Abstract:
Component malfunctions in passive optical networks (PON) can increase bit error rates and decrease signal-to-noise ratio in communications signals. These faults may cause the receivers of the signals, either the optical line terminal (OLT) or optical network terminals (ONTs), to experience intermittent faults and/or may result in misinterpreted commands that disrupt other ONT&#39;s communication, resulting in a rogue ONT condition. Existing PON protocol detection methods may not detect these types of malfunctions. An embodiment of the present invention identifies faults in a PON by transmitting a test series of data patterns via an optical communications path from a first network node to a second network node. The test series is compared to an expected series of data patterns. An error rate may be calculated as a function of the differences between the test series and expected series. The error rate may be reported to identify faults in the PON.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    In a passive optical network (PON), multiple optical network terminals (ONTs) or optical network units (ONUs) transmit data to an optical line terminal (OLT) using a common optical wavelength and fiber optic media. Various components of the optical distribution network (ODN), including the OLT, optical components, and ONT(s), can malfunction in such a way that upstream and/or downstream communications signals have too low a signal-to-noise ratio (SNR). This can make it difficult for the receiver of that signal, either the ONT or OLT, to communicate consistently and may result in misinterpreted commands that disrupt other ONT&#39;s communications, resulting in a rogue ONT condition. 
         [0002]    Existing error detection techniques, such as those described in the various PON protocols, may not detect SNR types of faults or if detected (e.g., by system failure), they may not be identified as faults due to low SNR. For example, in certain situations, a faulty ONT may not exceed the International Telecommunications Union (ITU) G.983.1 BIP-8 detection threshold levels when the faults are due to a bursty error sequence that has multiple bit errors. Thus, these faults may not be detected by either the BIP-8 or the CRC-8 values within the Physical Layer Operations, Administration and Maintenance (PLOAM) message fields. These bursty, intermittent types of errors may not occur long enough to generate the G.983.1 standard SDi, LCD, OAML or FRML type error conditions. However, these faulty communications can lead to incorrect OLT to ONT map communications and result in collision between upstream data communications. 
         [0003]    Two ONT malfunctions not currently detected using existing standards, such as G.943.1, may include the following. First, is an occurrence of an OLT receiving too low a SNR on the upstream signal from the ONT. This can occur for a variety of reasons, including but not limited to: too low a jitter tolerance on the OLT&#39;s clock recovery device; too high a jitter output on the ONT&#39;s transmitting device; too low a power level output from the ONT&#39;s laser; too low a SNR of the signal from the ONT due to defects in the ODN, such as kinked fiber, too long a fiber, and dirty fiber terminations. 
         [0004]    Second, is an occurrence of an ONT receiving too low a SNR on the downstream signal from the OLT. This can occur for a variety of reasons, including, but not limited to: too low a jitter tolerance on the ONT&#39;s clock recovery device; too high a jitter output on the OLT&#39;s transmitting device; too low a power level output from the OLT&#39;s laser; too low a SNR of the signal from the ONT due to defects in the ODN, such as a kinked fiber; too long a fiber; and dirty fiber terminations. 
       SUMMARY OF THE INVENTION 
       [0005]    A method and apparatus of identifying a fault in a passive optical network (PON) according to an example embodiment of the invention may include transmitting a test series of at least one data pattern via an optical communications path from a first network node to a second network node in a passive optical network. The example method may include comparing the test series to an expected series of at least one data pattern expected to be observed in the test series transmitted via the optical communications path, and calculating an error rate as a function of differences between the test series and expected series. The example embodiment may further include reporting the error rate to identify a fault in the passive optical network. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
           [0007]      FIG. 1  is a network diagram of an example passive optical network (PON); 
           [0008]      FIG. 2  is a network diagram of an example portion of a PON in which optical elements are configured to identify faults in a PON in accordance with one embodiment of the present invention; 
           [0009]      FIG. 3  is a network diagram of an example portion of a PON in which an Optical Line Terminal (OLT) and an Optical Network Unit (ONU) or Optical Network Terminal (ONT) are configured to identify faults in the PON in accordance with one embodiment of the present invention; 
           [0010]      FIG. 4  is a network diagram of an example portion of a PON in which an external node is configured to identify faults in the PON in accordance with one embodiment of the present invention; 
           [0011]      FIG. 5  is a flow diagram performed in accordance with an example embodiment of the invention; 
           [0012]      FIG. 6  is a flow diagram performed in accordance with an example embodiment of the invention; and 
           [0013]      FIG. 7  is a flow diagram performed in accordance with an example embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    A description of example embodiments of the invention follows. 
