Interfacing System for an International-Type Pay-Telephone

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The present invention is directed to an interfacing unit for an international-type coin-operated pay telephone, for example that manufactured by Sodeco, Ltd. of Switzerland, and commonly referred to as a Landis-Gyr international-type coin operated telephone. European, and other international, pay-telephone systems differ from their U.S. counterpart in that the telephone system's central office determines the consumption of the initial coins inserted into the coin-operated telephone via the generation of periodic tone-bursts, commonly within a 12K to 16k range. The frequency of the generation of these tone-bursts by the central office determines the frequency of the debiting at the payphone terminal of the coins inserted. Therefore, when making a long distance call that is more expensive than another long distance call, the central office will generate more frequent tone-bursts to the international-type coin-operated telephone, thereby debiting the terminal more frequently in the base coin-units of that particular country.

It is known to retrofit a conventional, U.S.-type, coin-operated telephone, such that the local payphone terminal is equipped with tariffing information, by which the payphone is monitored and charged via information stored at the local site. This is achieved by including at the local terminal site a listing of all of the exchanges to which one may make an outgoing call, and a listing of the associated tariff rates. There are retrofitting units that retrofit U.S. payphones such that tariffing is achieved at the local site. However, coin collection is still to be based upon the conventional, U.S. method of generation of reverse-polarity signals by a central office of the land-based, switched telephone-network. It is also known to couple such U.S. payphones to a cellular transceiver via a conventional cellular interface unit.

The present invention is directed to an interfacing unit that is coupled to an "International"-type payphone, such as the Landis-Gyr, coin-operated pay-telephone, which interfacing unit of the invention assumes all of the functions of the central office, so that private payphones may be readily and easily provided at any chosen site, whether such payphone be coupled directly to the land-based, switched telephone network, or be coupled to a cellular, or other radio, telephone system.

It is the primary objective of the present invention to convert a conventional, "International"-type, coin-operated pay-telephone, such that central office functions are generated locally at the payphone-terminal proper.

It is another objective of the present invention to, specifically, generate tone-bursts locally at the pay telephone site, by the generation of particular tone-frequencies determinative of the cost of the call, what is generally termed "tariffing."

It is yet another objective of the present invention to allow for such central-office functioning at the local, pay telephone-terminal site, such that tariffing itself is done locally, with the determination of a valid telephone call as well as all tone-detections being done at the local payphone-terminal site.

It is an objective of the present invention also to provide for the disconnection of the pay telephone proper from the central office, or, alternatively, to its connection to a cellular interface unit, during the call-progress monitoring connection of the call to the called party, so as to isolate the pay-telephone terminal so as to prevent interference with the tones generated during the call-progressing.

Toward these and other ends, the interfacing unit of the present invention comprises a microcomputer, and an associated EPROM in which is stored the exchanges of the telephone numbers that are accessible by that local payphone-terminal, which EPROM also stores a table indicative of the tariffing rates associated with the respective exchanges called. The invention also includes the tone-detectors for detecting the dialed DTMF digits of the coin-operated pay-telephone, for the conversion thereof for storage in the microcomputer for the determination of a valid telephone number dialed in order to determine the associated tariffing rates. The tone detectors also include conventional tone-detectors for detecting the tones received from the central office, or, alternatively, tones received via the over-the-air radio transmission, such as the cellular network, via a conventional cellular interfacing unit, manufactured by Telular, Inc., which tone-detectors determine the various signals common to the generation and completion of a telephone call, such as tones representative of busy signals, as well as ringback signals. The invention also includes "isolating" switching circuitry for isolating the coin-operated pay terminal from its couplement to the telephone system until the telephone call has been connected. This isolation, achieved through switching circuitry, is performed in order to prevent any noise or feedback from the pay telephone terminal that would in any way disrupt the call-progressing signals generated by the central office to the payphone-terminal. The switching circuitry, after having separated, or isolated, the payphone-terminal from its connection with the central office, will, however, switch over to a secondary unit that couples the payphone-terminal to the tone detectors in order that the person making the call may be able to hear the tones received from the central office, such as busy signals, audible ring signal, and the like, in order to simulate a conventional telephone.

