Patent Publication Number: US-6912269-B2

Title: Test unit for use at a network interface device

Description:
TECHNICAL FIELD 
   The present invention relates generally to telecommunication systems and more particularly to a test unit for use at a network interface device, including long distance lines, local lines and subscriber equipment. 
   BACKGROUND OF THE INVENTION 
   The United States Public Switched Telephone Network (PSTN) includes a number of different components. Each of these components was originally under the ownership and control of a single telephone service provider. Currently, however, respective components in the PSTN may be owned and/or under the responsibility of different parties. For example, a long distance telephone company may be responsible for long distance lines, whereas a local telephone company may be responsible for local lines, and a subscriber may be responsible for equipment at the subscriber premises. 
   When a malfunction in the PSTN arises, it is necessary to identify whether the malfunction is due to a problem located at the subscriber premises, in the subscriber loop or in the network of a chosen service provider. Responsibility for correcting the problem lies with the party responsible for the component where the problem lies. Matters are complicated by multiple service providers competing for local telephone communication services. As a result, the subscriber loop may be owned and maintained by one company yet leased by another company that provides local services to subscribers. Hence, each local service provider needs a way to immediately test for proper functioning of the network as far as a network interface device (NID). The NID is positioned at the DEMARC, i.e., the demarcation point where a local telephone company responsibility stops and the subscriber responsibility begins. Typically, the NID is located either adjacent to a subscriber&#39;s premises or a short distance away from the subscriber&#39;s premises. Thus, there is a need to be able to determine the location of a problem within the PSTN without incurring significant overhead and without suffering substantial delay. 
   SUMMARY OF THE INVENTION 
   The present invention addresses limitations of the conventional system by providing a remotely activated test unit at a NID. The test unit can perform a number of different tests to identify malfunctions and to determine the location of problems. For example, the test unit may be able to generate tones, silence a line and identify latency for transmitted signals. The test unit may be remotely activated to eliminate the need for sending maintenance personnel out to the NID. 
   In accordance with one aspect of the present invention, a component for testing a portion of a network is provided in a NID. The component includes a testing module for performing testing on a portion of the network as well as an activation module for activating the testing module to perform the testing. The activation module includes a remote activator for remote activation. The remote activator may take the form of a tone detector for detecting a characteristic tone or a radio frequency detector for detecting at least one characteristic radio signal for activating the testing module. The testing module includes a tone generator for generating a test tone. In addition, the testing module includes a silencing element for silencing a portion of the network or a loop-back element for echoing signals over a portion of the network. 
   In accordance with a further aspect of the present invention, a system is provided in a communications network that provides communications with customer premises. A network includes a local exchange carrier wiring. The system includes a NID for providing an interface between local exchange carrier wiring and customer premises. The system also includes a testing device for testing a portion of the network terminating at the NID. 
   In accordance with an additional aspect of the present invention, a test unit is positioned at a NID within a communications network. The NID is in proximity to subscriber premises. The test unit is operative to test at least a portion of the communications network. The test unit includes at least one element for initiating such a test. 
   In accordance with a further aspect of the present invention, a communications network includes a NID. Tests are performed with a test unit at the NID to determine whether the communications network is running properly and whether any problems exist in the communications network. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An illustrative embodiment of the present invention will be described below relative to the following drawings. 
       FIG. 1  is a diagram depicting connections between a central switching office and a subscriber&#39;s premises. 
       FIG. 2  is a diagram depicting major components utilized in the operation of a subscriber loop between a central switching office and a subscriber&#39;s premises of FIG.  1 . 
       FIG. 3  is a diagram depicting in more detail components employed in a network interface device and subscriber premises. 
       FIG. 4  depicts a test unit in an illustrative embodiment of the present invention. 
       FIG. 5  is a flow chart that provides an overview of the steps performed to complete testing in the illustrative embodiment. 
       FIG. 6  is a diagram illustrative of a logical component of the test unit. 
