US 4,658,395 AGrant
Method for Locating Faults in a Carrier Subscriber Communication System
Issue Date:1987-04-14
•11 Claims
•3 Drawing Sheets
Abstract
Method and apparatus is disclosed for identifying faults in a subscriber carrier telephone system utilizing out-of-band pilot signals and comprising pluralities of cables and repeaters that are alternately connected in series between carrier equipment at a central office location and a subscriber station. Equipment at the office location transmits selected numbers of test pulses, having a test frequency that is between the transmitted and received channel and pilot frequencies, to the first cable. The pulses are detected at the first repeater and counted. A microprocessor is responsive to the test pulse count in the repeater for initiating associated tests on the cable and/or repeater, or for retransmitting test pulses on the next cable to the next repeater for causing it it perform designated tests. The results of the tests are sent to the office equipment in the form of reply pulses having a frequency that is below the lowest channel frequency.
Metadata
Assignee
- GTE Communication Systems Corporation
Inventor
- Tom L. Blackburn
Application Information
Application Number:US 6802060
Filing Date:1984-12-10
Priority Date:1984-12-10
Art Unit:263
Classifications
IPC:
H04J 116H04J 314
Field of Search:
37017913;75;71;14175;31 R
Patent Drawings (3 sheets)
Description
Background of Invention
This invention relates to telephone systems and more particularly to a method for locating faults in a carrier subscriber telephone system.
A typical carrier subscriber telephone system comprises carrier equipment that is normally collocated with central office telephone equipment at an office facility, a plurality of repeaters, and carrier subscriber equipment that is located at different subscriber stations or which is collocated at a cluster subscriber station. The repeaters are connected in series between the central office and station carrier equipment by means of associated cable sections which may be lengths of coaxial cable or twisted pair telephone cable.
In a computer controlled ten channel cluster carrier subscriber telephone system, carrier equipment at the central office location typically comprises apparatus for transmitting high frequency signals (e.g., channel frequencies between 92 and 148 kHz together with low and high frequency out of band pilot signals such as 88 kHz and 160 kHz), apparatus for receiving low frequency signals (e.g, channel frequencies between 12 kHz and 68 kHz), and a computer means for controlling the operation of the system. The repeaters operate to periodically increase the signal to noise ratio and integrity of carrier signals. All of the repeaters are preferably identical and comprise high and low frequency sections for passing office location signals to subscriber stations, and vice/versa. The high frequency repeater section essentially comprises a pair of 84-184 kHz high frequency filters flanking amplifier circuitry that passes signals only in the direction of the subscriber stations. Conversely, the low frequency repeater section comprises a pair of 8-72 kHz, for example, low frequency filters flanking amplifier circuitry that passes signals only in the direction of the office. Each repeater also comprises a microprocessor or microcomputer or other type of computer means that is responsive to control signals from the office computer for controlling the operation and/or characteristics of the repeater, e.g. the slope of the filter characteristics and the gain of the amplifiers.
From time to time, communication between the office and the cluster station may be faulty due to an entire or partial failure of one of the components in the repeater, damage to a cable, improper power supply voltage, or some other malfunction in the system. In order to avoid undue interruption of service for any of the above reasons, it is desirable to check the integrity and operation of the carrier subscriber system periodically for faults. It is also desirable to make such a check while the system is being operated in a normal communication mode. If a fault is found to exist, it is further desired to determine the location of the fault so that repair and/or preventative maintainence can be judiciously assigned and readily facilitated.
An object of this invention is the provision of an improved method of testing components of a carrier subscriber communication system.
Another object is the provision of an improved method of identifying and/or indicating the location of faults in components of carrier subscriber equipment.
Another object is the provision of a method for detecting and/or locating faults in a carrier subscriber communication system which utilizes existing system components, which requires few additional components, and which may be performed without interrupting normal use of the system.
