Abstract:
A novel method and system for fault identification is provided. A test head that is operable to generate a test signal along a pathway is employed. The test head is based on time domain reflectometry, and is thus operable to provide an estimated physical distance of where a fault occurs along the pathway. The response test signal is matched with a known set of information about the cable and junctions and other components associated with the pathway, including information about the physical location of those components. As part of the matching, an actual real-world physical location can be identified as to where the fault likely occurs, thereby reducing the need for a service technician to attempt to physically locate the fault himself.

Description:
PRIORITY CLAIM 
   The present application is a continuation application claiming priority from PCT Patent Application Number PCT/CA2004/001738, filed Sep. 24, 2004, the contents of which are incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates generally to telecommunications and more particularly relates to a system and method for fault identification. 
   BACKGROUND OF THE INVENTION 
   Telecommunications has advanced such that there is now a vast array of services and technologies available to consumers. As services become more sophisticated, and competition more widespread, there is a natural pressure to reduce costs and improve efficiencies in the administration of a telecommunication network. 
   Significant costs in network administration arise any time there is a need for a so-called “truck roll”, as a service technician is dispatched to find and repair a fault in the network. As a more specific example, in wired telephone networks based on traditional copper twisted-pair, very often a problem will require the dispatching of a service technician to physically attend at the central office that services the customer, and/or the customer sites, and/or a variety of locations in between in order to find and repair the fault. Where the distance between the central office and the customer is great, the costs are often higher. 
   To help pinpoint the location of the fault, it is known to locate “test heads” along the path between the central office and the customer sites. Such test heads can be based on a variety of technologies, and are intended to look perform discrete metal readings along a designated pathway, with a view to identifying ground shorts, crosses and the like. 
   The introduction of digital subscriber line (“DSL”) to twisted-pair networks has only increased the demand for physical integrity of each twisted-pair circuit. By the same token, the digital subscriber line access module (“DSLAM”) is typically located intermediate legacy test heads and the subscriber sites, such that the DSLAM effectively filters out the signal generated by the test head and therefore interfering with the ability of the test head to provide meaningful fault identification. Legacy test heads located inside central offices are further hampered by the sheer complexity of the circuitry in the central office, as the central office itself effectively filters out signals generated by the test head. 
   It is known to employ more sophisticated types of test heads to address the foregoing issues, and in particular by positioning those test heads at different locations along the twisted pair circuit when performing the test. One such sophisticated type of test head are those test heads used in locating faults on DSL lines that are based on a Time Domain Reflectometer (TDR). See for example, U.S. Pat. Nos. 5,461,318 and 6,385,561, the contents of which are incorporated herein by reference. Such prior art uses of TDR can be helpful in actually providing an indication of the distance from the test head to the fault, however, it still does not provide a location of the fault, thereby requiring that a service technician trace the length of the twisted pair until the indicated distance is reached. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a novel system and method for fault identification that obviates or mitigates at least one of the above-identified disadvantages of the prior art. 
   According to an aspect of the invention there is provided a method for identifying a fault along a link comprising the steps of:
         receiving a response signal representing a test signal sent along said link;   receiving data representing location information corresponding to a physical pathway of said link;   comparing said response signal with said information; and,   outputting at least one potential physical location of said fault based on said comparing step.       

