United States Patent [19]
`Bowie
`
`US005956323A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,956,323
`Sep. 21, 1999
`
`[54] POWER CONSERVATION FOR POTS AND
`MODULATED DATA TRANSMISSION
`
`[75] Inventor: Bruce H. Bowie, Santa Rose, Calif.
`
`[73] Assignee: Nokia High Speed Access Products
`Inc., Petaluma, Calif.
`
`[21] Appl. No.: 08/903,504
`[22]
`Filed:
`Jul. 30, 1997
`
`Int. Cl.6 ........................... .. H04M 11/00; H04Q 1/00
`[51]
`[52] US. Cl. ........................................... .. 370/241; 379/413
`[58] Field Of Search ................................... .. 370/216, 241,
`370/242, 244, 249, 250, 251, 204, 205,
`212, 213; 379/1, 2, 5, 9, 15, 23, 26, 27,
`32, 93.06, 399, 412, 413, 377
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,484,028 11/1984 Kelley et al. ...................... .. 379/93.14
`4,979,208 12/1990 Pruden et al.
`379/145
`
`5,483,574
`
`1/1996 Yuyama . . . . . . .
`
`. . . . .. 379/32
`
`455/426
`5,590,396 12/1996 Henry ............. ..
`364/705.05
`5,742,527
`4/1998 Rybicki et a1. ..
`5,799,064
`8/1998 Sridhar et a1. ........................ .. 375/222
`
`Primary Examiner—Chi H. Pham
`Assistant Examiner—KWang B. Yao
`Attorney, Agent, or Firm—Fish & Richardson RC.
`
`[57]
`
`ABSTRACT
`
`Methods and apparatus for conserving poWer in terminal
`units that transmit and receive modulated data over a com
`munications loop that is shared With voiceband telephone
`equipment are disclosed. The methods include monitoring
`the loop to detect a shut-down condition and reducing poWer
`consumption of certain of the electronic circuits in the
`terminal unit upon detection of a shut-down condition. The
`methods also include monitoring the loop With a monitoring
`circuit to detect a resume signal outside the voiceband
`frequency range on the loop and restoring poWer to the
`electronic circuits When the resume signal is detected. The
`apparatuses include a modulated data transmitting and
`receiving unit having a connector for coupling the unit to a
`communications loop, circuitry to transmit and receive a
`modulated data signal in a frequency range above
`voiceband, and circuitry to detect a resume signal in the
`frequency range above voiceband and then to initiate a
`poWer up sequence for the transmit and receive circuitry.
`
`27 Claims, 3 Drawing Sheets
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`300 \
`
`301
`
`302
`
`303
`
`CPE Unit
`Receives Start-up
`Signal
`
`CPE Unit
`Restores Saved
`Parameters
`
`CPE Unit
`Transmits
`Resume Signat
`
`304
`
`COT Unit Detects
`Resume Signal
`
`Yes
`
`ow-Power a
`COT?
`
`305
`
`7
`COT Unit
`Restores Saved
`Parameters
`
`306
`
`No
`7
`v
`COT and CPE
`Units Exchange
`Handshal-ung
`lnformatlon
`
`7 Exchange Data
`
`l
`CPE Sends Shut
`Down Signal
`l
`Monitor Loop until
`shut-down is
`detected
`
`'
`Store Parameters
`l
`Reduce Power
`Consumption
`
`307
`
`308
`
`309
`
`310
`
`311
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`CSCO-1005
`Cisco v. TQ Delta
`Page 1 of 10
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`

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`U.S. Patent
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`Sep. 21, 1999
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`Sheet 1 of 3
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`5,956,323
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`CSCO-1005
`Page 2 of 10
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`U.S. Patent
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`Sep.21, 1999
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`Sheet 2 of3
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`5,956,323
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`CSCO-1005
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`U.S. Patent
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`Sep.21, 1999
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`Sheet 3 of3
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`5,956,323
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`300 \
`
`301
`
`302
`
`303
`
`CPE Unit
`Receives Start-up
`Signal
`
`7
`CPE Unit
`Restores Saved
`Parameters
`
`'
`CPE Unit
`Transmits
`Resume Signal
`
`304
`
`COT Unit Detects
`Resume Signal
`
`7 Exchange Data
`
`l
`CPE Sends Shut
`DOWn slgnal
`
`Monitor Loop ‘until
`shut-down IS
`detected
`
`307
`
`308
`
`309
`
`P
`— OW‘ ower a
`Yes
`cor?
