Methods and systems for recovery in coherent optical networks

A method for receiving, by circuitry of an optical node adapted for wavelength multiplexing and wavelength switching, over an OSC an optical signal comprising overhead information indicative of status of at least one of an optical layer in an OTN; terminating the optical signal; notifying software of the status of the optical layer; detecting, based on the status of the optical layer, a uni-directional or bi-directional failure of a working path between the optical node and a second optical node, wherein the working path carries data traffic from the first optical node to the second optical node in the OTN when there is no failure in the working path; and switching, triggered by the uni-directional or bi-directional failure of the working path, to select the data traffic from a protection path, wherein the protection path carries data traffic between the optical node and the second optical node.

FIELD OF THE DISCLOSURE

The disclosure generally relates to methods and apparatuses for recovery in coherent optical transport networks (OTN) using Operation, Administration & Maintenance (OAM) data at the optical layer. More particularly the disclosure relates to use of OAM data transmitted at the optical level for status and failure management in coherent OTNs.

BACKGROUND

An Optical Transport Network (OTN) is comprised of a plurality of switch nodes linked together to form a network. The OTN includes a data layer, a digital layer, and an optical layer. The optical layer contains multiple sub-layers. OTN structure, architecture, and modeling are further described in the International Telecommunication Union recommendations, including ITU-T G.709, ITU-T G.872, and ITU-T G.805, which are well known in the art. In general, the OTN is a combination of the benefits of SONET/SDH technology and dense wavelength-division multiplexing (DWDM) technology (optics).

The construction and operation of switch nodes (also referred to as “nodes”) in the OTN is well known in the art. In general, the nodes of an OTN are generally provided with a control module, input interface(s) and output interface(s). The control modules of the nodes in the OTN function together to aid in the control and management of the OTN. The control modules can run a variety of protocols for conducting the control and management (i.e. Operation, Administration and Maintenance—referred to as OAM) of the OTN. One prominent protocol is referred to in the art as Generalized Multiprotocol Label Switching (GMPLS).

Generalized Multiprotocol Label Switching (GMPLS) is a type of protocol which extends multiprotocol label switching (MLS) to encompass network schemes based upon time-division multiplexing (e.g. SONET/SDH, PDH, G.709), wavelength multiplexing, and spatial switching (e.g. incoming port or fiber to outgoing port or fiber). Multiplexing is when two or more signals or bit streams are transferred over a common channel.

Wave-division multiplexing is a type of multiplexing in which two or more optical carrier signals are multiplexed onto a single optical fiber by using different wavelengths (that is, colors) of laser light.

Generalized Multiprotocol Label Switching (GMPLS) includes multiple types of label switched paths including protection and recovery mechanisms which specify (1) working connections within a network having multiple nodes and communication links for transmitting data between a headend node and a tailend node; and (2) protecting connections specifying a different group of nodes and/or communication links for transmitting data between the headend node to the tailend node in the event that one or more of the working connections fail. Working connections may also be referred to as working paths. Protecting connections may also be referred to as recovery paths and/or protecting paths and/or protection paths. A first node of a path may be referred to as a headend node or a source node. A last node of a path may be referred to as a tailend node or end node or destination node. The headend node or tailend node initially selects to receive data over the working connection (such as an optical channel data unit label switched path) and, if a working connection fails, the headend node or tailend node may select a protecting connection for passing data within the network. The set up and activation of the protecting connections may be referred to as restoration or protection.

Lightpaths are optical connections carried over a wavelength, end to end, from a source node to a destination node in an optical transport network (OTN). Typically, the lightpaths pass through intermediate links and intermediate nodes in the OTN. At the intermediate nodes, the lightpaths may be routed and switched from one intermediate link to another intermediate link. In some cases, lightpaths may be converted from one wavelength to another wavelength at the intermediate nodes.

As previously mentioned, optical transport networks (OTN) have multiple layers including a data packet layer, a digital layer, and an optical layer (also referred to as a photonic layer). The data and digital layers include an optical channel transport unit (OTU) sub-layer and an optical channel data unit (ODU) sub-layer. The optical layer has multiple sub-layers, including the Optical Channel (OCh) layer, the Optical Multiplex Section (OMS) layer, and the Optical Transmission Section (OTS) layer. The optical layer provides optical connections, also referred to as optical channels or lightpaths, to other layers, such as the electronic layer. The optical layer performs multiple functions, such as monitoring network performance, multiplexing wavelengths, and switching and routing wavelengths. The Optical Channel (OCh) layer manages end-to-end routing of the lightpaths through the optical transport network (OTN). The Optical Multiplex Section (OMS) layer network provides the transport of optical channels through an optical multiplex section trail between access points. The Optical Transmission Section (OTS) layer network provides for the transport of an optical multiplex section through an optical transmission section trail between access points. The OCh layer, the OMS layer, and the OTS layer have overhead which may be used for management purposes. The overhead may be transported in an Optical Supervisory Channel (OSC).

The Optical Supervisory Channel (OSC) is an additional wavelength that is adapted to carry information about the network and may be used for management functions. The OSC is carried on a different wavelength than wavelengths carrying actual data traffic and is an out-of-band channel. Typically, the OSC is used hop-by-hop and is terminated and restarted at every node.

