`De Nicolo
`
`USOO6115468A
`Patent Number:
`11
`(45) Date of Patent:
`
`6,115,468
`Sep. 5, 2000
`
`54) POWER FEED FOR ETHERNET
`TELEPHONES VIA ETHERNET LINK
`
`75 Inventor: Maurilio Tazio De Nicolo, Saratoga,
`Calif.
`73 Assignee: Cisco Technology, Inc., San Jose, Calif.
`
`21 Appl. No.: 09/048,922
`22 Filed:
`Mar 26, 1998
`9
`(51) Int. Cl." ....................................................... H04B 3700
`52 U.S. Cl. .......................... 379/413; 379/412; 379/900;
`379/324; 375/258; 375/257; 375/285
`58 Field of Search ..................................... 379/413, 412,
`379/900, 324; 375/285,257, 258
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,723,267 2/1988 Jones et al. ............................... 379/93
`5,285.477 2/1994 Leonowich ...
`... 375/258
`5,311,518 5/1994 Takato et al. .
`370/110.1
`5,541,957 7/1996 Lau ......................................... 375/258
`
`5,574,748 11/1996 Vander Mey et al................... 375/204
`5,799,040 8/1998 Lau ......................................... 375/258
`5,994,998 11/1999 Fisher et al. ....................... 340/310.01
`Primary Examiner David R. Hudspeth
`Assistant Examiner Vijay B Chawan
`Attorney, Agent, or Firm-D’Alessandro & Ritchie
`57
`ABSTRACT
`An Ethernet device power transmission System includes an
`input transformer, an output transformer and a pair of
`twisted pair conductors. The input transformer includes a
`pair of primaries for connection to a Source of Ethernet data.
`The input transformer also includes a pair of Secondaries,
`each having a center-tap. A first twisted pair conductor is
`connected across the first Secondary, a Second twisted pair
`conductor is connected across the Second Secondary and a
`DC-bias is provided between the respective center taps of
`the first and Second Secondaries. At the local end, the output
`transformer includes a first and Second center-tapped pri
`mary and a first and Second Secondary for connection to the
`load device. The first and Second primary center taps are
`connected to a power processor for extraction of DC power.
`
`17 Claims, 3 Drawing Sheets
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`49
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`PROCESSOR
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`144
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`132
`116 148
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`POWER
`SUPPLY
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`148a
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`110
`106 86
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`1
`POWER FEED FOR ETHERNET
`TELEPHONES VIA ETHERNET LINK
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`6,115,468
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`2
`At the telephone end of the twisted-pair link 28, a
`similarly structured transformer 58 receives the data signal
`as well as the DC bias. First primary 60 and second primary
`62 are AC-coupled with capacitor 64 so as to be able to
`couple data Signals from twisted-pair link 28 with trans
`former 58 while holding off a DC bias. The DC bias of
`twisted-pair link 28 is applied to a power processor 66 and
`from there provides to local equipment to be powered by the
`twisted pair System. A typical embodiment of a power
`processor 66 is shown in FIG. 2. It comprises a filter 68, a
`rectifier 70, a filter capacitor 72 and a DC-DC converter 74.
`While fit for its intended purpose, the above-described
`System has Some drawbacks which make it a less than ideal
`choice for an Ethernet environment. For example, each
`secondary 42 and 44 of transformer 34 and each primary 60
`and 62 of transformer 58 will experience a net current flow
`equal to the total amount of current drawn by the load at the
`distal end of the twisted-pair link. This current will affect the
`choice of transformer core size at each end of the link and
`will affect the choice of wire gauge used for the link.
`It would be desirable to provide an improved method and
`apparatus for powering Ethernet telephones over a 4-wire
`link. Such a System would be able to take advantage of
`existing wiring without the need to rewire the premises to
`install Such devices. Furthermore, by providing power over
`the Ethernet connection, power transformers are not
`required at the device location, and a central uninterruptible
`power Supply is made possible to provide power to the entire
`telephone System in case of a power failure.
