O
`
`Ulllt€d States Patent [19]
`Wagner et a].
`
`[54] SIMULTANEOUS TRANSFER OF CONTROL
`INFORMATION WITH VOICE AND DATA
`OVER A PUBLIC SWITCHED TELEPHONE
`NETWORK LINE
`[75] Inventors: glagrytizagner. OaklandbCali?; Raéph
`E’ ml l‘jPt‘greitgmvc’ amt] R‘ 0x‘
`“gem ° 0 “*9
`-
`'
`.
`-
`[ 3] Asslgnee Intel Carpomhon Santa Clara Cahf
`_
`[21] Appl‘ No" 912’947
`[22] Filed:
`Aug. 14, 1997
`
`_
`
`Related Us. Application Data
`
`[63] Continuation of Ser. No. 687,773, Jul. 26, 1996, abandoned,
`which is a continuation of Ser. No. 597,352, Feb. 6, 1996,
`abandoned, which is a continuation of Ser. No. 254, Jan. 4,
`
`1993, abandoned.
`
`[51] Int. Cl.6 .................................................. .. H04M 11/06
`[52] US. Cl. ................. .. 379/229; 379/9309; 379/9326;
`370/463; 370/522
`[58] Field of Search ............................... .. 379/229. 9301,
`379/9309‘ 93.14‘ 9326; 348/14_ 15_ 16;
`370/522. 264_ 265_ 28L 437‘ 468
`
`[56]
`
`.
`Referencw cued
`U.S, PATENT DOCUMENTS
`
`pMelggéagtgi """"""""""""""" "
`4435804 3/1984 Tan ..........
`‘570/6911
`43442540 4/1984 Allen ......... ..
`370/691
`4,476,559 10/1984 Brolin et al. ...... ..
`. 370/1101
`4,715,059 12/1987 Cooper-Hart etal. ..
`.... .. 348/18
`4,757,495
`7/1988 Decker et a1. ..
`370/691
`4,932,047
`6/1990 Emmo?s 6‘ =11‘ - - - ‘
`- ' ~ ~ ~- 343/13
`
`FOREIGN PATENT DOCUMENTS
`0084125 12/1982 European Pat. 01f. .
`2187611
`9/1987 European Pat. 0ft.
`0 501 435 A2 2/1992 European Pal- 01?‘ a
`63'l3li?gg 1%;
`iapan -
`b20206,‘
`8 1,1989 Japan I
`2-198264
`8/1990 Japan .
`3-292047 12/1991 Japan .
`
`apan I
`
`_
`
`USOO5761 292A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,761,292
`Jun. 2, 1998
`
`2268665 6/1993 United Kingdom .
`
`OTHER PUBLICATIONS
`Technische Rundschau, vol. 84, No. 4, 24 Jan. 1992, Bern
`Ch . 36-38. XP247737 Braun “Auf der Schiene: Zuni
`corg?utcr Inmgratcd Railroad-“git
`Mitel Corporation Data Sheet for “Data Over Voice Modem
`Chip”. Part #MT8840. issue 3. Dec. 1987.
`Schwartz. Je?rey. “User Deploys Data-Voice System”.
`article appearing in COM/11101166111071 Week, Sep. 28, 1992.
`Stockford, Paul. “VoiceView otters Voice and Data Over a
`Single Analog Line”, article appearing in Voice Processing
`Magazine, 191- 1991
`
`Primary Examiner-Ahmad F, Matar
`Attorney, Agent, or Firm—Blakely. Sokoloff, Taylor &
`Za?mn
`
`[57]
`
`ABSTRACT
`
`.
`
`.
`
`.
`
`.
`
`A transceiver providing simultaneous transfer of control
`information with voice and data over a public switched
`telephone network line is disclosed In a typical system
`application, the transceiver is coupled to a public switched
`‘91911099 "Work (P5P? via a single telepmlnefiine. The
`transceiver includes logic or generating contro in ormation
`and for combining the controlinformation with voice signals
`or data signals for transrmssion and reception through the
`PSTN using a single telephone line. The present invention
`provides a PSTN channel having two component
`subchannels, a main channel and a side channel. The main
`channel is provided for the transfer of voice signals and data
`signals at the same time the side channel is transferring
`°°mI°1 infmma?o“ and/or additional data signals- The con‘
`“91 mfmmatm "finsfemd 0“ the S399 chafmelils used
`Prmm?y for 5919699‘; the transfer of elth?r V9196 slgllals of
`data signals on the main channel. By providing a separate
`and independent side channel for controlling the main
`channel. the present invention eliminates the inherent delays
`caused in the prior art design by switching between a voice
`transfer mode and a data transfer mode using a single
`channel. The present invention also allows the transfer of
`data signals on the side channel simultaneously with the
`transfer of voice signals on the main channel. These advan
`tages are provided by the present invention without rede
`?ning the bandwidth of the standard PSTN channel.