`
`'
`Store Parameters
`
`310
`
`7
`
`305
`COT Unit
`Restores Saved
`Parameters
`
`No
`>
`
`COT and CPE
`Units Exchange
`Handshalung
`lnformatlon
`
`306
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`311
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`Rceduce P<:_wer
`onsump '00
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`FIG. 3
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`CSCO-1005
`Page 4 of 10
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`
`1
`POWER CONSERVATION FOR POTS AND
`MODULATED DATA TRANSMISSION
`
`The present invention is directed to a power conservation
`system for modulated data communications, and more par
`ticularly to a poWer conservation system for transmission
`systems in Which data is modulated over a communications
`loop from a central office location to a customer premises.
`
`BACKGROUND
`
`Wire loops extending from a telephone company central
`office to a customer premises are a ubiquitous part of the
`existing communications infrastructure. These Wire loops
`form a communications netWork often referred to as the
`plain old telephone service’ (POTS) netWork. The POTS
`netWork originated to support analog voice phone service.
`The POTS netWork currently supports a Wide range of
`communications services in addition to analog voice phone
`calls. These services include digital data transmissions from
`facsimile
`machines and computer modems. Voice
`calls, FAX connections, and computer modem transmissions
`all operate Within the frequency spectrum of traditional
`POTS calls, thus ensuring compatibility With the existing
`Wire loop infrastructure and alloWing transport of these
`services end-to-end through the POTS phone netWork.
`HoWever, the use of POTS-compatible transmission fre
`quencies severely limits the maximum information carrying
`capacity of the Wire loop.
`Certain transmission technologies may use carrier fre
`quencies greater than those required for POTS services to
`exceed the information capacity limits of POTS calls over
`Wire loops. HoWever, since the existing POTS loop infra
`structure Was not designed for carrying such high frequency
`signals, severe impediments to such transmission exist. In
`particular, as a result of electromagnetic coupling among
`Wire loops, electromagnetic noise signals are induced on the
`loops. This electromagnetic coupling may occur among the
`large number of loops in the Wire bundles that extend from
`the central office to various customer distribution points.
`Noise signals induced on the loops by electromagnetic
`coupling may not be perceptible on POTS voice calls.
`HoWever, such signals may signi?cantly interfere With Wide
`bandWidth modulated data transmissions that use high fre
`quency signals. To reduce interference problems, sophisti
`cated signal processing circuitry, such as digital signal
`processors (DSPs), are used Within modulated data receiver
`and transmitter units to remove noise, to encode and decode
`desired signals, and to perform error correction functions.
`To minimiZe the number of Wire loops needed to service
`a customer’s premises, POTS signals and modulated data
`transmission signals may be combined on a single Wire loop.
`To combine POTS and Wide-bandWidth modulated data
`transmission signals, the Wide-bandWidth modulated data is
`transported using frequencies (spectrum) greater than those
`of POTS services. This spectrum usage alloWs a POTS
`service connection to be supported by its traditionally allo
`cated spectrum While simultaneously supporting high fre
`quency modulated data transmission. Thus, current technol
`ogy permits POTS and high bandWidth data may be carried
`betWeen customer premise equipment (CPE) and a central
`office (CO) on a single Wire loop. At the central office, the
`POTS signal frequencies are separated from the high fre
`quency data signal; the POTS signal is then handled by the
`existing POTS sWitch and netWork, While the high fre
`quency spectrum is directed to separate processing compo
`nents.