The International Telecommunications Union (ITU) recommendation ITU-T G.709 further defines the OTS, OMS and OCh layers and recommends use of the OSC to carry overhead corresponding to the layers. Additionally, ITU-T recommendation G.872 specifies defects for the OTS, OMS, and OCh layers as well as specifying Operation, Administration & Maintenance (OAM) requirements.

ITU-T recommendations suggest that the OSC utilize a Synchronous Transport Signal (STS) Optical Carrier transmission rate OC-3. Optical Carrier transmission rates are a standardized set of specifications of transmission bandwidth for digital signals that can be carried on fiber optic networks. The OC-3 frame contains three column-interleaved STS Level 1 (STS-1) frames; therefore, the line overhead consists of an array of six rows by nine columns (that is, bytes). The OC-3 frame format is further defined in Telecordia's Generic Requirements GR-253, “Synchronous Optical Network Common Generic Criteria,” Issue 4. The OC-3 frame format contains a transport overhead portion. Within the transport overhead portion, bytes designated as D4, D5, D6, D7, D8, D9, D10, D11, and D12 are defined by GR-253 for use by Data Communication Channel (DCC).

The patent application identified by U.S. Ser. No. 13/452,413, titled “OPTICAL LAYER STATUS EXCHANGE OVER OSC—OAM METHOD FOR ROADM NETWORKS” filed on Apr. 20, 2012, discloses methods for supporting OAM functions for the optical layers, for example, for carrying defect information and overhead in the OSC. The application discloses methodology and apparatuses for supporting OAM functions such as continuity, connectivity, and signal quality supervision for optical layers. The methodology discloses mapping optical layer overhead OAM information to specific overhead bits and assigning the overhead bits to specific OSC overhead bytes. This provides reliable exchange of overhead bytes over OSC between nodes.

However, current systems and publications do not disclose mechanisms for optical layer recovery (e.g. protection and/or restoration). Current protocols define mechanisms for supporting protection in digital layers (SDH, OTN Networks) such as GR-253 and G.873.1; however, optical nodes may not have access to the digital layer. Further, there are no protocols for supporting protection functions in optical layers (OMS & OCh layers).

Additionally, current systems and protocols have at least the following limitations at the optical layer: no bi-directional switchover (which may be necessary in latency sensitive applications), no support for reversions, GMPLS restorations are not possible in some failure scenarios, avoiding protection or restoration when there is client signal failures is not possible, and path monitoring schemes do not work in coherent networks unless additional and expensive hardware is deployed.

For example, in current systems there is no bi-directional switchover. Therefore, a failure in a uni-directional fiber carrying optical data traffic from a headend node to a tailend node would be detected by the tailend node, since the tailend node would detect the lack of received optical data traffic, but not by the headend node transmitting the optical data traffic signals. The tailend node would switch to selecting received optical data traffic from a protection path, but the headend node would continue to select received data traffic from the working path. This can result in errors in latency sensitive applications.

The present disclosure addresses these deficiencies utilizing OAM data transmitted at the optical level for status and failure management at the optical layer in coherent OTNs.

SUMMARY

Method and nodes are disclosed. The problems caused by the lack of mechanisms for optical layer-based recovery are addressed by utilizing mapped optical layer overhead OAM information in the OSC to implement recovery mechanisms to manage status information and failures in coherent OTNs at the optical layer.

DETAILED DESCRIPTION

The mechanisms proposed in this disclosure circumvent the problems caused by the lack of mechanisms for optical layer recovery. The present disclosure describes methods and apparatuses utilizing mapped optical layer overhead OAM information in the OSC to implement recovery mechanisms to manage status information and failures in coherent OTNs at the optical layer.

DEFINITIONS

If used throughout the description and the drawings, the following short terms have the following meanings unless otherwise stated:

BDI stands for Backward Defect Indication. A single-bit BDI field, for example, can convey, towards the source, a signal fail status detected in a tandem connection termination sink function. BDI-P stands for Backward Defect Indication for Payload signal fail status. BDI-O stands for Backward Defect Indication for Overhead signal fail status.

DWDM stands for dense wavelength division multiplexing. DWDM multiplexes multiple optical carrier signals, such as Optical Channel (OCh) signals or Super Channel (SCh) signals, onto a single optical fiber by using different laser light wavelengths (colors).

FDI stands for Forward Defect Indication. FDI-P stands for Forward Defect Indication for Payload signal fail status. FDI-O stands for Forward Defect Indication for Overhead signal fail status.

FEC stands for forward error correction.

FPGA stands for field programmable gate array. FPGAs can be programmed after deployment in a system.

FRU stands for field replaceable unit.

GMPLS stands for Generalized Multi-Protocol Label Switching which extends Multi-Protocol Label Switching to encompass time-division (for example, SONET/SDH, PDH, G.709), wavelength (lambdas), and spatial multiplexing (e.g., incoming port or fiber to outgoing port or fiber). The GMPLS framework includes a set of routing protocols which runs on a control module. The Generalized Multiprotocol Label Switching architecture is defined, for example in RFC 3945.

LOS stands for Loss of Signal.

LSP stands for Label Switched Path which is a path through a Generalized Multi-Protocol Label Switching network. Note that Label Switched Paths can be bidirectional or unidirectional; they enable packets to be label switched through the Multiprotocol Label Switched network from a port on an ingress node (which can be called a headend node) to a port on an egress node (which can be called a tailend node).

