connected to the input ports of the plurality of OCSs in a one-to-one relationship, each bidirectional node line amplifier being located between a respective input port and the corresponding optical transmission fiber. In some examples, each bidirectional node line amplifier may include a band splitter configured to split an optical signal received from a respective optical transmission fiber into different frequency bands, and a plurality of ingress amplifiers, each ingress amplifier being connected to a respective output port of the band splitter. Each bidirectional node line amplifier may further include a band combiner configured to combine optical signals of different frequency bands received from respective OCSs of the OTN node, and a plurality of egress amplifiers, each egress amplifier being connected to a respective input port of the band combiner. In some examples, the band splitter may be a C+L band splitter. In some examples, the band combiner may be a C+L band combiner.

[0008] In some examples, the first switching layer may be a fiber switched layer, and the second switching layer may be a wavelength switched layer.

[0009] In some examples, at least two OCSs further include at least one third output port connected to a third switching layer having a third granularity level different from the first granularity level and the second granularity level.

[0010] In some examples, the first switching layer may be a fiber switched layer, and the second switching layer may be a band switched layer. The band switched layer may include a plurality of band splitters, and the output ports of each of the plurality of band splitters may be connected to the input ports of a second plurality of OCSs in a one-to-one relationship. At least one output port of each OCS of the second plurality of OCSs may be connected to a wavelength switched layer. In some examples, the fiber switched layer, the band switched layer, and the wavelength switched layer may be arranged in parallel. The fiber switched layer, the band switched layer, and the wavelength switched layer may be arranged either in a nested configuration or in a cascaded connection configuration.

[0011] In some examples, each OCS may include respective input ports configured to be connected to respective optical transmission fibers outside the OTN node, at least one respective first output port connected to the first switching layer, and at least one respective second output port connected to the second switching layer.

[0012] In some examples, the OTN node may further include a first switched layer and a second switched layer.

[0013] Another aspect of the present disclosure is directed to a method that includes connecting a plurality of paths of colorless / directionless (CD) nodes or colorless / directionless / contentionless (CDC) nodes to a plurality of optical circuit switches (OCS) in a one-to-one relationship, connecting a fiber switched layer to the plurality of OCS, and controlling the plurality of OCS for rerouting at least some of the received optical signals from the CDC nodes to the fiber switched layer.

[0014] Yet another aspect of the present disclosure is directed to an OTN node that includes a plurality of OCS. Each OCS may be a respective path of the OTN node, and at least one OCS includes an input port configured to be connected to a respective optical transmission fiber outside the OTN node, at least one first output port connected to a first switching layer, at least one second output port connected to a second switching layer, and at least one third output port connected to a different one of the plurality of OCS.

[0015] In some examples, each of the first switching layer and the second switching layer may be a respective wavelength switched layer that includes a plurality of wavelength selective switches (WSS), and the third output ports of the plurality of OCS may be connected to each other such that an optical signal transmitted between two of the third output ports does not pass through one of the plurality of WSS.

[0016] In some examples, each of the first switching layer and the second switching layer may be a respective wavelength switched layer, and the OTN node may have a total number of paths that is greater than the number of paths of the first switching layer and greater than the number of paths of the second switching layer.

[0017] In some examples, the OTN node may further include a plurality of band splitters, and each band splitter is connected between a corresponding input port and its respective optical transmission fiber. The OTN node may be configured to route an entire optical band from one path of the OTN node to another path of the OTN node without passing through the wavelength switched layer.

[0018] In some examples, the first switching layer and the second switching layer may have different granularity levels, and at least one of the switching layers may be one of a wavelength switched layer, a band switched layer, or a fiber switched layer.

[0019] In some examples, the OTN node may further include a first switching layer and a second switching layer.

[0020] In some examples, the OTN node may further include a third switching layer, and each of the first switching layer, the second switching layer, and the third switching layer may have different granularity levels.