         [0015]      FIG. 1  is a network diagram of a passive optical network (PON)  100  illustrating aspects of an example embodiment of the invention. The PON  100  includes an optical line terminal (OLT)  115 , an optical splitter/combiner (OSC)  125 , and at least one optical network unit (ONT)  135   a - n ,  160   a - n . In other network embodiments, optical network units (ONUs) (not shown) may be in optical communication with multiple ONT(s)  135   a - n ,  160   a - n  directly in electrical communication with end user equipment, such as routers, telephones, home security systems, and so forth (not shown). As presented herein, ONU&#39;s are typically found at a curb and ONT(s) extend to a premise, but both generally behave the same with respect to embodiments of this invention. Data communications  110  may be transmitted to the OLT  115  from a wide area network (WAN)  105 . “Data” as used herein refers to voice, video, analog, or digital data. 
         [0016]    Communication of downstream data  120  and upstream data  150  transmitted between the OLT  115  and the ONT(s)  135   a - n ,  160   a - n  may be performed using standard communications protocols known in the art. For example, downstream data  120  may be broadcast with identification (ID) data to identify intended recipients for transmitting the downstream data  120  from the OLT  115  to the ONT(s)  135   a - n . Time division multiple access (TDMA) may be used for transmitting the upstream data  150  from an individual ONT(s)  135   a - n ,  160   a - n  back to the OLT  115 . Note that the downstream data  120  is power divided by the OSC  125  into downstream data  130  matching the downstream data  120  “above” the OSC  125  but with power reduced proportionally to the number of paths onto which the OSC  125  divides the downstream data  120 . It should be understood that the terms downstream data  120 ,  130  and upstream data  150 ,  145   a - n  are optional traffic signals that typically travel via optical communications paths  127 ,  140 , such as optical fibers. 
         [0017]    The PON  100  may be deployed for fiber-to-the-premise (FTTP), fiber-to-the-curb (FTTC), fiber-to-the-node (FTTN), and other fiber-to-the-X (FTTX) applications. The optical fiber  127  in the PON  100  may operate at bandwidths such as 155 mega bits per second (Mbps), 622 Mbps, 1.244 giga bits per second (Gbps), and 2.488 Gbps or other bandwidth implementations. The PON  100  may incorporate asynchronous transfer mode (ATM) communications, broadband services such as Ethernet access and video distribution, Ethernet point-to-multipoint topologies, and native communications of data and time division multiplex (TDM) formats or other communications suitable for a PON  100 . ONT(s)  135   a - n ,  160   a - n , may receive and provide communications to and from the PON  100  and may be connected to standard telephones (PSTN and cellular), Internet Protocol telephones, Ethernet units, video devices, computer terminals, digital subscriber lines, wireless access, as well as any other conventional customer premise equipment. 
         [0018]    The OLT  115  generates, or passes through, downstream communications  120  to an OSC  125 . After flowing through the OSC  125 , the downstream communications  120  are broadcast as power reduced downstream communications  130  to the ONT(s)  135   a - n , where each ONT  135   a - n  reads data  130  intended for that particular ONT  135   a - n . The downstream communications  120  may also be broadcast to, for example, another OSC  155 , where the downstream communications  120  are again split and broadcast to additional ONT(s)  160   a - n  and/or ONUs (not shown). 
         [0019]    Data communications  130  may be transmitted to an ONT  135   a - n  in the form of voice, data, video, and/or telemetry over fiber connection  140 . The ONT(s)  135   a - n  transmit upstream communication signals  145   a - n  back to the OSC  125  via an optical link, such as fiber connection  140 . The OSC  125 , in turn, combines the ONT&#39;s  135   a - n  upstream signals  145   a - n  and transmits a combined signal  150  back to the OLT  115  employing, for example, a time division multiplex (TDM) protocol to determine from which ONT  135   a - n  portions of the combined signal  150  are received. The OLT  115  may further transmit the communication signals  112  to a WAN  105 . 
