United States Patent [19J
`De Nicolo
`
`111111111111111111111111111111111111111111111111111111111111111111111111111
`US006115468A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,115,468
`Sep. 5,2000
`
`(54) POWER FEED FOR ETHERNET
`TELEPHONES VlA ETHERNET LINK
`
`[75]
`
`Inventor: Maur ilio Tazio De Nicolo, Saratoga,
`Calif.
`
`[73] As.signee: Cisco Technology, [nc., San Jose, Calif.
`
`[2!] Appl. No.: 09/048,922
`
`[22] Filed:
`
`Mar. 26, 1998
`
`Int. C l.7
`...................... . . ... . ...... . ... ....... .......... H04B 3/00
`[51]
`[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
`5,285,477
`5,311,518
`5,541,957
`
`2/ 1988 Jones et al. ............................... 379/93
`2/ 1994 leonowich .............................. 375!258
`5/1994 Takato et al. ........................ 370/110.1
`7/1996 Lau ......................................... 375!258
`
`5,574,748 11/1996 Vander Mey et al. .................. 375/204
`5,799,040
`8/1998 l..au ..................•...................... 375!258
`5,994,998 11/ 1999 Fisher et al. ...... ................. 340/310.01
`Primary Examiner-David R. Hudspeth
`AssislanL Examiner-Vijay B Chawan
`A/forney, Agent, or Firm-D' Alessandro & Ritchie
`(57]
`ABSTRACT
`
`An Etbcroet 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 fi rst 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 cod, the output
`transformer includes a first and second center-tapped pri(cid:173)
`mary and a first and second secondary for connection to the
`load device. The fi rst and second primary center taps are
`connected to a power processor fo r extraction of DC power.
`
`17 Claims, 3 Drawing Sheets
`
`149
`
`POWER
`PROCESSOR
`
`PORT1 T 80
`
`POAT2
`
`T
`
`82
`
`PORT3
`
`;
`
`84
`
`Page 1
` Dell Inc.
` Exhibit 1006
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`PHONE DATA 1
`
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`PHONE DATA3
`
`Page 2
`
`

`
`U.S. Patent
`
`Sep.S, 2000
`
`Sheet 2 of 3
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`6,115,468
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`
`Page 4
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`

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`6,115,468
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`1
`POWER FEEO FOR ETHERNET
`TELEPHONES VIA ETHERNET LINK
`
`IJACKGROUND OF TilE INVENTION
`
`1. Field of the Invention
`The present invention is directed to a method and appa(cid:173)
`ratus which provide electrical power to ethernet-based tele(cid:173)
`phones over an ethemet 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(cid:173)
`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 fo r
`emergency power to be supplied. While it is normal to
`provide an uni nterruptible power supply to an office's PBX
`or telephone switch, it is not desirable for cost and other 20
`reasons to provide e lectrica l 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(cid:173)
`nections to the telephone switch.
`The growth of the Internet and similar local and wide area
`networks based on Ethernet technology bas created a poten-
`tial market for telephone systems which would connect
`directly to existing Ethernet connections. The Ethernet 30
`protocol, however, does not provide a mechanism for pow(cid:173)
`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 35
`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 us ing the bias to power a local Ethernet
`telephone is risky because the bias is not part of the Ethernet 40
`protocol and might damage Ethernet compliant equipment
`not designed to handle such a bias.
`1\1rning to FIGS. 1 and 2, a prior art scheme for providing
`power over a sing le twisted pair connection is shown. In tbe
`prior art, system lO and power supply 11 provides DC power 45
`over I ines 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 so
`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 ss
`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 SO 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 60
`link 28 and the other end 54 of secondary winding 44 is
`connected to the negative lead 14 of power supply 11. Leads
`SO and 54 are AC-coupled to one another with capacitor 56
`as shown. This blocks DC current (rom flowing and allows
`a DC' bias to be established over the two conductors of 65
`twisted pair link 28 while simultaneously allowing the flow
`of data over the link.
`
`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(cid:173)
`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
`10 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 o f transformer 34 and each primary 60
`JS and 62 of trans former 58 will experience a oct current flow
`equa l to the total amou nt of current drawn by the load at the
`distal end o f the tw~'>ted -pair link. This current will affect the
`choice of transformer core s ize at each end of the link and
`will a[ect 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
`25 the Ethernet connection, power transformers are not
`required at the device location, and a central uninterrupti~le
`power supply is made possible to provide power to the enure
`telephone system in case of a power failure.