Brief Description of the Drawings

[0021]

Fig. 1A

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DETAILED DESCRIPTION OF THE INVENTION

[0022] Detailed Description Overview Each path of the switching node architecture can be connected to any number of paths via a series of interconnected optical circuit switches (OCS), or namely 1×N optical switches. The OCS determines the route that the optical signal received by the switch takes through the node. For example, each OCS may include a plurality of output ports, at least one output port connected to a first switching layer having a first granularity, and at least one other output port connected to a second switching layer having a second granularity.

[0023] For example, the first switching layer may be a wavelength-switched architecture, and the second switching layer may be a fiber-switched architecture. With such an arrangement, it would be possible to deploy additional optical fibers to the fiber-switched architecture while setting the optical signal to be relayed to the wavelength-switched architecture. Then, if a later transition from wavelength switching to fiber switching is desired, this transition may be as simple as switching the OCS settings to relay some or all of the optical signal to the fiber-switched architecture.

[0024] In some arrangements, at least some of the output ports of an OCS may be directly connected to ports of another OCS. In this way, some or all of the paths of a node can be interconnected, and the routing of optical signals between them can be performed without the need to route the optical signals through a WSS. This is also beneficial for nodes that include filtering or branching elements for signals that do not require wavelength switching. For example, for a C+L band system, each path of a node may include a C / L band splitter configured to split an incoming optical signal between the C optical band and the L optical band. Thereby, the OCS of the node can switch the entire optical band that comes in on one path and goes out on a different path without the optical signal passing through a WSS.

[0025] In some arrangements, a switching layer of a certain granularity may include a plurality of switched domains in parallel. In an example of such an arrangement, a node may include a plurality of wavelength switched domains. The number of paths connecting to each of the parallel wavelength switched domains may be less than the number of optical fibers connecting to the entire node, but the individual parallel wavelength switched domains may be interconnected via a series of interconnected OCSs, via another switching layer of a different granularity, or both. Such an arrangement has the potential to be more cost-effective as it avoids the need to increase the number of ports of the WSS modules in the wavelength switched layer.

[0026] In a further arrangement, layers of different granularity levels may be cascade-connected to each other or nested within each other. This allows the switching layers of the switching nodes to share at least some components with each other. For example, in a node that includes both a band-switched layer and a wavelength-switched layer, the wavelength-switched layer may be nested within the band-switched layer. In such an arrangement, a conventional CD node or CDC node may be connected between the OCSs of the band-switched layer such that all optical signals are routed between the paths of the band-switched layer, while a subset of these optical signals is further routed through the conventional CD node or CDC node for wavelength switching of this subset of optical signals.

[0027] The arrangements described herein enable efficient node scaling by combining various switching technologies such as wavelength switching, band switching, and fiber switching with each other. Furthermore, these arrangements can be two-way and can be easily incorporated into existing switching architectures. These arrangements provide a straightforward path for evolving the network architecture as the switching requirements and demands change over time, such as migrating from a predominantly wavelength-switched architecture to a predominantly fiber-switched architecture. Additionally, these arrangements described herein avoid the cost and optical losses associated with adding a WSS module, adding ports to the WSS module, or both, which would otherwise be necessary to expand the routing functionality of a conventional CD node or CDC node.

[0028] System Example Figure 1A is a schematic diagram of a switching node 100 within an optical transport network (OTN). The switching node 100 is an N - port node, where N is a positive integer greater than 2. An optical signal from one of the ports may be received at the node 100 and routed through the switching network of the switching node 100 to one or more of the other ports. Each port includes an optical circuit switch (OCS) for connecting the switching node 100 to each respective optical transport fiber pair 101 of the OTN and to the outside of the switching node 100. In the example of Figure 1A, the first port (port 1) is shown as being connected to the optical transport fiber pair 101 by the first OCS 102, and the second port (port N) is shown as being connected to another optical transport fiber pair by the second OCS 104. The switching node 100 may include other ports having their respective OCSs, and thus the first OCS 102, the second OCS 104, and the other OCSs may be interconnected.