MPLS stands for multi-protocol label switching which is a scheme in telecommunications networks for carrying data from one node to the next node. MPLS operates at an OSI model layer that is generally considered to lie between traditional definitions of layer 2 (data link layer) and layer 3 (network layer) and is thus often referred to as a layer 2.5 protocol.

OAM stands for Operation, Administration and Maintenance. Examples of OAM functions include continuity, connectivity and signal quality supervision.

OADM stands for optical add/drop multiplexer. ROADM stands for reconfigurable optical add/drop multiplexer. Network operators can remotely reconfigure the multiplexer by sending soft commands with a ROADM.

OC stands for optical carrier. Optical carrier transmission rates are a standardized set of specifications of transmission bandwidths for digital signals that can be carried on fiber optic networks.

OCh stands for Optical Channel layer.

OLT stands for Optical Line Terminal.

OMS stands for Optical Multiplex Section layer.

OSC stands for Optical Supervisory Channel.

OTN stands for Optical Transport Network which includes a set of optical switch nodes which are connected by optical fiber links. ITU-T recommendations G.709 and G.872 define OTN interface requirements and network architecture respectively.

OTS stands for Optical Transmission Section layer.

SCh stands for Super Channel. A Super-Channel (SCh) is a collection of one or more frequency slots to be treated as a unified entity for management and control plane purposes. A Frequency Slot is a range of frequency allocated to a given channel and unavailable to other channels within the same flexible grid. A frequency slot is a contiguous portion of the spectrum available for an optical passband filter. A frequency slot is defined by its nominal central frequency and its slot width. A frequency slot is further defined in the International Telecommunications Union Recommendation ITU-T G.694.1, “Spectral grids for WDM applications: DWDM frequency grid”. A contiguous spectrum Super-Channel is a Super-Channel with a single frequency slot. A split-spectrum Super-Channel is a Super-Channel with multiple frequency slots.

SF stands for Signal Failure.

SONET/SDH stands for Synchronous Optical Networking/Synchronous Digital Hierarchy which are standardized multiplexer protocols that transfer multiple digital bit streams over optical fiber using lasers or light emitting diodes.

STS stands for Synchronous Transport Signal. STS-1 stands for Synchronous Transport Signal—Level 1.

TCM stand for Tandem Connection Monitoring.

TTI stands for Trail Trace Identifier. An exemplary TTI for optical transport networks is defined in ITU G.709.

DESCRIPTION

Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the quantifying device, the method being employed to determine the value, or the variation that exists among the study subjects. For example, but not by way of limitation, when the term “about” is utilized, the designated value may vary by plus or minus twelve percent, or eleven percent, or ten percent, or nine percent, or eight percent, or seven percent, or six percent, or five percent, or four percent, or three percent, or two percent, or one percent.

The use of the term “at least one” or “one or more” will be understood to include one as well as any quantity more than one, including but not limited to, 1, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 100, etc. The term “at least one” or “one or more” may extend up to 100 or 1000 or more depending on the term to which it is attached. In addition, the quantities of 100/1000 are not to be considered limiting, as lower or higher limits may also produce satisfactory results.

In addition, the use of the phrase “at least one of X, V, and Z” will be understood to include X alone, V alone, and Z alone, as well as any combination of X, V, and Z.

The use of ordinal number terminology (i.e., “first”, “second”, “third”, “fourth”, etc.) is solely for the purpose of differentiating between two or more items and, unless explicitly stated otherwise, is not meant to imply any sequence or order or importance to one item over another or any order of addition.

As used herein, any reference to “one embodiment,” “an embodiment,” “some embodiments,” “one example,” “for example,” or “an example” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearance of the phrase “in some embodiments” or “one example” in various places in the specification is not necessarily all referring to the same embodiment, for example.

In accordance with the present disclosure, messages transmitted between nodes can be processed by circuitry within the input interface(s), and/or the output interface(s) and/or the node controller. Circuitry could be analog and/or digital, components, or one or more suitably programmed microprocessors and associated hardware and software, or hardwired logic. Also, certain portions of the implementations have been described as “components” that perform one or more functions. The term “component,” may include hardware, such as a processor, an application specific integrated circuit (ASIC), or a field programmable gate array (FPGA), or a combination of hardware and software. Software includes one or more computer executable instructions that when executed by one or more component cause the component to perform a specified function. It should be understood that the algorithms described herein are stored on one or more non-transient memory. Exemplary non-transient memory includes random access memory, read only memory, flash memory or the like. Such non-transient memory can be electrically based or optically based. Further, the messages described herein may be generated by the components and result in various physical transformations. Additionally, it should be understood that the node can be implemented in a variety of manners as is well known in the art.

An exemplary optical transport network (OTN)20is shown inFIG. 1, by way of example.FIG. 1illustrates a channel status flow for a service in channel protection. The optical transport network20includes optical switch nodes22A-22n(hereinafter referred to as “nodes” or “optical nodes” or “photonic nodes”). The optical transport network20may include any number of optical nodes22A-22n. For exemplary purposes, the optical transport network20ofFIG. 1includes five optical nodes22A-22E. The optical transport network20may be configured in any topology, for example, linear, ring, or mesh.

