Abstract:
A processor controlled mechanism automatically determines from a location such as a central office whether termination equipment installed at a remote end of a wireline link is span-powered, or is powered locally. It then applies a voltage to the wireline link that is appropriate for the identified type of termination equipment. This eliminates the need for two separate central office loop-powering devices. In the course of making the determination, nothing higher than a safety extra low voltage is applied to the wireline link, to comply with Underwriter&#39;s Laboratory standards for locally powered customer premises equipment.

Description:
FIELD OF THE INVENTION 
     The present invention relates in general to wireline telecommunication communication systems, and is particularly directed to mechanism for automatically determining from a location such as a central office whether equipment installed at a remote end of a wireline link is span-powered, or is powered locally exclusive of the wireline link, and then applying a voltage to the wireline link that is appropriate for the identified type of remote termination equipment. 
     BACKGROUND OF THE INVENTION 
     In addition to sending telecommunication signals, such as audio (e.g., voice), video and data over (copper) wirelines, service providers may also use the same set of copper lines to supply power (typically referred to as ‘loop powering’) to a piece of telecommunication equipment (terminating device) that is installed at a location up to several miles away. While the power required may be very small or relatively large, depending upon device type, loop powering often requires the application of a relatively large voltage (e.g., on the order of 130 VDC) to the wireline link, and is used extensively on mid-span devices of digital dataphone service (DDS), integrated services digital network (ISDN), digital T1 transport, and high data rate digital subscriber loop (HDSL) networks. 
     For other types of telecommunication equipment, the terminating device is located inside the customer&#39;s premises, and is powered ‘locally’ from within the customer&#39;s premises. Where the termination device is locally powered, there is no need to apply a very large voltage to the wireline link from the central office for powering the remote device; instead, it is only essential that the link carry a relatively small ‘sealing current’—in order to prevent corrosion in the copper of the wireline loop. Operation of a termination device in the customer&#39;s premises does not depend upon the presence of sealing current. 
     Due primarily to the continuing improved performance of telecommunication equipment, the distance at which the termination device may be located relative to the central office, and therefore the length of the connecting phone lines has increased. Because of this increase in copper loop length, the use of high voltage sources in the central office is necessary, in order to provide any significant amount of power to a remote termination device that is loop powered. 
     On the other hand, for the case of a very long copper loop to a remotely powered termination device, the voltage that must be applied to the loop for providing sealing current remains relatively low, since sealing current itself is a very small current. Moreover, it is an Underwriter&#39;s Laboratory (UL) requirement that any voltage supplied from the central office and made available at a customer&#39;s premises must be a ‘Safety Extra Low Voltage’ (SELV), the current specification for which is a voltage not to exceed a value on the order of 60 volts. 
     It will be appreciated therefore that the type of device installed in the telephone company&#39;s central office for powering the (copper) wireline will depend on what type of termination device is located at the remote end of the loop. On the one hand a central office device having a SELV type voltage supply is needed for terminating devices that are locally powered; on the other hand, a central office device with a high voltage supply is needed for devices that are span powered. This creates two problems. 
     First, the telephone company must purchase and stock two types of central office loop powering devices. In addition to being more costly to the telephone company, using two different devices adds to the complexity of the overall communication system. Secondly, since the person installing the central office device cannot see what terminates the remote end of the copper loop, there is the possibility that a high voltage device will be installed at the central office, when in reality the remote end is terminated by locally powered customer&#39;s premises equipment. Delivering a substantial loop powered voltage (e.g., on the order of 130 VDC) to a locally powered remote termination device is prohibited. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, this twofold problem is effectively obviated by a new and improved central office-installable scheme, that is operative to automatically determine whether a termination device installed at a remote end of a wireline link is span-powered, or is powered locally exclusive of the wireline link. Once this determination has been made, the invention is effective to apply a voltage to the wireline link that is appropriate for the determined type of termination device. This eliminates the need for two separate central office loop-powering devices. In the course of making this determination, nothing higher than an SELV is supplied to the wireline link, so as to comply with UL standards for locally powered customer premises equipment. 
