Telephone handset interface for automatic switching between voice and data communications

We claim:

1. In a telephone communications system for automatically switching between voice and data communications over a telephone line, said system including:

a telephone set for voice communication having a handset with a pair of speaker lines and a pair of microphone lines; and having a telephone base with corresponding pairs of base microphone and speaker lines; and

a modem for data communications having an off-hook state while communicating data and an on-hook state while not communicating data;

the improvement comprising a telephone handset interface having:

sensor means for sensing the on-hook/off-hook state of said modem;

switching means controlled by said sensor means for automatically switching between an off-hook state in which said handset speaker lines are decoupled from said base speaker lines and said base microphone and speaker lines are coupled to said modem, and an on-hook state in which said handset speaker lines are coupled to said base speaker lines; and

differential amplifier means coupled to said base speaker lines for enabling said modem to monitor said base speaker lines.

2. The telephone communications system of claim 1, wherein said modem is switchably connected to said base microphone lines by said switching means; and wherein said switching means in said on-hook state:

(a) couples said handset speaker lines to said base speaker lines;

(b) couples said handset microphone lines to said base microphone lines; and

(c) disconnects said modem from said base microphone lines; and

in said off-hook state, said switching means:

(a) disconnects said handset speaker lines from said base speaker lines;

(b) disconnects said handset microphone lines from said base microphone lines; and

(c) couples said modem to said base microphone and speaker lines.

3. The telephone communications system of claim 1, wherein said sensor means comprises means for detecting increased current conducted by said modem while in said off-hook state.

4. In a telephone communications system for automatically switching between voice and data communications with a remote unit over a telephone line, said system including:

a telephone set for voice communication having a handset with a pair of speaker lines and a pair of microphone lines; and having a telephone base with corresponding pairs of base microphone and speaker lines;

a modem for data communications having an off-hook state while communicating data and an on-hook state while not communicating data; and

start signal detector means for detecting a preselected start signal transmitted by said remote unit over said telephone line and directing said modem to change to said off-hook state in preparation for receiving data transmitted by said remote unit;

the improvement comprising a telephone handset interface having:

sensor means for sensing the on-hook/off-hook state of said modem;

switching means controlled by said sensor means for automatically switching between an off-hook state in which said handset speaker lines are decoupled from said base speaker lines and said base microphone and speaker lines are coupled to said modem, and an on-hook state in which said handset speaker lines are coupled to said base speaker lines; and

differential amplifier means coupled to said base speaker lines for enabling said start signal detector means to monitor said base speaker lines.

5. The telephone communications system of claim 4, wherein said modem is switchably connected to said base microphone lines by said switching means; and wherein said switching means in said on-hook state:

(a) couples said handset speaker lines to said base speaker lines;

(b) couples said handset microphone lines to said base microphone lines; and

(c) disconnects said modem from said base microphone lines; and

in said off-hook state, said switching means:

(a) disconnects said handset speaker lines from said base speaker lines;

(b) disconnects said handset microphone lines from said base microphone lines; and

(c) couples said modem to said base microphone and speaker lines.

6. The telephone communications system of claim 4, wherein said sensor means comprises means for detecting increased current conducted by said modem while in said off-hook state.

7. The telephone communications system of claim 4, wherein said start signal comprises a signal indicating the transmission rate for data.

8. The telephone communications system of claim 7, wherein said modem is capable of selectively communicating data at any of a plurality of data rates; said start signal comprises a tone having a frequency selected from a corresponding plurality of predetermined frequencies to indicate one of said data rates; and said system further comprises means to set said modem data rate according to the frequency of said start signal tone.

9. The telephone communications system of claim 4, further comprising means for generating and transmitting said start signal prior to transmitting data.

10. The telephone communications system of claim 4, wherein said start signal comprises a signal indicating the format of data to be transmitted.

