United States Patent (19)
`Beggs et al.
`
`11
`45
`
`Patent Number:
`Date of Patent:
`
`4,755,629
`Jul. 5, 1988
`
`(54) LOCAL AREA NETWORK CABLE
`(75
`Inventors: Richard D. Beggs, Duluth; Harold W.
`Friesen, Dunwoody; David M.
`Mitchell, Dunwoody; Wendell G.
`Nutt, Dunwoody; Palmer D.
`Thomas, Tucker, all of Ga.
`73 Assignees: AT&T Technologies, Berkeley
`Heights; AT&T Bell Laboratories,
`Murray Hill, both of N.J.
`(21) Appl. No.: 910,848
`22 Filed:
`Sep. 24, 1986
`Related U.S. Application Data
`Continuation-in-part of Ser. No. 780,859, Sep. 27, 1985.
`63
`51) Int. Cl* ............................................. HOB 11/02
`52 U.S. C. ........................................ 174/34; 174/36;
`174/115
`58 Field of Search ...................... 174/32, 34, 36, 115
`56)
`References Cited
`U.S. PATENT DOCUMENTS
`2,623,093 12/1952 Smith .................................. 74/15
`3,209,064 9/1965 Cutler ....
`... 174/36
`3,489,844 1/1970 Motley .................................. 174/34
`3,546,357 12/1970 MacPherson et al. .
`... 174/34 X
`3,644,659 2/1972 Campbell .......
`3,927,247 12/1975 Timmons .............................. 174/36
`4,058,669 11/1977 Nutt et al. .
`
`4,096,346 6/1978 Stine et al. ............................ 174/36
`4,153,332 5/1979 Longoni .
`4,412,094 10/1983 Dougherty et al. .............. 174/34 X
`4,468,089 8/1984 Brorein ............................. 174/36 X
`4,533,790 8/1985
`Johnston et al. .
`FOREIGN PATENT DOCUMENTS
`100222 2/1937 Australia ............................... 74/36
`Primary Examiner-Morris H. Nimmo
`Attorney, Agent, or Firm-Edward W. Somers
`57
`ABSTRACT
`A cable (20) which is particularly suited to the transmis
`sion of substantially error-free data at relatively high
`rates over relatively long distances includes at least two
`pairs of individually insulated conductors (42-43).
`Each pair of individually insulated conductors is en
`closed individually in its own tubular member (51) con
`prising a plastic material. A metallic shield (60) encloses
`the tubular members, and in a preferred embodiment, a
`plastic jacket (80) encloses the shield. In the preferred
`embodiment, two pairs of voice communications con
`ductors are disposed at opposed locations between the
`shield and the jacket. The thickness of the tubular mem
`ber is such that each insulated conductor of each
`twisted pair is caused to be spaced from the shield a
`distance which is not less than one half the diameter of
`the metallic wire portion of each pair enclosed by the
`tubular member.
`
`19 Claims, 5 Drawing Sheets
`
`NSUAED
`CONDUCTOR
`42 44 METALLIC PORTION
`
`
`
`46NSULATION
`COWER
`STUBLAR
`MEMBER
`
`90 INSUATED
`CONDUCTOR
`
`
`
`
`
`
`
`
`
`NSUA
`
`OUTER 94
`AYER
`
`

`

`U.S. Patent Jul. 5, 1988
`
`Sheet 1 of 5
`
`4.755,629
`
`80 OUTER
`JACKET
`
`DRAIN WIRE
`6.
`SAE 4: 5
`CABLE 32
`M
`NSULATED N
`TWISTED 45-N
`CONDUCTOR
`PAR
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`9B
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`TUBULAR MEMBER SHIELD
`Zzz 9A
`ZO CABLE
`30 OUTER 2
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`6
`
`ess
`
`DRAN 68
`WRE
`INSULATED 12
`
`6OSHIELD Az71
`TUBULAR ZZ
`MEMBER
`TWISTED PAIR 43 12
`INSULATED CONDUCTOR
`
`
`
`
`
`26
`
`24 PERPHORAL
`EQUIPMENT
`
`23 PERSONAL
`COMPUTER
`
`

