Abstract:
A computer controlled system for the diagnostic testing of two wire telephone lines. The system comprises a control means having a programmed digital computer and associated memory, a line test network, a user station and an interface for interconnecting these elements and one or more telephone exchanges and a plurality of two wire telephone lines extending from the exchanges. The line test network is responsive to the digital computer and includes means for generating a plurality of line characteristic signals during a test cycle for a selected line. The characteristic signals are representative of the resistance and reactance between a reference potential and each of the two wires of a selected line, and between the two wires of the selected line. The line characteristic signals are transformed to signals indicative of the line identity, line length, type of termination, type and location of equipment connected to the line and existence, approximate location and type of faults along the line. The latter signals are categorized according to selected line condition, and stored in the memory for selective retrieval in response to control signals generated by a user at the user station.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is related to the subject matter of U.S. Patent application Ser. No. 622,054 now U.S. Pat. No. 4,113,998 filed on Oct. 14, 1975 and assigned to the same assignee as the present invention. That application is hereby incorporated by reference in the present application. 
     The present invention relates to computer test systems, and more particularly to a computer controlled system for performing a series of diagnostic test procedures on selected telephone subscriber lines extending from a central office. 
     In the service and maintenance of telephone system equipment, one important aspect is a rapid determination of the existence and location of problems directly related to the two-line subscriber telephone lines themselves. A telephone system central office has a large number, typically 10,000, &#34;two wire&#34; telephone lines extending to subscriber equipment. Each telephone line includes two wires, commonly referred to as &#34;tip&#34; and &#34;ring&#34;, with a large number of these wire pairs being included in a cable having a cable jacket being connected to ground. At the central office, connections to a 50 volt battery provide enabling power on the line. In the United States, the average length of lines extending from the central office is 2.5 miles with the maximum length of approximately 10 miles. 
     One of the problems associated with maintenance service of the telephone lines lies in the relatively stringent requirements for maintaining the subscribers &#34;on-line&#34;. If a faulty line is detected or reported and the fault cannot be located and serviced in a relatively short period, then the subscriber is usually re-connected to a new pair of wires in order to keep his equipment in service. When this is done, the previous pair of wires is abandoned. Consequently, after a period of time, cables typically have a large number of pairs of telephone wires which is only fractionally utilized. Increasing demand for telephone connections then require the very expensive project of laying new cables. 
     As would be expected, a great variety of approaches have been employed in an attempt to resolve this problem. Most such approaches have employed attempts at fault detection and location using test signals at frequencies in the range of voice frequencies, since these are the operating frequencies of the lines. One significant problem associated with the use of frequencies of this value in long line testing lies in the difficulty of making determinations of susceptance and conductance for the entire length of the line. Such measurements are needed to determine capacitative loading along the line. The resistive portion of the impedance increases with distance along the line, while the reactive portion decreases with distance along the line and for frequencies on the order of one kilohertz, these impedance values are approximately equal at a distance of 3 miles. Accordingly, this factor presents a limited distance for the determination of the characteristics of capacitive loading with a test frequency of 1 kilohertz. Additional problems arise from the necessity of protecting any measurement circuit from damage arising either from continuous direct low impedance connection to the battery through a short to the telephone wire connected to the battery, or from catastrophic high voltage, such as lightning striking the line when it is connected to the measurement circuit. 
     Furthermore, for many prior art test systems, the sheer mass of testing operations required for the large number of lines associated with each central office present a complex operating test procedure for the test station user. In order to improve the efficiency of these prior art test systems, central computers have been employed to perform testing algorithms on the various combinations of test results in order to determine which lines contain faults, as characterized by specific combinations of the measurement results. Such testing systems generally include means to store a data base for updated information concerning all of the lines emanating from a particular central office. This data base information would normally include length of the line, types of terminations and the types of equipment tied on to a line. Since many of these factors change fairly frequently, this data base is continually up-dated in the prior art test systems. 
     However, the test methods used for such systems and their implementation by the test systems are limited by the speed at which the tests can be performed, and the precision with which faults can be located so that correction may be achieved by a repairperson. Furthermore, the large data base which must be maintained requires a relatively high expenditure in order to provide the equipment necessary for storing and up-dating that data base. In addition, the data base storage portions of the prior art systems are configured so that a user must posses a relatively high skill level and to extract selected portions of the data base for display. 
     It is an object of the present invention to provide a system for testing telephone lines extending from one or more central offices whereby the lines are subjected to a series of diagnostic test routines to rapidly and economically determine both the existence and location of faults. 
     It is another object to provide a system for operation by a relatively unskilled operator wherein selected portions of a stored data base may be readily extracted. 
     It is a further object to provide a system for testing a large plurality of telephone lines extending from one or more central offices at a relatively high speed without requiring access to a data base generally representative of the previous condition of all the lined emanating from the central offices. 
     It is a further object of the present invention to provide a system for testing a large plurality of telephone lines emanating from one or more central offices wherein the plurality of a.c. and d.c. test signals are automatically applied in sequence to the lines, and the resultant test response signals are automatically processed in a corresponding sequence to detect the presence, character and location of faults and terminations. 
     It is still another object of the present invention to provide a test system for testing a large plurality of telephone lines extending from one or more central offices and for automatically diagnosing problems detected from the test measurements. 
     SUMMARY OF THE INVENTION 
     Broadly speaking, the present invention is a computer controlled system for testing of telephone subscriber lines. The system comprises a control means having a programmed digital computer and associated memory, a line test network, a user station and an interface for interconnecting these elements and one or more telephone exchanges and the plurality of telephone lines extending from such exchanges. 
