Ulllted States Patent [19]
`De Nicolo
`
`US006115468A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,115,468
`Sep. 5, 2000
`
`[54] POWER FEED FOR ETHERNET
`
`5,574,748 11/1996 Vander Mey et a1. ................ .. 375/204
`
`TELEPHONES VIA ETHERNET LINK
`
`5,799,040
`
`8/1998 Lau . . . . . . . . . . . . . . . . . . . .
`
`. . . .. 375/258
`
`[75] Inventor: Maurilio Tazio De Nicolo, Saratoga,
`Cahf-
`_
`_
`_
`[73] Ass1gnee: Clsco Technology, Inc., San Jose, Cal1f.
`
`[21] Appl' NO‘: 09/048,922
`[22] Filed:
`Man 26 1998
`’
`[51] Int. Cl.7 ..................................................... .. H0413 3/00
`[52] US. 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
`2/1988 Jones et a1. ............................. .. 379/93
`2/1994 Leonowich
`375/258
`5/1994 Takato et a1. .
`370/1101
`7/1996 Lau ....................................... .. 375/258
`
`4,723,267
`5,285,477
`5,311,518
`5,541,957
`
`5,994,998 11/1999 Fisher et al. ..................... .. 340/31001
`Primary Examiner_David R_ Hudspeth
`Assistant Examiner—Vij ay 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 ?rst tWisted pair conductor is
`connected across the ?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 ?rst and second secondaries. At the local end, the output
`transformer includes a ?rst and second center-tapped pri
`mary and a ?rst and second secondary for connection to the
`load device' The ?rst 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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`OUT
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`POWER
`PROCESSOR
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`POWER
`PROCESSOR
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`/149
`POWER
`PROcEssOR
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`QIN
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`(O LKB
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`PORT 2
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`5
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`POWER
`SUPPLY
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`PORT 1
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`a
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`PORT 3
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`1
`POWER FEED FOR ETHERNET
`TELEPHONES VIA ETHERNET LINK
`
`BACKGROUND OF THE INVENTION
`
`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 ?lter 68, a
`recti?er 70, a ?lter capacitor 72 and a DC-DC converter 74.
`While ?t 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 ?oW
`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
`?rst tWisted pair conductor is connected across the ?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 ?rst and second
`secondaries. At the local end, the output transformer
`includes a ?rst and second center-tapped primary and a ?rst
`and second secondary for connection to the load device. The
`?rst 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.
`
`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 of?ce’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
`of?ce 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 ?lter
`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 ?oWing and alloWs
`a DC bias to be established over the tWo conductors of
`tWisted pair link 28 While simultaneously alloWing the How
`of data over the link.
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`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`Those of ordinary skill in the art Will realiZe that the
`folloWing description of the present invention is illustrative
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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 ?rst 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 ?rst 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 ?rst and second secondaries
`130, 132 of ?rst transformer 112 to ?rst 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 ?rst secondary
`130 to ?rst 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 ?rst 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 ?ltering components 148a, 148b, 1486 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 ?rst 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
`?ltering 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 ?oW 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 modi?cations 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 ?rst transformer including a ?rst primary, a second
`primary, a ?rst secondary With a ?rst center-tap and a
`second secondary With a second center-tap, said ?rst
`primary for coupling to a ?rst pair of conductors, said
`second primary for coupling to a second pair of con
`ductors;
`a second transformer including a ?rst primary With a ?rst
`center-tap, a second primary With a second center-tap,
`a ?rst secondary and a second secondary, said ?rst 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 ?rst secondary of said ?rst transformer
`With said ?rst primary of said second transformer and
`said fourth pair of conductors connecting said second
`secondary of said ?rst transformer With said second
`primary of said second transformer;
`a direct current poWer supply having a ?rst output poten
`tial on a ?rst line and a second output potential different
`from said ?rst output potential on a second line, said
`?rst line connected to said ?rst center-tap of said ?rst
`transformer and said second line connected to said
`second center-tap of said ?rst transformer;
`a ?rst potential input of an Ethernet telephone coupled to
`said ?rst 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. ApoWer feed system for Ethernet telephones according
`to claim 1, Wherein said third pair of conductors is a tWisted
`pair.
