PATENT ABSTRACT
Systems and methods for identifying a fault location in an optical network are disclosed. In accordance with one embodiment of the present disclosure, a method for identifying a fault location in an optical network comprises monitoring, by a network element, an eastward optical path and a westward optical path for faults. The method further comprises transmitting, by the network element, a first data packet along the eastward path and a second data packet along the westward path. The first and second data packets comprise an eastward fault indicator and a westward fault indicator comprising information associated with any eastward or westward faults occurring on the eastward or westward paths. The fault indicators indicate the existence of an eastward or westward fault and the network element that detected the fault.

PATENT DESCRIPTION
TECHNICAL FIELD 
     The present invention relates generally to the field of communication systems and more specifically to identifying the location of faults in an optical network. 
     BACKGROUND OF THE INVENTION 
     Communication networks are typically configured to detect faults within the networks. Faults may disrupt the traffic transported along the communication networks and cause a loss of communication between nodes in the networks. Communication networks seek to isolate the faults in a timely manner to avoid losses of data and to maintain communication within the network. 
     SUMMARY OF THE INVENTION 
     In accordance with the present disclosure, disadvantages and problems associated with previous techniques for identifying a fault location in an optical network may be reduced or eliminated. 
     In accordance with one embodiment of the present disclosure, a method for identifying a fault location in an optical network comprises monitoring, by a network element, an eastward optical path for faults and monitoring, by the network element, a westward optical path for faults. 
     The method further comprises transmitting, by the network element, a first data packet along the eastward path. The first data packet comprises a first eastward fault indicator comprising information associated with any eastward faults occurring on the eastward path. The first eastward fault indicator indicates the existence of an eastward fault and the network element that detected the eastward fault. The first data packet also comprises a first westward fault indicator comprising information associated with any westward faults occurring on the westward path. The first westward fault indicator indicates the existence of a westward fault and the network element that detected the westward fault. 
     The method further comprises transmitting, by the network element, a second data packet along the westward path. The second data packet comprising a second eastward fault indicator comprising information associated with any eastward faults occurring on the eastward path. The second eastward fault indicator indicates the existence of an eastward fault and the network element that detected the eastward fault. The second data packet further comprises a second westward fault indicator comprising information associated with any westward faults occurring on the westward path. The second westward fault indicator indicates the existence of a westward fault and the network element that detected the westward fault. 
     In accordance with another embodiment of the present disclosure a network element comprises a controller configured to monitor an eastward optical path for faults and monitor a westward optical path for faults. The controller further configured to generate a first data packet and a second data packet. 
     The first data packet comprises a first eastward fault indicator comprising information associated with any eastward faults occurring on the eastward path. The first eastward fault indicator indicates the existence of an eastward fault and the network element that detected the eastward fault. The first data packet further comprises a first westward fault indicator comprising information associated with any westward faults occurring on the westward path. The first westward fault indicator indicates the existence of a westward fault and the network element that detected the westward fault. 
     The second data packet comprises a second eastward fault indicator comprising information associated with any eastward faults occurring on the eastward path. The second eastward fault indicator indicates the existence of an eastward fault and the network element that detected the eastward fault. The second data packet further comprises a second westward fault indicator comprising information associated with any westward faults occurring on the westward path. The second westward fault indicator indicates the existence of a westward fault and the network element that detected the westward fault. 
     The network element further comprises one or more interfaces communicatively coupled to the controller. The one or more interfaces are configured to transmit the first data packet along the eastward optical path and transmit the second data packet along the westward optical path as directed by the controller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following written description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an example system configured to transmit data within a network; 
         FIG. 2  illustrates a portion of an Optical Data Unit header in an Optical Transport Unit (OTU) frame that may include information that identifies a fault location in a network; 
         FIG. 3  illustrates an example system that may be used to identify a fault location within a network; 
         FIG. 4  illustrates another example system that may be used to identify a fault location within a network; 
         FIG. 5  illustrates another example system that may be used to identify a fault location within a network spanning across multiple operators; and 
         FIGS. 6A and 6B  illustrate an example of a method for identifying a fault location in a network. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present disclosure and its advantages are best understood by referring to  FIGS. 1-6 , where like numbers are used to indicate like and corresponding parts. 
       FIG. 1  illustrates an embodiment of a system  100  configured to transmit data or signals within a network. A communication network may include nodes and transmission media that facilitate communication between nodes within the network. The communication of signals or data between and within nodes may be referred to as “traffic.” 
     In some embodiments the nodes may be network elements  102  that receive or transmit traffic within the network. Transmission media  103  may be configured to couple network elements  102  and carry traffic between network elements  102 . 
