United States Patent
`
`[19]
`
`Puvogel
`
`[11] Patent Number:
`
`4,733,389
`
`[45] Date of Patent:
`
`Mar. 22, 1988
`
`[54] DROP CABLE FOR A LOCAL AREA
`NETWORK
`
`[75]
`
`Inventor:
`
`John M. Puvogel, Lawndale, Calif.
`
`[73] Assignee: Xerox Corporation, Stamford, Conn.
`
`[21] Appl. No.: 890,210
`[22] Filed:
`Jul. 28, 1935
`
`Int. c1.4 .............................................. H04J 15/00
`[51]
`[52] U.S. Cl.
`.. ...... .. .
`... . .. ... . . .. 370/5
`[58] Field of Search ................................ 370/5, 85, 89
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`1,374,221
`4/1921 Osborne ......
`4,583,214 4/1986 Miyashita et
`FOREIGN PATENT DOCUMENTS
`
`370/5
`.. 370/5
`
`Primary Examiner—-Douglas W. Olms
`Attorney. Agent, or Firm—Frank1yn C. Weiss
`[57]
`ABSTRACT
`
`A multipoint data communication system is disclosed
`for transmitting data to and from a plurality of commu-
`nicating devices via an interconnecting cable. This in-
`terconnecting drop cable couples a transceiver unit to a
`communicating device, such as a personal computer,
`workstation, printer, or the like. The drop cable herein
`has only two twisted, jointly shielded, pairs of wires to
`transmit the three signals (transmit, receive, collision)
`and power. AC differences in the pairs constitute the
`third, phantom, signal channel. DC differences in the
`pairs provide the power source for transceiver opera-
`tions. This cable is considerably less expensive than the
`industry standard cable.
`
`0198932 10/1986 European Pat. Off.
`
`.............. .. 370/5
`
`2 Claims, 6 Drawing Figures
`
`I+
`TRANSMIT
`"$-35 SIGNAL
`38:
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`
`COLLISION
`
`RECEIVE
`SIGNAL
`48
`
`-1. POWER FOR
`TRANSCEIVER
`- CIRCUITRY
`
`II '
`
`HOST_S';ATlON
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`+ 9'
`TRANSMIT
`SIGNAL :>- I
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`5
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`
`n.I.-15.75 .,.
`VOLTS D. c.
`
`42
`
`PROPOSED AND DEMONSTRATED
`ETHERNET DROP CABLE CONCEPT
`
`Aerohive - Exhibit 1022
`
`

`
`U.S. Patent
`
`Mar. 22, 1988
`
`Sheet 1 of 5
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`4,733,389
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`

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`U.S. Patent
`
`Mar. 22, 1988
`
`Sheet 2 of 5
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`4,733,389
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`Sheet 3 of 5
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`4,733,389
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`

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`U.S. Patent
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`Sheet 4 of 5
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`U.S. Patent
`
`Mar. 22. 1988
`
`Sheet 5 of 5
`
`4,733,389
`
`

`
`1
`
`4,733,389
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`2
`to convey the three signals (transmit, receive, and colli-
`sion) and power. AC differences in the pairs constitute
`the third signal channel. DC difference in the pairs
`provides the power source for transceiver operation.
`Using standard 9 pin subminiature “D” connectors and
`lower cost cable, the cable assembly is less expensive
`than the IEEE standard drop cable.
`DESCRIPTION OF THE DRAWINGS
`
`For a more complete understanding of the invention,
`reference may be had to the following detailed descrip-
`tion of the invention in conjunction with the drawings
`wherein:
`FIG. 1 is a prior art schematic diagram of the Ether-
`net drop cable defined by IEEE specification 802.3;
`FIG. 2 is a schematic diagram of the Ethernet drop
`cable in conjunction with the present invention;
`FIGS. 3A and 3B are schematic diagrams of the
`phantom circuit elements and phantom circuit equiva-
`lent, and
`FIGS. 4A and 4B are schematic diagrams of dual
`in-line package isolation transformer circuits.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`DROP CABLE FOR A LOCAL AREA NETWORK
`
`This invention relates to a drop cable which connects
`a user host station, i.e., terminal, printer, workstation,
`etc., to a transceiver module attached to an Ethernet ®
`coaxial cable. The drop cable allows transfer of three
`signals and power with two twisted pairs.
