Abstract:
A method and apparatus for selectively terminating sealing current in an asymmetric digital subscriber line modem is provided. The technique comprises providing a mechanism (e.g., a resistor or suitable current sink) to a DSL modem (e.g. an ADSL modem or any XDSL modem used where POTS is underlying service). The mechanism is operable to be dynamically switched on and off and to operate under low current conditions. The system allows for provision of DSL (e.g., ADSL or XDSL where POTS is the underlying current) in the absence of plain old telephone service (POTS) and for improved performance.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a method and apparatus for selectively terminating sealing current in a digital subscriber line (DSL) modem such as an ADSL modem or any XDSL modem used where POTS is the preferred underlying service. More particularly, the present technique comprises providing a mechanism (e.g. a resistor or suitable current sink) to a DSL modem, wherein the mechanism is operable to be dynamically switched between on and off states and to selectively operate under low current conditions. This system allows for provision of DSL (e.g., ADSL or XDSL where POTS is the underlying service) in the absence of plain old telephone service (POTS) and for improved performance. 
   While the invention is particularly directed to the art of ADSL service, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may be used in other types of remote communication devices requiring termination of current such as in other XDSL services such as SHDSL, VDSL, VDSL2, ADSL 2+. 
   By way of background, traditional DSL service was designed to operate in conjunction with Plain Old Telephone Service (POTS) devices. As shown in  FIG. 1(   a ), a network  10  includes a core network  12  in communication with a central office  14 . Central office  14  is in communication with a customer through customer premises equipment (CPE)  16 . Existing copper lines or loops  18  connect the central office (CO)  14  and the CPE  16 . It will be understood by those skilled in the art that the lines or loops  18  comprise a twisted pair of lines (e.g., a tip (T) line and a ring (R) line). In the drawings, the split pair is shown where advantageous for explanation but is not shown in every possible location for ease of viewing. 
   The central office  14  includes a DSL modem  20 , as well as a plain old telephone system (POTS) line card  22 . Also shown are high pass filter  21  and low pass filter  23 , which facilitate the implementation of the DSL service. 
   The customer premises equipment (CPE)  16  includes a DSL modem  24 , a POTS phone  26  and a personal computer  29  (or the like). Also shown are high pass filter  25  and low pass filter  27 , which facilitate the implementation of the DSL service. 
   The underlying POTS service and equipment shown allows for DC current (that also acts as a sealing current) to flow from the POTS line card  22  disposed within the central office (CO)  14 , through the copper lines or loops  18 , to a POTS phone  26 . The POTS phone  26  terminates the current by completing the circuit. This current is typically run through the copper lines  18  for purposes of powering the POTS phone and also cleaning the copper splices in the copper loops  18 . It is known that, absent the DC current, a certain percentage of the copper loops  18  would deteriorate and become obstacles to providing POTS or ADSL service of sufficient quality. 
   Notably, the DSL modem  24  that is a part of the customer premises equipment (CPE)  16  does not include any mechanism for terminating current. There is no need for such an enhancement to the DSL modem  24  in these circumstances because traditional DSL service is implemented in conjunction with POTS service. As noted above, the POTS phone is operable to terminate current. 
   However, DSL service is now increasingly being demanded in circumstances where no POTS service is available, e.g., in voice-over-Internet-Protocol (VOIP) networks. Without underlying POTS service, there is consequently no manner of terminating the sealing current—which should be advantageously provided to clean the copper loops on the ADSL lines. 
   While it is understood that problematic loops in such implementations of DSL service currently constitute only a small percentage of DSL subscriber installations, this small percentage nonetheless translates to a high number of modems. As such, this is a situation that demands a practical solution. 
