BACKGROUND

[0001] Network devices, such as routers, switches, hubs, and the like, communicably connect devices to each other. A network may include multiple network devices connected to one another in a particular arrangement to form a communication infrastructure of the network. The manner in which the various network devices and/or other devices are connected to each other may be referred to as the topology of the network.

[0002] One such network topology is a ring topology, in which a group of network devices are connected to each other in a ring, such that each of the network devices in the ring shares a first link with the peer network device adjacent to the network device on one side and shares a second link with the peer network device adjacent to the network device on the other side. Thus, there are two paths from any one network device in the ring to any other network device in the ring (a clockwise path and a counterclockwise path), providing redundancy in the event any link fails. Other devices, such as server blades, personal computers, storage arrays, and the like, may be connected to the network devices that form the ring, and may communicate with each other via the ring of network devices.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Fig. 1 is a conceptual diagram illustrating an example system.

[0004] Fig. 2 is a conceptual diagram illustrating an example network device

[0005] Fig. 3 is a process flow diagram illustrating an example process.

[0006] Fig. 4 is a process flow diagram illustrating an example process.

[0007] Fig. 5 is a process flow diagram illustrating another example process.

[0008] Fig. 6 is a conceptual diagram illustrating an example non-transitory computer readable medium. DETAILED DESCRIPTION

[0009] Fig. 1 illustrates an example system 100. The example system 100 illustrated in Fig. 1 includes example network devices 1 10, an example customer network 120, and example customer devices 130.

[0010] The network devices 1 10 are connected to each other in a ring topology, and thus they may be referred to collectively as a ring network. The network devices 1 10 are also connected to the customer network 120 via uplinks 1 12 and to the customer devices 130. The network devices 1 10 may allow the customer network 120 to access the customer device 130 or vice- versa, and thus the network devices 1 10 may also be referred to collectively as an access network.

[001 1 ] The network devices 1 10 include ports 1 1 1 that allow the network devices 1 10 to connect to other devices. In particular, each of the network devices 1 10 includes two ring ports 1 1 1 -L and 1 1 1 -R, which are each connected to a ring port 1 1 1 -L or 1 1 1 -R of the adjacent network devices 1 10. The network devices may also have ports 1 1 1 -D that may be connected to other devices, such as the customer devices 130. In certain example configurations in which a processing block 150 of the network device 1 10 (discussed further below) and the ports 1 1 1 of the network device 1 10 are housed in separate chassis, a port 1 1 1 -D may be used to connect the processing block 150 to the portion of the network device 1 10 that houses the ports 1 1 1 . The number of ports 1 1 1 -D illustrated in Fig. 1 is merely an example, and any number of such ports 1 1 1 -D (including zero) may be included in any given network device 1 10. The network devices 1 10 may also have an uplink port 1 1 1 -U, which is connected to the customer network 120.

[0012] In some example configurations, any one of the ports 1 1 1 of a given network device 1 10 could serve as any one of the ring ports 1 1 1 -L and 1 1 1 -R, the uplink port 1 1 1 -U, and the ports 1 1 1 -D. Whether a given port 1 1 1 is a ring port 1 1 1 -L or 1 1 1 -R, an uplink port 1 1 1 -U, or a port 1 1 1 -D may be determined by which device the given port 1 1 1 is connected to. For example, whichever ports 1 1 1 of a given network device 1 10 are connected to another one of the network devices 1 10 may be identified as the ring ports 1 1 1 -L 1 1 1 -R. As another example, whichever port 1 1 1 is connected to the customer network 120 may be identified as the uplink port 1 1 1 -U. As another example, whichever ports 1 1 1 are connected to customer devices 130 may be identified as ports 1 1 1 -D. In other words, prior to the ports 1 1 1 being connected to any other devices, none of the ports 1 1 1 are necessarily reserved to be the ring ports 1 1 1 -L or 1 1 1 -R, the uplink port 1 1 1 -U, or the ports 1 1 1 -D.

[0013] In other example configurations, one or more ports 1 1 1 may be reserved specifically to operate as one of the ring ports 1 1 1 -L or 1 1 1 -R, the uplink port 1 1 1 -U, or the ports 1 1 1 -D. For example, each network device 1 10 may have one port 1 1 1 that is specifically configured to function as the uplink port 1 1 1 -U.

