Abstract:
A system for transmitting data signals across a data transmission line in accord with a specified digital data transport protocol utilizes a powering shelf for powering the line. To that end, the line electrically couples the powering shelf with a signal converter that converts the data signals to optical signals. The signal converter includes a first interface for receiving a first data signal complying with the protocol from the line, and a housing. The powering shelf, which is external to the converter housing, preferably includes a first powering circuit for the first interface.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to communication networks and, more particularly, to powering data transmission lines in a communication network. 
     BACKGROUND OF THE INVENTION 
     Data signals in a communication network commonly are transmitted in a line in accordance with a data transport protocol (i.e., a physical layer protocol of the O.S.I. model). “T1” is one such transport protocol in which digital data is transmitted, in the format of a DS1 signal, across copper transmission lines at a rate of about 1.54 megabits per second. Like data signals utilizing other data transport protocols, the signal quality of a signal utilizing the T1 protocol (a “T1 signal”) must be restored about every 6,000 feet by repeaters or other signal regeneration devices. In addition, the T1 protocol requires line powering so that equipment such as, for example, a transmitting device may be energized merely by connecting to the transmission line. 
     T1 signals typically are transmitted from a transmitting device (e.g., a modem) to a destination device (e.g., a central office) via a series of transmission lines and repeaters. Accordingly, a T1 signal requires a relatively large number of repeaters to transmit a single signal many miles. This requirement, however, increases the overall cost of a T1 communications system. The art has responded to this problem by coupling signal converters to the transmission line to convert T1 signals (and their accompanying DS I signals) into fiber optic signals. Once converted, the fiber optic signals may be transmitted long distances, via fiber optic cable, to the destination device. Fewer repeaters thus are necessary. Such signal converters typically include a circuit board having interlace circuitry for receiving a T1 signal (and their accompanying DS1 signals) prior to converting the signal. In addition, signal converters that receive T1 signals include powering circuitry for providing line powering in accord with the T1 protocol. One commonly used signal converter, for example, is a DDM-2000™ signal converter, available from Lucent Technologies Inc. of Murray Hill, N.J. 
     Although fewer are required when using a signal converter, repeaters frequently are necessary in the portion of the line between the transmitter and the signal converter. Accordingly, there still is a need to reduce the number of repeaters to improve cost effectiveness. The art has responded to this need by developing the High-Bit-Rate Digital Subscriber Line digital data transport protocol (“HDSL”). As is known in the art, an HDSL carrier signal typically can be transmitted up to about 2.0 miles over existing copper lines and thus, requires fewer repeaters (if any) between the transmitter and the signal converter. Another advantage of HDSL is that it provides improved signal quality that is comparable to fiber optic data transmission. A DS1 signal may be interleaved upon an HDSL carrier signal to carry such DS1 signal up to about 2.0 miles. For more information relating to HDSL, see “CopperOptics, Enhancing the Performance and Application of Copper Cable with HDSL: A Technology Brief from PairGain Technologies, Inc.” at http://www.pairgain.com/copperop.htm.” 
     In a manner similar to signal converters that receive and convert T1 signals, signal converters that receive and convert HDSL signals also have a circuit board with both interface circuitry for receiving an HDSL signal prior to conversion, and line powering circuitry for powering the line in accordance with the HDSL protocol. Undesirably, however, the line powering circuitry for the HDSL protocol physically is much larger and generates much more heat than the powering circuitry that may be utilized with the T1 protocol. As a result, a signal converter that can accept four T1 signals may not be large enough to receive four HDSL signals absent significant redesign. For example, the DDM-2000™ signal converter can be configured to receive either multiple independent T1 signals, or one HDSL signal. Accordingly, several times as many DDM-2000™ signal converters are required when using the HDSL protocol than those that are necessary for use with the T1 protocol. Of course, this requirement necessarily increases the ultimate cost of such a data communication network, thus offsetting some of the benefits of utilizing the HDSL protocol. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, a system for transmitting data signals across a data transmission line in accord with a specified digital data transport protocol utilizes a powering shelf for powering the line. To that end, the line electrically couples the powering shelf with a signal converter that converts the data signals to optical signals. The signal converter includes a first interface for receiving a first data signal complying with the protocol from the line, and a housing. The powering shelf, which is external to the converter housing, preferably includes a first powering circuit for the first interface. 
