HYBRID FIBER IN THE LOOP TELEPHONY SYSTEM

Abstract: A hybrid fiber in the loop telephony system. The system provides for highly reliable telephone service, even during electric utility company power failures. The system generally includes an ONU (4) for conversion of optical signals to electrical, digital signals. The electrical, digital signals are transmitted to a subscriber location (12). The subscriber location utilizes an NID (20) having a ring generator (306) and analog-to-digital conversion equipment (304). Mechanical features of the system are also disclosed.

Description: HYBRID FIBER IN THE LOOP TELEPHONY SYSTE BACKGROUND OF THE INVENTION The present invention relates to the field of telephony systems and methods of operation thereof. For instance, in one embodiment the invention provides an improved telephony system having fiber or other digital media based digital signal transmission combined with metallic based signal transmission to the subscriber. Fiber based telephony networks have become increasingly commonplace in recent years. Fiber based systems have a wide variety of advantages over metallic transmission systems including vastly higher bandwidth. Unfortunately, most subscriber facilities in the United States telephone system and elsewhere continue to rely on metallic (generally copper) based transmission media. One important limitation in the transmission of telephone signals to the home in such hybrid systems has been the need for powering the subscribers telephone equipment. Since optical fibers do not conduct electricity, it is apparent that other facilities must be provided for power transmission to the central office and subscriber. Accordingly, telephony systems have been developed which provide for transmission of optical signals to a centralized location such as a central office. Such signals are converted to electronic signals for final transmission to the subscriber. Those combined optical/electronic transmission systems are commonly referred to as "hybrid" systems. This problem is made particularly difficult because FCC communications require that the telephone operating company supply enough power to ring five standard telephone extensions on every telephone line. Since standard phones have high ring- power requirements, such systems must be designed with substantial capacity. One prior system for providing power in a hybrid system is illustrated in Fig. l, such systems commonly referred to today as "fiber to the curb" or "FTTC" systems. As shown therein, a fiber 2 is used to communicate optical digital data signals to a optical network unit (ONU) 4. The ONU is placed in a neighborhood near a subscriber location and is referred to herein as a "curbside" ONU. Optical/electronics (O/E) conversion system 6 converts the optical signals to a serial bit stream of electronic digital signals for transmission to multiplexing/demultiplexing system 8. Multiplexing/ demultiplexing system 8 converts the serial bit stream from the O/E convertor to a plurality of digital signals. These digital signals are converted to analog signals in digital/analog, analog/digital convertor 10 (CODEC) and transmitted to a subscriber facility 12 such as a home or office over one or more metallic conductors 14. Network interface device (NID) 18 in the subscriber facility provides protection against lightening strikes and power crossing. The NID also provides multiple connection points for connection of individual pieces of subscriber equipment 22 to the incoming twisted pairs 14. The incoming twisted pairs are often referred to by those skilled in the art as "drops." Power is supplied to several ONUs (and the subscribers) via a power plant 16. Power plant 16 is located near the ONU, and serves relatively few ONUs (about 14 to 10) to keep the size of power transmission cable 16 within manageable limits. Power plant 16 preferably serves several ONUs within a few square block area. Four houses could use as much as 20 watts of peak power, given the requirement to power five standard phones in each home. Therefore, there is often a need for large gauge wires to supply power to the ONU, particularly if the distance is large. Moreover, power is wasted because a 20 Hz square wave may not be used to ring the phones. The higher harmonies of a square wave must be filtered out of a supply line to ring a phone because cross-talk to other lines will occur, particularly over long distances. Removal of these higher harmonies increases power consumption. To adequately service customer needs and to satisfy regulatory requirements, it also necessary to provide power to operate the phone system even when the electric utility company fails to provide power to the power plant or remote power supply (RPS) 16. Accordingly, it has been proposed to provide batteries in each ONU. While meeting with substantial success, the system shown in Fig. 1 has also met with certain limitations. For example, since the peak power requirements of the phones is high, the power plant must be of reasonably large size, and must frequently be located in residential neighborhoods to maintain a small conductor size to the ONU. These assemblies are sufficiently large that it often becomes necessary to purchase land or right-of-way for placement of the power plant, and local residents often object to the appearance of the power plants. Also, the batteries present maintenance difficulties, particularly since they are placed in an out-doors environment. Other difficulties with such systems include short battery life, particularly in high temperature enclosures. Also, since the power and fiber to the ONU come from separate sources, additional engineering and importantly, ditching is required. Other solutions have been proposed. For example, it has been proposed to run the fiber directly to the subscriber facility, and provide each subscriber with O/E, MUX, and D/A equipment. Such systems suffer from a variety of limitations including 1) a requirement that the subscriber provide power, 2) a limitation on the efficiencies of scale that are achieved, and 3) concerns regarding the reliability of back-up facilities such as batteries when normal