The present invention may be used for land-line connection through a standard, land-telephone switching network, by which the pay-telephone is directly connected to the central office via land lines, or, may, alternatively, be used with a cellular network, by coupling the interface unit of the present invention to a conventional cellular interface unit that is coupled to a standard cellular transceiver, such cellular interface unit being conventional and manufactured by Telular, Inc., of Wilmette, Illinois, which cellular interface unit is disclosed in U.S. Pat. Nos. 4,658,096 and 4,737,975. There is, therefore, achieved at the local payphone terminal-site all of the functions hitherto generated by the central office. By localizing such central-office functions at the local payphone-terminal site, private payphones may be easily and readily provided. After a call has been made according to the invention, the microcomputer, after having determined the tariffing schedule for that particular call made, will generate 12K to 16k or 50 hertz tone-bursts to the international-type payphone terminal required for debiting the required amount from the coins or credit initially inserted into the payphone, which debiting occurs by decrements in the base currency unit of the respective country. The more expensive the call being made, the more frequent the 12K to 16k or 50 hertz tone-bursts are generated.

The invention will be more readily understood with reference to the accompanying drawings, wherein:

FIG. 1 is a block diagram of the overall system of the present invention coupled between a cellular transceiver via a conventional cellular interface unit and to a conventional international-type, coin-operated pay-telephone;

FIG. 2 is a flow diagram showing the sequence of events for completing a call over the system of the invention;

FIG. 3 is a schematic diagram of the microcomputer used in the present invention and its coupling to an oscillator-filter for generating the tone-bursts required for the tariffing of the call made;

FIG. 4 is a schematic diagram showing the switching circuitry for isolating the pay-telephone terminal from its coupling to the central office, or to the cellular transceiver, after a call has been determined as being valid and sent on for further, processing and completion;

FIG. 5 is a hardware diagram showing the coupling of the microcomputer of the invention, its inputs and outputs, and its connections to the tone-detectors;

FIG. 6 is a schematic diagram showing in greater detail the switching circuitry shown in FIG. 4;

FIG. 7 is a flow chart showing the operation of the system of the invention from initialization to the completion of a call;

FIG. 8 is a flow chart showing the flow of events during call-progressing and tone-detection of the invention; and

FIG. 9 is a flow chart showing the procedural steps for rate-determination at the outset upon having completed the dialing of a telephone number at the local pay telephone terminal site.

Referring now to the drawings in great detail, FIG. 1 shows the elements of the invention. A conventional international-type, coin-operated pay-telephone 10 is coupled to the cellular network, in this embodiment, via the interfacing system 12 of the present invention. The interfacing system of the invention, in turn, is coupled to a conventional cellular interface-unit 14, such as that manufactured by Telular, Inc. of Wilmette, Illinois, which, in turn, is coupled to a conventional, cellular transceiver 16 for over-the-air radio transmission to a base site, for subsequent connection to either a land-based switched telephone network, or to the cellular base station and another cellular phone. In the alternative embodiment, the interface unit 12 may be coupled directly via the land line to the conventional, land-based switched telephone network. Power is derived via conventional power supply 18 and batteries 20.

