IMPROVEMENTS RELATING TO CALLER IDENTIFICATION

Abstract: A device for connection to a switched communication network to identify a calling subscriber (1) to a receiving subscriber (2) comprises a frequency generating device (36). The frequency generating device (36) generates a set of frequencies by which a calling subscriber (1) may be identified in response to connection between the calling subscriber (1) and receiving subscriber (2). The system may use monofrequencies on a chromatic scale capable of being generated by a human voice or DTMF frequencies. For DTMF frequencies the system may work automatically, semi-automatically by pressing a switch to activate the frequency generating assembly (36), or at fixed intervals.

Description: IMPROVEMENTS RELATING TO CALLER IDENTIFICATION The invention relates to a device for connection to a switched communication network to identify a calling subscriber to a receiving subscriber. With the increasing ease with which communication can be achieved around the world, there is an increasing problem with anonymous and threatening telephone calls and the like. A receiving subscriber is unable to prevent such calls being made and it is very difficult to trace the source of such calls when they are unexpected. In accordance with one aspect of the present invention, a device for connection to a switched communication network to identify a calling subscriber to a receiving subscriber comprises a frequency generating assembly for generating a set of frequencies capable of being generated by the human voice, the assembly being responsive to the connection between a calling subscriber and a receiving subscriber to generate a group of frequencies from the set identifying the calling subscriber; and connection means for connecting the frequency generating assembly to the receiving subscriber. The problems outlined above are solved by the invention which causes a set of frequencies within a frequency band capable of being generated by a human voice to be transmitted to the receiving subscriber so as to identify the calling subscriber. For example, in the case of a public switched telephone network, each subscriber is allocated a unique code or number and this can be represented by a corresponding set of frequencies. The advantage of using frequencies within the human voice range is that they can be reproduced clearly and do not cause any disturbance to modern electronic transmission instruments. Furthermore, the frequencies can be easily recorded on conventional audio magnetic tape and the like. Preferably, each frequency of the set of frequencies lies on the chromatic scale. This is particularly convenient since the transmission and reception of the sound frequencies correlated with the notes of a musical scale is very simple and reliable and it is easy even for a non-expert to decode the musical notes. In accordance with a second aspect of the present invention, a device for connection to a switched communication network to identify a calling subscriber to a receiving subscriber comprises a frequency generating assembly for generating a set of frequencies lying on a chromatic scale, the assembly being responsive to the connection between a calling subscriber and a receiving subscriber to generate a group of frequencies from the set identifying the calling subscriber; and connection means for connecting the frequency generating assembly to the receiving subscriber. The frequency generating assembly typically comprises an oscillator, a frequency modulator coupled with the oscillator to generate each of the frequencies making up the set of frequencies, and selector means for causing the frequency modulator to pass selected frequencies corresponding to the calling subscriber identifier to the connection means. For example, the selector means may include a multiplexer controlled by a selector. In accordance with a third aspect of the present invention, a device for connection to a switched communication network to identify a calling subscriber to a receiving subscriber comprises a frequency generating assembly for generating dual tone multi-frequency (DTMF) signals, the assembly being responsive to the connection between a calling subscriber and a receiving subscriber to generate a signal identifying the calling subscriber; and connection means for connecting the frequency generating assembly to the receiving subscriber. The frequency generating device typically comprises means to receive a bifrequency pulse from the receiving subscriber, a programmable memory to store the identifier of the calling subscriber entered by a detachable keyboard unit, and a switch to pass the signal corresponding to the calling subscriber identifier to the connection means under the control of the pulse receiving means. Preferably, there are at least ten different frequencies within the set of frequencies to enable the digits 0-9 to be individually coded. In some examples, the set of frequencies includes eleven or twelve frequencies, the additional frequency or frequencies being used to code one or both of the sign separating an area code from the remainder of the subscriber identifier and a control signal for activating an associated display device which provides a visual display of the caller's identifier. With monofrequency transmission the use of frequencies defining notes on the chromatic scale is particularly suitable since up to twelve such frequencies are available. Preferably when DTMF signals are generated, the frequencies used are the twelve standard international frequencies. In general, for both monofrequency transmission and DTMF signals one device will be connected to each subscriber and be programmed to cause the same set of frequencies to be generated on each occasion that that subscriber initiates a call. A device may be connected either in the calling telephone itself, for example in public telephones, or, preferably, at the exchange connected to any calling lines of interest. However, a more complex system can be