`

`US. Patent
`
`Jul. 5, 1988
`
`Sheet 2 of 5
`
`4,755,629
`
`40 SYSTEM
`
`32
`HUB
`INTERCONNECT
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`CONDUCTORS
`
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`29 SIGNAL source!
`
`DIGITAL
`
`

`

`U.S. Patent Jul. 5, 1988
`
`Sheet 3 of 5
`
`4.755,629
`
`
`
`TWSTED 43
`PAR
`
`
`
`INNER LAYER 47
`OUTER 49
`
`INNER 92
`NSULA-
`TION
`LAYER
`
`OUTER 94
`NSULATION
`LAYER
`
`SHIELD 60
`
`NSULATED
`CONDUCTOR
`42 44 METALLIC PORTION
`
`46 INSULATION
`COWER
`5) TUBULAR
`MEMBER
`
`A-90 INSULATED
`A
`CONDUCTOR
`NNER LAYER
`
`3 O JACKET
`6|SEAM
`68 DRAIN WIRE
`
`66 FILM
`
`
`
`5 TUBULAR
`MEMBER
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`N
`NY avana reactical
`ZZZZYYYZ
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`6 O SHIELD
`BORf6N 64 40 JACKET
`
`www.axa, AaySYYYY
`
`
`
`

`

`U.S. Patent Jul. 5, 1988
`
`Sheet 4 Of 5
`
`4.755,629
`
`60SHIELD
`5 e BUFFER
`MEMBER
`
`5 PRE-
`FORM
`68DRAIN 42
`WRE
`
`
`
`56
`TUBULAR
`PORTION
`
`
`
`
`
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`42-y2)
`NSULATED NX2
`CONDUCTORWNYCé
`l S
`S. MQM
`
`NSULATED 12
`
`CONDUCTOR
`
`1
`
`6
`
`58 PREFORM
`
`4
`2
`NINSULATED
`CONDUCTOR
`42.
`NSULATED
`CONDUCTOR
`
`A
`
`NSULATED
`CONDUCTOR 7/
`
`73 SIESCRIBING
`44 METALLC
`PORTION
`44
`METALLC
`PORTION
`
`4
`
`75 NSULATED CONDUCTOR
`
`/
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`SHIELD
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`^ TUBULAR 5
`MEMBER
`METALLC i
`Z77-8c RF Z77.8 D.
`
`
`
`

`

`U.S. Patent Jul. 5, 1988
`
`Sheet S of 5
`
`4.755,629
`
`
`
`METALLC LAYER
`
`2 INSULATED
`104 SFR 100 CABLE
`
`TUBULAR MEMBER /04
`
`| lis
`JACKET
`
`02 NSULATED
`CONDUCTOR
`
`Zzz 1 O
`
`