   To address the problem currently, service providers simply dispatch service personnel in trucks to the customer premises to install a resistor in the network interface device (NID) at the customer premises. The resistor simulates the off hook condition of the POTS phone  26  and provides a mechanism to terminate the sealing current. To illustrate, referring now to  FIG. 1(   b ), the customer premises equipment (CPE)  16  differs from that of  FIG. 1(   a ) in that underlying POTS service is not available. So, a POTS phone  26  is not present at the premises. Also, the configuration of the filters is different. As shown, a resistor  28  is installed between the tip line and ring line of the twisted pair of loop  18  (in, for example, a network interface device (NID)  17 ). A low pass filter  27  is also provided. 
   This approach, though, has its drawbacks. For example, it is expensive to dispatch personnel. Moreover, this approach requires the DC current to be dissipated continuously. This wastes power and, therefore, does not allow for reduction of power consumption. In addition, this approach does not allow for any remote control of the installed resistor. 
   The present invention contemplates a new and improved system and technique that resolves the above-referenced difficulties and others. 
   SUMMARY OF THE INVENTION 
   A method and apparatus for selectively terminating current in an asymmetric digital subscriber line (ADSL) modem are provided. 
   In one aspect of the invention, a system comprises an ADSL modem, a current terminating device housed within the modem and a control module operative to control the current terminating device. 
   In another aspect of the invention, the current terminating device comprises a resistor. 
   In another aspect of the invention, the current terminating device comprises a current sink device. 
   In another aspect of the invention, the control module is operative to control the current terminating device by selectively switching the current terminating device between on and off states. 
   In another aspect of the invention, the control module is operative to control the current terminating device by selectively switching the current terminating device between on and off states through a message. 
   In another aspect of the invention, the message is one of an embedded operations channel (EOC) message and an ADSL operations channel (AOC) message. 
   In another aspect of the invention, the control module is housed within an ADSL element management system. 
   In another aspect of the invention, a method comprises transmitting a first message to the ADSL modem, the first message including data to activate a current terminating device, activating the current terminating device based on the first message, sending a sealing current to the current terminating device through copper lines, transmitting a second message to the modem, the second message including data to deactivate the terminating device, and deactivating the current terminating device based on the second message. 
   In another aspect of the invention, the method is implemented using appropriate means. 
   In another aspect of the invention, a method comprises querying to determine if plain old telephone service (POTS) is available in a customer premises, determining if a current terminating device is available in the modem if the plain old telephone service (POTS) is not available, and controlling the current terminating device if it is available. 
   An advantage of the presently described embodiments is that such embodiments allow for the provision of ADSL service in circumstances where POTS service is not desired or provided, such as is the case in voice-over-internet-protocol (VOIP) environments. 
   An advantage of the presently described embodiments is that such implementations reduce cost to the service provider, inasmuch as they do not require the dispatch of personnel and equipment, as described above. 
   Another advantage of the presently described embodiments is that less power is consumed in the central office. 
   Another advantage of the presently described embodiments is that less power is consumed by the customer premises equipment (CPE). 
   Another advantage of the presently described embodiments is that less power is consumed overall by virtue of controlling the time that power may be dissipated. 
   Another advantage of the presently described embodiments is that the sealing current mechanism is remotely controllable. 
   Further scope of the applicability of the present invention will become apparent from the detailed description provided below. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 

   
     DESCRIPTION OF THE DRAWINGS 
     The present invention exists in the construction, arrangement, and combination of the various parts of the device, and steps of the method, whereby the objects contemplated are attained as hereinafter more fully set forth, specifically pointed out in the claims, and illustrated in the accompanying drawings in which: 
       FIGS. 1(   a ) and  1 ( b ) are graphic illustrations of prior art networks; 
       FIG. 2  is a graphic illustration of a network incorporating an embodiment of the present invention; 
       FIGS. 3(   a ),  3 ( b ), and  3 ( c ) are graphic illustrations of selected elements of the network of  FIG. 2 ; 
       FIG. 4  is a flow chart illustrating a method according to the present invention and, 
       FIG. 5  is a flow chart illustrating a method according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings wherein the showings are for purposes of illustrating the preferred embodiments of the invention only and not for purposes of limiting same,  FIG. 2  provides a view of an exemplary network into which the present invention may be incorporated. As shown, a network  100  includes a core network  102  in communication with a central office (CO)  104 . The central office (CO)  104  is connected to a customer through customer premises equipment (CPE)  106 . Copper lines or loops  108  typically connect the central office (CO)  104  with the customer premises equipment (CPE)  106 . The copper lines or loops  108  are typically comprised of copper line pairs that connect directly to the customer premises equipment (CPE)  106 . As noted above, it will be understood by those skilled in the art that the lines or loops  108  comprise a twisted pair of lines (e.g., a tip (T) line and a ring (R) line). In the drawings, the split pair is shown where advantageous for explanation but is not shown in every possible location for ease of viewing. For example, the split pair is shown within the customer premises equipment (CPE)  106  but is only represented as a single line in the central office (CO)  104  and between the customer premises equipment (CPE)  106  and the central office (CO)  104 . 