       FIG. 7  is a flow chart illustrating the steps that are performed during a tone test. 
       FIG. 8  is a flow chart illustrating the steps that are performed in silencing a phone line by a test unit. 
       FIG. 9  is a flow chart illustrating the steps that are performed to loop-back a signal by a test unit. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The illustrative embodiment of the present invention includes a test unit at a network interface device (NID). The positioning of the test unit at the NID enables testing to determine whether the problem resides at a given subscriber premises or in other portions of the communications network. The test unit can perform a number of different tests to determine whether portions of a communications network are operating properly. The test unit is remotely activated. It can be activated, for example, by sending a characteristic radio frequency (RF) signal pattern or a characteristic tone sequence. 
     FIG. 1  depicts a portion  100  of a communications network between a central switching office  102  and subscriber premises  104  and  106 . The subscriber premises  104  and  106  may be a home, an office or other facility in which a telephone set is present. Each of the subscriber premises  104  and  106  includes respective telephone sets  110  and  112 . Copper wires  114  and  116  connect the telephone sets  110  and  112  to respective NIDs  124  and  126 . 
   External telephone lines  120  extend from port card  122  at the central switching office  102  to the NID  124 . Similarly, external telephone lines  118  extend from port card  125  to NID  126 . Port cards  122  and  125  connect telephone lines with a central office switch  108 . The switch  108  is responsible for switching calls to appropriate destinations. The switch  108  may effect an electrical connection between port card  122  and port card  125  to establish an end to end telephone connection between telephone  110  and telephone  112 . 
   The “subscriber loop” between central switching office  102  and customer premises  104  is formed by the set of wires and connections that run between the port card  122  and the telephone set  110 . The “subscriber loop” between the central switching office  102  and the customer premises  106  is formed by the set of wires and connections extending from port card  125  to telephone set  112 . 
   Those skilled in the art will appreciate that the depiction of the communication network  100  shown in  FIG. 1  is a somewhat simplified view of a typical communications network. Additional components may be contained within the communications network  100 . Moreover, the organization of the communications network may differ from that depicted in FIG.  1 . The depiction in  FIG. 1  is intended to be merely illustrative and not limiting of the present invention. 
     FIG. 2  depicts components in the central switching office  102  and subscriber premises (in this case, subscriber premises  104 ), that are used during normal operation of a telephone subscriber loop. The subscriber loop extends from port card  122  at the central switching office  102  through external telephone lines  120  and through NID  124 . The central switching office  102  includes a ground  206  and a DC power source, such as battery  204 . The battery  204  may provide a specified potential, such as 48 volts. The battery  204  drives current around the subscriber loop whenever the circuit (described in more detail below) is closed by effecting connection between the external telephone lines  120  that run through the NID  124 . A switch  214  is provided at the subscriber premises  104 . The switch  214  is open whenever a telephone (including earpiece  210  and mouthpiece  212 ) is “on hook” (e.g. when the telephone handset is resting on the cradle). The switch  214  is closed when the telephone is “off hook” (i.e. when the handset is not resting in the cradle). The closure of the switch  214  effects the closed circuit between the battery  204  and the ground  206  at the central switching office  102 . As a result, a potential voltage is created that is sufficient to drive currents carrying voice (e.g. conversations) and data signals over the telephone lines  120 . When switch  214  is open (i.e. the telephone is on hook), DC potential voltage on the subscriber loop is still there, but no current can flow. 
   When a call arrives at the central switching office  102  to be connected to a telephone that includes earpiece  210  and mouthpiece  212  at the subscriber premises  104 , the central switching office takes steps to signal the need for the subscriber to answer the phone. The signaling is done by means of a ring generator  202  and a ring detector  208 . A switch  222  connects the ring generator  202  with port card  122 . When switch  222  is closed, an alternating current is generated by the ring generator  202  and placed onto the telephone line  120 . The ring detector  208  recognizes the alternating current, and generates an audible ring signal at the subscriber premises  104 . When the subscriber hears the telephone ring, the subscriber answers the telephone, resulting in the opening of the switch  222  and the removal of the alternating current from the subscriber loop. When the telephone call is completed, switch  214  is opened to remove the voltage potential across the telephone lines  120 . Capacitor  216  isolates the ring detector  208  from the DC subscriber loop, so that the ring detector can be activated only by alternating current. 