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`Signal processing, transmitting, and receiving circuitry
`for such high frequency modulated data signals requires a
`substantial amounts of poWer, typically up to 5 Watts per
`loop served. For a large central office, potentially serving
`many thousands of such data connections, this poWer usage
`is substantial.
`
`SUMMARY
`
`In general, in one aspect, the invention features a method
`of conserving poWer in a terminal unit having a transmitter
`and receiver for modulated data communication over a
`communications loop that is shared With voiceband tele
`phone equipment. The method includes monitoring the loop
`to detect a shut-doWn condition, reducing poWer consump
`tion of certain of the electronic circuits in the terminal unit
`upon detection of a shut-doWn condition, monitoring the
`loop With a monitoring circuit to detect a resume signal
`outside the voiceband frequency range on the loop, and
`restoring poWer to the electronic circuits When the resume
`signal is detected.
`Implementations of the invention may include one or
`more of the folloWing features. The modulated data may be
`a bit stream including framing information, and a shut-doWn
`condition may be indicated by a loss of framing information.
`The modulated data may include a signaling channel and a
`shut doWn condition may be indicated by bits transmitted in
`the signaling channel. The resume signal may be an AC
`signal at a frequency above voiceband, such as a 16 kHZ AC
`signal.
`In general, in another aspect, the invention features a
`modulated data transmitting and receiving unit. The unit
`includes a connector for coupling the unit to a communica
`tions loop, circuitry to transmit and receive a modulated data
`signal in a frequency range above voiceband, and circuitry
`to detect a resume signal in the frequency range above
`voiceband and then to initiate a poWer up sequence for the
`transmit and receive circuitry.
`Implementations of the invention may include one or
`more of the folloWing features. The connector may be a
`tWo-Wire connector. The transmit and receive circuitry may
`include Asymmetric Digital Subscriber Line transmit and
`receive circuitry. The resume signal detection circuitry may
`be a 16 kHZ frequency detector. The communications loop
`may be a Wireless communications loop. The resume signal
`may be an AC signal greater than 4 kHZ or may be a
`multi-tone AC signal. The unit may also include a control
`signal interface to receive a start-up signal, and circuitry to
`transmit a resume signal upon receipt of the start-up signal.
`In general, in another aspect, the invention features a
`modulated data transmitting and receiving unit. The unit
`includes a connector for coupling the unit to a communica
`tions loop, a control signal interface for receiving a start-up
`signal, circuitry to transmit and receive a modulated data
`signal at frequencies above voiceband, and circuitry to
`transmit a resume signal on the loop upon receipt of a
`start-up signal on the control signal interface.
`Implementations of the invention may include one or
`more of the folloWing features. The communications loop
`may a Wireless loop. The control signal interface may be a
`data interface, such as a peripheral component interconnect
`(PCI) interface. The start-up signal may be indicated by
`receipt of data on the control signal interface. The control
`signal interface may be used for the exchange of both the
`start-up signal and of data betWeen the modulated data
`transmitting and receiving unit and customer premise equip
`ment.
`
`CSCO-1005
`Page 5 of 10
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`

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`5,956,323
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`3
`Among the advantages of the invention are the following.
`Modulated data signal processing, transmitting, and receiv
`ing circuitry can be placed in a loW poWer state When
`inactive, and then re-energiZed to resume full poWer opera
`tion as needed. Central office terminals (COTs) and cus
`tomer premises equipment (CPE) units can exchange shut
`doWn and resume signals Without interfering With POTS
`services on the Wire loop. Additionally, either a CPE or a
`COT unit can initiate both a loW poWer state and resumption
`to a full poWer state.
`
`DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of an ADSL unit in accordance
`With the invention.
`FIG. 2 is a diagram of a central of?ce With a central office
`terminal (COT) ADSL unit connected by a tWo-Wire loop to
`a customer premises equipment (CPE) ADSL unit in accor
`dance With the invention.
