CA2311146A1 - A telephone jack for isolating faults on a wire loop - Google Patents

Abstract

A telephone jack for isolating faults on a wire loop. The jack consists of a half ringer, a throw switch, a loop qualification circuit, an input port, and an output port. In one embodiment the loop qualification circuit consists of a voltage sensing circuit in parallel with a voltage polarity detection circuit. In a second embodiment the voltage sensing circuit is placed at the center of four-diode full rectifier. In either embodiment the application of a predetermined voltage across the jack provides a visual indication of the status of line.

Description

KimseylMistry A TELEPHONE JACK FOR ISOLATING
FAULTS ON A WIRE LOOP
Field of the Invention s This invention relates to fault isolation in a communications network and specifically to determining the condition of a line or loop in a communications network.
Background of the Invention Fault detection, isolation, and repair are costly and difficult tasks that are ~o performed daily by communications network providers, e.g., regional telephone companies. Specifically, with the millions of miles of wire cable in the Public Switched Telephone Network (PSTN) loop plant, remotely detecting, locating, and, as much as possible, troubleshooting a fault helps to minimize cost by dispatching craft personnel to the appropriate location and, more importantly, ~s dispatching craft only when absolutely necessary.
Recent changes in government regulation have made remedying service affecting faults on the loop plant even more economically precarious for network providers. In particular, recent regulation deemed the wires or cables within the customer premise those of the customer. Accordingly, if a fault is Zo due to a wiring problem within the customer premise, a network provider is normally not required to dispatch craft unless the customer is willing to pay -separately for the service call. On one hand, even when repair of customer premise wiring is requested by a consumer willing to pay, the price charged the consumer often does not cover the cost of dispatching craft. In fact, there are 2s many cases where craft personnel return without finding a problem and thus n~
fee is charged to the consumer. On the other hand, in some instances network providers have allowed consumers to opt-into wire maintenance plans, where for a monthly fee, the network provider accepts responsibility for maintaininglservicing the wiring within the customer premise. Even where a 3o customer chooses to participate in a wire maintenance plan, dispatching craft is not economically justifiable to the network provider because the wire KimseylMistry maintenance fees charged the consumer almost invariably do not cover the cost of dispatching craft. All in all, in the current environment network providers try to avoid or minimize dispatching craft. Furthermore, with the advent of datalinternet access over customer premise telephone wiring the number of s calls complaining of service affects to network providers has increased dramatically - particularly since many network providers are also Internet service providers - thus the dollars at stake have risen acutely and continue to rise.
Furthermore, many of the electronic devices, such as fax machines, io modems, electronic telephones, etc., connected to the loop plant or phone line located within the customer premises, are not as robust or resilient as leased telephone sets were to traditional environmental effects. As such, environmental effects have a greater chance of causing faults within the customer premise. For example, lightning striking the outside loop plant can is damage an electronic phone, fax machine, modem, or other electronic device hanging off the phone line. The damaged electronic equipment typically takes the line off-hook. After the line is off hook for some period of time the switch generates short tones indicating that line is off-hook and should be placed back on-hook. If there is no response the switch eventually disables the line, i.e., the 20 line goes dead. The only way that the line will be then restored is if an on-hook condition is present for some predetermined period of time. Of course the damaged electronic device is not going to hang up the line so to both the switch and the customer the line appears dead. As such, in these circumstances it is customer premise equipment that actually is the root of the problem.
Zs Accordingly, the ability to properly locate, and to a larger extent determine the root cause of, a fault is of great utility to a network provider.