`BACKGROUND OF THE INVENTION
`
`5
`
`U.S. Pat. No. 4,063,220, which issued Dec. 13, 1977,
`entitled “Multipoint Data Communication System With
`Collision Detection”, discloses a bit serial receiver
`transceiver network continuously connected to a plu-
`rality of communicating devices. Such is accomplished 15
`by forming the network of any one of a plurality of
`transmitting media, such as coaxial cable, optical fiber
`or other, connected together into one branched net-
`work by constantly active devices, like repeaters, by
`which communications necessarily adapted to one me-
`dium are translated into another medium. The patent
`further goes on to state that distributed along the com-
`municating cable network are a plurality of stations,
`each including a using device generally categorized as
`either a computer, an auxiliary memory, or an input-
`/output terminal. Each using host device, whether it be
`a computer or a remote terminal, is tied to the coaxial
`cable by way of a T-connector, or tap, connecting to a
`transceiver in series with an interface stage which in
`turn connects to the using device.
`Three signals (transmit, receive, and collision) and
`power are transferred through the cable which con-
`nects the host equipment with the transceiver module.
`Host generated transmit signals are transferred to the
`transceiver. Transceiver generated receive and collision
`signals are transferred to the host equipment. Power for
`energizing the transceiver circuitry is transferred from
`the host source.
`V
`The system described is generally now publicly
`known as an Ethernet connection which, as set forth
`above, employs a drop cable between the transceiver
`module and the user host equipment. The transceiver
`module is attached to the Ethernet coaxial cable. User
`host equipment is a terminal, personal computer, work-
`station, printer, file server, gateway, etc.
`IEEE specification 802.3 contains an industry ac-
`cepted definition of the drop cable. Attention is drawn
`to FIG. 1 of the present application. This cable has five
`twisted pairs, with individual pair shields and an overall
`shield. One pair is used for each of the three signals and
`another for power. The fifth pair is user defined. Each
`twisted pair has a characteristic impedance of 78 ohms.
`Cable connections are through 15 pin sub-miniature
`“D” connectors, male to host and female to transceiver.
`Each pair shield has a specific pin assignment. The
`overall shield is connected through the conductive
`connector housing.
`Transmit and receive signals are Manchester encoded
`data at a 10 megabit per second data rate. Transmit and
`receive waveforms have fundamental frequencies of 10
`Mhz with continuous “1” or “0” data patterns or 5 Mhz
`with alternate “1”/“0” data patterns. A collision signal
`is a burst of l0 Mhz square wave. All three signals are
`essentially switching waveforms with controlled rise
`and fall times. Power is from an 11.4 to 15.75 volt DC
`supply within the host station.
`According to the present invention, the proposed
`cable herein has only two twisted, jointly shielded pairs
`
`FIG. 2 shows the Ethernet drop cable in accordance
`with the principles of the present invention. The inven-
`tion utilizes just four wires, i.e., two twisted pairs 20, 22
`and an overall shield 24, as seen in FIG. 2. Three signal
`paths are provided by the technique commonly referred
`to as a phantom circuit. “Phantom circuits” may be best
`described by the textbook “Communication Engineer-
`ing”, by W. L. Everitt and W. E. Anner, McGraw-Hill,
`Third Edition, 1956, Section 5-13, Page 204. By the
`principle of superposition, the signals may be consid-
`ered one at a time. Transmit and receive signals are
`transferred over the standard two wires, or physical
`circuits. Their operation is similar to that of IEEE stan-
`dard 802.3. Both collision and power are transferred
`over. the phantom circuit. Separation of the 10 Mhz
`collision signal and power is accomplished with capaci-
`. tors ‘and inductors as pass and reject filter elements.