`

`1.
`
`LOCAL AREA NETWORK CABLE
`
`4,755,629
`2
`ized by an unbalanced mode because most of the indus
`try is not amenable to investing in additional compo
`nents for each line. In an unbalanced mode transmission
`system, voltages and currents on the conductors of a
`pair are not characterized by equality of amplitude and
`opposition of polarity. However, given other advan
`tages of a balanced system such as, for example, less
`crosstalk particularly at longer distances, computer
`equipment manufacturers may be inclined to install such
`a system.
`Of importance to the design of local area network
`copper conductor cables are the speed and the distances
`over which data signals must be transmitted. In the past,
`this need has been one for interconnections operating at
`data speeds up to 20 kilobits per second and over a
`distance not exceeding about 150 feet. This need has
`been satisfied in the prior art with single jacket cables
`which may comprise a plurality of insulated conductors
`that are connected directly between a computer, for
`example, and receiving means such as peripheral equip
`ment. Additional components at the ends of each pair to
`convert to the balanced mode have not been used.
`In today's world, however, it becomes necessary to
`transmit data signals at much higher speeds over dis
`tances which may include several thousands of feet.
`Both the data rates and the distances for transmission
`may be affected significantly by the topology of some
`presently used local area network arrangements. In one,
`for example, each of a plurality of terminal stations is
`connected to a common bus configured in a ring such
`that signals generated at one station and destined for
`another must be routed into the wiring closet and seria
`tim out to each station intermediate the sending and
`receiving stations. The common bus, of course, requires
`a very high data rate to serve a multiplicity of stations
`and the ring configuration doubles the path length over
`which the data signals must be transmitted from each
`station to the wiring closet.
`Even at these greatly increased distances, the trans
`mission must be substantially error-free and at relatively
`high rates. Often, this need has been filled with coaxial
`cable comprising the well-known center solid and outer
`tubular conductor separated by a dielectric material.
`The use of coaxial cables, which inherently provide
`unbalanced transmission, presents several problems.
`Coaxial connectors are expensive and difficult to install
`and connect, and, unless they are well designed, in
`stalled and maintained, can be the cause of electromag
`netic interference. Of course, the use of coaxial cables
`does not require components such as transformers at
`each end to provide balanced mode transmission, but
`the size and connectorization of coaxial cables outweigh
`this advantage.
`Shielding often is added to a twisted pair of insulated
`conductors to confine its electric and magnetic fields. In
`this way, susceptibility to electromagnetic interference
`is reduced. However, as the electric and magnetic fields
`are confined, resistance, capacitance and inductance all
`change, each in such a way as to increase transmission
`loss. One company markets a cable in which each pair
`of conductors is provided with a shield and a braid is
`provided about the plurality of pairs. In order to con
`pensate for the increased losses, the conductor insula
`tion must be increased in thickness. As a result, the
`insulated conductors cannot be terminated with con
`ventional connector hardware.
`On the other hand, a cable shield surrounding all
`conductor pairs in a cable may be advantageous. Con
`
`45
`
`50
`
`60
`
`O
`
`15
`
`30
`
`This application is a continuation-in-part of applica
`tion Ser. No. 780,859 filed Sept. 27, 1985.
`TECHNICAL FIELD
`This invention relates to a local area network cable.
`More particularly, it relates to a cable which is capable
`of providing substantially error-free data transmission
`at relatively high rates over relatively long distances.
`BACKGROUND OF THE INVENTION
`Along with the greatly increased use of computers
`for offices and for manufacturing facilities, there has
`developed a need for a cable which may be used to
`connect peripheral equipment to mainframe computers
`and to connect two or more computers into a common
`network. A number of factors must be considered in
`order to arrive at a cable design which is readily mar
`20
`ketable for such uses.
`Cable connectorability is very important and is more
`readily accomplished with twisted insulated conductor
`pairs than with any other medium. A widely used con
`nector for insulated conductors is one which is referred
`25
`to as a split beam connector. See, for example, U.S. Pat.
`No. 3,798,587 which issued on Mar. 19, 1974 in the
`names of B. C. Ellis, Jr. et al. Desirably, the outer diam
`eter of insulated conductors of the sought-after cable is
`sufficiently small so that the conductors can be termi
`nated with such existing connector systems.
`The jacket of the sought-after cable should exhibit
`low friction to enhance the pulling of the cable into
`ducts or over supports. Also, the cable should be strong,
`flexible and crush-resistant, and it should be conve
`35
`niently packaged and not unduly weighty. Because the
`cable may be used in occupied building spaces, flame
`retardance also is important.
`To satisfy present, as well as future needs, the sought
`after cable should be capable of suitable high frequency
`data transmission. This requires a tractable loss for the
`distance to be covered, and crosstalk and electromag
`netic interference (EMI) performance that will permit
`substantially error-free transmission. Also, the cable
`must not contaminate the environment with electro
`magnetic interference.
`The sought-after data transmission cable should be
`low in cost. It must be capable of being economically
`installed and be efficient in terms of space required.
`Generally, for cables in buildings, which are used for
`such interconnection, installation costs outweigh the
`cable material costs. Building cables should have a rela
`tively small cross-section inasmuch as small cables not
`only enhance installation but are easier to conceal, re
`quire less space in ducts and wiring closets and reduce
`55
`the size of associated connector hardware. At the same
`time, however, peripheral connection arrangements
`must meet attenuation and crosstalk requirements.
`Another cost consideration is whether or not the
`system is arranged to provide transmission in what is
`called a balanced mode. In balanced mode transmission,
`voltages and currents on the conductors of a pair are
`equal in amplitude but opposite in polarity. This re
`quires the use of additional components, such as trans
`formers, for example, at end points of the cable between
`65
`the cable and logic devices thereby increasing the cost
`of the system. Generally, computer equipment manu
`facturers have preferred the use of systems character
`
`