envisaged in which a group of devices is used for a number of different subscribers within which each device can be dedicated at any one time to a given subscriber, but rededicated at a later stage to another subscriber, and so on. Typically, the device or devices will be sited at a public exchange for ease of maintenance and security. The device may be formed by separate hardware components or by a suitably programmed microprocessor and can be coupled to an existing, conventional switched communication network without any changes being made to that network. When using monofrequencies on the chromatic scale the identity of a calling subscriber can be determined simply by listening, but preferably the device further comprises decoding means to decode the signal generated by the frequency generating device to provide a visual display of the calling subscriber identifier. Preferably the decoding means is connected at the receiving set to identify the frequencies and to determine the identifier of the calling subscriber. The calling subscriber identifier may be displayed on a visual monitor or printed out by a printing unit. Preferably, the decoding means further comprises a generator to generate the bifrequency pulse. The generator may be powered by depressing a switch on the receiving subscriber set, but preferably the generator is powered by a signal from the calling subscriber such that the calling subscriber identifier is automatically output. Examples of a device according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic circuit diagram showing an example of the device, for use for monofrequency transmission, connected between a calling telephone and a receiving telephone; and, Figure 2 is a schematic circuit diagram showing an example of the device, for use for DTMF transmission, connected between a calling telephone and a receiving telephone. Working prototype models of the devices shown in Figures l and 2 have been developed. The apparatus shown in Figure 1 comprises a pair of telephones 1, 2 in which, in this example, the telephone 1 comprises a calling telephone and the telephone 2 comprises a receiving telephone. The telephones are coupled to a conventional switch positioned at an exchange 3 remote from both telephones. A device 4 for generating a set of frequencies identifying the number of the calling telephone 1 is preferably installed within that telephone's local exchange, where all aspects of its functioning can be monitored. The device is coupled to the wires 5 linking the exchange 3 with the calling telephone 1. The device 4 is coupled to a power source 6 and includes an oscillator 7 which generates a base frequency which is fed to a frequency divider 8. The frequency divider 8 divides the base frequency into 12 frequencies defining a chromatic scale and these are fed to a multiplexer 9. The multiplexer 9 is driven by a binary counter 10 coupled with a flip-flop oscillator 11. The oscillator 11 activates a transistor switch 12 coupled with a relay 13 which in turn is coupled with the wires 19 which link the exchange with the receiving telephone. In this example, each of the twelve musical notes generated by the frequency divider 8 is allocated a particular meaning 20. For example, the note "do" corresponds to the figure 1, "do sharp" to the figure 2, "re" to the figure 3, and so on, with "la sharp" equivalent' to the conventional sign separating the area codes from the specific number of the telephone set that is calling, and "ti" to the impulse required for an optional display unit. Of course, other correlations could also be devised but the correlation just described is particularly useful in a conventional telephone network where each subscriber is allocated a unique identifying number. In operation, when the calling subscriber has dialled the full area code and telephone number of the receiving subscriber, the exchange connects the calling and receiving subscribers together and, by means of an extremely rapid, passing "contact", sends an initial impulse to a capacitor 14 coupled to the flip-flop oscillator 11. The capacitor 14 initiates the oscillator 11 which in turn activates the binary counter 10 which consequently activates the multiplexer 9 to pass through the sequence of sound frequencies corresponding to the digits of the area code and telephone number of the calling subscriber. The oscillator 11 also activates the transistor switch 12. The transistor switch 12 activates the relay 13 so as to connect a loudspeaker 16 to the wires 19. The loud speaker 16 admits the sound frequencies from the multiplexer 9, which have been amplified by a transistor 15, to the wires 19 for transmission to the receiving subscriber 2. It will be noted that activation of the relay 13 will momentarily exclude the calling telephone from the connection and this avoids any disturbances which may be produced during transmission. The duration of the transmission of the set of frequencies is regulated by a resistor 17 but in any case this duration is much less than the time needed to lift the hand set to the ear of the person who is taking the call. It should be noted that the loudspeaker 16 is optional and the output of the multiplexer 9 could be connected directly via the relay 13 to the wires 19. Where the loudspeaker 16 is used, a resistance 18 of about 10 kohm is * provided to ensure stability of the line. In Figure 2 apparatus for use for DTMF transmission is shown. A calling telephone 1 is connected via wires 37 to a frequency generating device 36 preferably installed in the local exchange of the calling telephone, where all aspects of its functioning can be monitored. The device 36 is connected via wires 38 to a receiving telephone 2 and a decoding device 23. The device 36 comprises a detachable keyboard 21 connected to an integrated circuit IC1, 35 which combines the functions of memorising and generating bifrequencies. The keyboard 21 preprogrammes the bifrequencies which the integrated circuit IC1, 35 memorises, after which