`SUMMARY OF 1l rE 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 baving an existing 4-wire
`Ethernet system. lne 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 pos.<>ible to provide back-up power to all such
`equipment. The system includes an input transformer, an
`output transformer and a pair of twisted 1>air conductors. The
`input trans former includes a pair of primaries for connection
`to a source of Ethernet data. The input transformer alo;o
`includes a pair o f secondaries, each having a center-tap. A
`first twisted pair conductor is connected across the first
`secondary, a second twis ted pair conductor is connected
`across the second secondary and a OC-bias is provided
`between the respective center taps of the first and second
`secondaries. At the loca I end, the output transformer
`includes a first and second center-tapped primary and a lirst
`and second secondary for connection to the load device. The
`first and second primary center taps arc 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 Etheroet
`telephone power distribu tion system according to a presently
`preferred embodiment of the present invention.
`
`DESC'RIP'IlON OF 111E PREFERRED
`EMBODIMENTS
`Those of ordinary skill in the art will realize that the
`following description o f the present invention is illustrative
`
`Page 5
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`6,115,468
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`only and is not intended to be in any way limiting. Other
`embodiments of the invention will readily suggest them(cid:173)
`selves 10 such skilled persons from an examination of the
`within disclosure.
`Thming now to FIG. 3, in accordance with a presently
`preferred embodiment of the presem iovemioo, a system
`including a plurality of data ports 80, 82, 84 is provided to
`tran">mit 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 10
`devices requiring power to be transmitted to them in addi(cid:173)
`tion to data over Ethernet twisted pair lines.
`Turning to Port l (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. 15
`Receiver 106 receives from twisted pair 110. First tra ns(cid:173)
`former 112 includes a lirst primary 114 and a second primary
`116. First primary 114 is connected to twisted pair 108 and
`second primary ll 6 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 arc respectively connected to twisted
`pairs 124 and 126 which arc, in turn, connected through
`receiver 125 and transmiuer 127 to load device 98.
`Ethernet link 128 couples first and second secondaries
`130, 132 of first transformer 112 to first and second prima(cid:173)
`ries 134, 136 of second transformer ll8. Ethernet link 128
`preferably comprises a pair of twisted pair conductors l 28a
`and 128b wherein twisted pair 128a connects first secondary 30
`130 to first primary 134 of the twisted pair U8b connects
`second secondary B2 to several primary 136.
`Power coupling is provided as follows. Secondaries 130
`and 132 of first transformer LL2 each include a center tap,
`138, 140 respectively. Center tap 138 is connected to the 35
`positive lead 142 of a power supply 144 and cemer 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. 40
`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 allachcd to
`center taps 150, 152, respectively, of first and second pri- 4s
`maries 134 and 136 of second transformer U S 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. so
`The present invention provides a number of advantages
`over the prior an. First, power delivered to the load device
`is split cquaUy 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 traosmiued power is applied at and removed at
`center taps, there is no net current now 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 oct 60
`current, as in the system of FIG.1. This permits off-the-shelf
`transformers for Ethernet applications to be used maintain(cid:173)
`ing compatibility with Ethernet systems not having this
`power delivery requirement. Note that if the prior art system
`of FIG. l were used with a load device lacking decoupling 65
`between the lWO primaries On lhe network side Of the
`transformer, the power supply would be effectively shorted.
`
`4
`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 usc of the power available there
`s 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 an after perusal of this application. In
`particular, the usc of the term primary and secondary in
`referring to transformer windings herein is for explanation
`only. As the links arc bi-directional, the terms primary and
`secondary may be intcrcbangcd as wou ld be known to those
`of ordinary skill in the art. '!be invention, therefore, is not to
`be limited except in the spirit of the appended claims.
`What is c laimed is:
`l. A power feed system for Ethernet telephones, said
`system comprL;;ing:
`a first transformer including a first primary, a second
`primary, a first secondary with a first center-tap and a
`second secondary witb a second center-lap, 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(cid:173)
`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 !irst primary of said second transformer and
`said fourtb 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(cid:173)
`tial on a first line and a second output potential diJicrcnt
`from said first output potential on a second line, said
`first I inc connected to said Jirst center-tap of said first
`transformer and sa id 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 l , wherein said third pair of conductors is a twisted
`pair.