`SUMMARY OF THE INVENTION
`An Ethernet device power transmission System provides
`electrical power to devices Such as Ethernet telephones and
`related equipment over a 4-wire Ethernet connection without
`any need for rewiring premises having an existing 4-wire
`Ethernet System. The System eliminates any requirement for
`local power Such as transformers to power Such equipment
`as all power can be provided over the existing Ethernet
`wiring. A central uninterruptible power supply (UPS) is
`thereby made possible to provide back-up power to all Such
`equipment. The System includes an input transformer, an
`output transformer and a pair of twisted pair conductors. The
`input transformer includes a pair of primaries for connection
`to a Source of Ethernet data. The input transformer also
`includes a pair of Secondaries, each having a center-tap. A
`first twisted pair conductor is connected across the first
`Secondary, a Second twisted pair conductor is connected
`acroSS the Second Secondary and a DC-bias is provided
`between the respective center taps of the first and Second
`Secondaries. At the local end, the output transformer
`includes a first and Second center-tapped primary and a first
`and Second Secondary for connection to the load device. The
`first and Second primary center taps are connected to a power
`processor for extraction of DC power.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is an electrical Schematic diagram of a prior art
`telephone power distribution System for use over a two-wire
`twisted pair System.
`FIG. 2 is an electrical Schematic diagram of a prior art
`telephone power extraction System or power processor.
`FIG. 3 is an electrical Schematic diagram of an Ethernet
`telephone power distribution System according to a presently
`preferred embodiment of the present invention.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`Those of ordinary skill in the art will realize that the
`following description of the present invention is illustrative
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention is directed to a method and appa
`ratus which provide electrical power to ethernet-based tele
`phones over an ethernet wire link.
`2. The Background Art
`Telephones require electrical power in order to operate.
`The power can be delivered over the telephone lines or via
`a separate power connection, typically through a power
`transformer connected to the electrical power grid. Tele
`phones powered in the latter fashion will be inoperable
`during a power failure unless provision is made both locally
`at the telephone and at the PBX or local telephone Switch for
`emergency power to be Supplied. While it is normal to
`provide an uninterruptible power Supply to an office's PBX
`or telephone Switch, it is not desirable for cost and other
`reasons to provide electrical power back up Systems to each
`telephone location. In the past, the power problem was
`frequently Solved by using an 8-wire telephone connection
`to the telephone Switch. With 8 wires there is more than
`enough capability for analog audio digital and power con
`nections to the telephone Switch.
`The growth of the Internet and similar local and wide area
`networks based on Ethernet technology has created a poten
`tial market for telephone Systems which would connect
`directly to existing Ethernet connections. The Ethernet
`protocol, however, does not provide a mechanism for pow
`ering Such telephones. A typical Ethernet connection to an
`office location would include a pair of unshielded twisted
`pair (UTP) lines for a total of four conductors-one pair for
`transmit, one for receive. The transmit pair is dedicated to
`Send packets of data over the Ethernet connection; the
`receive pair receives packets of data over the Ethernet
`connection. Simply placing a DC bias on two or more of
`these conductors and using the bias to power a local Ethernet
`telephone is risky because the bias is not part of the Ethernet
`protocol and might damage Ethernet compliant equipment
`not designed to handle Such a bias.
`Turning to FIGS. 1 and 2, a prior art scheme for providing
`power over a Single twisted pair connection is shown. In the
`prior art, system 10 and power supply 11 provides DC power
`over lines 12 (positive lead) and 14 (negative lead) to a
`series of ports on the network. Filter capacitor 16 and filter
`inductors 18 and 20 are preferably provided to insure a clean
`Source of DC power and to avoid AC cross-talk between the
`network and the power Supply. Each port 22, 24 and 26 of
`the network is coupled to a twisted pair link 28, 30 and 32,
`respectively, via a transformer, 34, 36, and 38, respectively.
`Transformer 34, for example, operates as follows: Data on
`port 1 (22) is applied to the primary 40 of transformer 34 and
`coupled to a pair of Secondary winding 42, 44 of transformer
`34 through transformer core 46 in a conventional manner.