         [0020]    Communications between the OLT  115  and the ONT(s)  135   a - n  occur using a downstream wavelength, such as 1490 nanometers (nm), and an upstream wavelength, such as 1310 nm. The downstream communications  120  broadcast from the OLT  115  to the ONT(s)  135   a - n  may be provided at 2.488 Gbps, which is shared across all ONT(s). The upstream communications transmitted  145   a - n  from the ONT(s)  135   a - n  to the OLT  115  may be provided at 1.244 Gbps, which is shared among all ONT(s)  135   a - n  connected to the OSC  125 . Other communication data rates known in the art may also be employed. 
         [0021]    In an example embodiment of the invention, a method, or corresponding apparatus of identifying a fault in a PON includes transmitting a test series of at least one data pattern via an optical communications path from a first network node to a second network node. The test series may be compared to an expected series of at least one data pattern expected to be observed in the test series transmitted via the optical communications path. The embodiment may include calculating an error rate as a function of differences between the test series and expected series and reporting the error rate to identify a fault in the passive optical network. 
         [0022]    An alternative embodiment may include determining a trend of the error rate across a length of the test series and may further include storing an error rate and using the stored error rate to monitor a trend of the error rate over time. The error rate information may also be stored and reported at a later time, such as when network communications are intermittent or temporarily disabled and later enabled. 
         [0023]    The embodiment may also include monitoring the error rate for intermittent changes in the error rate, monitoring SNR changes over time, or monitoring increases in error rates over long period of time relative to the test series to detect optical network degradation effects. The embodiment may further include adjusting parameters at the first or second network node to compensate for the degradation effects. For example, long-term monitoring of a PON&#39;s error rate may provide baseline operating parameters for the PON. A slow increase in error rate may indicate component aging. In this case, parameters, such as a power output level, may be increased to compensate for the degradation effects. 
         [0024]    Another embodiment may include transmitting the test series via separate communications signals or adding the test series to network traffic communications signal and may include transmitting at least 10 kilobits representing the test series. The rate of test series of data patterns may be adjusted to detect different types of faults or the same fault with different accuracies. For example, increasing the rate of test series of data patterns may increase error rate measurement resolution, allowing the identification of high error rates that occur in short periods of time. Different types of errors, such as intermittent, bursty, or degradation may also be determined. 
         [0025]    Still another embodiment may include multiple second network nodes and may further include turning off transmitter communications in at least one of the second network nodes and monitoring error rate at a given one of the second network nodes to identify cross communications between the second network nodes. 
         [0026]    During a ranging process, another embodiment may include determining whether the error rate exceeds a threshold, terminating the ranging process in an event the error rate exceeds the threshold, and preventing a given second network node from accessing the network in an event the error rate exceeds the threshold. 
         [0027]      FIG. 2  is a detailed block diagram of a PON  200  employing fault identification units  210 ,  225 ,  240  in optical network node components  205 ,  220   a - n , according to an example embodiment of the invention. Communications between an OLT  205 , OSC  215 ,  230 , and ONT(s)  220   a - n ,  235   a - n  may be conducted in a manner similar to that as described in  FIG. 1 . Communication signals  202  are transmitted between the OLT  205  and a WAN (not shown). A transmitting optical network node, such as an OLT  205 , transmits optical signals  212  to an OSC  215 . After splitting and flowing through the OSC  215 , the optical signals  222  continue on to a receiving optical network node, such as the ONT  220   a . The OLT  205  and/or the ONT  220   a  may include a fault identification unit  210 ,  225  configured to identify optical faults in the PON, by measuring performance characteristics such as bit error rate (BER) and low signal-to-noise (SNR). Faults may also be determined by monitoring SNR changes over time. 
         [0028]    In one example embodiment, the OLT  205  may initiate the fault identification technique by causing the fault identification unit  210  to generate a test series of at least one data pattern. Alternatively, the test series of at least one data pattern may be read from a storage location. Several bit error rate detection test patterns are known, such as a quasi random signal source bit sequence (QRSS) patterns. The OLT  205  then transmits the series of known test data patterns, for example, QRSS patterns. The test data pattern is communicated to, and split by, the OSC  215 , and is then further communicated to the appropriate ONT(s)  220   a - n.    