[0029] A bidirectional node line amplifier 105 may be included in each port of the switching node 100. In some examples, the bidirectional node line amplifier 105 may include unidirectional elements positioned in both directions. For example, the bidirectional node line amplifier 105 may include a pair of erbium doped fiber amplifiers (EDFAs). For each port, the bidirectional node line amplifier 105 may be positioned between the respective optical transport fiber of that port and the OCS of that port. The bidirectional node line amplifier 105 may be configured to amplify both the incoming optical signal entering the node 100 and the outgoing optical signal exiting the switching node 100.

[0030] In some examples, each OCS may be a 1×N switch, and each of the paths of the switching node 100 may be connected to each of the other paths by its respective OCS. Thus, the OCSs of the switching node 100 may form a non-blocking matrix switch. In other examples, each OCS may be connected to some of the other OCSs of the switching node 100, so that some of the N paths of the switching node 100 may be indirectly connected to each other via the OCSs of the other paths of the switching node 100.

[0031] Each OCS may include one input port 112 for connection to the optical transmission fiber pair of its respective path and a plurality of output ports for connection to the various switching layers of the switching node 100. In the example of FIG. 1A, one or more first output ports 114 connect the second OCS 104 to the first switching layer 120, and one or more second output ports 116 connect the second OCS 104 to the second switching layer 130.

[0032] The first switching layer and the second switching layer may have different granularity levels. For example, in FIG. 1A, the first switching layer may be a wavelength switched layer for selectively routing optical signals belonging to a selected wavelength or wavelength range, a band switched layer for selectively routing optical signals belonging to a selected wavelength band, or a fiber switched layer for selectively routing optical signals according to the optical fiber from which the received signal originated, any of which may be the case.

[0033] Figure 1B shows an example of the arrangement of the switching node 100 in Figure 1A. In this arrangement, the first switched layer 120 is a wavelength switched domain or a wavelength switched layer, and the second switched layer 130 is a fiber switched domain or a fiber switched layer. Each of the first switching layer 120 and the second switching layer 130 is connected to the OCSs 102, 104 such that an incoming optical signal can be routed from either OCS to one of the first switching layer 120 and the second switching layer 130, and an outgoing optical signal can be routed from one of the first switching layer 120 and the second switching layer 130 to either OCS.

[0034] The wavelength switched layer 120 includes a wavelength selective switch (WSS) 122, through which an incoming optical signal is routed. The WSS 122 may control whether an optical signal is carried based on the wavelength of the optical signal. When carrying an optical signal, a multi-node mesh such as a fiber shuffle module (FSM) 124 connected to an add-drop architecture such as a multi-cast switch (MCS) may be used to combine or separate optical signals with different wavelengths from each other. In a wavelength switched layer corresponding to a CDC architecture, the add-drop architecture may be contentionless, such as a contentionless M×N WSS 126, where "M" is the number of paths and "N" is the number of add / drop ports.

[0035] Substantially, the wavelength switched layer 120 may operate as a CD node or a CDC node, and may further include an OCS 128 at the output of the CD node or the CDC node to control a specific path of the switching node 100 to which the combined or separated optical signal is routed. The OCS of the switching node 100 may be wrapped around the CD node or the CDC node so that the optical signal entering the node can be surely routed to any other path of the node, thereby providing complete switching programmability of the node.

[0036] The fiber switched layer 130 includes a switching architecture for controlling the routing of optical signals based on the optical fibers through which the optical signals are carried. The fiber switched layer 130 may include a WSS 132 for multiplexing / demultiplexing wavelength division multiplex (WDM) signals, and may further include an OCS 134 at the output of the fiber switched layer 130 to control a specific path of the switching node 100 to which the combined or separated optical signal is routed.