Summary of Invention
In accordance with one aspect of this invention, a method of checking for faults in a carrier subscriber communication system in which pluralities of cables and repeaters are alternately connected in series between office and subscriber station terminal carrier equipment, each of which repeaters is connected to one end of a first one of the cables of a first node and to the other end of a second one of the cables at a second node, comprises the steps of: transmitting a selected number of test pulses having a test frequency from the office location on the first cable to a first node of the first repeater; first determining a first number of test pulses that are received at the first node of the first repeater; first incrementing the first number of received test pulses by a first prescribed number to produce a second number of test pulses; first coupling a first predetermined number of reply pulses having a reply frequency from the first repeater into the first node at the first repeater for transmission over the first cable to the office equipment if the second number of test pulses is equal to a second prescribed number for testing the integrity of the first cable; and second determining the number of reply pulses that are achieved at the office equipment location for indicating whether there is a fault on the first cable. The method may comprise the additional steps of: second incrementing the second number of test pulses by a third prescribed number to produce a third number of test pulses if the second number of test pulses is not equal to the second prescribed number; performing one or more predetermined tests in the first repeater if the third number of received test pulses is equal to a fourth prescribed number which may be equal to the second prescribed number; second coupling a second number of reply pulses to one the first and second nodes of the first repeater for transmission to the office equipment for indicating the results of the predetermined tests; and third determining the number of reply pulses that are received at the office location for indicating whether there is a fault in the first cable or first repeater. The method may further comprise the steps of: generating in the first repeater an output signal having the same test frequency as the test pulses; and third coupling a plurality of pulses of output signal that are generated at the first repeater to the second node of the first repeater for transmission on the second cable to the first node of the adjacent-next repeater that is connected in the series if the third number of test pulses is not equal to the second or fourth prescribed numbers; the number of the plurality of output pulses being related to the value of the third number of test pulses.
Brief Description of Drawings
This invention will be more fully understood from the following detailed description of preferred embodiments thereof, together with the drawings in which:
FIG. 1 is a schematic block diagram of a carrier subscriber telephone system embodying this invention.
FIG. 2 is a schematic block diagram of the repeater 106 in FIG. 1.
FIGS. 3A and 3B are a flow diagram of operation of the microprocessor in FIG. 2.
Description of Preferred Embodiments
Referring now to FIG. 1, a cluster station carrier subscriber telephone communication system embodying this invention generally comprises office located equipment 100, cables 101-104, repeaters 106 and 107, and cluster station carrier subscriber equipment 109. The equipment 100 generally comprises carrier equipment 112; a central office unit 116; a computer means 120 that is associated with an input device 121, switches 122, and a utilization device 123; an 80 kHz test frequency oscillator 132 and a switch means 133; and a 5 kHz bandpass filter 117 feeding a detector 118.
The carrier equipment 112 is operative for converting 10 each, for example, voice frequency signals on lines 113 from the central office unit 116 into associated carrier subscriber channels on line 110 that are in a 92-148 kHz band of carrier channel frequencies. The carrier equipment 112 also produces 88 and 160 kHz out of band pilot frequency signals on line 110 for transmission to the subscriber station 109. The carrier equipment 112 is also responsive to carrier subscriber channel signals from the equipment 109 that are in the frequency band of 12-68 kHz. The low frequency carrier channel signals are converted to associated voice frequency signals that are applied on lines 113 to the central office unit 116 which transmits them on lines 114 to other equipment (not shown).
The computer means 120 is operative for controlling the operation of the systems, including the repeaters, and for remotely testing the operation of the cables, repeaters and subscriber station equipment. The computer generally comprises a controller 125 and a signal processor 124 which is responsive to detected 5 kHz reply pulses on line 101. The controller may be caused to initiate testing of the system by manually actuating one of the switches 122 or by automatically programming the computer for performing a sequence of tests with the input device 121. The results of the tests, i.e., what units are faulty, are applied to a utilization device 123 which may be a display unit. The controller is operative during a test of a paticular component for sequentially opening and closing the switch 133 a prescribed number of times for producing a sequence of 80 kHz test pulses 147 on line 134 which are transmitted on the first cable 101 in the direction of the repeaters. The carrier equipment 112 and detector 118 are not responsive to the test pulses since the 80 kHz test frequency is spaced apart from the channel and pilot frequency passbands and the low frequency passband of the filter 117. The test pulses are typically of 30 milliseconds duration with a 150 millisecond delay time between test pulses. Thus, the pulse period or test pulse time interval TI is 180 milliseconds.
Since all of the repeaters are substantially identical, only the repeater 106 will be described in detail. Referring now to FIG. 2, the repeater 106 comprises a high frequency section 135, a low frequency section 136, a test frequency detection circuit 137, a pilot frequency detection circuit 138, a microprocessor 139, and a test and reply pulse generator circuit 140. The high frequency section 135 comprises a one way amplifier 143 and a pair of high-pass filters 142 and 144 having 84-164 kHz passbands. The filters 142 and 144 pass the pilot and high channel frequencies from the carrier equipment 112 while blocking any low channel frequencies, 5 kHz reply pulses, and 80 kHz test pulses on the cables. Conversely, the low frequency section 136 comprises a one way amplifier 153 and a pair of low-pass filters 152 and 154 having an upper cutoff frequency of approximately 72 kHz for passing the low channel frequencies from the station equipment 109 and any 5 kHz reply pulses on the cables (as is described more fully hereinafter) while blocking the high frequency channel and pilot signals and 80 kHz test pulses.