`
`.
`
`.
`
`15 Claims, 3 Drawing Sheets
`
`Data
`In
`>129
`
`Data
`Out
`422'
`
`Control
`Logic
`430-
`
`Voice Voice
`In
`Out
`‘124-
`126-
`
`1 4
`
`1 4
`
`Pub“;
`Switd'md
`telephone
`Netwotk
`~112
`
`Data
`In
`-120-
`
`Data
`Out
`422
`
`Control
`Logic
`43!}
`
`Voice Voice
`In
`Out
`-124
`126»
`
`31 >———PSTN Channel—4 14
`
`31M
`
`//
`
`200
`
`2900 a
`
`D3400
`
`H2
`
`

`

`US. Patent
`
`Jun. 2, 1998
`
`Sheet 1 of 3
`
`5,761,292
`
`110
`
`Data
`In
`-12D-
`
`Data
`Out
`422-
`
`Control
`Logic
`-130-
`
`Voice Voice
`In
`Out
`-124-
`-126-
`
`110
`
`Data
`In
`-120-
`
`Data
`Out
`-122
`
`Control
`LOQiP
`-130
`
`Voice Voice
`In
`Out
`-124-
`-12e
`
`1 4
`
`1 4
`
`Public
`Switched
`Telephone
`Network
`-112
`
`FIGURE1
`
`|-—-——PSTN Channel—-—l
`
`-210
`jl/za/
`
`r
`200
`
`I
`3400
`
`HZ
`
`FIGURE 2 (Prior Art)
`
`31 i—————PSTN ChanneI—-i 14
`
`200
`
`'
`
`2900 a 03400
`
`HZ
`
`FIGURES
`
`

`

`US. Patent
`
`Jun. 2, 1998
`
`Sheet 2 of 3
`
`5,761,292
`
`mmmn.26..
`
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`
`5:520
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`
`
`
`
`

`

`US. Patent
`
`Jun. 2, 1998
`
`Sheet 3 of 3
`
`5,761,292
`
`5520
`
`6:80
`
`_-omm-
`.BmSuoEmo
`
`9mg
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`
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`

`

`5.761.292
`
`1
`SINIULTANEOUS TRANSFER OF CONTROL
`INFORMATION WITH VOICE AND DATA
`OVER A PUBLIC SWITCHED TELEPHONE
`NETWORK LINE
`
`This is a continuation of application Ser. No. 081687.773.
`?led Jul. 26. 1996. now abandoned. which is a continuation
`of application Ser. No. 08/597352. ?led Feb. 6. 1996. now
`abandoned. which is a continuation of application Ser. No.
`08/000254. ?led Jan. 4. 1993. now abandoned.
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to the ?eld of information
`transfer across public switched telephone systems.
`Speci?cally. the present invention pertains to the transmis
`sion of binary information or facsimile data with voice
`signals on a public switched telephone network.
`2. Related Art
`Several prior art designs provide various levels of voice
`and data transmission capabilities. In one implementation. a
`system provides two separate communication links: one link
`for data and the other link for voice signals. In a typical
`implementation of this type. two telephone lines are used to
`handle a data conference. One telephone line is used for
`transmission of data. The other telephone line is used for the
`transmission of voice. This implementation. however. con
`sumes at least two telephone lines for each such data
`conference. In a multipoint conference con?guration. two
`separate telephone bridges would be required to handle such
`a data conference.