`

`10
`
`15
`
`4,755,629
`4.
`3
`included in the preferred embodiment are at least two
`sider that the pairs may be inside a cabinet and may be
`exposed a high speed digital signals. Stray radiation will
`pairs of insulated conductors which are used for voice
`be picked up in the longitudinal mode of the twisted
`communications. These are disposed between the me
`tallic shield and the plastic jacket and are in generally
`pairs. If the pairs are then routed outside the cabinet,
`diametrically opposite locations.
`they may radiate excessively. If there is a cable shield
`enclosing the plurality of pairs, the shield may be
`BRIEF DESCRIPTION OF THE DRAWINGS
`grounded at the cabinet wall so that the shield will not
`itself carry stray signals to the outside environment.
`Other features of the present invention will be more
`readily understood from the following detailed descrip
`Thus, a shield disposed about all the pairs in a cable can
`be effective in preventing electromagnetic interference
`tion of specific embodiments thereof when read in con
`junction with the accompanying drawings, in which:
`and yet not increase appreciably the attenuation of each
`FIG. 1 is a perspective view of a cable of this inven
`pair.
`tion for providing substantially error-free data transmis
`The sought after cable should be one that may be
`sion over relatively long distances;
`used to replace the well known D-inside wiring which
`comprises a plurality of twisted insulated conductor
`FIG. 2 is an elevational view of a building to show a
`mainframe computer and printers linked by the cable of
`pairs. The pairs are non-shielded and are enclosed in a
`jacket. Improved pair isolation has long been sought in
`this invention;
`such wiring to reduce crosstalk. Hopefully, the cable of
`FIG. 3 is a schematic view of a pair of insulated con
`ductors in an arrangement for balanced mode transmis
`this invention also could be used for burglar alarm sys
`tems and for today's sophisticated thermostat systems,
`20
`S1On;
`for example.
`FIG. 4 is a schematic view of a data transmission
`Seemingly, the solutions of the prior art to the prob
`system which includes the cable of this invention;
`lem of providing a local area network cable which can
`FIG. 5 is an end view in section of the cable of FIG.
`be used to transmit, for example, data bits error-free at
`1;
`relatively high rates over relatively long distances have
`FIG. 5A is a detail view of a portion of the cable of
`25
`not yet been totally satisfying. What is needed and what
`FIG. 5;
`is not provided by the prior art is a cable which is com
`FIGS. 6 and 7 are end views in section of alternative
`embodiments of a portion of the cable of FIG. 5;
`patible with balanced or unbalanced mode transmission
`equipment and which can be readily installed, fits easily
`FIGS. 8A-8D are end views in section of prior art
`into building architectures, and is safe and durable.
`cables and the cable of this invention;
`FIGS. 9A-9B are perspective views of other embodi
`SUMMARY OF THE INVENTION
`ments of the cable of this invention; and
`The foregoing problems have been overcome by a
`FIG. 10 is an end cross-sectional view of still another
`cable of this invention. The cable of the preferred em
`embodiment of the cable of this invention.
`bodiment of this invention is capable of high rate trans
`35
`DETAILED DESCRIPTION
`mission of data streams and is capable of balanced or
`Referring now to FIG. 1, there is shown a data trans