11. A telephone communications system for providing voice and data communications with a remote unit over a telephone line via a telephone set having a handset with a pair of speaker lines and a pair of microphone lines, and a base with corresponding pairs of base microphone and speaker lines, said system comprising:

a modem for data communications having an off-hook state while communicating data and an on-hook state while not communicating data over said telephone line;

start signal detector means for detecting a preselected start signal transmitted by said remote unit over said telephone line;

start signal generating means for transmitting a preselected start signal over said telephone line to said remote unit;

a processor in communication with said modem for directing said modem to change to said off-hook state in preparation for receiving data from said remote unit when said start signal detector means detects said start signal; said processor also directing said start signal generating means to transmit said start signal and directing said modem to change to said off-hook state in preparation for transmitting data provided by said processor; and

interface circuitry having:

(a) sensor means for sensing the on-hook/off-hook state of said modem;

(b) switching means controlled by said sensor means for automatically switching between said off-hook state in which said handset speaker lines are decoupled from said base speaker lines and said base microphone and speaker lines are coupled to said modem, and said on-hook state in which said handset speaker lines are coupled to said base speaker lines; and

(c) differential amplifier means coupled to said base speaker lines for enabling said start signal detector means to monitor said base speaker lines.

12. The telephone communications system of claim 11, wherein said modem is switchably connected to said base microphone lines by said switching means; and wherein said switching means in said on-hook state:

(a) couples said handset speaker lines to said base speaker lines;

(b) couples said handset microphone lines to said base microphone lines; and

(c) disconnects said modem from said base microphone lines; and

in said off-hook state, said switching means:

(a) disconnects said handset speaker lines from said base speaker lines;

(b) disconnects said handset microphone lines from said base microphone lines; and

(c) couples said modem to said base microphone and speaker lines.

13. The telephone communications system of claim 11, wherein said sensor means comprises means for detecting increased current conducted by said modem while in said off-hook state.

14. The telephone communications system of claim 11, wherein said modem is capable of selectively communicating data at any of a plurality of data rates; said start signal comprises a tone having a frequency selected from a corresponding plurality of predetermined frequencies to indicate one of said data rates; and said system further comprises means to set said modem data rate according to the frequency of said start signal tone.

15. The telephone communications system of claim 11, wherein said start signal comprises a signal indicating the format of data to be transmitted.

16. A telephone communications system for providing voice and data communications with a remote unit over a telephone line via a telephone set having a handset with a pair of speaker lines and a pair of microphone lines, and a base with corresponding pairs of base microphone and speaker lines, said system comprising:

a modem for data communications having an off-hook state while communicating data over said telephone line in which said modem conducts current and an on-hook state while not communicating data over said telephone line in which said modem does not conduct current;

start signal detector means for detecting a preselected start signal transmitted by said remote unit over said telephone line;

start signal generating means for transmitting a preselected start signal over said telephone line to said remote unit;

a processor in communication with said modem for directing said modem to change to said off-hook state in preparation for receiving data from said remote unit when said start signal detector means detects said start signal; said processor also directing said start signal generating means to transmit said start signal and directing said modem to change to said off-hook state in preparation for transmitting data provided by said processor; and

interface circuitry having:

(a) sensor means for sensing the on-hook/off-hook state of said modem by monitoring said current conducted by said modem;

(b) switching means controlled by said sensor means for automatically switching between said on-hook state in which said switching means:

(1) couples said handset speaker lines to said base speaker lines;

(2) couples said handset microphone lines to said base microphone lines; and

(3) disconnects said modem from said base microphone and speaker lines; and

said off-hook state in which said switching means:

(1) disconnects said handset speaker lines from said base speaker lines;

(2) disconnects said handset microphone lines from said base microphone lines; and

(3) couples said modem to said base microphone lines; and

(c) differential amplifier means coupled to said base speaker lines for enabling said start signal detector means to monitor said base speaker lines.

17. The telephone communications system of claim 16, wherein said start signal comprises a signal indicating the data transmission rate.

18. The telephone communications system of claim 16, wherein said modem is capable of selectively communicating data at any of a plurality of data rates; said start signal comprises a tone having a frequency selected from a corresponding plurality of predetermined frequencies to indicate one of said data transmission rates; and said system further comprises means to set said modem data rate according to said start signal tone.

19. The telephone communications system of claim 16, wherein said start signal comprises a predetermined signal indicating the format of data to be transmitted.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of telephony. More specifically, the present invention discloses an interface system for insertion between the telephone handset and base that provides for automatic switching between voice and data communications.