utility power is unavailable to the subscriber. Other difficulties with such systems include short battery life and high cost since a laser is required for each subscriber. High power demands are made to support the laser. Further, additional fiber splicing is needed. Still further solutions to the above problems have been proposed. For example, it has been proposed to eliminate the power plant, and provide extra metallic wires from the home to the ONU over which power is provided by the users to the ONU. In such embodiments, it has been proposed to provide battery back-up through placement of batteries at the subscriber facility. This system and other similar systems also suffer from a variety of limitations. For example, if the ONU provides service to 4 subscribers, users will quickly realize that they can "unplug" the power at their location, and the system will continue to function normally, albeit at the expense of the other users on the system. If all 4 users remove power, battery back-up will allow the system to continue operation for a short period of time, but phone service to all 4 users will eventually fail. Also, when only a portion of the 4 users unplug their system, the remaining users will provide power for operation of their neighbors phones, creating an obviously unfair situation. This arrangement is also unfair to subscribers who use their phones much less than their neighbors. Other limitations include the normal concerns with battery back-up power, the down-time needed when the E/O equipment is serviced, and the like. Still other problems include limited backup. From the above it is seen that an improved hybrid optical telephony system is needed. SUMMARY OF THE INVENTION An improved telephony system is provided by virtue of the present invention. According to one aspect of the invention, the system is "hybrid" in the sense that optical fibers carry telephone signals to a centralized facility, but metallic wires carry telephone signals to subscriber locations from the centralized facility. According to one aspect of the invention, an ONU houses optical to electronic conversion equipment and multiplexing/demultiplexing equipment. The ONU is placed at, for example, a curbside location or on a telephone pole in a residential neighborhood and serves several users. Digital signals are conveyed to a subscriber facility (meaning, normally, a home or office) from the ONU over metallic connections such as conventional twisted pair wires. At the subscriber facility digital to analog conversion equipment and a ring generator are located in, for example, a network interface device enclosure. During normal operations power is provided to the D/A conversion equipment, the ring generator, and th subscriber phones from utility power supplied by the subscriber via, for example, a transformer. According t one specific aspect of the invention, power failures are backed up by providing power to the ONU from a telephone company central office. Such power is provided over metallic wires that are strung, generally in tandem with the optical fiber, to the ONU from the central office. Power to the ONU is extremely reliable because the central office will be provided with not only utility company power, but back-up generators, batteries, and the like. The user is provided with a low power phone. The low power phone is operated during a power failure, in both ring and handset off modes, with batteries at the subscriber location. Conventional phones are, accordingly, disabled during power failures according to one embodiment of the invention. According to another specific aspect of the invention, the metallic wires between the ONU and the subscriber location are used to transmit not only the digital signals from the ONU to the subscriber location, but are also used to transmit the power necessary for operation of a low power phone during power failures. Alternatively, an additional set of wires (generally small gauge) are provided between the ONU and the subscriber location. Accordingly, like the first embodiment, conventional phones are preferably disabled during power failures. Since the power necessary to ring the low power phone is very small, small gauge wires may be used between the ONU and the subscriber location to power the low power phone. During normal operation power is provided to the conventional user phones from a transformer at the subscriber location, and power is provided to the ONU from the CO. Accordingly, the high power requirements of conventional phones may be met without the need to install large gauge wires from the central office to the ONU and from the ONU to the subscriber location. According to further aspects of the invention, the need for a low power phone is eliminated. According to these aspects of the invention power is also transmitted from the CO to the subscriber location during power failure conditions. During a power failure, the ring cycle of the phone is altered to reduce the duty cycle of the ringer. A storage capacitor is used to average the power demand to the subscriber location to a low level. According to further aspects of the invention, the ring cycle is altered only if the user has connected more phones than the power feed and storage capacitor can accommodate. The various embodiments of the invention provide lower power consumption, smaller or no remote batteries, smaller less expensive ONUs, and easier migration to Tl, broadband, and fiber to the home services, among other advantages. Accordingly, one embodiment of the invention provides a telephony system comprising an optical fiber, the optical fiber adapted to transmit digital signals representing telephone communications. The system also includes an optical interface with an optical/electronic conversion system coupled to the optical fiber; and a multiplexing/demultiplexing system coupled to the optical/electronic conversion system. A plurality of metallic wires for transmission of digital signals extend from the multiplexing/demultiplexing system to a plurality of subscriber locations. At the subscriber location, the system provides for a network interface device having a digital to analog