Even a crude determination that the fault is in the customer premise and not the network is of considerable value. For example, if the fault is within the customer premise, then, in many instances, over the phone instructions to the 3o customer can solve the problem thereby alleviating the need for dispatching craft. And in those instances where repair of customer premise wiring facilities KimseylMistry is the responsibility of the consumer, if the fault is in the customer premises, then the network provider's responsibility ends unless the customer requests repair service.
There are tools currently available to communications network providers s for isolating and, to a certain extent, correcting service-affecting faults within the network without the need for dispatching craft. Conceptually, many of these tools consist of placing recognizable terminations in devices at or before a Network Interface Device (NID). The NID defines the demarcation point between network equipment and customer premise equipment. These devices ~o then can provide an indication of network integrity up to and including the device in response to a manual or automatic test performed remotely from a central location (usually at a serving Central Office (CO)). A few of the automatic test or maintenance systems located in the serving CO include Local Test Desk (LTD), Mechanized Loop Testing (MLT), and Switched Access is Remote Test System (SARTS).
One device that is used in conjunction with the MLT system is a half-ringer. A half ringer is a termination that provides a recognizable or known signature in response to a signal from an MLT system. The half-ringer derives it name from the fact that ideally the impedance of a half ringer is half the ringer 2o equivalence number (REN); one REN is considered the average circuit impedance for an electromechanical telephone set. Specifically, a half-ringer is placed on a loop before or at the NID of a customer. As either part of routine maintenance or troubleshooting an end office MLT alternately applies either a voltage or a current to the loop having the half ringer. The MLT system then 2s measures the impedance of the loop. If the measured impedance matches the signature of that loop's half ringer, then the loop is considered to be electrically continuous. Half-ringers are therefore capable of providing only an indication of whether the entire loop is continuous and without an open circuit.
Accordingly, half-ringers are incapable of indicating the location of a fault. Furthermore, half 3o ringers, because of their normal placement, do not help in deciphering whether there is a fault in the customer premise. In fact, before divestiture of the Bell KimseylMistry Telephone System in 1984, there was no need for half ringers as the telephone sets leased to consumers had an average circuit impedance of one REN.
Thus, before 1984 network providers could determine continuity all the way out to the electromechanical phone set terminating an outlet. With the many s different telephone sets, fax machines, etc., terminating a telephone outlet today, there is now no telling what the REN is at a particular outlet in a premise.
A more sophisticated device for localizing faults than a half-ringer currently used in the PSTN is a Maintenance Terminal Unit (MTU). Two of the maintenance systems used in conjunction with the MTU include a Local Test ~o Desk (LTD) and Mechanized Loop Testing (MLT). A MTU is a two port device having one set of ports connected to the tip and ring of the loop or network and the other set of ports connected to the tip and ring of the customer's wiring.
The MTU can be placed by the network provider on customer premises at the demarcation point between the customer's wiring and the terminal equipment.
is The MTU operates in two modes, idle and active. In the idle mode the device is transparent to the network allowing service to be established. In the active mode the device isolates the customer equipment from the network and interacts with the testing system to determine the location of a fault or the performance of the loop.
2o One problem with a test system utilizing a MTU is that the customer does not have access to the information or system. Accordingly, the customer is not able to aid in troubleshooting the problem. Also, although the MTU can be used to determine whether the fault lies in the customer premise or the network, the MTU system is unable to pinpoint where within the customer 2s premise the problem is located. As such, if the problem is within the customer premise, craft personnel may nonetheless have to be needlessly dispatched.
It is therefore an object of the present invention to provide an apparatus, specifically a telephone jack, that can be used by a network provider to determine the operability of a loop up to and including the telephone outlets 3o within a customer premise.

