United States Patent
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`Krimmel
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`[19]
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`[11] Patent Number:
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`[45] Date of Patent:
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`6,134,035
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`
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`Oct. 17, 2000
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`US006134035A
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`
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`FOREIGN PATENT DOCUMENTS
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`0024618
`8/1980 European Pat. Off.
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`2/1983
`3129752
`Germany .
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`4/1995
`4433793
`Germany .
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`
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`4436818 10/1995
`Germany .
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`4434918
`4/1996
`Germany .
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`19505578
`8/1996
`Germany .
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`19508394
`9/1996
`Germany .
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`OTHER PUBLICATIONS
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`Gottlicher, Gerhard, Selb, Michael, Bender, Rolf. Digitale
`Ubertragung von Analogsignalen iiber LWL—Strecken. In:
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`Electronik 1, 8.1, 1988, pp. 64-68.
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`Primary Examiner—Leslie Pascal
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`Assistant Examiner—Hanh Phan
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`Attorney, Agent, or Firm—Ware, Fressola, Van Der Sluys &
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`Adolphson LLP
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`.
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`[57]
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`ABSTRACT
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`In a hybrid fiber/coax access network (NET) with a forward
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`channel and a return channel, the return channel serves to
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`transmit voice and video signals as well as data signals from
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`groups of terminals (NT1; NT2) to a subcenter (HUB).
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`Access by a group of terminals (NT1; NT2) to a shared
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`electric line (KOAX1; KOAX2) is obtained by TDMA,
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`FDMA, or CDMA, for example. An optical network termi-
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`nation unit (ONU) is connected to one or more electric lines
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`(KOAX1; KOAX2). For each line or for each separate
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`frequency range of the return channel, the optical network
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`termination unit (ONU) contains an analog-to-digital con-
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`verter (A/D1, A/D2) which digitizes the received signal. If
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`two or more analog-to-digital converters (A/D1, A/D2) are
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`provided, the individual digitized signals are multiplexed in
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`a multiplexer (MUX) and then fed to a digital electrical-to-
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`optical transducer (E/O2). The electrical-to-optical trans-
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`ducer (E/O2) converts the multiplexed signals to optical
`signals, which are then transmitted over an optical cable
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`(FIBRE) to the subcenter (HUB), where they are processed
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`digitally.
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`7 Claims, 1 Drawing Sheet
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`[54] OPTICAL NETWORK TERMINATION UNIT
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`OF A HYBRID FIBER/COAX ACCESS
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`NETWORK
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`[75]
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`Inventor: Heinz Krimmel, Korntal-Miinchingen,
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`Germany
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`[73] Assignee: Alcatel, Paris, France
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`[22]
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`[21] Appl. No.: 08/961,442
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`Oct. 30, 1997
`Filed:
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`Foreign Application Priority Data
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`[30]
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`[DE]
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`Oct. 31, 1996
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`Germany ......................... .. 196 43 872
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`[51]
`Int. Cl.7 .................................................... .. H04J 14/02
`[52] U.S. Cl.
`........................ .. 359/125; 359/145; 359/118;
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`359/137
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`[58] Field of Search ................................... .. 359/145, 118,
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`359/125, 137
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`References Cited
`U.S. PATENT DOCUMENTS
`
`
`
`
`
`
`
`
`3,701,146
`........................... .. 340/347
`10/1972 Haga et al.
`3,940,759
`2/1976 Zitelli et al.
`340/347
`..
`
`
`
`
`
`
`
`6/1976 Gustafsson
`73/88.5
`3,960,010
`
`
`
`
`
`9/1980 Yamada ...... ..
`359/280
`4,222,077
`
`
`
`
`
`9/1980 Judell
`................. ..
`4,222,110
`364/724
`
`
`
`
`
`364/757
`9/1981 Buchanan et al.
`4,291,387
`
`
`
`
`1/1982 De Niet et al.
`375/19
`4,312,073
`
`
`
`
`
`
`11/1982 Tamada et al.
`..
`340/347
`4,358,752
`
`
`
`
`
`
`3/1984 Powers . . . . . . . . . . . . .