     In accordance with another aspect of the invention, the signal converter includes a second interface for receiving, from the line, a second data signal complying with the protocol. The powering shelf correspondingly includes a second powering circuit for the second interface. In preferred embodiments, the protocol is HDSL and the line is a copper line. The powering shelf also may include transmission circuitry that receives and transmits the first data signal without significantly modifying it. In preferred embodiments, the transmission circuitry includes a one to one transformer. 
     The first data signal may be transmitted from a transmitting device and the powering circuitry may be configured to power the transmitting device. In some embodiments, the transmitting device is an HDSL modem. Moreover, the powering shelf may include signal converter powering circuitry for powering the signal converter, or it may include sealing current circuitry for providing sealing current to the line. The powering shelf also may include circuitry for providing a current of no greater than about 100 milliamps, and a voltage of up to about 200 volts. 
     In yet other aspects of the invention, the powering shelf may include powering circuitry for powering the line in accord with the protocol, an input line interface for receiving data signals from the line, and an output interface for transmitting data signals to the line. In preferred embodiments, the powering shelf is external to the signal converter housing and communicates with the signal converter via the line. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects and advantages of the invention will be appreciated more fully from the following further description thereof with reference to the accompanying drawings wherein: 
     FIG. 1 schematically shows a network utilizing a preferred embodiment of the invention. 
     FIG. 2 schematically shows a powering shelf configured in accordance with preferred embodiments of the invention. 
     FIGS. 3A-3H schematically show various embodiments of the powering circuitry modules for an HDSL implementation. 
     FIGS. 4A-4H schematically show various embodiments of the powering circuit modules for a single-ended HDSL implementation. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 schematically shows one of many network arrangements that may utilize a preferred embodiment of the invention with the HDSL data transport protocol. It should be noted, however, that this network configuration is exemplary and is not intended to limit the scope of the invention. Moreover, although the HDSL data transfer protocol is discussed with reference to preferred embodiments of the invention, the concepts discussed herein may be applied to other data transport protocols. 
     The network includes remote equipment  10  for interleaving a digitized signal in DS1 format with an HDSL carrier signal, a signal converter  12  for converting the HDSL carrier signal (and its accompanying DS1 signal) into an optical signal, a data transmission line  14  coupling the signal converter  12  and the remote equipment  10 , and a powering shelf  16  for powering the line  14  in accordance with the HDSL protocol. In preferred embodiments, the line  14  is a twisted pair line  14  manufactured substantially from copper. A fiber optic cable  18  is coupled to the output of the signal converter  12  for directing the fiber optic signal to a central office  20 . Once at the central office  20 , the signal may be demultiplexed from DS1 format and distributed as necessary. In preferred embodiments, the distance between the remote equipment  10  and the signal converter  12  is no greater than about 2.0 miles, while the distance between the signal converter  12  and central office  20  may be many miles. 
     The signal converter  12  preferably is an add/drop multiplexer, or a digital-access service multiplexer such as, for example, the DDM-2000™ signal converter, available from Lucent Technologies. The DDM-2000™ is configured to include signal interface circuitry  19  (on an interface circuitry circuit board) within a housing  21  for receiving four independent HDSL, carrier signals from the line  14 . The signal interfaces  19  preferably are HDSL interfaces, available from PairGain Technologies, Inc. of Tustin, Calif. Each received HDSL signal is converted to an optical signal by converting circuitry (not shown) in accordance with conventional processes. In preferred embodiments, the optical signal is formed in accord with conventionally known SONET (Synchronous Optical Network) technology. 
     In accordance with preferred embodiments of the invention, line powering circuitry is not mounted within the housing  21  of the signal converter  12 . Instead, line powering circuitry is included in the powering shelf  16  and thus, is coupled to the signal converter  12  via the transmission line  14 . As such, the shelf  16  is a stand-alone network component that is configured to both power the data transmission line  14 , and transmit received data signals with a minimum of distortion or signal modification. In preferred embodiments, the line powering circuitry is contained within a rectangularly-shaped housing (not shown) having height of about 5 inches, a width of about 11 inches, and a length of about 23 inches. 