     For this purpose, the present invention employs a loop powering switch that is controlled by a microprocessor to selectively apply to the wireline loop one of two loop-powering voltages: an SELV compliant +/−48 volts, readily available in most central offices, and +/−130 volts. The default connection is the +/−48 volt supply to ensure compliance with the UL code requirement referenced above. Via a differential amplifier coupled to a loop current resistor installed in the wireline loop, an amplified voltage representative of the magnitude of wireline current is coupled to a comparator to determine the presence of loop current. The output of the comparator is coupled to the control processor, which is programmed to execute a prescribed remote termination sensing and wireline powering routine. 
     Pursuant to this routine, the line is first checked to detect whether it is connected to any remote termination device. For this purpose, an SELV voltage is applied to the loop via the switch and the voltage across the current sense resistor is monitored for the presence of loop current. If there is no loop current, it is inferred that there is no remote termination, and the wireline remains default-coupled to the SELV voltage. Once loop current is detected, implying that the wireline is coupled to a remote termination device, the routine determines what type of remote termination is at the far end of the loop. 
     To this end, the connection with the SELV supply is interrupted, to reduce the voltage applied to the loop to zero volts and, using the digital communication line card, a digital communication connection over the loop with the remote termination is attempted. If there is a response from the remote termination device, it is inferred that the remote termination is locally powered, and the loop voltage is changed back to the SELV voltage, so as to provide sealing current to the loop. If there is no response, it is inferred that the remote termination is span-powered, and the span-powering voltage (130 V) is coupled through the switch to the wireline loop. 
     Once the voltage appropriate for the identified type of remote termination has been applied to the loop, a data connection may be established between the line card and the remote termination device. If there is a loss of power during the data connection, the routine described above is reinitiated. In addition, the quality of the digital signal is continuously monitored. In response to an unacceptable degradation in signal quality, the link is first checked for the presence of loop current. If loop current is present, the data connection is reestablished. If there is no loop current, however, the entire routine is reinitiated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 diagrammatically illustrates the architecture of the automatic remote termination sensing and wireline-powering mechanism of the invention; and 
     FIG. 2 is a flow chart of the remote termination sensing and wireline-powering routine executed by the supervisory control processor of the architecture of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     Before describing in detail the automatic remote termination sensing and wireline-powering mechanism of the present invention, it should be observed that the invention resides primarily in a prescribed arrangement of conventional communication circuits and associated digital signal processing components and attendant supervisory control circuitry therefor, that controls the operations of such circuits and components. Consequently, the configuration of such arrangements of circuits and components and the manner in which they are interfaced with other equipment have, for the most part, been illustrated in the drawings by readily understandable block diagrams, which show only those specific details that are pertinent to the present invention, so as not to obscure the disclosure with details which will be readily apparent to those skilled in the art having the benefit of the description herein. Thus, the block diagram illustrations are primarily intended to show the major components of the invention in a convenient functional grouping, whereby the present invention may be more readily understood. 
     Attention is initially directed to FIG. 1, wherein the architecture of the automatic remote termination sensing and wireline-powering mechanism of the invention is diagrammatically illustrated. As described briefly above, and as shown in FIG. 1, the sensing and loop powering mechanism of the invention is readily installed in the central office switching bay of a telecommunication service provider, from which telecommunication (telephony/data) service to termination devices located in customer premises sites remote with respect to the central office. A remote termination  20  of a respective customer premises site is coupled to receive service by way of a respective copper wireline loop  30 , sourced from the central office  10 . 
     Within the central office,. the sensing and loop powering mechanism comprises a double-pole, double-throw (DPDT) relay  11  that is operative, under the control of a supervisory microprocessor  12 , to selectively apply to the wireline loop  30  one of two loop-powering voltages (+/−48 volts, +/−130 volts), respectively provided by an SELV supply  13  and a span supply  14 . As shown in FIG. 1, the default connection condition for the relay  11  is the +/−48 volt supply. Not only does this insure compliance with the above-referenced UL requirement that any voltage supplied from the telephone company&#39;s central office and made available at a customer&#39;s premises be SELV (currently defined as a voltage no greater than 60 volts), but it is a readily available voltage, as most central offices provide power through a +/−48V battery system. 
     A relatively small valued loop current resistor  31  is installed in the wireline loop for detecting loop current. End terminals of the resistor  31  are coupled over links  32  and  33  to a differential amplifier  40 , the output  43  of which is an amplified voltage that is representative of the magnitude of current flowing in the wireline. This amplified voltage is coupled to a first input  51  of a comparator  50 , a second input  52  of which is coupled to a reference voltage source  54 . The output  53  of comparator  50  is coupled to the control processor  12 . Control processor  12  is programmed to execute the remote termination sensing and wireline powering routine shown in the flow chart of FIGS. 2, including the operation of a standard digital communication line card  60 , as follows. 