     Faults or errors may occur in transmission media  103  or network elements  102  and the faults may disrupt traffic within the network. Network elements  102  may be configured to detect and report faults to allow isolation and correction of the faults and maintain communication throughout the network. 
     In certain embodiments, the network may be a communication network. A communication network allows nodes (e.g., network elements  102 ) to communicate with other nodes. A communication network may comprise all or a portion of one or more of the following: a public switched telephone network (PSTN), a public or private data network, a local area network (LAN), a metropolitan area network (MAN), a wide area network (WAN), a local, regional, or global communication or computer network such as the Internet, a wireline or wireless network, an enterprise intranet, other suitable communication link, or any combination of any of the proceeding. 
     In some embodiments, system  100  may comprise an Optical Transport Network (OTN). Traffic may be transmitted by network elements  102  within an OTN according to various protocols such as ITU G.709. Network elements  102  may transmit traffic in data packets or frames known as Optical Transport Unit (OTU) frames. 
     Traffic may be information transmitted, stored, or sorted within the communication network. Such traffic may comprise optical or electrical signals configured to encode audio, video, textual, or any other suitable data. The data may also be real-time or non-real-time. Traffic may be communicated via any suitable communications protocol, including, without limitation, the Open Systems Interconnection (OSI) standard and Internet Protocol (IP). Additionally, traffic may be structured in any appropriate manner including, but not limited to, being structured in frames, packets, or an unstructured bit stream. 
     A transmission medium  103  may include any system, device or apparatus configured to couple corresponding ports of nodes (e.g., network elements  102 ) to each other and transmit traffic between the corresponding ports. For example, a transmission medium  103  may include an optical fiber, a T1 cable, a WiFi signal, a Bluetooth signal, or any other suitable medium. 
     A link may describe the communicative connection between two adjacent network elements  102 . A link may be a physical or logical connection between adjacent nodes. A physical link may include the corresponding ports  108 - 114  and transmission media  103  that couple adjacent network elements  102  to each other. 
     In some embodiments, traffic may travel from one network element  102  (a source network element  102 ) to another network element  102  (a destination network element  102 ) along an eastward path  104  or a westward path  106 . Eastward path  104  and westward path  106  may include the source network element  102 , one or more transmission media  103 , zero, one, or more intermediate network elements  102  and the destination network element  102 . 
     Although eastward path  104  and westward path  106  are labeled as such, the labels do not mean that the paths are actually travelling east and west. The labels are merely to indicate that traffic on eastward path  104  is being sent in an opposite direction of traffic being sent on westward path  106 . 
     Network elements  102  may be configured to monitor eastward path  104 , westward path  106  or both eastward path  104  and westward path  106  for faults or errors. Network elements  102  may be further configured to detect a fault on eastward path  104 , westward path  106  or both eastward path  104  and westward path  106 . Network elements  102  may be further configured to identify and transmit the location of a fault by identifying network element  102  that detected the fault and the port associated with the network element  102  that detected the fault and associated with the link where the fault may have occurred. 
     A network element  102  may be any system, apparatus or device that may be configured to route traffic through, to, or from a network. Examples of network elements  102  include routers, switches, reconfigurable optical add-drop multiplexers (ROADMs), wavelength division multiplexers (WDMs), access gateways, intra-connected switch pair, endpoints, softswitch servers, trunk gateways, or a network management system. 
     Network elements  102  may include various components including, but not limited to, interfaces  116  and  118 , ports  108 - 114 , controller  120 , logic, memory or other suitable element. 
     Interfaces  116  and  118  may include any system, apparatus or device configured to receive input, send output, process the input or output, or perform other suitable operations. Interfaces  116  and  118  may comprise hardware, software or a combination of both. In some embodiments interfaces  116  and  118  may comprise a peripheral interface unit (PIU). Further, although network elements  102  are depicted with two interfaces, network elements  102  may include any number of network interfaces. 
     Ports  108 - 114  may include any system, device or apparatus configured to serve as an interface between a corresponding transmission medium and network interfaces  116  and  118 . Ports  108 - 114  may also include the hardware, software or a combination of both configured to facilitate the flow of traffic through ports  108 - 114  and the transmission medium. Ports  108 - 114  may comprise physical or logical interfaces. In some embodiments, ports  108 - 114  may include, but are not limited to an Ethernet port, a USB port, a Firewire port, a WiFi transmitter/receiver, a Bluetooth transmitter/receiver or an OTN port. Although network elements  102  are depicted with four ports, network elements  102  may include any number of ports. Further, although ports  110  and  114 , and ports  108  and  112  are depicted as being separate ports, in some embodiments ports  110  and  114  may be a single, bi-directional port, and ports  108  and  112  may be another single, bi-directional port. 