`FIG. 3 is a ?oWchart of a data exchange betWeen tWo
`connected ADSL units in accordance With the invention.
`
`DETAILED DESCRIPTION
`Asymmetric Digital Subscriber Line (ADSL) technology
`is used to transmit Wide-bandWidth modulated data over a
`25
`tWo-Wire loop using high frequency carrier signals. ADSL
`alloWs a tWo-Wire loop to simultaneously transport POTS
`analog voice phone services along With high speed modu
`lated digital data over Wire loops of up to 18,000 feet. This
`simultaneous support of POTS and modulated digital ser
`vices is provided by transporting POTS services using their
`traditionally allocated spectrum While transporting modu
`lated digital data using spectrum outside of the POTS range.
`FIG. 1 is a block diagram of an ADSL unit. To send and
`receive modulated digital data, the ADSL unit 100 employs
`high speed signal processing electronics 111 that includes,
`for example, digital signal processing (DSP) circuitry. Sig
`nal processing electronics 111 eliminate stray electronic
`noise induced on the tWo-Wire loop 120 and, along With
`transmit circuitry 112 and receive circuitry 113, are used to
`send and receive modulated data. In addition, signal pro
`cessing circuitry 111 may implement error correcting
`algorithms, such as the Reed-Solomon algorithm, to further
`reduce data errors that arise during transmission. The signal
`processing, transmit, and receive functions may be provided
`by, for example, a Motorola CopperGold chip set or a
`GlobeSpan Technologies STAR or SLADE chip set. Control
`circuitry 117 is provided to control operation of the ADSL
`unit 100, to control poWer usage by ADSL unit circuitry, and
`for storage of ADSL unit parameters.
`To provision ADSL service, an ADSL unit 100 is located
`at each end of a Wire loop 120. Referring to FIG. 2, an ADSL
`unit 100 located at the subscriber premises 240 is referred to
`as a customer premises equipment (CPE) ADSL unit 242. A
`second ADSL unit 100, typically located at a telephone
`55
`company central of?ce 230, is knoWn as the central office
`terminal (COT) unit 232. The CPE unit and the COT unit are
`connected by a tWo-Wire loop 220 of up to 18,000 feet.
`Central of?ce and customer premises equipment connects
`to the ADSL unit through a data interface 116 (FIG. 1). At
`the central of?ce end of the loop 230, the data interface of
`the COT unit 232 is connected to central of?ce data sWitch
`ing equipment 234. At the subscriber end of the loop 240, the
`data interface of the CPE unit 242 is connected to customer
`premise equipment such as a personal computer 244.
`Data to be transmitted by an ADSL unit is arranged in a
`structure knoWn as a ‘frame’ prior to being transmitted. A
`
`4
`frame is an arrangement of bits including both user data and
`signaling information required by the ADSL units. When
`there is nothing to transmit betWeen ADSL units, the user
`data portion of the frame may be ?lled With idle packets.
`Within the ADSL framing structure is a loW bit rate signaling
`channel over Which handshaking information can be
`exchanged betWeen ADSL units. This signaling channel may
`be used, for example, to test the Wire loop transmission path
`and to send ADSL device status information.
`Circuitry Within each ADSL unit 232 and 242 is used to
`remove noise, to perform error correction, to multiplex data,
`and to transmit and receive data. This is done Without
`interfering With POTS audio and signaling transmissions
`over the tWo-Wire loop 220, Which uses spectrum beloW 4
`kilohertZ (kHZ). Modulated data from the ADSL units 232
`and 242 is transmitted using spectrum above 4 kHZ, typi
`cally using a range of frequencies of 40 kHZ and greater.
`Signal ?lters 233 and 243 (knoWn as “splitters”) are used to
`join signals being transmitted from one location, for
`example, the central of?ce 230, and to separate signals When
`they are received at the distant location, for example, the
`customer premises 240.