     The line test network is responsive to the digital computer and includes means for generating a plurality of line characteristic signals during a test cycle for a selected line. The characteristic signals are representative of the resistance and reactance between a reference potential and each of the two wires of a selected line, and between the two wires of a selected line. Generally, a test cycle for a selected line includes a direct current test of the resistance between the tip and ring wires, as well as tests of resistance between battery and both the tip and ring wires, and between the ground and both the tip and ring wires. In a second portion of the measurement cycle, a measurement is also made of the total amount of alternating current hum or noise on the wire by means of rectification of any signals on the tip and ring wires, with the central office battery disconnected. In a third portion of the measurement cycle, measurements are made by applying a.c. voltage signals between combinations of the tip wire, the ring wire, the ground conductor, and measuring the in-phase and quadrature components of the resulting currents on those wires. The line response signals generated in response to the test signals are integrated over a predetermined measurement period to from line characteristic signals which are then transferred from the line test network to the digital computer. 
     In one form of the invention, the frequency of the test signal produced by the line test network is established at 30 Hz (or a sub-multiple thereof or an odd harmonic thereof no greater than 250 HZ) and the measurement period is established as 33.33 milliseconds (or equal to an integral multiple thereof) so that measurements of susceptance and conductance may be made for lines as long as 10 miles. With this measurment method, during the negative-going half-cycle of the test signal, the polarity of the response is reversed and the resultant waveform is integrated over the measurement period. As a result, contributions to noise from 60 Hertz sources are eliminated. It will be understood that multiples of one full cycle of the test signal can also be employed as the measurement period without losing the advantage of noise suppression and signal enhancement achieved. Preferably the measurement period equals one cycle period of the test frequency. 
     At the computer, the line characteristic signals are transformed to signals representative of the susceptance and conductance between each pair of conductors, thereby providing an indication of the capacitive load across the line, which are in turn adaptively processed to be transformed to signals representative of the line length, type of termination, line faults, and type and location of equipment connection to the line. These latter signals are then categorized according to line condition. 
     The control means provides three operating modes: ROUTINING, ADVISORY and LINE TEST. In the ROUTINING mode, the computer automatically directs diagnostic testing of the entire set of telephone lines of a single exchange (typically, on a daily basis in a few low usage hours) by accessing an exchange and directing the line test network to initiate its sequence of a.c. and d. c. measurements on each line extending from the exchange. Based on the results of these measurements, i.e. the line characteristic signals, the computer generates ROUTINING mode test result signals for qualitatively classifying each of the lines as &#34;O.K.&#34;, &#34;permanent busy&#34;, &#34;trouble line&#34; or &#34;suspect line&#34;. The term &#34;suspect line&#34; is used to identify which show whichshow degradation but still possess satisfactory transmission and similar characteristics for commercial use. A &#34;trouble line&#34; is defined as a line in iminent danger of generating a customer complaint. This category of lines is further classified to specify the fault as a &#34;short&#34; , &#34;cross&#34;, &#34;ground&#34;, &#34;high background noise&#34; or &#34;activated pressure contactor&#34;. The computer further establishes a record of the permanent busy lines, suspect lines, trouble lines, and subclassifications thereof for a current time. In addition, the computer generates and stores test result signals which establish and up-date an historical record showing lines that have been classified as trouble lines or suspect lines for predetermined periods of time, e.g., up to one week, one - four weeks, one - two months, or over two months. Of course, these time periods are merely exemplary and in other embodiments different definitions may be utilized. Furthermore, any line that is reported by the computer as either a trouble or suspect line is automatically maintained in the historical record until the line is found to test o.k. for a predetermined period, e.g. fourteen consecutive days. 
     In the ADVISORY mode, the user may direct the computer to display selected portions of data generated and stored during ROUTINING mode, such as test result signals representative of: 
     (1) the lines in an exchange which currently are categorized as permanent busy lines, shorts, crosses and grounds, high background lines, suspect wet cable lines, suspect lines, activated pressure contactors, and high voltage lines; 
     (2) the history of trouble and suspect lines in an exchange, including the particular lines so classified for various time periods, and the history of particular lines for those time periods; and 
     (3) a summary of the line status within a service area, including a current trouble summary, trouble line historical summary, suspect line historicial summary, severe shorts, crosses and grounds, and severe high background lines. 
     In the LINE TEST mode for a selected line, the digital computer may operate in response to specific directives entered at a user station to direct the line test network to initiate its sequence of a.c. and d.c. tests (or selected portions thereof) for a selected line of an exchange. For this operation for a selected line, the computer generates and displays to the user test results signals representative of the length of the line in miles and feet from the central office, also the number and types of termination (telephones, PABX, keyset, subscriber carrier, unbypassed loop extenders, foreign exchanges) and where applicable, the method of connection (bridged, tip to ground, ring to ground). In addition, the computer may provide signals indicative of specific faults such as excessive hum leakage, shorts, crosses, grounds, imbalance, improper battery voltage, residual a.c. and d.c. voltages, and the distance to shorts or crosses. Accordingly, the LINE TEST mode of operation is particularly useful in correcting identified faults. The computer in effect may direct a repairperson to a location where a test is needed and guides the repairperson in correcting the fault, since the type of fault is specified along with the approximate location of that fault. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects of this invention, the various features thereof, as well as the invention itself, nay be more fully understood from the following description, when read together with the accompanying drawings in which: 
     FIG. 1 shows, in block diagram form, a telephone line test system in accordance with the present invention; 
     FIG. 2 shows, in block diagram form, an alternative configuration for the system of FIG. 1; 
     FIGS. 3A and 3B show the user command tree for the ADVISORY mode; and 
     FIG. 4 shows the user command tree for the LINE TEST mode. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 generally shows one preferred embodiment 10 of the present invention as connected to a switching machine 12 having a plurality of telephone lines extending therefrom. In that embodiment, a user station 16 with an associated display, line test network 18 and control means 20 are interconnected with the switching machine 12 by way of an interface 22. The control means 20 includes digital computer 24 and associated memory system 26. The system 10 selectively performs at least one diagnostic test upon selected ones of the two wire telephone lines extending from the switching machine 12, wherein the performance of each test includes a step of applying a test signal to a line under the test, receiving a line response signal, and generating a line characteristic signal. 