[0014] The links between adjacent network devices 1 10 may be referred to as ring links. A broadcast communication on the ring network will be passed from each network device 1 10 to its adjacent peers via the ring links, and because all of the network devices 1 10 are connected in a circle such a broadcast communication will end up being distributed to every network device 1 10 in the ring network. However, if left unchecked this could result in a loop condition in which the message is repeatedly sent around the ring from network device 1 10 to network device 1 10 without end. Thus, the network devices 1 10 are configured to prevent such loops within the ring network by keeping at least one ring link blocked at any given time, which ensures that any user traffic flowing around the ring will eventually meet a dead-end and stop. An example protocol that implements this may be found in Recommendation G.8032 of the

International Telecommunication Union Telecommunication Standardization Sector (ITU-T), which may be referred to as an Ethernet Ring Protection Switching (ERPS) protocol. The ring link that is designated to be blocked may be referred to the ring-protection-link (RPL), and one of the network devices 1 10 may be designated as the owner of the RPL (referred to as the RPL owner). In the example system 100 shown in Fig. 1 , the RPL is link 1 13 and hence link 1 13 is blocked. In the example system 1 10, the RPL owner is the network device 1 10-1 . The RPL owner is responsible for blocking the RPL under normal operating conditions. If another link in the ring fails at some point, the RPL owner unblocks the RPL until the failed link is repaired.

[0015] The customer network 120 can be any network or network segment that uses the network devices 1 10 to access the customer devices 130. It is referred to herein as a "customer" network 120 because it uses the services of the network devices 1 10 to access the customer devices 130, and thus may be considered as a customer of the network devices 1 10. However, this usage of the word "customer" should not be interpreted to imply that the customer network 120 necessarily purchases these services, or that an owner and/or operator of the customer network 120 are necessarily a different entity from the owner and/or operator of the network devices 1 10.

[0016] The customer devices 130 may be any devices that can be connected to the network devices 1 10 and that can communicate with the customer network 120. For example, the customer devices 130 may be servers, workstations, personal computers, storage devices (such as hard disk drives), security cameras, sensors, and so on. In the example shown in Fig. 1 , two network devices 1 10 are connected to each customer device 130 for redundancy, but this is merely one example configuration and other configurations could be used. The customer devices 130 are referred to herein as "customer" devices 130 because the customer network 120 accesses the customer devices 130 via the network devices 1 10 (or vice versa). However, this usage of the word "customer" should not be interpreted to imply that the customer devices 130 are owned and/or operated by the same entity as the customer network 120, or that the customer devices 130 are exclusive to the customer network 120.

[0017] In one example arrangement, the network devices 1 10 and the customer devices 130 may form a storage-area-network (SAN), which provides data storage for the customer network 120. In this case, the customer devices 130 may be storage arrays. In one application of this example, a service provider may own and/or operate the SAN, and may run the customer devices 130 and provide access thereto (via the network devices 1 10) as a service to the customer network 120. In another application of this example, the customer network 120 and the SAN are merely different segments of a larger network owned and/or operated by the same entity.

[0018] The network devices 1 10 may be configured to form a customer virtual local-area-network (VLAN), which may include the customer devices 130. A VLAN is a broadcast domain of a computer network that is isolated from other broadcast domains of the network at the data link layer, where a broadcast domain is a logical division in which all nodes thereof can reach each other by broadcast or multicast at the data link layer. A VLAN may be formed, for example, by assigning certain ports 1 1 1 of a network device 1 10 to the VLAN, such that when the network device 1 10 receives a broadcast message for the VLAN, the network device 1 10 passes that message on to only those of its ports that are assigned to that VLAN. A VLAN may also be formed, for example, by logically associating specific devices with VLANs and tagging packets with a VLAN identifier, such that the network device 1 10 passes received packets on to only those devices that are associated with the VLAN that is indicated by the packet's tag. The customer VLAN may allow the customer network 120 to access the customer devices 130, while keeping other domains of the network logically isolated from the customer network 120 and/or the customer devices 130. Although only one customer VLAN is illustrated in Fig. 1 , there may be multiple customer VLANs formed on the network devices 1 10, which may each be connected to a different customer network.