A headend node and a tailend node may be denoted for a particular path in accordance to the path setup direction. In this example, optical node22A functions as a headend node (also known as a source node); while optical node22C functions as a tailend node (also known as a destination node). Other optical nodes22between the headend node22A and tailend node22C in a particular path are known as intermediate nodes. In this example, the optical nodes22B,22D, and22E act as intermediate nodes. In between the optical nodes22A-22nare communication links30A-30m. For purposes of simplicity of explanation, links30A-30G are illustrated inFIG. 1, but it will be understood that there may be more or fewer links30.

The optical nodes22A-22nare adapted to facilitate the communication of data traffic (which may be referred to herein as “traffic” and/or “data”) between optical nodes22A-22nin the optical transport network20over communication links30A-30m, as well as into and out of the optical transport network20. Control information is also sent and received by optical nodes22A-22nover communication links30A-30m. The control information may be carried via an Optical Supervisory Channel (OSC)32through the communication links30A-30m. As previously described, the OSC32is an additional wavelength that is adapted to carry information about the optical transport network20and may be used for management functions. The OSC32is carried on a different wavelength than wavelengths carrying actual data traffic and is an out-of-band channel. Typically, the OSC32is used hop-by-hop and is terminated and restarted at every node.

The communication links30can be implemented in a variety of ways, such as a physical link including electrical (e.g., copper wire or coax) and/or optical signal (e.g., optical fiber or other waveguide) carrying capabilities, or as a wireless link. The communication links30can be fiber optic cables, electronics cables, wireless communication links, or the like.

Data traffic and control information may follow one or more paths through the optical transport network20. A working path34(for example, OCh #1) may be established by one or more optical nodes22A-22n, or by a controller (not shown) separate from the optical nodes22A-22nand/or separate from the optical transport network20. In the example shown inFIG. 1, the working path34is established between headend node22A and tailend node22C through intermediate node22B. The working path34initially carries data traffic and control information, and continues to carry data traffic and control information while there is no failure on the working path34.

A protection path36(for example, OCh #1) may also be established to carry data traffic and control information. The headend node22A and the tailend node22C may select data traffic from the protection path36if there is a failure on the working path34. InFIG. 1, the protection path36is illustrated between headend node22A and tailend node22C through intermediate nodes22D and22E.

The working path34and the protection path36can be established by one or more nodes22A-22n, such as headend node22A, prior to any failure in the optical transport network20, as illustrated inFIG. 1. Additionally, or alternately, one or more protection path36may be established after a failure in the optical transport network20(seeFIGS. 9-10). The working path34and the protection path36may be established, for example, by using GMPLS protocols. The working path34and the protection path36may be bi-directional or co-routed.

In general, the term “dedicated protection,” as used herein, refers to a situation in which the headend node22A or tailend node22C sets up a dedicated protection path36for a particular working path34, as illustrated inFIG. 1, in case of failure of the working path34, before failure of the working path34. A type of dedicated protection in accordance with an embodiment of the present disclosure is known in the art as “1+1 Protection.” In dedicated protection, the data traffic is simultaneously transmitted from the headend node22A (and/or tailend node22C) on both the working path34and protection path36. Dedicated protection may be used with unidirectional and bidirectional protection, as described in RFC 4872, “RSVP-TE Extensions for E2E GMPLS Recovery” (May 2007).

Referring toFIGS. 2 and 3, shown therein are block diagrams of aspects of an exemplary optical node22A constructed in accordance with the present disclosure. In general, the optical nodes22A-22ntransmit and receive data traffic and control signals.

The optical nodes22A-22ncan be implemented in a variety of ways. Nonexclusive examples include optical line terminals (OLTs), optical crossconnects (OXCs), optical line amplifiers, optical add/drop multiplexer (OADMs) and/or reconfigurable optical add/drop multiplexers (ROADMs), interconnected by way of intermediate links. OLTs may be used at either end of a connection or intermediate link. OADM/ROADMs may be used to add, terminate and/or reroute wavelengths or fractions of wavelengths. Optical nodes are further described in U.S. Pat. No. 7,995,921 titled “Banded Semiconductor Optical Amplifiers and Waveblockers”, U.S. Pat. No. 7,394,953 titled “Configurable Integrated Optical Combiners and Decombiners”, and U.S. Pat. No. 8,223,803 (Application Publication Number 20090245289), titled “Programmable Time Division Multiplexed Switching,” the entire contents of each of which are hereby incorporated herein by reference in its entirety.

As shown inFIG. 2, the exemplary optical node22A is provided with one or more input interfaces52, one or more output interfaces54, and circuitry such as one or more line card56, one or more switch58, and one or more control module60. The node22A may also include non-transitory memory (not shown), either within the control module60and/or the switch58, or separate from the control module60and/or the switch58. As is well known to one having skill in the art, the optical node22A may include other components, nonexclusive examples of which include one or more multiplex card61, one or more demultiplex card63, and/or one or more amplifier card65.

In general, the control module60serves to control the operations of the optical node22A. The control module60may have software62installed on the control module60. In some implementations, the control module60and/or software62controlling the operations of the optical node22A may be located separately from the optical node22A. In one implementation, the software62may be network control software.

In general, the line card56receives and transmits data traffic signals67indicative of data traffic. The line card56is capable of coherent detection. The line card56may have firmware installed on the line card56, as is well known to those having skill in the art. Nonexclusive examples of line card56include Field Programmable Gate Arrays and ASICs. The line card56may monitor health of the data traffic received by the optical node22A.