conversion system, and a ring generator. A further understanding of the nature and advantages of the inventions herein may be realized by reference to the remaining portions of the specification and the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an illustration of one prior art hybrid telephony system; Fig. 2 is an illustration of one embodiment of the invention; Fig. 3 is an illustration of another embodiment of the invention; Fig. 4 is an illustration of another embodiment of the invention; Fig. 5 illustrates a NID according to one embodiment of the invention in greater detail; Fig. 6 illustrates a ring generator according to one embodiment of the invention in greater detail; Fig. 7 illustrates a high density embodiment of the invention; Fig. 8 is an illustration of mechanical features of one embodiment of the invention; Fig. 9 illustrates a CATV/FITL system; and Fig. 10 illustrates an enclosure. DESCRIPTION OF THE PREFERRED EMBODIMENTS CONTENTS I. Terminology II. Description of a First Preferred Embodiment (Low Power Phone) III. Description of a Second Preferred Embodiment IV. Description of a Third Preferred Embodiment (Variable Ring Cycle) V. Description of a Fourth Preferred Embodiment (High Density User Environment) VI. Advanced Applications VII. Testability VIII. Enclosure Assembly and Mechanical Configuration IX. Conclusion I. Terminology The following abbreviations are intended to have the following meanings herein: CO - Central Office ONU - Optical Network Unit E/O - Electro/optic conversion equipment, which will generally include systems for both conversion of electrical signals to optical signals and systems for conversion of optical signals to electrical signals. D/A - Digital to analog conversion equipment, which will also generally include systems for conversion of analog signals to digital signals and for conversion of digital signals to analog signals. Similarly, multiplexing/demultiplexing equipment will generally be bidirectional. FITL - Fiber in the loop. FTTC - Fiber to the curb. MUX - Multiplexing/demultiplexing equipment. REN - Ring equivalent number. SLIC - Subscriber Loop Interface Circuit. Standard Phone - A phone that generally complies with the requirements of WEL0500 station sets, normally having a ring equivalent number of about 1. Low Power Phone - A phone with a ring equivalent number of less than about 1/2 of a standard phone, preferably having a ring equivalent number of less than about 0.5, more preferably less than about 0.1, and most preferably less than about 0.03. RPU - Remote power unit, otherwise referred to as a "power plant." II. Description of a First Preferred Embodiment (Low Power Phone) Fig. 2 is an overall block diagram illustrating aspects of one embodiment of the present invention. As shown therein, digital telephone signals are transmitted from a CO 202 to ONU 4 via optical fiber 2 using means well known to those of skill in the art. Power is transmitted over metallic wires 204 from the CO to the ONU. According to one preferred embodiment of the invention the power supply in the CO and the wires between the CO and the ONU are sized to provide adequate power to the ONUs connected to the CO, but not for facilities in the subscriber locations, which will generally have large peak power demands. In particular, it is desirable for the CO not to provide power to subscriber locations for ring generation of the phones at the subscriber locations. Power is provided to the ONU during both normal operation and utility failures from the CO. The CO is able to provide power to the ONUs during utility power failure using means well known to those of skill in the art such as generators and batteries. Since the peak power demand of the ONUs will be small (due in large part to the lack of a need to provide power during ring cycles of conventional phones) , it is not necessary to provide large gauge wires between the CO and the ONU or large capacity back-up facilities. In the ONU, E/O conversion equipment and multiplexing equipment are connected to output digital transmission signals over wires 14 such as conventional twisted pairs to subscriber locations 12. Although only a single line is shown to the subscriber facility in Fig. 2, it will be apparent that multiple lines may be provided. At the subscriber locations, a NID 20 is provided, which includes conventional lightning protection. The NID 20 also includes D/A conversion equipment and ring generation equipment of the type well known to those of skill in the art. From the NID, analog telephone signals are provided to subscriber equipment 22, which will often include standard analog phones. Many of the phones in use subscriber locations today demand a large amount of power, particularly during a ringing cycle. For example, ring generation may require 3-4 watts to ring 5 RENs, plus one watt for each additional REN. Sufficient power is provided to the subscriber equipment during normal operations from utility lines 206 via AC/DC transformer 208. When a power failure is detected, however, the conventional phones 22 are disabled. According to some embodiments, the conventional phones are disabled during power failures only to the extent that they will not ring, but they will remain functional to the extent that they can be used for normal conversation and the like. Since the ring generator provides power to the phones over environment without lines of other subscribers, higher harmonies of the 20 Hz ring cycle need not be filtered, or fewer of the higher harmonies may be filtered. Accordingly, the power demand of the ring generator may be further reduced. To permit the subscriber to have full use of the phones during a power failure, the subscriber is provided with at lower power phone 210. Such phones require only a minimum amount of power, and are particularly efficient in the sense that they require only a limited amount of power during a ring cycle (e.g., less than 1 watt and preferably less than 0.3 to 0.5 watts to the ring generator). Accordingly, it becomes possible to provide for all of the power needs of the subscriber during utility failures over the twisted pair wire 14 from the