[0019] The network devices 1 10 may also be configured to form a

management VLAN. The management VLAN may include the network devices 1 10 themselves, and may also include other management devices (not illustrated), such as management servers. In certain example configurations in which the processing block 150 of the network device 1 10 and the ports 1 1 1 of the network device 1 10 are housed in separate chassis, the chassis housing the processing block 150 of the network device 1 10 may also be included within the management VLAN. The management VLAN may allow messages related to managing the network devices 1 10 to be communicated between the network devices 1 10 while keeping these messages logically isolated from other domains of the network, such as the customer VLAN.

[0020] As illustrated in Fig. 1 , logical links associated with the customer VLAN (shown in solid lines) and logical links associated with the management VLAN (shown in dashed lines) may share the same physical link in some

circumstances. For example, the ring links, which connect the ring port 1 1 1 -L of one network device 1 10 to the ring port 1 1 1 -R of another network device 1 10, may carry both customer VLAN and management VLAN traffic. Management VLAN traffic may be given a higher priority than customer VLAN traffic.

[0021] The uplink port 1 1 1 -U of each network device 1 10 that is connected to the customer network 120 forms part of an uplink 1 12 to the customer network 120. In Fig. 1 , each of the network devices 1 10-1 through 1 10-4 has an uplink 1 12 to the customer network 120, but this need not necessarily be the case. A minimum of one network device 1 10 should have an uplink 1 12 to the network 120. Multiple uplinks to the network 120 may provide redundancy and allow for load balancing. Generally, the network devices 1 10 attempt to keep at most one of the uplinks 1 12 unblocked (i.e., able to carry traffic to/from the customer network 120) at any given time, with the other uplinks 1 12 being blocked. This is done in order to prevent loops occurring between the ring network and the customer network 120. When two uplinks 1 12 are unblocked at the same time, a loop could occur between the ring network and the customer network 120, which can result in diminishing the performance of the network.

[0022] The blocking of an uplink 1 12 may include, for example, deactivating the associated uplink port 1 1 1 -U, which cuts the connection to the network 120 entirely. However, the uplink 1 12 may also be blocked without deactivating the associated uplink port 1 1 1 -U; for example, the uplink port 1 1 1 -U may be assigned to a VLAN that is isolated from the customer VLAN. This has the effect of preventing any customer traffic from flowing through the uplink port 1 1 1 -U (i.e., blocking the uplink 1 12), but allows the connection to remain active with the customer network 120. The blocked uplinks 1 12 are indicated in Fig. 1 with an X on their link. [0023] Although the network devices 1 10 attempt to keep at most one of the uplinks 1 12 unblocked at any given time in order to prevent loops between the ring network and the customer network 120, the network devices 1 10 are not always able to ensure that this is the case. In particular, there are scenarios in which multiple uplinks 1 12 might end up being unblocked at the same time despite the efforts of the network devices 1 10. For example, two uplinks 1 12 might be activated simultaneously, which could potentially result in both uplinks 1 12 remaining unblocked. Thus, the network devices 1 10 are configured to detect such loops and to resolve the loops appropriately (discussed further below). These loops between the ring network and the customer network 120 are different than the loops within the ring network that were described above, and the loops between the ring network and the customer network 120 are not prevented or corrected by the ring protection protocols such as G.8032.

[0024] Hereinafter, references to a loop should be understood to mean a loop between the ring network and the customer network 120, rather than a loop within the ring network, unless specifically indicated otherwise.

[0025] Each of the network devices 1 10 may be configured to detect the existence of a loop between the ring network and the customer network 120. Any methods for detecting such loops may be used. For example, the network device 1 10 may have a switch driver that is programed with a field processor rule that identifies any received packets whose source MAC address is the same as a MAC address associated with the network device 1 10. If such a packet is received, this would indicate a loop exists that includes the network device 1 10.

[0026] The network devices 1 10 may each be configured to take certain actions in response to detecting a loop. In particular, the network device 1 10 that detects the loop may automatically block its own uplink 1 12 to the customer network 120 (if it has an uplink 1 12). For example, the uplink port 1 1 1 -U may be disabled or placed into an isolated VLAN. In addition, the network device 1 10 that detected the loop may automatically broadcast a message to all of the other network devices 1 10 via the management VLAN notifying them that the loop was detected and instructing them to block their uplinks 1 12 (if they have one). Upon receiving this notification, each network device 1 10 may

automatically block its own uplink 1 12. Because the management VLAN may have a higher priority than the customer VLAN, the loop detection message may be ensured to be delivered to the network devices 1 10 despite the network congestion that may result from a loop.