The switch58, also referred to as a selector, may be a Wavelength Selective Switch (WSS). When the node22A receives data traffic, the switch58is used to select data traffic from either the working path34or the protection path36based on the status of the optical layer, as detected from the data path and the control path in accordance with the present disclosure, as will be further described herein. The switch58is in communication with the line card56and the control module60.

The input interface(s)52and the output interface(s)54of the optical node22A are adapted to communicate with corresponding input interface(s)52, and output interface(s)54of one or more other node22B-22nwithin the optical transport network20via communication links30, as shown inFIG. 1. An example of an input interface52and/or an output interface54is an Ethernet card or optical port. In general, each of the input interface(s)52and/or the output interface(s)54may have a unique logical identification, such as an IP address.

The implementation of the input interface(s)52, and the output interface(s)54will depend upon the particular type of communication link30that the particular input interface52and/or output interface54is designed to communicate with. For example, one of the input interfaces52can be designed to communicate wirelessly with another optical node22within the optical transport network20, while one of the output interfaces54of the node22can be designed to communicate optically through a fiber-optic link. For a particular node22, multiple input interfaces52can be of the same type or different types; multiple output interfaces54can be of the same type or different types; and the input interface(s)52and output interface(s)54can be of the same type or different types.

The input interface52and the output interface54are shown separately for purposes of clarity. However, it should be understood that one or more of the input interfaces52and/or the output interfaces54could be connected to a single communication link30and implemented as a single device, such as a line module.

The components of the optical node22may be implemented as separate devices, which may have their own power supply, local memory, and processing equipment. In another example, the optical node22can be implemented as a single device having a shared power supply, memory and processing equipment. Or, in another example, the node22can be implemented in a modular manner in which one or more components share a power supply and/or housing.

As illustrated inFIG. 3, the exemplary optical node22A, may receive one or more optical control signal64, from one or more other optical nodes22B-22nin the optical transport network20, containing information regarding the Operation, Administration, and/or Maintenance (OAM) of optical layers in the optical transport network20. The optical control signal64may be carried via the Optical Supervisory Channel (OSC)32, or any suitable optical control channel. The optical layer OAM information, such as status and defect information, is mapped to specific bits in OSC32. The OAM information communicated for a given data signal may be based at least in part on the health of the hardware in the path of the data signal and the health of the optical data path itself. Methods and systems for transmitting and receiving OAM data within the OSC32are more fully described in the patent application identified by U.S. Ser. No. 13/452,413, titled “OPTICAL LAYER STATUS EXCHANGE OVER OSC—OAM METHOD FOR ROADM NETWORKS” filed on Apr. 20, 2012.

In general, the optical control signal64is terminated at the optical node22A, as illustrated inFIG. 3, where the control module60extracts the optical layer overhead OAM information from the optical control signal64in the OSC32. The optical node22A may notify software62in the optical node22A and/or may notify other optical nodes22B-22nin the optical transport network20of the status of the optical layer, as indicated by the overhead information. In one embodiment, the optical node22A inspects the optical control signal64for stable values before notifying the software62of the status of the optical layer. The filtering for stable values may be done in hardware, in which case, the association of filtering characteristics to fields may be fixed in the hardware code, for example, in a FPGA's code. Also, if granular notifications (interrupts) are provided to the software62, the association of fields to interrupt bits may be fixed in the hardware code.

Additionally, the optical node22A may write, with the software or with hardware, Operation, Administration, and/or Maintenance (OAM) information of the optical layers in the optical transport network20into overhead of the optical control signal64to be transmitted from the optical node22A via the OSC32. This information may include, for example, equipment status, incoming signal status, and/or connectivity information. Of course, the information may include any OAM information. The optical node22A may then initiate, with the software, transmission of the optical control signal64via the Optical Supervisory Channel (OSC)32, or any suitable optical channel.

The optical supervisory channel32(OSC) may utilize a Synchronous Transport Signal (STS) Optical Carrier transmission rate OC-3. Alternatively, the OSC32may utilize a concatenated Optical Carrier transmission rate OC-3c. Alternately, the OSC32may utilize an Optical Carrier transmission rate OC-N, such as OC-3, OC-12, OC-48, OC-192, or OC-768, or any suitable OC-N. Optical Carrier transmission rates are a standardized set of specifications of transmission bandwidth for digital signals that can be carried on fiber optic networks. OC-3 can have an optical carrier transmission rate of up to 155.52 megabits per second. Bytes within the OC-3 can be designated to carry OAM overhead for the optical layers in the optical transport network20. OAM information for the optical layers, OTS, OMS, and OCh/Super Channel, may be assigned to defined overhead fields with a defined number of bits. The overhead fields and bits may be assigned to defined bytes in the STS-1 frames of the OC-N. This method is further described in the patent application identified by U.S. Ser. No. 13/452,413, titled “OPTICAL LAYER STATUS EXCHANGE OVER OSC—OAM METHOD FOR ROADM NETWORKS” filed on Apr. 20, 2012.

Access to the OC-3 overhead bytes in the OSC32is provided for each fiber direction supported by the optical node22A. As illustrated inFIG. 3, for example, in a typical node22A, the number of fiber directions may be 1, 2, 3 4, 5, 6, 7, 8, or 9, directions. The status of individual channels transmitted on the fiber is dependent on one or more factors, nonexclusive examples of which include signal strength of the incoming signal, the health of the hardware, and connectivity information (provisional and physical). The optical node22A inspects the overhead bytes in the OSC32and may look for stable values before notifying the software62of the status of the incoming data traffic.