CO. Since the power demands of the low power phone will be small, and since there will generally be only one low power phone connected during power failures, users may be supplied with power over the wires connected to their home. The wires will not be large gauge wires between either the CO and ONU or between the ONU and the subscriber location due to the low peak power demand. According to one variation of the system shown in Fig. 2, the low power phone is replaced with a low power ringer. According to this embodiment, the conventional phones are still used for conversation and the like, but the phones will not ring during power failures. Instead, the users will be notified of incoming calls with the ringer. According to one preferred aspect of the invention, the package containing the transformer is designed to hold the low power ringer, minimizing the possibility that a user will loose the ringer. Such low power ringers are energized by, for example, reversing the polarity of the DC voltage on the line. A diode and a choke or time delay would be used to prevent the ringer from sounding during normal DC polarity or normal ringing. Alternatively, a 800 to 1000 Hz signal is sent out on the line for energizing the ringer. According to these embodiments, the ringers would have a very high impedance to this high frequency, but the sounders would resonate at this frequency. III. Description of a Second Preferred Embodiment According to alternative embodiments, power is not supplied from the CO even under electric utility failures, as shown in Fig. 3. where similar parts are labeled with the same reference numerals. Instead the user maintains a set of back-up batteries with sufficient capacity for operation of the low power phone only. Since the demands of the low power phone will be small, the battery capacity needed by the user will also be small. As shown in Fig. 3 the twisted pair wires, such as 500 feet of 22 awg copper wire, enter the subscriber location, and are again provided with lightening protection. A line card 302 is provided with a ring generator 306 and D/A conversion equipment 304. During normal operations, the conventional phones and the line card are powered by AC/DC convertor 308 from utility power at the subscriber location. The convertor also serves to maintain batteries 306 in a charged state with charger 308. During a power failure, power is provided to the low power phone 310 from the batteries. Table 1 illustrates the power requirements of a typical 4 phone system as illustrated in Fig. 3. TABLE 1 CALCULATED POWER VALUES CEV Power Source Voltage 48 volts DC CEV Power Loop Resistance 5000 ft Loop, 24 ga 257 ohms With 1 Phone On Hook: Power to phone 0.00 watts Power from AC/DC converter 0.00 watts Power to AC/DC converter 0.00 watts With 1 Phone Off Hook: Power to phone 0.49 watts Power from AC/DC converter 0.65 watts Power to AC/DC converter ....0.86 watts Power to ONU 1.800 watts Power Loop Current to ONU 0.052 amps Power from CO 2. 94 watts Average Power for 4 Phone System 2.93 watts Battery Capacity/Phone Required at -17C 2.59 watt hrs. Battery Capacity/Phone at +20C 5.18 watt hrs. By comparison, similar calculations for a system wherein the ONU is provided with batteries for emergency powering of the phones according to proposed standard TA-NWT-00909 indicate that the required battery capacity will be about 81 watts at 20 β C. Even at -17°C the expected amount of power that must be supplied by the batteries would be about 40 watts. Accordingly, it is seen that a local line card arrangement in accordance with the above described embodiments is highly desirable. IV. Description of a Third Preferred Embodiment (Variable Rinσ Cycle) According to one preferred aspect of the invention illustrated in Fig. 4, the system may utilize standard phones exclusively. According to this aspect of the invention the ONU 4 is arranged in a manner similar to that shown in Fig. 3. Under normal operating conditions, the ONU is provided with power from the a central location such as the CO, while the subscriber equipment is powered from the subscriber's own utility lines via AC/DC conversion equipment 208. During a utility failure at the subscriber location, power is provided to the subscriber location via the ONU from the CO. Such power is transmitted over the twisted pair lines, but at a relatively low rate. By transmitting the power at a relatively low rate, the twisted pair lines and the power lines to the ONU from the CO may be of relatively small gauge. The level of power transmission available from the ONU will often be insufficient to ring conventional phones, particularly when several such phones are connected to the subscriber location. Accordingly, when a power failure condition is detected, a capacitor 402 is maintained in a charged condition through transmission of power over the twisted pair lines. When a ring signal is detected in the NID, the conventional phones are powered for ringing with the charge stored on the capacitor. Such capacitors will be between about 500 and 1,000 μF in preferred embodiments, although it will be immediately apparent that a wide range of values will be acceptable depending on the application. During normal use of the telephone under power failure conditions, sufficient power can be provided for recharging the capacitor and for the normal off hook power requirements over the twisted pair to the home. Accordingly, it becomes possible to provide short bursts of power at a high rate (about 0.15 to 0.5 watts) for ringing conventional phones. At the same time, it is not necessary to install large gauge wire to the subscriber location from the ONU. Furthermore, the need for customer maintenance is largely eliminated through elimination of batteries at the subscriber location. According to this embodiment, the line will often not be able to provide sufficient power for ringing when a large number of standard phones are connected at the subscriber location, even when the storage capacitor averages the power demand. Therefore, according to one preferred aspect of the invention the NID 20 is provided with a ring cycle modification circuit 404. According to