Abstract:
A system, method, and computer readable medium for a metallic test method in a digital subscriber line system in which a subscriber&#39;s voice service has been switched from plain old telephony service to an inband digital subscriber line data stream characterized in that a direct current loop current used for plain old telephony service is replicated for testing, comprising, providing a sealing line current to a transmission line via a digital subscriber line device serving the subscriber and supervising the provided sealing line current between the digital subscriber line device and a subscriber&#39;s premises for determining a connectivity therebetween.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention is generally related to utilization of sealing current on Digital Subscriber Lines (DSL) without Plain Old Telephony Service (POTS) to test metallic line integrity and, more specifically, to an autonomous metallic supervision with sealing current of DSL lines without underlying POTS.  
         [0002]     With the increase in use of cellular phones and Voice over Internet Protocol (VoIP), many residences and other users are discontinuing their use of POTS. DSL was initially created to be used in conjunction with POTS, where POTS utilized the frequency band below 4 Kilo Hertz (KHz) and DSL utilized the frequency band above 4 kHz. POTS utilizes a sealing or wetting current which is a direct current injected into a line to prevent galvanic corrosion of metallic (copper) lines and to prevent oxidation at splices. With the switch by residences to utilize DSL without underlying POTS, the benefits of the sealing or wetting current built into POTS is no longer present. Such a use of DSL without underlying POTS is referred to as dry DSL as there is no wetting current injected into the line.  
         [0003]     Therefore, what is needed is dry DSL metallic connectivity testing with sealing current. More specifically, what is needed is autonomous metallic supervision with sealing current of DSL lines without underlying POTS that overcomes the limitations described above. The present invention injects a wetting (sealing) current into dry DSL lines to allow measurement of Direct Current (DC) loop resistances and to provide the benefits of corrosion and oxidation resistance previously only enjoyed from utilizing POTS. The measurement of DC loop resistance allows insight into metallic connectivity integrity of the dry DSL connection.  
       SUMMARY OF THE INVENTION  
       [0004]     POTS utilizes sealing current to prevent corrosion and oxidation of metallic lines and splices. POTS inherently provides wetting current by means of an off-hook loop current. Sealing current is alternatively termed wetting current. Sealing current is the minimum amount of electric current necessary to keep mechanical switch contacts from undergoing galvanic corrosion. Sealing current reduces oxidation at line splices and reduces galvanic corrosion which causes contacts to gain excessive resistance and prematurely fail. The sealing current is direct current injected into the line. POTS termination devices such as Subscriber Line Integrated Circuits (SLICs) measure loop impedance in order to detect ON/OFF hook. Measuring a Direct Current (DC) loop resistance is part of normal POTS operation.  
         [0005]     Digital Subscriber Line Access Multiplexers (DSLAMs) designed as an overlay for existing POTS networks, typically consist of DSL transceivers and POTS splitters. The POTS splitter consists of a High Pass (HP) and a Low Pass (LP) filter. The POTS splitter is designed to separate narrow band voice and broad band DSL signals and avoid interference. The high pass filter is situated between the twisted pair and the DSL transceiver while the low pass filter is situated between the POTS and narrow band Message Listener Type (MLT) test equipment and the telephone line.  
         [0006]     The present invention is a cost effective methodology to ensure metallic connection from DSLAMs to customer premises by reusing sealing current infrastructure. Verifying a proper metallic connection from DSLAMs to customer premises is implicitly done during DSL Showtime. DSL Showtime is used to describe a scenario where a user and a network can begin communications over an access network. In instances where DSL Showtime is not possible, another technique would be required to diagnose if a problem that occurred was related to metallic issue. One method of diagnosing a metallic issue is to add a test signature at the customer premises. Test heads at a central office (CO) are typically capable of detecting this type of signature and thus provide feedback on metallic connectivity from the test head to the demarcation point at the customer premises where the test signature is installed. Asymmetric Digital Subscriber Line (ADSL) and Very High Rate Digital Subscriber Line (VDSL) circuitry is inserted into the line via a high pass filter and has no visibility to DC. Therefore it can not measure DC loop resistance like POTS SLICs can.  