`. . . . .. 358/13
`4,438,452
`6/1984 Powers
`364/760
`4,455,611
`
`
`
`
`10/1985 Powers ...................................... .. 358/1
`4,550,335
`
`
`
`
`5/1986 Byrne .................................... .. 340/347
`4,588,986
`
`
`
`
`
`
`
`
`
`2/1991 Graves et al.
`4,994,909
`358/86
`5,058,102 10/1991 Heidemann ........ ..
`359/125
`
`
`
`
`
`5,517,232
`5/1996 Heidemann et al.
`..... .. 348/7
`
`
`
`
`
`
`8/1998 Schmid .............. ..
`5,793,506
`359/125
`
`
`
`
`
`5,815,105
`9/1998 Ohie ...................................... .. 341/155
`
`
`
`
`1/1999 Pomp et al.
`............................ .. 379/29
`5,859,895
`
`
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`[56]
`
`
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`HUB
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`NET
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`
`
`Netflix, Inc. Exhibit 1026
`
`Netflix, Inc. Exhibit 1026
`
`

`
`
`U.S. Patent
`
`
`
`Oct. 17, 2000
`
`
`
`
`6,134,035
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`Netflix, Inc. Exhibit 1026
`
`Netflix, Inc. Exhibit 1026
`
`

`
`6,134,035
`
`
`
`1
`
`OPTICAL NETWORK TERMINATION UNIT
`
`
`
`OF A HYBRID FIBER/COAX ACCESS
`
`
`
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`NETWORK
`
`TECHNICAL FIELD
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`
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`This invention relates to an optical termination unit of a
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`hybrid fiber/coax access network with a forward channel and
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`a return channel. It is also directed and to a method of
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`transmitting electric signals from two or more terminals of
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`a hybrid fiber/coax access network over an electric line and
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`an optical line.
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`BACKGROUND OF THE INVENTION
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`A hybrid fiber/coax access network is, for example, a
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`cable television distribution network with a forward channel
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`and a return channel, over which different bidirectional
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`services, such as telephony, Internet communication, or
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`video telephony, can be provided. DE 44 36 818 C1 dis-
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`closes a subscriber access network for transmitting digital
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`signals of bidirectional interactive telecommunications ser-
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`vices. Behind the coaxial cable repeater of a CATV coaxial
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`cable tree network which is closest
`to a respective
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`subscriber,
`the optical fibers of a fiber-optic network are
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`bidirectionally connected to the branches of the tree net-
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`work. Transmission on the optical fibers is digital,
`for
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`example in the ATM format. This requires a demodulation
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`and/or a frequency conversion of the electric subscriber
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`signals.
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`SUMMARY OF THE INVENTION
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`is therefore an object of the invention to transmit
`It
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`electric signals of a plurality of terminals of a hybrid
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`fiber/coax access network over significant distances, e.g., 50
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`km, with a smaller amount of technical complexity.
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`This object is attained by an optical network termination
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`unit of a hybrid fiber/coax access network with a forward
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`channel and a return channel which serves to receive and
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`electrically transmit optical signals in the forward channel
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`and to receive quasi-analog electric signals and optically
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`retransmit said quasi-analog electric signals to digital form
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`in the return channel, which for this purpose comprises an
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`optical-to-electrical transducer, a digital electrical-to-optical
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`transducer, and an analog-to-digital converter, wherein the
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`received electric signals are digitized in the analog-to-digital
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`converter, and wherein the digitized signals are converted to
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`digital optical signals in the digital electrical-to-optical
`transducer.
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`The object is also attained by a method of transmitting
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`electric signals from two or more terminals of a hybrid
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`fiber/coax access network over an electric line and an optical
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`line, comprising the steps of transmitting the electric signals
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`of the two or more terminals together over the electric line
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`to an optical network termination unit; and digitizing the
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`signals received in the optical termination unit and then
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`converting the digitized signals to optical signals by means
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`of a digital electrical-to-optical transducer.
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`A particular advantage of the invention is that a smaller
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`amount of circuitry is required in the optical network
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`termination units to convert the electric signals to optical
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`signals.
