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`US005594726A
`
`United States Patent
`
`[19]
`
`Thompson et a1.
`
`5,594,726
`[11] Patent Number:
`
`[45] Date of Patent:
`Jan. 14, 1997
`
`[54]
`
`[75]
`
`[73]
`
`[21]
`
`[22]
`
`[53]
`
`[51]
`[52]
`
`[58]
`
`[56]
`
`FREQUENCY AGILE BROADBAND
`COMMUNICATIONS SYSTEM
`
`Inventors: Leo J. Thompson, Lilburn; Gregory T.
`Dubberly, Atlanta; John A. Ritchie,
`Jr., Duluth, allof Ga.
`
`4,912,552
`4,926,255
`4,955,048
`4,961,109
`
`3/1990 A111son,HIeta].
`..................... 358/84
`5/1990 Von Kohom .......... 358/84
`
`..... 379/53
`3/1990 Iwamura et a1.
`
`10/1990 Tanaka ............... 358/84
`
`(List continued on next page.)
`FOREIGN PATENT DOCUMENTS
`
`Assignee: Scientific-Atlanta, Inc., Atlanta, Ga.
`
`WO90/13956
`
`11/1990 WIPO .
`
`Appl. No.: 219,848
`
`Filed:
`
`Mar. 30, 1994
`
`Related US. Application Data
`
`Continuation-impart of Ser. No. 123,363, Sep, 17, 1993, Pat.
`No. 5,499,241.
`
`Int. Cl.6 ........................................................ H04J 1/00
`US. Cl. ........................... 370/485; 370/524; 455/5.1;
`455/61; 348/12
`Field of Search .................................. 348/12, 11, 14,
`348/15; 370/691, 71, 73, 110.1, 112; 375/219,
`222, 202; 455/5.1, 6.10, 4.1, 6.3, 6.2, 3.1
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`2,236,501
`4/1941 Goldsmith .
`3,275,746
`9/1966 Beltrami.
`3,529,088
`9/1970 Hauer ........................................ 370/76
`
`3,992,589
`.. 370/120
`11/1976 Kuegler ..
`4,099,202
`7/1978 Cavanaugh
`358/85
`
`4,367,548
`1/1983 Cotten, Jr. et a].
`358/86
`
`4,485,400 11/1984 Lemelson et a1.
`358/85
`
`. 370/951
`4,633,462 12/1986 Shitle et a].
`
`11/1987 Fox eta]. ............. 455/612
`4,709,418
`
`.
`.. 370/1041
`4,742,512
`5/1988 Akashi et a].
`
`..
`..... 370/941
`4,748,618
`5/1988 Brown eta].
`
`4,761,684
`8/1988 Clark et a1.
`358/84
`
`. 370/581
`4,763,317
`8/1988 Lehman eta].
`
`7/1989 Kleinerman .......
`4,849,811
`358/133
`
`
`12/1989 Guichard et a1
`.. 358/143
`4,887,158
`
`12/1989 Bohn .................. 358/84
`4,888,638
`
`4,888,795
`12/1989 Ando et al.
`379/53
`1/1990 Way ..................
`. 358/86
`4,891,694
`
`4,905,080
`2/1990 Watanabe et a].
`358/84
`............................. 358/84
`4,907,079
`3/1990 Turner ct a1.
`
`TELEPHOHVMTEJPHONY
`NE
`nxr. Marv/011K]?
`
`OTHER PUBLICATIONS
`
`A Passive Optical/Coax Hybrid Network Architecture for
`Delivery of CATV, Telephony and Data Services; 1993. by
`M. Mesiya, pp. 358—364.
`
`Primary Examinerf—Benedict V. Safourek
`Assistant Examiner—Ajit Patel
`Attorney, Agent, or Firmilones & Askew
`
`[57]
`
`ABSTRACT
`
`A broadband communications system for coupling tele-
`phony or other digital networks to a CATV network. The
`system transmits a multiplex of telephony signals in the
`forward band of the CATV network. Each forward channel
`is QPR modulated on a carrier and contains multiple sub-
`scriber telephony signals. The forward telephony channels
`are demodulated and demultiplexed by a plurality of sub-
`scriber terminals into the individual
`telephony signals
`directed to an addressed subscriber. Audio and control
`signals returning from the subscriber are digitized into
`standard telephony signals and QPSK modulated on a carrier
`onto the reverse band of the CATV network. The multiplic-
`ity of reverse band telephony channels are demodulated and
`multiplexed into a standard telephony signal which is
`directly interfaced to the telephony network. The reverse
`band modulators are frequency agile and modulate tele-
`phony signals from a subscriber in a selected one or more
`frequency subbands in the reverse band of the subscription
`network, so as to provide selectably changeable frequencies
`and selectably variable bandwidth in the reverse band com—
`mensurate with a selected subscriber communication fea-
`ture. e.g. a single voice line, multiple voice lines, ISDN
`service, data communications services, security monitoring
`services, etc.
`
`113 Claims, 15 Drawing Sheets
`
`, \ HEADEND
`
`FIBER
`Nuns
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`
`Petitioner Cisco Systems - Exhibit 1009 - Page 1
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 1
`
`