Referring to FIG. 2 for now, there is shown, in summary manner, the sequence of events by which a call may be made and completed via the present invention. After initial reset (block 22) and initialization of the system (block 24), the system of the invention awaits "off-hook" detection (block 26), which means that the phone has been taken off-hook, and loop-current flowing, by which a call is ready to be made. During the dialing of the digits of the telephone number on the payphone, the system of the invention reads such DTMF signals (block 28), converts them to binary code for storage in the microcomputer of the invention, and also determines the last digit of the telephone number dialed (block 30). This last-digit determination may be achieved via digit-determination, such as that set forth in U.S. Pat. No. 4,658,096, or may be accomplished by a simple time-out process, i.e., after a preset time has elapsed, it will be assumed that the last digit has been dialed. Typically, such a time period may be between 4 and 10 seconds. After determining the last digit of the dialed telephone number, the system of the invention will determine if the telephone number dialed is, in fact, a valid number, which is accomplished by "lookinq up" the first two or three digits of the dialed number, or what may be termed the "exchange" thereof, in its "look-up" table, which is stored in EPROM or nonvolatile RAM, and, if such exchange is valid, it is then checked for a respective tariffing rate associated with it. If such a rate is found (block 32), then the system of the invention will automatically calculate the rate of tone-pulse generation for tariffing purposes (block 34). The system will then send the dialed telephone number to the central office for the land-based, switched telephone network, or to the radio base station via over-the-air transmission in a cellular network. After such time, the system of the invention will perform answer-supervision (block 36), during which there will be determined whether the called party has picked up the phone at that end, or whether there is a slow busy signal generated, or the like. Assuming that the call has been answered, with the concomitant breaking of the ringback tone-signals, which indicates that the called phone has been answered, then the call is monitored and tariffing tone-pulses are generated at periodic intervals depending upon the cost of the call, all of which is initially determined during the validation process (block 38). The system will continually check to see if the phone has again been placed "on-hook" again (block 40), and, if it has, then the system returns to the "wait" state, disconnecting the call, with tariffing also being terminated.

Referring to FIG. 4, there is shown a schematic diagram for coupling the pay-telephone terminal to the switched telephone network, or to the cellular network, and for isolating it during the answer-supervision process. The conventional, international-type coin-operated pay-telephone 10 has associated with it a conventional "off-hook" current detector 24 for determining when the phone is taken off-hook. The pay-telephone 10 is coupled to the telephone network 26, which may be a land-line central office, or may be the cellular system, via first relay-switch K1, in a first state thereof. The switch K1, during the initial operation of the payphone, which is during the making of a telephone call, isolates the payphone from the telephone network 26. While the call is being dialed on the payphone 10, and the DTMF signals generated, the DTMF signals are sent to conventional tone-detectors, which form part of an overall series of conventional tone-detectors 30, for DTMF conversion thereby, into binary-coded information for subsequent transmission to microcomputer 32. The tone-detectors 30 are conventional and may be that manufactured by Mitel Corporation, Model No. MT8880. The DTMF signals are transferred to the tone-detectors via a second relay-switch K2 and transformer T2. Capacitor C1 eliminates DC loading. After the digits of the telephone number have been dialed on the pay-telephone unit 10, and the DTMF signals separately converted by the tone-detectors 30 and subsequently sent for storage to the microcontroller 32, the dialed telephone number is checked against a "look-up" table for a valid telephone number, and is also checked for a valid tarrifing rate structure associated therewith. If the microcontroller 32 does determine that it is a valid telephone number that has been dialed, the call is allowed to continue, which, as described above, may be either the central office of the land-based, switched telephone network, or the base station of a cellular network, otherwise, the call is discontinued. With switch K1, which is controlled by the microcontroller 32, in its first state thereof, the pay-telephone unit 10 is disconnected, or isolated, from the telephone network 26. This isolation is necessary to ensure that any input from the pay telephone unit 10 does not affect the answer-supervision process that is to be carried on by the system of the invention, to be described below in greater detail. With the switch K1 in its first state thereof, by which the pay telephone unit 10 has been isolated from the telephone network 26, this switch connects the pay-telephone unit to a transformer T1 operatively coupled to the tone-detectors 30, by which the pay-telephone unit 10 may monitor the progress of the telephone call, by either hearing a busy signal, the ring-back signal, or the like, so that the caller may hear. Amplifier A drives the transformer T1. After the telephone number has been sent to the telephone network 26, the second relay K2 is energized, placing the switch thereof in a second state thereof, by which the coupling of the transformer T2, and, therefore, the tone-detectors 30 is opened from the connection with the pay-telephone unit 10, and switched over to connection to the telephone network 26, whether it be the land-based switched telephone network, or the cellular network. In this state, which is shown in FIG. 4, the process of callanswering supervision is carried out by the invention. The tone-detectors 30 detect the unique tones received via the telephone network 26, which tones are either indicative of a busy signal, the ringing signal, or the like. That is, the frequency tones, as well as the spaces or periods between frequency tones, define a tone-cadence signal from the telephone network by which a number of states may be indicated: The first one indicating a fast busy signal, the second one indicating a slow busy signal, and a third one indicating a ringback signal which indicates the called phone is ringing. Under the first two signals generated, the system of the invention, in the conventional manner, via the microcontroller 32 and the software associated therewith, will terminate the call, as will be described below in greater detail. For the third signal, the ringback signal, the software of the invention will determine if and when the called phone has been taken "off-hook" and the call answered. This is achieved by detecting a break in the normal pattern of the ringback-generation signal, which is conventional. Alternatively, after, for example, ten ringback signals, the system of the invention will automatically terminate the call as indicating that the called party is not at home. The tone-signals with associated cadence, or intervals between tone pulses, are generated by the telephone network 26 and are conventional. It is understood, that in the case of a cellular network, as described above, the telephone network (block 26) will include not only the base cellular station, but also the transceiver unit 16 and cellular interface unit 14, described above in regards to FIG. 1.