The test frequency detection circuit 137 is connected on line 156 to a node or junction N1 of the input cable 101 and repeater 106, and comprises a narrow-band high-Q 80 kHz bandpass filter 158, a pulse detector circuit 159, and a pulse shaper circuit 160. Detected test pulses on line 161 comprise the SI input signal to the microprocessor 139.
The pilot detection circuit 138 is connected on line 147 to the node or junction N2 of the repeater and one end of the second cable 102. The pilot detection circuit comprises a pair of narrow-band high-Q 88 and 160 kHz bandpass filters 163 and 164 and associated pulse detector circuits 165 and 166, and an AND gate 167. The output signals of these detectors are high and low when the associated low and high frequency pilot signals are present and absent, respectively, at the node N2. The detected pilot signals are combined in AND gate 167 and applied as a logic signal SP to the processor 139.
The signal generator circuit 140 comprises a switch means 171 including a plurality of switching transistors Q1, Q2 and Q3; a decoder-driver circuit 172 for selectively driving ones of the switching transistors; and an oscillator 173 and divider circuit 175 which are operative for producing an 80 kHz test frequency signal on line 174 and a 5 kHz reply frequency signal on line 176. The switching transistors Q1 and Q2 are caused by the microprocessor to produce one or more 5 KHZ reply pulses on lines 178 and 179 that are applied to nodes N1 and N2, respectively. The switching transistor Q3 is caused by the microprocessor to produce designated numbers of 80 kHz test pulses on line 180 that are applied to the node N2 for transmission on the next cable 102 to the next repeater 107.
The microprocessor 139 operates in accordance with a stored program that is specified in FIGS. 3A and 3B for testing system components for faults in response to one or more detected test pulses on the SI input line 161. The microprocessor includes a plurality of registers 181-186 which are designated the [1,7], [2,3], [1,5], [1,6], [1,3], and [1,4] registers, respectively. The status of individual bits in or the full contents of various ones of these registers are periodically checked and/or incremented during the prescribed operation of the microprocessor in checking system components for faults.
All of the four bits of the [1,7] or operation register 181 are reset to 0 during an initialization procedure such as when the processor is turned on or reset. Each of these bits contains status information as to whether the S0 and SK outputs of the microprocessor will be toggled (i.e., made to go high for a prescribed time interval) as follows:
The [2,3] or toggle generation register 182 is employed within the program in FIGS. 3A and 3B for making S0 and/or SK go high during operation of the program. In contrast with the other registers here, all of the four bits of the register 182 are set to a binary 1 during the initialization procedure. Operations established by the status of individual bits of the register 182 are as follows:
The [1,5] register is a four bit count register 183 which is incremented for each detected test pulse on the SI input line 161. The contents of the register 183 is the number of detected test pulses that have been previously counted, not including any overflow. The four bit [1,6] or count overflow register 184 is incremented each time count register 183 overflows and therefore contains an indication of the number of detected test pulses that have already been counted, in multiples of 15 which is the number F in hexidecimal. Thus, the contents of the two registers 183 and 184 must be considered together to determine the total number of detected test pulses that have previously been counted. Both of the count registers 183 and 184 are reset during initialization.
The [1,3] register is a four bit detected test pulse integrity register 185 which is incremented whenever the SI input pulse is high at prescribed times during a given time interval. In operation, a detected test pulse is determined to be present in SI if the count in the [1,3] register is 3 during a particular 20-30 millisecond time interval (program steps 4-19 in FIG. 3A). The register 185 is reset to 0 to make bits thereof a logic 0 during initialization of the microprocessor.
The four bit [1,4] register is an SI end-of-test pulse train register. It stores the number of times that a program in FIGS. 3A and 3B is cycled through ones of the program steps 1 through 23 without detecting a test pulse in SI following detection of at least one test pulse on line 161. More particularly, if at least one of the count registers contains a count and the register 186 contains a count of four, indicating that there has not been a detected test pulse on the SI input line 161 for the past three passes through this part of the program, it is determined that an input stream of test pulses is terminated. The microprocessor then cycles through ones of the program steps 25-65 in FIGS. 3A and 3B for toggling one or both of the output lines SK and S0 thereof for performing or initiating prescribed tests.