     Before it can be determined what power is to be applied to a line under test, it is necessary to detect whether the wireline  30  is actually connected to a remote termination. For this purpose, after power up in step  200  of the routine of FIG. 2, a low SELV type voltage is applied to the loop in step  201 , by turning on the +/−48 volt (default) supply for the relay  11 . Once this SELV voltage is turned on, the voltage across the current sense resistor  31  is monitored in query step  202  for the presence of loop current. If there is no loop current (the answer to query step  202  is NO), then it is inferred that there is no remote termination and the central office leaves the wireline  30  coupled to the (+/−48V) SELV voltage via the loopback to step  201 , until loop current is detected. Once loop current is detected (the answer to query step  202  is YES), it is inferred the wireline  30  is coupled to a remote termination device, and the routine must determine what type of remote termination  20  is at the far end of the loop  30 . 
     To this end, in step  203 , the connection with the +/−48v supply  13  is interrupted, so as to reduce the voltage applied to the loop  20  from the default SELV to zero volts. Next, in step  204 , using the line card  60 , a digital communication connection over the loop  30  with the remote termination  20  is attempted. It should be noted that a span-powered termination will not be able to communicate unless it is receiving power through the wireline loop  30 . In contrast, a locally powered remote termination does not need loop current to communicate. With the loop voltage reduced to zero volts, a communication with the remote termination  20  can be attempted. 
     If there is a response from the remote termination device  20  (the answer to query step  205  is YES), it is inferred that the remote termination is piece of locally powered customer premises equipment, rather than a span-powered device. In this case, in step  206 , a customer premises flag is set in the microprocessor  12 . Next, in step  207 , with the customer premises flag set, a set SPAN voltage=48V signal is asserted, and the loop voltage is changed back to 48 volts to provide sealing current to the wireline loop  30 . 
     On the other hand, if the answer to query step  205  is NO, it is inferred that the remote termination  20  is a span-powered device, and the routine transitions to step  208 , wherein a span power flag is set in the microprocessor. Next, in step  209 , a set SPAN voltage=130 V signal is asserted, and the 130 V supply  14  is turned on. Also, the relay  11  is operated to couple the wireline loop  30  to the span power supply  14 . 
     Once the routine has determined the type of remote termination and completed the wireline powering connection in either of steps  207  or  209 , it transitions to step  210 , wherein a data connection is established between the line card  60  and the remote termination device  20 . With a data connection established, data is transmitted in step  211 . If there are no problems with the connection, data continues to be transmitted. However, should there be a loss of power —the answer to step  212  is YES, the routine transitions back to step  200  and the process is restarted. 
     As long as there is no loss of power (the answer to step  212  is NO), the routine continues to check the quality of the digital signal on the wireline link  30  in step  213 . Unless there is an unacceptable degradation in signal quality (the answer to step  213  is YES), the routine loops back to step  211  and data continues being sent over the wireline loop. However, for an unacceptable degradation in signal quality (the answer to step  213  is NO), the routine transitions to step  214 , wherein the link is checked for the presence of loop current. If the answer to step  214  is YES, indicating that loop current is present, then before data transmission can proceed, a digital connection must be reestablished in step  210 . If there is no loop current (the answer to step  214  is NO), the routine transitions back to step  201  and the process is reinitiated. 
     As will be appreciated from the foregoing description, the above-described problem of having to purchase and stock two types of central office loop powering devices, and the possibility of erroneously connecting a high voltage to a wireline loop terminated by locally powered customer&#39;s premises equipment, are effectively obviated by the central office-installable line powering mechanism of the invention, which automatically determines the termination device is span-powered, or is locally powered, and then powers the wireline link with a voltage that is appropriate for the determined type of termination device. The invention not only eliminates the need for two separate central office loop-powering devices, but ensures that nothing higher than an SELV is supplied to the wireline link unless and until it has been determined that the loop is terminated by locally powered customer premises equipment. 
     While we have shown and described an embodiment in accordance with the present invention, it is to be understood that the same is not limited thereto but is susceptible to numerous changes and modifications as known to a person skilled in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are obvious to one of ordinary skill in the art.