[0027] The instruction to the network devices 1 10 to block their uplinks 1 12 may be any message that will automatically cause a recipient network device 1 10 to block its uplink 1 12 (if it has one), regardless of whether the message may be described as a notification, a command, an instruction, a request, or anything else. Thus, for example, a notification that a loop was detected may also be an instruction to a network device 1 10 to block its uplink 1 12 if the network device 1 10 is configured to automatically block its uplink in response to being notified that a loop exists.

[0028] The network device 1 10 that is the RPL owner may perform additional operations beyond those described above in response to a loop detection event. In particular, if the RPL owner receives a message that includes the notification that a loop exists, the RPL owner may automatically broadcast another message to all of the network devices 1 10 via the management VLAN instructing them to block their uplinks 1 12. This additional message provides a layer of redundancy to ensure that all of the network devices 1 10 receive a message instructing them to block their uplink 1 12. This message from the RPL owner may also serve as an acknowledgement to the network device 1 10 that detected the loop, acknowledging that the RPL owner received the initial loop- detected message.

[0029] Thus, after the various loop-detection messages have been sent (which may include messages from both the network device 1 10 that detected the loop and from the RPL owner), every uplink 1 12 in the system 1 10 should be blocked. This will automatically stop any loop between the ring network and the customer network 120. [0030] Because the network device 1 10 that detects the loop not only blocks its own uplink 1 12, but also instructs the other network devices 1 10 to block their uplinks 1 12, the loop is more assuredly shut down than if the network device 1 10 had only shut down its own uplink 1 12, since multiple network devices 1 10 do not have to independently detect the loop before all of the uplinks 1 12 are blocked.

[0031] In addition to the operations described above, the network device 1 10 that is the RPL owner may also be responsible for automatically recovering from the loop and the shutdown of traffic that results. In particular, when the RPL owner becomes aware of the existence of a loop (whether by detecting the loop itself, or by being notified by another network device 1 10), the RPL owner may start a recovery timer and wait for a particular amount of time to elapse. If another loop detection message is not received before the designated amount of time elapses, then the RPL owner may automatically select an uplink 1 12 to unblock, and send a message via the management VLAN instructing only the network device 1 12 that has the selected uplink 1 12 to unblock the uplink 1 12. Note that, as used herein, selecting an uplink 1 12 may include indirectly selecting the uplink 1 12; for example, selecting a network device 1 10 may be an indirect selection of the uplink 1 12 that is associated with the selected network device 1 10.

[0032] Thus, the system 100 automatically recovers from the loop condition and resumes normal operations without requiring an administrator to recover the system. Furthermore, because all of the uplinks 1 12 are blocked when the RPL owner begins recovery operations, and because only one network device 1 10 is instructed by the RPL owner at this time to unblock its uplink 1 12, it can be ensured that after the recovery operation only one uplink 1 12 will be unblocked, which should prevent any loops from recurring (at least until some network configuration is changed that might result in a loop).

[0033] The uplink 1 12 that is selected by the RPL owner for unblocking may be the same uplink 1 12 that was previously unblocked, or may be a different uplink 1 12. The RPL owner may know which network devices 1 10 have uplinks 1 12 by, for example, having each network device 1 10 that has an uplink 1 12 send a message to the RPL owner notifying the RPL owner that it has a uplink 1 12, and the RPL owner may maintain a table of the network devices 1 10 with uplinks 1 12. The RPL owner may select the uplink 1 12 (or select a network device 1 10 that has an uplink 1 12) based on any criteria. For example, the RPL owner may use information about previous network traffic of the ring network and/or the customer network 120 to select an uplink 1 12 that will result in suitable network performance. For example, if a particular edge device of the customer network 120 is highly congested, selecting the uplink 1 12 that connects to this edge device may result in less than suitable network

throughput, while selecting an uplink 1 12 that is connecting to an edge device with comparatively little congestion may result in suitable network throughput. As another example, the RPL owner may select the uplink 1 12 that is to be unblocked randomly or in a round-robin fashion. As another example, the RPL owner may maintain a list of network devices 1 10 that have uplinks 1 12 and may select a first network device 1 10 registered in the list.