The operation of the decoder 172 is specified in the following table, where a binary 1 on one of the output lines A, B and C causes the associated switch to close.
In accordance with one aspect of this invention, ones of the components 101-109 are tested by periodically transmitting different-unique series of 80 kHz test pulses 147 on line 134 to cable 101, each component to be tested and/or test being designated by a different-unique number of test pulses. By way of example, testing of the first cable 101, first repeater 106, second cable 102, and second repeater 107 may be designated by transmitting one, two, three and four test pulses, respectively. In operation, the controller 125 periodically closes switch 133 for 30 millisecond, for example, time intervals for passing the output signal of oscillator 132 onto line 134 to create the selected number of 30 millisecond 80 kHz test pulses 147. The test pulses are blocked by filters in the carrier equipment 112 and the filter 117 and coupled on the input cable 101 to the first repeater. Although the test pulses are blocked from upstream components such as the cable 102 and repeater 107 by the high-pass filter 142 and low-pass filter 154 in the repeater 106, they are passed by filter 158 and detected for producing detected test pulses of a logic-binary 1 on line 161.
The microprocessor 139 is synchronized with the operation of the office computer 120, in the conventional manner, so that it will automatically cycle through ones of the program steps 1 through 60 in FIGS. 3A and 3B during at least certain portions of each time interval TI during which at test pulse 147 may be transmitted by office equipment. After determining that each detected test pulse on line 161 is a valid test pulse (program steps 1-19), the microprocessor counts the number of test pulses SI in step 17. It then tests during successive TI's for the end of a train of test pulses in ones the programs steps 20 through 25 by determining that there is no test pulse present in 3 consecutive time intervals TI during which they may be transmitted.
The microprocessor then subtracts 1 from the test pulse count in registers 183 and 184 in the program steps 26-28. If the remainder in registers 183-184 is 0, (programs steps 29 and 39) indicating that only a single test pulse was transmitted from the office, the microprocessor operates to make output line SK thereof go high for a prescribed time interval such as 30 milliseconds (program steps 40-45). This causes Q1 to turn on for the prescribed time interval for producing a 5 kHz reply pulse on line 178 which is coupled onto the input cable 101 for transmission to the office equipment. Although the 5 kHz reply pulse frequency is within the passband of low-pass filter 154, it is blocked from upstream cables and repeaters by the amplifier 153. If the input cable 101 is unimpaired, this single 5 kHz reply pulse is passed by filter 117, detected and applied to the processor 124. The processor 124 is responsive to the detected reply pulse for producing a binary output signal on 127 which tells the controller that the input cable is operational and that test pulses can be generated for testing the next component in the system. If a single detected reply pulse is not received within a prescribed time interval that is required for generation and transmission of a reply pulse to the office equipment, the processor produces a binary output signal on line 127 which tells the controller that cable 101 or repeater 106 is faulty. The controller then causes the utilization device 123 to indicate that the input cable 101 is faulty and discontinues further test on the system components.
If after the first subtraction of 1 from the detected test pulse count in registers 183 and 184 the remainder there is not 0, the microprocessor again subtracts 1 from the count registers 183 and 184 in ones of the program steps 26A, 30 and 41. If the remainder in the registers 183 and 184 following the second subtraction is 0 (steps 31-33), then the microprocessor operates for testing the repeater 106 in ones of the program steps 35-38 and 61-65. By way of example, testing of the repeater 106 may comprise checking for the presence of one or more pilot signals at the output node N2 of the high frequency section 135 of repeater 106. Detection of the low and high frequency pilot signals is readily accomplished with bandpass filters and detectors of the circuit 138. If both of the pilot signals are present, the SP output of AND-gate 167 is high for causing the output signal on line S0 to go high during two each successive 30 millisecond time intervals, for example, (steps 35, 36, 38 and 61-65) for turning on Q2 and coupling two each 5 kHz reply pulses on line 179 to the input of the low frequency section of the repeater 106. If one or both pilot signals are not present at the node N2 of repeater 106, the SP signal is low for causing the microprocessor output line S0 to go high for only a single 30 millisecond time interval (steps 35, 36 and 61-65) for turning on Q2 so as to inject only a single 5 kHz reply pulse at the input of the low frequency section 136 of the repeater. Receipt of two or one or no detected reply pulses by the processor 124 indicates that both the high and low frequency sections 135 and 136 of the repeater 106 are operable, that only the high frequency section 135 is inoperable, and that one or both of the low and high frequency sections of the repeater 106 are inoperable.