   Against the above-described background, the operation of the test unit may be better understood. As shown in  FIG. 3 , the test unit  304  is positioned in the NID  124  for customer premises  104 . For the portion  100  of the communications network depicted in  FIG. 1 , the NID  126  and customer premises  106  may have similar configurations to NID  124  and customer premises  104 , respectively, depicted in FIG.  3 . In fact, each NID within a communications network may optionally include such a test unit. 
   As shown in  FIG. 3 , the NID  124  includes an activation signal detector  306 . This activation signal detector  306  detects a distinct signal for activating the test unit  304 . The distinct signal may be remotely generated and sent over the telephone lines  203  to the detector  306 . The distinct signal may be transmitted from a transmitter  207 , shown in  FIG. 2 , at the central switching office  102 , which attaches to port card  122  as the ring generator  202  via switch  222 . In one embodiment, the signal from the central switching office  102  is a low-level radio frequency signal. The preferred signal is the 20-25 kHz range in a band that is not allocated for commercial broadcasting. Nevertheless, those skilled in the art will appreciate that other bands may be used and that different distinct signals may be used to practice the present invention. The activation signal detector  306  may be implemented as the detector of the designated radio frequency via a phase locked loop tone detector. Capacitor  320  isolates the activation signal detector  306  from the rest of the subscriber loop. Resistor  322  assures that current does not flow into the activation signal detector  306  when the A/C ring signals are transmitted to the subscriber premises  104 . 
   The NID  124  includes an off hook detector  307 . The off hook detector  307  detects the increase in DC voltage that occurs when the telephone at the subscriber premises  104  goes off hook. The off hook detector  306  communicates the change to the off hook state to the switch  308 . Those skilled in the art will appreciate that a number of different types of electronic modules may be utilized to implement the off hook detector. There are a number of off-the-shelf commercially available modules for implementing such functionality. 
   The NID  124  contains a standard current limiter  310 . The current limiter  310  is tied to ground and provides protection against surges of electricity on the external telephone lines. The current limiter  310  may take the form of a fuse, an electronic surge protector or a ground shunt that automatically opens the subscriber loop circuit or runs the current ground when the voltage on the telephone line exceeds a threshold. 
   Switch  308  controls the behavior of the test unit  304 . If the off hook detector  306  detects an off hook condition, the test unit  304  is deactivated by opening switch  308 . Switch  308  is also controlled by input from the activation signal detector  306 . The activation signal detector  306  will close the switch (presuming no off hook signal has been detected) when the activation signal is detected. Those skilled in the art will appreciate that a number of commercially available components may be utilized to implement switch  308 . 
   The test unit  304  may be implemented using different alternatives.  FIG. 4  depicts a preferred alternative where the test unit  304  is implemented as a special purpose microcomputer  400 . The microcomputer  400  boots up anytime there is a non-negligible voltage between contact points  312  and  314  (see FIG.  3 ). The microcomputer  400  includes a microprocessor  402  and storage  404 . The storage may include both primary and secondary memory and may include computer-readable media, such as optical disks, magnetic disks and the like. The storage  404  holds both data  406  and computer instructions  408 . The data  406  and instructions  408  are used to implement the various tests performed by the test unit  304 . 
   Those skilled in the art will appreciate that the test unit  304  may be also be implemented using dedicated electronic circuitry. The test unit  304  need not be implemented as a microcomputer. The test unit  304  may be implemented as servo-activated telephone response module, implementing functionality such as that described in co-pending application entitled “Interactive Telephone Response Module” which was filed on Feb. 5, 1998, application Ser. No. 09/019,323, which is explicitly incorporated by reference herein. U.S. patent application Ser. No. 09/019,323 issued on Aug. 22, 2000 as U.S. Pat. No. 6,108,404 and is entitled. “Method and System for Testing a Connection in a Telephone Network Using Interactive Telephone Response Module.”Moreover, computing systems other than microcomputers may be utilized for implementing the test unit  304 . 