`3 . A power feed system for Ethernet telephones according
`ss 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 Ethcroctlelcphones 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 ftrst center-tap and a
`second secondary with a second center-tap, said first
`
`Page 6
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`primary for coupling to a first pair of conductors, said
`second primary for coupling to a second pair of con(cid:173)
`ductors;
`a second transformer including a first primary with a first
`center-tap, a second primary with a second center-tap, 5
`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
`connecti ng said first secoodary of said first transformer lO
`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- 15
`tial on a first line and a second output potential different
`from said fi rst output potential on a second line, said
`first line conoected to said first center-tap of said fi rst
`transformer and said second line connected to said
`second center-tap of said first transfo rmer;
`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, 35
`said system comprising:
`a first transformer including a first primary, a second
`primary, a fi rst 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 40
`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 45
`center-tap, a second primary with a second center-tap,
`a first secondary and a second secondary, said second(cid:173)
`ary for coupling to a third pair of conductors over
`which said first da ta signal is to be communicated with
`the second device, and said second secondary for 50
`coupling to a fourt h 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 55
`said fi rst 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 lirst transfomJer with sa id 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 l ine, said fust line connected to
`said first center-tap of said first transformer and said 65
`second line connected to said second center-tap of said
`first transformer;
`
`60
`
`Page 7
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`6
`a first potential input of the second device coupled to said
`first center-tap of said second traosfom1er; 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 i.ncludiog a first data signal
`and a second data signal, said method comprising:
`transmitting the flrst da ta signal to a first primary windi ng
`of a first transfom1er;
`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 fr<lm a second primary
`winding of said second transforrmer to a second sec(cid:173)
`ondary winding of said first transformer;
`transmilling the lirst data signal to tlhe 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 signa.! from a center-tap of said fi rst
`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
`transforme r;
`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 lirst winding of a second
`transformer;
`fourth coupling means for coupling a second conductor of
`said second pair of cooductors 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(cid:173)
`ductor;
`a first and second center-tapped winding disposed in said
`second transformer, each said winding baving a first
`conductor, a second conductor and a center-tap con(cid:173)
`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 cooductor of sa.id 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 fo r applying a power signa.( to said first center-tap
`conductor and said second center-tap conductor of said
`first traosfom1er;
`means for extracting a power signal from said first center(cid:173)
`tap conductor and said second center-tap conductor of 5
`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 10
`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 ftrst winding of a second
`transformer;
`fourth coupling means for coupling a second conductor of 20
`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 aod secood cooductor of said second pair of
`conductors;
`a first aod second center-Lapped winding disposed in said
`first transformer, each said winding baving a f'irst
`conductor, a second conductor and a center-tap con-
`ductor;
`a first and second center-tapped winding disposed in said
`secood transformer, each said winding having a first
`conductor, a second cooductor and a center-tap coo(cid:173)
`ductor;
`means for connecting said first conductor of said first
`center-tapped winding of said first transformer to said
`first cooductor of said second ceoter-tapped wioding of
`said second transformer;
`means for connecting said second conductor of said first 40
`center-tapped winding of said first trans[orruer to said
`second conductor of said second center-tapped winding
`of said second transformer;
`means for applying a power signa l to said first center(cid:173)
`tapped conductor and said second center-tapped coo- 45
`ductor of said first transformer;
`
`30
`
`8
`means for extracting a power signal from said fi.rst center(cid:173)
`tap conductor and said secood center-tap conductor of
`sa id second transformer and for applying sa id 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 transmi<>sion of data packets from said
`remote device and a second twisted pair of conductors for
`reception of data packets at said remo te device, the method
`comprising:
`applying a first polarity of the DC power to a center tap
`o( a first traosfom1er wioding connected across a distal
`cod 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
`djstal end of the second twisted pair of conductors;
`extractiog said first polarity from a center tap o[ a third
`traosformer winding coonected across a proximal end
`of the lirst twisted pair of conductors; and
`extracting said second polarity from a center tap of a
`fourth transformer winding connected across a proxi(cid:173)
`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
`25 of conductors for transmission of data packets from sajd
`remote device and a second twisted pair of conductors for
`reception of da ta packets at said remote device, the system
`comprising:
`means for applying a first polarity of tbe DC power to a
`center tap of a first transformer winding connected
`across a distal end of the first twisted pair of conduc(cid:173)
`tors;
`means for applying a second polarity of the DC power to
`a center tap of a second transfom1er winding conoected
`across a distal end of tbe 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 fi rst twisted pair of conductors; and
`means for extracting said second polarity from a center
`tap of a fourt h transformer winding connected across a
`proximal cod of tbe second twisted pair of conductors.
`17. A system according to claim 16 furtber comprising an
`uninterruptible power supply for sourcing the DC power.
`
`35
`
`* * * * *
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