`Within the central of?ce 230, a splitter 233 is used to
`combine outgoing signals from the POTS sWitching equip
`ment 231 and the COT ADSL unit 232 for transmission on
`the loop 220. The splitter 233 also provides signals received
`on the tWo-Wire loop 220 to both the POTS sWitching
`equipment 231 and to the COT ADSL unit 232. Signals to
`be sent to the POTS sWitching equipment 231 are ?ltered by
`the splitter 233 so as to remove frequencies above voice
`band. The resulting ?ltered signal may be handled by the
`POTS sWitch 231 as if it had originated on a traditional
`analog POTS connection. The signal from the splitter 233 to
`the COT ADSL unit 232 may contain the full frequency
`spectrum as it arrives over the Wire loop 220 or may be
`?ltered to remove voice band frequencies.
`At the customer premises 240, a splitter 243, Which may
`serve as a telephone company netWork interface (NI) device,
`is used to combine outgoing signals from customer premises
`POTS-compatible equipment 241 and the CPE ADSL unit
`242 for transmission on the loop 220. The splitter 243 is also
`used to direct signals received on the tWo-Wire loop 220 to
`both customer premises POTS equipment 241, such as an
`analog telephone or a FAX machine, and to the CPE ADSL
`unit 242.
`Signals to be sent to the customer premises POTS equip
`ment 241 are ?ltered to remove frequencies above voice
`band. The resulting ?ltered signal may be handled by the
`customer premises POTS equipment 241 as if it had origi
`nated on a traditional analog POTS connection. The signal
`from the splitter 243 to the CPE ADSL unit 242 may contain
`the full frequency spectrum as it arrives over the Wire loop
`220 or it may be ?ltered to remove voiceband frequencies.
`The CPE ADSL unit 242 may be incorporated in, for
`example, an ADSL modem connected to a personal com
`puter 244 that is programmed to send and receive over the
`ADSL connection. Circuitry to handle POTS and ADSL data
`functions may be combined Within a single physical device
`handling signal splitting and ?ltering, POTS call processing
`and modulated data processing, transmitting, and receiving.
`Alternatively, these functions may be achieved using a
`number of physically separate devices.
`Prior to initiating transport of modulated data over the
`loop 220, signals are exchanged over the loop 220 betWeen
`the COT unit 232 and the CPE unit 242 to adapt the ADSL
`units to the electronic characteristics of the particular Wire
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`loop 220. For example, loop loss characteristics, Which are
`a function of loop length, Wire gauge, Wire composition, and
`other factors, are exchanged. This exchange of information
`is often referred to as handshaking. Once handshaking is
`completed, transmission of user data may begin.
`To reduce poWer requirements, the ADSL units 232 and
`242 may enter loW poWer mode When user data transmission
`is complete. Either unit may initiate the loW poWer mode. If,
`for example, the CPE unit 242 initiates loW poWer mode, it
`does so by sending a shut-doWn signal to the COT unit 232.
`This shut-doWn signal may be conveyed in the ADSL loW bit
`rate signaling channel; alternatively, an out-of-band signal
`on the loop may be used, for example, a 16 kHZ AC signal.
`Still another alternative is for the CPE unit to stop sending
`ADSL framing information (such as Would happen if the
`CPE unit Were poWered doWn).
`Upon receipt of the shut-doWn signal, the COT unit 232
`optionally stores in memory 117 characteristics of the loop
`220 that Were determined by CPE to COT handshaking.
`Likewise, upon sending the shut-doWn signal, the CPE unit
`242 may also optionally store the loop characteristics that it
`obtained through CPE to COT handshaking. Storing loop
`characteristics enables rapid resumption of user data trans
`mission When the units are returned to full poWer mode.