     FIG. 2 schematically shows a preferred embodiment of the powering shelf  16 . Among other things, the powering shelf  16  includes powering circuitry  22  and a plurality of interfaces  24  to the powering circuitry  22 . For example, the powering shelf  16  may have four input interfaces  24  and four corresponding output interfaces  24  that form four input/output interface pairs. Each input/output pair includes an HDSL powering module  26  (FIGS. 3A-3H and  4 A- 4 H) that provides line powering for each of the four HDSL signal interfaces  19  on the signal converter  12 . In preferred embodiments, the powering shelf  16  includes twenty-eight input/output interface pairs and twenty-eight corresponding HDSL powering modules  26  to provide line powering for twenty-eight different HDSL signal interfaces  19 . Since the preferred signal converter  12  includes only four HDSL signal interfaces  19 , the twenty-eight HDSL signal interfaces preferably are distributed across various signal converters  12 . 
     Each powering module  26  may be configured to provide a preselected output voltage and current. In preferred embodiments, each module  26  provides an output voltage of about  1440  volts D.C. and a current of no greater than about 100 milliamps. Other preselected output voltages (e.g., about 200 volts) and current values, however, may be utilized. In addition. each powering module  26  preferably includes an output port (FIGS. 3A-3H) for delivering the output voltage and providing a port for testing the output voltage, and a current limiting element or limiting the maximum amount of current that may be delivered. For example, a conventional fuse may be utilized for such purposes. The current limiting element may be used to protect against overcurrent conditions caused by different events such as, for example, a lightening strike in the line  14 . In preferred embodiments, the current limiting element is configured in accord with the well known Bellcore standard GR-1089-CORE See “Generic Requirements for High-Bit-Digital-Subscribe-Lines (TA-NWT-001210), published by Bellcore of Morristown, N.J., for additional information relating to the Bellcore standard GR-1089-CORE. Such document is incorporated herein, in its entirety, by reference. 
     Each powering module  26  also may include a relay coupled to a light emitting diode to visually indicate if a fault condition exists within such powering module  26 . For example, the relay initially may be set to a zero value to indicate a no fault condition, and automatically switch to a one value when a fault condition is detected. The light emitting diode may be energized when the relay is set to a one value. In addition, each of the relays in the powering circuit may be coupled via a logical “OR” gate to indicate whether a fault condition exists within the powering shelf  16 . A single light emitting diode  28  may be illuminated when a fault condition is detected by the logical OR gate. More particularly, power may be supplied to the light emitting diode  28  when a one value is detected by the OR gate, thus visually indicating that a fault condition exists within one of the powering modules  26 . 
     The powering shelf  16  also includes a heat dissipating apparatus for dissipating heat produced by the powering modules  26 . The heat dissipating apparatus preferably is a plurality of baffles  30 . In preferred embodiments, the baffles are arranged to dissipate up to about 86 watts (i.e., about three watts per interface pair). Although not necessary, cooling fans also may be used to further dissipate generated heat. 
     Each powering module  26  preferably is configured to conform with Bellcore standard GR-1089-CORE for electromagnetic emissions and immunity. Furthermore, each powering module  26  preferably conforms with that standard with regard to maximum voltage and current level allowed for a connection. 
     The powering modules  26  may be configured for powering different portions of the line  14 . FIGS. 3A-3H show various exemplary line powering network configurations that may be utilized for each powering module  26 . Specifically, the powering modules  26  may be configured to provide various combinations of energizing voltage and sealing current to either or both of the remote equipment  10  and the signal converter  12 . As is known in the art, sealing current provides a low current flow (e.g., about ten milliamps) through a current loop to limit line corrosion. 
     In each of the line powering configurations shown in FIGS. 3A-3H, the signal converter  12  includes two converter transformers  32 , the powering shelf  16  includes two shell transformers  34 , and the remote equipment  10  includes two remote transformers  36 . The shelf transformers  34  preferably are configured to enable data signals to pass through the powering shelf  16  without being distorted or otherwise modified. Accordingly, the transformers preferably include one to one inductors. In preferred embodiments, the shelf transformers  34  may have the following requirements: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 Isolation: 
                   1500 VAC; 
               