`One end 48 of secondary winding 42 is connected to twisted
`pair 28 and the other end 50 of secondary winding 42 is
`connected to the positive lead 12 of power supply 11. One
`end 52 of Secondary winding 44 is connected to twisted pair
`link 28 and the other end 54 of secondary winding 44 is
`connected to the negative lead 14 of power Supply 11. Leads
`50 and 54 are AC-coupled to one another with capacitor 56
`as shown. This blocks DC current from flowing and allows
`a DC bias to be established over the two conductors of
`twisted pair link 28 while simultaneously allowing the flow
`of data over the link.
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`only and is not intended to be in any way limiting. Other
`embodiments of the invention will readily Suggest them
`Selves to Such skilled perSons from an examination of the
`within disclosure.
`Turning now to FIG. 3, in accordance with a presently
`preferred embodiment of the present invention, a System
`including a plurality of data ports 80, 82, 84 is provided to
`transmit data on lines 86, 88,90, 92,94, 96 to and from load
`devices 1 (98), 2 (100) and 3 (102). Load devices 98, 100
`and 102 may be Ethernet telephones and/or other Ethernet
`devices requiring power to be transmitted to them in addi
`tion to data over Ethernet twisted pair lines.
`Turning to Port 1 (80) as an example, data on lines 88 and
`86 is provided to transmitter 104 and from receiver 106,
`respectively. Transmitter 104 drives twisted pair 108.
`Receiver 106 receives from twisted pair 110. First trans
`former 112 includes a first primary 114 and a Second primary
`116. First primary 114 is connected to twisted pair 108 and
`second primary 116 is connected to twisted pair 110.
`At load 98 a similar arrangement exists. Second trans
`former 118 includes a first secondary 120 and a second
`Secondary 122. These are respectively connected to twisted
`pairs 124 and 126 which are, in turn, connected through
`receiver 125 and transmitter 127 to load device 98.
`Ethernet link 128 couples first and second secondaries
`130, 132 of first transformer 112 to first and second prima
`ries 134, 136 of second transformer 118. Ethernet link 128
`preferably comprises a pair of twisted pair conductors 128a
`and 128b wherein twisted pair 128a connects first secondary
`130 to first primary 134 of the twisted pair 128b connects
`second secondary B2 to several primary 136.
`Power coupling is provided as follows. Secondaries 130
`and 132 of first transformer 112 each include a center tap,
`138, 140 respectively. Center tap 138 is connected to the
`positive lead 142 of a power supply 144 and center tap 140
`is connected to the negative lead 146 of power supply 144
`which may preferably be an uninterruptible power Supply
`(UPS). DC filtering components 148a, 148b, 148c may be
`provided as well known to those of ordinary skill in the art.
`Now the entire loop of twisted pair 128a is at the potential
`of positive lead 142 while the entire loop of twisted pair
`128b is at the potential of negative lead 146. A power
`processor 149, as in FIG. 2, may preferably be attached to
`center taps 150, 152, respectively, of first and second pri
`maries 134 and 136 of second transformer 118 So as to
`provide a DC power source to power processor 149. Power
`processor 149 performs any DC-DC power conversion and
`filtering required and provides power over leads 154, 156 to
`load 98 which may be an Ethernet telephone or other device.
`The present invention provides a number of advantages
`over the prior art. First, power delivered to the load device
`is split equally over four wires rather than two reducing the
`current carrying requirements of all four wires over a two
`wire System delivering the Same amount of power. Second,
`because the transmitted power is applied at and removed at
`center taps, there is no net current flow due to the DC bias
`through either primary or Secondary of each respective
`twisted pair 128a, 128b. This reduces the size requirements
`for the transformer 112, 118 core over a system with a net
`current, as in the system of FIG.1. This permits off-the-shelf
`transformers for Ethernet applications to be used maintain
`ing compatibility with Ethernet Systems not having this
`power delivery requirement. Note that if the prior art System
`of FIG. 1 were used with a load device lacking decoupling
`between the two primaries on the network side of the
`transformer, the power supply would be effectively shorted.