         [0007]     Adding a test signature at the customer premises adds cost and requires a test head to detect it. DSL can also operate in an environment where the underlying POTS is no longer present. In such a scenario, also known as Dry DSL, voice services can for instance be delivered inband the DSL data stream via technologies such as Voice over Internet Protocol (VoIP). By removing POTS from the line, the DC loop current that is part of normal POTS operation disappears. In the present invention, dry DSL DC loop current is provided to seal the line and prevent corrosion.  
         [0008]     Further, in the present invention the DSLAM provides sealing current for dry DSL lines to additionally perform the metallic connectivity test by measuring the loop current from the Sealing Current source (SC) to the Sealing Termination (ST). If the measured current is too low, then the DC resistance is too high, indicating a problem. Every time sealing current is applied to a line, the measurement can be applied. Consequently, an applied sealing current will implicitly provide a metallic connectivity check. Detected problems can be reported to a central office via autonomous alarms. Upon such notification, the CO can decide whether further investigation is required and issue a standard metallic test procedure.  
         [0009]     The present invention also provides a method to report metallic faults autonomously without additional hardware cost, to autonomously report metallic faults without the need for regular testing by a test head. Further, no additional cost are added to DSLAMs that already support sealing current. As VoIP technologies mature, DSL speeds increase and Class 5 switches age, VoIP will become a more viable alternative to POTS and Dry DSL lines will need to support sealing current.  
         [0010]     In one embodiment of the present invention, a metallic test method in a digital subscriber line system in which a subscriber&#39;s voice service has been switched from plain old telephony service to an inband digital subscriber line data stream, wherein a direct current loop current used for plain old telephony service is replicated for testing, comprises: providing a sealing line current to a transmission line via a digital subscriber line device serving the subscriber and supervising the provided sealing line current between the digital subscriber line device and a subscriber&#39;s premises for determining a connectivity therebetween. The system may measure a leakage current of the supervised sealing line current, measure a return voltage of the supervised sealing line current and measure a loop resistance between the digital subscriber line device and the subscriber&#39;s premises. The sealing current may be provided continuously, intermittently or during periods when the digital subscriber line device is utilized during the subscriber&#39;s voice service. The method may also send an alert based upon the determined connectivity.  
         [0011]     In another embodiment of the present invention, a method of testing metallic integrity of a transmission line of a dry digital subscriber line system, comprising: providing a sealing line current to the transmission line and measuring a loop resistance of the transmission line to determine a connectivity of the transmission line. The sealing line current may be direct current. The method may additionally measure a leakage current of the transmission line and a return voltage of the transmission line. The sealing current may be provided continuously, intermittently or during periods when the digital subscriber line device is utilized during the subscriber&#39;s voice service. The method may also send an alert based upon the determined connectivity.  
         [0012]     In a further embodiment of the present invention, a computer readable medium comprises instructions for: providing a sealing line current from a digital subscriber line access multiplexer to a transmission line of a dry digital subscriber line and measuring a loop resistance from the digital subscriber line access multiplexer to a subscriber&#39;s premises. The computer readable medium may provide instructions for determining a connectivity of the transmission line based upon the measured loop resistance, for measuring a leakage current of the transmission line, for measuring a return voltage of the transmission line and for sending an alert based upon the measured loop resistance.  