[0037] Figure 2 shows another arrangement example of the switching node 200 having a plurality of switching layers with different granularity levels. In particular, in Figure 2, the first switching layer is the wavelength switched layer 220, and the second switching layer is the band switched layer 230. To provide band switching instead of fiber switching, a bidirectional node line amplifier is arranged to include a band splitter 202 for splitting an incoming optical signal between multiple bands, respective ingress amplifiers 204, 206 for each of the bands split by the band splitter 202, a band combiner 212 for combining transmitted optical signals belonging to different bands, and respective egress amplifiers 214, 216 for each of the bands recombined by the band combiner 212. Further, each separated band split by the band splitter 202 and recombined by the band combiner 212 is connected to the separated OCS 208 of the switching node 200. For example, in the example of Figure 2, the optical signal is split between the C band and the L band by the band splitter 202. In Figure 2, the first OCS 208 is connected to the first ingress amplifier 204 so as to receive the optical signal in the C band amplified by the first ingress amplifier 204. Further, a second OCS (not shown) may be connected to the second ingress amplifier 206 so as to receive the optical signal in the L band amplified by the second ingress amplifier 206. Similarly, the separated OCS may be connected to each of the egress amplifiers 214 and 216 to route the transmitted optical signal to each of the outgoing paths of the switching node 200. In the example of Figure 2, each amplifier handles a single band, and each amplifier may be an EDFA.

[0038] Although the wavelength switched layer in FIG. 2 represents only one wavelength switched domain, it should be understood and appreciated that the switching node 200 may include a plurality of wavelength switched domains. The total number of paths included in each wavelength switched domain can vary depending on the switching node and can also vary depending on the various wavelength switched domains of one switching node. Each wavelength switched domain may be connected to a different OCS of the switching node 200, and thus the switching within the node may involve routing of optical signals through a plurality of wavelength switched domains.

[0039] The examples of FIGS. 1B and 2 show a node including two switching layers having different granularities. However, the number of types of switching layers can be further increased. For example, three or more switching layers having different granularities may be provided.

[0040] FIG. 3 shows an example of a parallel arrangement of a switching node 300 for arranging a plurality of types of switching layers in parallel with each other. In the example of the switching node 300 in FIG. 3, each wavelength switched layer 310, band switched layer 320, and fiber switched layer 330 are provided. An OCS 340 may be provided in each path of the switching node 300. The OCS 340 may include an input port and a plurality of output ports connected to respective optical transmission fibers, whereby each of the switching layers is connected to at least one of the output ports.

[0041] During operation, through the switching process in the OCS 340, it may be controlled to which of the switching layers 310, 320, 330 the incoming optical signal is transmitted. Further, each of the switching layers 310, 320, 330 may include its own OCS between the OCS 340 and the filtering element and switching element of the switching layer. Each OCS may be used to route the transmitted optical signal to any of the paths of the switching node 300.

[0042] FIG. 4 shows an example of a cascade connection arrangement of a switching node 400 for arranging a plurality of types of switching layers in a cascade connection configuration. In the example of the switching node 400 of FIG. 4, each wavelength switched layer 410, band switched layer 420, and fiber switched layer 430 are provided. Each first cascade-connected OCS 440 is provided in each path of the switching node 400 to receive an optical signal from an optical transmission fiber in the path and direct the incoming optical signal either to the coarsest-grained switching layer or to the next cascade-connected path. In the example of FIG. 4, the switching layer with the coarsest grain size is the fiber switched layer 430. The next cascade-connected path sends the incoming optical signal to the next cascade-connected OCS 460 and directs the incoming optical signal either to the next coarsest-grained switching layer or to a more distant cascade-connected path. In the example of FIG. 4, the next coarsest-grained switching layer is the band switched layer 420. By a more distant cascade-connected path, the incoming optical signal is sent to the switching layer with the finest grain size, in this case the wavelength switched layer 410. Further, in the example of FIG. 4, a band splitter 450 is provided in front of the OCS 460 for the band switched layer 420. Similar to the band splitter of FIG. 2, the band splitter 450 may split the incoming optical signal between the C-band and the L-band, and thus separated OCSs 460 may be provided for each of the C-band and the L-band.