`3. ApoWer feed system for Ethernet telephones according
`to claim 2, Wherein said fourth pair of conductors is a tWisted
`pair.
`4. ApoWer feed system for Ethernet telephones according
`to claim 3, Wherein said ?rst pair of conductors is a tWisted
`pair.
`5. ApoWer 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 ?rst transformer including a ?rst primary, a second
`primary, a ?rst secondary With a ?rst center-tap and a
`second secondary With a second center-tap, said ?rst
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`primary for coupling to a ?rst pair of conductors, said
`second primary for coupling to a second pair of con
`ductors;
`a second transformer including a ?rst primary with a ?rst
`center-tap, a second primary With a second center-tap,
`a ?rst secondary and a second secondary, said ?rst 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 ?rst secondary of said ?rst transformer
`with said ?rst prirnary of said second transformer and
`said fourth pair of conductors connecting said second
`secondary of said ?rst transformer with said second
`primary of said second transforrner;
`a direct current poWer supply having a ?rst output poten
`tial on a ?rst line and a second output potential different
`from said ?rst output potential on a second line, said
`?rst line connected to said ?rst center-tap of said ?rst
`transformer and said second line connected to said
`second center-tap of said ?rst transforrner;
`a ?rst potential input of the remote device coupled to said
`?rst center-tap of said second transformer; and
`a second potential input of the remote device coupled to
`said second center-tap of said second transforrner.
`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 ?rst 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
`sirnultaneously betWeen a ?rst device and a second device,
`said system comprising:
`a ?rst transforrner including a ?rst prirnary, a second
`primary, a ?rst secondary With a ?rst center-tap and a
`second secondary With a second center-tap, said ?rst
`primary for coupling to a ?rst pair of conductors over
`Which a ?rst data signal is to be communicated With the
`?rst device, said second primary for coupling to a
`second pair of conductors over Which a second data
`signal is to be communicated With the ?rst device;
`a second transforrner including a ?rst primary with a ?rst
`center-tap, a second primary With a second center-tap,
`a ?rst secondary and a second secondary, said second
`ary for coupling to a third pair of conductors over
`Which said ?rst data signal is to be communicated With
`the second device, and said second secondary for
`coupling to a fourth pair of ?rst conductors over Which
`said second data signal is to be communicated With the
`second device;
`a link including a ?fth pair of conductors and a siXth pair
`of conductors, said ?fth pair of conductors connecting
`said ?rst secondary of said ?rst transformer with said
`?rst prirnary of said second transformer and said siXth
`pair of conductors connecting said second secondary of
`said ?rst transformer with said second primary of said
`second transforrner;
`a direct current poWer supply associated With the ?rst
`device having a ?rst output potential on a ?rst line and
`a second output potential different from said ?rst output
`potential on a second line, said ?rst line connected to
`said ?rst center-tap of said ?rst transformer and said
`second line connected to said second center-tap of said
`?rst transforrner;
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`a ?rst potential input of the second device coupled to said
`?rst 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 ?rst data signal
`and a second data signal, said method comprising:
`transmitting the ?rst data signal to a ?rst primary winding
`of a ?rst transforrner;
`receiving the second data signal from a second primary
`Winding of said ?rst transforrner;
`transmitting the ?rst data signal from a ?rst secondary
`Winding of said ?rst transforrner to a ?rst primary
`winding of a second transforrner;
`transmitting the second data signal from a second primary
`Winding of said second transforrner to a second sec
`ondary Winding of said ?rst transforrner;
`transmitting the ?rst data signal to the device over a ?rst
`secondary Winding of said second transforrner;
`receiving the second data signal from the device over a
`second secondary Winding of said second transforrner;
`applying a DC signal betWeen a center-tap of said ?rst
`secondary Winding of said ?rst transformer and a
`center-tap of said second secondary Winding of said