they can be transmitted in the same order in which they have been programmed. A second integrated circuit IC2, 39 has the function of recognising the single bifrequency 15 generated by a bifrequency generator IC6, 31 which is connected to the receiving telephone 2. The bifrequency corresponds to the asterisk key in the keypad on the receiving telephone set 2. A relay 22 in the device 36, has the function of excluding contact between the wires 37, and the device 36 and wires 38 during transmission of the bifrequencies. The decoding device 23 is powered by the same alternating current that is used to obtain the ringing tone in the receiving telephone 2. A single bifrequency corresponding to the asterisk key in the keypad is generated by the generator 31. This is only necessary in the case of automatic or semi-automatic identification; in the case of identification at predetermined intervals (from the moment when the calling telephone initiates a call) , the generator 31 is absent, or, if present, is not activated. In the semi-automatic mode, the asterisk key on the keypad can be pressed by someone receiving a call at any moment after the receiver has been lifted. In the case of the automatic mode, the bifrequency is produced as soon as the incoming call reaches the receiving telephone 2 and the ringing tone is produced. As soon as the integrated circuit IC2, 39 in the device 36 has actually recognised that bifrequency, it activates IC1, 35 which then transmits as many bifrequencies as there are signs in the identifier of the calling telephone 1. Connected to the generator 31 (when present) and to the receiving telephone 2 is an integrated circuit IC3, 32 which acts as an amplifier of the signals transmitted along the wires 38. Thus, the sequence of bifrequencies reaching 23 is first amplified by IC3, 32. The output from the amplifier 32 is then decoded in IC4, 30 by converting it into four bit binary sequences which are input to IC5, 34 which sorts the sequences and drives the display 24. At present, virtually any telephone number can be visualised on a twelve-digit display (any initial zeros can be shown or not shown, as preferred) , but, since the integrated circuit ICl, 35 in the device 36 can memorise and generate up to thirty bifrequencies at a time, a display unit with a higher digital display capacity can visualise identifiers comprising many more digits than twelve. As soon as an identifier has been visualised on the display it can, in addition, be read on a print out supplied by a printing unit 25, if so desired. In operation each device 36 is preprogrammed using the detachable keyboard 21 to store the identifier of the associated calling set in ICl, 35. When the calling subscriber dials the full area code and number of the receiving subscriber audio contact between calling and receiving telephones is set up as usual by the standard impedance relay 22 in the telephone exchange. Whichever operational mode is chosen, the calling telephone 1 will be excluded from audio contact with the receiving telephone 2 throughout the transmission of the set of bifrequencies that identify the calling telephone 1. In the case of the automatic mode, however, that exclusion occurs before the handset is lifted and it is therefore not perceptible to the caller; in the case of the semi¬ automatic mode it occurs after the handset is lifted, at any moment chosen by the receiving subscriber. In the case of transmission at fixed intervals, a timer T, 40 is installed in the frequency generating device 36, where it is connected to the relay 22, and at predetermined intervals it activates the relay, excluding contact with line 37, and sending the sequential set of bifrequencies along wires 38 to the decoding device 23 (e.g. every 30 or 50 seconds) . During automatic transmission the receiving subscriber typically has about 30-60 seconds during which the decision can be made as to whether to raise the handse . The time required to transmit the DTMF frequencies during which the calling set 1 is excluded from audio contact, is very short, typically less than two-tenths of a second per display place i.e. about 3 seconds for an identifier comprising 12 digits. Each of twelve standard International DTMF frequencies is allocated a particular meaning, either the figures 0-9, the sign separating the area codes from the number and the display signal. The DTMF frequencies are transformed by the decoder device 23, and displayed as digits corresponding to those of the national and area codes followed by those of the telephone number itself or those of any conventional number attributed to it as a labelling or ciphered number to reduce the total number of digits required for caller identification. During the automatic process the handset of the receiving telephone 2 is never lifted and the person who is beside the phone can read from the display and on a print¬ out, the numbers that identify the national and area codes, and then the telephone number of the calling telephone, 1. The person near the receiving telephone 2, may during any part of a predetermined time period, e.g. the first thirty seconds after the first ringing tone begins, decide whether to pick up the handset or not. If he or she decides to reply, the handset is picked up and a conversation can begin. If the called person wishes to check further, to gain confirmation of the number as first seen on the display (and, if required, on the print-out) , he or she using the semi-automatic mode, can press the asterisk key at any desired moment of the conversation, and the decoder device 23 will then activate recovery of the number, making it appear on the display and print out. Semi-automatic mode alone may be provided in which the person who picks up the handset on the called phone 2 presses a dedicated key e.g. that marked with an asterisk *. The pressing of this key * generates a bifrequency, by activating the generator IC6, 31 and so activates the device 36. Table 1 refers to the integrated circuit marked ICl 