   The central office (CO)  104  includes a DSL modem  110  and a control module  112  that, in at least some embodiments, may be disposed within an element management system (EMS)  114 . Also shown are a high pass filter  105  and a low pass filter  107 , which facilitate the implementation of the DSL service. The high pass filter  105  and the low pass filter  107  connect to the line  108  as those of skill in the art will appreciate. 
   The customer premises equipment (CPE)  106  includes a DSL modem  115  (shown in dashed lines) having a DSL module  116  and a current terminating device  118  disposed therein. The current terminating device  118  may also have a switch  113  to conveniently allow for activation or deactivation of the current terminating device. As will be described below, this switch could be opened or closed in response to control data or messages to dynamically control the device  118 . This will also provide the service provider with the option of providing the same modem to all customers, whether or not those customers require the use of the current terminating device. Of course, different types of modems could also be provided depending on whether a customer requires the current terminating device. The customer premises equipment (CPE)  106  also includes a high pass filter  117 , a low pass filter  119  (having associated therewith switches  119 - 1  that are closed in response to control module  112  when the current terminating device is to be used) and a personal computer  121  or other internet connecting device. 
   As shown, the copper wire lines or loops  108  connect to the DSL modem  115 . The lines  108  connect to the DSL module  116  through the high pass filter  117  and to the current terminating device  118  through the low pass filter  119 . In addition, the lines  108  connect (through the low pass filter  119 ) to the current terminating device  118  by having the tip (T) line connect to one side or port of the current terminating device  118  and the ring (R) line connect to another side or port of the current terminating device  118 . The high pass filter  117  and the low pass filter  119  may be a part of the DSL modem  115  as shown or may be disposed outside the modem. The precise configuration will vary based on the objectives of the design implemented. For example, if the filters were both external to the modem, more than one connection of lines  108  to the DSL modem  115  may be required. As a further example, if a DC current sink is used as the current terminating device, then a low pass filter may not be necessary because such a DC current sink would not disturb the DSL signal. As a still further example, the functionality of switches  113  and  119 - 1  may be incorporated into a single device, depending on the components used. 
   Also shown is a controller  123  that will read the control data or messages that are sent to the DSL modem and act accordingly to, for example, activate or deactivate the current terminating device  118 . For example, the controller  123  may read a bit in the control message and send a signal to the device  118  and/or switches  113  and/or  119 - 1  to open or close one or more of these switches, e.g. switches  113  and/or  119 - 1 , or otherwise activate/deactivate the device. However, the precise technique for accomplishing these techniques will vary and will depend on the form of the current terminating device. 
   Referring now to  FIGS. 3(   a ),  3 ( b ) and  3 ( c ), it should be appreciated that the current terminating device  118  may take a variety of forms. For example, as shown in  FIG. 3(   a ), the current terminating device  118  may take the form of a resistor or a resistor network  120  connected at each end to the lines or loops  108 . As shown, the network of resistors includes resistors of varying values (e.g. 500 ohms, 1 kilo-ohm, 2 kilo-ohms, etc.) to allow for variation in the desired overall impedance of the device. To facilitate the contemplated variation, a series of switches is illustrated. These switches may be activated through software controls or may be manually set or reset by a technician. Of course, other switching techniques may be used. Likewise, other suitable impedance changing techniques may be implemented. In addition, a single resistor may be used. 