   The response signal can comprise a distance from a point where said test signal was generated to said fault. The location information can be stored in a geographic information system database. 
   The link can be a copper twisted pair that spans an outside plant interface and a subscriber premises. The link can be less than or equal to about five thousand meters in length. The link can be less than or equal to about three thousand meters in length. The link can be less than or equal to about one thousand meters in length. The test signal can be generated by a test head mounted in the outside plant interface. The test head can be remotely activatable in order to generate the test signal. 
   The comparing step of the method can comprise the steps of determining a physical length along the link where the fault is potentially occurring and matching the physical length with information derived from a database representing a known physical location along the link corresponding to the length. 
   The known physical location can include a set of geographic coordinates. The geographic coordinates can be derived from the global positioning system (“GPS”) and the method can further comprise the step of delivering the coordinates to a client device accessible to a service technician to be deployed for repairing the fault. 
   The link can also be coaxial cable, or a fibre optical cable, or an electrical transmission line. 
   Another aspect of the invention provides a system for identifying a fault along a link comprising a test head for sending a test signal along the link. The test is also for receiving a response signal corresponding to the test signal. The system also includes a computing device for receiving the response signal from the test head. The computing device is operable to access a storage device connected to the computing device. The storage device is for storing location information corresponding to the link. The computing device is further operable to receive location information from the storage device and perform a comparison between the response signal and the location information to generate at least one potential physical location of the fault. 
   Another aspect of the invention provides a computing device for identifying a fault along a link. The computing device is connectable to a test head. The test head is operable to send a test signal along the link. The test head is further operable to receive a response signal corresponding to the test signal and deliver the response signal to the computing device. The computing device is further operable to access a storage device connectable to the computing device for storing location information corresponding to the link. The computing device is further operable to receive location information from the storage device and perform a comparison between the response signal and the location information to generate at least one potential physical location of the fault. 
   Another aspect of the invention provides a computer readable medium containing a plurality of programming instructions for a computing device for identifying a fault along a link, the programming instructions including the steps of:
         receiving a response signal representing a test signal sent along the link;   receiving data representing location information corresponding to a physical pathway of the link;   comparing the response signal with the information; and,   outputting at least one potential physical location of the fault based on the comparing step.       