[0034] Of course, it is possible that the RPL owner is also the network device 1 10 that initially detects the loop, in which case the RPL owner may perform the same operations that any other network device 1 10 would perform if they detected the loop, in addition to the operations described above that are specific to the RPL owner.

[0035] Fig. 2 is a conceptual diagram illustrating an example configuration of one of the network devices 1 10. The example network device 1 10 may include a processing block 150 in addition to the ports 1 1 1 that were already mentioned above. The processing block 150 may include, for example, processing circuitry 151 and a memory 152. The processing circuitry 151 may be any circuitry capable of executing machine-readable instructions, such as a central processing unit (CPU), a microprocessor, a microcontroller device, a digital signal processor (DSP), etc. The memory 152 may be any non-transitory machine readable medium, which may include volatile storage media (e.g., DRAM, SRAM, etc.) and/or non-volatile storage media (e.g., PROM, EPROM, EEPROM, NVRAM, hard drives, optical disks, etc.). The memory 152 may store machine-readable instructions that, when executed by the processing circuitry 151 , cause the network device 1 10 to perform operations described herein. For example, the memory 153 may include loop resolution instructions 153, which may include instructions to perform any of the operations described herein, such as the operations described in Figs. 3-6. The memory 152 may be one example of the non-transitory computer readable medium 1000 illustrated in Fig. 6, in which case the interface controller instructions 153 would correspond to the interface controller instructions 1010 (described below). The processing block 150 may also include, in addition to or in lieu of the processing circuitry 151 and memory 152, an application-specific integrated circuit (ASIC), a field- programmable gate array (FPGA), an application-specific instruction set processor (ASIP), or the like, configured to perform certain operations described herein. Although only one processing circuitry 151 and one memory 152 are illustrated, multiple instances of these may be included as components of the network device 1 10.

[0036] In certain examples, the processing block 150 is not necessarily included within the same chassis or physical device as the ports 1 1 1 . For example, the network device 1 10 could be a collection of physically distinct devices or modules that are communicably connected, such as one device that includes the ports 1 1 1 and another device that includes some or all of the processing block 150. For example, a network switch may include the ports 1 1 1 and a separate switch controller may include some or all of the processing block 150. In such an example, the switch controller may be connected to its corresponding network switch via a communications interface, such as via one of the ports 1 1 1 or via some other dedicated interface. In such an example, certain portions of the processing block 150 might be included in the switch, such as a switch driver and/or various DSPs, ASICs, FPGAs, or ASIPs, while certain other portions of the processing block 150, such as processing circuitry 151 and a memory 152, may be included in the switch controller. In such an example, the various portions of the processing block 150, which may be distributed across the switch device and the separate controller device, may work together to control various operations of the network device 1 10. [0037] In other examples, all of the processing block 150 may be included within the same chassis as the ports 1 1 1 . For example, the network device 1 10 may be a network switch that has its own internal processing circuitry 151 that is sufficient to allow the switch to perform the operations described herein without requiring a distinct switch controller. For example, the network device 1 10 may be a network switch that includes its own processing circuitry 151 and memory 152, where the memory 152 includes instructions to perform operations described herein.

[0038] Fig. 3 illustrates an example process for resolving a loop. The example process may be performed, for example, by the processing block 150 of the example network device 1 10. For example, processing circuitry 151 may execute machine-readable instructions that cause the network device 1 10 to perform the operations of the example process.

[0039] In block 301 , a network device 1 10 detects that a loop exists between the customer network 120 and the ring network.

[0040] In block 302, in response to the detection of block 301 , the network device 1 10 that detected the loop automatically blocks its own uplink 1 12 to the customer network 120.

[0041] In block 303, the network device 1 10 that detected the loop

automatically sends a message to the other network devices 1 10 of the ring that instructs them to block their own uplinks.

[0042] Fig. 4 illustrates another example process for resolving a loop. The example process may be performed, for example, by the processing block 150 of the example network device 1 10. For example, processing circuitry 151 may execute machine-readable instructions that cause the network device 1 10 to perform the operations of the example process.

[0043] In block 401 , a network device 1 10 receives a notification from another network device 1 10 that a loop between the ring network and the customer network 120 was detected. [0044] In block 402, in response to the notification of block 401 , the network device 1 10 that received the notification automatically blocks its own uplink 1 12 to the customer network 120.