`In another implementation of systems combining voice
`and data information. a communications medium separate
`from the telephone network is provided. This separate
`communications medium can be implemented as a separate
`and independent twisted pair high speed data communica
`tions medium. Because these independent transmission
`media can be optimized for the transmission of voice and
`data. satisfactory data and voice information rates can be
`achieved. These systems. however. require that costly instal
`lation of the independent communications medium be
`undertaken. In many cases. the high cost of such an instal
`lation is not justified by the need for a combined voice and
`data system. In other cases. the installation of such a
`communications medium may not even be possible.
`Still other prior art systems can transmit voice signals and
`data on a single telephone line; however. the transmission of
`data and voice does not occur simultaneously with control
`information. In various forms. these systems provide a
`means to select between a voice transmission mode or a data
`transmission mode. Each of these modes of transmission are
`mutually exclusive of the other mode. Thus. a single tele
`phone line may be used to transfer voice information during
`a ?rst time frame and binary computer data during a second
`time frame. In many of these systems. a signi?cant time
`delay is required to change from one mode to the other;
`because no independent control method is provided.
`Although these systems carry the bene?t of using only a
`single line of a public switched telephone network. several
`inefficiencies result from the need to switch between a voice
`mode or a data mode without independent control. Because
`in some cases switching between modes is a slow operation.
`loss of voice or data signals may occur. At the very least. the
`speed of information transfer across the public switched
`telephone line is signi?cantly reduced. In other cases. the
`lack of an independent control mechanism for switching
`
`20
`
`25
`
`30
`
`35
`
`40
`
`50
`
`55
`
`65
`
`2
`between a voice transfer and a data transfer mode causes the
`need for a signi?cant level of operator interaction with the
`system. Increased levels of operator interaction again
`decrease the speed of information transfer.
`Thus. a better means for transferring voice information
`and data across a single public switched telephone network
`line is needed.
`
`SUMMARY OF THE INVENTION
`
`The present invention is a transceiver providing simulta
`neous transfer of control information with voice and data
`over a public switched telephone network line. In a typical
`system application. the transceiver is coupled to a public
`switched telephone network (PSTN) via a single telephone
`line. The transceiver includes a Voice In interface. a Voice
`Out interface. a Data In interface. and a Data Out interface.
`The transceiver includes logic for generating control infor
`mation and for combining the control information with voice
`signals or data signals for transmission through the PSTN
`using a single telephone line. Similarly. this control logic
`includes logic for receiving the control information as
`combined with voice and data signals via a single telephone
`line. The control logic further includes logic for isolating the
`voice signals received via the telephone line and routing the
`voice signals through the Voice Out interface. The control
`logic includes logic for isolating data signals received on the
`telephone line and for transferring the data signals to a host
`computer through the Data Out interface. In this manner. the
`present invention provides a means for transmitting and
`receiving control information with voice information and
`computer data via a single standard telephone line.
`The present invention modi?es the prior art PSTN chan
`nel to create a new PSTN channel having two component
`subchannels. a main channel and a side channel. By dividing
`the PSTN channel into a main channel and a side channel.
`the present invention gains the advantage of providing the
`main channel for the transfer of voice signals and data
`signals at the same time the side channel is transferring
`control information and/or additional data signals. The con
`trol information transferred on the side channel is used
`primarily for selecting the transfer of either voice signals or
`data signals on the main channel. By providing a separate
`and independent side channel for controlling the main
`channel. the present invention gains the advantage over the
`prior art of eliminating the inherent delays caused in the
`prior art design by switching between a voice transfer mode
`and a data transfer mode using a single channel. The present
`invention also provides the advantage of allowing the trans
`fer of data signals on the side channel simultaneously with
`the transfer of voice signals on the main channel. In this
`manner. the transfer of voice signals does not completely
`suppress the simultaneous transfer of computer information.
`These advantages are provided by the present invention
`without rede?ning the bandwidth of the standard PSTN
`channel.
`It is therefore an object of the present invention to provide
`a system for the simultaneous transfer of control information
`with voice and data across a single public switched tele
`phone network line. It is a further object of the present
`invention to provide a system wherein two transmission
`channels are provided on a single public switched telephone
`line. It is a further object of the present invention to provide
`a system wherein control information is transmitted simul
`taneously on the same public switched telephone network
`line with voice signals and data signals. It is a further object
`of the present invention to provide a system for automati
`
`

`

`5.761.292
`
`3
`cally switching between a voice transfer mode and a data
`transfer mode using independent control information trans
`mitted with the voice signals or data signals.