`unbalanced mode transmission. The cable comprises a
`mission cable which is designated generally by the nu
`plurality of transmission media each of which includes a
`meral 20. Typically the cable 20 may be used to net
`twisted pair of individually insulated conductors with
`work one or more mainframe computers 22-22, many
`each of the insulated conductors a metallic conductor
`40
`personal computers 23-23, and peripheral equipment
`and an insulation cover which encloses the metallic
`24 on the same or different floors of a building 26 (see
`conductor. A buffer system includes a plurality of por
`FIG. 2). The peripheral equipment 24 may include a
`tions each of which comprises a dielectric material and
`high speed printer, for example. Desirably, the inter
`each of which is associated individually with a pair of
`connection system minimizes interference on the system
`conductors. Each buffer portion encloses substantially
`45
`in order to provide substantially error-free transmission.
`the associated pair of insulated conductors and is effec
`The cable 20 of this invention is directed to providing
`tive to inhibit distortion of the twist configuration of the
`substantially error-free data transmission in a balanced
`associated pair of conductors. As a result of the physical
`separation of the conductor pairs and the maintenance
`or in an unbalanced mode. A balanced mode prior art
`transmission system which includes a plurality of pairs
`of the twist configuration of each pair, crosstalk perfor
`mance is improved. Also, the cable of the preferred
`of individually insulated conductors 27-27 is shown in
`embodiment includes a sheath system which includes a
`FIG. 3. Each pair of conductors 27-27 is connected
`from a digital signal source 29 through a primary wind
`shield that protects the cable against electromagnetic
`ing 30 of a transformer 31 to a secondary winding 32
`interference. The shield is a laminate which comprises a
`which is center-tap grounded. The conductors are con
`metallic material and a plastic film and encloses the
`55
`plurality of transmission media which are used for data
`nected to a winding 33 of a transformer 34 at the receiv
`ing end which is also center-top grounded. A winding
`transmission. In a preferred embodiment, a jacket which
`is made of a plastic material encloses the shield. The
`35 of the transformer 34 is connected to a receiver 36.
`thickness of each buffer portion is such that each insu
`With regard to outside interference, whether it be from
`lated conductor of each pair is spaced from the shield
`power induction or other radiated fields, the electric
`60
`currents cancel out at the output end. If, for example,
`by a distance which is equal at least to one half the
`the system should experience an electromagnetic inter
`diameter of the metallic portion of each insulated con
`ductor enclosed by the buffer portion.
`ference spike, both conductors will be affected equally,
`resulting in a null, with no change in the received signal.
`In a preferred embodiment, each of the conductors is
`For unbalanced transmission, a shield may minimize
`enclosed with a dual insulation cover. The cover in
`65
`cludes an inner layer of an expanded cellular material
`these currents but cannot cancel them.
`such as expanded polyethylene and an outer layer of a
`Computer equipment manufacturers frequently have
`solid material such as polyvinyl chloride material. Also,
`not found it advisable to use balanced mode transmis
`
`30
`
`50
`
`