[0045] In block 403, it is determined whether the network device 1 10 that received the notification is the RPL owner node. If so (block 403 = YES), then the process proceeds to block A, which continues in Fig. 5. If not (block 403 = NO), the process ends.

[0046] Fig. 5 illustrates a continuation of the example process of Fig. 4 starting with block A. Block A is reached when the network device 1 10 that received the notification is the RPL owner node (block 403 = YES).

[0047] In block 501 , the RPL owner sends a message to all of the network devices 1 10 in the ring network instructing them to block their uplinks 1 12 to the customer network 120.

[0048] In block 502, the RPL owner starts a recovery timer.

[0049] In block 503, it is determined whether another loop-detected message is received from one of the network devices 1 10. If so (block 503 = YES), then the process proceeds to block 504 and the recovery timer is canceled, another message is sent (block 501 ), and the recovery timer is restarted (block 502). If not (block 503 = NO), then the process proceeds to block 505.

[0050] In block 505, it is determined whether the recovery timer has reached a specific value T (i.e., whether a recovery waiting period has ended). If not (block 505 = NO), then the process returns to block 503, and continues to loop between blocks 503 and 505 until either another loop-detected message is received (block 503 = YES) or the recovery waiting period ends

(block 505 = YES). When block 505 is eventually answered YES, then the process proceeds to block 506.

[0051] In block 506, the RPL owner selects one of the uplinks 1 12 to unblock.

[0052] In block 507, the RPL owner instructs the network device 1 10 that has the selected uplink 1 12 to unblock the selected uplink 1 12. [0053] Fig. 6 illustrates an example non-transitory computer readable medium 1000. The non-transitory computer readable medium 1000 may include volatile storage media (e.g., DRAM, SRAM, etc.) and/or non-volatile storage media (e.g., PROM, EPROM, EEPROM, NVRAM, hard drives, optical disks, etc.). The non-transitory computer readable medium 1000 may store machine-readable instructions that are configured to, when executed by processing circuitry (such as the processing circuitry 151 ) of a network device (such as the network device 1 10), cause the network device to perform operations described above, such as the operations described in Figs. 3-5. The memory 152 may be one example of the non-transitory computer readable medium 1000.

[0054] For example, the non-transitory computer readable medium 1000 may include loop resolution instructions 1010. The loop resolution instructions 1010 may be to implement certain operations described above, such as the operations described in Figs. 3-5. The loop resolution instructions 1010 may include, for example, instructions to respond to detecting a loop 101 1 , instructions to respond to receiving a loop-detection notification 1012, instructions to respond to receiving a loop-detection notification as an RPL owner 1013, and instructions to recover from a loop as an RPL owner 1014. The loop resolution instructions 1010 may include additional instructions (not illustrated) to implement any or all of the operations described herein.

[0055] The instructions to respond to detecting a loop 101 1 may include, for example, instructions to detect that a loop exists between an access network in a ring topology and a customer network 1 12, and in response to detecting the loop, automatically: block any uplink 1 12 to the customer network 120 that the network device 1 10 may have, and send a message to all of the peer network nodes instructing them to block any uplinks 1 12 to the customer network 120 they may have.

[0056] The instructions to respond to receiving a loop-detection notification 1012 may include, for example, instructions to, in response to receiving a message from a peer network nodes instructing the network device 1 10 to block its uplink 1 12, block any uplink 1 12 to the customer network 120 that the network device 1 10 may have.

[0057] The instructions to respond to receiving a loop-detection notification as an RPL owner 1013 may include, for example, instructions to, in response to receiving a notification that a loop exists between a ring network and a customer network 120, automatically send a message to all network nodes of the ring network instructing them to block any uplinks 1 12 they may have to the customer network 120.

[0058] The instructions to recover from a loop as an RPL owner 1014 may include, for example, instructions to, if a particular period of time elapses after sending the message without receiving another notification that a loop exists between the ring network and the customer network 120, automatically select one of the network nodes that has an uplink 1 12 connection to the customer network 120 and instruct the selected network node to unblock its uplink to the customer network 120.

[0059] The foregoing describes techniques for automatically responding to loops between a ring network and a customer network, and techniques for automatically recovering from the same. While the above disclosure has been shown and described with reference to the foregoing examples, it should be understood that other forms, details, and implementations may be made without departing from the spirit and scope of this disclosure.