[0043] During operation, through switching processing at the first cascade-connected OCS 440, it may be controlled whether to transmit the incoming optical signal to the coarsest-grained switching layer or to a different switching layer. Similarly, it is also possible to control, using the next cascade-connected OCS 460, whether to push the incoming signal deeper into the cascade connection arrangement or to a switching layer connected to the cascade-connected OCS.

[0044] Furthermore, each of the switching layers 410, 420, 430 may each include its own OCS for routing the transmitted optical signal to any one of the paths of the switching node 400.

[0045] FIG. 5 shows a nested arrangement example of a switching node 500 for arranging a plurality of types of switching layers in a nested configuration. In the example of the switching node 500 in FIG. 5, each wavelength switched layer 510, band switched layer 520, and fiber switched layer 530 are provided. The arrangement of this nested configuration is the same as the cascade connection configuration in FIG. 4. For example, each first nested OCS 540 is provided in each path of the switching node 500 so as to receive an optical signal from an optical transmission fiber in the path and direct the incoming optical signal either to the coarsest granularity switching layer or the next nested level, and a second nested OCS 560 is provided to receive the optical signal from the first nested OCS 540 and direct the received optical signal either to the remaining switching layer 510 or 520. Further, similar to the example in FIG. 4, a band splitter 550 may be provided in front of the second nested OCS 560 for the band switched layer 520 to split the incoming optical signal between the C-band and the L-band, and for this purpose, a separated OCS 560 may be provided for each of the C-band and the L-band. Different from the cascade connection configuration in FIG. 4, each of the nested OCSs 540 and 560 may also be used as an OCS for interconnecting the paths of the switching node 500 inside each of the switching layers.

[0046] The configurations shown in FIGS. 2 to 5 have directional symmetry, that is, each switching layer is symmetric and bidirectional. Due to this, an optical signal can cross each switching layer in either direction. Other configurations may be unidirectional or partially bidirectional, whereby at least some of the symmetric elements are omitted. For example, in the case of the wavelength switching layer, each path of the switching node may be connected to the wavelength switching layer by either a WSS for receiving an optical signal from the path or an OCS for routing the optical signal to the path. The same principle may be applied to the remaining types of switching layers.

[0047] Although the above-described example shown in the figures shows three switching layers, it should be understood that the same or similar principle may be applied to further increase the total number of switching layers. For example, in the parallel arrangement of FIG. 3, the OCS 340 may include additional output ports for connecting to additional switching layers other than the three switching layers shown in the figure. Further, for example, in the cascade connection arrangement of FIG. 4, additional OCSs cascade-connected to advance the optical signal to additional switching layers other than the three switching layers shown in the figure may be added behind the OCS 460. Further, for example, in the nested arrangement of FIG. 5, additional OCSs may be added in front of the OCS 540 to split the optical signal between additional switching layers and the three switching layers shown in the figure. These principles may be further repeated as many times as necessary to provide the desired number of granularity levels.

[0048] The above-described arrangement example can be arranged to facilitate the evolution of the network architecture over time. For example, at the first installation, routing of optical signals may be sufficient with the CD nodes or CDC nodes of the wavelength switched layer of the switching node, but as traffic increases, it may become necessary to activate other switching layers of the switching node. In the above-described arrangement example, this can be facilitated in the OCS switch by first routing the incoming optical signal to the wavelength switched layer and increasingly routing at least some of the optical signals to the remaining switching layers as traffic increases. Alternatively, when the added switching layer is a fiber switched layer, since the fiber switched layer has a lower cost and a smaller optical loss, the optical signal may be routed to pass through the fiber switched layer first and then the remaining layers second. Due to the uniform nature of these arrangements, the architecture of any arbitrary switching node can be adapted to the current or future specific requirements of the arbitrary node, thereby continuously facilitating the evolution of the node.