`

`5,594,726
`
`Page 2
`
`US. PATENT DOCUMENTS
`
`4,974,252
`4,975,902
`4,995,071
`5,003,384
`5,008,926
`5,014,125
`5,029,333
`
`11/1990 Osborne .................................... 379/92
`
`. 370/62
`12/1990 Damany
`2/1991 Weber a a1.
`..
`' 379,53
`
`3,199] Burden et a1__
`. 358,84
`
`4/1991 Misholi
`..........
`.379/54
`5/1991 Pocock e1 a1. ..................... 358/86
`7/1991 Graves et a1.
`......................... 370/58.1
`
`5,063,587
`5,075,771
`5,084,903
`5,088,111
`5,124,980
`5,351,234
`5,440,335
`5,469,495
`
`............................ 379/53
`11/1991 Semasa et a1.
`12/1991 Hashimoto ................................ 358/84
`1,1992 McNamara a a1.
`...................... 375/18
`
`2/1992 McNamara et a1..
`.. 375/18
`6/1992 Maki
`................
`370/77
`9/1994 Beierle et a1.
`.. 370/50
`8/1995 Beveridge
`348/13
`11/1995 Beveridge
`._ 379/56
`
`
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 2
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 2
`
`

`

`US. Patent
`
`Jan. 14, 1997
`
`Sheet 1 of 15
`
`5,594,726
`
`TELEPHONY1 0 TELEPHONY
`NETWORK N NETWORK 19
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`Petitioner Cisco Systems - Exhibit 1009 - Page 3
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 3
`
`

`

`US. Patent
`
`Jan. 14, 1997
`
`Sheet 2 of 15
`
`5,594,726
`
`fREVERSE BAND
`DIPLEX CROSSOVER REGION
`
`CATV
`FREQUENCY
`
`ALLOCATION
`
`FORWARD
`
`/ BAND
`
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`
`FIG. 3C
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 4
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 4
`
`

`

`US. Patent
`
`Jan. 14, 1997
`
`Sheet 3 of 15
`
`5,594,726
`
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`Petitioner Cisco Systems - Exhibit 1009 - Page 5
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 5
`
`

`

`US. Patent
`
`Jan. 14, 1997
`
`Sheet 4 of 15
`
`5,594,726
`
`62
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`Petitioner Cisco Systems - Exhibit 1009 - Page 6
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 6
`
`

`

`US. Patent
`
`Jan. 14,1997
`
`Sheet 5 of 15
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`5,594,726
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`Petitioner Cisco Systems - Exhibit 1009 - Page 7
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 7
`
`

`

`US. Patent
`
`Jan. 14, 1997
`
`Sheet 6 of 15
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`5,594,726
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`Petitioner Cisco Systems - Exhibit 1009 - Page 8
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 8
`
`
`
`
`

`

`US. Patent
`
`Jan. 14, 1997
`
`Sheet 7 of 15
`
`5,594,726
`
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`Petitioner Cisco Systems - Exhibit 1009 - Page 9
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 9
`
`

`

`US. Patent
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`Petitioner Cisco Systems - Exhibit 1009 - Page 10
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 10
`
`
`