   Alternatively, the current terminating device  118  may simply take the form of a current sink device  122 , as shown in  FIG. 3(   b ), connected to the lines  108 . Current sink devices can take a variety of forms that would be suitable here. For example, a DC current sink device is preferred in some situations. As noted above, in this case, a low pass filter may not be required. 
   For example, with reference to  FIG. 3(   c ), a current sink device  124  may comprise a transistor  130 , a first resistor  132 , a second resistor  134 , a third resistor  136 , and a fourth resistor  138 . The values for each of these components will vary depending on the implementation. Also shown are a series of switches associated with each of the resistors  134 ,  136 , and  138 . This network of resistors and switches allows for variance in the overall impedance of the device and thus the resulting current flow. As with the embodiment shown in  FIG. 3(   a ), the switches can be selectively activated in any of a number of manners. For example, the switching may be implemented through software control or it may be manually implemented. In addition, as illustrated, the tip (T) line of line  108  connects to the transistor  130  while the ring (R) line of line  108  connects to the resistor network  134 ,  136 , and  138 . 
   In one form of the invention, the current sink limit on the current terminating device  118  may be limited to five milli-amps (mA) or some other number of mA instead of the 50 mA or higher that is currently used in POTS phones. This will allow for a reduction in required power and, thus, improved overall performance. 
   Notably, the addition of the current terminating device  118  within the DSL modem  115  will also allow the DSL modem  115  to complete the circuit that is required to effectively terminate a sealing current from the central office (e.g., the central office POTS line card  111  or other source), to the customer premises equipment (CPE)  106 . As noted above, the addition of this current terminating device  118  will allow for proper cleaning of the splices in the copper lines of loops  108  to ensure improved life span of the copper lines or loops  108 . 
   In addition, the implementation of the control module  112  in the architecture of the central office (CO)  104  allows for dynamic switching control of the current terminating device  118 . This dynamic control of the current terminating device  118  results in improved performance and consumption of less power. 
   More particularly, use of the current terminating device  118 , and the system contemplated herein including the control module  112 , requires provisioning of the connection, upon initialization, between the central office (CO)  104  and the DSL modem  115 . It will be understood that when the DSL modem  115  is installed as a part of the customer premises equipment (CPE)  106 , an initialization routine is conducted. There are a variety of known routines that will allow the DSL modem  115  to communicate with the DSL modem  110  in the central office (CO)  104 . These routines use a G.hs handshake protocol, which is likewise known. The methods according to the present invention use a G.hs handshake protocol; however, the initialization of the current terminating device, if available and usable, is also accomplished. It should be understood that other initialization functions may be accomplished, but these will not be described for ease of explanation. 
   With reference to  FIG. 4 , during the initialization process, a method  400  is implemented wherein the control module  112  queries appropriate storage tables and/or databases (such as databases storing customer subscription data) that are present in the network to determine if POTS service is available within the customer premises equipment (CPE)  106  (at  402 ). If so, normal processing and further conventional initialization is conducted (at  404 ). If POTS service is not available, the control module  112  determines if a current terminating device, such as current terminating device  118 , is available in, for example, the DSL modem (at  406 ). This information is stored on the modem itself. For example, the status of the switch  113  or switches  119 - 1  may be stored. In addition, information on the availability of a modem having this capability may be stored on the network. If no current terminating device is available, then the control module  112  triggers the initiation of other procedures to provide DSL service to this site (at  408 ). For example, the control module  112  may issue a service ticket to prompt customer service personnel to dispatch technicians and a truck to the customer premises to install a resistor in the network interface device (NID), as has been done in the past. 