2. Statement of the Problem

The present invention is intended to address two separate, but related problems in communicating both voice and data by telephone. First, it is often desirable to be able to transmit data over a single telephone line interspersed with verbal discussions between the parties. This data can be in the form of visual images relevant to the conversation. For example, a travel agent might wish to show a telephone customer a travel itinerary as they discuss it, or a broker might want to show a customer a visual confirmation of a financial transaction that the customer has just made orally over the telephone. Image data can be transmitted over a telephone line, for example, using conventional facsimile machines or the VoiceView.TM. products marketed by Radish Communications Systems, Inc. of Boulder, Colo. Alternatively, this data can be in the form of one or more data files to be transferred by modem between the parties' computers. A number of telephone systems have been invented in the past to allow transmission of both voice and data over a single telephone line by switching between voice and data modes, including the following:

______________________________________ Inventor Patent No. Issue Date ______________________________________ Davis 5,164,982 Nov. 17, 1992 Emmons et al. 4,932,047 June 5, 1990 Yoshida 4,815,121 Mar. 21, 1989 Artom 4,387,271 June 7, 1983 ______________________________________

Davis discloses a telecommunications display system for accommodating both voice and data over a single telephone line. The receiving party ("subscriber") is provided with a display terminal 14 that is connected to the telephone line 22, 52 between the telephone network 50 and the base of the user's telephone 12 as shown in FIG. 1. The display terminal includes a voice/data selector that can automatically recognize digital data and switches from voice communication to data communication modes. This patent discusses one embodiment of the VoiceView.TM. products marketed by Radish Communications Systems, Inc.

Emmons et al. disclose an example of a conversational video phone. The device communicates both audio signals and freeze-frame video images over a standard telephone line.

Yoshida et al. disclose a telephone communication system that recognizes speech and automatically switches from data to speech transmission.

Artom discloses another example of a telephone system for combining voice and data communications over a single telephone line.

The second problem addressed by the present invention arises from the difficulty of interfacing with the multitude of existing PBX telephone systems that employ proprietary communications protocols between the PBX and its station telephones. Conventional modems, fax machines, and the like are designed to interface only with a standard analog telephone line (i.e., plain old telephone service, or POTS). In facilities having a PBX system, the common solution has been to install additional dedicated analog telephone lines that are not routed through the PBX to service these data devices. This solution adds substantial expense, unnecessary complexity, and wasted telephone line capacity.

The proprietary communications protocols commonly used by PBX systems do not extend farther than the base of the telephone set at each station. In particular, the telephone base and handset are connected by a handset cord that has a pair of speaker lines and a pair of microphone lines for analog communication with the handset speaker and microphone, respectively. Therefore, an alternative approach has been to interface the data device (e.g., a modem or fax) to the handset cord by means of a manually operated switch. The speaker and microphone lines in the handset cord appear to the data device simply as a conventional four-wire analog telephone circuit. This allows the data device to transmit and receive analog-encoded data over the handset cord without having to contend with the communication protocol of the PBX system. A number of prior art patents discuss switching arrangements to accommodate both voice and data transmission by inserting a manual switch into the handset cord, including the following:

______________________________________ Inventor Patent No. Issue Date ______________________________________ Gutzmer 4,907,267 Mar. 6, 1990 Serrano 4,367,374 Jan. 4, 1983 ______________________________________

Gutzmer discloses a manual switch for insertion between a telephone handset and base to accommodate both voice and data transmission. Serrano discloses another example of a manual switch inserted between a telephone handset and base to allow both voice and data transmission. A number of similar manual switches are also on the market.

The shortcoming of a manual switch is that the user must manually operate the switch to change from voice to data transmission. In addition, in order to receive data, the sending party must verbally advise the user that data is about to be transmitted and wait while the user at the receiving end manually changes the switch to data mode. This is relatively slow and cumbersome. It also presents the possibility that data can be inadvertently lost or damaged, and voice communications can be lost or clipped due to mis-timed operation of the manual switch. This possibility is further increased if both parties are manually switching between voice and data modes.