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`Petitioner Cisco Systems - Exhibit 1009 - Page 11
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 11
`
`
`
`
`
`
`

`

`US. Patent
`
`Jan. 14, 1997
`
`Sheet 10 of 15
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`5,594,726
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`Petitioner Cisco Systems - Exhibit 1009 - Page 12
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 12
`
`
`

`

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`Petitioner Cisco Systems - Exhibit 1009 - Page 13
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 13
`
`
`
`
`

`

`US. Patent
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`Jan. 14, 1997
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`Sheet 12 of 15
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`5,594,726
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`Petitioner Cisco Systems - Exhibit 1009 - Page 14
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`Petitioner Cisco Systems - Exhibit 1009 - Page 14
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`US. Patent
`
`Jan. 14, 1997
`
`Sheet 13 of 15
`
`5,594,726
`
`128 kHz
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`
`Petitioner Cisco Systems - Exhibit 1009 - Page 15
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`Petitioner Cisco Systems - Exhibit 1009 - Page 15
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`

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`US. Patent
`
`Jan. 14, 1997
`
`Sheet 14 of 15
`
`5,594,726
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`Petitioner Cisco Systems - Exhibit 1009 - Page 16
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`Petitioner Cisco Systems - Exhibit 1009 - Page 16
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`US. Patent
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`Jan. 14, 1997
`
`Sheet 15 of 15
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`5,594,726
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`
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`Petitioner Cisco Systems - Exhibit 1009 - Page 17
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`Petitioner Cisco Systems - Exhibit 1009 - Page 17
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`5,594,726
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`1
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`FREQUENCY AGILE BROADBAND
`COMMUNICATIONS SYSTEM
`
`CROSS REFERENCE TO RELATED
`APPLICATION
`
`This application is a continuation-in-part of application
`Ser. No. 08/123,363, filed Sep. 17, 1993, now U.S. Pat. No.
`5,499,241, entitled “Broadband Communications System”.
`
`FIELD OF THE INVENTION
`
`The system pertains generally to broadband communica—
`tions systems, such as cable or community antenna televi-
`sion (CATV) networks, and is more particularly directed to
`communicating telephony signals, and other or similar sig-
`nals, over CATV and equivalent networks.
`
`BACKGROUND OF THE INVENTION
`
`In order to introduce the present invention and the prob-
`lems that it solves, it is useful to overview a conventional
`CATV broadband communication system, and then examine
`certain prior approaches to problems encountered when
`attempting to introduce telephony signals into the broadband
`environment.
`
`Conventional Cable Television Systems (CATV)
`Cable television systems, sometimes referred to as com—
`munity-antenna television (CATV) systems, are broadband
`communications networks of coaxial cable and optical fiber
`that distribute television, audio, and data signals to sub-
`scriber homes or businesses. In a typical CATV system, a
`single advantageously located antenna array feeding a cable
`network supplies each individual subscriber with a usable
`television signal.
`'
`Since the pioneer days, cable networks have experienced
`enormous growth and expansion in the United States, par—
`ticularly in urban networks. It is estimated that CATV
`networks currently pass approximately 90% of the popula-
`tion in the United States, with approximately 60—65% of all
`households actually being connected. While cable systems
`originally had very simple architectures and provided a
`limited number of different television signals, the increase in
`the number of television broadcasters and television owners
`over the last several decades has resulted in much more
`complex and costly modern cable distribution systems.
`A typical CATV system comprises four main elements: a
`headend, a trunk system, a distribution system, and sub-
`scriber drops.
`The “headend” is a signal reception and processing center
`that collects, organizes and distributes signals. The headend
`receives satellite-delivered video and audio programming,
`over-the-air broadcast TV station signals, and network feeds
`delivered by terrestrial microwave and other communication
`systems. In addition, headends may inject local broadcasting
`into the package of signals sent
`to subscribers such as
`commercials and live programming created in a studio.
`The headend contains signal-processing equipment that
`controls the output level of the signals, regulates the signal-