`Another advantage of the invention is the flexibility of the
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`application of the optical network termination units as a
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`result of the conversion of the electric signals without
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`previous demodulation and the resulting applicability to
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`arbitrarily modulated signals.
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`2
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`The invention will become more apparent from the fol-
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`lowing description of an embodiment when taken in con-
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`junction with the accompanying drawing.
`The single FIGURE of the drawing is a schematic repre-
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`sentation of a novel hybrid fiber/coax access network with a
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`forward channel and a return channel.
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`BEST MODE FOR CARRYING OUT THE
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`INVENTION
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`The hybrid fiber/coax access network NET serves to
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`transmit analog and digital television signals as well as data
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`signals, for example, from a subcenter HUB to a plurality of
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`terminals NT1, NT2, and analog and digital voice signals as
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`well as data signals, for example, from the terminals NT1,
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`NT2 to the subcenter HUB. The signals to be transmitted are
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`converted from electrical
`to optical form, E/O1, at
`the
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`subcenter HUB, and transmitted in the forward channel over
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`a distribution network consisting of optical cables, e.g., glass
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`fiber cables FIBRE, and optical splitters to a plurality of
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`optical network termination units ONU, of which one is
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`shown. In each optical network termination unit ONU, the
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`received signals are converted from optical
`to electrical
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`form. Then they are electrically transmitted over coaxial
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`cables KOAX1, KOAX2 to the plurality of terminals NT1,
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`NT2, of which two are shown by way of example. The video
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`signals are, for example, movies, educational programs, or
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`the like, which are selected by subscribers in an interactive
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`mode. The selection of the video signals and the transmis-
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`sion of the data signals, e.g. for Internet access, take place
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`via a return signal which occupies a frequency band
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`between, for example, 5 MHz and 30 MHz.
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`Groups of terminals NT1; NT2 each have access to the
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`frequency range of the return channel via an electric line
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`associated with the respective group, a coaxial cable
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`KOAX1; KOAX2. The access method used is TDMA (time
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`division multiple access), FDMA (frequency division mul-
`tiple access), or CDMA (code division multiple access), for
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`example. In all these methods, one electric line is shared by
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`a number of subscribers. Subcarrier modulation is used, so
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`that the signal received at the optical network termination
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`unit ONU is a quasi-analog signal.
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`Each optical network termination unit ONU has an
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`analog-to-digital converter A/D1, whose input is connected
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`to an electric line, the coaxial cable KOAX1. The quasi-
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`analog signal received over the coaxial cable KOAX1 from
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`the group of terminals NT1 is digitized in the analog-to-
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`digital converter A/D1. The digitization takes place at 80
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`MHz and with a resolution of 10 bits, for example. Each
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`analog-to-digital converter A/D1 may be preceded by a
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`bandpass filter or a low-pass filter, for example to form
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`frequency subbands or suppress interference, respectively.
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`The digitization is carried out without previous demodula-
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`tion and without frequency conversion. The received quasi-
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`analog signal is thus fed to the analog-to-digital converter
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`A/D1 unchanged, except that it may have been filtered.
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`One advantage of the digitization is that by means of
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`line equipment containing a digital electrical-to-
`digital
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`optical transducer, the digitized quasi-analog signal can be
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`retransmitted, which eliminates the need for the complicated
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`subcarrier signal transmission over optical fibers required
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`with the FDMA method. To transmit the digitized signal, all
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`conventional digital transport methods can be used regard-
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`less of the type of modulation employed. Furthermore,
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`processing of the digitized signal at the subcenter HUB by
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`means of a digital signal processor is simpler and lower in
`
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`
`
`
`
`
`Netflix, Inc. Exhibit 1026
`
`Netflix, Inc. Exhibit 1026
`
`

`
`6,134,035
`
`5
`
`
`3
`cost, since it can be digital, in contrast to analog processing
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`in the case of FDMA.
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`A disadvantage of the digitization is that in comparison
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`with the transmission over the coaxial cable KOAX1, a
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`wider transmission bandwidth is necessary, which, however,
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`is available on the optical cable FIBRE. The necessary
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`signal-to-noise ratio, however,
`is substantially reduced
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`because of the digitization. Thus, the transmission of the
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`digitized signal improves the utilization of the capacity of
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`the optical cable FIBRE.