The manual switching arrangement described in the Gutzmer patent has been improved upon in two products manufactured by Unlimited Systems Corp., Inc., of San Diego, Calif. These products are described in the "KONEXX Model 112 Operating Instructions" and the "KONEXX Model 108 Operating Instructions." Both KONEXX devices are intended to provide an interface between the telephone base and handset for a data device, such as a fax machine or a modem. The user manually takes the telephone handset off-hook and places a call to a remote station. For example, when used with a fax machine, the user would place a call to the remote fax machine. Similarly, when used with a modem, the user would place a call to the remote modem (e.g., a bulletin board service). When the remote station answers the call, the user must then manually prompt the data device (i.e., the fax machine or modem) to go off-hook and begin communications with the remote station. The KONEXX device detects the increased current through the telephone line connecting the KONEXX device to the local data device when the data device goes off-hook and automatically couples the data device to the telephone base. The KONEXX device employs inductive coupling (e.g., transformers) to couple the local data device to the telephone line and to isolate the base microphone lines from the base speaker lines.

3. Solution to the Problem

None of the prior art references show an interface system connected between the telephone base and handset to provide automatic voice and data communications. The present invention automatically switches between voice and data communications over a single telephone line, and also circumvents the problems associated with interfacing to PBX systems that use proprietary communications protocols.

SUMMARY OF THE INVENTION

This invention provides a telephone handset interface that is inserted between the telephone handset and base for automatic switching between voice and data modes of communication. Each station includes a telephone set with a base and handset, interface circuitry, and modem. The interface circuitry includes relay switches to couple the modem to the telephone base microphone and speaker lines in data mode and to couple the telephone handset to the telephone base in voice mode. The relay switches are controlled by a sensor that monitors the on-hook/off-hook status of the modem as an indication of when the modem is preparing to transmit or receive data. The interface circuitry also includes differential amplifier circuitry coupled to the telephone base speaker lines to enable the modem to continually monitor the telephone line.

In one embodiment, each modem includes means for generating a start signal to cause a remote station at the other end of the communication link to enter data mode prior to transmitting data. Similarly, the modem includes a start signal detector that is coupled to the telephone base speaker lines through the differential amplifier circuitry to detect a start signal sent by the remote unit that causes the modem to switch into data mode in preparation for receiving data. The start signal can also include signals designating the rate at which data will be transmitted and its format.

A primary object of the present invention is to provide a telephone handset interface that automatically switches between voice and data communications.

Another object of the present invention is to provide a telephone interface for data communications that can be inserted between the telephone base and handset of virtually any telephone set to circumvent proprietary telecommunications protocols commonly found in PBX systems.

Yet another object of the present invention is to provide a telephone interface that can be readily incorporated into a wide variety of data devices, such as modems, fax machines, and VoiceView.TM. products.

These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more readily understood in conjunction with the accompanying drawings, in which:

FIG. 1(a) is a schematic block diagram showing the overall invention.

FIG. 1(b) is a schematic diagram of the handset interface circuitry 20.

FIG. 2 is a schematic block diagram of the modem 24.

FIG. 3 is a simplified flowchart of the procedure for transmitting data.

FIG. 4 is a simplified flowchart of the procedure for receiving data.

FIG. 5 is a flowchart of the procedure for establishing a link prior to transmitting data.

FIG. 6 is a flowchart of the procedure for establishing a link prior to receiving data (i.e., in response to the link establishment procedure initiated in FIG. 5).

FIG. 7 is a flowchart of the link turn-around procedure for the unit receiving data.

FIG. 8 is a flowchart of the link turn-around procedure for the unit transmitting data.

FIG. 9 is a flowchart of the retry procedure for link establishment.

FIGS. 10(a) and 10(b) are flowcharts of the link tear-down procedure.

DETAILED DESCRIPTION OF THE INVENTION

Overview

Turning to FIG. 1(a), a schematic block diagram is provided showing the handset interface 20 installed between the telephone base 10 and handset 11, 12. In particular, a conventional telephone handset has an earpiece speaker 11 for converting an analog electrical signal into audible speech, and a microphone 12 associated with its mouthpiece for converting speech into an analog signal. It should be understood that other equivalent units could be substituted for the handset, such as a headset used by telephone operators or a teleconferencing speaker unit used for conference calls.