     The user station 16 includes user controlled means for generating at least one line select signal for identifying selected lines to be tested in the LINE TEST mode, and for generating a test sequence initiate (test select) signal associated with each of the user entered line select signals for identifying the particular a.c. and d.c. tests which are to be applied to the identified lines. 
     The computer 24 includes means responsive to the line select and test select signals produced by user station 16 (in the LINE TEST mode) to generate corresponding line select command and test select command signals, the latter signal being for directing line test network 18 to apply the specified tests to the selected line. 
     The computer 24 includes a means for automatically generating a sequence of line select command signals (in the ROUTINING mode) for identifying lines to be tested, and a test sequence initiate (test select) command signal for directing the network 18 to apply its sequence of a.c. and d.c. tests to each selected line. 
     In addition, the computer 24 includes means responsive to the line characteristic signals in the ROUTINING and LINE TEST modes to generate test result signals representative of line length, type of termination, type and location of attached equipment, and existence, location and type of faults on the associated line. In the ROUTINING mode, the test result signals are stored in memory 26, and in the LINE TEST mode the test result signals are transferred to user station 16 for display. 
     The line test network 18 includes means responsive to a test select command signal for selectively generating test signals, means for receiving line response signals, and means for generating a line characteristic signal for the selected line. 
     Generally, the line test network 18 is the same as the network disclosed in FIGS. 1-6 of the above-referenced application Ser. No. 622,054. Accordingly, the test signals generated by network 18 are substantially the same as those generated by the referenced network. Furthermore, response signals from the lines (as transferred by way of the switching machine 12 and interface 22, to network 18) are processed in substantially the same manner as that disclosed in the abovereferenced application, with the line characterization signals produced by network 18 corresponding to the digital output produced by the referenced network. The program input to the circuit in the above-referenced application corresponds to the test select command signal provided by interface 22 from digital computer 24 in the present invention. 
     The user station 16 further includes a user controlled means for generating test result select signals for specifying selected portions of the test result signals stored in the control means 20. The computer 24 includes means responsive to the test result select signals in the ADVISORY mode to transfer the specified portions to user station 16 for display. The display at station 16 is responsive to test result signals received from computer 24 to display those signals to the user. 
     In the present embodiment, the interface 22 serves to interconnect the user station 16, line test network 18, control means 20 and switching machine 12. In FIG. 1, interface 22 is shown in a single block. However, for alternative embodiments, the interface may be distributed throughout the system so that the particular geographical location of elements 12, 16, 18 and 20 may be conveniently arranged. Accordingly, in such embodiments appropriate modems and data transfer channel are included in the interface 22. 
     As illustrated in FIG. 1, the digital computer 24 is centrally located. In alternative embodiments, the computer 24 may be configured with remote portions which together perform the same function as computer 24 but wherein the specific subfunctions are performed at the remote locations. 
     One such alternative embodiment is shown in FIG. 2 In the embodiment of FIG. 2, blocks having substantially similar functions to the embodiment of FIG. 1 are identified with identical reference numerals in FIG. 2. The lower case referece subscripts associated with such blocks identify the various remote portions. Substantially similar blocks within FIG. 2 are identified with common primary reference designations with differing appended reference numerals. 
     In the configuration of FIG. 2, four central offices 30-1 through 30-4 are shown interconnected to control means 20 and three user stations 16-1 through 16-3 via interface portions 22a and 22b. It will be understood that each central office includes switching machine 12 and plurality of telephone lines extending therefrom, a line test network 18 and an interface portion 22c. The various interface portions 22a, 22b and 22c act in concert to function in a manner corresponding to interface 22 in the system of FIG. 1. 
     In the FIG. 2 embodiment, the control means is configured in a manner having a central portion 20a and remote portions 20b-1 through 20b-4 located at the offices 30-1 through 30-4, respectively. As a result, any of the user stations may be interconnected with a selected one of the central offices. It will be understood that the central computer 24 is connected via trunk interface and modem 22b and by dedicated trunk lines to central offices 30-1 and 30-2, and by dial-up trunk lines to central offices 30-3 and 30-4 or other central offices. The user station interface 22a permits each of the user stations to interact with the selected central office on a time shared basis to computer 24. 
     As shown in FIG. 2, each user station includes a CRT display and keyboard (reference numerals 34-1 and 36-1, respectively for station 16-1) for transmitting user entered test select and line select signals to central computer 24. In some embodiments, the user may initiate LINE TEST mode operation wherein he may select particular ones of the a.c. and d.c. tests to be applied to a selected line. In all embodiments, the user may initiate the full battery of tests for a selected line. 
     The interface portions of the central office (reference numeral 22c-1 of central office 30-1) include a modem (42-1) and an automatic dialer (46-1) which controls access to the lines of the switching machine 12-1 through a test distributor associated therewith. 
     The central computer 24 controls the central office access as requested from the various user stations, provides message switching between the various central offices and user stations, provides interactive line analysis of the line characterization signals and conversion thereof to test result signals, and provides data storage as noted above (in conjunction with the ADVISORY mode operation). 
     In the configuration of FIG. 1, the control means 20 comprises a mini-computer, such as the M-365 manufactured by Teradyne, Boston, Massachusetts, which operates in conjunction with an associated memory. The computer is programmed as shown in Appendix I. 
     In the configuration of FIG. 2, the control means may comprise an M-365 at block 20a and a local controller at block 20b. Controller 20b also may be an M-365 mini-computer. In the FIG. 2 embodiment, local controller 20b may be programmed to transform the line characteristic signal to the test result signals, while the computer 24 may be programmed to perform the overall system administrative tasks, and ADVISORY mode data retrieval. The CRT display 34-1 may consist of an M-367 display manufactured by Teradyne, or any of a number of other commercially available well-known alternatives. The trunk interface 22b and modem 42-1 can be linked via standard telephone lines using Bell 103 full duplex 300 baud modems. The switching machine 12-1 may be typically an Automatic Electric type 20, step-by-step office. It will be understood that other embodiments may utilize well-known equivalent networks. Similarly, the automatic dialer in interface 22c-1 may be one of well-known forms in the telephone industry. The local controller 20b routes the line select command signals to the automatic dialer 46-1 and the test select command signals to the test network 18-1. The local controller further receives the line characteristic signals from network 18-1 and transfers the test result signals in suitable form to modem 42-1 for transmission to computer 24. As noted above, the test network 18-1 is substantially as disclosed in the above-referenced U.S. Patent Application. 