`The “phantom” circuit principle works on a balanc-
`ing technique similar to that of a bridge circuit. The
`terminal equipment required is very simple, consisting
`only of a pair of transformers at each end of the phan-
`tom circuit. By the principle of superposition, the sig-
`nals may be considered one at a time. A voltage im-
`pressed on the phantom circuit at the right end of FIG.
`2, will cause a current to enter the mid-tap of the wind-
`ing of each transformer. Thus, a collision signal intro-
`duced into the center tap of transformer 36 will cause a
`like signal to be generated at the center tap of trans-
`former 30. Likewise, the voltage signals introduced at
`the center tap of transformer 40 will cause a like signal
`to be generated at the center tap of transformer 34.
`If the impedances of the line wires are equal, the
`current will divide equally and produce inductances
`which cancel each other out. The currents due to the
`signals impressed on the phantom terminals produce
`equal and opposing inductances at the other end of the
`cable in the respective transformers so that no magnetic
`flux is produced.
`Thus the absence of magnetic flux, due to the cur-
`rents resulting from the phantom signals, prevents these
`signals from being further propogated. Thus, three dis-
`crete signal paths are provided with only two pair of
`wires. The wires are “twisted” to prevent the currents
`
`

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`4,733,389
`
`5
`
`10
`
`3
`flowing in one pair of wires in a cable from inducting a
`voltage in another pair.
`Since all the host stations on an Ethernet system
`receive all the transmitted signals, as described in the
`aforementioned patent, a collison signal must be de-
`tected and presented to the host user when any two
`stations attempt simultaneous transmission.
`In order to eliminate having to run electrical power
`to the transceiver module, which is often placed in the
`drop ceiling of modern office buildings, a voltage sup-
`ply in the host station provides that power.
`The phantom signal path is used to convey DC
`power from the host system to the transceiver module
`and collision signals from the transceiver to the host.
`FIG. 3A shows the elements of the phantom circuit.
`With equal line impedances and equal/opposing induc-
`tances, the equivalent circuit is shown in FIG. 3B. Ca-
`pacitors present low impedance coupling of collision
`signals, but high impedance blockage for DC potentials.
`Inductors present low impedance passage of DC cur-
`rents, but high impedance to 10 Mhz collision signals.
`Thus FIG. 2 can be seen to include transformer 38 for
`transferring collision signals from transceiver circuits to
`the phantom circuit through capacitor 52. Likewise,
`capacitor 50 couples collision signals to transformer 32
`which supplies signals to the host. DC power from the
`host (42) is transferred through inductors 44 to the
`phantom path. Likewise, DC power is transferred from
`the phantom path, through inductors 46, to the trans-
`ceiver’s DC/DC converter 48.
`Instead of each twisted pair shield having its own
`ground terminal,
`the overall
`shield is connected
`through the connector housing and through one pin to
`chassis ground. With the savings in terminals, a smaller 35
`plug and jack connector can be used. Connection of the
`new drop cable is through 9 pin sub-miniature “D”
`connectors, male to host and female to transceiver.
`Several suppliers provide a triple transformer device
`for the transceiver in the IEEE 802.3 application. Such
`a triple transformer dual in line package is seen in FIG.
`4A. These devices have the pin numbering configura-
`tion of the standard 16 pin dual in-line (DIP) package. A
`center tap triple transformer device as seen in FIG. 4B
`and connecting the taps to two available pins has been
`shown and tested in a modification of the standard triple
`transformer device as seen in FIG. 4A.