In a conventional telephone set, a handset cord normally extends between the telephone base and the handset. The handset cord typically has a pair of speaker lines and a pair of microphone lines providing full-duplex analog communication from the telephone base with the handset earpiece speaker 11 and microphone 12, respectively. The handset cord is also usually equipped with standard jacks at each end allowing the handset cord to be easily connected or disconnected from corresponding connectors in the telephone base and handset. As shown in FIG. 1(a), the telephone base 10 is connected to a PBX or telephone company central office in the conventional manner using the appropriate communications protocol for the specific telephone system.

Interface Circuitry

Interface circuitry 20 is inserted along the pair of speaker lines 15, 13 and the pair of microphone lines 16, 14 that would otherwise normally extend from the telephone base 10 to the handset speaker 11 and the handset microphone 12, respectively, as depicted in FIG. 1(a). The interface circuitry includes a number of relay switches to selectively couple the telephone handset 11, 12 and base 10 for voice communications (voice mode), and to selectively couple a modem 24 to the telephone base 10 for data communications (data mode). The interface circuitry also includes a differential amplifier enabling the modem 24 to monitor the telephone line for a preselected start signal indicating that the remote station intends to transmit data. Reception of a start signal triggers the modem 24 to switch from voice mode to data mode in preparation for receiving data from the remote station. It should be noted that the local processor 30 can also direct the modem 24 to switch to data mode in preparation for transmitting data to be supplied by the processor 30, such as a screen display, fax transmission, or data file. In either case, the modem changes from an on-hook state to an off-hook state when entering data mode. The interface circuitry 20 includes a sensor to monitor the on-hook/off-hook status of the modem and automatically change the position of the relay switches to couple the modem 24 to the telephone base 10 when the modem goes off-hook. The on-hook/off-hook sensor automatically returns the relay switches to their voice mode positions when the modem is on-hook. In the preferred embodiment, the on-hook/off-hook state of the modem is sensed by measuring the current drawn by the modem port.

FIG. 1(b) is a detailed schematic diagram of the interface circuitry 20. The interface circuitry 20 is connected to the telephone handset 11, 12 and telephone base 10 by means of at least one jack J2. In the interest of clarity, the reference numerals of the pairs of connecting wires 13-16 extending from the jack J2 within the interface circuitry in FIG. 1(b) are consistent with the reference numerals of the external wire pairs shown in FIG. 1(a). The interface circuitry 20 is also connected to the modem 24 by means of another jack J1. For a two-wire modem, the tip and ring connectors serve as both the receive port and the transmit port for the modem. Therefore, only the tip and ring connectors are connected to the interface circuitry when dealing with a two-wire modem. It should be expressly understood that a three-wire or four-wire modem could be readily substituted with only minor corresponding changes to the interface circuitry 20.

Two relay switches S1 and S2 are used to switch the interface circuitry between data mode or voice mode. The position of the relay switches S1 and S2 is determined by two corresponding coils K1 and K2 shown in FIG. 1(b). The default positions for the relay switches shown in FIG. 1(b) correspond to the voice mode of operation in which the base microphone lines 16 are directly coupled to the handset microphone lines 14 and the base speaker lines 15 are directly coupled to the handset speaker lines 13 to provide normal voice communications via the handset 11, 12. In voice mode, the base speaker lines 15 are also coupled through differential amplifier circuitry U2, U3, and U4 to the modem jack J1. The differential amplifier circuitry provides four-wire to two-wire conversion of the telephone signals for the modem 24 and also enables the tone detectors 242 and 244 in the modem 24 to continually monitor the telephone line for the start sequence. In data mode, the base speaker lines 15 are disconnected from the handset earpiece by relay switch S1. Also, relay switch S2 couples the modem to the base microphone lines 16 to allow transmission of data by the modem. The signal output by the modem is buffered by a variable gain amplifier U6. The gain is set by means of a switch S3 to select one or more of an array of resistor values R13-R24.

The interface circuitry 20 also includes means to automatically switch from voice mode to data mode whenever the modem desires to transmit or receive data. There are any number of ways to accomplish this result. For example, the interface circuitry can be directly controlled by the processor 30 or modem 24. However, in the preferred embodiment, the interface circuitry monitors the on-hook/off-hook state of the modem by measuring the current drawn by the modem through its tip and ring connectors. Consistent with standard practice in the telephone industry, the modem port appears essentially as an open circuit or a very high impedance to DC signals when the modem is on-hook. Consequently, little or no current is drawn when the modem is on-hook (i.e., in voice mode). In contrast, when the modem goes off-hook in preparation for transmitting or receiving data (i.e., data mode), the tip and ring connectors appear as a circuit having a nominal resistance. The modem will draw significant current in response to a voltage placed across the tip and ring connectors.