If the remainder count in the registers 183 and 184 is some number M after the second subtraction rather than 0 (program steps 26A, 31, 33 and 41) the microprocessor proceeds through many of the program steps 42 through 60 and/or 1 through 3B during M successive time intervals TI for simultaneously causing the SK and S0 output signals to go high for 30 milliseconds time intervals. This causes Q3 to conduct for impressing M 80 kHz test pulses on line 180 which are coupled to node N2 and onto the second cable 102 to the next repeated 107. These 80 kHz test pulses on line 180 are blocked from the office equipment by the high-pass and low-pass filters 144 and 152 of the repeaters since all of the repeaters are substantially identical. The aforementioned operation is repeated in the next repeater 107. More specifically, the M test pulses on line 102 are detected and applied as input pulses on the SI input of the associated microprocessor. The detected test pulses are then counted and reduced by one. If the remainder (M-1) is 0, a single 5 kHz reply pulse is outputted from the repeater 107 onto cable 102 and transmitted through repeater 106 and cable 101 to the office equipment. Detection of this reply pulse by circuit 138 tells the processor that the second cable 102 is operating satisfactorily. Conversely, if a detected reply pulse is not received within a prescribed time interval, the processor knows that either the second cable or the second repeater 107 is faulty.
If the remainder count M-1 is not 0, the microprocessor again subtracts 1 from it. If the remainder (M-2) is now 0, the microprocessor is operative for testing the repeater as was previously described. If the remainder count M-2 is not 0, then the microprocessor operates for generating M-2 test pulses that are applied to the other side N4 of repeater 107 for transmission to a subsequent repeater or station equipment for causing similar testing operation as was previously described here. The number of pulses required to test the cable preceeding the last or nth repeater is 2n-1 pulses. There are 2n pulses required to test the nth repeater. If the subscriber station equipment is caused to include circuitry similar to the repeaters, then 2n+2 and 2n+1 pulses are employed to test the subscriber equipment and the length of cable between it and the last or nth repeater.
Although this invention is described in relation to preferred embodiments thereof, variations or modifications are possible. By way of example, numbers which are different values and which are other than 1 may be subtracted from the count of detected test pulses; the remainders remaining after a subtraction can be other than 0 and different values; incrementation of the counts may be by addition rather than subtraction; the numbers of test pulses that are transmitted by the office equipment may be coded to components of the series chain of cables and repeaters rather than be directly related to the progressive numbers of the series elements in the chain; and the microprocessor may operate directly on the numbers of detected test pulses rather than by performing a number of incrementations. Also, other tests may be performed on or in the cable and on repeaters such as checking the signal level at prescribed points in the systems and repeaters and on the cables; monitoring power supply voltages in the repeaters; monitoring the output signal levels of the directional amplifiers in the repeaters; etc. Further, the test and reply frequencies may be other than 5 and 80 kHz. Additionally, the high-pass filters 142 and 144 in the repeaters may be bandpass filters having a high frequency cutoff frequency that is below the test frequency. Also, both the test and reply frequency may be between the lower and upper cutoff frequencies of the high-pass and low-pass filters of the repeaters. This method of fault locating may also be used in a PCM carrier system by using A/D and D/A converters at appropriate locations and synchronization. The scope of this invention will therefore be determined from the appended claims rather than from the aforementioned detailed descriptions of preferred embodiments and methods thereof.