`Each unit 232 and 242 may then enter loW-poWer mode by
`shutting off the noW unnecessary sections of signal process
`ing 111, transmitting 112, and receiving 113 circuitry. The
`loop 220 Will then be in an inactive state. Circuitry 115 to
`detect the resume signal must remain capable of signal
`detection during loW poWer operation. If the COT unit 232
`Were to initiate loW poWer mode, signals Would be
`exchanged With the CPE unit 242 in a like fashion.
`In alternative embodiments, both CPE 242 and COT 232
`units may be capable of reduced poWer operation.
`Alternatively, only the COT 232 unit may reduce its poWer
`consumption, or only the CPE unit 242 may reduce its poWer
`consumption. If only the COT unit 232 is to reduce its poWer
`consumption, the COT unit 232 Will not require resume
`signal generation 114 circuitry, nor Will the CPE unit 242
`require resume signal detection circuitry 115. Similarly, if
`only the CPE unit 242 is to reduce poWer consumption, the
`CPE unit 242 Will not require resume signal generation 114
`circuitry nor Will the COT unit 232 require resume signal
`detection circuitry. Thus, the particular circuit components
`that can be placed in a loW poWer mode may vary among
`differing brands, models, and versions of ADSL units.
`To return a unit that is in loW poWer mode to full poWer
`operation, a resume signal is sent to the unit. In one
`embodiment, a COT ADSL unit resumes full poWer opera
`tion upon receipt of a 16 kHZ AC signal that is sent over the
`Wire loop by a CPE ADSL unit. This resume signal may be
`detected by the COT unit using a 16 kHZ AC signal detector
`115 that employs conventional frequency detection tech
`niques. This detector 115 remains operative When the unit
`232 is in loW-poWer mode. If the CPE unit 242 is capable of
`reduced poWer operation, a resume signal sent from the COT
`unit 232 to the CPE unit 242 Would be similarly received at
`the customer premises and detected by the CPE unit 242.
`Upon receipt of the resume signal, the receiving ADSL
`unit returns the signal processing 111, transmitting 112, and
`receiving 113 circuitry to full poWer mode. If loop trans
`mission characteristics had been stored, these parameters are
`retrieved from memory 117 and used to enable data trans
`mission to resume quickly by reducing the time needed to
`determine loop transmission characteristics. After resump
`tion of full poWer mode, additional handshaking between
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`ADSL units 232 and 242 may occur. Upon reaching a fully
`operational state, transmission of user data may resume.
`Referring to FIGS. 2 and 3, one exemplary application of
`the invention is to reduce poWer requirements needed to
`maintain a link betWeen a personal computer (PC) 244 and
`a remote data source 250. The remote data source 250 may
`be, for example, an Internet service provider (ISP) or an
`online service provider (OSP). In an exemplary
`con?guration, a CPE ADSL unit 242 is connected by a
`digital interface 247 to a personal computer 244 pro
`grammed to send and receive data over the ADSL unit 242.
`The CPE ADSL unit 242 may be incorporated in an ADSL
`modem that is installed in, or connected to, the PC 244. The
`CPE ADSL unit 242 is connected by a Wire loop 220 to a
`COT ADSL unit 232 at a central office 230 at Which a link
`to the remote data source 250 exists.
`In the exemplary con?guration, the Wire loop 220 is
`initially inactive, thus preventing information flow between
`the CPE 242 and COT 232 ADSL units. To return the loop
`220 to an active state, a start-up signal is sent to the CPE
`ADSL unit (step 301). The start-up signal is, for example, a
`command sent over the digital interface 247 from a device
`driver or other program module running in the PC 244 or
`may be represented by poWer to the CPE ADSL unit being
`turned on. Upon receipt of the start-up signal, the CPE
`ADSL unit may restore saved loop characteristic parameters
`(step 302). The CPE ADSL unit then transmits a 16 kHZ
`resume signal on the loop (step 303) The resume signal is
`subsequently detected by loop monitoring circuitry in the
`COT unit (step 304). If the COT unit is in a loW poWer state,
`it Will return to full poWer operation upon detection of the
`resume signal from the CPE unit, this may include restoring
`loop characteristic parameters (step 305). If the COT unit
`Was not in a loW poWer state, the resume signal may be
`ignored by the COT unit. CPE and COT ADSL units may
`then exchange handshaking information to establish reliable
`data communication betWeen the units (step 306). Hand
`shaking information may be required Where, for example,
`loop characteristics have changed due, for example, to
`temperature-dependent changes in loop resistance.