`

`10
`
`5
`
`35
`
`4,755,629
`5
`6
`sion, primarily because of costs. For unbalanced mode
`together (see FIG. 6). The preform may be comprised
`transmission, it is unnecessary to connect additional
`of a solid or expanded polyvinyl chloride plastic mate
`components such as transformers into circuit boards at
`rial. Further, the preform 55 is provided with a longitu
`the ends of each conductor pair. Use in an unbalanced
`dinally extending slit 56 in each outer wall thereof. In
`this way, the preform 55 may be provided in a supply
`mode avoids the need for additional terminus equip
`ment and renders the cable 20 compatible with present
`roll to a manufacturing line and a pair of the insulated
`equipment. However, because of the distances over
`conductors 42-42, twisted or untwisted, is caused to be
`which the cable of this invention is capable of transmit
`inserted into each tubular portion 56 as the tubular
`ting data signals substantially error-free at relatively
`portion is opened along its slit 57. In FIG. 7, on S
`high rates, there may be a willingness to invest in the
`shaped preform 58 provides an individual buffer for
`additional components at the ends of the cable which
`each conductor pair. As in the preferred embodiment,
`are required for balanced mode transmission.
`the thickness of each portion of the preform is equal at
`Further, there is a requirement that the outer diame
`least to the radius of the metallic portion of each insu
`ter of the cable 20 not exceed a predetermined value and
`lated conductor enclosed by the buffer.
`that the flexibility of the cable be such that it can be
`Disposed about the plurality of belted pairs of indi
`installed easily. The cable 20 has a relatively small outer
`vidually insulated conductors is a shield 60 (see FIGS. 1
`diameter and is both rugged and flexible thereby over
`and 5) having an overlapped seam 61. The metallic
`coming the many problems encountered when using a
`shield 60 in a preferred embodiment is a laminate (see
`cable with individually shielded pairs.
`FIG. 5A) which comprises a metallic portion 64, such
`Referring now to FIG. 4, there is shown a system 40
`as an aluminum foil, and a plastic layer or film 66. Typi
`20
`in which the cable 20 of this invention is useful. In FIG.
`cally, the thickness of the metallic portion is about 0.002
`4, a transmitting device 37 at one station is connected
`inch while that of the plastic film is 0.001 inch. In the
`along a pair of conductors 42-42 of one cable to an
`preferred embodiment, the metallic portion 64 faces
`outwardly.
`interconnect hub 39 and then back out along another
`cable to a receiving device 41 at another station. A
`A drain wire 68 also is included in the cable 20 in
`25
`plurality of the stations comprising transmitting devices
`engagement with the metallic portion 64 of the shield
`37-37 and receiving devices 41-41 are connected to
`60. It may be disposed between the metallic shield 60
`the interconnect hub in what is referred to as a ring
`and one of the tubular members which covers a pair of
`individually insulated conductors. In the preferred em
`network. As can be seen, the conductors are routed
`from the transmitting device at one terminal to the hub
`bodiment, the metallic portion 64 of the shield faces
`30
`39 and out to the receiving device at another terminal,
`outwardly and the drain wire 68 is disposed adjacent to
`thereby doubling the transmission distance.
`the outer surface of the shield 60 so that the metallic
`More particularly, the cable 20 of this invention in
`portion is oriented toward and in engagement with the
`cludes a plurality of twisted pairs 43-43 of the individ
`drain wire.