   Another aspect of the invention provides a method for identifying fault along a pathway comprising the steps of:
         receiving data representing the pathway from a source location to a target location;   generating a test signal along the pathway;   receiving a response signal along at least a portion of the pathway;   receiving data representing cable information associated with the pathway, the cable information including a plurality of physical locations;   matching the response signal with the cable information; and,   determining a potential physical location of the fault based on the matching step.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described by way of example only, and with reference to the accompanying drawings, in which: 
       FIG. 1  is a schematic representation of a system for fault identification in accordance with an embodiment of the invention; 
       FIG. 2  is a flowchart depicting a method of fault identification in accordance with another embodiment of the invention; 
       FIG. 3  shows the system of  FIG. 1  during the performance of one of the steps of the method in  FIG. 2 ; 
       FIG. 4  shows the system of  FIG. 1  during the performance of one of the steps of the method in  FIG. 2 ; 
       FIG. 5  shows the system of  FIG. 1  during the performance of one of the steps of the method in  FIG. 2 ; 
       FIG. 6  shows the system of  FIG. 1  during the performance of one of the steps of the method in  FIG. 2 ; 
       FIG. 7  shows a test head and a subscriber premises connected via a fibre optic cable in accordance with another embodiment of the invention; and, 
       FIG. 8  shows a test head and a subscriber premises connected via a coaxial cable in accordance with another embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIG. 1 , a system for fault identification is indicated generally at  50 . In a present embodiment, system  50  is built upon the plain old telephone system (“POTS”) and thus comprises a plurality of subscriber sites  54   1 ,  54   2  . . .  54   n  (generically referred to herein as subscriber site  54 , and collectively as subscriber sites  54 ). Each subscriber site  54  in turn includes a computing device  58  and a telephony device  62 . A service provider  66  allows computing devices  58  to connect to the Internet  70 , and allows telephony devices  62  to connect to the public switched telephone network (“PSTN”)  74 . 
   More specifically, service provider  66  includes a central office switch  78  which carries calls from telephony devices  62  over PSTN  74 . In turn, switch  78  connects to an outside plant interface  82  (“OPI”) via a feeder  86 . In a present exemplary embodiment, feeder  86  comprises a plurality of manholes  90 , but it is to be understood in general that feeder  86  comprises any combination of cabling, bridges, junctions etc. that would normally be found between central office switch  78  and OPI  82 . 
   OPI  82  comprises a junction panel  94 , a DSLAM  98 . An exemplary DSLAM is the Stinger® Compact Remote from Lucent Technologies, 600 Mountain Ave, Murray Hill, N.J. 07974-0636, but other DSLAMs can be used. OPI  82  also includes a test head  102 . Junction panel  94  is used to couple twisted pairs arriving from feeder  86  with corresponding twisted pairs destined for subscriber sites  54  so that calls can be carried between telephony devices  62  and PSTN  74 . DSLAM  98  joins Internet  70  with twisted pairs destined for subscriber sites  54  so that data connections can be carried between computing devices  58  and Internet  70 . Test head  102 , which in a present embodiment is based on TDR technology, can be used to test for faults along twisted pairs destined for subscriber sites  54 . An example of a TDR test head that can be used is a CableSHARK™ from Consultronics Limited, 160 Drumlin Circle, Concord, Ontario, Canada, L4K 3E5, that is modified to complement the other features of the present embodiment, but other test heads can be used as desired. OPI  82  is typically located on a street or other outdoor location and is within a predefined range of each subscriber sites  54  such that a given service level (i.e. bit rate) can be guaranteed for a particular computing device  58  accessing Internet  70  via DSLAM  98 . In a present embodiment, OPI  82  is within about one thousand meters of all subscriber sites  54 . In other embodiments, OPI  82  is within about five thousand meters of all subscriber sites  54 , and in still other embodiments OPI  82  is within about three thousand meters of all subscriber sites  82 . In general such distances can be varied according to the performance characteristics of the particular DSLAM  98  and/or test head  102  that is being employed. Accordingly, it should now be apparent that system  50  is scalable. For example, a central office such as central office  78  can service a plurality of OPIs and in turn service a plurality of subscriber sites. System  50  can also include a plurality of central offices, each serving a plurality of OPIs. 
   System  50  also includes a customer care workstation  106  that is operated by a customer service representative associated with service provider  66 . Workstation  106  in turn is connected to a management and diagnostics system  110 , which in a present embodiment is based on the Access Care Operating Support Systems (“OSS”) from Nortel Networks, 8200 Dixie Road, Brampton, Ontario L6T 5P6 Canada. A customer service representative operating workstation  106  is thus able to receive calls from subscribers for each site  54  and to provide the usual management and diagnostic support as is currently offered by a system such as system  110 . Additionally, however, system  110  is also connected to a database  114  that includes information about the twisted pairs running between OPI  82  and subscriber sites  54 . In a present embodimetn, the information in database  114  is geographic information that can be coordinated and/or matched with TDR signals for a given pathway. As will be discussed in greater detail below, in addition to the functionality traditionally associated with system  110 , system  110  is also operable to access database  114 , and communicate with test head  102 , in order to identify faults in twisted pairs running between OPI  82  and sites  54 . 
   Thus, the twisted pair between each subscriber site  54  and OPI  82  follows a set of pathways, indicated generally at  118  on  FIG. 1 . Pathways  118  can be characterized by cable bundles of twisted pairs, each bundle being based on different cable designs. Pathways  118  can also be characterized by junctions, bridge points, splice points, wire locations, etc. As can be seen on  FIG. 1 , in system  50  pathways  118  include a plurality of paths P and junctions J. Such characterizations are stored as information in database  114 . Table I shows an exemplary format of such information, that corresponds with the specific pathways  118  shown in  FIG. 1 . 
   
     
       
             
           
             
             
             
             
             
             
             
             
             
           
         
             
               TABLE I 
             
           
           
             
                 
             
             
               Cable information about pathways 118 
             
             
               Stored in Database 114 
             
           
        
         
             
                 
                 
                 
                 
                 
               Field 5 
                 
                 
                 
             
             
                 
                 
                 
               Field 3 
               Field 4 
               Twisted 
               Field 6 
               Field 7 
             
             
                 
               Field 1 
               Field 2 
               Begin 
               Cable 
               Pair 
               Cable 
               End 
               Field 8 
             
             
                 