`to-noise ratio, and suppresses undesired out-of-band signals.
`Typical signal-processing equipment includes a heterodyne
`processor or a demodulator-modulator pair. The headend
`then modulates received signals onto separate radio fre-
`quency (RF) carriers and combines them for transmission
`over the cable system.
`The “trunk system” is the main artery of the CATV
`network that carries the signals from the headend to a
`number of distribution points in the community. A modern
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`trunk system typically comprises of a combination of
`coaxial cable and optical fibers with trunk amplifiers peri-
`odically spaced to compensate for attenuation of the signals
`along the line. Such modern trunk systems utilizing fiber
`optics and coaxial cable are often referred to as “fiber/coax"
`systems.
`The “distribution systems" utilize a combination of opti-
`cal flbers and coaxial cable to deliver signals from the trunk
`system into individual neighborhoods for distribution to
`subscribers. In order to compensate for various losses and
`distortions inherent in the transmission of signals along the
`cable network, line-extender amplifiers are placed at certain
`intervals along the length of the cable. Each amplifier is
`given just enough gain to overcome the attenuation loss of
`the section of the cable that precedes it. A distribution
`network is also called the “feeder”.
`There is a strong desire in the CATV and telecommuni-
`cations industry to push optical fiber as deeply as possible
`into communities, since optical fiber communications can
`carry more signals than conventional networks. Due to
`technological and economic limitations,
`it has not yet
`proved feasible to provide fiber to the subscriber’s home.
`Present day “fiber deep” CATV distribution systems includ-
`ing optical fibers and coaxial cable are often called “fiber-
`To—the—Serving—Area” or “FFSA” systems.
`“Subscriber drops” are taps in the distribution system that
`feed individual 75 Q coaxial cable lines into subscribers’
`television sets or subscriber terminals, often referred to as
`“subscriber premises equipment” or “customer premises
`equipment” (“CPE”). Since the tap is the final service point
`immediately prior to the subscriber premises, channel autho-
`rization circuitry is often placed in the tap to control access
`to scrambled or premium programming.
`Cable distribution systems were originally designed to
`distribute television and radio signals in the “downstream”
`direction only (i.e., from a central headend location to
`multiple subscriber locations, also referred to as the “for-
`ward” path). Therefore, the component equipment of many
`older cable systems, which includes amplifiers and compen-
`sation networks, is typically adapted to deliver signals in the
`forward direction only. For downstream transmissions, typi-
`cal CATV systems provide a series of video channels, each
`6 MHz in bandwidth, which are frequency division multi-
`plexed across the forward band, in the 50 MHz to 550 MHz
`region of the frequency spectrum. As fiber is moved more
`deeply into the serving areas in fiber/coax and FI‘SA con-
`figurations, the bandwidth of the coax portion is expected to
`increase to over 1 GHz.
`The advent of pay-per-view services and other interactive
`television applications has fueled the development of bidi—
`rectional or “two—way” cable systems that also provide for
`the transmission of signals from the subscriber locations
`back to the headend. This is often referred to as the
`“upstream” direction or the “reverse” path. This technology
`has allowed cable operators to provide many new interactive
`subscriber services on the network, such as impulse—pay—
`per—view (IPPV). In many CATV systems, the band of
`signals from 5 MHz to 30 MHz is used for reverse path
`signals.
`However, the topology of a typical CATV system, which
`looks like a “tree and branch” with the headend at the base
`and branching outwardly to the subscriber’s, creates tech-
`nical diificulties in transmitting signals in the upstream
`direction back to the headend. In the traditional tree and
`branch cable network, a common set of downstream signals
`are distributed to every subscriber home in the network.
`Upstream signals flowing from a single subscriber toward
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`Petitioner Cisco Systems - Exhibit 1009 - Page 18
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`Petitioner Cisco Systems - Exhibit 1009 - Page 18
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`5,594,726
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`3
`the headend pass by all the other upstream subscriber homes
`on the segment of distribution cable that serves the neigh—
`borhood.
`The standard tree and branch topology has not proven to
`be well suited for sending signals from each subscriber
`location back to the headend, as is required for bidirectional
`communication services. Tree and branch cable distribution
`systems are the most efficient in terms of cable and distri-
`bution usage when signals have to be distributed in only the