`Handshaking information may also be exchanged for
`other device initialiZation purposes.
`Once reliable data transmission from the CPE to the COT
`ADSL units is established, information may be exchanged
`over the established data path (step 307). Referring to FIG.
`2, the personal computer 244 may use the data path betWeen
`ADSL units to communicate With a remote data source by
`sending information over a digital interface 247 to the CPE
`ADSL unit 242. This digital interface may be an industry
`standard computer interface such as a small computer sys
`tems interface (SCSI), an Ethernet interface, or a peripheral
`component interconnect (PCI) interface, or other industry
`standard or vendor proprietary interfaces alloWing tWo-Way
`data exchange. Information from the PC to the CPE unit may
`include both user data and signaling information to control
`CPE ADSL unit operation or, by relaying such signaling
`over an ADSL to ADSL unit signaling channel, to control
`COT ADSL unit operation. User data provided to the CPE
`unit by the PC is transmitted to the COT unit over the
`established CPE to COT data transmission path.
`Data received at the COT unit may be converted to a data
`signal format compatible With standard telephone company
`sWitching equipment, for example, a 1.544 million bits per
`second (Mbps) T1 data signal, or to asynchronous transfer
`mode (ATM) cells over an optical carrier level 3 (OC-3)
`synchronous optical netWork (SONET) interface. The
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`received data, noW in a central of?ce equipment compatible
`format, may be provided over a standard telephony interface
`236 to telephone company high speed data switching equip
`ment 234, such as a digital cross connect sWitch or multi
`plexing equipment to a second interface 251 that connects to
`a remote data source 250. Alternatively, the data may ?oW
`from the COT ADSL unit 232 directly to the remote data
`source 250 Without handling by intermediary sWitching
`equipment 234. TWo Way data transfers betWeen the remote
`data source 250 and the PC 244 may then take place over the
`resulting path from PC 244 to CPE unit 242 to COT unit 232
`to sWitching equipment 234 to remote data resource 250.
`Referring again to FIG. 3, the COT unit may be returned
`to loW poWer mode by sending a shut-doWn signal from the
`CPE unit to the COT unit (step 308). The shut-doWn signal
`may be an expressly transmitted signal or may be inferred.
`For example, the shut doWn signal may be expressly sent as
`a series of signaling bits transmitted betWeen the CPE and
`COT ADSL units. Alternatively, if the PC and COT ADSL
`unit are shut off, a shut-doWn signal may be inferred from
`the loss of transmitted framing information betWeen the CPE
`unit and the COT unit. The shut-doWn signal is subsequently
`detected by monitoring circuitry in the COTADSL unit (step
`309). Upon detecting a shut-doWn signal, the COT unit may
`save loop characteristics (step 310) and enter loW poWer
`mode by reducing poWer to noW unnecessary circuitry (step
`311). The described procedure 300 may be repeated to
`resume data transmission. Essentially the same sequence
`may occur to reduce poWer at a CPE ADSL unit 242. A CPE
`ADSL unit may enter a loW poWer mode When, for example,
`a preset or programmed period of time passes Without any
`user activity on the data path or an appropriate signal is sent
`from the COT ADSL unit.
`Other embodiments are Within the scope of the folloWing
`claims. For example, While the invention has been described
`in the context of ADSL units providing an asymmetric data
`channel, the invention may be applied to other terminal units
`Wherein voice band services share a loop With modulated
`data transmission, such as in Symmetric Digital Subscriber
`Line (SDSL) and Rate Adaptive Digital Subscriber Line
`(RADSL) terminal units. Similarly, While systems With
`tWo-Wire loops have been described, the invention may be
`used in systems including Wireless loops and loop segments.