`?rst transforrner;
`extracting a DC signal from a center-tap of said ?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:
`?rst coupling means for coupling a ?rst conductor of a
`?rst pair of conductors to a ?rst Winding of a ?rst
`transforrner;
`second coupling means for coupling a second conductor
`of said ?rst pair of conductors to a second Winding of
`said ?rst transforrner;
`third coupling means for coupling a ?rst conductor of a
`second pair of conductors to a ?rst Winding of a second
`transforrner;
`fourth coupling means for coupling a second conductor of
`said second pair of conductors to a second Winding of
`said second transforrner;
`?fth coupling means for coupling a ?rst and second
`conductor, respectively, of an Ethernet telephone to
`said ?rst and second conductor of said second pair of
`conductors;
`a ?rst and second center-tapped Winding disposed in said
`?rst transforrner, each said Winding having a ?rst
`conductor, a second conductor and a center-tap con
`ductor;
`a ?rst and second center-tapped Winding disposed in said
`second transforrner, each said Winding having a ?rst
`conductor, a second conductor and a center-tap con
`ductor;
`means for connecting said ?rst conductor of said ?rst
`center-tapped Winding of said ?rst transforrner to said
`?rst conductor of said second center-tapped Winding of
`said second transforrner;
`means for connecting said second conductor of said ?rst
`center-tapped Winding of said ?rst transforrner to said
`second conductor of said second center-tapped Winding
`of said second transforrner;
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`means for applying a power signal to said ?rst center-tap
`conductor and said second center-tap conductor of said
`?rst transformer;
`means for extracting a poWer signal from said ?rst 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. Asystem for supplying DC poWer to a remote device,
`said system comprising:
`?rst coupling means for coupling a ?rst conductor of a
`?rst pair of conductors to a ?rst Winding of a ?rst
`transformer;
`second coupling means for coupling a second conductor
`of said ?rst pair of conductors to a second Winding of
`said ?rst transformer;
`third coupling means for coupling a ?rst conductor of a
`second pair of conductors to a ?rst 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;
`?fth coupling means for coupling a ?rst and second
`conductor, respectively, of the remote device to said
`?rst and second conductor of said second pair of
`conductors;
`a ?rst and second center-tapped Winding disposed in said
`?rst transformer, each said Winding having a ?rst
`conductor, a second conductor and a center-tap con
`ductor;
`a ?rst and second center-tapped Winding disposed in said
`second transformer, each said Winding having a ?rst
`conductor, a second conductor and a center-tap con
`ductor;
`means for connecting said ?rst conductor of said ?rst
`center-tapped Winding of said ?rst transformer to said
`?rst conductor of said second center-tapped Winding of
`said second transformer;
`means for connecting said second conductor of said ?rst
`center-tapped Winding of said ?rst transformer to said
`second conductor of said second center-tapped Winding
`of said second transformer;
`means for applying a poWer signal to said ?rst center
`tapped conductor and said second center-tapped con
`ductor of said ?rst transformer;
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`means for extracting a poWer signal from said ?rst 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. Amethod for supplying DC poWer to a remote device
`over a 4-Wire Ethernet connection having a ?rst 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 ?rst polarity of the DC poWer to a center tap
`of a ?rst transformer Winding connected across a distal
`end of the ?rst 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 ?rst polarity from a center tap of a third
`transformer Winding connected across a proximal end
`of the ?rst 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 ?rst 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 ?rst polarity of the DC poWer to a
`center tap of a ?rst transformer Winding connected
`across a distal end of the ?rst 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 ?rst polarity from a center tap
`of a third transformer Winding connected across a
`proximal end of the ?rst 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.
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`Juniper Ex 1027 - 8
`Juniper v Chrimar
`IPR2016-01397
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