KimseylMistry Summary of the Invention Our invention is a detachable telephone jack or apparatus that can be used by either the customer or the network provider to determine the condition of a customer loop including the customer premise wiring.
s Our invention includes the following functional blocks: a recognizable termination such as a half ringer or a Maintenance Test Unit; a manual tester;
a circuit for verifying loop integrity; and a visual indicator. By including this functionality in a single apparatus that may be placed at the network interface device or within the customer premise, the network provider may be able to io verify the continuity of the telephone wire up to and including individual telephone outlets within the customer premise. Our invention also allows the user to aid in determining the continuity of a line within a customer premise by pushing a button.
In one embodiment of our invention a circuit for verifying loop integrity is Is selectively connected to a front-end half ringer. The loop verification circuit includes a voltage sense circuit having two zener diodes, a resistor, a green LED, and a diode that are connected in series and a reverse polarity circuit having a red LED, a diode, and a resistor connected in series. The voltage sense circuit and the reverse polarity circuit are themselves connected in 2o parallel.
In another embodiment of our invention the voltage sense circuit is connected across the center of four diodes configured as a full bridge rectifier.
A telephone jack made in accordance with either embodiment may be used as a portable test unit or be permanently connected to the network, and, 2s in either case, there is no degradation of network integrity.
When placed at the network interface device our invention provides a recognizable signature to mechanized loop testers thereby indicating network functionality. In cases where mechanized loop testers detect marginal performance on a tested line or when the customer's participation is needed to 3o identify and troubleshoot the line, network, or customer premise equipment, the manual tester is exercised giving feedback to the customer. When the manual tester or switch is operated, an electrical open circuit is created that isolates the KimseylMistry network at the location of our apparatus while our loop verification circuit is connected to the network. Our verification circuit determines the voltage level and the polarity of the loop. If the voltage level is above a predetermined threshold, then the verification circuit provides a first visual indication whereas if s the voltage is below the predetermined threshold a second visual indication or no indication is given.
It is therefore an object of the present invention to provide the above described apparatus at fairly low 'cost.
It is also an object of the present invention to provide an apparatus that Io is simple enough to be used effectively by a lay person who does not possess specialized knowledge of telephony.
It is also an object of this invention to provide an apparatus that facilitates troubleshooting the equipment attached to a telephone outlet, e.g., a telephone, fax machine, modem, etc., without the need of dispatching network ~s provider craft personnel.
These and other objects of my invention may be realized by reference to the drawings and detailed description described below.
Brief Description of the Drawings FIG. 1 is a representation of a first embodiment of our invention 2o employing a reverse polarity circuit; and FIG. 2 is a representation of a second embodiment of our invention employing a full bridge rectifier.
Detailed Description Turning to FIG. 1, there is depicted a first embodiment of our invention 2s which may be conveniently referred to as a reverse polarity unit 100. At a high level, unit 100, going from left to right on FIG. 1, consists of an RJ-11 male jack 105, a half ringer 120, a throw switch 130, a loop qualification circuit 150, and an RJ-11 female jack 165.
The RJ-11 male jack 105 provides an input for signals on the loop into 3o the unit 100. When unit 100 is connected, one end of a jumper cable 107 is plugged into jack 105 while the other end of the jumper cable 107 is plugged KimseylMistry into a telephone outlet 108. The telephone outlet 108 is connected or coupled to a customer loop 110 that is connected to a serving Central Office (CO) 111.
The serving CO will contain various automated testing equipment and software maintenance tools that can be used to isolate faults on the customer loop s including the wiring or line within the customer's premises.
On the output side of jack 105 are tip and ring wires 115. Across wires 115 is connected circuitry to form a half ringer 120. Half ringer 120 includes a resistor 121 of approximately 15 kf2, a zener diode 122 of approximately 4.5 volts (V), a capacitor 123 of approximately 0.47 NF, and another zener diode io 124 of approximately 4.5 V. As FIG. 1 shows the half-ringer circuit elements 121 through 124 are in series, respectively. The half-ringer circuit 120 functions as any other half ringer circuit does. Specifically, when a large enough AC
voltage is applied across the tip and ring wires 115 to reverse bias zener diode 122 then capacitor 123 is charged with a time constant that depends on the is resistor 121 and the capacitor 123. 4.5V zener diodes were chosen to implement the half ringer 150 so that MLT testing would not present an off-hook reading to the switch by limiting current flow. Essentially, our half-ringer implementation limited the amount current flowing through the half ringer 120 loop to approximately 5 mA. When the half-ringer circuit is stimulated by an AC
2o voltage applied via a MLT system, it presents a particular signature to the MLT
system. Once the MLT system verifies this signature, it can provide an indication that the loop is continuous up to and including the half ringer. Of course when a DC voltage is applied across tip and ring wires 115, capacitor 123 prevents any current from flowing in the half-ringer 120 and the half-ringer 2s 120 is therefore non-responsive.
The operation of the half-ringer 120 within the unit 100 is dependent on the position, open or close, of switch 130. An exemplary double-pole double-throw switch 130 is shown in FIG. 1. When switch 130 is in its normal position loop qualification circuit 150 is bypassed and the half-ringer circuit 120 is 3o directly coupled to the output of the unit 100, i.e., the RJ-11 female jack 165. In other words, the normal position of the switch is for the arm 131 to be KimseylMistry connected to line 133. When switch 130 is in a test position the loop qualification circuit 150 is switched into the loop and the RJ-11 female jack is isolated from the network thereby isolating any electrical equipment normally connected to outlet 108. Although the exemplary embodiments shown in FIG.