     Controller  120  may include any system, device or apparatus communicatively coupled to network element  102  and the components within network element  102 . Controller  120  may also be configured to control the operations of network element  102 . For example, controller  120  may be communicatively coupled to interfaces  116  and  118 , or ports  108 - 114 , or both interfaces  116  and  118 , and ports  108 - 114 . Controller  120  may to direct the routing of input signals to their appropriate output destination through interfaces  116  and  118  and ports  108 - 114 . 
     Further, controller  120  may monitor paths and detect faults within the network. Controller  120  may also be configured to generate data packets that identify the location of the faults. Controller  120  may further be configured to direct interfaces  116  and  118  to transmit the data packets to other network elements  102  via ports  108 - 114 , and thus, report the faults to other network elements  102  or a system administrator. 
     Although network elements  102  are depicted with one controller  120 , the disclosure should not be limited to such. Network elements  102  may include multiple controllers  120  that may perform various operations. For example, network interfaces  116  and  118 , and ports  108 - 114  may include controllers  120  that may perform the operations of these components. 
     Logic within components of network elements  102  may perform the operations of the components within network elements  102 . For example, logic may execute instructions to route input signals to their appropriate output destination. Logic may include hardware, software, other logic or any combination thereof. Logic may be encoded in one or more tangible media and may perform operations when executed by a computer. Certain logic, such as a processor, may manage the operation of a component. Examples of a processor include one or more computers, one or more microprocessors, one or more applications, or other logic. 
     In particular embodiments, components of network elements  102  may include computer readable media encoded with a computer program, software, computer executable instructions, or instructions capable of being executed by a computer. The computer readable media may perform the operations of the network elements  102  or components within network elements  102 . In other embodiments, computer readable media storing a computer program, embodied with a computer program, encoded with a computer program, having a stored computer program or having an encoded computer program may perform the operations of the embodiments. 
     Components of network elements  102  may also include memory that may comprise one or more tangible, computer-readable, or computer executable storage medium that stores information. Examples of memory include computer memory (e.g., Random Access Memory (RAM), Read Only Memory (ROM)), mass storage media (e.g., a hard disk), removable storage media (e.g., a Compact Disk (CD), a Digital Video Disk (DVD), or a flash memory drive), database or network storage (e.g., a server), or other computer-readable medium. 
     Modifications, additions, or omissions may be made to system  100  without departing from the scope of the disclosure. For example, although three network elements  102  are depicted, system  100  may include more or fewer than three network elements  102 . Further, more or fewer paths may be included in network  100  than eastward and westward paths  104  and  106 . 
       FIG. 2  illustrates a portion of an OTU frame that may include information that identifies a fault location in a network. In the present embodiment, the OTU frame may include an Optical Data Unit (ODU) having a Fault Type Fault Location (FTFL) field  200 . FTFL field  200  may include a forward FTFL field  202  and a backward FTFL field  204 . FTFL field  200  may comprise two hundred fifty-six bytes for carrying information. Forward FTFL field  202  may comprise one hundred twenty-eight bytes and backward FTFL field  204  may also include one hundred twenty-eight bytes. FTFL field  200  may include information related to faults that may occur along paths within a network (e.g., eastward path  104  and westward path  106 ). 
     Forward FTFL field  202  may provide the ability to send forward path fault indicators throughout network  100 . Backward FTFL field  204  may provide the ability to send backward path fault indicators throughout network  100 . 
     Forward FTFL field  202  may include information associated with faults occurring along the path that the OTU frame is travelling on. Backward FTFL field  204  may include information associated with faults occurring along the path that is opposite to the path that the OTU frame is travelling on. 
     For example, an FTFL field  200  of an OTU frame travelling along eastward path  104  may include a forward FTFL field  202  that includes fault information associated with eastward path  104 . The FTFL field  200  of the OTU frame travelling along eastward path  104  may also include a backward FTFL field  204  that includes fault information associated with westward path  106 . 
     Alternatively, an FTFL field  200  of an OTU frame travelling along westward path  106  may include a forward FTFL field  202  that includes fault information associated with westward path  106 . The FTFL field  200  of the OTU frame travelling along westward path  106  may also include a backward FTFL field  204  that includes fault information associated with eastward path  104 . 
     Forward FTFL field  202  and backward FTFL field  204  may include fault indication fields  206  and  212 , operator ID fields  208  and  214 , and operator specific fields  210  and  216 . Fault indication fields  206  and  212  may include fault indication codes that indicate whether a fault has occurred and the type of fault that may occur along the paths within a network. Fault indication codes may include codes found in ITU G.709 such as “signal fail,” “signal degrade,” and “no fault.” 