               
                 Turns Ratio: 
                 1 to 1; 
               
               
                 Sec. Inductance: 
                 3.24 mH plus or minus five percent; 
               
               
                 Total Inductance: 
                 9.985 mH plus or minus five percent; and 
               
               
                 Longitudinal Balance: 
                 55 dB minimum, 2.5 kHz to 200 kHz. 
               
               
                   
               
             
          
         
       
     
     Though not having identical requirements, a WV-16854 SMT transformer also may be utilized to provide suitable termination. In addition, the longitudinal balance of the shelf transformers  34  preferably comply with the Bellcore TA-NWT-0001089 standard. This requirement recommends that there be identical components between each line and earth ground, and that the transformer be carefully designed to have high longitudinal balance. As is known in the art, high longitudinal balance prevents common-mode power supply noise on a wire pair from becoming a differential voltage that interferes with data transmission. 
     Each of the powering modules  26  shown in FIGS. 3A-3H also requires a DC power supply  38 . In preferred embodiments, this power supply  38  is about 48 volts DC. Power may be supplied by a battery, or from some external AC source. When supplied from an AC source, the powering shelf  16  includes voltage regulation circuitry to convert the AC voltage into a DC signal. Zener diode based regulator circuits should provide satisfactory power conversion for these purposes. 
     FIG. 3A shows a first line powering configuration in which energizing voltage is provided to both the remote equipment  10  and the signal converter  12 . More particularly, the power supply  38  is coupled to the center taps of each inductor in the two shelf transformers  34 , a remote voltage port  40  is provided at the remote equipment  10 , and a converter voltage port  42  is provided at the signal converter  12 . As shown in FIG. 3A, the remote voltage port  40  and converter voltage port  42  are provided across the center taps of their respective pairs of transformers. This configuration forms a first low side loop  44  and a first high side loop  46  between the converter  12  and the powering shelf  16 . The low side loop has a more negative voltage than the high side loop. Accordingly, connection of remote equipment  10  (e.g., an HDSL modem) across the remote voltage port  40  completes the circuit, thus powering such remote equipment  10 . 
     In a similar manner to the circuit between the powering shelf  16  and remote equipment  10 , the circuit between the powering shelf  16  and signal converter  12  includes a second low side loop  48  and a second high side loop  50 . The low side loop has a more negative voltage than that of the high side loop. Accordingly, connection of the signal converter circuitry across the converter voltage port  42  completes the circuit, thus powering such signal converter  12 . 
     FIG. 3B shows another line powering configuration in which energizing voltage is provided to the signal converter  12  only. No powering voltage therefore is provided to the remote equipment  10 . To that end, the power supply  38  is coupled to one inductor in each of the two shelf transformers  34 . The coupled inductors respectively also form a part of the second low side loop  48  and the second high side loop  50  between the powering shelf  16  and the signal converter  12 . The converter voltage port  42  thus is utilized to receive the powering voltage. It should be noted that this embodiment does not include a remote voltage port  40  since the remote equipment  10  is not powered. 
     FIG. 3C shows another line powering configuration that provides energizing voltage to the remote equipment  10  only. In a manner similar to the configuration shown in FIG. 3B, the power supply  38  is coupled to one inductor in each of the two shelf transformers  34 . The coupled inductors respectively also form a part of the first low side loop  44  and the first high side loop  46  between the powering shelf  16  and the remote equipment  10 . The remote voltage port  40  thus is utilized to receive the powering voltage. It should be noted that this embodiment does not include a converter voltage port  42  since the signal converter  12  is not powered. 