`These and other objects of the present invention will
`become apparent as presented and described in the following
`detailed description of the preferred embodiment.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 illustrates the present invention as coupled to a
`public switched telephone network.
`FIG. 2 illustrates the frequency range of a prior art PSTN
`channel.
`FIG. 3 illustrates the frequency range provided in the
`present invention for a main channel and a side channel.
`FIG. 4 illustrates the structure of the transmitter of the
`present invention.
`FIG. 5 illustrates the structure of the receiver of the
`present invention.
`
`15
`
`25
`
`35
`
`4
`ordinary skill in the art that many conventional methods
`exist for transferring digital data to and from transceiver 110
`through Data In interface 120 and Data Out interface 122. In
`a typical implementation. Data In interface 120 and Data
`Out interface 122 are coupled to a host computer.
`Transceiver 110 includes control logic 130. Control logic
`130 includes logic for receiving voice information (i.e. voice
`signals) via Voice In interface 124 and computer or facsimile
`data (Le. data signals) via Data In interface 120. Control
`logic 130 also includes logic for generating control infor
`mation and for combining the control information with voice
`signals or data signals for transmission through PSTN 112
`using a single telephone line 114. Similarly. control logic
`130 includes logic for receiving the control information as
`combined with voice and data signals via a single telephone
`line 114. Control logic 130 further includes logic for isolat
`ing the voice signals received via line 114 and routing the
`voice signals through Voice Out interface 126. Similarly.
`control logic 130 includes logic for isolating data signals
`received on line 114 and for transferring the data signals to
`a host computer through Data Out interface 122. In this
`manner. the present invention provides a means for trans
`mitting and receiving both voice information and computer
`data via a single standard telephone line. The internal
`structure and operation of control logic 130 is described in
`more detail in connection with FIGS. 4 and 5.
`Referring now to FIG. 2. a graph illustrates the frequency
`band or range 210 used for transferring voice information
`across line 114 and through PSTN 112. As shown. this
`frequency band of a conventional PSTN channel 210 con
`sumes a frequency range extending from approximately 200
`Hz to 3.4 kHz. The amplitude of the PSTN channel 210 is
`capped at a prede?ned voltage level. Voice signals or modu
`lated data signals may occupy the entire frequency band
`within the PSTN channel 210. Signals outside of the PSTN
`channel 210 may not be transferred via line 114 through
`PSTN 112. In some cases. signals outside the frequency
`range of the PSTN channel 210 may be ?ltered out and thus
`lost. It is critical therefore that any signals transferred
`through PSTN 112 must reside within the range of pre
`de?ned PSTN channel 210 frequencies. The PSTN channel
`210 illustrated in FIG. 2 is well known to those of ordinary
`skill in the art. It will be apparent to those of ordinary skill
`in the art that the speci?c frequency values identi?ed in FIG.
`2 are not critical to the operation of the present invention. A
`PSTN channel existing in a different frequency range may
`also bene?t by use of the concepts taught herein.
`Referring now to FIG. 3. the modi?ed PSTN channel 310
`of the present invention is illustrated. The present invention
`modi?es the prior art PSTN channel 210 to create a new
`PSTN channel 310 having two component subchannels. a
`main channel 312 and a side channel 314. Note that main
`channel 312 and side channel 314 are con?gured to ?t within
`the frequency range de?ned by the prior art PSTN channel
`210. By dividing PSTN channel 310 into main channel 312
`and side channel 314. the present invention gains the advan
`tage of providing main channel 312 for the transfer of voice
`signals and data signals at the same time side channel 314 is
`transferring control information and/or additional data sig
`nals. The control information transferred on side channel
`314 is used primarily for selecting the transfer of either voice
`signals or data signals on main channel 312. By providing a
`separate and independent side channel 314 for controlling
`main channel 312. the present invention gains the advantage
`over the prior art of eliminating the inherent delays caused
`in the prior art design by switching between a voice transfer
`mode and a data transfer mode using a single channel such
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`The present invention is a transceiver providing simulta
`neous transfer of control information with voice and data
`over a public switched telephone network line. In the
`following description. numerous speci?c details are set forth
`in order to provide a thorough understanding of the present
`invention. However. it will be apparent to one of ordinary
`skill in the art that these speci?c details need not be used to
`practice the present invention. In other circumstances. well
`known structures. circuits. and interfaces have not been
`shown in detail in order not to unnecessarily obscure the
`present invention.