`Some of the advantages of the new drop cable over
`that described in the IEEE specification, are smaller
`diameter, with a more flexible cable; smaller connectors 50
`with smaller foot prints; fewer connection contacts for
`improved reliability; anticipated greater electrostatic
`discharge protection; and a reduction in cost of the
`Ethernet connection. For example, the standard IEEE
`cable utilizing five twisted, individually shielded pairs
`with separate ground connection for each shield would
`cost about thirty five dollars. This cable is rather inflexi-
`ble and resembles a large power cord instead of a serial
`communication cable. However, the cable of the pres-
`ent invention would cost approximately twelve to fif-
`teen dollars. This is a substantial savings when thou-
`sands of machines are involved.
`While the invention has been described with refer-
`ence to a specific embodiment, it will be understood by
`those skilled in the art that various changes may be
`made and equivalents may be substituted for elements
`thereof without departing from the true spirit and scope
`of the invention. In addition, many modifications may
`
`40
`
`45
`
`4
`be made without departing from the essential teachings
`of the invention.
`What is claimed is:
`1. A multipoint data communication system for trans-
`mitting data to and from a plurality of communicating
`devices via an interconnecting cable, comprising‘
`transceiver means coupled to said interconnecting
`cable for coupling the interconnecting cable to a
`communication device and a communicating de-
`vice to the interconnecting cable,
`drop cable means for coupling said transceiver means
`to said communicating device, and said communi-
`cating device to said transceiver means, said drop
`cable comprising two twisted pairs of wires with an
`overall shield, and
`circuit means at said communicating device for inter-
`facing between said communicating device and
`said drop cable, wherein three distinct signals and
`power are conveyed over the two twisted wire
`pairs in said drop cable utilizing a phantom signal
`technique of signal transmission,
`wherein said transceiver means includes three trans-
`former means for transmitting said three distinct
`signals,
`the outputs of one of said transformers
`being connected to the center taps of the other two
`transfonners, such that a signal introduced by said
`one transformer is directed to and forwarded by
`the other two of said transformers, wherein said
`three distinct signals are alternating current signals
`while the fourth element is direct current power,
`and wherein said fourth element
`representing
`power is kept separate from said third signal via
`capacitor means between the output of the other
`transformer and the center tap of one of said two
`transformers in both said transceiver means and
`said circuit means.
`2. A multipoint data communication system for trans-
`mitting data to and from a plurality of communicating
`devices via an interconnecting cable, comprising
`transceiver means coupled to said interconnecting
`cable for coupling the interconnecting cable to a
`communication device and a communicating de-
`vice to the interconnecting cable,
`drop cable means for coupling said transceiver means
`to said communicating device, and said communi-
`cating device to said transceiver means, said drop
`cable comprising two twisted pairs of wires with an
`overall shield, and
`circuit means at said communicating device for inter-
`facing between said communicating device and
`said drop cable, wherein three distinct signals and
`power are conveyed over the two twisted wire
`pairs in said drop cable utilizing a phantom signal
`technique of signal transmission,
`wherein said transceiver means includes three trans-
`former means for transmitting said three distinct
`signals, the outputs of one of said transformers
`being connected to the center taps of the other two
`transformers, such that a signal introduced by said
`one transformer is directed to and forwarded by
`the other two of said transformers, wherein said
`circuit means at said communicating device in-
`cludes three transformer means connected together
`in the same manner as set forth in said transceiver
`means such that the outputs of one of said trans-
`former means in said circuit means is connected to
`the center taps of the other two transformers such
`that a signal received at the center taps of said
`
`

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`4,733,389
`
`5
`other two transformers is directed to other trans-
`formers to generate said third signal at said other
`transformers, said third signal being a phantom
`signal, wherein said three distinct signals are alter-
`nating current signals while the fourth element is
`direct current power, wherein said fourth element
`
`5
`
`6
`representing power is kept separate from said third
`or phantom signal signal via capacitor means be-
`tween the output of the other transformer and the
`center tap of one of said two transformers in both
`said transceiver means and said circuit means.
`*
`*
`"'
`*
`*