FIG. 4illustrates a flow diagram of a monitoring and reporting process100in accordance with the present disclosure. In process100, in step102, an exemplary optical node22A in accordance with the present disclosure continuously monitors the status of the optical transport network20by monitoring the overhead transmitted in the optical control signal64in the OSC32and monitoring the data traffic of the working path34and the protection path36. The optical node22A reports the status, in step106, to the control module60, and/or software62, and/or components or circuitry. The status may also be reported to hardware, for example a FPGA or ASIC. In decision step104, the optical node22A determines if there is a change in the status of the optical transport network20. If there is no change, the optical node22A continues monitoring the status and reports the status in step106, as previously described. If there is a change in status, the optical node22A reports the status in step106, as previously described.

Turning now toFIG. 5, shown therein is the exemplary optical transport network20ofFIG. 1, in which a failure, designated by “X”, has occurred in the working path34. In this example, the failure “X” is the failure of a uni-directional fiber70in communication link30between optical node22A and optical node22B. Each node22A-22nis capable of detecting failures and providing status updates to both downstream nodes22and upstream nodes22over the control path OSC32. For example, the optical nodes22A,22B, and22C in the working path34are monitoring the overhead in the OSC32. The OSC32terminates at the optical nodes22A,22B, and22C, and the OAM information is extracted from the OSC32, as previously described. The optical nodes22A,22B, and22C are also monitoring the data traffic in the working path34and/or protection path36, such as with the firmware in the line cards56, and/or other circuitry, such as the one or more multiplex card61, one or more demultiplex card63, and/or one or more amplifier card65. Node22B detects uni-directional failure “X” and provides status information using the overhead bits in the OSC32to the headend node22A as well as to the tailend node22C.

Upon detection in the monitored OAM information from the OSC32, and/or upon detection in the monitored data traffic, of the failure “X” in working path34, the headend node22A and tailend node22C, may switch to the protection path36as the provider of the data traffic, using switches58. The switch to the protection path36may be carried out by software62on the control module60or by hardware, for example a FPGA or ASIC.

Because the headend node22A and the tailend node22C are both monitoring the OAM information from the OSC32, the headend node22A and the tailend node22C may both detect the failure “X”. Additionally, the intermediate node22B may detect the failure and notify the headend node22A and the tailend node22C. Therefore, both the headend node22A and the tailend node22C may switch to the same path, such as protection path36, irrespective of the uni-directional nature or bi-directional nature of the failure “X”.

FIG. 6is a flow diagram of an exemplary protection process200in accordance with the present disclosure. In this embodiment, in step202, the optical node, such as optical node22B and/or22C, for example, has detected a uni-directional or bi-directional failure in the optical transport network20, by monitoring the OAM information from the OSC32as well as status information from the line card56, and/or other circuitry, such as the one or more multiplex card61, one or more demultiplex card63, and/or one or more amplifier card65, as previously described. In step204, the optical node22B determines whether or not the failure is in the working path34. In step206, if the failure is in a path other than the working path34, the optical node22B and/or22C may send a Backward Defect Indication (BDI) to the headend node22A over the optical control channel in the overhead of the OSC32, indicating the failure details.

If the failure is in the working path34, in step208, the tailend node22C may then determine, by monitoring the OAM information from the OSC32as well as status information from the circuitry (such as line card56, and/or other circuitry, such as the one or more multiplex card61, one or more demultiplex card63, and/or one or more amplifier card65), whether or not the protection path36has a good status, that is, whether or not there is a failure in the protection path36. If the status of the protection path36is bad, that is, if a failure is detected in the protection path36, the tailend node22C will not switch to the protection path36as the provider of the data traffic. The tailend node22C may, in step210, report the failure to switch to the protection path36.

As shown in step212, if the status of the protection path36is good, that is, if no failure is detected in the protection path36, the switch58in the tailend node22C will switch to the protection path36as the provider of the data traffic. The control module60of the tailend node22C may report the switch to the protection path36to the other optical nodes22A,22B,22D-22n, the optical transport network20, software62, and/or a network controller (not shown). The headend node22A will switch to the protection path36as the provider of the data traffic.

Next, once again in step206, the optical node22B and/or22C may send a Backward Defect Indication (BDI) regarding the working path34to the source node22A of the path over the optical control channel in the overhead of the OSC32.

In the case of a bi-directional failure, both the headend node22A and the tailend node22C detect the failure of the working path34and switch to the protection path36as the provider of the data traffic. In the case of uni-directional failure “X”, as shown in the example, one of the headend node22A and the tailend node22C detects the failure of the working path34, whereas the other receives Backward Defect Indication (BDI) from the one detecting the uni-directional failure “X”, and both the headend node22A and the tailend node22C switch to the protection path36as the provider of the data traffic. The BDI is sent over the optical control channel in the overhead of the OSC32. Additionally, intermediate node22B in the working path34may detect the uni-directional failure “X” in the working path34, using the OAM information from the OSC32as well as status information from the line card56, and notify the headend node22A and/or the tailend node22C of the uni-directional failure “X” in the working path34, over the optical control channel in the overhead of the OSC32.