`ually insulated conductors 42-42 (see FIGS. 1 and 5).
`Each of the tubular 51-51 functions as a buffer
`The twist length is generally less than 3 inches with the
`which causes the individually insulated conductor pairs
`shortest being about 1.8 inches. In the embodiment as
`to be isolated from the shield 60 with respect to attenua
`shown in FIGS. 1 and 5, the core comprises two pairs of
`tion. Otherwise, the closer a pair of insulated conduc
`individually insulated conductors 42-42 which are
`tors is to the metallic shield, the higher the attenuation.
`used for data transmission. Each of the conductors
`Because of the thickness of the buffer members 51-51,
`42-42 includes a metallic portion 44 and an insulation
`each insulated conductor of each twisted pair of con
`cover 46. In a preferred embodiment which is shown in
`ductors is separated from the metallic shield by a dis
`FIGS. 1 and 5, the insulation cover comprises an inner
`tance which is not less than one half the diameter of the
`layer 47 of cellular material such as for example, ex
`wire which comprises the metallic portion 44 of each
`panded polyethylene and an outer skin layer 49 of a
`conductor. The tubular members or portions of the
`45
`solid plastic material such as a polyvinyl chloride com
`buffer system may take other forms as long as they
`position. In a preferred embodiment, the metallic con
`comprise material having a relatively low dielectric
`ductor is 22 gauge copper, the thickness of the inner
`constant. For example, each of the tubular members
`layer is about 0.018 inch and that of the outer layer is
`51-51 may comprise material in strip form which is
`wrapped helically or longitudinally, for example, about
`about 0.004 inch.
`Each of the pairs of insulated conductors 42-42 is
`its associated pair of individually insulated conductors
`enclosed individually by a portion of a buffer system
`42-42. Also, the S-shaped preform 58 in FIG.7 may be
`such as by a tubular member 51 (see FIGS. 1 and 5)
`replaced with a tape which is made of a dielectric mate
`which in a preferred embodiment comprises a polyvinyl
`rial and which is wrapped about the conductor pairs to
`chloride composition. The thickness of the tubular
`cause each pair to be enclosed substantially in a dielec
`member 51 is equal at least to the radius of the metallic
`tric portion of the buffer system.
`portion 44 of each insulated conductor of the pair en
`In the drawings, FIGS. 8A-8D depict the evolution
`closed by the tubular member. In this way, each of the
`of cable changes beginning with a conventional twisted
`pairs of individually insulated conductors is said to be
`pair cable and ending with the preferred embodiment of
`belted or buffered. In an alternative embodiment, the
`this invention. These views are intended to depict the
`60
`tubular member comprises an expanded polyvinyl chlo
`changes with the conductor portions 44-44 being the
`ride plastic material. The thickness of the tubular mem
`same diameter in all the views, although the figures
`ber 51 in a preferred embodiment is about 0.030 inch.
`have been scaled differently for convenience of illustra
`Other embodiments of the individual conductor pair
`tion. As can be imagined from a review of the drawings,
`buffering are shown in FIGS. 6 and 7. It is within the
`the opportunity for the insulated conductors 42-42 of
`65
`scope of this invention to replace the tubular members
`one pair to interlock physically with the conductors of
`51-51 with a preform 55 comprising dual tubular
`an adjacent pair is negated. As is known, it is common
`buffer portions or members 56-56 which are joined
`place in packed cores for at least one individually insu
`
`40
`
`50
`
`55
`
`

