Abstract:
An adaptive unit that taps into an existing POTS line, DLC POTS line, DLC channel unit designed for sealing current outputs, or AC-DC transformer designed for sealing current output, to provide sealing current to a DSL circuit thereby avoiding having to deploy a separate sealing current unit to supply the desired sealing current to the DSL circuit. The adaptive unit, or sealing current derivation device, is preferably deployed at remote terminals thereby facilitating the offering of new DSL service, but may also be utilized in a central office.

Description:
BACKGROUND 
   1. Field of the Invention 
   The present invention relates generally to telecommunications networks and, more particularly, to employing sealing currents in such networks. 
   2. Background of the Invention 
   DSL (Digital Subscriber Line) technology provides high-speed data services over ordinary copper telephone lines. ADSL (Asymmetrical Digital Subscriber Line) is a type of DSL common for residential use. ADSL can download data much faster than it can upload data. SDSL (Symmetric Digital Subscriber Line) is a type of DSL service commonly made available to business users. Unlike ADSL, SDSL offers equal upload and download speeds. Types of SDSL service include SHDSL (Symmetric High Bit-rate Digital Subscriber Line) and EDSL (Enterprise Digital Subscriber Line), both of which are increasingly being offered to corporate users. 
     FIG. 1  illustrates a typical communication network architecture that provides SDSL services and POTS (Plain Old Telephone Service).  FIG. 1  includes telephone user  108  and computer system  118 . Computer system  118  may be any type of computer system capable of receiving and transferring data such as a personal computer or a main frame computer. 
   Telephone user  108  connects to OE (Office Equipment)  104  through connector module  106 , via twisted-pair POTS line  110 . Connector module  106  may be a lightning surge protector module. Connector module  106  may be located in a Central Office building  101  or a Remote Terminal enclosure  111 . OE  104  connects telephone users  108  to the PSTN (Public Switched Telephone Network)  102  thereby providing well-known POTS functionality to customers. 
   Computer system  118   a  connects to DSLAM (DSL Access Multiplexer)  114  through connector module  116 , via twisted-pair DSL service line  120 . Connector module  116  may also be a lightning surge protector module. Connector module  116  and DSLAM  114  may be located in a central office building  101  or a Remote Terminal enclosure  111 . DSLAM  114  connects computer system  118  to Network  112 , such as the Internet, thereby providing DSL services to customers in a known fashion. 
   As is well-known in the art, OE  104  and DLC  126  both provide a sealing current that causes a small amount of DC current to flow through POTS lines  110 . OE  104  may be a Line Port at the central office of PSTN  102  or a Line Port on the PSTN that is extended to a Remote Terminal enclosure  111  over a DLC system  126 . Sealing current prevents corrosion build-up, reduces poor connections and noisy lines and improves overall transmission characteristics. Sealing current is a major contributor to telephone network reliability in the POTS arena. 
   In the DSL arena, however, and more particularly, in connection with SHDSL and EDSL services, the DSLAM that provides the SHDSL and EDSL services does not always have the capability of generating sealing current. Accordingly, when these DSL services are provided, a separate sealing current unit must be installed to provide and connect sealing current to the DSL twisted copper pair. When the DSLAM  114  is located in a Remote Terminal Enclosure  111 , the addition of the sealing current unit must be co-located inside the corresponding remote enclosure, requiring mounting space and power, as commercially-available sealing current units are typically provided in the form of separate rack-mounted units. To complicate matters, particularly in the context of a large telecommunications service provider, an OSPE (Outside Plant Engineering) EWO (Engineering Work Order) is typically required to purchase physical plant devices such as sealing current units. Since sealing current units must be deployed before service is first made available from a RT (Remote Terminal) site, service to the customer may be unnecessarily delayed until after the EWO can be processed and the sealing current unit is purchased and installed. 
   Further, it is difficult to determine whether a given customer facility might require sealing current service. Thus, to ensure quality service and customer satisfaction, sealing current units are often preinstalled at all remote sites, thereby increasing cost, perhaps unnecessarily, to the telecommunications service provider. 
   SUMMARY OF THE INVENTION 
   To address the deficiencies of prior art sealing current implementations in the DSL arena, and to advantageously further the state of the art, the present invention provides a sealing current derivation option for DSL service by deriving desirable sealing current from existing resources by way of a unique circuit tapping or bridging configuration. As a result, the present invention reduces capital requirements to provide SDSL services, reduces delays in offering SDSL services, reduces engineering and construction efforts, and ensures quality customer service without providing devices that may or may not be required. 