[0049] FIG. 6 shows another configuration example for the evolution of the network architecture in the switching node 600, in which the CDC node 620 included in the switching node 600 may be evolved and connected to an additional path. In the example of FIG. 6, the CDC node is connected to N paths. Each of the paths 602, 604 is connected to a corresponding WSS 622, 624 by connecting to each optical transmission fiber pair of the OTN, facilitating the routing and switching of optical signals in the same or similar manner as shown in FIG. 1B. Similar to FIG. 1B, this may include the add-drop of optical signals at the CDC node based on the programming of the WSS, FSM, and contentionless M×N WSS. An additional WSS 626 is illustrated. The additional WSS 626 is connected to a virtual path 606 represented as path M in the figure, which in turn may connect the CDC node 602 to another path 608 of the switching node 600 represented as path L in the figure. The virtual path can control the connection between the CDC node 620 and the additional path 608 using the OCSs 630 and 640 located therebetween. One of the OCSs 630 may control the transmission of the transmitted optical signal from the CDC node 620 to the additional path 608, and the other OCS may control the transmission of the incoming optical signal from the additional path 608 to the CDC node 620. In this way, the OCSs 620, 630 can control when and under what conditions the additional path 608 may be added to the switching architecture of the switching node 600.

[0050] In the above example, no specific ratio between the OCS-OCS connection and the wavelength switched layer is specified. This ratio should be understood and evaluated as being variable for each node, depending on the specific demands and requirements of each node. Also, the number of paths in each wavelength switched domain may be much less than the total number of paths in the switching node, but the wavelength switched domain may still be fully connected via additional switched domains, for example, a plurality of wavelength switched domains located in parallel with each other. Additional switching capabilities may be realized through the OCS connected thereto, the remaining switching layers connected thereto, or any combination thereof. As a result, it may not be necessary to increase the number of paths supported by each of the individual wavelength switched domains, i.e., the current 8-path or 16-path wavelength switched domains may be sufficient even for future, evolved arrangements of switching layers and switching node architectures.

[0051] The above example also generally describes and explains an OTN node that supports two-way communication in each of its paths. However, it should be recognized that the basic principles of the present disclosure may also be equally applicable to node architectures that include at least some paths that support one-way communication. In such cases, the paths may have one or more optical transmission fibers instead of a transmission fiber pair and may include components for one-way amplification instead of two-way amplification. The exemplary node may be further programmed only to route optical signals to nodes having transmission performance, as opposed to nodes having only reception performance.

[0052] More generally, it should be recognized that the switching node of any of the above examples may have a total number of paths greater than the number of paths of any of the switched domains included therein. In practice, a plurality of parallel switched domains may be used to provide complete connectivity and switching performance within the switching node.

[0053] Example of method Figure 7 is an example of routine 700 for evolving the architecture of a switching node included in an OTN according to the arrangements and configurations described herein. In a first stage, the switching node may be limited to include only wavelength switching, for example, it may include one CD node or one CDC node.

[0054] In block 710, the paths of one CD node or one CDC node are connected to the OCS in a one-to-one relationship. The OCS may be wrapped around the CD node or the CD node so that an optical signal entering the node through one path can surely exit the node through any other path. Further, the provided OCS may be connected to one or more CD nodes or CDC nodes, for example, by providing a plurality of CD nodes or CDC nodes in parallel and connecting the CD nodes or CDC nodes to each other through the interwiring of the OCS.

[0055] In block 720, the OCS provided in block 710 may be further connected to a second switched layer having a different granularity level from the CD or CDC. For example, the OCS may be connected to a fiber switched layer. The fiber switched layer can provide more cost-effective switching than the CD node and the CDC node, and can achieve a reduction in the optical loss of the optical signal crossing the fiber switched layer instead of the CD node or the CDC node. The OCS may be arranged to control whether the incoming optical signal is directed to the CD node or the CDC node, or whether the incoming optical signal is directed to the fiber switched layer.