         [0029]    The appropriate ONT(s)  220   a - n  receives the series of test data patterns. The test data patterns may also be known to the ONT(s)  220   a - n  (e.g., both the OLT  205  and the ONT(s)  220   a - n  may store the same known test data pattern). The ONT(s)  220   a - n  may then compare the known test data patterns with an expected series of data patterns to identify error rate information related to the downstream communication signals  222 , such as the rate of errors and/or a rate of change in the error rate. The ONT(s)  220   a - n  may transmit the error rate information upstream (e.g., reported via a management channel) embedded within a communication signal  227 ,  229 ,  237 . The upstream communication signals  227 ,  229 ,  237  are combined at the OSC  215 ,  230 , and the resulting signal  242 , including error rate information, is then transmitted back to the OLT  205  via the combined communication signal  242 . 
         [0030]    Test data patterns may be contained within a standard communications signal, or within a maintenance signal transmitted in a sub-band channel, or the like. The OLT  205  may transmit thousands, or millions, of ATM payloads containing the test data patterns to the ONT(s)  220   a - n . In this way, intermittent and bursty errors not detectable using conventional error detection methods, such as that described in ITU G.983.1, are readily observable. Fault identification may occur as part of a system maintenance operation, in response to operator input  255 , or operator defined conditions, such as when the error rate exceeds a threshold value. 
         [0031]    In addition, or alternatively, the ONT(s)  220   a - n  may also generate a series of similarly known test data patterns, such as QRSS patterns, and transmit the test data patterns within the upstream communication signals  227 ,  229 ,  237 . The test data pattern may be embedded within a standard communications signal, or within a maintenance signal transmitted in a sub-band channel, or the like. The upstream communication signals  227 ,  229 ,  232 , including the test data patterns, are combined at the OSC  215  and further transmitted to the OLT  205 . The test data patterns may also be known to the OLT  205 . 
         [0032]    The OLT  205  may then compare the series of known test data patterns with an expected series of data patterns to identify an error rate of the upstream communication signals  222 . In this way, the error rate information of upstream, and/or downstream communications signals may be identified. This error rate information  202  may then be transmitted as, for example, a report or alarm  265  to a system operator, element management system  250 , or the like. The OLT  205  may also use the error rate information to attempt to fix the error (e.g., increase laser power). 
         [0033]      FIG. 3  is a block diagram of a PON  300  illustrating in further detail the fault identification units  210 ,  225 ,  257  shown in  FIG. 2 . In an example embodiment of the present invention illustrated in  FIG. 3 , an OLT  305  may contain a storage unit  352  and a fault identification unit  320 . The fault identification unit  320  may include a test data pattern generator  325 , comparison unit  345 , transceiver unit  330 , calculation unit  350 , a reporting unit  360 , and processing unit  355 . 
         [0034]    In operation, according to the example embodiment, a “directional test data path”  371  is used. A series of known test data patterns may be stored in a storage unit  352 , such as in non-volatile memory, RAM, or magnetic disk, or alternatively may be communicated to the fault identification unit  320  via an external node  365 . The test data pattern generator  325  generates and communicates a series of test data patterns to the transceiver unit  330 . The transceiver unit  330  may include a transmitter unit (Tx)  335  and a receiver unit (Rx)  340  internally, externally, or independently. The transmitter  335  transmits the test data patterns via communications signal  307  to the OSC  310  where the signal  307  is split and further flows to at least one ONT  315 . 
         [0035]    The signal  312  is received by a receiver  341  in the transceiver unit  331  and further communicated to a comparison unit  346 . The comparison unit  346  compares the series of test data patterns to a series of expected data patterns expected to be observed in the test series transmitted by the OLT  305 . The comparison information is communicated to a calculation unit  351 , where BER and SNR values may be calculated. Alternatively, or in addition, calculation results may be determined by a processing unit  356  or may be further processed, for example, tested against a threshold value. Error rate information is communicated to a reporting unit  361  and further communicated to the transceiver unit  331 . 
         [0036]    A transmitter (Tx)  336  then communicates error rate information embedded within an upstream communications signal  322  to the OSC  310  where the signal may be combined with other ONT signals (not shown) and further communicated to the OLT  305 . This information may be indicative of downstream error rate conditions. 