   If, however, a current terminating device is available for use, then a notation is made by the control module  112  (e.g. set flag, . . . etc.) to initiate control procedures for the current terminating device at appropriate times (at  410 ). These control procedures and parameters which are implemented and maintained by the control module  112  are described in more detail below. 
   As an option, and depending upon the intelligence capability of the DSL modem, a further step of configuration may take place. For example, the control module  112  may download parameters of operation to the DSL modem  115  (e.g. DSL module  116 ) relating to the current terminating device. The downloaded parameters may be set by the control module  112  or may be input thereto by a technician. These parameters may inform the DSL modem of the times and circumstances in which the DSL modem should activate the current terminating device to provide the sealing current. 
   In any event, the parameters set for controlling the current terminating device, whether applied by the control module  112  or the DSL modem  115  or any other control means, may vary widely depending on the objectives of the user setting the parameters. These parameters will typically define the frequency and time periods of activation of the current terminating device. These parameters may be pre-defined and set for particular installations depending on the equipment used, objectives of the technician, etc. 
   For example, the parameters may indicate that the current terminating device simply be kept on at all times. Of course, while this consumes more power than other methods, it nonetheless makes use of a low power current terminating device (unlike prior known methods). Another approach may be to simply activate the current terminating device when a connection is made. This may occur when a user attempts to access the internet through a personal computer. As a further example, the current terminating device  118  may be activated, based on predetermined time periods and frequencies, for one hour per day or one hour per week or the like. The current terminating device  118  may also be controlled to pulse or quickly switch between on and off states so that less heat dissipation results. 
   In operation, a variety of methods could be implemented to dynamically control the current terminating device  118  through the control module  112 . The current terminating device could be dynamically controlled, based on the parameters set as above, through use of embedded operations channel (EOC) messages or an ADSL operations channel (AOC) messages. Of course, other suitable messages may also be used. 
   In any event, these messages preferably include data to dynamically turn the current terminating device  118  from an on state to an off state to allow the modem to selectively be activated. The control module  112  and current terminating device  118  can be used advantageously to provide DSL service where POTS service is not available and also provide for improved overall performance. 
   Typically, the methods will be implemented in software routines that control the hardware as desired. These methods also provide for the generation of appropriate messages, such as the EOC messages or the AOC messages noted above. These software routines may be implemented in a variety of single locations, or may be distributed in various elements of the network, but—in at least one form of the invention—the routines are stored in and run by the control module  112 . 
   The control module  112  and its described functionality of initializing the DSL modem, using the G.hs handshake protocol, and/or controlling the current terminating device of the DSL modem, using EOC or AOC messages, are controlled and monitored by the element management system (EMS)  114 , in at least one form of the invention. In alternative embodiments, a DSLAM module may be used for such control and monitoring. 
   The actual operation of the system contemplated herein will vary from application to application once the system is initialized, as noted above. However, at least one of these processes includes the transfer of messages between the control module  112  and the DSL modem  115  to control the current terminating device  118  of the DSL modem  115 . This is based on the procedures and parameters noted above. As will be seen, this particular approach involves control of the current terminating device by the network (e.g. the control module  112 ). 
   In this regard, referring now to  FIG. 5 , an exemplary method  500  includes transmitting a first message to an ADSL modem (e.g. modem  116 ) (at  502 ). It should be appreciated that this first message includes data to activate the current terminating device. Next, the current terminating device is activated based on the first message (at  504 ). A sealing current then flows through the current terminating device through the copper lines (e.g. lines  108 ) (at  506 ). This, of course, provides for appropriate cleaning of the copper lines to avoid problems noted above. 
   When it is determined that the transmission of sealing current should cease, a second message is transmitted to the modem (at  508 ). The second message, of course, includes data to deactivate the terminating device. The current terminating device is then deactivated (at  510 ). 
   The above description merely provides a disclosure of particular embodiments of the invention and is not intended for the purposes of limiting the same thereto. As such, the invention is not limited to only the above-described embodiments. Rather, it is recognized that one skilled in the art could conceive alternative embodiments that fall within the scope of the invention.