         [0013]     In yet a further embodiment, a system adapted to provide testing metallic integrity of a transmission line of a dry digital subscriber line system, comprises: a digital subscriber line access multiplexer coupled to the transmission line and a sealing line current source coupled to the digital subscriber line access multiplexer. The sealing current may be direct current. The system may include a low pass filter connected to the sealing line current source, a sealing termination coupled to the transmission line, a resistance measurement device coupled to the transmission line to measure a loop resistance, a voltage measurement device coupled to the transmission line to measure a return voltage and a current measurement device coupled to the transmission line to measure a leakage current.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  depicts a system adapted to provide testing metallic integrity of a transmission line of a dry digital subscriber line system in accordance with a preferred embodiment of the present invention;  
         [0015]      FIG. 2  depicts a first method of testing metallic integrity of a transmission line of a dry digital subscriber line system in accordance with a preferred embodiment of the present invention;  
         [0016]      FIG. 3  depicts a second method of testing metallic integrity of a transmission line of a dry digital subscriber line system in accordance with a preferred embodiment of the present invention;  
         [0017]      FIG. 4  depicts a third method of testing metallic integrity of a transmission line of a dry digital subscriber line system in accordance with a preferred embodiment of the present invention;  
         [0018]      FIG. 5  depicts a fourth method of testing metallic integrity of a transmission line of a dry digital subscriber line system in accordance with a preferred embodiment of the present invention;  
         [0019]      FIG. 6  depicts a first software flow block of testing metallic integrity of a transmission line of a dry digital subscriber line system in accordance with a preferred embodiment of the present invention;  
         [0020]      FIG. 7  depicts a second software flow block of testing metallic integrity of a transmission line of a dry digital subscriber line system in accordance with a preferred embodiment of the present invention; and  
         [0021]      FIG. 8  depicts a third software flow block of testing metallic integrity of a transmission line of a dry digital subscriber line system in accordance with a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Referring now to  FIG. 1 , a method of testing  10  metallic integrity of a transmission line of a dry digital subscriber line system is depicted. The system shown is the dry DSL system in which the communication from a DSLAM to a customer&#39;s premises does not have an underlying POTS system. POTS utilizes a sealing (wetting) line current which is a direct current injected into the transmission line to prevent galvanic corrosion of metallic (copper) lines and to prevent oxidation at splices. This sealing line current is injected into the transmission line from a sealing line current source  12 . With the transition by many residences to utilize DSL without underlying POTS the benefits of the sealing or wetting current built into POTS is no longer present. The present invention injects the wetting (sealing) current into dry DSL lines to allow measurement of Direct Current (DC) loop resistances and to provide the benefits of corrosion and oxidation resistance previously only enjoyed from utilizing POTS.  
         [0023]     An Access Management System (AMS)  14  is communicably coupled to a Test Operating System (Test-OS)  16  and to the DSLAM  18 . DSLAMs were designed as overlay for existing POTS networks, typically consisting of a downstream DSL transceiver  20  and a downstream POTS splitter. The downstream POTS splitter consists of a downstream High Pass  22  (HP) and a downstream Low Pass (LP)  24  filter. The downstream POTS splitter is designed to separate narrow band voice, low frequency, and broad band DSL signals, high frequency, to avoid interference. The downstream high pass filter  22  is situated between the transmission line  26  (twisted pair) and the downstream DSL transceiver  20  while the downstream low pass filter  24  is situated between the transmission line  26  and the sealing line current source  12 . The transmission line  26  communicably couples the DSLAM  18  to the customer&#39;s premises. The transmission line  26  is coupled to an upstream high pass filter  32  which can communicate broad band signals to an IP configured devices 34  including a VoIP  36  capable device. The transmission line  26  is coupled to the upstream low pass filter  28  which terminates at a sealing termination  30 . These blocks or modules are software, hardware, firmware, and/or the combination of software, hardware, and/or firmware.  
         [0024]     The transfer of information between the DSLAM and the customer&#39;s premises occurs via at least one of the wireless protocol, the wired protocol and the combination of the wireless protocol and the wired protocol. For example, the presence infrastructure may be accessed by the cellular phone or the computer with external wireless capability (such as the wireless card) or internal wireless capability (such as 802.11 or any of the other 802 variants), or by the Internet Protocol enabled phone.  
         [0025]     Referring now to  FIG. 2 , the first method of testing  40  metallic integrity of the transmission line of the dry digital subscriber line system in accordance with the preferred embodiment of the present invention is depicted. The sealing current is provided  42  to the dry DSL line. The sealing current is supervised  44  between the DSLAM and the customer&#39;s premises to determine whether corrosion or the current leakage is occurring and an alert is sent  46  based upon the supervised sealing current. These blocks or modules are software, hardware, firmware, and/or the combination of software, hardware, and/or firmware. The transfer of information between the DSLAM and the customer&#39;s premises occurs via at least one of the wireless protocol, the wired protocol and the combination of the wireless protocol and the wired protocol.  