               Site 
               Path 
               Point 
               Identifier 
               Identifier 
               Type 
               Point 
               Length 
             
             
                 
             
             
               Row 1 
               54 1   
               P 1   
               OPI 82 
               1 
               1 
               A 
               Junction 
               300 m 
             
             
                 
                 
                 
                 
                 
                 
                 
               J 1   
             
             
               Row 2 
               54 1   
               P 2   
               Junction 
               2 
               1 
               B 
               Customer 
               100 m 
             
             
                 
                 
                 
               J 1   
                 
                 
                 
               Sites 54 1   
             
             
               Row 3 
               54 2   
               P 1   
               OPI 82 
               1 
               2 
               A 
               Junction 
               300 m 
             
             
                 
                 
                 
                 
                 
                 
                 
               J 1   
             
             
               Row 4 
               54 2   
               P 3   
               Junction 
               3 
               1 
               A 
               Junction 
               200 m 
             
             
                 
                 
                 
               J 1   
                 
                 
                 
               J 2   
             
             
               Row 5 
               54 2   
               P 4   
               Junction 
               4 
               1 
               B 
               Customer 
               100 m 
             
             
                 
                 
                 
               J 2   
                 
                 
                 
               Sites 54 2   
             
             
               Row 6 
               54 3   
               P 1   
               OPI 82 
               1 
               3 
               A 
               Junction 
               300 m 
             
             
                 
                 
                 
                 
                 
                 
                 
               J 1   
             
             
               Row 7 
               54 3   
               P 3   
               Junction 
               3 
               2 
               A 
               Junction 
               200 m 
             
             
                 
                 
                 
               J 1   
                 
                 
                 
               J 2   
             
             
               Row 8 
               54 3   
               P 5   
               Junction 
               5 
               1 
               A 
               Junction 
               200 m 
             
             
                 
                 
                 
               J 2   
                 
                 
                 
               J 3   
             
             
               Row 9 
               54 3   
               P 6   
               Junction 
               6 
               1 
               B 
               Customer 
               100 m 
             
             
                 
                 
                 
               J 3   
                 
                 
                 
               Sites 54 3   
             
             
                 
             
           
        
       
     
   