     FIG. 3D shows yet another line powering configuration in which sealing current is provided to the remote equipment  10  and powering voltage is provided to the signal converter  12 . In this embodiment, the power supply  38  is coupled to one of the inductors of each of the shelf transformers  34  that are used with the signal converter  12  (similar to those in FIG.  3 B). In addition, the power supply  38  also is coupled to the other of the inductors that are used with the remote equipment  10  (i.e., the first low side and first high side loops  44  and  46 ). Resistors  52  are coupled between the power supply  38  and the other of the remote inductors to reduce the current to about ten milliamps. The resistor values are selected based upon a number of circuit factors such as, for example, the length and inductance of the line  14 . The center taps of the remote transformers  36  are electrically coupled to complete the circuit. thus providing the sealing current. 
     FIG. 3E shows another embodiment that is similar to that shown in FIG.  3 D. The primary difference is that the powering module  26  provides powering voltage to the remote equipment  10  and sealing current to the signal converter  12 . As can be ascertained by those skilled in the art, the powering module  26  includes substantially identical elements to that configuration shown in FIG.  3 D. As shown in FIG. 3E, those elements are coupled in an opposite manner to those shown in FIG.  3 D. 
     FIGS. 3F,  3 G, and  3 H respectively show line powering configurations that provide sealing current to:1) the remote equipment  10  only (FIG.  3 F), 2) the signal converter  12  only (FIG.  3 G); and 3) both the signal converter  12  and the remote equipment  10  (FIG.  3 H). As shown in the figures, the elements in each of these embodiments may be coupled in a manner substantially similar to those shown in FIG. 3D and 3E. 
     FIGS. 4A-4H also show various line powering configurations when utilizing an alternative embodiment of the invention with single-ended HDSL. In a manner similar to the configurations shown in FIGS. 3A-3H, the remote equipment  10  includes two remote transformers  36 , the powering shelf  16  includes two shelf transformers  34 , and the signal converter  12  includes two converter transformers  32 . In addition, the powering shelf  16  also includes a power supply  38 . Each of the configurations provide corresponding sealing current and/or powering voltage to one or both of the signal converter  12  and the remote equipment  10 . 
     More particularly, the configuration in FIG. 4A provides powering voltage to both the signal converter  12  and the remote equipment  10 . The configurations in FIGS. 4B and 4C respectively provide powering voltage to the signal converter  12  and the remote equipment  10 . The configuration in FIG. 4D provides powering voltage to the signal converter  12  and sealing current to the remote equipment  10 . Converse to the configuration shown in FIG. 4D, the configuration shown in FIG. 4E provides powering voltage to the remote equipment  10  and sealing current to the signal converter  12 . The configurations shown in FIGS. 4F,  4 G, and  4 H respectively show line powering configurations that provide sealing current to: 1) the remote equipment  10  only (FIG.  4 F), 2) the signal converter  12  only (FIG.  4 G); and 3) both the signal converter  12  and the remote equipment  10  (FIG.  4 H). 
     It should be noted that the line powering configurations shown in FIGS. 3A-3H and FIGS. 4A-4H are exemplary. Accordingly, other line powering configurations that provide substantially the same line powering functions as those shown in the figures may be utilized. 
     Use of the powering shelf  16  therefore enables line powering to be performed from a location that is remote to the signal converter  12 . The signal converter  12  thus may utilize the additional space on the signal interface circuitry circuit board for additional signal interfaces  19 . Moreover, less heat dissipation is required in the signal converter  12  since the powering circuitry  22  is not mounted on such interface circuit board. 
     Although various exemplary embodiments of the invention have been disclosed, it should be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the true scope of the invention. These and other obvious modifications are intended to be covered by the appended claims.