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`In the System according to FIG. 3, as long as the Separate
`data channels are not shorted (which would not normally
`occur), any interface can be used on the load Side of the
`network whether it makes use of the power available there
`Or not.
`Alternative Embodiments
`Although illustrative presently preferred embodiments
`and applications of this invention are shown and described
`herein, many variations and modifications are possible
`which remain within the concept, Scope, and Spirit of the
`invention, and these variations would become clear to those
`of skill in the art after perusal of this application. In
`particular, the use of the term primary and Secondary in
`referring to transformer windings herein is for explanation
`only. AS the links are bi-directional, the terms primary and
`Secondary may be interchanged as would be known to those
`of ordinary skill in the art. The invention, therefore, is not to
`be limited except in the Spirit of the appended claims.
`What is claimed is:
`1. A power feed System for Ethernet telephones, Said
`System comprising:
`a first transformer including a first primary, a Second
`primary, a first Secondary with a first center-tap and a
`Second Secondary with a Second center-tap, Said first
`primary for coupling to a first pair of conductors, Said
`Second primary for coupling to a Second pair of con
`ductors,
`a Second transformer including a first primary with a first
`center-tap, a Second primary with a Second center-tap,
`a first Secondary and a Second Secondary, Said first and
`Second Secondaries for coupling to an Ethernet tele
`phone,
`an Ethernet link including a third pair of conductors is and
`a fourth pair of conductors, Said third pair of conductors
`connecting Said first Secondary of Said first transformer
`with Said first primary of Said Second transformer and
`Said fourth pair of conductors connecting Said Second
`Secondary of Said first transformer with Said Second
`primary of Said Second transformer;
`a direct current power Supply having a first output poten
`tial on a first line and a Second output potential different
`from Said first output potential on a Second line, Said
`first line connected to Said first center-tap of Said first
`transformer and Said Second line connected to Said
`Second center-tap of Said first transformer,
`a first potential input of an Ethernet telephone coupled to
`Said first center-tap of Said Second transformer; and
`a Second potential input of an Ethernet telephone coupled
`to Said Second center-tap of Said Second transformer.
`2. A power feed System for Ethernet telephones according
`to claim 1, wherein Said third pair of conductors is a twisted
`pair.
`3. A power feed System for Ethernet telephones according
`to claim 2, wherein Said fourth pair of conductorS is a twisted
`pair.
`4. A power feed System for Ethernet telephones according
`to claim 3, wherein Said first pair of conductorS is a twisted
`pair.
`5. A power feed System for Ethernet telephones according
`to claim 4, wherein Said Second pair of conductorS is a
`twisted pair.
`6. A System for Supplying DC power to a remote device,
`Said System comprising:
`a first transformer including a first primary, a Second
`primary, a first Secondary with a first center-tap and a
`Second Secondary with a Second center-tap, Said first
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`primary for coupling to a first pair of conductors, Said
`Second primary for coupling to a Second pair of con
`ductors,
`a Second transformer including a first primary with a first
`center-tap, a Second primary with a Second center-tap,
`a first Secondary and a Second Secondary, Said first and
`Second Secondaries for coupling to the remote device;
`an Ethernet link including a third pair of conductors and
`a fourth pair of conductors, Said third pair of conductors
`connecting Said first Secondary of Said first transformer
`with Said first primary of Said Second transformer and
`Said fourth pair of conductors connecting Said Second
`Secondary of Said first transformer with Said Second
`primary of Said Second transformer;
`a direct current power Supply having a first output poten
`tial on a first line and a Second output potential different
`from Said first output potential on a Second line, Said
`first line connected to Said first center-tap of Said first
`transformer and Said Second line connected to Said
`Second center-tap of Said first transformer,
`a first potential input of the remote device coupled to Said
`first center-tap of Said Second transformer, and
`a Second potential input of the remote device coupled to
`Said Second center-tap of Said Second transformer.
`7. A System according to claim 6, wherein Said third pair
`of conductorS is a twisted pair.
`8. A System according to claim 7, wherein Said fourth pair
`of conductorS is a twisted pair.