FIG. 7is a flow diagram of exemplary process sequence250in the optical transport network20ofFIG. 1. Initially, the status of the working path34between headend node22A and tailend node22C through intermediate node22B is good, with no failures. The status of the working path34is transmitted in the overhead of the OSC32, as represented by arrows252and254, between the nodes22A-22C in the working path34. Additionally, the status of protection path36between headend node22A and tailend node22C through optical nodes22D and22E is good, with no failures. The status of the protection path36is transmitted in the overhead of the OSC32between the optical nodes22A,22D,22E,22C, as represented by arrows256,258, and260. Then, in sequence262, the intermediate node22B detects the failure “X” in the working path34, by monitoring the OAM information from the OSC32as well as data traffic status information from the line card56, multiplex card(s)61, demultiplex card(s)63, and/or amplifier card(s)65. In sequence264, the intermediate node22B sends a Forward Defect Indication (FDI) over the optical control channel in the overhead of the OSC32to the tailend node22C.

In sequence266, the tailend node22C may detect the failure “X” of the working path34by monitoring the OAM information from the OSC32as well as status information from the line card56(and/or multiplex card(s)61, demultiplex card(s)63, and/or amplifier card(s)65), and receives the FDI from the OSC32from intermediate node22B indicating the failure “X”. As indicated by sequence268, the tailend node22C sends a BDI to the headend node22A over the optical control channel in the overhead of the OSC32. Additionally, the intermediate node22B may send a BDI, received from tailend node22C, to the headend node22A over the optical control channel in the overhead of the OSC32.

In sequences270and272, the headend node22A and the tailend node22C check the status of the protection path36, by monitoring the OAM information from the OSC32as well as status information from the line card56, as previously described. If the status is good (no failures in the protection path36), then the headend node22A and the tailend node22C switch to the protection path36as the provider of the data traffic. Both the headend node22A and the tailend node22C may switch, even if the failure is simply uni-directional failure.

FIG. 8illustrates a flow diagram of another exemplary process sequence280, in which, after the headend node22A and the tailend node22C switch to the protection path36as discussed in relation toFIG. 7, the headend node22A and the tailend node22C may both revert back to the working path34after the failure “X” clears. For example, in sequence284, the optical node22B, monitoring the OAM information from the OSC32and monitoring status information from the line card56, multiplex card(s)61, demultiplex card(s)63, and/or amplifier card(s)65, detects that the failure “X” on the working path34has been cleared. In sequence286, the optical node22B detects that the failure “X” in the working path34is cleared, by monitoring the OAM information from the OSC32as well as status information from the line card56(and/or multiplex card(s)61, demultiplex card(s)63, and/or amplifier card(s)65).

In sequence286, the optical node22B sends an indication of the cleared status of the working path34, and/or stops sending the FDI, over the optical control channel in the overhead of the OSC32to tailend node22C.

In sequence288, the tailend node22C sends an indication of the cleared status of the working path34over the optical control channel in the overhead of the OSC32to the headend node22A. Additionally, the intermediate node22B may send an indication of the cleared status of the working path34and/or, stop sending the BDI, to the headend node22A over the optical control channel in the overhead of the OSC32.

Both the headend node22A and the tailend node22C, in sequences290and292, may run a wait-to-restore (WTR) timer after receiving notification of the cleared status of the working path34. After the timer expires, the headend node22A and the tailend node22C may check the status of the working path34to ensure that the failure “X” has truly been resolved, by monitoring the OAM information from the OSC32and monitoring status information from the line card56.

As shown in sequences294and296, if the status of the working path34is good, the headend node22A and the tailend node22C both select the working path34as the provider of the data traffic. This bi-directional reversion is useful, for example, in low latency applications where both directions of data traffic experience the same amount of delays.

If the protection path36fails before the WTR timer expires, the headend node22A and the tailend node22C may switch back to the working path34as the provider of the data traffic, without waiting for the WTR timer to expire.

It will be understood in dedicated protection schemes that the protection path36may continue to carry a duplicate of the data traffic.

FIG. 9is a block diagram of an exemplary optical transport network20a, similar to optical transport network20, except that the protection path36or a restoration path36ais not originally established. Rather, GMPLS is used to dynamically setup an optical working path34a, referred to as an Optical-SubNetwork Connection (O-SNC). The working path34amay be configured at headend node22A and setup from headend node22A. GMPLS uses OSPF-TE to discover topology information and RSVP-TE to signal for optical path setup. In this example, restoration features allow recovery of the data traffic in case of a failure along the working path34a. The restoration performed by the headend node22A is triggered by detection of a failure. That is, in this case the headend node22A waits to configure and setup the restoration path36auntil there is a known failure. The failure may be detected by monitoring the OAM information from the OSC32and monitoring data traffic status information from the line card56, multiplex card(s)61, demultiplex card(s)63, and/or amplifier card(s)65.

For example,FIG. 10illustrates the exemplary optical transport network20aofFIG. 9in which a failure, designated as “X”, has occurred in the optical transport network20a, such as a cut in uni-directional fiber70in communication link30between optical node22A and optical node22B in the working path34a. The optical nodes22A,22B, and22C in the working path34aare monitoring the overhead in the OSC32. The OSC32terminates at the optical nodes22A,22B, and22C, and the OAM information is extracted from the OSC32. The optical nodes22A,22B, and22C are also monitoring the data traffic in the working path34, such as with the firmware in the line cards56, multiplex card(s)61, demultiplex card(s)63, and/or amplifier card(s)65.