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`Each optical network termination unit ONU includes a
`
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`digital electrical-to-optical transducer E/O2 for converting
`the digitized signal to an optical signal. The electrical-to-
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`optical transducer E/O2 is a directly modulated laser diode,
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`for example. The optical signal
`is transmitted over the
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`optical cable FIBRE to the subcenter HUB. The optical
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`network termination units use wavelength-division multi-
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`plexing with different wavelengths. One optical network
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`termination unit has a laser diode which emits light with a
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`wavelength of 1520 nm, for example, and another has a laser
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`diode which emits light with a wavelength of 1550 nm. The
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`subcenter HUB contains an optical-to-electrical transducer
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`O/E1 for converting the received optical signal back to an
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`electric signal and a digital signal processor DSP for
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`demodulating the electric signal and, for example, for con-
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`verting the protocol into that of an integrated services digital
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`network. Conventional, analog demodulation after digital-
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`to-analog conversion is also possible.
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`Each optical network termination unit ONU may further
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`include a second analog-to-digital converter A/D2 and a
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`multiplexer MUX. The analog-to-digital converter A/D2 is
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`connected to a line separated from the electric line KOAX1,
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`namely to the coaxial cable KOAX2. The coaxial cable
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`KOAX2 is connected to a group of terminals NT2 which all
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`have access to the coaxial cable KOAX2. The access method
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`used is TDMA, FDMA, or CDMA, for example.
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`The analog-to-digital converter A/D2 digitizes the quasi-
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`analog signal received from the terminals NT2 and passes
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`the digitized signal on to the multiplexer MUX. In the
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`multiplexer, the digitized signal from the analog-to-digital
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`converter A/Dl is multiplexed with the digitized signal from
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`the analog-to-digital converter A/D2. The multiplexer MUX
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`combines the two digitized signals into, for example, a
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`signal of double bit rate or operates as a time-division
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`multiplexer, for example. The output of the multiplexer
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`MUX is fed to the digital electrical-to-optical transducer
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`E/O2, where it is converted to an optical signal which is
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`optically transmitted to the subcenter HUB.
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`The optical network termination unit ONU may also
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`contain three or more analog-to-digital converters. The
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`number of analog-to-digital converters is limited by the ratio
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`of the transmission capacity on the optical cable FIBRE to
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`the sum of the transmission capacities on the electric lines
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`and by the resolution of the analog-to-digital converters. The
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`maximum is reached when the sum of the transmission
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`capacities of the digitized signals is equal to the transmission
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`capacity on the optical cable FIBRE. The transmission
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`capacity available on the optical cable FIBRE can thus be
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`optimally utilized.
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`In the embodiment, each separate electric line is con-
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`nected to a
`respective analog-to-digital converter.
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`Alternatively, two or more electric lines may be connected
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`to only one analog-to-digital converter, or one line may be
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`connected to two or more analog-to-digital converters. The
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`choice of the assignment of electric lines to analog-to-digital
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`converters is dependent on the capacity of the analog-to-
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`10
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`55
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`60
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`65
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`4
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`digital converters. If an analog-to-digital converter is
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`designed for a bandwidth which is smaller than the fre-
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`quency range of the return channel, it is appropriate to divide
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`the return channel, for example by means of bandpass filters
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`with different passbands, into separate frequency ranges and
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`to assign a respective analog-to-digital converter to each
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`frequency range. Furthermore, equal frequency ranges of
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`different electric lines could be assigned to one analog-to-
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`digital converter.