`9. A System according to claim 8, wherein Said first pair
`of conductorS is a twisted pair.
`10. A System according to claim 9, wherein Said Second
`pair of conductorS is a twisted pair.
`11. A System for transmitting data and a DC Signal
`Simultaneously between a first device and a Second device,
`Said System comprising:
`a first transformer including a first primary, a Second
`primary, a first Secondary with a first center-tap and a
`Second Secondary with a Second center-tap, Said first
`primary for coupling to a first pair of conductors over
`which a first data Signal is to be communicated with the
`first device, Said Second primary for coupling to a
`Second pair of conductors over which a Second data
`Signal is to be communicated with the first device;
`a Second transformer including a first primary with a first
`center-tap, a Second primary with a Second center-tap,
`a first Secondary and a Second Secondary, Said Second
`ary for coupling to a third pair of conductors over
`which Said first data Signal is to be communicated with
`the Second device, and Said Second Secondary for
`coupling to a fourth pair of first conductors over which
`Said Second data Signal is to be communicated with the
`Second device;
`a link including a fifth pair of conductors and a sixth pair
`of conductors, Said fifth pair of conductors connecting
`said first secondary of said first transformer with said
`first primary of Said Second transformer and Said Sixth
`pair of conductors connecting Said Second Secondary of
`Said first transformer with Said Second primary of Said
`Second transformer;
`a direct current power Supply associated with the first
`device having a first output potential on a first line and
`a Second output potential different from Said first output
`potential on a Second line, Said first line connected to
`Said first center-tap of Said first transformer and Said
`Second line connected to Said Second center-tap of Said
`first transformer;
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`a first potential input of the Second device coupled to Said
`first center-tap of Said Second transformer, and
`a Second potential input of the Second device coupled to
`Said Second center-tap of Said Second transformer.
`12. A method for Supplying a DC power connection and
`a bi-directional data connection to a remote device, Said
`bi-directional data connection including a first data Signal
`and a Second data Signal, Said method comprising:
`transmitting the first data Signal to a first primary winding
`of a first transformer;
`receiving the Second data Signal from a Second primary
`winding of Said first transformer;
`transmitting the first data Signal from a first Secondary
`winding of Said first transformer to a first primary
`winding of a Second transformer;
`transmitting the Second data Signal from a Second primary
`winding of Said Second transformer to a Second Sec
`ondary winding of Said first transformer;
`transmitting the first data Signal to the device over a first
`Secondary winding of Said Second transformer;
`receiving the Second data Signal from the device over a
`Second Secondary winding of Said Second transformer;
`applying a DC signal between a center-tap of Said first
`Secondary winding of Said first transformer and a
`center-tap of Said Second Secondary winding of Said
`first transformer;
`extracting a DC Signal from a center-tap of Said first
`primary winding of Said Second transformer and a
`center-tap of Said Second primary winding of Said
`Second transformer; and
`applying Said DC Signal to the remote device.
`13. A power feed System for Ethernet telephones, said
`System comprising:
`first coupling means for coupling a first conductor of a
`first pair of conductors to a first winding of a first
`transformer;
`Second coupling means for coupling a Second conductor
`of Said first pair of conductors to a Second winding of
`Said first transformer;
`third coupling means for coupling a first conductor of a
`Second pair of conductors to a first winding of a Second
`transformer;
`fourth coupling means for coupling a Second conductor of
`Said Second pair of conductors to a Second winding of
`Said Second transformer;
`fifth coupling means for coupling a first and Second
`conductor, respectively, of an Ethernet telephone to
`Said first and Second conductor of Said Second pair of
`conductors,
`a first and Second center-tapped winding disposed in Said
`first transformer, each said winding having a first
`conductor, a Second conductor and a center-tap con
`ductor;
`a first and Second center-tapped winding disposed in Said
`Second transformer, each Said winding having a first
`conductor, a Second conductor and a center-tap con
`ductor;
`means for connecting Said first conductor of Said first
`center-tapped winding of Said first transformer to Said
`first conductor of Said Second center-tapped winding of
`Said Second transformer;
`means for connecting Said Second conductor of Said first
`center-tapped winding of Said first transformer to Said
`Second conductor of Said Second center-tapped winding
`of Said Second transformer;
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`means for applying a power signal to Said first center-tap
`conductor and Said Second center-tap conductor of Said
`first transformer;
`means for extracting a power Signal from Said first center
`tap conductor and Said Second center-tap conductor of
`Said Second transformer and for applying Said extracted
`power Signal to Said Ethernet telephone.