     At user station 16-1, keyboard 36-1 is a conventional keyboard having twelve keys, each corresponding to one of numerals 0-9, &#34;#&#34; and &#34;*&#34;. In other embodiment, further keys may be utilized to accommodate different functions, e.g. interactive trouble diagnostics, or generation of hard copy records. The # key is used to prefix the accessing of a particular telephone line in the LINE TEST mode, and the * key is used to begin a new primary command operation, as described below. In this embodiment, signals representative of the keys depressed by the user are transferred to the computer 24 (or &#34;entered&#34;) on a time shared basis. 
     For the FIG. 1 embodiment, computer 24 establishes the user station-to-central office link in both the ROUTINING and LINE TEST modes, directs (at its own initiative) the commencement of the ROUTINING mode test operations performed by network 18, directs (at user initiative) the commencement of the LINE TEST mode test operations performed by network 18, transforms the line characteristic signals to test result signals, stores the ROUTINING mode test result signals, transfers the LINE TEST mode test results signals to the user station, and also performs the ADVISORY mode data retrieval operations. For the FIG. 2 embodiment, computer 24 establishes the user station-to-central office link in both the ROUTINING and LINE TEST modes, while the local controller 20b directs (at its own initiative or in response to a control signal initiated at the computer 24) the ROUTINING mode test operations performed by network 18, directs (in response to a user-generated control signal applied by way of computer 24) the LINE TEST mode test operations performed by network 18 and transforms the line characteristic signals to test result signals and transfers those latter signals to computer 24. The computer 24 stores the ROUTINING mode test result signals, transfers the LINE TEST mode test result signals to the user station, and performs the ADVISORY mode data retrieval operations. 
     Using the above-described configurations, in the ROUTINING mode, the control means 20 directs the sequential accessing of each line in an exchange and, for each accessed line, directs line test network 18 to perform the plurality of a.c. and d.c. tests described in the referenced application within a short period of time (such as two seconds). Thus, in the ROUTINING mode, the testing of all telephone lines of a typical exchange may be accomplised in a few low usage hours each night. After the ROUTINING operations, each morning, for example, the user at the service center can generate a complete test result summary for all lines by interrogating the computer 24 in the ADVISORY mode to retrieve for display selected portions of the ROUTINING mode test result signals from the memory 26. 
     For the embodiment of FIG. 2, at one of the user stations, a user may operate the system in the ADVISORY mode by interacting with the computer 24 through the entry of user commands in accordance with the ADVISORY mode command tree illustrated in FIGS. 3A and B. For the embodiment shown, the user first enters a primary level command (comprising &#34;*&#34; and a digit), and then one or more secondary level commands associated with the primary level command. If desired, following entry of a secondary level command, the user may enter one or more of the associated tertiary level commands associated with the entered secondary level command. In the present embodiment, the user may only initiate operations corresponding to a new command at the same command level and associated with the previously entered higher level command without first retrieving to the primary command level. However, at any time, the user may interrupt a current ADVISORY mode operation and initiate a different such operation by entering a new primary level command and a desired sequence of secondary and tertiary level commands. In other embodiments of this invention, alternative command trees may be utilized which permit such command switching. A set of exemplary ADVISORY mode operations are described below in conjunction with Tables 1-15. These Tables illustrate the CRT display screen under the described conditions, and show computer-generated messages, and operator-generated responses. In Tables 1-15, the operator responses are underscored for clarity. The symbols &#34;&gt;&#34; and &#34;&gt;&gt;&#34; represent prompters displayed to the user to indicate that secondary and tertiary level commands may be respectively entered by the user at a current time. 
     After the user selects an exchange, e.g., #837 in Table 1, the computer 24 directs the CRT display at the user station to read &#34;4-TEL SERVICE, TYPE 0 FOR HELP,&#34; (line 1 of Table 1), followed by the selected exchange (line 2 of Table 1), thereby indicating a &#34;ready&#34; status. The user may then enter a primary command prefixed by * for ADVISORY mode operation, or enter a menu request &#34;*0&#34; (line 3 of Table 1) at his keyboard, to which the computer responds by displaying a primary command menu (as shown in lines 4-11 of Table 1). In response to this display, the user may change exchanges, select one of the three types of advisory information available, i.e., CURRENT TROUBLE ADVISORY, HISTORICAL ADVISORY, SERVICE AREA SUMMARY, by activating the * (or primary command) key followed by the appropriately numbered key on his keyboard associated with the desired advisory information. Alternatively the operator may switch to the LINE TEST mode and initiate an individual line test procedure in the LINE TEST mode for a selected line by activating the #key followed by the line number for the desired telephone line. The user may skip the * 0 step if he knows the menu, and merely perform one of the latter steps, i.e., enter * or # and the appropriate number. 
     If the user elects to change exchanges, he enters * 1 and then the NNX number of the desired exchange. Table 2 illustrates the CRT display for such an operation wherein the user successively entered four invalid exchange numbers, followed by 415-862, a valid exchange number. 
     When the user selects CURRENT TROUBLE ADVISORY, by entering * 2, he must then select one or more of the trouble categories: 
     1. permanent busy line 
     2. shorts, crosses and grounds 
     3. high background lines 
     4. suspect wet cable 
     5. suspect lines 
     6. activated pressure contactors 
     7. high voltage lines 
     The user may request display of this menu by entering 0 before making his selection. In that case, the user is presented with the display shown in Table 3. When selecting one or more of these categories through the activation of the correspondingly numbered keys from his keyboard, the user may obtain the listing of all lines in the exchange that presently fall within the selected category. An exemplary listing for all six categories at exchange #415-862 is shown in Table 4 where the user has sequentially entered * 2, 1, 2, 3, 4, 5, 6, 7 at his keyboard. Thus, the CURRENT TROUBLE ADVISORY function provides the results of daily exchange routine testing. 
     When the user selects HISTORICAL TROUBLE ADVISORY, by entering * 3, he must then specify whether he desires an individual line history, or survey history for either trouble or suspect lines. The user may request display of this menu by entering 0 before making his selection. In that case, the user is presented with the display shown in Table 5 for exchange #837. 