     Fault indication fields  206  and  212  may be one byte long and fault indication field  206  may be the first byte of forward FTFL field  202  (byte  0  of FTFL field  200 ). Fault indication field  212  may be the first byte of backward FTFL field  204  (byte  128  of FTFL field  200 ). 
     Forward FTFL field  202  and backward FTFL field  204  may also include operator identification (ID) fields  208  and  214 . Operator ID fields  208  and  214  may identify the network operator associated with the network where a fault may have occurred or been detected. Operator ID fields  208  and  214  may include further sub-fields including an international segment field and a national segment field. The international segment field may include a country code (e.g., a three character International Organization for Standardization (ISO) 3166 geographic/political country code (G/PCC)) that identifies the country of the network operator. The national segment field may include an identifier of the network carrier or operator based on a standardization such as an International Telecommunications Union (ITU) carrier code (ICC). 
     Operator ID fields  208  and  214  comprise nine bytes after the bytes for fault indication fields  206  and  212  (e.g. bytes  1 - 9  of FTFL field  200  for operator ID field  208  and bytes  129 - 137  for operator ID field  214 . 
     Forward FTFL field  202  and backward FTFL field  204  may also include operator specific fields  210  and  216 . In the present embodiment, operator specific fields  210  and  216  may include additional information related to the location of an error in a network. In one embodiment, operator specific fields  210  and  216  may include information indicating the network element  102  that may have detected the fault. The network element  102  that detected the fault may be identified using a node Target Identifier (“&lt;TID&gt;”) or any other suitable identifier. 
     Operator specific fields  210  and  216  may further include information indicating a port  108 - 114  associated with the link where a fault may occur. Ports  108 - 114  may be identified using a port access identifier (“&lt;ODU AID&gt;”). 
     Therefore, in some embodiments, operator specific fields  210  and  216  may pinpoint the location of a fault by including network element and port identifiers (e.g., &lt;TID&gt; and &lt;ODU AID&gt;) within operator specific fields  210  and  216 . By pinpointing the location of faults, the faults may be isolated quickly and disruption of traffic within a network may be reduced or eliminated. 
     In some embodiments, the network element that detects a fault may automatically include &lt;TID&gt; and &lt;ODU AID&gt; information in an FTFL field or other suitable data packet. In other embodiments, the operator of a network may determine how to identify the location of a fault in another manner and may insert that identification in operator specific fields  210  and  216 , or any other suitable data packet. 
     Modifications, additions, or omissions may be made to data packet  200  without departing from the scope of the disclosure. For example, operator specific fields  212  and  216  may include more or less information that may pinpoint the location of a fault occurring along a path. Additionally, although FTFL field  200  and its sub-fields are specifically noted as including information indicating the location and type of a fault, any other suitable data packet may also be used. 
       FIG. 3  illustrates an example system  300  that may be used to identify a fault location within a network. System  300  may include network elements  102 A- 102 F similar to network elements  102  depicted in  FIG. 1 . System  300  may also include eastward path  104  and westward path  106 . A fault  302  may occur between network elements  102 B and  102 C on eastward path  104 . Fault  302  may occur due to a problem with a transmission medium or port associated with the link between network elements  102 B and  102 C. After detecting fault  302 , network element  102 C may transmit a data packet along eastward path  104  to network element  102 D to notify other network elements  102  along eastward path  104  of fault information. In the present embodiment, the data packet may comprise an OTU frame that includes an FTFL field  304  similar to FTFL field  200  depicted in  FIG. 2 . FTFL field  304  may include a forward FTFL field  306  that includes information associated with faults occurring on eastward path  104 . FTFL field  304  may also include a backward FTFL field  308  that includes information associated with faults occurring on westward path  106 . 
     As previously noted, the forward FTFL field may indicate fault information relating to the path that the OTU frame containing the FTFL field is travelling along. The backward FTFL field may indicate fault information relating to the path opposite to the path that the OTU frame containing the FTFL field is travelling along. In the present embodiment the OTU frame containing FTFL field  304  is travelling along eastward path  104 , therefore forward FTFL field  306  may include fault information relating to eastward path  104 . Backward FTFL field  308  may include fault information relating to westward path  106  because traffic on westward path  106  may travel in the opposite direction of the OTU frame containing FTFL field  304 —which may be travelling on eastward path  104 . 
     Forward FTFL field  306  may include a fault identification field  314  that may identify the type of fault  302  that occurred on eastward path  104  (e.g., “signal fail,” “signal degrade,” etc.). Forward FTFL field  306  may further include an operator ID field  312  that identifies the network operator of the network depicted by system  300 . Operator ID field  312  may include an international segment identifying the operator&#39;s country, and an ICC that identifies the network operator. In the present embodiment, the network operator may be located in the United States and the ICC for the operator may be “123,” therefore, the operator ID field may be “USA123.” 