`downstream direction. A cable distribution system is gener-
`ally a very noisy environment, especially in the reverse path.
`Interfering signals may originate from a number of cornmon
`sources, such as airplanes passing overhead or from Citizens
`Band (CB) radios that operate at a common frequency of 27
`MHZ, which is within the typical reverse channel bandwidth
`of CATV networks. Since the reverse direction of a tree and
`branch configuration appears as an inverted tree, noise is
`propagated from multiple distribution points to a single
`point, the headend. Therefore, all of the individual noise
`contributions collectively add together to produce a very
`noisy environment and a communications problem at the
`headend.
`Present day FFSA systems facilitate the communication
`of signals in the reverse direction by dividing the subscriber
`base of a cable network into manageable serving areas of
`approximately 400—2500 subscribers. This allows for the
`reuse of limited reverse band frequency ranges for smaller
`groups of subscribers. The headend serves as the central hub
`of a star configuration to which each serving area is coupled
`by an optical communications path ending in a fiber node.
`The fiber node is connected to the serving area subscribers
`over a coaxial cable distribution sub-network of feeders and
`drops in each serving area. In the FI‘SA configuration, some
`of the signals in the forward direction (e.g.,
`television
`program signals) are identical for each serving area so that
`the same subscriber service is provided to all subscribers. In
`the reverse direction, the configuration provides an indepen-
`dent spectrum of frequencies confined to the particular
`serving area. The FTSA architecture thus provides the
`advantage of multiplying the bandwidth of the reverse
`portions of the frequency spectrum times the number of
`serving areas.
`The Desire for Telephony Service
`The ever-expanding deployment of fiber optic technology
`in CATV systems across the country has cable operators
`looking to provide a whole new range of interactive services
`on the cable network. One area that is of particular interest
`is telephony service. Because of recent advances in tech-
`nology as well as the loosening of regulations, the once
`distinct lines between the cable television network and the
`telephone network have blurred considerably. Currently
`there is a great demand for a broadband communication
`system that can efiiciently provide telephone service over
`the existing cable distribution network.
`Moreover, there is substantial interest expressed by tele-
`phone system operating companies in the idea of increased
`bandwidth for provision of new services to telephone sub-
`scribers, such as television;
`interactive computing, shop-
`ping, and entertainment; videoconferencing, etc. Present day
`“copper” based telephony service (so called because of the
`use of copper wires for telephone lines) is very bandwidth
`limited—about 3 kHz—and cannot provide for
`such
`enhanced services by the telephone companies without
`massive changes to the telephone networks infrastructure.
`Existing communications systems, however, have not
`proven to be well suited for the transmission of telephony
`signals on the cable network. A system for transmitting
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`telephony signals must be configured to allow single point to
`single point distribution (i.e., from a single subscriber to a
`single subscriber). However, unlike the telephone compa-
`nies with their well-established national two-way networks,
`the cable industry is fragmented into thousands of individual
`systems that are generally incapable of communicating with
`one another. The cable network is instead ideally configured
`for single point to multiple point signal transmission (i.e.,
`from a single headend downstream to multiple subscriber
`locations).
`Moreover, CATV systems do not have the switching
`capabilities necessary to provide point to point communi—
`cations. A communications system for the transmission of
`telephone signals must therefore be compatible with the
`public switched telephone networks (“PSTN”) operated by
`the telephone operating companies. To be useful in the
`carriage of telephony signals, a CATV network must be able
`to seamlessly interface to a telephony network at a point
`where it is commercially viable to carry telephony signals.
`It must also provide signals that can pass to other parts of the
`interconnected telephone systems without extensive modu-
`lation or protocol changes to thereby become part of the
`international telephone system.
`Telephony on Data Communications Network
`One approach taken to provide a bidirectional broadband
`communications system is shown in US. Pat. No. 5,084,903
`of McNamara et al., assigned to First Pacific Networks
`(hereinafter referred to as “FPN”). This patent describes an
`approach to the communication of telephony signals that
`appears primarily designed to operate in an ofiice-type data
`communications network environment (e.g., Ethernet). Data
`communications networks are typically bandwidth sym-
`metrical, that is, the forward and reverse signal paths con-