         [0037]    In the example embodiment, a similar fault identification technique occurs at the ONT  315  when communicating upstream communications signals  322 . A series of known test data patterns may be stored in a storage unit  353 , such as in non-volatile memory, RAM, or magnetic disk, or alternatively may be communicated to the fault identification unit  321  from an external node  365  via OLT  305 . A test data pattern generator  326  generates and communicates a series of test data patterns to the transceiver unit  331 . The transmitter  336  transmits the test data patterns via communications signal  322  to the OSC  310  where the signal  322  is split and further flows upstream to the OLT  305 . 
         [0038]    The signal  328  is received by a receiver  340  in the transceiver unit  330  and further communicated to a comparison unit  345 . The comparison unit  345  compares the series of test data patterns to a series of expected data patterns expected to be observed in the test series transmitted by the ONT  315 . The comparison information is communicated to a calculation unit  351  where BER and SNR values may be calculated. Alternatively, or in addition, calculation results may be determined by a processing unit  355  or may be further processed, for example, tested against a threshold value. Error rate information is communicated to a reporting unit  360 . Thus, error rate information may help identify which particular fiber link(s) and ONT(s) the errors occur, but also the direction (i.e., downstream and/or upstream) as well. 
         [0039]    In an alternative example embodiment, a “loop-back test data path”  370  may be employed. In this embodiment, a series of known test data patterns may be stored in a storage unit  352 , such as in non-volatile memory, RAM, or magnetic disk, or alternatively may be communicated to the fault identification unit  320  via an external node  365 . The OLT&#39;s  305  test data pattern generator  325  generates and communicates a series of test data patterns to the transmitter unit  335  which transmits the test data patterns via communications signal  307  to the OSC  310  where the signal  307  is split and further flows to at least one ONT  315 . 
         [0040]    The signal  312  is received by the ONT&#39;s  315  receiver unit  341 . However, with the loop back technique, rather than identifying the error rate at the ONT  315 , the test data pattern is simply ‘looped back’ and transmitted back to the OLT  305 . The test data pattern may be embedded within a communications signal  322 , and the transmitter  336  communicates the signal  322  upstream to the OLT  305 . 
         [0041]    The signal  328  is received by the receiver  340  and further communicated to the comparison unit  345 . The comparison unit  345  compares the series of test data patterns to a series of expected data patterns expected to be observed in the test series as transmitted by the OLT  305 . The comparison information is communicated to the calculation unit  350 , where BER and SNR values may be calculated. Alternatively, or in addition, calculation results may be determined and/or further processed by the processing unit  355 . Error rate information may be communicated to a reporting unit  360  to generate, for example, a report or alarm. 
         [0042]    The “loop-back” technique described above and shown in  FIG. 3  may be useful for ONT(s)  315  that lack the appropriate comparison unit  346 , calculation unit  351 , or processing unit  356  necessary to identify directionality of the error rates. While the loop back data path  370  may not identify directional rate information (i.e., upstream v. downstream) to the same degree as techniques employing the directional test data path  371 , valuable information is still provided in that it identifies on which fiber link(s) and/or ONT(s) the error rate is observed. Furthermore, if the ONT(s)  315  is made aware of the location of the downstream signal&#39;s  312  checksum, the ONT(s)  315  may calculate a downstream error rate and then report the downstream error rate, in addition to the data being looped back, upstream to the OLT  305 . 
         [0043]      FIG. 4  is a network block diagram  400  of example embodiments in which an external node  465 , such as a server or element management system (EMS), is configured to identify faults in a PON. In one embodiment, using a “loop-back test data path”  470 , the test data pattern  407  is generated by the external node  465 , communicated to an ONT  415 , and is then looped back to the external node  465 . In an alternative embodiment, using a “directional test data path”  471 , the downstream test data pattern  407  is similarly generated by the external node  465  and the upstream test data pattern is generated by the ONT(s)  415 . The directional path and loop-back path techniques are conceptually similar to that as described in reference to  FIG. 3  with the addition of the external node. 
         [0044]    The external node  465  may contain a fault identification unit  420  and a storage unit  454 , such as in non-volatile memory, RAM, or magnetic disk. The fault identification unit  420  may contain a test data pattern generator  425 , comparison unit  445 , input/output (I/O) interface unit  430 , calculation unit  450 , reporting unit  460 , and processing unit  455 . 