[0056] At block 730, the optical signals reaching the switching node may be rerouted by the OCS from or to the CD node, instead, to the fiber switched layer. The presence of an OCS in each path of the CD node or the CDC node enables any optical signal arriving at the node to be rerouted to the fiber switched layer instead. This arrangement allows the switching node architecture to adapt and evolve over time, for example, by utilizing fiber cabling added after the initial deployment of the CD node or the CDC node, to accommodate the demand for additional capacity.

[0057] By the method described above, during the increase in demand for capacity, the need to scale the CD node or the CDC node or other wavelength-based switching solutions is avoided, and instead, those solutions can be incorporated into other solutions such as a newly added fiber switched domain. Over time, and as the switching requirements and demands change, it is possible to migrate mainly from a wavelength switched architecture to a fiber switched architecture.

[0058] Furthermore, the presence of an OCS in each path of the CD node or the CDC node, or more generally, in each path of a larger switching node that includes both the wavelength switched layer and the fiber switched layer, provides complete programmability of the switching node and a two-way switching solution. Also, using an additional OCS to connect the fiber switched domain instead of an additional WSS to create a new wavelength switched domain is advantageous for many reasons, such as the lower cost of the OCS compared to the WSS, the reduction of optical loss by the OCS compared to the WSS, and the higher flexibility offered by the fiber switched architecture compared to the wavelength switched architecture.

[0059] Although the technology of this specification has been described with reference to specific embodiments, it should be understood that these embodiments merely illustrate the principles and applications of the technology of this application. Therefore, it should be understood that numerous changes can be made to these exemplary embodiments, and other arrangements can be devised without departing from the spirit and scope of the technology of this application as defined in the appended claims.

[0060] Most of the above - mentioned alternative examples are not mutually exclusive and may be implemented in various combinations to achieve their respective advantages. Since these and other variations and combinations of the above - mentioned features are available without departing from the subject matter defined by the claims, the above description of the embodiments should be construed as illustrative means rather than limiting the subject matter defined by the claims. For example, the preceding processes do not have to be performed in the exact order described above. Rather, the various steps may be handled in a different order, such as in reverse or simultaneously. Steps may also be omitted, unless otherwise stated. Also, the examples described in this specification and phrases expressed such as "such as" and "including" should not be construed as limiting the claimed subject matter to a specific example. Rather, these examples are intended to illustrate only one of many possible embodiments. Further, the same reference numerals in different drawings identify the same or similar elements.

Claims

1. An optical transport network (OTN) node, comprising: a first switching layer included in the OTN node and having a first granularity level; a second switching layer included in the OTN node and having a second granularity level different from the first granularity level; a plurality of optical circuit switches (OCS); each OCS is a respective path of the OTN node, and at least two OCSs include an input port configured to be connected to a respective optical transmission fiber outside the OTN node; at least one first output port connected to the first switching layer; and at least one second output port connected to the second switching layer.

2. The OTN node according to claim 1, wherein the first switching layer is one of a wavelength switched layer, a band switched layer, or a fiber switched layer, and the second switching layer is a different one of the wavelength switched layer, the band switched layer, or the fiber switched layer.

3. The OTN node according to claim 1, further comprising a plurality of bidirectional node line amplifiers connected to the input ports of the plurality of OCSs in a one-to-one relationship, and each bidirectional node line amplifier is located between a respective input port and the corresponding optical transmission fiber.

4. Each bidirectional node line amplifier includes a band splitter configured to split an optical signal received from the respective optical transmission fiber into different frequency bands; a plurality of ingress amplifiers, each ingress amplifier being connected to a respective output port of the band splitter, and each bidirectional node line amplifier further includes a band combiner configured to combine the optical signals of the different frequency bands received from the respective OCSs of the OTN node; and a plurality of egress amplifiers, each egress amplifier being connected to a respective input port of the band combiner.

5. The OTN node according to claim 4, wherein the band splitter is a C+L band splitter, and the band combiner is a C+L band combiner.