   More specifically, the present invention provides an adaptive unit that taps into either existing POTS lines or DLC slots. In accordance with one embodiment, sealing current may also be derived from a common AC convenience outlet in combination with an AC-DC transformer. 
   In accordance with a method of the present invention, sealing current is supplied to a digital subscriber line (DSL) circuit by identifying a facility through which sealing current flows, identifying a DSL circuit for which sealing current is desired, and providing a bridging circuit, i.e., an adaptive unit, between the facility and the DSL circuit, whereby sealing current is supplied to the DSL line. The sealing current can be supplied by a POTS line, a DLC POTS line, a DLC channel unit with sealing current outputs, an AC-DC transformer or any other apparatus from which sealing current can be derived. 
   The present invention is also related to a method of obtaining sealing current from existing facilities by locating a POTS line that carries a DC sealing current, tapping into the POTS line on a telecommunications provider-side of a protector module, removing substantially all of any AC component being carried by the POTS line, and feeding the DC sealing current carried by the POTS line to another circuit such that the another circuit also carries a DC sealing current. 
   The present invention also provides an apparatus for deriving sealing current, comprising a sealing current derivation device having a first pair of connectors and a second pair of connectors, the first pair of connectors being electrically connected to a pair of conductors of a first circuit and the second pair of connectors being electrically connected to a pair of conductors of a second circuit, wherein the first circuit carries a sealing current whereas the second circuit does not carry a sealing current and both the first and second circuits are one of voice and data circuits, wherein the sealing current derivation device bridges the first and second circuits thereby supplying sealing current from the first circuit to the second circuit. 
   In several possible implementations, the present invention derives sealing current from one line and provides sealing current to the other line, wherein both lines are preferably operating telecommunications carrier lines. 
   In one embodiment of the present invention, sealing current is derived from a working POTS line. In another embodiment, the present invention derives sealing current from a specialized DLC channel unit. In still another embodiment, the present invention derives sealing current from an AC powered device installed on the customer&#39;s premises. 
   These and other aspects and advantages of the present invention will be apparent to those skilled in the art upon reading the following detailed description in conjunction with the associated drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a high level schematic diagram of a POTS and DSL service implementation. 
       FIG. 2  shows a schematic configuration of a first embodiment of the present invention. 
       FIG. 3  shows an exemplary circuit diagram according to the first embodiment of the present invention. 
       FIG. 4  shows a schematic diagram according to a second embodiment of the present invention. 
       FIG. 4A  shows a circuit diagram of main components of a sealing current device according to the second embodiment of the present invention. 
       FIG. 5  shows a circuit diagram of main components of a sealing current device according to a third embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. While the present invention is described in embodiments directed to SHDSL services, it should be appreciated that the present invention may also be useful in providing sealing current in the context of other (DSL or other telecommunications) services. 
     FIG. 2  illustrates a schematic block diagram of a system according to an embodiment of the present invention. 
   DLC  204  provides POTS service to customers (i.e., telephone users). DLC  204  is connected to DLC OSP connector module  210  via POTS line  206 . DLC OSP connector module  210  may be, for example, a lightning protector module. It is noted, as shown in  FIG. 2 , that DLC  204 , as a source of sealing current, can also be a standard copper POTS line, or a sealing current DLC channel unit (CU) port. 
   DSLAM  214  provides DSL services to a computer system. DSLAM  214  is connected to DSL OSP connector module  220  via DSL line  216 . DSL OSP connector module  220  may also be, for example, a lightning protector module. DSLAM  214  includes DSL unit  214 A, for example, a SHDSL unit for providing SDSL services. 
   In accordance with an embodiment of the present invention, a sealing current derivation device  230  derives available sealing current from POTS line  206  and bridges POTS line  206  and DSL line  216 , thereby feeding sealing current to DSL line  216 . In one possible implementation, sealing current derivation device  230  is connected between DLC OSP connector module  210  and DSLAM OSP connector module  220 . In another possible implementation, sealing current derivation device  230  may be incorporated into one of the protector modules  210 ,  216  (albeit with wires still interconnecting the two separate paths  206  and  216 ). In other words, sealing current derivation device  230  may be incorporated into a well-known snap-in type protector module. 
     FIG. 3  shows a circuit diagram of main components of DLC OSP connector module  210 , DSLAM OSP connector module  220  and sealing current derivation device  230  according to an embodiment of the present invention. 