35 at the telephone exchange. Table l Four out of sixteen bifrequencies corresponding to letters A, B, C, D in the hexadecimal system serve no pupose in the DTMF system of the present invention in identifying the telephone set that is calling, so these have been omitted from Table l. Table 2 refers to the encoding carried out by integrated circuit IC4 30. IC4, 30 is a binary decoder and provides the identification of each bifrequency by means of sets or sequences of four bits i.e. series of four binary digits, " 0 " or " 1 " : " 0001 " , " 0010 ", etc. according to the correspondences shown in Table 2. Again the final four hex representations are not required. Table 2 The filters contained in IC4, 30 use as their terms of reference the basic frequency of quartz, 3.579 MHz, which is also used by integrated circuit ICl, 35 shown in Fig.2. The term filters here includes various technical elements, possibly resistance, capacitance and diode elements, whose function is to keep free, clear and undisturbed the high and low frequencies that are being transmitted. Lastly, IC5, 34 is another binary decoder of four bit sets or sequences of information output from IC4, 30 . Each such sequence, there being 12 utilised out of 16 available, corresponds to a dual tone bifrequency that may thus be identified. Such identification in its turn acts as an input for the respective reed relays in each of the twelve display spaces within the display monitor 24. Each of the twelve reed relays used for the various display spaces is related to a respective figure in Table 2 ( "1, 2, 3...9, 0"), or to the asterisk sign *, or to the hash sign . In summary, the only function of IC3, 32 is to act as an amplifier; the function of IC4, 30 is to decode the bifrequency input reaching it from IC3, 32 by turning it into four bit binary sequences; these in their turn act as an input for IC5, 34 which functions as a sorter of those binary sequences, in practice identifying each one as 1 of 12 possible pre-selected combinations. According to the information input received from IC5, 34 each space in the display will then provide a display in response to that one of the 12 possible signals that is transmitted to it by IC5, 34 producing in each space either one of the figures comprised in the series: 1, 2, 3...8, 9, 0, or else responding to an indication symbolised by * , as a full stop on the display; or responding to a signal symbolised by a ≠ by interpreting it as an end of message, in which case the printing unit may also be activated.

Claims: CLAIMS 1. A device for connection to a switched communication network to identify a calling subscriber (1) to a receiving subscriber (2) comprising a frequency generating assembly (36) for generating dual tone multi-frequency (DTMF) signals, the assembly (36) being responsive to the connection between a calling subscriber and a receiving subscriber; and connection means for connecting the frequency generating assembly (36) to the receiving subscriber (2) . 2. A device according to claim 1, wherein the frequency generating assembly (36) comprises means (39) to receive a bifrequency pulse from the receiving subscriber (2) , a programmable memory (35) to store the identifier of the calling subscriber (1) entered by a detachable keyboard unit (21) , and a switch (22) to pass the signal corresponding to the calling subscriber identifier to the connection means under the control of the pulse receiving means (39) . 3. A device for connection to a switched communication network to identify a calling subscriber to a receiving subscriber, the device comprising a frequency generating assembly (4) for generating a set of frequencies capable of being generated by the human voice, the assembly (4) being responsive to the connection between a calling subscriber (1) and a receiving subscriber (2) to generate a group of frequencies from the set identifying the calling subscriber (1) ; and connection means for connecting the frequency generating assembly (4) to the receiving subscriber (2) . 4. A device according to claim 3, wherein each frequency of the set of frequencies lies on the chromatic scale. 5. A device for connection to a switched communication network to identify a calling subscriber (l) to a receiving subscriber (2) , the device comprising a frequency generating assembly (4) for generating a set of frequencies lying on a chromatic scale, the assembly being responsive to the connection between a calling subscriber (1) and a receiving subscriber (2) to generate a group of frequencies from the set identifying the calling subscriber (2) ; and connection means for connecting the frequency generating assembly to the receiving subscriber. 6. A device according to any of the preceding claims, wherein the frequency generating assembly (4) comprises an oscillator (11) , a frequency modulator coupled with the oscillator (11) to generate each of the frequencies making up the set of frequencies, and selector means for causing the frequency modulator to pass selected frequencies corresponding to the calling subscriber identifier to the connection means. 7. A device according to any of the preceding claims, wherein there are at least ten different frequencies within the set of frequencies to enable the digits 0-9 to be individually coded. 8. A device according to any of the preceding claims, further comprising decoding means (30,34) to decode the signal generated by the frequency generating assembly (36) to provide a visual display of the calling subscriber identifier. 9. A device according to claim 8, when dependent on claim βwherein the decoding means further comprises a generator (31) to generate the bifrequency pulse. 10. A device according to claim 9, wherein the generator (31) is powered by a signal from the calling subscriber (1) such that the calling subscriber identifier is automatically output.

Inventors: DISTRATIS COSIMO, DISTRATIS, COSIMO
Applicants: POLESTAR SA, POLESTAR S.A.
Application year: 1992
Main classification: H04M1
IPC codes: H04M1