Network architecture with variable granularity optical routing

Abstract

To provide an OTN node for evolving a network architecture.SOLUTION: An optical transport network (OTN) node (100) includes a plurality of optical circuit switches (OCSs) (102, 104), each OCS being a respective degree of the OTN node, at least two of the OCSs including an input port (112) configured to be connected to a respective optical transport fiber (101) outside of 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 and second switching layers (120, 130) have different levels of granularity, such as but not limited to a wavelength switched layer, a band switched layer or a fiber switched layer.SELECTED DRAWING: Figure 1A

Description

[Background technology]

[0001] Transmission and multiplexing via optical transport network (OTN) This provides a widely adopted framework for routing optical signals over optical fiber networks using a combination of wavelength-switched and switching elements. Current systems support wavelength-switched architectures that control optical path routing at the wavelength level. For example, colorless / directionless (CD) systems Optical fiber 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 signals' respective frequencies or wavelengths.

[0002] The growth in the amount of traffic carried over optical transport networks is already outpacing advances in optical fiber capacity and is expected to continue accelerating. Therefore, it is inevitable that optical fiber will receive increased attention to meet the growing demand. As the amount of fiber paths deployed increases, which correlates substantially with the increase in capacity of each path, wavelength-switched architectures will likely be replaced by fiber-switched architectures to ensure cost-efficiency and scalability.

[0003] However, current wavelength-switched architectures present several challenges for the transition from wavelength-switched to fiber-switched architectures. First, the number of ports on WSS modules in wavelength-switched architectures 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-degree integration. Second, in CD and CDC systems, the optical loss occurring in modules used to add and drop optical signals, such as reconfigurable optical add / drop multiplexer (ROADM) nodes that use multicast switch (MCS) modules for signal addition / drop, is It varies with the number of degrees present at the node. There is a limit to the number of degrees that can be included at any point, at which point the optical loss becomes so great that additional amplification is required to avoid performance degradation. Third, the WSS module is one of the most expensive components of a ROADM node. Summary of the Invention [Means for solving the problem]

[0004] Quick summary The present disclosure provides an alternative switching architecture that is flexible to accommodate both wavelength-switched and fiber-switched domains as well as switching elements at other levels of granularity.

[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, and at least two OCSs including input ports configured to be connected to respective optical transmission fibers outside the OTN node, at least one first output port connected to a first switching layer having a first level of granularity, and at least one second output port connected to a second switching layer having a second level of granularity different from the first level of granularity.

[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, with each bidirectional node line amplifier located between a respective input port and a corresponding optical transmission fiber. In some examples, each bidirectional node line amplifier may include a band splitter configured to split optical signals received from a respective optical transmission fiber into different frequency bands and a plurality of ingress amplifiers, with each ingress amplifier 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 a respective OCS of the OTN node and a plurality of egress amplifiers, with each egress amplifier 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, the at least two OCSs further include at least one third output port connected to a third switching layer having a third level of granularity different from the first level of granularity and the second level of granularity.

[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, each of which may have an output port connected to an input port of a second plurality of OCSs in a one-to-one relationship, and at least one output port of each of the second plurality of OCSs may be connected to the 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 in either a nested or cascaded configuration.

[0011] In some examples, each OCS may include a respective input port configured to be connected to a 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.

[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 multiple degrees of a colorless / directionless (CD) node or a colorless / directionless / contentionless (CDC) node to multiple optical circuit switches (OCSs) in a one-to-one relationship, connecting a fiber-switched layer to the multiple OCSs, and controlling the multiple OCSs for rerouting at least some optical signals received from the CDC node to the fiber-switched layer.

[0014] Yet another aspect of the present disclosure is directed to an OTN node including a plurality of OCSs, each of which may be a respective direction of the OTN node, and at least one OCS may 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 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 OCSs.

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

[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 degrees greater than the number of degrees in the first switching layer and greater than the number of degrees in the second switching layer.

[0017] In some examples, the OTN node may further include a plurality of band splitters, each band splitter 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 degree of the OTN node to another degree of the OTN node without passing through a wavelength-switched layer.