     Forward FTFL field  306  may further include an operator specific field  310  that indicates the network element and port associated with fault  302 . In the present embodiment, operator specific field  310  may identify network element  102 C as the network element that detected fault  302 . Operator specific field  310  may further indicate that port  108 C within network element  102 C is associated with fault  302 . Port  108 C is associated with the link between network elements  102 B and  102 C where fault  302  occurred and, thus, port  108 C may also be associated with fault  302 . Therefore, operator specific field  310  may pinpoint the location of fault  302  on eastward path  104  within network  300 . 
     In the present embodiment operator specific field  310  may identify network element  102 C using a &lt;TID&gt; &lt;ODU AID&gt; identifier where the &lt;TID&gt; identifier may identify network element  102 C and the &lt;ODU AID&gt; identifier may identify port  108 C. For example, the &lt;TID&gt; &lt;ODU AID&gt; identifier for network element  102 C and port  108 C may be “TIDC OS10-5-PE1.” 
     Backward FTFL field  308  may also include a fault identification field  320 , an operator ID field  318 , and an operator specific field  316  to provide information associated with any faults occurring on westward path  106 . In the present example, no faults have occurred on westward path  106 , and therefore fields  320 ,  318  and  316  may be set to “0” or “&lt;null&gt;” to indicate such. 
     As network element  102 D receives FTFL field  304  from network element  102 C, network element  102 D may send an OTU frame containing FTFL field  304  along eastward path  104  to network element  102 E, which may forward FTFL field  304  to network element  102 F etc. By receiving FTFL field  304 , which includes information indicating that network element  102 C and port  108 C are associated with fault  302 , each network element  102  following network element  102 C on eastward path  104  may more specifically know the location of fault  302  on eastward path  104 . 
     Additionally, network element  102 C may transmit a data packet, along westward path  106  to network element  102 B to notify other network elements  102  along westward path  106  of any fault information. In the present embodiment, the data packet may comprise an OTU frame that includes an FTFL field  322 . FTFL field  322  may include a forward FTFL field  324  that includes information associated with faults occurring on westward path  106 . FTFL field  322  may also include a backward FTFL field  326  that includes information associated with faults occurring on eastward path  104 . 
     Forward FTFL field  324  may include fault information related to westward path  106  because the OTU frame containing FTFL field  322  may travel along westward path  106 . Backward FTFL field  326  may include fault information related to eastward path  104  because the OTU frame containing FTFL field  322  may travel in a direction opposite of eastward path  104 —along westward path  106 . 
     Forward FTFL field  324  may also include a fault identification field  332 , an operator ID field  330 , and an operator specific field  328  to provide information associated with any faults occurring on westward path  106 . In the present example, no faults have occurred on westward path  106 , and therefore fields  332 ,  330 , and  328  may be set to “0” or “&lt;null&gt;” to indicate such. 
     Backward FTFL field  326  may include a fault identification field  338  that may identify the type of fault  302  that occurred on eastward path  104  (e.g., “signal fail,” “signal degrade,” etc.). Backward FTFL field  326  may further include an operator ID field  336  that includes similar or identical information to that included in operator ID field  312  of forward FTFL field  306  in FTFL field  304 . 
     Backward FTFL field  326  may further include an operator specific field  334  that indicates the network element and port associated with fault  302 . In the present embodiment, operator specific field  334  may include similar or identical information to that included in operator specific field  310  of forward FTFL field  306  in FTFL field  304 . 
     As network element  102 B receives the OTU frame containing FTFL field  322 , network element  102 B may send an OTU frame containing FTFL field  322  along westward path  106  to network element  102 A, which may send an OTU frame containing FTFL field  322  along westward path  106  to other network elements  102 . By receiving an OTU frame containing FTFL field  322 , which may include information indicating that network element  102 C and port  108 C are associated with fault  302 , each network element  102  following network element  102 C on westward path  106  may more specifically know the location of fault  302  on eastward path  104 . 
     Modifications, additions, or omissions may be made to system  300  without departing from the scope of the disclosure. For example, system  300  may include more than the six network elements  102  depicted or system  300  may include fewer than the six network elements depicted. Further, system  300  may include more or fewer paths than eastward path  104  and westward path  106 . 
       FIG. 4  illustrates another example system that may be used to identify a fault location within a network. 