If the dialed telephone number has been determined to be correct and the called phone actually goes off-hook, then detection thereof will be achieved via the software associated with the microcontroller 32, by the detection of a break in the ringback tone-signals. Upon such detection via the microcontroller 32, there will begin the tariffing of the phone call; that is, the microcontroller will, according to the invention, generate the tone-bursts via oscillating circuitry 34, which oscillating circuitry produces a tone-pulse typically in the 12K to 16k range via transformer T3. The rate at which these tone bursts are generated depends upon the cost of the call, as determined initially by the microcontroller and the look-up table associated with the exchange of a dialed telephone number. The more expensive the long distance call made, the more frequent will be generated the tone-bursts by the oscillating circuitry 34. When the microcomputer has determined that the call has been answered, it will energize relay K1 in order to place the switch associated therewith into the second state thereof, which second state couples the pay-telephone terminal to the telephone network.

In accordance with international standards, at the outset of placing a call, the calling party will place a fixed amount of money into the coin slot associated with the pay telephone, or, alternatively, receive initial credit via a credit card, from which the system of the invention will debit at specified intervals, which debiting takes place at each tone-burst generated by the oscillating circuitry 34. Typically, according to the invention, each tone-burst will subtract one currency unit from the amount placed initially into the pay telephone. Of course, such units will vary from country to country.

FIG. 5 shows a schematic of the microcontroller 32 and its coupling to the tone-detectors 30, which tone-detectors 30 are indicated in dashed-line block 55. As mentioned above, the tone detectors 30 are conventional. The microcontroller 32 may be that manufactured by Intel Inc., Microprocessor BOC451-LCC. Associated with the microprocessor 32 is EPROM 40. The software for controlling the microcontroller 32 is described below in greater detail.

FIG. 6 shows the schematic switching diagram, discussed above in reference to FIG. 4, in greater detail. One additional element shown in FIG. 6 is the ring-detect indicated in block 42, which generates a ring-sequence generation for the pay-telephone by which a ringing thereof may be achieved, which is conventional. The elements C1, T2, K1 and K2 discussed above are shown in respective blocks in FIG. 6.

Referring now to FIG. 7, there is shown the call-management routine of the invention. At the outset, there is initialization (block 50), and the detection of loop-current (block 52), which detects if the phone has been taken off-hook. The dialed digits are collected (block 54), and the last digit determined by a timer (block 56). Thereafter, the dialed telephone number is checked against the "look-up" table in EPROM, and the call-rate procedure (block 58) is initiated to determine whether a valid rate (block 60) is present. If a valid rate is present, then the call-progress monitoring process is carried out (block 62) and the system waits to see if the call is answered (block 64), and, if it is, then the initial burst-interval is calculated (block 66) which determines the initial period, such as one minute, after which overtime will commence; at such point, the timers are loaded. Typically, there are two timers (block 68), and a tone-burst is produced (block 70) for tariffing, which in the case of the initial period, will be the first tone-burst representing the base or non-overtime rate for that call. If the initial time period has expired (block 72), which typically may be up to 1 minute from the beginning of the call, then the overtime timer takes over, and the overtime burst-intervals are calculated (block 74). If the overtime burst interval has expired, then another tone-burst will be generated (block 76), if loop-current detection is present (block 78) which means the phone is still off-hook, with the procedure repeated from block 68 through 78, with that tone-burst being generated for collecting the appropriate amount. The process will go on until off-hook current detector (block 78) detects that no further current is present, meaning that the phone has been placed "on-hook" again, thereby indicated the phone call has been terminated, and, thereby, disconnecting the telephone from the telephone network (block 80). The phone would also be disconnected (block 80) if the called party does not answer the phone, which is typically up to 10 rings (block 64).