     FIG. 5  provides a flow chart of the steps that are performed during testing. Initially, the test unit  304  is activated by sending an activation signal from the central switching office  102  toward the subscriber premises  104  (step  502  in FIG.  5 ). As was mentioned above, the activation signal is detected by activation signal detector  306 . The activation signal detector  306  generates an output that closes switch  308  so that the test unit  304  becomes active. The test unit  304  is already running because of the presence of a voltage across end points  312  and  314 . The test unit  304  then initiates one or more tests to identify the presence of problems within the telephone network and to identify the location of the problems within the telephone network (step  504  in FIG.  5 ). When the testing is completed, the test unit  304  may be deactivated by opening switch  308  (step  506  in FIG.  5 ). 
     FIG. 6  depicts the logical components of test unit  304 . The test unit  304  includes a tone generator  602  for the generation of one or more tones for transmission over the communications network.  FIG. 7  is a flow chart illustrating the steps that are performed during a tone test in which one or more tones are generated by the tone generator  602 . Referring to  FIG. 7 , initially, a tone is generated at a first test unit within the communications network (step  702  in FIG.  7 ). The tone may, for example, constitute a sinusoidal signal with a predetermined amplitude and frequency. The tone is then transmitted to a second test unit position within another NID, where the tone is received (step  704  in FIG.  7 ). The second test unit compares the generated tone with the received tone to identify the extent of line loss over the line that connects the two test units (step  706  in FIG.  7 ). 
   The test unit  304  also includes a silencing element  604  as shown in FIG.  6 . The silencing element  604  is used to silence a portion of the communications network.  FIG. 8  depicts steps that are preformed in using the silencing element  604 . A first test unit remains quiescent (step  802  in FIG.  8 ). While the first test unit is silent, a second test unit takes measurements (step  804  in FIG.  8 ). These measurements may include a measurement of line noise or echo path delay, for example. 
   The test unit  304  may also include a loop-back element  606 . The loop-back element  606  seeks to return signals in the form in which they were received.  FIG. 9  provides a flow chart of the steps that are performed using such a loop-back element  606  to perform a test by the test unit. A first test unit transmits a signal to a second test unit. The signal is received at the second test unit (step  902  in FIG.  9 ). The second test unit transmits the signal towards the first test unit such that the signal is in the same form and at the same level (step  904  in FIG.  9 ). In other words, the second test unit seeks to echo the signal back towards the first test unit that generated the test signal. The signal is received at the first test unit (step  906  in FIG.  9 ), and the first test unit records the time at receipt of the signal so that the roundtrip signal delay may be measured (step  908  in FIG.  9 ). 
   The test unit  304  may include a number of other different types of elements. The logical components  602 ,  604  and  606  depicted in  FIG. 6  are intended to be merely illustrative and not limiting of the present invention. For example, the test unit  304  may include components for playing or for recording and analyzing digitally encoded voice data. It may also include capabilies to play or record and analyze digitally encoded signals representing semantically-encoded waveforms designed to test transmission and receipt of data over acoustic data links or digital subscriber links in the manner taught in U.S. Pat. No. 5,748,876, entitled, “System and Method For Testing Acoustic Modems With Semantically Encoded Waveforms, issued on May 5, 1998, which is incorporated by reference herein. Furthermore, the test unit  304  may include an acoustic data link with a remote test device for transmitting instructions and data to the remote test device. This acoustic data link may be used to send signals to play and record signals to receive processed data from the remote test device. 
   While the present invention has been described with reference to an illustrative embodiment thereof, those skilled in the art will appreciate that various changes in form and detail may be made without departing from the intended scope of the present invention as defined in the appended claims.