Claims
What is claimed is:
1. The method of checking for faults in a carrier subscriber communication system in which pluralities of cables and repeaters are alternately connected in series between office carrier equipment and subscriber station terminal carrier equipment, each of which repeaters being connected to one end of a first one of said cables at a first node and to the other end of a second one of said cables at a second node, comprising the steps of: transmitting a selected number of test pulses having a test frequency from the office on the first cable to said first node of said first repeater, said test frequency being outside the frequency bandwidth passed by said repeaters between office carrier equipment and subscriber station carrier equipment; first determining the first number of test pulses that are received at said first node of said first repeater; first incrementing said first number of received test pulses by a first prescribed number to produce a second number of test pulses; first coupling a first predetermined number of reply pulses having a reply frequency from said first repeater to said first node at said first repeater for transmission over said first cable to said office equipment if the second number of test pulses is equal to a second prescribed number for testing the integrity of said first cable, said reply frequency being within a frequency bandwidth passed by said repeaters between subscriber station carrier equipment and office carrier equipment; second determining the number of reply pulses that are received at the office equipment on the other end of said first cable for indicating whether there is a fault on said first cable; second incrementing the second number of test pulses by a third prescribed number to produce a third number of test pulses if the second number of test pulses is not equal to the second prescribed number; performing one or more predetermined tests in said first repeater if the third number of received test pulses is equal to a fourth prescribed number which may be equal to said second prescribed number; second coupling a second number of reply pulses to one of said first and second nodes of said first repeater for transmission to the office equipment at the other end of the first cable for indicating the results of the predetermined tests; third determining the number of reply pulses that are received at the other end of the first cable for indicating whether there is a fault in the first cable or first repeater; generating in said first repeater an output signal having the same test frequency as the test pulses; ;p1 third coupling a plurality of pulse output signals, which correspond to test pulses and that are generated at the first repeater, to said second node of the first repeater for transmission on said second cable to said first node of the adjacent-next repeater that is connected in said series if the third number of test pulses is not equal to the second or fourth prescribed numbers; the number of said plurality of output pulses being related to the value of the third number of test pulses.
2. The method according to claim 1 wherein said selected number of test pulses comprises a plurality of sets of test pulses, each of said sets comprising a number of pulses which correspond to a selected one of said pluralities of cables and repeaters.
3. The method according to claim 1 wherein said office equipment transmits a pilot signal to said repeaters and said performing step comprises detecting the presence or absence of the pilot signal at the second node of the first repeater.
4. The method according to claim 3 wherein said second coupling step comprises coupling second or third numbers of reply pulses to said second node of the first repeater for transmission to the other end of the first cable for indicating whether the pilot signal is present or absent, respectively, from the second node of the first repeater.
5. The method according to claim 1 wherein the first and third prescribed numbers are the same values so that said first and second incrementing steps increment the associated first and second numbers of test pulses by the same number.
6. The method according to claim 1 wherein said first and second incrementing means increment the associated first and second numbers of test pulses by subtracting associated first and third prescribed numbers therefrom.
7. The method according to claim 6 wherein the associated first and third prescribed numbers that are subtracted from the associated first and second numbers of test pulses are the same values.
8. The method according to claim 7 wherein the said second prescribed number is zero.
9. The method according to claim 8 wherein said fourth prescribed number is zero.
10. The method according to claim 9 wherein both of the first and third prescribed numbers are one.
11. In a carrier subscriber communication system comprising pluralities of cables and repeaters that are alternately connected in series between office carrier equipment and subscriber terminal equipment, each of the repeaters being connected to one end of one of the cables at a first node and to the other end of an other of the cables at a second node, the method of testing for faults in ones of said repeaters and/or cables comprising the steps of; selecting one of the pluralities of repeaters and cables to be checked for a fault therein; transmitting a first predetermined number of test pulses having a test frequency from the office location on a first cable to a first repeater that is closest to the office equipment said test frequency being outside first and second frequency bandwidth passed by repeaters between office equipment and subscriber station equipment and vice versa, respectively, said first predetermined number corresponding to the selected one of the pluralities of repeaters and cables that is to be tested; detecting a first number of test pulses that are received at the associated first node of the first repeater; counting the detected test pulses; coupling a first number of reply pulses having a reply frequency to the first node of the first repeater if the first number count of detected test pulses is a first prescribed number count, said reply frequency being within the second frequency bandwidth passed by the repeaters between subscriber station and office equipment; detecting reply pulses that are received at the other end of the first cable; and counting detected reply pulses; indicating from the absence of one or more expected reply pulses, as required of the operation dictated by said selecting step, the presence of a fault in the selected one of the repeaters and cables; performing predetermined test in the first repeater if the first number count of detected test pulses is a second prescribed number count; coupling a second number of reply pulses, which may be equal to the first number of reply pulses, to one of the first and second nodes of said first repeater for transmission on the first cable; said indicating step being responsive to the number of received reply pulses for indicating the results of the predetermined test(s); coupling a second predetermined number of test pulses, which is related to the number count of detected test pulses, to the second node at the first repeater for transmission to the next-adjacent repeater if the number count of detected test pulses is different from the first and second prescribed number counts; transmitting a pilot signal through the repeaters and cables; detecting the presence of the pilot signal at the second node of the first repeater if the number of detected test pulses is the second prescribed number count; and coupling third or fourth numbers of reply pulses to one of the first and second nodes of the first repeater if said detecting step indicates the presence and absence, respectively, of the pilot signal at the second node of the first repeater.