Transistor Q1 and resistors R1-R3 serve as a current source. When the modem goes off-hook, the modem tip and ring connectors begin to conduct significant current and the voltage across the tip and ring connectors drops to a nominal value. This current triggers the photo-amplifier U1, which in turn actuates the coils K1 and K2 to change the relay switches S1 and S2 to their data mode positions. It should also be noted that the loop current and voltage presented by the interface circuitry 20 through Q1 to the modem 24 emulates a conventional central office loop. In particular, the interface circuitry uses a current source that delivers about 20 mA into loads that can vary from 0 ohms to about 500 ohms. Typical off-hook characteristics require the modem to sink at least 20 mA with not more than 8 volts across the modem's tip and ring connectors.

The interface circuitry 20 employed in the present system offers a number of advantages. The differential amplifier circuitry enables the modem to continually monitor the telephone line for a predetermined start sequence while the modem remains on-hook. While the modem is off-hook and the interface circuitry is in data mode, the very high impedance inputs to the differential amplifier provide isolation between the telephone base microphone 16 and the handset earpiece 15 pairs. The interface circuitry 20 also provides complete isolation of the handset earpiece 11 in data mode, unlike the prior art approach discussed in U.S. Pat. No. 4,907,267 of Gutzmer, which provides only a reduced signal level from the telephone base to the handset earpiece in data mode. Finally, the interface circuitry 20 provides both gain and low-pass filter functions for receiving data. Active circuitry provides true signal power gain and not simply a voltage gain that is available when using a transformer.

Modem

It should be expressly understood that the interface circuitry 20 can be used in association with a wide variety of different types of modems. In the simplest embodiment, even a conventional modem can be used. For example, a traveler with a portable computer having a conventional modem may wish to call out through a hotel's telephone system to exchange e-mail or other data with a home office. In this scenario, the user would first unplug the existing handset cord and substitute appropriate connections between the interface circuitry 20 and the telephone base 10, handset 11, 12, and modem 24 as shown in FIG. 1(a). The user's portable computer is turned on and the appropriate e-mail or telecommunications software is executed to control the modem. If necessary, the software is configured for establishing a data link with the home office's computer using the appropriate communications protocol, data rate, parity, etc. The user then places an outgoing call to the home office in the conventional manner using the key pad on the telephone base 10. Alternatively, in some types of telephone systems, the modem can be used to dial the home office after the telephone has manually been taken off-hook. The user then waits until the home office computer answers the telephone call and emits a tone indicating that its modem is prepared to establish a data link. When the user hears the modem tone over the handset, he presses a key or clicks on the appropriate icon to trigger the telecommunications software to direct the local modem to go off-hook in preparation for establishing a data link with the home office computer's modem. The two modems can then exchange data over the telephone line in the conventional manner. This embodiment does not necessarily include a start sequence to automatically cause the modem to switch into data mode, but rather is completely dependent upon manual operation of the computer by the user. However, for the scenario described above, a one-time switch into data mode is typically sufficient to enable a traveler to exchange e-mail and data files.

The present invention is also intended to provide a handset interface for VoiceView.TM. modems, as well as modems that support a VoiceView.TM. mode of operation plus other modes (e.g., facsimile, data, etc.). The remainder of this specification discusses these embodiments in detail. For example, the components of a modem 24 supporting the VoiceView.TM. protocol are shown in greater detail in the block diagram provided in FIG. 2. The signal level at the receive port of the modem is regulated by an automatic gain control amplifier 248. The analog telephone signal is demodulated by the data receive block 256 to deliver corresponding digital data to the modem's controller 246. In the preferred embodiment, the data receive block 256 can be configured by the processor 30 and modem controller 246 to selectively operate at any of a number of different data rates (e.g., V.21 300 bps FSK, V.27ter 4800 bps DPSK, or V.29 9600 bps QAM). The analog signal received by the modem is also monitored by a number of tone de