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`
`35
`
`20
`
`4,755,629
`8
`7
`lated conductor 71 of one twisted pair to invade the
`of 2.8 and the diameter of the metallic conductor 44. In
`space of another pair as defined by a circumscribing
`one prior art local area network cable, each conductor
`pair is shielded and has a diameter-over-dielectric
`circle 73 (see FIG. 8A). Pair invasion also results, unde
`sirably, in the distortion of the twist configurations,
`(DOD) of 0.096 inch. The belted pair of the cable of this
`particularly those of longer twist lengths by conductors 5
`invention has a DOD of 0.070 inch which is accepted by
`a conventional cross-connect panel, for example.
`of pairs having shorter twist lengths. In FIG. 8A, the
`In a preferred embodiment, the cable 20 is provided
`outer diameter of the insulated conductor, which is
`with an outer jacket 80 (see FIGS. 1 and 5) which com
`referred to as its diameter-over-dielectric (DOD), is
`prises a polyvinyl chloride material. Advantageously,
`equal about to the product of 1.7 and the diameter of a
`the jacket material is fire-retardant. Further in a pre
`metallic conductor portion 44. For the pairs of individu
`ferred embodiment, the thickness of the jacket 80 is in
`ally insulated conductors which are shown in FIG. 8A,
`there is relatively high capacitance and low inductance.
`range of about 0.025 inch.
`It is within the scope of this invention to provide a
`Transmission loss is proportional to the square root of
`cable 82 (see FIG. 9A) which includes a plurality of the
`the quotient of capacitance and inductance. Accord
`ingly for a twisted pair of conductors having relatively
`insulated conductors 42-42 with each pair enclosed
`15
`individually with a tubular member 51 and a shield 60
`thin wall insulation such as the pair shown in FIG. 8A,
`but without the jacket 80. Of course, the jacket 80 of the
`the loss is relatively high.
`preferred embodiment provides mechanical protection
`In FIG. 8B, there are shown insulation portions
`for the cable. It is also within the scope of this invention
`75s,75 of a low capacitance cable with standard pair
`to enclose the buffer system with a jacket only (see
`twists. The DOD of each insulated conductor 75 is
`equal about to the product of 4 and the diameter of the
`FIG. 9B) should a shield not be needed such as in a
`replacement for D-inside wiring, or to bind together the
`metallic conductor portion 44. For this cable, capaci
`individual buffer members. Of course, if the preform 55
`tance is reduced and inductance is increased, both of
`or 58 is used, a binder may not be necessary.
`which reduce the loss. Surprisingly, resistance also is
`For voice communications, the cable 20 may be pro
`reduced, thereby further reducing the loss. However,
`25
`vided with a plurality of pairs of individually insulated
`the DOD is so large that the insulated conductors can
`conductors 90-90 (see FIGS. 1 and 5). Each of the
`not be terminated with conventional connector hard
`conductors 90-90 of each of the pairs includes an elon
`Wae.
`gated metallic member such as 22 gauge wire, a solid
`In each pair of conductors of the cable of FIG. 8B is
`polyethylene inner layer 92 of insulation and an outer 94
`confined in a metallic shield 79 (see FIG. 8C), the ca
`30
`layer of insulation comprising polyvinyl chloride mate
`pacitance increases, there is no space sharing and as in a
`coaxial cable the transmission loss is higher. The shield
`rial.
`When considering a combination high speed data and
`... is effective in terminating the field that otherwise would
`telephone wire pair, it is common knowledge that the
`... extend out from the conductors into the shared space.
`maximum practical data rate on twisted copper pairs is
`As such, a shield is very effective in retaining all the
`electromagnetic energy inside its periphery, but the
`about 1 Mb/s. Given the limited range required for
`building distribution systems, up to 10 Mb/s may be
`transmission loss increases. Also, the DOD remains too
`allowed for twisted pairs. Limitations usually involve
`... large to facilitate termination with conventional con
`crosstalk and, at times, EM1. Whatever the limitations
`nector hardware.
`imposed by these interferences, the impulse noise gener
`...
`As should be apparent, the conductor pairs in FIG.
`40
`ated by the telephone switchhook operation can be 20
`.8D which are not individually shielded but which are
`"... individually buffered, share the electromagnetic space
`to 30 dB greater than the signal power in a data stream.
`therebetween, but not the physical space of each pair as
`Therefore, limitations imposed by crosstalk between
`two data streams are escalated 20 to 30 dB if telephone
`defined by the circumscribing circles. Neither conduc
`signals are placed in the same cable with no isolation
`tor of one pair of the cable 20 of this invention invades
`45
`the circled circumscribed space of another pair. In the
`therebetween.
`It should be observed from the drawings, that, unlike
`cable 20, this results from the provision of an individual
`tube 51 for each conductor pair, which arrangement is
`the conductors 42-42 which are used for data transmis
`shown schematically in FIG. 8D. The buffer or belt
`sion, the voice communication pairs of insulated con
`ductors 90-90 are disposed between the metallic shield
`about each pair prevents the invasion of space of one 50
`pair by a conductor 42 of an adjacent pair.
`60 and the outer jacket 80. This is done in order to
`prevent so-called impulse noise from interfering with
`The use of individual buffer portions such as tubular
`members 51-51 for each conductor pair results in
`data transmission. Also, as can be observed from the
`lower attenuation and improved crosstalk performance.
`drawings, the voice communication pairs of insulated
`conductors 90-90 are diametrically opposed to each
`Each buffer portion functions to maintain a space be
`55
`other. Again this provides better isolation for those
`tween the associated conductor pair and the shield
`pairs with respect to voice-to-voice and impulse noise
`which reduces the excess loss which otherwise would
`be caused