[0018] In some examples, the first switching layer and the second switching layer may have different levels of granularity, 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 a different level of granularity. [Brief explanation of the drawings]

[0021] [Figure 1A] 1 is a schematic diagram of a switching node in an optical transport network according to an aspect of the disclosure. [Figure 1B] 1 is a schematic diagram of a switching node in an optical transport network according to an aspect of the disclosure. [Figure 2] FIG. 10 is a schematic diagram of another example configuration of a switching node according to an aspect of the disclosure. [Figure 3] FIG. 10 is a schematic diagram of another example configuration of a switching node according to an aspect of the disclosure. [Figure 4] FIG. 10 is a schematic diagram of another example configuration of a switching node according to an aspect of the disclosure. [Figure 5] FIG. 10 is a schematic diagram of another example configuration of a switching node according to an aspect of the disclosure. [Figure 6] 1 is a schematic diagram of a modified example configuration of a CDC node according to an aspect of the disclosure. [Figure 7] FIG. 1 is a flow diagram of an example routine according to an aspect of the disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0022] Detailed Description overview Each direction in the switching node architecture is a series of interconnected optical circuit switches. An optical circuit switch (OCS), or 1×N optical switches, can connect to any number of paths. The OCS determines the route that an optical signal received at the switch takes through the node. For example, each OCS may include multiple output ports, at least one output port connecting to a first switching layer having a first granularity and at least one other output port connecting 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. Such an arrangement would allow additional optical fibers to be deployed in the fiber-switched architecture while optical signals are configured to be relayed to the wavelength-switched architecture. Then, if a transition from wavelength switching to fiber switching is later desired, this transition could be as simple as switching the OCS configuration to relay some or all of the optical signals 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 manner, some or all of the node's directions may be interconnected, allowing routing of optical signals between them without the need to route the optical signals through a WSS. This is also beneficial for nodes that include signal filtering or splitting elements that do not require wavelength switching. For example, for a C+L band system, each direction of a node may include a C / L band splitter configured to split an incoming optical signal between the C and L optical bands. This allows the node's OCS to switch entire optical bands, arriving in one direction and leaving in a different direction, without the optical signal passing through a WSS.

[0025] In some arrangements, a switching layer of a given granularity may include multiple switched domains in parallel with one another. In one example of such an arrangement, a node may include multiple wavelength-switched domains. The number of degrees connecting to each parallel wavelength-switched domain may be less than the number of optical fibers connecting to the overall node, but the individual parallel wavelength-switched domains may be interconnected via a series of interconnected optical communication switches (OCSs), via another switching layer of a different granularity, or both. Such an arrangement may be potentially more cost-effective because it avoids the need to increase the port count of the WSS modules in the wavelength-switched layer.

[0026] In further arrangements, layers at different levels of granularity may be cascaded with each other or nested within each other, such that the switching layers of a switching node may share at least some components with each other. For example, in a node including both a band-switched layer and a wavelength-switched layer, the wavelength-switched layer may be nested within the band-switched layer. In such arrangements, conventional CD or CDC nodes may be connected between OCSs of the band-switched layer such that all optical signals are routed between the directions of the band-switched layer, while a subset of those optical signals is further routed through the conventional CD or CDC node for wavelength switching of the subset of optical signals.

[0027] The arrangements described herein allow for efficient node scaling by combining various switching technologies such as wavelength switching, band switching, and fiber switching. Furthermore, these arrangements are bidirectional and can be easily integrated into existing switching architectures. As switching requirements and demands change over time, such as moving from primarily wavelength-switched architectures to primarily fiber-switched architectures, these arrangements provide significant benefits. This provides a simple path for evolving network architectures. Furthermore, the arrangements described herein avoid the cost and optical loss associated with adding WSS modules, adding ports to WSS modules, or both, that would otherwise be required to extend the routing functionality of conventional CD or CDC nodes.

[0028] System example FIG. 1A is a schematic diagram of a switching node 100 in an optical transport network (OTN). Switching node 100 is an N-degree node, where N is a positive integer greater than 2. An optical signal from one of the degrees may be received at node 100 and routed to one or more of the other degrees through a switching network of switching node 100. Each degree includes an optical circuit switch (OCS) for connecting switching node 100 to a respective optical transmission fiber pair 101 of the OTN and to the outside of switching node 100. In the example of FIG. 1A, a first degree (Degree 1) is shown connected to optical transmission fiber pair 101 by a first OCS 102, and a second degree (Degree N) is shown connected to another optical transmission fiber pair by a second OCS 104. Switching node 100 may include other paths with their own respective OCSs, so that first OCS 102, second OCS 104, and other OCSs may be interconnected.