     System  400  may include network elements  102 A- 102 F similar to network elements  102 A- 102 F as depicted in  FIG. 3 . System  400  may also include eastward path  104  and westward path  106 . Instead of occurring on just one path like fault  302  in  FIG. 3 , a fault  402  may occur at the links between network elements  102 B and  102 C on both eastward path  104  and westward path  106 . Network element  102 C may detect fault  402  on eastward path  104  and network element  102 B may detect fault  402  on westward path  106 . 
     Because fault  402  on eastward path  104  may be similar to fault  302  depicted in  FIG. 3 , Network element  102 C may transmit a data packet, such as an OTU frame that includes an FTFL field  404  identical or similar to FTFL field  304  described with respect to  FIG. 3 . 
     FTFL field  404  may include a forward FTFL field  406  that includes similar or identical information as forward FTFL field  306  depicted in  FIG. 3 . FTFL field  404  may also include a backward FTFL field  408  that includes similar or identical information as backward FTFL field  308  depicted in  FIG. 3 . 
     Network elements  102 D- 102 F may also send OTU frames along eastward path  104  to notify other network elements of the occurrence and location of fault  402  on eastward path  104 . 
     Additionally, network element  102 C may attempt to transmit a data packet, such as an OTU frame that includes an FTFL field, along westward path  106  to network element  102 B, similar to FTFL field  322  described in  FIG. 3 . However, in the present example, the data packet may not reach network element  102 B from network element  102 C along westward path  106  because fault  402  may affect the transmission of traffic along westward path  106  between network elements  102 B and  102 C. 
     But, network element  102 B may transmit a data packet, such as an OTU frame, along westward path  106  to network element  102 A indicating that network element  102 B has detected fault  402  at the link between network elements  102 B and  102 C on westward path  106 . In the present embodiment, the data packet may comprise an OTU frame that includes an FTFL field  422 . FTFL field  422  may include a forward FTFL field  424  that includes information associated with faults occurring on westward path  106 . FTFL field  422  may also include a backward FTFL field  426  that includes information associated with faults occurring on eastward path  104 . 
     Forward FTFL field  424  may include a fault identification field  432  that may identify the type of fault  402  that occurred on westward path  106 . (e.g., “signal fail,” “signal degrade,” etc.). 
     Forward FTFL field  424  may further include an operator ID field  430  that indicates the network operator of the network depicted by system  400 . As in  FIG. 3 , the network operator may be located in the United States and the ICC for the operator may be “123,” therefore, the operator ID field may be “USA123.” 
     Forward FTFL field  424  may further include an operator specific field  428  that indicates the network element and port associated with fault  402 . In the present embodiment, operator specific field  428  may identify network element  102 B as the network element that detected fault  402  on westward path  106 . Operator specific field  428  may further indicate that port  114 B within network element  102 B is associated with fault  402 . In the present embodiment operator specific field  428  may identify network element  102 B and port  114 B using a &lt;TID&gt; &lt;ODU AID&gt; identifier where the &lt;TID&gt; identifier may identify network element  102 B and the &lt;ODU AID&gt; identifier may identify port  114 B. For example, the &lt;TID&gt; &lt;ODU AID&gt; identifier for network element  102 B and port  114 B may be “TIDB OS12-7-PE2.” 
     Backward FTFL field  426  may also include a fault identification field  438 , an operator ID field  436 , and an operator specific field  434  to provide information associated with any faults occurring on westward path  106 . In the present example, network element  102 B has not detected that any faults have occurred on eastward path  104 . Network element  102 B may not receive—due to fault  402 —information from network element  102 C along westward path  106  indicating that fault  402  also occurred on eastward path  104  between network elements  102 B and  102 C. Therefore, network element  102 B may set fields  438 ,  436  and  434  to “0” or “&lt;null&gt;” to indicate that network element  102 B has not detected an error on eastward path  104  and that network element  102 B has not received information indicating that an error has occurred on westward path  106 . 
     Network element  102 A may receive the OTU frame containing FTFL field  422  and also transmit an OTU frame containing FTFL field  422  along westward path  106  to notify other network elements  102  along westward path  106  of the occurrence and location of fault  402  on westward path  106 . 
     Additionally, network element  102 B may attempt to transmit a data packet, such as an OTU frame, along eastward path  104  to network element  102 C. However, in the present example, the data packet may not reach network element  102 C from network element  102 B along eastward path  104  because fault  402  may affect the transmission of traffic between network elements  102 B and  102 C along eastward path  104 . 
     Modifications, additions, or omissions may be made to system  400  without departing from the scope of the disclosure. For example, system  400  may include more than the six network elements  102  depicted or system  400  may include fewer than the six network elements depicted. Further, system  400  may include more paths than eastward path  104  and westward path  106 . 
       FIG. 5  illustrates another example system that may be used to identify a fault location within a network. 