         [0026]     Referring now to  FIG. 3 , the second method of testing  50  metallic integrity of the transmission line of the dry digital subscriber line system in accordance with the preferred embodiment of the present invention is depicted. The sealing current is provided  52  to the dry DSL line. The sealing current is supervised  54  between the DSLAM and the customer&#39;s premises to determine whether corrosion or the current leakage is occurring and a leakage current is measured  56 . These blocks or modules are software, hardware, firmware, and/or the combination of software, hardware, and/or firmware. The transfer of information between the DSLAM and the customer&#39;s premises occurs via at least one of the wireless protocol, the wired protocol and the combination of the wireless protocol and the wired protocol.  
         [0027]     Referring now to  FIG. 4 , the third method of testing  60  metallic integrity of the transmission line of the dry digital subscriber line system in accordance with the preferred embodiment of the present invention is depicted. The sealing current is provided  62  to the dry DSL line. The sealing current is supervised  64  between the DSLAM and the customer&#39;s premises to determine whether corrosion or the current leakage is occurring and a return voltage is measured  66 . These blocks or modules are software, hardware, firmware, and/or the combination of software, hardware, and/or firmware. The transfer of information between the DSLAM and the customer&#39;s premises occurs via at least one of the wireless protocol, the wired protocol and the combination of the wireless protocol and the wired protocol.  
         [0028]     Referring now to  FIG. 5 , the fourth method of testing  70  metallic integrity of the transmission line of the dry digital subscriber line system in accordance with the preferred embodiment of the present invention is depicted. The sealing current is provided  72  to the dry DSL line. The sealing current is supervised  74  between the DSLAM and the customer&#39;s premises to determine whether corrosion or the current leakage is occurring and a loop resistance is measured  76 . These blocks or modules are software, hardware, firmware, and/or the combination of software, hardware, and/or firmware. The transfer of information between the DSLAM and the customer&#39;s premises occurs via at least one of the wireless protocol, the wired protocol and the combination of the wireless protocol and the wired protocol.  
         [0029]     The first computer readable medium of the method  80  of testing metallic integrity of the transmission line of the dry digital subscriber line is depicted. This algorithm is preferably embodied in the computer readable medium or software but may also be embodied in firmware and is utilized via hardware. The algorithm includes the steps of providing  82  the sealing current into the dry DSL transmission line and measuring  84  the loop resistance of the dry DSL transmission line to determine connectivity of the dry DSL transmission line.  
         [0030]     The second computer readable medium of the method  90  of testing metallic integrity of the transmission line of the dry digital subscriber line is depicted. This algorithm is preferably embodied in the computer readable medium or software but may also be embodied in firmware and is utilized via hardware. The algorithm includes the steps of providing  92  the sealing current into the dry DSL transmission line, measuring  94  the loop resistance of the dry DSL transmission line to determine connectivity of the dry DSL transmission line and measuring  96  the leakage current of the DSL transmission line.  
         [0031]     The third computer readable medium of the method  100  of testing metallic integrity of the transmission line of the dry digital subscriber line is depicted. This algorithm is preferably embodied in the computer readable medium or software but may also be embodied in firmware and is utilized via hardware. The algorithm includes the steps of providing  102  the sealing current into the dry DSL transmission line, measuring  104  the loop resistance of the dry DSL transmission line to determine connectivity of the dry DSL transmission line and measuring  106  the return voltage of the DSL transmission line.  
         [0032]     Although the exemplary embodiment of the system of the present invention has been illustrated in the accompanied drawings and described in the foregoing detailed description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit of the invention as set forth and defined by the following claims. For example, the capabilities of the invention can be performed fully and/or partially by one or more of the DSLAMs. Also, these capabilities may be performed in the current manner or in the distributed manner and on, or via, any device able to provide and/or receive broadband signals. Further, although depicted in the particular manner, various modules or blocks may be repositioned without departing from the scope of the current invention. For example, the functionality performed by the DSLAM can be self contained. Still further, although depicted in the particular manner, the greater or lesser number of customer&#39;s devices, DSLAMs, high pass filters, low pass filters and access management systems can be utilized with the present invention. Further, the lesser or greater number of DSLAMs may be utilized with the present invention and such DSLAMs may include known complementary functionality in order to accomplish the present invention, to provide additional known features to the present invention, and/or to make the present invention more efficient.