     Table 6 illustrates the display following the selection of exchange #837 and the sequential entry of * 3 (selecting historical advisory), 3 (selecting suspect line history) and 0 (requesting a menu). Table 7 shows the display for the subsequent sequential entry of 1, 2 and 9 where the &#34;9&#34; entry directs the computer to advance to the next &#34;page&#34; of output display data. 
     Table 8 illustrates the display following the selecting of exchange #837 and the sequential entry of * 3, and the subsequent entry of 2 (selecting trouble line history), 0, 3 and 4. Tables 9 and 10 illustrate the display following selecting exchange #837 and the sequential entry of * 3, 0, 1 (selecting line numbers 837-3408 and 837-9889, respectively). The exemplary display (Table 9) for line number 837-3408 states that trouble history for the line in the past 204 days is unsatisfactory (with only sixteen &#34;tested o.k.&#39;s&#34;) and then indicates the status for each of the previous 8 days. In general, for the present embodiment, a trouble history is maintained in the memory for any line until it &#34;tests o.k.&#34; for fourteen consecutive days, at which point the trouble history on that line would be deleted from the memory. 
     The user may also select service area summary data for a group of exchanges by entering * 4. The user may then request the menu illustrated in Table 11 (by entering 0) or may directly enter a number corresponding to one of the categories specified by that menu to specify what data he desired. Table 12 illustrates the display following the sequential entry of 1 (selecting current trouble summary), 0 (requesting a current trouble menu). Table 13-15 show the display for the sequential entry of 5, 2, and 7, respectively (following the entry of * 4, 1). Similar summary reports are produced for other service summary area menu entrees. 
     Using the above described configurations, in the LINE TEST mode, the user may initiate tests for individually selected lines through the entry of user commands in accordance with the LINE TEST command thus illustrated in FIG. 4. For the embodiment shown, the user may activate the # key of his keyboard, followed by entry of the number of the line to be tested. The control means 20 responds by automatically accessing and testing the line and indicating its condition via the user display. If the line passes all tests, the display indicates &#34;tested o.k.&#34; and the cable and termination characteristics. If the line is on file as a trouble line (i.e., if is not &#34;tested o.k.&#34; for 14 consecutive days), the line is identified as having a &#34;trouble history&#34;. If the line is busy, that &#34;busy&#34; status is presented to the operator via the display. 
     Test results of problem lines are automatically converted by the computer into diagnostic display reports such as &#34;suspect wet cable&#34;, &#34;severs background&#34;. The display further presents the user with the number and type of terminations (e.g., &#34;two straight line ringers - bridged), and in addition, the cable length in &#34;truck miles&#34; and in feet from the central office to the line termination. In the presently described embodiment, a truck mile is defined to be 5800 feet. 
     Following the test, the user may also enter 0 to direct the display of the LINE TEST menu: 
     1. line history 
     2. short circuit diagnostic 
     3. open circuit diagnostic 
     4. extra data 
     5. override and test By actuating the appropriate keys following the individual LINE TEST mode operation, the user directs the computer to display the data related to the menu entrees. The &#34;extra data&#34; category provides the user with data representative of the battery, a.c. and d.c. voltage and background on both the tip and ring wires, and line insulation status. Tables 16-18 illustrate typical displays provided to the user in response to the user operations described below. In these tables the user-entered characters are underscored for identification. The symbol &#34;&gt;&#34; is displayed to the user as a prompter, indicating that a secondary command may be entered at a current time. 
     Table 16 illustrates an individual LINE TEST mode operation for testing line number 3470 for a selected exchange. The initial display indication was a tip-to-ground insulation fault for the particular line. The display further indicates that the line has a 20 Hz ringer with a bridged connection, and the cable length is 0.9 miles or 5400 feet. The line is characterized with negligible capacitance imbalance. In this example, after the computer directed the display of the basic line test result data, the user requested (by entering 0) the display of the LINE TEST menu, from which the user selected number 2, i.e., short circuit diagnostic. The computer responded at the display with &#34;partial tip ground&#34;, and the trouble shooting instruction &#34;test needed at subscriber drop&#34;. 
     Table 17 illustrates the user display for an individual LINE TEST mode operation for line number 9834, which tested o.k. and was indicated to have three &#34;straight line ringers &#34; in a bridged connection, with cable length 1.8 miles or 10,500 feet, with negligible capacitance imbalance. The user in this case also requested display of the LINE TEST menu, and from the requested menu, the user selected number 4 i.e., extra data. In response thereto, the computer directed the display of the battery, d.c. volts, a.c. volts and background measurements for the ring and tip lines and an indication that the line insulation was o.k. 
     Table 18 illustrates the user display for an individual LINE TEST mode operation for line number 9874. Initially the user entered #9874 from his keyboard. The computer then indicated that the line tests &#34;busy&#34; and automatically displayed the menu comprising &#34;5 - over-ride and test&#34;, &#34;# line test&#34;, and &#34;* primary command level&#34;. 
     As indicated in Table 18, the user entered &#34;5&#34; from his keyboard and computer 24 responded by indicating that the line is categorized as having a trouble history and further that the line has 1205 ohm short, that there are no ringers connected to the line, that the cable length is 3.1 mile or 18,600 feet, and that there is capacitance imbalance. The computer then offered the operator the opportunity to obtain further data relating to the line. If the user were to enter &#34;0&#34;, the LINE TEST MENU as included would have been displayed. However, in this example, it is assumed that the user is familiar with the LINE TEST menu and that he does not enter 0 but instead successively enters 2, 3, and 4 to which the computer respectively responds as shown in Table 18. Accordingly, in response to 2, the display indicates a partial tip ring short and a test is needed at the subscriber drop. In response to entering of 3, the display indicates that there is an &#34;open&#34; at 3.2 miles of 18,600 feet from the central office and that open calibration is required at or near load point 3. In response to entry of 4, the display indicates the battery, d.c. volts, a.c. volts and background test values are given for both the tip and ring wires. In addition, the computer displays again that the line is characterized by a 1205 ohm short. Thus, for this example the line tests &#34;busy&#34; brought about by the short on the line, but the user elects to override and test. A partial tip to ring short is diagnosed and short circuit test called for at the subscriber drop. 
     In the present embodiment for the case where the user has performed a LINE TEST mode operation to a dial-up central office (e.g. block 30-3 in FIG. 2), the use may direct computer 24 to disconnect the trunk link by entering * 8. Otherwise, the computer 24 maintains the link for a predetermined time to permit the user to repeat the test or test a different line in the exchange, or to permit another user to test a line in the exchange. In this manner, the various users may save the dial-up testing time. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 
     