`14. A System for Supplying DC power to a remote device,
`Said System comprising:
`first coupling means for coupling a first conductor of a
`first pair of conductors to a first winding of a first
`transformer;
`Second coupling means for coupling a Second conductor
`of Said first pair of conductors to a Second winding of
`Said first transformer;
`third coupling means for coupling a first conductor of a
`Second pair of conductors to a first winding of a Second
`transformer;
`fourth coupling means for coupling a Second conductor of
`Said Second pair of conductors to a Second winding of
`Said Second trans former;
`fifth coupling means for coupling a first and Second
`conductor, respectively, of the remote device to Said
`first and Second conductor of Said Second pair of
`conductors,
`a first and Second center-tapped winding disposed in Said
`first transformer, each said winding having a first
`conductor, a Second conductor and a center-tap con
`ductor;
`a first and Second center-tapped winding disposed in Said
`Second transformer, each Said winding having a first
`conductor, a Second conductor and a center-tap con
`ductor;
`means for connecting Said first conductor of Said first
`center-tapped winding of Said first transformer to Said
`first conductor of Said Second center-tapped winding of
`Said Second transformer;
`means for connecting Said Second conductor of Said first
`center-tapped winding of Said first transformer to Said
`Second conductor of Said Second center-tapped winding
`of Said Second transformer;
`means for applying a power Signal to Said first center
`tapped conductor and Said Second center-tapped con
`ductor of Said first transformer;
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`means for extracting a power Signal from Said first center
`tap conductor and Said Second center-tap conductor of
`Said Second transformer and for applying Said extracted
`power Signal to the remote device.
`15. A method for supplying DC power to a remote device
`over a 4-wire Ethernet connection having a first twisted pair
`of conductors for transmission of data packets from Said
`remote device and a Second twisted pair of conductors for
`reception of data packets at Said remote device, the method
`comprising:
`applying a first polarity of the DC power to a center tap
`of a first transformer winding connected acroSS a distal
`end of the first twisted pair of conductors;
`applying a Second polarity of the DC power to a center tap
`of a Second transformer winding connected acroSS a
`distal end of the Second twisted pair of conductors,
`extracting Said first polarity from a center tap of a third
`transformer winding connected acroSS a proximal end
`of the first twisted pair of conductors, and
`extracting Said Second polarity from a center tap of a
`fourth transformer winding connected acroSS a proxi
`mal end of the Second twisted pair of conductors.
`16. A System for Supplying DC power to a remote device
`over a 4-wire Ethernet connection having a first twisted pair
`of conductors for transmission of data packets from Said
`remote device and a Second twisted pair of conductors for
`reception of data packets at Said remote device, the System
`comprising:
`means for applying a first polarity of the DC power to a
`center tap of a first transformer winding connected
`acroSS a distal end of the first twisted pair of conduc
`tors,
`means for applying a second polarity of the DC power to
`a center tap of a Second transformer winding connected
`acroSS a distal end of the Second twisted pair of
`conductors,
`means for extracting Said first polarity from a center tap
`of a third transformer winding connected acroSS a
`proximal end of the first twisted pair of conductors, and
`means for extracting Said Second polarity from a center
`tap of a fourth transformer winding connected acroSS a
`proximal end of the Second twisted pair of conductors.
`17. A System according to claim 16 further comprising an
`uninterruptible power Supply for Sourcing the DC power.
`
`k
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`k
`
`k
`
`k
`
`k
`
`8
`
`CISCO 1029
`Cisco v. ChriMar
`
`