6. The OTN node according to claim 5, wherein the first switching layer is a fiber switched layer, and the second switching layer is a wavelength switched layer. **Claim 7**: Further comprising a third switching layer having a third granularity level different from the first granularity level and the second granularity level, The at least two OCSs further include at least one third output port connected to the third switching layer, the OTN node according to claim 1 or 2. **Claim 8**: An optical transmission network (OTN) node comprising a plurality of optical circuit switches (OCS), Each OCS is a respective path of the OTN node, and at least two OCSs An input port configured to be connected to each respective optical transmission fiber outside the OTN node, At least one first output port connected to a first switching layer having a first granularity level, And at least one second output port connected to a second switching layer having a second granularity level different from the first granularity level, The first switching layer is a fiber switched layer, the second switching layer is a band switched layer, the band switched layer includes a plurality of band splitters, and each output port of the plurality of band splitters is connected to an input port of a second plurality of OCSs in a one-to-one relationship. At least one output port of each OCS of the second plurality of OCSs is connected to a wavelength switched layer, the OTN node. **Claim 9**: The fiber switched layer, the band switched layer, and the wavelength switched layer are arranged in parallel, the OTN node according to claim 8. **Claim 10**: The fiber switched layer, the band switched layer, and the wavelength switched layer are arranged either in a nested configuration or a cascade connection configuration, the OTN node according to claim 8. **Claim 11**: Each OCS Each respective input port configured to be connected to each respective optical transmission fiber outside the OTN node, At least one respective first output port connected to the first switching layer, And at least one respective second output port connected to the second switching layer, the OTN node according to claim 1 or 2. **Claim 12**: Further comprising the first switching layer and the second switching layer, the OTN node according to claim 1 or 2. **Claim 13**: An optical transmission network (OTN) node, A first switching layer included in the OTN node and having a first granularity level, and a second switching layer included in the OTN node and having a second granularity level different from the first granularity level, and a plurality of optical circuit switches (OCS), each OCS is a respective path of the OTN node, and at least one OCS has an input port configured to be connected to each optical transmission fiber outside the OTN node, at least one first output port connected to the first switching layer, at least one second output port connected to the second switching layer, and an OTN node including at least one third output port connected to a different one of the plurality of OCSs. **Claim 14**: An optical transmission network (OTN) node comprising a plurality of optical circuit switches (OCS), each OCS is a respective path of the OTN node, and at least one OCS has an input port configured to be connected to each optical transmission fiber outside the OTN node, at least one first output port connected to a first switching layer, at least one second output port connected to a second switching layer, and includes at least one third output port connected to a different one of the plurality of OCSs, each of the first switching layer and the second switching layer is a respective wavelength switched layer including a plurality of wavelength selective switches (WSS), and the third output ports of the plurality of OCSs are connected to each other such that an optical signal transmitted between two of the third output ports does not pass through one of the plurality of WSSs. An OTN node. **Claim 15**: An optical transmission network (OTN) node comprising a plurality of optical circuit switches (OCS), each OCS is a respective path of the OTN node, and at least one OCS has an input port configured to be connected to each optical transmission fiber outside the OTN node, at least one first output port connected to a first switching layer, at least one second output port connected to a second switching layer, and includes at least one third output port connected to a different one of the plurality of OCSs, Each of the first switching layer and the second switching layer is a respective wavelength switched layer, and the OTN node has a total number of paths greater than the number of paths of the first switching layer and greater than the number of paths of the second switching layer. OTN node.

16. Further comprising a plurality of band splitters, each band splitter being connected between a corresponding input port and its respective optical transmission fiber, the OTN node being configured to route an entire optical band from one path of the OTN node to another path of the OTN node without passing through the wavelength switched layer. The OTN node according to claim 14.

17. The OTN node according to claim 13, wherein at least one of the first and second switching layers is one of a wavelength switched layer, a band switched layer, or a fiber switched layer.

18. The OTN node according to claim 13, further comprising a third switching layer having a third granularity level different from the first granularity level and the second granularity level.

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