`Referring to FIG. 1. the voice and data transceiver 110 of
`the present invention is illustrated. In a typical system
`application. transceiver 110 is coupled to a public switched
`telephone network (PSTN) 112 via telephone line 114.
`PSTN 112 and lines 114 are standard telephone system
`components which are Well known to those of ordinary skill
`in the art. In a typical prior art con?guration. a standard
`telephone handset may be coupled to PSTN 112 via line 114.
`In this con?guration. a standard voice conversation may
`occur between two callers through the PSTN 112. In another
`typical prior art con?guration. a computer with a modem
`45
`device may be coupled to PSTN 112 via line 114. In this
`case. a modem can convert digital computer signals to a
`form that can be transmitted to a receiving computer with a
`modem device through PSTN 112. In this manner. the PSTN
`112 may be used for the independent transfer of voice
`information or data typically generated by a computer or
`facsimile machine.
`The transceiver 110 of the present invention includes a
`Voice In interface 124 and a Voice Out interface 126. Voice
`In interface 124 is a standard connector or interface with a
`voice receiving device such as a microphone or record/
`playback device. Voice Out interface 126 is a standard
`connector or interface with a voice transmitting device such
`as a speaker or record/playback device. Many methods for
`receiving and transmitting voice signals will be apparent to
`those of ordinary skill in the art.
`Transceiver 110 includes a Data In interface 120 and a
`Data Out interface 122. Data In interface 120 is a standard
`digital computer interface such as a serial or parallel data
`communications interface. Similarly Data Out interface 122
`is a standard data communications interface such as a
`parallel or serial interface. It will be apparent to those of
`
`SO
`
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`

`5.761.292
`
`5
`as PSTN 210. The present invention also provides the
`advantage of allowing the transfer of data signals on side
`channel 314 simultaneous with the transfer of voice signals
`on main channel 312. In this manner. the transfer of voice
`signals does not completely suppress the simultaneous trans
`fer of computer information. These advantages are provided
`by the present invention without rede?ning the bandwidth of
`the standard PSTN channel.
`Referring again to FIG. 3. main channel 312 occupies a
`portion of PSTN channel 310. Because main channel 312
`shares the PSTN channel bandwidth with side channel 314.
`main channel 312 is necessarily a smaller bandwidth than
`PSTN channel 310. The transfer of voice information is
`therefore constrained to a smaller range of frequencies. This
`frequency range reduction. however. does not signi?cantly
`degrade the voice signals transferred through main channel
`312. In most cases. the signal degradation of voice signals
`transferred across a reduced range main channel 312 is
`almost imperceptible. As will be described below. voice
`enhancement logic may be used to arti?cially reconstruct
`voice signals degraded by transfer across main channel 312.
`As an additional option to reduce signal degradation. main
`channel 312 may be located at any frequency within PSTN
`channel 310. For the example illustrated in FIG. 3. main
`channel 312 is located at the lower end of the PSTN channel
`310 frequency spectrum and side channel 314 is located at
`the upper end of the spectrum Alternatively. side channel
`314 may be located at the lower end of the PSTN channel
`310 frequency spectrum and main channel 312 may be
`located at the upper end of the frequency spectrum. As
`another alternative. side channel 314 may be positioned in
`the middle of main channel 312 thereby splitting main
`channel 312 into a lower half and an upper half. In the
`preferred embodiment. however. side channel 314 must
`occupy a contiguous range of frequencies. By arranging side
`channel 314 above. below. or in the middle of main channel
`312. the signal degradation for the transfer of signals
`through main channel 312 may be minimized.
`Having de?ned a frequency range for main channel 312
`and side channel 314. the control logic 130 of the present
`invention provides a means for controlling the transfer of
`voice and data signals across main channel 312 and the
`transfer of control and data signals across side channel 314.
`In the preferred embodiment. data is transferred across main
`channel 312 using a high speed modern technology such as
`a quadrature amplitude modulation (QAM) technology.
`Control information and data is transferred across side
`channel 314 using a lower capacity transmission technology
`such as a frequency shift keying (FSK) technology. Using
`FSK. a binary “1” value may be represented as a particular
`frequency such as frequency “a” illustrated in FIG. 3.