this preferred embodiment of the invention the system detects the presence of an extremely high load (such as greater than about 0.75 watts) during a ring cycle. When the load is detected to be above a selected level the length of the ring during a ring cycle is modified by the ring cycle modification circuit 404 to decrease the length of the ring to a level which will not excessively drain the capacitor 402. Therefore, the duty cycle of the ring generator is decreased. According to some embodiments the ring cycle modification circuit will decrease the ring cycle in proportion to the load placed on the system. Accordingly, if many phones are installed at the subscriber location, short ring cycles will be observed during power failure, but operation of the phones will otherwise appear normal to the subscriber. Table 2 illustrates typical ring cycle times as a function of the number of connected phones for a typical system having a 1,000 μF storage capacitor. Table 2 Ring Cvcle Times Number of Phones Ring Cycle Time 1 1.5 sec. on, 0.4 sec. off 5 0.8 sec. on, 0.5 sec. off Fig. 5 is a block diagram illustrating the NID 20 according to the embodiment shown in Fig. 4 in greater detail. As shown therein, the twisted pair wires carry digital telephony signals, as well as DC voltage, the latter being supplied primarily for or exclusively in a power failure situation. The twisted pair wires enter the system by way of a hybrid or pulse transformer 502. In one specific embodiment the pulse transformer is a model number ZBK 505/103 made by Siemens. Under normal circumstances, 24 v. DC power is supplied to the system using a rectifier 504 coupled to the twisted pair wires and supplying power from a 120 v. AC power supply. Zener diodes 506 provide appropriate isolation. A voltage convertor 508 provides a 5 v. power supply to the various integrated circuits in the system, while the 24 v. supply is used to power a ring generator 306. During a power outage at the subscriber location, DC power is supplied via the twisted pair wires, also coupled to the ring generator and voltage convertor. Digital telephony signals are transmitted to/ received from CODECS, of which 3 are illustrated in Fig. 5 for purposes of illustration, although it will be apparent that a different number of CODECS 510 will be used depending upon the number of lines to be serviced by the system. CODECS 510 may be, for example, model number MC 145505 made by Motorola. Each of the CODECS has, among other pins, transmit (TR) , receive (REC) , clock (CLK) , balance (BAL) , and enable (E) . The primary purpose of these chips is to convert the incoming serial data stream into one or more analog signals for use on the subscriber lines. Analog transmitted signals are sent to and received signals are received from SLICs 512 such as a Tamura TTC-124. SLICs 512 provide for two-wire to four-wire conversion among other functions. Operation of the CODECS is regulated under the direction of function generator 514. Timing of the system is regulated by synchro pulse acquisition chip 516, which is used for clock capture from the incoming data and control clock 518, which may be, for example, a model no. MP041 made by CTS. Function generator 514 may be implemented on, for example, an ASIC such as a 170 gate device made by AST. Data channel 520 is used for transmission of various data signals, alarms, test information, and the like. Ring relays 522 are used to generate ring signals for ringing the telephones under the direction of ring generator 306. When power is supplied from the twisted pair wires, the duty cycle of the ring generator may be altered, depending upon the load on the lines. When a large number of standard phones, for example, is connected to a single line, the ring generator will decrease the amount of time during which the phones are actually ringing, and/or increase the amount of time between rings. Ring relays operate by transmitting a signal frequency appropriate for ringing the phones. Data are transmitted and received from the phones by the system using pulse code modulation (PCM) in a ping-pong manner according to a preferred embodiment of the invention. For example, the system may use a first time slot for synchronization, a second, third and fourth time slot for outgoing data, and a fifth time slot for blanking. The next three time slots may be used for incoming data, and the next time slot for data transmission such as off-hook data, test data, or the like. It will be apparent to those of skill in the art that the above devices and circuit arrangements are merely illustrative of the arrangements which may be used according to specific embodiments of the invention in implementing the NID. Merely by way of example, operation of the NID may be controlled under the direction of an appropriately programmed microprocessor, or the circuit may be implemented entirely with discrete logic. Fig. 6 illustrates a ring generator 306 according to the embodiment shown in Figs. 4 and 5. Power is supplied to the ring generator either of two paths. First lines 602 derive power from the twisted pair lines and are used during power failures at the subscriber location. Second lines derive 604 power from a transformer, preferably in the subscriber's premises. During normal operation, when the phones are to ring, relays connect contacts 608 at a frequency of, for example, 20 Hz to ring the phones. Since power is not at a premium during normal operating conditions, RC circuit 608 may be used to remove high frequency components of the 20 Hz signal 613, reducing any cross-talk between lines while one line is ringing. Accordingly, relays 607 are placed in contact with output lines 611 to produce a 20 Hz sign wave. According to preferred embodiments, the RC circuit is not utilized to ring phones during a power failure, since removal of the high frequency components will waste power in the system. Accordingly, ringing of the phones is achieved by connecting contacts 608 of a relay at 20 Hz, but with the RC circuit out of operation by virtue of using pins 610 for output to the phones. The duty cycle of the ring cycle is also modified during power failure