                       TABLE 1______________________________________TEL SERVICE  TYPE 0 FOR HELP  EXCHANGE #837*0SELECT1 TO CHANGE EXCHANGE #2 FOR CURRENT ADVISORY3 FOR HISTORICAL ADVISORY4 FOR SERVICE AREA SUMMARY8 TO DISCONNECT LINE# LINE TEST* PRIMARY COMMAND LEVEL______________________________________ 
    
     
                       TABLE 2______________________________________INVALID NUMBER-5INVALID NUMBER-7INVALID NUMBER-5-555INVALID NUMBER-2*1 EXCHANGE #415-862______________________________________ 
    
     
                       TABLE 3______________________________________*2 CURRENT TROUBLE ADVISORY FOR EXCHANGE #415-862 TYPE 0 FOR HELP&gt;0SELECT1 PERMANENT BUSY LINES2 SHORTS, CROSES AND GROUNDS3 HIGH BACKGROUND LINES4 SUSPECT WET CABLE LINES5 SUSPECT LINES6 ACTIVATED PRESSURE CONTACTORS7 HIGH VOLTAGE LINES9 TO ADVANCE PAGE# LINE TEST* PRIMARY COMMAND LEVEL______________________________________ 
    
     
                       TABLE 4______________________________________*2 CURRENT TROUBLE ADVISORY FOR EXCHANGER #415-862 TYPE 0 FOR HELP&gt;1 PERMANENT BUSY LINES2045  2399   2790   6584SEVERERTS, CROSSES AND GROUNDS2007  2075   2413   2569 2743 2813 2864 2879 2870 60446182  6280   6477   6483 6614 6680 6716 6756 6864 SHORTS, CROSSES AND GROUNDS -MODERATE2225  2598   2620   2633 2705 2972 6290 6344 6536 68126894SEVEREH BACKGROUND LINES  NO FAULTS-MODERATEKGROUND LINES2331  2332   2334   2335 6141 6147 6518 6608&gt;4 SUSPECT WET CABLE LINES2040  2094   2410   2433 2434 2430 2457 2474 2562 28532955  6189   6548   6557 6705&gt;5 SUSPECT LINES2025  2238   2285   2491 2495 2518 2510 2579 2587 26302962  2998   6023   6073 6079 6143 6181 6183 6217 62256516  6527   6569   6622 6681 6687 6694 6709 6700 67916821  6848   6867&gt;6 ACTIVATED PRESSURE CONTACTORS  NO FAULTS-&gt;7 HIGH VOLTAGE LINES2106  2766   6372   9106______________________________________ 
    