`Similarly. a binary “0" value may be represented as a
`different frequency value such as frequency “b” illustrated in
`FIG. 3. The use of QAM and FSK modern technology is well
`known to those of ordinary skill in the art. Thus. control and
`data may be transmitted through side channel 314 without
`affecting the simultaneous transmission of voice and data in
`main channel 312.
`The ability to switch the main channel 312 to/from a voice
`transfer mode from/to a data transfer mode is much more
`e?icient using the side channel 314 or other independent
`control mechanism. Normally. to start a QAM modem data
`signal sequence. the receiver must ?rst perform tinting
`recovery. Next. the transmitter and receiver must execute a
`training sequence. This process can take up to a half second
`in a conventional system. Because of this delay in e?fecting
`a switch between a voice transfer mode and a data transfer
`
`55
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`
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`25
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`30
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`35
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`40
`
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`
`6
`mode. less data is transmitted during a voice gap. The side
`channel (as part of its control function) will maintain the
`receiver clocks thereby allowing a fast timing recovery and
`a very fast training sequence.
`The components of the present invention are roughly
`divided into transmitter logic and receiver logic. The trans
`mitter logic is used for transmitting voice signals and data
`signals across a single telephone line 114 through PSTN 112
`to a receiver. The receiver logic is used for receiving voice
`and data signals sent through PSTN 112. The transmitter
`logic of the present invention is illustrated in FIG. 4 and
`described below. The receiver logic is illustrated in FIG. 5
`and described below.
`Referring now to FIG. 4. the transmitter 410 of the present
`invention is illustrated. The transmitter 410 includes trans
`mitter channel control logic 412. Control logic 412 receives
`Data In signals on line 416. The Data In signals 416 are
`received from Data In interface 120. Data and control
`information may be supplied to control logic 412 from a host
`computer on Data In lines 416. In general. the data provided
`to control logic 412 on Data In lines 416 is routed for
`transfer to PSTN 112 via main channel 312. Data is so routed
`to main channel 312 by being output on the main data lines
`426 by control logic 412. As will be described below. the
`main data output on main data lines 426 is held in variable
`length buffer 422 for subsequent output on main channel
`312.
`A portion of the data provided on Data In lines 416 may
`be routed for transfer to PSI'N 112 via side channel 314.
`Data is routed to side channel 314 by being output on side
`data lines 462 by control logic 412. Control logic 412 routes
`incoming data on either main data lines 426 or side data lines
`462 as determined explicitly by command codes provided in
`the data received on Data In lines 416 or implicitly as
`determined by the availability of main channel 312. In some
`cases. main channel 312 will be unavailable for the transfer
`of data signals while voice signals are being transferred. In
`these cases. main data (i.e. data waiting to be sent on the
`main channel) is held in variable length bu?er 422 until
`main channel 312 again becomes available for transfer of
`data. On the other hand. side channel 314 will always be
`available for the transfer of control information or data.
`However. the side channel 314 typically operates at a slower
`data transfer rate. If data received by control logic 412 via
`Data In lines 416 indicates a side data transfer request as
`indicated by a predetermined command code or if main
`channel 312 is blocked by the transfer of voice information
`on main channel 312. control logic 412 routes incoming data
`out on side data lines 462. In other cases. data received on
`Data In lines 416 is routed to main channel 312 via main data
`line 426.
`Control logic 412 also receives two control lines in the
`preferred embodiment. First. a channel control line 420 is
`received. Channel control line 420 is used to instruct control
`logic 412 to explicitly switch between the transfer of voice
`signals or data signals on main channel 312. Channel control
`line 420 allows a host computer to override the automatic
`switching between a data transfer mode and a voice transfer
`mode on main channel 312. A signal on channel control line
`420 indicates either a voice transfer mode or a data transfer
`mode on main channel 312. This signal is used by control
`logic 412 to generate a signal on voice/data select line 446.
`Voice/data select line 446 is used to control transmit switch
`440 to output either data signals or voice signals on output
`lines 450.
`A second control line received by transmitter channel
`control logic 412 is provided by voice gap detect circuit 414.