`sume equal amounts of bandwidth, and the topology is star
`or serial, not tree and branch. In contrast, CATV networks
`are bandwidth asymmetrical, with heavy allocation of band—
`width for use in the downstream direction and limited
`upstream bandwidth. As the present inventors have discov-
`ered, the noise problem in the upstream direction is difficult
`in a broadband bandwidth-asymmetrical, tree and branch
`topology, as contrasted with a symmetrical oflice-type data
`communications network.
`
`The system described in the FPN patent employs two
`different modulation schemes for communicating informa-
`tion between a central headend and a plurality of subscriber
`nodes. For downstream communications, the FPN system
`transmits signals continuously in a plurality of 6 MHz
`bandwidth charmels. In a preferred embodiment, an AM-
`PSK modulator
`is used in the downstream path. For
`upstream communications, the FPN system transmits pack-
`ets of information in bursts to a headend using an offset
`quadrature phase shift keyed (OQPSK) modulator.
`While the FPN communications system may be suitable
`for communicating telephony signals on a data communi-
`cations network such as Ethernet, it does not solve certain
`problems that occUr in the carriage of telephony signals on
`a broadband cable network. Due to the single point to
`multiple point configuration (tree and branch) of the CATV
`network, upstream transmissions of telephony signals have
`to contend with multiple noise sources as the branch signals
`from each subscriber are merged together toward the head-
`end. It is believed, however, that the burst mode approach
`used in the reverse path of the FPN system is particularly
`susceptible to these noise issues. Specifically, it is believed
`that the framing bits and sequencing of the data streams are
`susceptible to interruption when an interference signal is
`sustained for any significant length of time (i.e., for longer
`
`Petitioner Cisco Systems - Exhibit 1009 - Page 19
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`Petitioner Cisco Systems - Exhibit 1009 - Page 19
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`5,594,726
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`5
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`than the length of a data frame) anywhere within one of the
`6 MHz bandwidth channels used to carry telephony signals.
`It is further believed that the interruption of the framing
`bits may result
`in the loss of content
`in all
`telephone
`conversations represented within the data frame interrupted.
`In a data communications environment, this signal interrup-
`tion may only be noticeable as a slowdown on the network,
`and, though inconvenient, may be considered acceptable.
`However, such degradation of signal quality in a cable and
`telephony environment is undesirable and may be unaccept-
`able.
`There is no discussion in the FPN patent of any means for
`insertion or removal of telephony signals from and to the
`public switched telephone network (PSTN). The FPN sys-
`tem appears to provide only a local area telephone network
`designed primarily for inter-oflice communications (such as
`oflice to ofiice intercom), as only limited access to the PSTN
`is suggested. There are a number of diiferent locations in the
`FPN equipment where telephony signal
`insertion and
`removal could occur, but the patent does not describe any
`means for signal insertion or removal, or discuss any of the
`issues associated with signal insertion and removal. At best,
`it appears that telephony signals would be inserted and
`removed at nodes directly connected to the broadband media
`(e.g., the coaxial cable), as suggested at col. 3, line 30. The
`patent does not indicate how such insertion and removal
`directly from the broadband medium should best be effected,
`and is silent on issues involving multiple telephony chan—
`nels.
`Therefore, there is a need for a broadband communica—
`tions system that is compatible with the existing public
`switched telephone networks and that is not sensitive to
`noise or other interference issues, particularly in the reverse
`path. There is also a need for a broadband communications
`system that is bandwidth efficient and provides a higher
`spectral efficiency than present systems, thereby increasing
`the number of subscribers that may be served by each
`broadband network with telephony and enhanced services
`offered by CATV system operators,
`telephone company
`operating companies, and others.
`
`SUMMARY OF THE INVENTION
`
`The invention includes methods and apparatus for pro-
`viding broadband communications, including bidirectional
`telephony communications, over a cable distribution net-
`work. In particular, the present invention provides an inte-
`grated CATV/telephony system that
`is compatible with
`today’s public switched telephone networks and can also
`deliver video, data, security monitoring, and other services
`without affecting current in—home wiring or equipment.
`In one embodiment, the method includes communicating
`telephony signals from a telephony network to the CATV
`subscribers in the forward band