     
                       TABLE 5______________________________________*3 HISTORICAL ADVISORY FOR EXCHANGE #837 TYPE 0 FOR HELP&gt;0SELECT1 FOR INDIVIDUAL LINE HISTORY2 FOR TROUBLE LINE HISTORY3 FOR SUSPECT LINE HISTORY# LINE TEST* PRIMARY COMMAND LEVEL______________________________________ 
    
     
                       TABLE 6______________________________________&gt;3 SUSPECT LINE HISTORY FOR EXCHANGE #837 TYPE 0 FOR HELP&gt;&gt;0SELECT1 SUSPECT LESS THAN 8 DAYS2 SUSPECT 8 TO 31 DAYS3 SUSPECT 32 TO 63 DAYS4 SUSPECT OVER 63 DAYS9 TO ADVANCE PAGE# LINE TEST* PRIMARY COMMAND LEVEL______________________________________ 
    
     
                       TABLE 7______________________________________&gt;3 SUSPECT LINE HISTORY FOR EXCHANGE #837 TYPE 0 FOR HELP&gt;&gt;1 SUSPECT LESS THAN 8 DAYS2062  2151   2270   2488 2497 3040 3167 3171 3185 34255273  5323   5340   5368 5424 5457 5579 5585 5749 57876385  6401   6418   6431 6719 6753 6750 6875 6906 71107922  7938   8113   8167 8168 8187 8201 8210 8310 83369041  9043   9092   9322 9376 9530 9549 9777 9876 99009995&gt;&gt;2 SUSPECT 8 TO 31 DAYS2019  2024   2073   2083 2087 2156 2263 2278 2334 23593225  3261   3326   3320 3341 3403 3406 3407 3422 34445564  5574   5612   5621 5663 5695 5808 5838 5850 58756924  6925   6966   6971 6982 6984 7014 7017 7026 70387742  7774   7789   7794 7797 7865 7870 7884 7937 79397970  7995   8034   8075 8177 8190 8225 8250 8263 82849014  9033   9037   9064 9070 9082 9093 9121 9122 9126PAGE 1  TYPE 9 TO ADVANCE PAGE&gt;&gt;9 SUSPECT 8 TO 31 DAYS9134  9171   9032   9311 9381 9433 9523 9548 9580 96059843  9851   9882   9880 9895 9907PAGE 2   LAST PAGE______________________________________ 
    
     
                       TABLE 8______________________________________&gt;2 TROUBLE LINE HISTORY FOR EXCHANGE #837 TYPE 0 FOR HELP&gt;&gt;0SELECT1 TROUBLE LESS THAN 8 DAYS2 TROUBLE 8 TO 31 DAYS3 TROUBLE 32 to 63 DAYS4 TROUBLE OVER 63 DAYS9 TO ADVANCE PAGE# LINE TEST* PRIMARY COMMAND LEVEL&gt;&gt;3 TROUBLE 32 TO 63 DAYS3237  3387   3890   5203 5594 5693 5965 6082 6935 71267182  7643   7652   7751 8260 8624 8878 8950 8969 91169356&gt;&gt;4 TROUBLE OVER 63 DAYS2316  3372   3408   3508 3884 5168 5169 5529 6408 64597082  7298   7325   7326 7383 7384 7435 7653 7736 81478698  8772   8814   9056 9835 9889______________________________________ 
    
     
                       TABLE 9______________________________________*3 HISTORICAL ADVISORY FOR EXCHANGE #837 TYPE 0 FOR HELP&gt;1 HISTORY FOR LINE #837-3408TROUBLE HISTORY FOR 204 DAYSTESTED OK ON 16 DAYSPAST 8 DAY HISTORY1 SUSPECT2 SUSPECT3 SUSPECT4 SUSPECT5 SUSPECT6 SUSPECT7 SUSPECT8 SUSPECT______________________________________ 
    
     
                       TABLE 10______________________________________*3 HISTORICAL ADVISORY FOR EXCHANGE #837 TYPE 0 FOR HELP&gt;1 HISTORY FOR LINE #837-9889TROUBLE HISTORY FOR 125 DAYSTESTED OK ON 65 DAYSPAST 8 DAY HISTORY1 PERMANENT BUSY2 PERMANENT BUSY3 PERMANENT BUSY4 PERMANENT BUSY5 PERMANENT BUSY6 PERMANENT BUSY7 OK8 PERMANENT BUSY______________________________________ 
    