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`What is claimed is:
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`1. An optical network termination unit (ONU) of a hybrid
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`fiber/coax access network (NET) with a forward channel and
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`a return channel to provide a direct link between an optical
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`line (FIBRE) and an electric line (KOAX1),
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`wherein said optical termination unit (ONU) serves to
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`receive and electrically transmit optical signals in the
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`forward channel and to receive quasi-analog electric
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`signals and optically retransmit said quasi-analog elec-
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`tric signals in digital form in the return channel,
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`said optical network termination unit (ONU) comprising
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`an optical-to-electrical transducer (O/E2) operatively
`connected to the optical
`line (FIBRE), a digital
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`electrical-to-optical transducer (E/O2), and an analog-
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`to-digital converter (A/D1),
`is
`transducer (O/E2)
`wherein the optical-to-electrical
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`operatively connected to the optical line (FIBRE) for
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`directly receiving optical signals from the optical line
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`(FIBRE) and converting the received optical signals
`into electric signals in order to electrically transmit the
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`received optical signals directly to the electric line
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`(KOAX1); and the analog-to-digital converter (A/D1)
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`is operatively connected to the electric line (KOAX1)
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`for directly receiving quasi-analog electric signals from
`the electric line (KOAX1), converting the quasi-analog
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`electric signals into digitized quasi-analog signals and
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`conveying the digital signals to the electrical-to-optical
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`transducer (E/O2) so as to allow the electrical-to-
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`optical transducer (E/O2) to convert the digitized quasi-
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`analog signals into optical signals for direct retrans-
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`mitting via the optical line (FIBRE).
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`2. An optical network termination unit (ONU) as claimed
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`in claim 1, characterized in that
`the digitization of the
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`received electric signals takes place without previous
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`demodulation.
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`3. An optical network termination unit (ONU) as claimed
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`in claim 1, characterized in that the optical network termi-
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`nation unit (ONU) comprises at least one further analog-to-
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`digital converter (A/D2) and a multiplexer (MUX) opera-
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`tively connected to the analog-to-digital converters (A/D1,
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`A/D2), that the at least one further analog-to-digital con-
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`verter (A/D2) serves to digitize the received signals in a
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`separate frequency range of the return channel, and that the
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`different digitized signals are directly conveyed from the
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`analog-to-digital converters (A/D1, A/D2) to the multiplexer
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`(MUX) in order for the different digitized signals to be
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`multiplexed in the multiplexer (MUX) and then directly fed
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`to the digital electrical-to-optical transducer (E/O2).
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`4. An optical network termination unit (ONU) as claimed
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`in claim 1, characterized in that a bandpass filter or a
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`low-pass filter is connected ahead of the analog-to-digital
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`converter (A/D1) to form frequency sub-bands or suppress
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`interference, respectively.
`
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`5. An optical network termination unit (ONU) as claimed
`
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`in claim 1, wherein the analog-to-digital converter (A/D1)
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`converts the quasi-analog electric signals into first digitized
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`electric signals, characterized in that the optical network
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`termination unit (ONU) comprises at
`least one further
`
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`
`
`Netflix, Inc. Exhibit 1026
`
`Netflix, Inc. Exhibit 1026
`
`

`
`
`
`6
`
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`6. An optical network termination unit (ONU) as claimed
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`in claim 5, wherein the quasi-analog electric signals are
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`converted into the first digitized electric signals with a first
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`bit rate and the multiplexer (MUX) combines the first and
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`second digitized electric signals into signals with a second
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`bit rate greater than the first bit rate.
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`7. An optical network termination unit (ONU) as claimed
`
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`in claim 1, wherein subcarrier modulation is used to generate
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`the quasi-analog electric signals in order to allow the electric
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`line (KOAX1) to be shared by a plurality of subscribers.
`
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`
`
`*
`*
`*
`*
`*
`
`6,134,035
`
`5
`
`
`(A/D2) and a multiplexer
`analog-to-digital converter
`
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`
`
`(MUX) having an output operatively connected to the
`
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`electrical-to-optical transducer (E/O2), wherein the at least
`
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`one further analog-to-digital converter (A/D2) operatively
`
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`
`connected to a separate electric line (KOAX2) serves to
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`digitize electric signals directly received from the separate
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`electric line (KOAX2) into second digitized electric signals
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`and wherein the multiplexer is operatively connected to the
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`analog-to-digital converters (A/D1, A/D2) in order to com-
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`bine the first and second digitized electric signals directly
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`received from the analog-to-digital converters (A/D1, A/D2)
`
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`into combined signals so as to directly provide the combined
`
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`signals to the electrical-to-optical transducer (E/O2).
`
`10
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`Netflix, Inc. Exhibit 1026
`
`Netflix, Inc. Exhibit 1026