         [0045]    In one embodiment, the directional path technique may be used. A series of known test data patterns may be stored in the storage unit  454 , or alternatively communicated to the fault identification unit  420  from an external source, such as a WAN (not shown). The test data pattern generator  425  generates a series of known test data patterns which are communicated to the I/O interface unit  430  which, in turn, transmits the test data patterns to the OLT  405 . The OLT  405  transmits the test data pattern, embedded in a downstream signal  407 , to the OSC  410  where the signal  407  is split and further flows to at least one ONT  415 . 
         [0046]    The downstream signal  418  is received by the fault identification unit  422 , where the series of test data patterns are compared to a known series of expected data patterns expected to be observed in the test series transmitted by the external node  465  via the OLT  405 . The fault identification unit  422  may then calculate downstream error rate information, such as BER and SNR and communicate the information, embedded in an upstream signal  427 , back to the OLT  405  where it may be further communicated to the external node  465 . Alternatively, the received test data patterns may be communicated back to the external node  465  via the OLT  405  where downstream error rate information, such as BER and SNR values may be calculated therein. 
         [0047]    A similar fault identification technique may be employed at the ONT(s)  415  when communicating upstream signals  427 . The fault identification unit  422  generates a series of known test data patterns which may be embedded in an upstream signal  427  and communicated back to the OLT  405  and further communicated to the external node  465 . 
         [0048]    The signal is received by the I/O interface unit  430  and further communicated to the comparison unit  445 . The comparison unit  445  compares the series of test data patterns to a series of expected data patterns expected to be observed in the test series transmitted by the ONT(s)  415 . The comparison information is communicated to the calculation unit  450  where fault information, such as BER and SNR values may be calculated. Alternatively, or in addition, calculation results may be performed by the processing unit  455  or may be further processed, for example, tested against a user provided threshold value. Error rate information is communicated to a reporting unit  460 . 
         [0049]    In this way, an external node using the directional test data path technique may provide error rate information useful in identifying not only which particular fiber link(s) and ONT(s) errors occur, but also the direction (i.e., downstream and/or upstream). 
         [0050]    In an alternative embodiment “the loop-back data path”  470  may be used. Continuing to refer  FIG. 4 , a series of known test data patterns may be stored in the storage unit  454 , or may be communicated to the external node  465  from, for example, a WAN (not shown). The external node&#39;s  465  test data pattern generator  425  generates and communicates a known series of test data patterns to the I/O interface unit  430  which, in turn, transmits the test data patterns to the OLT  405 . The OLT  405  then transmits the test data patterns, embedded in signal  407 , to the ONT  415 . 
         [0051]    The signal  418  is received and processed by the intended ONT(s)  415 . The test data pattern is then ‘looped back’ by retransmitting the received test data pattern back to the OLT  405 . The test data pattern is embedded in the upstream signal  427  and is communicated back to the OLT  405 , and further communicated to the external node  465 . 
         [0052]    The signal is received by the I/O interface unit  430  and further communicated to the comparison unit  445 . The comparison unit  445  compares the series of test data patterns to a known series of expected of data patterns expected to be observed in the test series as transmitted by the external node  465 . The comparison information is communicated to the calculation unit  450  where error rate information, such as BER and SNR values may be calculated. Alternatively, or in addition, calculation results may be calculated and/or further processed by a processing unit  455 . The error rate information may be used to identify faulty fiber link(s) and/or ONT(s). Error rate information may also be communicated to a reporting unit  460  to generate, for example, a report or alarm. 
         [0053]    In an alternative embodiment, the ONT(s)  415  is made aware (e.g., via information in the downstream signal  418 ) of the location of the downstream signal&#39;s  418  checksum. The ONT(s)  415  may then calculate a downstream error rate and report the downstream error rate, in addition to the data being looped back, upstream to the OLT  405  and the external node  465 . 
         [0054]    The external node embodiments described above with reference to  FIG. 4  consume little or no memory in the OLT  405  and ONT  415 , and effectively off-load fault identification processing to an external node  465 , while still providing valuable information with regard to faults observed on a particular fiber link(s) and/or ONT(s). 
         [0055]    The block diagrams of  FIGS. 3 and 4  are merely representative and that more or fewer units may be used, and operations may not necessary be divided up as described herein. Also, a processor executing software may operate to execute operations performed by the units, where the dashed lines (e.g., dashed lines  420 ,  421 ) may represent a processor. It should be understood that the block diagrams may, in practice, be implemented in hardware, firmware, or software. If implemented in software, the software may be any form capable of performing operations described herein, stored on any form of computer readable-medium, such as RAM, ROM, CD-ROM, and loaded and executed by a general purpose or application specific processor capable of performing operations described herein. 