   DLC OSP connector module  210  consists of five connection lines: tip A  310  and ring B  312  for connecting to DLC  204 , tip C  314  and ring D  316  for connecting POTS telephone line, and GRD  318  for connecting to ground. 
   Similarly, DSLAM OSP connector module  220  consists of five connection lines: tip E  320  and ring F  322  for connecting to DSLAM  214 , tip G  324  and ring H  326  for connecting to the computer system, and GRD  328  for connecting to ground. 
   Sealing current derivation device  230  preferably includes appropriate circuitry  334  for removing any AC component from POTS line  206  (i.e., tip and ring  310 ,  312 ). Circuitry  334  preferably also includes any necessary impedance matching circuitry, current limiters, and POTS line isolation circuitry; all of which are well-known in the telephony art. 
   As shown, sealing current derivation device  230  is connected to DLC OSP connector module  210  such that sealing current derivation device  230  bridges tip A  310  via wire  350  and ring B  312  via wire  352  to tip E  320  via wire  354  and ring F  322  via wire  356 . 
   With the bridging circuitry depicted in  FIG. 3  that is provided by sealing current derivation device  230 , it is possible to provide desirable sealing current to DSL service line  216  without having to install a separate sealing current device to service the DSL line  216 . 
     FIG. 4  shows a schematic diagram according to a second embodiment of the present invention. Sealing current device  404  is provided as a plug-in circuit module to a conventional rack-mounted DLC channel bank. Sealing current device  404  may include multiple sealing current circuits whereby sealing current is provided to a plurality of DSL lines. In a typical use, sealing current device  404  is inserted in a slot of conventional DLC channel unit  402 . 
     FIG. 4A  shows a circuit diagram of main components of sealing current device  404  according to the second embodiment of the present invention. In  FIG. 4A , sealing current device  404  includes N number of sealing current circuits, wherein each of the sealing current circuits consists of a single twisted-pair line. More specifically, sealing current circuit  406  consists of twisted-pair lines  412 . Each line  412  provides a source of sealing current. Thus, as is readily seen in  FIG. 4A  sealing current circuit  406  provides sealing current on a pair of wires  412  similar to sealing current provided on a POTS or DLC POTS lines  206 . Sealing current circuit  406  may also include, as appropriate, current limiting resistor  410  to limit the amount of sealing current that is fed to any selected circuit and impedance matching circuit  411 . 
   Sealing current derivation device  230  can then be connected to sealing current circuit  412 , as an alternative to connecting sealing current derivation device  230  to a POTS or DLC POTS line  206 , to derive the sealing current for the DSL service line  216  without having to install a traditional sealing current unit. 
     FIG. 5  shows a circuit diagram of main components of a sealing current device according to a third embodiment of the present invention. In this embodiment, sealing current is derived from a device located on the customer&#39;s premises. Here, the device is an AC-DC transformer  504  that may be provided within a customer-side modem. In this case, sealing current will actually flow in a direction opposite to the conventional direction. That is, unlike the two previous embodiments (and conventional POTS line sealing current) where sealing current is sourced from the telecommunications provider facilities, the sealing current in this embodiment is sourced from the customer premises and fed in the direction of a remote terminal  502  or similar facility. 
   As shown, an AC-DC transformer, located externally, or internally inside the customer&#39;s computer modem, provides the sealing current to the DSL OSP twisted pair wires between the customer&#39;s DSL modem and the DSLAM&#39;s OSP connector module  502 . The lightning surge arrestor installed in the DSLAM&#39;s OSP connector module  502  will include the circuitry necessary to provide a path to ground the sealing current and pass through the DSL signal, as well as provide the DSLAM equipment with foreign voltage and lighting protection. 
   In yet another embodiment, the AC-DC transformer can be designed to provide one or more sources of DC sealing current similar to DLC CU derived sealing current unit  404 , described as the second embodiment of the present invention. The AC-DC transformer can be installed at either the customer or the telephone company location. The AC-DC transformer provides the source of the sealing current on a pair of wires, with the same characteristics as described for DLC channel unit derived sealing current circuit  412 . 
   Derived sealing current device  230  can be used to bridge the DC sealing current provided by the AC-DC transformer circuit to the DSL line as another option for bridging the sealing current to a POTS line. This alternative also eliminates the need to install a traditional sealing current device. 
   As will be appreciated by those skilled in the art, the present invention can be used in remote solutions environments to enable optional application of sealing current on Non-Switched Special Service lines, ISDN lines and SDSL lines. 
   The foregoing disclosure of the preferred embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents. 
   Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.