   Thus, Field  1 , “Site” identifies the particular sites  54  associated with the cable information in the same row. Field  2 , “Path” identifies the particular path corresponding with the respective path P that is shown in  FIG. 2 , along which the cable in question runs. Field  3  “Begin Point”, identifies where the particular cable begins its run—or in other words where the path P of the respective cable bundle begins. Field  4 , “Cable Identifier”, identifies a unique number associated with the particular cable that runs along the respective path, where each cable itself contains a bundle of twisted pairs. In the present example, for reasons of simplicity, there is only one unique cable identifier per path P. Field  5 , “Twisted Pair Identifier” identifies the particular twisted pair within the corresponding cable. Field  6 , “Cable Type”, provides mechanical and/or other specifications about the cable. In the example in table I, Cable Type is limited to type “A” and type “B”. However, Cable Type can include information such as gauge, number of twisted pairs within the cable bundle, how the cable is designed (i.e. grease filled, air filled, etc.) and/or any other desired information. Field  7  “End Point”, identifies where the particular cable ends its run—or in other words where the path P respective to that cable bundle ends. Field  8 , “Length”, identifies the length of the particular path P respective to that cable bundle. While not shown in Table I, a map or address of a physical location of each particular OSI, junction or site, is also stored in database  114 , so that a service technician can immediately locate the OSI, junction or site and be dispatched thereto with relative ease. Also not shown in Table I is a map that shows each individual path P is also stored in database  114 , so that a service technician can readily trace the route of a particular P to reduce the amount of time that the technician need spend tracing the cable along that path P. 
   It should now be apparent that the plurality of rows having the same site  54  in Field  1  collectively identify the complete sequence of twisted pairs running from OPI  82  to that site  54 . More specifically, paths P 1  and P 2 , joined via junction J 1 , collectively identify the path from OPI  82  to site  54   1 . Paths P 1  and P 3  (joined via junction J 1 ) and paths P 3  and P 4  (joined via junction J 2 ), collectively identify the path from OPI  82  to site  54   2 . Paths P 1 , P 3 , (joined via junction J 1 ) and paths P 3  and P 5  (joined via junction J 2 ) and paths P 5  and P 6  (joined via junction J 3 ) respectively, collectively identify the path from OPI  82  to site  54   2 . The other information in Table I can thus be used by a service technician to identify which particular cables and twisted pairs within those cables belong to a specific site  54  for a particular path P or junction J. 
   Referring now to  FIG. 2 , a method for fault identification, in accordance with another embodiment of the invention, is indicated generally at  200 . In order to assist in the explanation of the method, it will be assumed that method  200  is operated using system  50 . Furthermore, the following discussion of method  200  will lead to further understanding of system  50  and its various components. It should be understood that the steps in method  200  need not be performed in the exact sequence shown. Further, it is to be understood that system  50  and/or method  200  can be varied, and need not work exactly as discussed herein in conjunction with each other, and that such variations are within the scope of the present invention. 
   Beginning at step  210 , an identity of a subscriber site with a reported problem is received. When performed on system  50 , this step will occur when a subscriber at a particular site  54  has difficulty with either voice or data services, and contacts a customer service representative at workstation  106  to notify service provider  66  of the problem. As an example, it will be assumed that the subscriber at site  54   2  is experiencing difficulties with data services (i.e. computing device  58   2  is having difficulty communicating over Internet  70 ), and thus contacts the customer service representative at workstation  106  to notify service provider  66  of the problem. This step is represented in  FIG. 3  by the dotted line indicated at “A”, which represents a telephone call between telephony device  62   2  and workstation  106 . (It is to be understood that line A and the subsequent lines indicated by letter characters are intended to denote communications between particular components in system  50 , and are not intended, unless so indicated, to denote the actual pathway over which such communications occur). 
   Method  200  then advances to step  215 , at which point a test head is activated along the subscriber site&#39;s pathway. Continuing with the example in relation to system  50 , the customer service representative at workstation  106  will enter an instruction into workstation  106  to remotely activate test head  102  to cause test head  102  to test the integrity of the path(s) P from OPI  82  to site  54   2 . This step is represented in  FIG. 4  by the dotted line indicated at “B”, which represents an instruction from workstation  106  to test head  102  to commence a test along the pathways P belonging to subscriber site  54   2 . 
   Method  200  then advances to step  220 , at which point a test signal is generated. Continuing with the example in relation to system  50 , test head  102  will generate a waveform along the paths P corresponding to site  54 . This signal is represented in  FIG. 5  by the dotted line indicated at “C”, which represents a test signal in the form of a waveform being generated by test head  102 . 
   Method  200  then advances to step  225 , at which point a response to the test signal is received. Continuing with the example in relation to system  50 , test head  102  will receive a reflection of signal C generated at step  220 . This reflection is represented in  FIG. 6  by the dotted line indicated at “D”. (In this example, signal C was reflected once signal C reached junction J 1 , to indicate that a fault exists at junction J 1 , but it is to be understood that the signal C and reflection could occur anywhere along the paths P from OPI  82  to site  54  depending on where, and whether, there were any faults along that paths P.) Reflection D thus originates at junction J 1  and is returned to test head  102 . In turn, test head  102  assembles the data representing signal C and reflection D, and sends that data to system  110  for further analysis. 