In the case of uni-directional failure “X” as in the example ofFIG. 10, the headend node22A does not detect the uni-directional failure “X” from monitoring data traffic by the line card56, since the failure is downstream. Rather, the headend node22A detects the downstream failure by monitoring the OAM information from the OSC32. More particularly, the headend node22A may be notified of the failure through BDI information sent in the OSC32from the tailend node22C and/or intermediate node22B. Once the BDI information is received, the headend node22A computes an alternate path for the data traffic, referred to as the restoration path36a, and switches to the restoration path36a. In this example, the restoration path36ais setup between headend node22A and tailend node22C through intermediate nodes22D and22E. The restoration path36ais set up dynamically using GMPLS signaling.

In the case of bi-directional failure, the headend node22A may detect the failure “X” in either, or both of, the data traffic through the line card56(and/or multiplex card(s)61, demultiplex card(s)63, and/or amplifier card(s)65) and the OAM information from the OSC32.

FIG. 11is a flow diagram of an exemplary process sequence300in the optical transport network20aofFIG. 10. As described in regards toFIG. 10, in this example, in sequence302, the tailend node22C transmits in the OSC32Backward Detection Indication (BDI) of the failure “X” to the headend node22A. Again, the intermediate node22B may also transmit in the OSC32Backward Detection Indication (BDI) of the failure to the headend node22A. The headend node22A has restored the data traffic on restoration path36a, as indicated in sequence304. Tailend node22C has selected the restoration path36aas the provider of the data traffic, as indicated in sequence306. In this example the data traffic is also still bridged to the original working path34aby the headend node22A and the tailend node22C. That is, the same data traffic is still broadcast to both the original working path34aand the new restoration path36a.

In sequence308, the optical node22B detects that the failure in the working path34ais cleared, by monitoring the OAM information from the OSC32, and may also be detected by monitoring the status information from the line card56, multiplex card(s)61, demultiplex card(s)63, and/or amplifier card(s)65. In sequence310, the optical node22B sends an indication of the cleared status of the working path34a, and/or stops sending the FDI, over the optical control channel in the overhead of the OSC32to tailend node22C.

In sequence312, the optical node22C sends an indication of the cleared status of the working path34aover the optical control channel in the overhead of the OSC32to the headend node22A. Additionally, the intermediate node22B may send an indication of the cleared status of the working path34aand/or, stop sending the BDI, to the headend node22A over the optical control channel in the overhead of the OSC32.

Both the headend node22A and the tailend node22C, in sequences314and316, may run a wait-to-restore (WTR) timer after receiving notification of the cleared status of the working path34a. After the timer expires, the headend node22A and the tailend node22C may check the status of the working path34ato ensure that the failure has truly been resolved, by monitoring the OAM information from the OSC32and monitoring status information from the line card56. If the restoration path36awere to fail during the running of the timer, the headend node22A and the tailend node22C may switch back to the working path34abefore the timer expires, as long as the status of the working path34ais good.

As shown in sequences318and320, if the status of the working path34ais good, the headend node22A and the tailend node22C both select the working path34aas the provider of the data traffic. The restoration path36amay then be deleted and its resources released to the optical transport network20a.

Further, in prior art systems, a failure of an incoming client signal, for example, to headend node22A, could trigger the headend node22A and tailend node22C to switch to receiving traffic from the protection path36and/or restoration path36aunnecessarily. By using the previously disclosed protection and recovery mechanisms utilizing the overhead bytes of the OSC32to transmit status and failure data, the headend node22A and tailend node22C detect failures in the client signal entering the optical transport network20,20a. Upon detection, the headend node22A may write the client failure information into the overhead of the OSC32and transmit the information via the OSC32to one or more other optical nodes22B-22nin the optical transport network20,20a. With this information, the nodes22A-22nmay avoid unnecessary switching to alternate paths.

The examples described above are not exclusive as to the use of the present invention. OAM information for optical layers transmitted at the optical level in coherent optical transport networks20may be useful in other status monitoring, dedicated protection, fast restoration, and reversion situations, for example.

CONCLUSION

Currently, optical transport systems use digital layer mechanisms for path recovery; however, there are no mechanisms or protocols defined for supporting protection functions in Optical Layers (OMS and OCh layers). In accordance with the present disclosure, methods and apparatus are described for supporting protection functions in Optical Layers using OAM information for the optical layers carried over an optical channel.

The foregoing description provides illustration and description, but is not intended to be exhaustive or to limit the inventive concepts to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the methodologies set forth in the present disclosure.

Also, certain portions of the implementations may have been described as “components” or “circuitry” that perform one or more functions. The term “component” or “circuitry” may include hardware, such as a processor, an application specific integrated circuit (ASIC), or a field programmable gate array (FPGA), or a combination of hardware and software.

In addition, information regarding the optical channel (OCh) or Super Channel (SCh) label switched paths can be stored and processed in a distributed fashion, or in a centralized fashion. Frequency slot information can be stored in a distributed fashion (distributed storage having multiple memory/storage devices) and processed in a distributed manner preferably by using a hop-to-hop processing. In another implementation, distributed storage may be replaced by a centralized memory that stores the frequency slot information for all, or a subset, of the nodes. In this situation, the nodes may include communication paths to obtain the connection information from the centralized memory.

No element, act, or instruction used in the present application should be construed as critical or essential to the invention unless explicitly described as such outside of the preferred embodiment. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.