conditions. Voltage controlled oscillator (VCO) 612 monitors the voltage on 613, and based on the voltage thereon, outputs a square wave with either a high or low duty cycle. The output of VCO 612 controls optoelectric isolators/solid state relays 614, and is enabled by switch 609 during a power failure. The relays alternately connect the incoming DC to either a storage capacitor 616, or connect the storage capacitor to relays 608. As the voltage detected by the VCO decreases, the amount of time the capacitor outputs to the phone line is decreased. For example, when 65 v. is detected on the line, the phones will ring for 1.5 seconds and be off for 4 seconds. As the voltage on line 613 decreases to 60 v., the ring time decreases to 1.2 seconds, with a ring time of 0.9 seconds for 55 v. and 0.8 seconds for less than 55 v. It will be apparent to those of skill in the art that the above devices and circuit arrangements are merely illustrative of the arrangements which may be used according to specific embodiments of the invention. Merely by way of example, operation of the ring generator may be controlled under the direction of an appropriately programmed microprocessor, or the circuit may be implemented entirely with discrete logic. According to still further embodiments of the invention, powering of the NID/subscriber equipment is at different voltage levels during power failure conditions. According to these embodiments the subscriber equipment is powered using a 48 v. power supply during normal operations. During a power failure, the subscriber is provided with a first voltage power supply over the twisted pair in an off-hook condition, and a second, higher voltage supply during an off hook condition. For example, the user may be provided with 6 v. , 10 ma power over the twisted pair in an off-hook condition during a power failure, but with 21 v. power during an on-hook condition during a power failure. As will be appreciated by those of skill in the art upon review of this disclosure, conversion of the above described system to a Tl transmission system up to the subscriber location will be greatly facilitated since the system is digital up to the NID. Such conversions will require the installation of a new board at the NID, but will otherwise be easily accomplished without the installation of additional drop wires to the subscriber location. According to preferred embodiments, the system will be provided with a low power SLIC in the NID. During an AC power outage the line card in the NID must be powered from the central office, for example, so it is important that the line card and, importantly, the SLIC requires little power in an power failure mode. The low power SLIC will use a hybrid transformer. Preferably the low power SLIC will shut down entirely when the phone is on hook during a power failure. This mode will be triggered by, for example, a Hall effect device that will monitor for current in the loop and when it is zero, will turn off most of the SLIC electronics. V. Description of a Fourth Preferred Embodiment (High Density User Environment) Fig. 7 illustrates a preferred embodiment of the invention that will have particular application in a high density urban environment. As shown therein, a CO provides optical signals to an ONU 708 using conventional means. At the ONU E/O conversion equipment converts the optical signals to electrical, digital signals. The electrical digital signals are transmitted over twisted pair wires to several (l to 150, preferably more than 20) living units, which contain D/A conversion equipment. Accordingly, conventional analog subscriber equipment 22 is provided with conventional analog telephone signals. According to one aspect of the invention power to the ONU is normally provided with power from a power supply 702 and power is supplied to the subscriber equipment over the twisted pair wire from the ONU. The ONU and the power supply are mounted in one or more weather tight enclosures 704, which are in one embodiment mounted on a telephone pole or the like. Power is supplied to the ONU and the subscriber equipment during utility power failures via a metallic wire 706. Since the distances involved in high density areas will be small, excessively large gauge wires will not be necessary. Such systems will be particularly useful in areas having living unit densities of greater than about 20/ONU, and preferably greater than about 40/ONU. Fig. 8 illustrates the mechanical arrangement of a preferred embodiment of the equipment 704. As shown, the system is served by a conventional utility power line 804. The power line is connected to an AC/DC convertor 802 mounted in a weather tight enclosure. The AC/DC convertor will vary in capacity widely from application to application, but may be a 40 watt DC power supply. The AC/DC convertor services the ONU 708 during normal operations and, via the ONU, the subscriber facilities. The ONU is also connected to a composite fiber/copper cable 808 having, for example, 24 individual fibers and copper cables therein. The ONU is connected to a copper terminal box 810, which may include, for example, about 50 Terminator 11 connectors, made by the assignee of the present invention. The individual subscriber facilities are serviced by lines extending from the copper terminal box to the subscriber facilities. VI. Advanced Applications The arrangements discussed above are easily converted to advanced technologies and applications. For example, it will be possible to adapt to Tl transmission to the subscriber with only electronics card changes. Similarly, other applications will be readily available. Fig. 9 illustrates one such application, in which will provide interactive video to the home. As shown, the system therein includes a NID 901 which includes a line card 902 containing D/A conversion equipment and the like, as discussed above. Also included in the NID is CATV amplifier and interdiction electronics 904. Power requirements for the line card are provided according to the embodiments above, while power for the CATV electronics is not provided during electric utility company failures. Instead, the CATV electronics are non-operational, but