     System  500  may include network elements  102 A- 102 F similar to network elements  102 A- 102 F depicted in  FIGS. 3 and 4 . System  500  may also include eastward path  104  and westward path  106 . Unlike systems  300  and  400  depicted in  FIGS. 3 and 4 , system  500  may also include a sub-network  501  managed by a system operator and a sub-network  503  managed by another system operator. 
     A fault  502 , similar to fault  402  depicted in  FIG. 4 , may occur between network elements  102 B and  102 C on eastward path  104  and westward path  106  in sub-network  501 . Network element  102 C may detect fault  502  on eastward path  104  and network element  102 B may detect fault  502  on westward path  106 . 
     Network element  102 C may send a data packet, such as an OTU frame that includes an FTFL field  504  similar or identical to FTFL field  404  depicted in  FIG. 4 , along eastward path  104 . FTFL field  504  may include a forward FTFL field  506  that includes similar or identical information as forward FTFL fields  306  and  406  depicted in  FIGS. 3 and 4 . FTFL field  504  may also include a backward FTFL field  508  that includes similar or identical information as backward FTFL fields  308  and  408  depicted in  FIGS. 3 and 4 . 
     Network element  102 B may also send a data packet, such as an OTU frame that includes an FTFL field  522  similar or identical to FTFL field  422  depicted in  FIG. 4 , along westward path  106 . FTFL field  522  may include a forward FTFL field  524  that includes similar or identical sub-fields and information as forward FTFL field  424  depicted in  FIG. 4 . FTFL field  522  may also include a backward FTFL field  526  that includes similar or identical sub-fields and information as backward FTFL field  426  depicted in  FIG. 4 . 
     However, unlike in systems  300  and  400  depicted in  FIGS. 3 and 4 , system  500  explicitly includes two sub-networks—sub-network  501  and sub-network  503 . Sub-network  501  may be managed in the United States by a network operator with an ICC of “123,” and the operator ID for sub-network  501  may be “USA123” like the operators in the embodiments in  FIGS. 3 and 4 . Sub-network  503  may also be managed in the United States but by a different network operator with an ICC of “456,” and the operator ID for sub-network  503  may be “USA456.” 
     Fault  502  may occur in sub-network  501 , and the operator ID field  512 —included in forward FTFL field  506  contained in an OTU frame sent along eastward path  104 —may comprise the operator ID “USA123,” indicating that fault  502  occurred in sub-network  501 . Accordingly, the operator ID field  530 —included in forward FTFL field  524  contained in an OTU frame sent along westward path  106 —may also comprise the operator ID “USA123.” If fault  502  were to occur in sub-network  503  instead of sub-network  501 , operator ID fields  512  and  530  may comprise an operator ID of “USA456” instead of “USA123.” 
     When network elements  102 D and  102 E receive the OTU frame that includes FTFL field  504  and an operator ID field  512  with an operator ID of “USA123,” network elements  102 D and  102 E may know that fault  502  occurred in sub-network  501  and not sub-network  503  or any other sub-networks that may be included in system  500 . Also, when network element  102 A receives the OTU frame that includes FTFL field  522  and an operator ID field  530  with an operator ID of “USA123,” network element  102 A may know that fault  502  occurred in sub-network  501 , and not sub-network  503  or any other sub-networks that may be included in system  500 . 
     Modifications, additions, or omissions may be made to system  500  without departing from the scope of the disclosure. For example, system  500  may include more than the six network elements  102  depicted or system  500  may include fewer than the six network elements depicted. Further, system  500  may include more or fewer paths than eastward path  104  and westward path  106 . Additionally, system  500  may include fewer or more sub-networks than the two sub-networks explicitly mentioned. 
       FIGS. 6A and 6B  illustrate an example of a method for identifying a fault location in a network or system such as that depicted in  FIG. 1 . 
     At step  600 , in  FIG. 6A , a network element  102 , may monitor eastward path  104  for faults. Network element  102  may also monitor westward path  106  for faults at step  602 . Network element  102  may determine whether it detected a fault on eastward path  104  at step  604 . If network element  102  detects a fault at step  604 , network element  102  may then determine if it has detected a fault on westward path  106  at step  606 . In another embodiment, network element  102  may perform steps  600  and  602  simultaneously. Network element  102  may also perform steps  604  and  606  simultaneously in other embodiments. 
     If network element  102  has detected a fault on westward path  106  at step  606 , at step  608 , network element  102  may transmit a forward FTFL field along eastward path  104 . The forward FTFL field may indicate that network element  102  detected a fault on eastward path  104 . The forward FTFL field may indicate the type and location of the fault detected on eastward path  104 . The location information may include the network operator ID of the network where the fault occurred. The location information may also include the “&lt;TID&gt;” of the network element that detected the fault and may further include the port “&lt;ODU&gt; &lt;AID&gt;” of the port associated with the link where the fault on the eastward path occurred. 