   Next, at step  230 , location information for the cabling for the relevant subscriber site is received. In system  50 , this step is performed by system  110 , which loads cable information, such as the cable information stored in Table I, into system  110  from database  114 . 
   Next, at step  235 , the test signal from step  225  is matched with the location information from step  235 . The way in which the particular matching is performed is not particularly limited, and a variety of operations can be conceived of which make use of the signal, waveform or other data from test head  102  and match it with cable information such as the cable information from Table I. The present example helps illustrate. Recall it was assumed that reflection D originated at junction J 1 . Using known TDR technology, an analysis of reflection D indicates, for example, that reflection D commenced about three-hundred meters, from test head  102 . By the same token, a review of Rows three through five (i.e. the rows associated with site  54   2 ), and in particular an analysis of Row three, in Table I indicates that junction J 1  is located about three-hundred meters from OPI  82 . Since three-hundred meters corresponds with the TDR measurement, a match is made between the location of the fault identified by test head  102  and the location of where that fault likely occurred based on analysis of Table I. 
   Next, at step  240 , a determination is made as to where the fault is located. Since at step  230  a match was found in Table I suggesting that the fault is located at junction J 1  the determination at this step would arise directly from the match made at step  235 . 
   Next at step  245 , an output of the list of expected problem locations is generated. This step is performed by system  110 , which can generate a specific report that identifies that a fault is expected to be found at junction J 1 . This report can then be used to generate a work order that specifically instructs the service technician to attend at junction J 1  to repair the problem. This work order can thus reduce the amount of time, as the technician need not try to trace the entire set of paths P between OPI  82  and site  54   2  to find the fault, but can be dispatched directly to a location where the fault is expected to lie. The list can include a primary location where potential problem is expected, and then a list of one or more additional, potential secondary fault locations to either side of primary location. 
   While only specific combinations of the various features and components of the present invention have been discussed herein, it will be apparent to those of skill in the art that desired subsets of the disclosed features and components and/or alternative combinations of these features and components can be utilized, as desired. For example, it is to be reiterated that the particular operations used at steps  235  and  240  are not particularly limited. Operations based on cable type and cable length can be tailored to help further improve the likelihood of specifically identifying a particular fault, and/or location thereof. For example, certain types of waveform reflections may be expected for cables having a particular number of bundles of twisted pairs contained therein, and/or whether or not the cable is air-filled, grease filled etc. Those expected types of waveforms can be compared with actually received waveform reflections to help further identify a particular fault and/or location thereof. 
   Additionally, while the embodiments discussed herein refer to TDR sent along a copper twisted pair, in other embodiments other types of testing can be performed. For example, a combination of TDR and frequency domain reflectometry can also be used. Other types of testing can be performed that are complementary to the type of cabling used. For example, for optical fibre cabling, optical TDR can be used. This example is shown in  FIG. 7 , wherein a fibre optic test head is indicated at  102   a , and is connected to a subscriber premises  54   a  via a fibre optic cable P a . While not shown in  FIG. 7 , those of skill in the art will recognize that system  50  can be modified to accommodate fibre optic cable P a  in order to provide a link between subscriber premises  54   a  and the Internet  70  and/or the PSTN  74  and/or any other type of network as desired. Test head  102   a  can thus be introduced into that link to provide substantially the same testing as previously described. 
   In another embodiment, coaxial cable can be used in place of twisted pair, with appropriate TDR tests being performed. This example is shown in  FIG. 8 , wherein a coaxial cable test head is indicated at  102   b , and is connected to a subscriber premises  54   b  via a coaxial cable P b . Those of skill in the art will now recognize that system  50  can be modified to accommodate coaxial cable P b  in order to provide a link between subscriber premises  54   b  and the Internet  70  and/or the PSTN  74  and/or any other type of network as desired. Test head  102   a  can thus be introduced into that link to provide substantially the same testing as previously described. 
   Other types of cabling to which the teachings herein can apply, such as conventional power transmission lines which include appropriate equipment to carry data, with the appropriate selection of a test head generating the appropriate tests. Other types of testing will now occur to those of skill in the art. 
   Additionally, the types of reports generated at step  245  can be very sophisticated, including graphical maps, or computerized maps that appear on a computing console located in the service technician&#39;s truck. Additionally, global positioning system (“GPS”) data, or the like, can be associated with each item in Table I, and this GPS data can also be used to generate very specific maps and/or locations for a service technician to use when attending at the identified location to repair the fault. 
   The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.