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

[0030] In some examples, each OCS may be a 1×N switch, and each of the directions of switching node 100 may be connected to each of the other directions by its respective OCS. In this manner, the OCSs of 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 switching node 100, such that some of the N directions of switching node 100 may be indirectly connected to each other via the OCSs of the other directions of switching node 100.

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

[0032] The first and second switching layers may have different levels of granularity. For example, in Figure 1A, the first switching layer may be a wavelength-switched layer for selectively routing optical signals belonging to selected wavelengths or wavelength ranges, a band-switched layer for selectively routing optical signals belonging to selected wavelength bands, or a fiber-switched layer for selectively routing optical signals depending on the optical fiber from which the received signal comes.

[0033] 1A in which the first switched layer 120 is a wavelength-switched domain or layer and the second switched layer 130 is a fiber-switched domain or layer. Each of the first switching layer 120 and the second switching layer 130 is connected to the OCSs 102, 104 such that incoming optical signals can be routed from either OCS to either one of the first switching layer 120 and the second switching layer 130, and outgoing optical signals can be routed from either 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 incoming optical signals are routed. The optical signal 122 may control whether an optical signal is carried based on the wavelength of the optical signal. When carrying an optical signal, it may be connected to an add-drop architecture such as a multicast switch (MCS) to combine or separate optical signals of different wavelengths from each other. In the wavelength-switched layer corresponding to the CDC architecture, the add-drop architecture may use a contention-less M×N WSS 126. where "M" is the number of degrees and "N" is the number of add / drop ports.

[0035] In effect, wavelength-switched layer 120 may operate as a CD or CDC node and may further include an OCS 128 at the output of the CD or CDC node to control the particular direction through which the combined or separated optical signals are routed in switching node 100. The OCS of switching node 100 may be wrapped around the CD or CDC node to ensure that optical signals entering the node can be reliably routed to any other direction through the node, thereby providing full 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 multiplexes / multiplexes wavelength division multiplexed (WDM) signals. The fiber-switched layer 130 may include a WSS 132 for multiplexing and splitting, and may further include an OCS 134 at the output of the fiber-switched layer 130 to control the particular direction through the switching node 100 to which the combined or split optical signal is routed.

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

[0038] 2 depicts only one wavelength-switched domain, it should be understood and appreciated that switching node 200 may include multiple wavelength-switched domains. The total number of degrees included in each wavelength-switched domain may vary from switching node to switching node and may also vary among different wavelength-switched domains within a single switching node. Each wavelength-switched domain may be connected to a different OCS of switching node 200, such that switching within the node may involve routing optical signals through multiple wavelength-switched domains.

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

[0040] 3 illustrates an example of a parallel arrangement of switching node 300 for arranging multiple types of switching layers in parallel with each other. The example switching node 300 of FIG. 3 includes a wavelength-switched layer 310, a band-switched layer 320, and a fiber-switched layer 330. Each degree of switching node 300 may include an optical control system (OCS) 340. OCS 340 may include an input port connected to a respective optical transmission fiber and multiple output ports, such that each of the switching layers is connected to at least one of the output ports.

[0041] In operation, the switching process in OCS 340 may control to which of switching layers 310, 320, 330 an incoming optical signal is sent. Furthermore, each switching layer 310, 320, 330 may include its own OCS between OCS 340 and the filtering and switching elements of the switching layer. Each OCS may be used to route an outgoing optical signal to any of the paths in switching node 300.

[0042] FIG. 4 illustrates an example cascaded arrangement of a switching node 400 for arranging multiple types of switching layers in a cascaded configuration. The example switching node 400 of FIG. 4 includes a wavelength-switched layer 410, a band-switched layer 420, and a fiber-switched layer 430. A respective first cascaded OCS 440 is provided at each direction of the switching node 400 to receive an optical signal from the optical transmission fiber at that direction and direct the incoming optical signal to either the coarsest-grained switching layer or the next cascaded path. In the example of FIG. 4, the switching layer with the coarsest granularity is the fiber-switched layer 430. The next cascaded path sends the incoming optical signal to the next cascaded OCS 460, which directs the incoming optical signal to either the next coarsest-grained switching layer or a more distant cascaded path. In the example of FIG. 4, the next coarsest-grained switching layer is the band-switched layer 420. The further cascaded path routes the incoming optical signal to the switching layer with the finest granularity, in this case wavelength-switched layer 410. Furthermore, in the example of Figure 4, a band splitter 450 is provided for band-switched layer 420 before OCS 460. Similar to the band splitter of Figure 2, band splitter 450 may split the incoming optical signal between the C-band and the L-band, and thus a separate OCS 460 may be provided for each of the C-band and the L-band.