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`Voice gap detect circuit 414 receives Voice In signals on
`Voice In line 418. Voice In signals are provided by Voice In
`interface 124. The Voice In signals comprise voice infor
`mation as may be spoken by a caller on a telephone line.
`Voice gap detect circuit 414 is a conventional and well
`known circuit for detecting gaps or silence in a telephone
`conversation. Because a substantial portion of a typical
`telephone call is silent (i.e.. absent voice signals). the voice
`gaps may be used for the transfer of computer data on main
`channel 312. When voice tones are again detected on Voice
`In lines 418. the transfer of data on main channel 312 is
`suspended and the transfer of the voice signals from Voice
`In lines 418 to main channel 312 is enabled. Thus. voice gap
`detect circuit 414 provides a signal on line 419 to control
`logic 412 that indicates when a voice gap is present in the
`voice signals on Voice In lines 418. Voice gap detect circuit
`414 also provides an indication to control logic 412 that
`indicates when a voice gap is absent in the signals on Voice
`In lines 418. The control signals received on line 419 by
`control logic 412 are used to determine the condition of the
`signal output by control logic 412 on voice/data select line
`446. If the signal received on channel control line 420
`indicates a voice select request or if the control signal
`received on line 419 indicates the absence of a voice gap
`(i.e.. active voice tones are present on Voice In lines 418).
`control logic 412 generates a voice select signal on voice/
`data select line 446. Similarly. if the signal received on
`channel control line 420 indicates a data select request or if
`the control signal received on line 419 indicates the presence
`of a voice gap (i.e.. active voice tones are not present on
`Voice In lines 418). control logic 412 generates a data select
`signal on voice/data select line 446. In this manner. transmit
`switch 440 is controlled by voice/data select line 446 to
`output on lines 450 voice signals during active voice activity
`or data signals during gaps in the voice signals. A voice gap
`detect circuit such as circuit 414 is well known to those of
`ordinary skill in the art.
`In addition. control logic 412 generates control informa
`tion for transmission on the side channel 314. This control
`information corresponds to the select signal information
`generated on the voice/data select line 446. If the signal
`received on channel control line 420 indicates a voice select
`request or if the control signal received on line 419 indicates
`the absence of a voice gap (i.e.. active voice tones are
`present on Voice In lines 418). control logic 412 generates
`a voice select signal for transmission on side data line 462.
`Similarly. if the signal received on channel control line 420
`indicates a data select request or if the control signal
`received on line 419 indicates the presence of a voice gap
`(i.e.. active voice tones are not present on Voice In lines
`418). control logic 412 generates a data select signal for
`transmission on side data line 462. In this manner. receive
`switch 528 (illustrated in FIG. 5) is controlled by voice/data
`select information transmitted on side channel 314.
`Transmitter logic 410 provides a buffer for both data
`signals transferred on main channel 312 and a buffer for
`voice signals transferred on main channel 312. In the pre
`ferred embodiment of the present invention. a variable
`length buffer 422 is provided for data transferred on main
`channel 312 (main data). Variable length buffer 422 is
`implemented in the preferred embodiment as a ?rst-in
`?rst-out (FIFO) buffer or random access memory of a size
`su?icient to retain data while main channel 312 is busy
`transferring voice information. A buffer 1 control line 428 is
`connected between control logic 412 and variable length
`buffer 422 to allow control logic 412 to enable or disable the
`output of main data by variable length buffer 422 on lines
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`8
`436. In addition. buffer 1 control line 428 provides a means
`by which variable length buffer 422 may indicate to control
`logic 412 that the buffer is full or nearly full. During normal
`operation. control logic 412 ?lls buffer 422 with main data
`received on Data In lines 416 and output on main data lines
`426. When a voice gap occurs as indicated by control line
`419. buffer 422 is enabled via buffer 1 control line 428 to
`output main data on lines 436. When main data transfer on
`main channel 312 is stalled by a voice transfer. control logic
`412 disables buffer 422 from outputting main data on lines
`436. As buffer 422 ?lls or nearly ?lls. an indication on line
`428 provided by butler 422 signals control logic 412 to
`suspend the transfer of main data on main data lines 426.
`The implementation of a FIFO buffer such as bulfer 422 is
`well known to those of ordinary skill in the art.
`A ?xed length buffer 424 is provided for the temporary
`storage of voice information received on Voice In lines 418