     Network element  102  may also transmit a backward FTFL field along eastward path  104  at step  610 . The backward FTFL field may indicate that network element  102  also detected a fault on westward path  106  in addition to the fault detected on eastward path  104 . 
     The backward FTFL field sent in step  610  may indicate the type and location of the fault detected on westward path  106 . The backward FTFL field may include information for the fault detected on westward path  106  similar to the information included in the forward FTFL field described in step  608 . 
     At step  612 , network element  102  may transmit another forward FTFL field, but along westward path  106  instead of along eastward path  104 . The forward FTFL field transmitted along westward path  106  may indicate the type and location of the fault detected on westward path  106 . In some embodiments, the information included in the forward FTFL field transmitted along westward path  106  in step  612  may be identical or similar to the information included in the backward FTFL field transmitted along eastward path  104  in step  610 . 
     At step  614 , network element  102  may transmit another backward FTFL field, but along westward path  106  instead of along eastward path  104 . The backward FTFL field transmitted along westward path  106  may indicate the type and location of the fault detected on eastward path  104 . In some embodiments, the information included in the backward FTFL field transmitted along westward path  106  in step  614  may be identical or similar to the information included in the forward FTFL field transmitted along eastward path  104  in step  608 . Following step  614 , the method may end. 
     If network element  102  does not detect a fault on westward path  106  at step  606 , the method may move to step  616  instead of step  608 . At step  616 , network element  102  may transmit a forward FTFL field along eastward path  104  indicating the type and location of the fault detected on eastward path  104 . The forward FTFL field transmitted in step  616  may be similar or identical to the forward FTFL field transmitted in step  608 . 
     However, at step  618 , network element  102  may transmit a backward FTFL field along eastward path  104  with the fault indication field, the operator ID field and the operator-specific field may each have a “0” or “&lt;null&gt;” inserted. The “0” or “&lt;null&gt;” may indicate to the network elements further along eastward path  104  that network element  102  has not detected an error on westward path  106 . 
     Following step  618 , network element  102  may also transmit a forward FTFL field along westward path  106 , with the fault indication field, the operator ID field and the operator specific field may also each have a “0” or “&lt;null&gt;” inserted. The “0” or “&lt;null&gt;” may also indicate to the other network elements further along westward path  106  that network element  102  has not detected an error on westward path  106 . 
     At step  622 , network element  102  may transmit a backward FTFL field along westward path  106  indicating the type and location of the fault on eastward path  106 , thus informing other network elements further along westward path  106  of the fault on eastward path  104 . Following step  622 , the method may end. 
     Returning to step  604 , if network element  102  does not detect a fault on eastward path  104  at step  604 , network element  102  may determine if it has detected a fault on westward path  106  at step  624 , in  FIG. 6B . If network element  102  has detected a fault at step  624  the method may move to step  626  where the network element may transmit a “&lt;null&gt;” or “0” forward FTFL field along eastward path  104  indicating that it has not detected any errors on eastward path  104 . 
     Network element  102  may transmit a backward FTFL field along eastward path  104  at step  628 . The backward FTFL field may include information indicating the type and location of the fault detected on westward path  106 . Network element  102  may also transmit a forward FTFL field along westward path  106  at step  630  that may also indicate the type and location of the fault detected on westward path  106 . Therefore, through steps  628  and  630 , network element  102  may notify the other network elements along eastward path  104  and westward path  106  of the type and location of the fault detected on westward path  106 . 
     At step  632 , network element  102  may transmit a “&lt;null&gt;” or “0” backward FTFL along westward path  106  to notify the other network elements further along westward path  106  that network element  102  has not detected a fault on eastward path  104 . Following step  632  the method may also end. 
     Returning now to step  624 , if network element  102  does not detect a fault at step  624 , the method may move to step  634 . If the method moves to step  634 , network element  102  has not detected a fault on either eastward path  104  or westward path  106 . Therefore, at step  634  network element  102  may transmit “&lt;null&gt;” or “0” forward and backward FTFL fields along both eastward path  104  and westward path  106 , indicating that network element  102  has not detected any faults in either path. Following step  634  the method may also end. 
     Modifications, additions, or omissions may be made to the method without departing from the scope of the disclosure. For example, the method may include more steps than those depicted or it may include fewer steps than those depicted. Further, although the information transmitted has been depicted as FTFL fields, any other suitable data packet may be used to transmit fault location information. 
     Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alternations can be made herein without departing from the spirit and scope of the disclosure as defined by the following claims.