`Wakeup signals may include multi tone signals and other
`signals outside the POTS spectrum. Terminal unit circuitry
`may include digital circuitry, analog circuitry, softWare,
`?rmWare, or a combination of these elements. The scope of
`the invention should be limited only as set forth in the claims
`that folloW.
`What is claimed is:
`1. Amethod of conserving poWer in a terminal unit having
`a transmitter and receiver for modulated data communica
`tion over a communications loop, comprising:
`monitoring the loop to detect a shut-doWn condition;
`reducing poWer consumption of demodulation circuitry in
`the terminal unit upon detection of a shut-doWn con
`dition;
`monitoring the loop With a monitoring circuit to detect a
`resume signal that is not a modulated data signal and
`that is outside the voiceband frequency range on the
`loop; and
`activating demodulation circuitry When the resume signal
`is detected.
`2. The method of claim 1 Wherein modulated data com
`prises a bit stream including framing information, and a
`shut-doWn condition comprises a loss of framing informa
`tion.
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`3. The method of claim 1 Wherein modulated data com
`prises a bit frame including signaling bits and data bits and
`monitoring the loop to detect a shut-doWn condition com
`prises monitoring the signaling bits in the bit frame.
`4. The method of claim 1 Where the resume signal
`comprises a 16 kHZ AC signal.
`5. The method of claim 1 further comprising:
`storing loop characteristic parameters in a memory circuit
`upon detection of the shut-doWn condition; and
`transferring loop characteristic parameters from the
`memory circuit to the demodulation circuitry upon
`activating the demodulation circuitry.
`6. The method of claim 5 further comprising performing
`handshaking to determine loop characteristics.
`7. A modulated data transmitting and receiving unit,
`comprising:
`a connector operatively coupling the unit to a communi
`cations loop;
`?rst circuitry coupled to the connector to transmit and
`receive a modulated data signal in a frequency range
`above voiceband;
`memory circuitry operatively coupled to the ?rst circuitry
`to store loop characteristic parameters in a loW-poWer
`state and to transfer loop characteristic parameters to
`the ?rst circuitry during a poWer up sequence; and
`second circuitry coupled to the connector to detect a
`resume signal in the frequency range above voiceband
`and then to initiate the poWer up sequence for the ?rst
`circuitry.
`8. The modulated data transmitting and receiving unit of
`claim 7 Wherein the connector comprises a tWo-Wire con
`nector.
`9. The modulated data transmitting and receiving unit of
`claim 7 Wherein the ?rst circuitry comprises asymmetric
`digital subscriber line data transmission circuitry.
`10. The modulated data transmitting and receiving unit of
`claim 7 Wherein the second circuitry comprises 16 kHZ
`frequency detection circuitry.
`11. The modulated data transmitting and receiving unit of
`claim 7 Wherein the communications loop comprises a
`Wireless communications loop.
`12. The modulated data transmitting and receiving unit of
`claim 7 Wherein the resume signal comprises an AC signal
`greater than 4 kHZ.
`13. The modulated data transmitting and receiving unit of
`claim 7 Wherein the resume signal comprises transmission of
`an AC signal at a ?rst frequency folloWed by transmission of
`an AC signal at a second frequency.
`14. The modulated data transmitting and receiving unit of
`claim 6 further comprising:
`a control signal interface for receiving a start-up signal;
`and
`third circuitry coupled to the connector to transmit a
`resume signal on the loop upon receipt of a start-up
`signal on the control signal interface.
`15. The apparatus of claim 7 Wherein the ?rst circuitry
`further comprises handshaking circuitry to determine loop
`characteristic parameters associated With the loop.
`16. A modulated data transmitting and receiving unit,
`comprising:
`a connector operatively coupling the unit to a communi
`cations loop;
`a c