[0043] In operation, the switching process in the first cascaded OCS 440 may control whether the incoming optical signal is sent to the coarsest switching layer or a different switching layer, and similarly, the next cascaded OCS 460 may be used to control whether the incoming signal is pushed deeper into the cascaded arrangement or into a switching layer connected to the cascaded OCS.

[0044] Additionally, each switching layer 410 , 420 , 430 may each include its own OCS for routing outgoing optical signals to any of the paths of switching node 400 .

[0045] FIG. 5 illustrates an example of a nested topology of switching nodes 500 for arranging multiple types of switching layers in a nested topology. The example switching node 500 of FIG. 5 includes a wavelength-switched layer 510, a band-switched layer 520, and a fiber-switched layer 530. This nested topology is similar to the cascaded topology of FIG. 4. For example, a respective first nested OCS 540 is provided at each degree of the switching node 500 to receive optical signals from the optical transmission fiber at that degree and direct the incoming optical signals to either the coarsest-grained switching layer or the next nested level. A second nested OCS 560 is provided to receive optical signals from the first nested OCS 540 and direct the received optical signals to either the remaining switching layer 510 or 520. 4, a band splitter 550 may be provided for band-switched layer 520 before second nested OCS 560 to split the incoming optical signal between the C and L bands, such that a separate OCS 560 may be provided for each of the C and L bands. Unlike the cascaded configuration of FIG. 4, each of nested OCSs 540 and 560 may double as an OCS to interconnect the paths of switching node 500 within its respective switching layer.

[0046] The configurations shown in Figures 2-5 have directional symmetry, i.e., each switching layer is symmetric and bidirectional. This allows optical signals to traverse each switching layer in either direction. Other configurations may be unidirectional or partially bidirectional, thereby omitting at least some of the symmetrical elements. For example, in the case of a wavelength switching layer, each degree of a switching node may be connected to the wavelength switching layer by either a WSS for receiving optical signals from the degree or an OCS for routing optical signals to the degree. Similar principles may be applied to the remaining types of switching layers.

[0047] While the illustrated examples above show three switching layers, it should be understood that the same or similar principles may be applied to further increase the total number of switching layers. For example, in the parallel arrangement of FIG. 3, OCS 340 may include additional output ports that connect to additional switching layers other than the three illustrated. Further, for example, in the cascaded arrangement of FIG. 4, additional cascaded OCSs may be added after OCS 460 to forward the optical signal to additional switching layers other than the three illustrated. Further, for example, in the nested arrangement of FIG. 5, additional OCSs may be added before OCS 540 to split the optical signal between the additional switching layers and the three illustrated. These principles may be further repeated as many times as needed to provide the desired number of levels of granularity.

[0048] The above deployment examples can be arranged to facilitate the evolution of the network architecture over time. For example, during initial installation, CD or CDC nodes in the wavelength-switched layer of switching nodes may be sufficient for routing optical signals. However, as traffic increases, it may become necessary to activate other switching layers of the switching node. In the example arrangement described above, this may be facilitated in an OCS switch by initially routing incoming optical signals through the wavelength-switched layer and incrementally routing at least some optical signals through the remaining switching layers as traffic increases. Alternatively, when the added switching layer is a fiber-switched layer, because the fiber-switched layer has lower cost and lower optical loss, optical signals may be routed first through the fiber-switched layer and second through the remaining layers. The uniform nature of these arrangements allows the architecture of any given switching node to be adapted to the specific current or future needs of the given node, thereby facilitating continuous node evolution.