s 1 and FIG. 2 show switches 130 and 230 as double-pole double throw switches requiring customer interaction, other switches can be used depending on the sophistication of the unit, which in turn depends on the sophistication of the customer. For example, other elements or circuitry may be added to loop qualification circuit 150 to troubleshoot other problems, e.g., special services io problems. In other embodiments of our invention we have used switches that are able to indicate four different states of operation. Accordingly, the sophistication of the switch really depends the sophistication of the unit 100.
When the unit 100 is operational the loop qualification circuit 150 is switched into the loop 110. In the embodiment of FIG. 1, the loop qualification is circuit consists of a voltage sense circuit having two zener diodes 151 and 152, a resistor 153, a green LED 154, and a diode 155 that are connected in series.
In parallel with the voltage sense circuit is a reverse polarity circuit having a red LED 158, a diode 159, and a resistor 160 connected in series. When a large enough DC voltage, i.e., more than 35 Vdc, to reverse bias zener diodes 151 2o and 152 is applied across the unit 100 with the switch 130 button depressed (operational position) the green LED 154 is illuminated. In this embodiment we used two zener diodes 151 and 152, each with a reverse bias voltage of 17 Vdc. The important consideration for choosing a zener diode is the prevention of the line appearing off-hook to a electronic circuit switch while at the same Zs time detecting a large enough DC voltage that assures loop integrity. As is known in the art, at about 6 mA a line will appear off hook to the switch.
Accordingly, we choose zener diodes 151 and 152 so that less than 6 mA, but enough current to light an LED, would flow in the voltage sense circuit at about 35 volts. As such, at approximately 35Vdc the LED 154 illuminates. If the LED
30 154 is illuminated, then more than likely the line, including the loop and the outlet, is operational and the problem is with the equipment attached to female KimseylMistry jack 165.
The reverse polarity circuit of FIG. 1 is used to detect if the voltage polarity at the output the outlet 108, is inverted. If while the switch 130 is depressed a voltage with the polarity to forward bias diode 159 is applied s across the loop 110 current flows through resistor 160 and the red LED 158 is illuminated. As before, the LED 158, diode 159, and resistor 160 were chosen to draw no less than 6 mA. As those in the art will note, when a reversed polarity voltage is applied across unit 100 and the switch 130 is depressed, diode 155 presents an open circuit and therefore no current flows through the io voltage sense circuit.
FIG. 1 therefore provides circuitry that allows determination of the operability of an outlet in a customer premise. This is a considerable improvement over the current remote capabilities of network providers. More importantly, unit 100 is extremely low cost. For devices that are mass produced is the price of a single unit is in the range of a few dollars or less.
Because of the low cost of making these devices they may be conveniently placed at all the outlets in customer premise. If so placed, it would eliminate the inconvenience of a customer having to move from outlet to outlet within a customer premise.
Furthermore, although the embodiments of FIG.1 and FIG. 2 verify only that the 20 outlet is operational with respect to receiving talk battery voltages the unit 100 may be enhanced to include other functionality, including tone detection for special service testing, etc.
Turning now to FIG. 2, there is depicted a second illustrative embodiment of our invention which we conveniently refer to as a bridge unit 2s 200. In unit 200 a loop qualification circuit 250 is formed by placing a voltage sense circuit having the two zener diodes 151 and 152, resistor 153, and green LED 154 connected across the center of four diodes, 251 through 254, configured as a full bridge rectifier. If the switch 130 is depressed and sufficiently large enough voltage of either polarity is applied to unit 200 break 3o down of zener diodes 151 and 152 occurs, and then LED 154 is illuminated.
As was the case in FIG. 1, illumination of LED 154 is an indication that proper talk KimseylMistry battery voltages is showing up on the outlet 108. Whereas unit 100 had a reverse polarity circuit unit 200 does not.
Although the embodiments of FIG. 1 and FIG. 2 appear simple, units 100 and 200 will aid network providers in resolving customer complaints or faults s that are a result of faulty terminating equipment and not the telephone loop plant. For example, if lightning were to strike a loop damaging a fax machine attached at the outlet of customer premise wire connected from that loop, the fax machine may take the line off hook. Eventually the line would be non-operable and quiet, i.e., no dial tone. If the customer premise had either unit io 100 or 200 attached to the fax machine outlet as indicated in either FIGS.
1 or 2, then, with the help of the customer, the fault could be traced to the fax machine. Therefore, our invention would enhance the current capabilities of network providers in troubleshooting faults within the customer premise.
The above description has been presented only to illustrate and describe Is the invention. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. Many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to enable others skilled in the art to best utilize the invention on various 2o embodiments and with various modifications as are suited to the particular use contemplated.

Claims (8)

1. A telephone jack for isolating faults on a telephone wire within a customer premise, said jack comprising:
a half-ringer;
a switch coupled to said half ringer; and a voltage sensing circuit for indicating the presence of a predetermined voltage across the telephone jack, said voltage sensing circuit being selectively coupled to the half-ringer by operation of said switch.

2. The telephone jack of claim 1 wherein said voltage sensing circuit comprises, in series, at least one zener diode providing a reverse bias voltage, a resistor, and a first LED.

3. The telephone jack of claim 2 wherein said voltage sensing circuit is connected between the center of a full bridge rectifier.

4. The telephone jack of claim 3 wherein said switch is a double-pole double-throw mechanical switch.

5. The telephone jack of claim 2 further comprising a first diode connected in series with said first LED.

6. The telephone jack of claim 5 further comprising a reverse polarity circuit having, in series, a second LED, a diode, and a resistor, said reverse polarity circuit being connected in parallel with said voltage sensing circuit.

7. The telephone jack of claim 6 wherein said switch is a double-pole double-throw mechanical switch.

8. The telephone jack of claim 2 wherein said reverse breakdown voltage is approximately 34Vdc and said resistor is of approximately three kilo-ohms.