this will cause little difficulty since televisions will also be non¬ functional during such periods of time. The line card serves to provide conventional telephone service to the subscriber equipment 22. The CATV card serves to provide conventional cable television service to televisions/VCRs and other equipment 906. Additional capabilities are provided by way of a track ball mouse, or other user interface device 908 having wire connections to the NID and an IR transmitter 910. The IR transmitter is used to control devices such as VCR's according to means well known to those of skill in the art. The user may, for example, select a show from a listing on the TV screen for recordation. The IR transmitter will then activate the VCR at the appropriate time. The track ball is preferably hard wired via jacks located alongside conventional telephone jacks. The track ball controls a cursor 912 that is displayed on the screen of the television 906. The cursor is generated on the television by overlaying a signal on the CATV signal in the interdiction electronics 904 by means well known to those of skill in the art. To conduct, for example, a home shopping session the user would move the cursor to a location of the screen and press select to identify a desired product. An overlay on the CATV signal contains instructions for ordering and is generated under the direction of telephone signals from the line card. This overlay responds to user inputs from the mouse. Similarly, video games and the like may be generated using the system described above. VII. Testability It-will be important that the telephone company be capable of verifying that the wire from the ONU to the NID, the NID itself, the transformer (if any) for providing DC power to NID, and a sounder (if any) be working correctly. To provide such testability it is preferred that the transformer be supplied with a switch that is activated when it is plugged into the wall in the home. AC voltages are sensed by a test circuit built into the transformer housing. The status information from the NID is transmitted to non-volatile memory in the NID via a digital signal. This would take place using capacitor stored energy or by sending some of the CO supplied DC to the sensor circuit for its operation. Within the NID, each card will preferably have a self test circuit on board. If it is "OK," an appropriate signal is transmitted to the ONU for later retransmission. The twisted pair to the subscriber will be tested by sending an appropriate test signal to the NID, which will open, short, or leave in service the drop wire. Simple test voltages and currents from the ONU would then be used to measure the state of the loop. Representative test techniques are disclosed in copending application Serial No. 584,325, assigned to the assignee of the present invention and incorporated herein by reference for all purposes. VIII. Enclosure Assembly Fig. 10 illustrates mechanical features of a NID which will be used at a subscriber facility according to one preferred aspect of the invention. As shown, the enclosure includes a body 1002, preferably containing three compartments. The compartments include an electronic equipment compartment 1004, a telephone company access side 1006 and a subscriber access side 1008. Details of various aspects of physical enclosures are provided in copending application Serial No. 584,325, filed September 17, 1990, assigned to the assignee of the present invention and previously incorporated herein by reference for all purposes. Preferably, the compartment 1008 provides easy access to the subscriber while the electronics compartment and telephone company access side are provided with only limited access via a lock or the like. The electronics compartment is preferably provided with vent holes 1010. Inside the electronics compartment, several sealed multi-pin connectors 1011 are provided. One of the multi-pin connectors is adapted to receive a card 1012 containing the primary electronic components of the NID such as the D/A conversion equipment. Another of the connectors is adapted to receive another card such as a CATV card 1014 in some embodiments. Certain of the cards may be provided with cooling fins 1016. In the telephone company compartment, several sealed drop pin connectors 1018 are provided for connections to drop wires from the ONU. Additional connections may be provided in this compartment for connection of a CATV coaxial line. Power is supplied via a power supply 1020, preferably with high voltage protection. The subscriber compartment is provided with test access ports, and the like. A cover or door 1022 covers the electrical components compartment, while doors cover the telephone company and subscriber compartments. IX. Conclusion The present invention provides a greatly improved telephony system. The above description is intended to be illustrative and not restrictive. Many variations of the invention will become apparent to those of skill in the art upon review of this disclosure. Merely by way of example the invention may utilize other specific circuit elements, or may accomplish certain functions of the above described circuit elements in software, or may accomplish certain of the above described software functions in hardware. Further, while specific manufacturers and models of various components have been illustrated throughout this disclosure, it will be apparent that a wide variety of components and manufacturers could be substituted without departing from the scope of the invention. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Claims: WHAT IS CLAIMED IS: 1. A telephony system comprising: an optical fiber, said optical fiber adapted to transmit digital signals representing telephony communications; an optical network interface comprising: i) an optical/electronic conversion system coupled to said optical fiber; and ii) a multiplexing/demultiplexing system coupled to said optical/electronic conversion system; a plurality of metallic wires for transmission of digital signals from said multiplexing/demultiplexing system to a plurality of subscriber locations; and a network interface device at said subscriber locations comprising: i) a digital to analog conversion system coupled to said metallic wires; and ii) a ring generator for ringing phones at said subscriber locations. 