[0049] 6 illustrates another example configuration for the evolution of a network architecture in a switching node 600, in which a CDC node 620 included in the switching node 600 may be evolved to connect to additional degrees. In the example of FIG. 6, the CDC node is connected to N degrees. Each degree 602, 604 connects to a respective pair of optical transmission fibers in the OTN and connects to a corresponding WSS 622, 624 to facilitate routing and switching of optical signals in a manner identical or similar to that shown in FIG. 1B. As in FIG. 1B, this includes programming the WSS, FSM, and contention-less M×N WSS. The CDC node 602 may include adding and dropping optical signals at the CDC node based on the routing. An additional WSS 626 is shown. The additional WSS 626 is connected to a virtual direction 606, designated as direction M in the figure, which in turn may connect the CDC node 602 to another direction 608 of the switching node 600, designated as direction L in the figure. The virtual direction may control the connection between the CDC node 620 and the additional direction 608 using OCSs 630 and 640 located therebetween. One OCS 630 may control the transmission of outgoing optical signals from the CDC node 620 to the additional direction 608, while the other OCS may control the transmission of incoming optical signals from the additional direction 608 to the CDC node 620. In this manner, the OCSs 620, 630 may control when and under what conditions the additional direction 608 may be added to the switching architecture of the switching node 600.

[0050] The above example does not specify a specific ratio between OCS-to-OCS connections and wavelength-switched layers. It should be understood and appreciated that this ratio may vary from node to node depending on the specific demands and requirements of each node. Also, the number of degrees in each wavelength-switched domain may be much less than the total number of degrees in the switching node, but the wavelength-switched domains may still be fully connected through additional switched domains, e.g., multiple wavelength-switched domains located in parallel with each other. Additional switching capabilities may be realized through the OCSs connected thereto, the remaining switching layers connected thereto, or any combination thereof. As a result, the number of degrees supported by each individual wavelength-switched domain does not need to be increased; i.e., the current 8-degree or 16-degree wavelength-switched domains will be sufficient for future, evolved deployments of switching layers and switching node architectures.

[0051] The above examples also generally describe and illustrate OTN nodes supporting bidirectional communication on each of their directions. However, it should be recognized that the underlying principles of the present disclosure may be equally applicable to node architectures including at least some directions supporting unidirectional communication. In such cases, the directions may have one or more optical transmission fibers instead of transmission fiber pairs and may include components for unidirectional amplification rather than bidirectional amplification. The example nodes may further be programmed only to route optical signals to nodes with transmit capabilities, as opposed to nodes with only receive capabilities.

[0052] More generally, it should be recognized that any of the above example switching nodes may have a total number of degrees greater than the number of degrees of any of the switched domains contained therein. In practice, multiple parallel switched domains may be used to provide full connectivity and switching capabilities within a switching node.

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

[0054] In block 710, the directions 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 CD node to ensure that an optical signal entering the node in one direction can exit the node in any of the other directions. Furthermore, a provided OCS may be connected to more than one CD or CDC node, for example, by providing multiple CD or CDC nodes in parallel and interconnecting the CD or CDC nodes through interconnections in the OCS.

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

[0056] At block 730, optical signals arriving at the switching node may be rerouted by the OCS from the CD or CDC node to the fiber-switched layer instead. The presence of an OCS at each direction of the CD or CDC node allows any optical signals 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, to accommodate demand for additional capacity by utilizing additional fiber runs added after the initial deployment of the CD or CDC node.

[0057] The above approach avoids the need to scale CD or CDC nodes or other wavelength-based switching solutions as capacity demands increase, and instead allows those solutions to be incorporated into other solutions, such as newly added fiber-switched domains. Over time, and as switching requirements and demands change, a primarily wavelength-switched architecture can be migrated to a primarily fiber-switched architecture.

[0058] Furthermore, the presence of an OCS at each direction of a CD or CDC node, or more generally at each direction of a larger switching node that includes both wavelength-switched and fiber-switched layers, provides full programmability of the switching node and a bidirectional switching solution. Also, using additional OCSs to connect fiber-switched domains instead of additional WSSs to create new wavelength-switched domains has the following advantages: OCSs are less costly than WSSs, OCSs reduce optical loss more than WSSs, and OCSs are more efficient than wavelength-switched architectures. This is advantageous for many reasons, including the greater flexibility that a switched architecture offers.

[0059] Although the technology herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the technology. It is therefore to be understood that numerous modifications can be made to these exemplary embodiments and that other arrangements can be devised without departing from the spirit and scope of the technology as defined in the appended claims.