         [0056]      FIG. 5  illustrates, in the form of a flow diagram, an exemplary embodiment of the present invention. It should, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the present invention. For example, some of the illustrated flow diagrams may be performed in an order other than that which is described. It should be appreciated that not all of the illustrated flow diagrams is required to be performed, that additional flow diagram(s) may be added, and that some may be substituted with other flow diagram(s). 
         [0057]    The embodiment of  FIG. 5  is depicts a process  500  illustrating an example embodiment of the invention. The process  500  begins ( 505 ) and may transmit a test series of data patterns ( 510 ) from a first network node, such as an OLT, to a second network, such as an ONT, in a PON. The test series of data patterns may be compared to an expected series of data patterns ( 515 ) expected to be observed in the test series transmitted via an optical network path. An error rate may be calculated as a function of differences between the test series and the expected series ( 520 ). The error rate identifying a fault in the PON may be reported ( 525 ), and the process ends ( 530 ). 
         [0058]      FIG. 6  is a flow diagram of a process  600  illustrating an example embodiment of the invention. The process  600  begins ( 605 ) and may request ONT(s) to start QRSS bit stream monitoring and error rate calculations for a given length of time, such as 10 seconds ( 610 ), which may be predetermined or dynamically determined during the monitoring. If the error rate is higher than a threshold ( 615 ), the process  600  continues to monitor and report error rate information, suspends ranging by the OLT, and waits, such as for 20 seconds ( 620 ), and then checks to see if the error rate is still higher than the threshold ( 625 ). If the error rate is higher than the threshold, the process again continues to monitor and report error rate information, suspends ranging by the OLT, and waits, for example, 20 seconds ( 620 ). If the error rate is not higher that the threshold ( 615 ,  625 ), the process  600  reports communications error rate information, continues the ranging sequence ( 630 ), and then ends ( 640 ). 
         [0059]      FIG. 7  is a flow diagram of a process  700  illustrating an example embodiment of the invention. The process  700  begins ( 705 ) and may request ONT(s) to start QRSS bit stream monitoring and error rate calculations for 10 seconds ( 710 ), for example. If the error rate is not higher than a threshold ( 715 ), the process  700  reports that the target ONT is not likely affected by a rogue ONT, reports communications error rate information, continues bit stream monitoring ( 730 ), and then ends ( 750 ). If the error rate is higher than a threshold ( 715 ), the process  700  continues to monitor and report error rate information, and disables all ONT(s) other than the first one with a high error rate ( 720 ). 
         [0060]    The error rate is again checked to see if it is higher than the threshold ( 725 ), and, if so, the process  700  reports that the target ONT is not likely affected by a rogue ONT, reports communications error rate information, continues bit stream monitoring ( 730 ), and then ends ( 750 ). 
         [0061]    If the error rate is not higher than the threshold ( 725 ), the process  700  checks to see if a rogue detected loop count is greater than a threshold ( 735 ). If not, the process  700  reports that the target ONT may be affected by the rogue ONT, and the rogue detected loop count is incremented. The process continues by repeating sequences  710  through  735  at least five times, re-enabling all ONT(s) and verifying the error returns, then disabling and verifying that the error decreases to ensure the error is due to a different ONT ( 745 ). If the rogue detected loop count is greater than a threshold ( 735 ), the process  700  reports that the target ONT is likely affected by the rogue ONT ( 740 ), and then the process  700  ends ( 750 ). 
         [0062]    It should be readily appreciated by those of ordinary skill in the art that the aforementioned steps are merely exemplary and that the present invention is in no way limited to the number of steps or the ordering of steps described above. 
         [0063]    Some or all of the steps may be implemented in hardware, firmware, or software. If implemented in software, the software may be (i) stored locally with the OLT, the ONT, or some other remote location such as the EMS, or (ii) stored remotely and downloaded to the OLT, the ONT, or the EMS during, for example, the begin sequence. The software may also be updated locally or remotely. To begin operations in a software implementation, the OLT, the ONT, or EMS loads and executes the software in any manner known in the art. 
         [0064]    While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.