     
                       TABLE 11______________________________________*4 SERVICE AREA SUMMARY TYPE 0 FOR HELP&gt;0SELECT1 CURRENT TROUBLE SUMMARY2 TROUBLE LINE HISTORICAL SUMMARY3 SUSPECT LINE HISTORICAL SUMMARY4 SEVERE SHORTS, CROSSES AND GROUNDS5 SEVERE HIGH BACKGROUND LINES9 TO ADVANCE PAGE# LINE TEST* PRIMARY COMMAND LEVEL______________________________________ 
    
     
                       TABLE 12______________________________________&gt;1 SERVICE AREA SUMMARYCURRENT TROUBLE SUMMARY TYPE 0 FOR HELP&gt;&gt;0SELECT1 PERMANENT BUSY LINES2 SHORTS, CROSSSES AND GROUNDS3 HIGH BACKGROUND LINES4 SUSPECT WET CABLE LINES5 SUSPECT LINES6 ACTIVATED PRESSURE CONTACTORS7 HIGH VOLTAGE LINES9 TO ADVANCE PAGE#LINE TEST* PRIMARY COMMAND LEVEL______________________________________ 
    
     
                       TABLE 13______________________________________&gt;&gt;5 SERVICE AREA SUMMARYCURRENT TROUBLE SUMMARY TYPE 0 FOR HELPNUMBER OF SUSPECT LINESEXCHANGE     FAULTS#415-862     53#609-666     12#609-837     25TOTAL        90______________________________________ 
    
     
                       TABLE 14______________________________________&gt;&gt;2 SERVICE AREA SUMMARYCURRENT TROUBLE SUMMARY TYPE 0 FOR HELPNUMBER OF SHORTS, CROSSES AND GROUNDS      SEVERE     MODERATE     TOTALEXCHANGE   FAULTS     FAULTS       LINES#415-862   19         11           30#609-666   5          2            7#609-837   7          6            13TOTAL      31         19           50______________________________________ 
    
     
                       TABLE 15______________________________________&gt;&gt;7 SERVICE AREA SUMMARY CURRENT TROUBLE SUMMARY TYPE 0 FOR HELPNUMBER OF HIGH VOLTAGE LINESEXCHANGE        FAULTS#415-862        4#609-666        0#609-837        5TOTAL           9______________________________________ 
    
     
                       TABLE 16______________________________________TEST #3470 DIAL TEST TROUBLE HISTORY  45 K TIP-GROUNDBRIDGEDRINGERCABLE LENGTH 0.9 MILES OR 5,400 FEETNEGLIGIBLE CAPACITANCE IMBALANCE 4-TEL SERVICE  TYPE 0 FOR HELP&gt;0SELECT1 LINE HISTORY2 SHORT CIRCUIT DIAGNOSTIC3 OPEN CIRCUIT DIAGNOSTIC4 EXTRA DATA# LINE TEST* PRIMARY COMMAND LEVEL&gt;2 PARTIAL TIP GROUNDTEST NEEDED AT SUBSCRIBER LOOP______________________________________ 
    
     
                       TABLE 17______________________________________TEST #9034 DIAL TEST TESTED OK3 STRAIGHT LINE RINGERS BRIDGEDCABLE LENGTH 1.8 MILES OR 10,500 FEETNEGLIGIBLE CAPACITANCE IMBALANCE 4-TEL SERVICE&gt;0SELECT1 LINE HISTORY2 SHORT CIRCUIT DIAGNOSTIC3 OPEN CIRCUIT DIAGNOSTIC4 EXTRA DATA#LINE TEST* PRIMARY COMMAND LEVEL                                BACK-&gt;4    BATTERY    DC VOLTS   AC VOLTS GROUNDRING50.0 V0.1 V 0.0 V      7 UATIP   0.2 V0.1 V 0.0 V      7 UAINSULATION OK______________________________________ 
    
     
                       TABLE 18______________________________________TEST #9874 DIAL BUSYSELECT5 TO OVERRIDE AND TEST# LINE TEST* PRIMARY COMMAND LEVEL&gt;5 TEST  TROUBLE HISTORY1205 OHM SHORTNO RINGERSCABLE LENGTH 3.2 MILES OR 18,600 FEETNEGLIGIBLE CAPACITANCE IMBALANCE 4-TEL SERVICE TYPE 0 FOR HELP&gt;2 PARTIAL TIP RING SHORTTEST NEEDED AT SUBSCRIBER DROP&gt;3 OPEN AT 3.2 MILES OR 18,600 FEET FROM CENTRAL OFFICEOPEN CALIBRATION REQUIRED AT OR NEAR LOAD POINT 3                                BACK-&gt;4    BATTERY    DC VOLTS   AC VOLTS GROUNDRING42.0 V0.1 V 0.0 V      14 UATIP 7.1 V0.1 V 0.0 V      15 UA1205 OHM SHORT______________________________________ ##SPC1##    10/888 ##SPC2## ##SPC3## ##SPC4## ##SPC5## ##SPC6## ##SPC7## ##SPC8## ##SPC9## ##SPC10## ##SPC11## ##SPC12## ##SPC13## ##SPC14## ##SPC15## ##SPC16## ##SPC17## ##SPC18## ##SPC19## ##SPC20## ##SPC21## ##SPC22## ##SPC23## ##SPC24## ##SPC25## ##SPC26## ##SPC27## ##SPC28## ##SPC29##