[0060] Most of the above-described alternative examples are not mutually exclusive but may be implemented in various combinations to achieve unique advantages. Because these and other variations and combinations of the above-described features can be utilized without departing from the subject matter defined by the claims, the above description of embodiments should be viewed as illustrative rather than limiting the subject matter defined by the claims. For example, the preceding processes need not be performed in the exact order described above. Rather, various steps may be performed in a different order, such as in reverse or simultaneously. Steps may also be omitted unless otherwise noted. Furthermore, the examples described herein, and terms such as "such as," "including," and the like, should not be construed as limiting the subject matter of the claims to any particular example; rather, these examples are intended to illustrate only one of many possible embodiments. Furthermore, the same reference symbols in different drawings may identify the same or similar elements.

Claims

1. 1. An optical transport network (OTN) node comprising a plurality of optical circuit switches (OCSs), Each OCS is a respective path of the OTN node, and at least two OCSs are: 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 having a first level of granularity; and at least one second output port connected to a second switching layer having a second level of granularity different from the first level of granularity.

2. 2. The OTN node of 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. 2. The OTN node of claim 1, further comprising a plurality of bidirectional node line amplifiers connected in a one-to-one relationship to input ports of the plurality of OCSs, each bidirectional node line amplifier being located between a respective input port and its corresponding optical transmission fiber.

4. Each bidirectional node line amplifier a band splitter configured to split the optical signals received from each of the optical transmission fibers into different frequency bands; a plurality of ingress amplifiers, each ingress amplifier connected to a respective output port of the band splitter, each bi-directional node line amplifier further comprising: a band combiner configured to combine the optical signals of the different frequency bands received from each OCS of the OTN node; and a plurality of egress amplifiers, each egress amplifier 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 of claim 5 , wherein the first switching layer is a fiber-switched layer and the second switching layer is a wavelength-switched layer.

7. The OTN node of claim 1 , wherein 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.

8. 2. The OTN node of claim 1, wherein 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, each output port of which is connected in a one-to-one relationship to an input port of a second plurality of OCSs, and at least one output port of each OCS of the second plurality of OCSs is connected to a wavelength-switched layer.

9. The OTN node according to claim 8 , wherein the fiber-switched layer, the band-switched layer, and the wavelength-switched layer are arranged in parallel.

10. The OTN node of claim 8 , wherein the fiber-switched layer, the band-switched layer, and the wavelength-switched layer are arranged in either a nested or cascaded configuration.

11. Each OCS: a respective input port configured to be connected to a 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.

12. The OTN node of claim 1 , further comprising the first switched layer and the second switched layer.

13. Connecting a plurality of paths of a colorless / directionless (CD) node or a colorless / directionless / contentionless (CDC) node to a plurality of optical circuit switches (OCS) in a one-to-one relationship; connecting a fiber-switched layer to the plurality of OCSs; and controlling the plurality of OCSs for rerouting at least some received optical signals from the CDC node to the fiber switched layer.

14. An OTN node including a plurality of OCSs, Each OCS is 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 the first switching layer; at least one second output port connected to the second switching layer; and at least one third output port connected to a different one of the plurality of OCSs.

15. 15. The OTN node of claim 14, wherein each of the first switching layer and the second switching layer is a respective wavelength-switched layer including a plurality of wavelength selective switches (WSSs), and the third output ports of the plurality of OCSs are connected to each other such that optical signals transmitted between two of the third output ports do not pass through one WSS of the plurality of WSSs.

16. 15. The OTN node of claim 14, wherein 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 directions greater than the number of directions of the first switching layer and greater than the number of directions of the second switching layer.

17. 16. The OTN node of claim 15, further comprising a plurality of band splitters, each band splitter connected between a corresponding input port and its respective optical transmission fiber, wherein the OTN node is configured to route an entire optical band from one direction of the OTN node to another direction of the OTN node without passing through the wavelength-switched layer.

18. The first switching layer and the second switching layer have different levels of granularity, and at least one of the switching layers is a wavelength-switched layer, a band-switched layer, or a 15. The OTN node of claim 14, wherein the OTN node is one of a fiber-switched layer or a fiber-switched layer.

19. The OTN node of claim 14 further comprising the first switching layer and the second switching layer.

20. 20. The OTN of claim 19, further comprising a third switching layer, wherein the first switching layer, the second switching layer, and the third switching layer each have a different level of granularity.

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