2. The telephony system as recited in claim 1 wherein said optical network interface is placed at a curbside location in a residential neighborhood. 3. The telephony system as recited in claim 1 further comprising an ONU power supply connected to said optical interface, and a separate subscriber power supply at said subscriber location for providing power to said ring generator from an electrical utility company. 4. The telephony system as recited in claim 3 wherein said optical network interface power supply is more than 12,000 feet from said subscriber locations. 5. The telephony system as recited in claim 4 wherein wires connecting said optical network interface power supply to said optical network interface are between 19 and 22 awg. 6. The telephony system as recited in claim 3 wherein said separate power supply is an AC/DC transformer for converting power to DC from an electrical socket at said subscriber location. 7. The telephony system as recited in claim 3 further comprising a low power phone, said low power phone adapted to ring when power from said electrical utility company fails. 8. The telephony system as recited in claim 7 wherein said low power phone is operably connected to a battery at said subscriber location during a power failure. 9. The telephony system as recited in claim 7 wherein said low power phone is operably connected to said metallic wires during a power failure and wherein said metallic wires provide power to said low power phone during a power failure. 10. The telephony system as recited in claim 7 further comprising conventional telephones at said subscriber location, and means for disabling at least ringers in said conventional phones during a power failure. 11. The telephony system as recited in claim 3 further comprising a ring cycle modification means, said ring cycle modification circuit adapted to modify a length of a ring cycle of phones at said subscriber location during a power failure at said subscriber location. 12. The telephony system as recited in claim 3 wherein said optical interface is adapted to provide power to said subscriber location over said metallic wires during a power failure at said subscriber location. 13. The telephony system as recited in claim 3 further comprising a storage capacitor, said storage capacitor charged during a power failure and discharged during a ring cycle at said subscriber location. 14. The telephony system as recited in claim 12 wherein said storage capacitor is charged with power provided from said metallic wires from said optical interface. 15. The telephony system as recited in claim 14 wherein said metallic wires are between about 22 and 26 awg copper. 16. The telephony system as recited in claim 3 further comprising a low power ringer, said low power ringer adapted to ring when power from said electrical utility company fails at said subscriber location. 17. A network interface device for installation in a telephone subscriber facility comprising: a digital to analog conversion circuit for converting incoming digital signals on a subscriber line to analog signals for transmission to telephones in said subscriber facility; a ring generator for ringing telephones in said subscriber location; and a power distribution circuit, said power distribution circuit providing power to said ring generator from said subscriber line during a power failure at said subscriber location, and from said subscriber location when electrical power is available at said subscriber location. 18. A network interface device as recited in claim 17 further comprising a ring duty cycle modification circuit for modifying a ring duty cycle of telephones during a power failure at said subscriber location. 19. A network interface device as recited in claim 18 wherein said ring duty cycle modification circuit further comprises a voltage controlled oscillator, said voltage controlled oscillator monitoring a voltage and reducing said ring duty cycle when said voltage falls below a selected value. 20. A network interface device as recited in claim 17 further comprising a storage capacitor, said storage capacitor charged by a DC voltage on said subscriber lines during a power failure, and discharging to ring a phone during said power failure. 21. A network interface device as recited in claim 20 further comprising a transformer for providing power to ring said phones when power is available at said subscriber location. 22. A network interface device as recited in claim 17 further comprising a high frequency component filter for removing high frequency components from a signal produced by said ring generator when power is available at said subscriber location, but not during a power failure at said subscriber location. 23. A method of providing power to a subscriber location in a fiber in the loop telephony system comprising: providing power to ring phones at said subscriber location from a power supply at said subscriber location; and during a power failure, providing power to ring phones at said subscriber location from a subscriber line coupled to an optical network unit. 24. The method as recited in claim 23 wherein said step of providing power during a power failure further comprises the step of alternately storing power from said subscriber line in a storage capacitor and discharging said capacitor to ring phones at said subscriber location. 25. The method as recited in claim 23 further comprising the step of removing high frequency components of a ring signal during said step of providing power to a subscriber location, and not removing at least some of said high frequency components from said ring signal during said power failure step of providing power.

Inventors: ALGOZER DENNIS, DIAZ STEPHEN H, GLIGA ALEXANDRU S, SHIMIRAK GERALD L, ALGOZER, DENNIS, DIAZ, STEPHEN, H., GLIGA, ALEXANDRU, S., SHIMIRAK, GERALD, L.
Applicants: RAYCHEM CORP, RAYCHEM CORPORATION
Application year: 1993
Main classification: H04M1
IPC codes: H04M1, H04M3, H04M11, H04M19, H04Q3, H04Q11