FIG. 8 is a flow chart showing call-progressing according to the invention. At the start (block 80), the tone-signal is received and detected via the tone detectors 30. The invention will measure the tone period, or length of the tone received (block 82), after all noise been eliminated (block 84). Thereafter, the interval, or cadence, between tones (block 86), or the "no-tone" period, is measured, and the software of the invention will determine what type of tone-cadence sequence has been received. In an example shown in FIG. 8, there are three possible types of signals that may be received: Bi indicating fast busy signal, B2 indicating a slow busy signal, and "ring-off" indicating the called the phone is ringing. For example, if it has been determined that the cadence of the received signal is indicative of B1, then the sequence of events will follow along the column for BI. If it is not B1, then the system will determine whether it is B2 or "ring-off" signaling. When any one of the three signals has been determined to have been received, then the flow of events is basically the same for each. For example, for Bl, if such is the signal received (blocks 88, 90), then the tone period thereof is measured (block 92), and it is thereafter determined whether the period of time that these tone-periods are "on" is within the required specifications for the B1 signal (block 94). If not, then the system will indicate a false signal (block 96) and return to initial state. If it is true, then the "no tone" period or cadence is measured (block 96) and the system will check to see if ten cycles have been achieved, after which, the system will automatically indicate a "false" signal and return to the initial state (block 98). If it had been less than ten cycles, the system repeats itself in a loop (90 through 98). If during any one loop, the "off" period between tones or the "on" period or the time of each tone, is not found to be within the parameters of the B1 signal, then a "false" signal is generated and the system returns to its original state. The same holds true for the other signals B2 or "ring off", indicated by blocks 100 through 1IO, and 112 through 132, respectively. Of course, the only signal by which further call-progressing is to be carried out is the "ring off" signal starting at block 112. Under this flow of events, after ten rings have been accomplished, then a "false" signal is generated (block 122, 96) to the microprocessor. However, if during call-progress monitoring, after it has been determined that the signal is a "ring-back" signal, starting with block l12, at any point during the ten loops of determination whether the call has been answered or not, if such signal has been terminated as indicated by a "no" in blocks 114 and 118, as well as in block 1-2 which would indicate initial answering of the phone before any ring generation has occurred, then a true response (block 126) is generated and the call is connected and proceeds in a normal fashion until no loop-current is detected (block 78 of FIG. 7), which would indicate that the phone has been placed "on hook" again. It is understood that while three separate signal types have been indicated (FIG. 8), that more or less may be used. The fast-busy signaling represented by B1 would indicate the lack of network connection, while the slow busy signal (B2) would be indicative of the called phone being in use. In fact, there may be up to five separate signals generated by which the invention may detect and control the payphone.

Referring to FIG. 9, there is shown an exemplary flow chart for rate determination, the one being shown being that for Thailand. At the start, (block 150) and when the dialed digits have been dialed in DTMF format into the payphone, there is initially checked to see whether the length of the phone number is either 3, 7 or 9 on blocks 152, 154 and 156. When the dialed number has been determined to have been dialed, either by the time-out method or last-digit analysis, as described above, that number is checked against the "lookup" table (block 154) in EPROM associated with the microcomputer 30, or, alternatively, in order to save time, each number after it has been dialed, is checked against the look-up table and if there is a match (block 156), then the call is allowed to be consummated at a free, no charge rate (block 158), while if there is no match, then an error is indicated (block 160). If the length is determined to be 7 (block 153), then it is indicative of a local call (block 156) and the phone number dialed is matched against the "look-up" table in EPROM (block 157); if it does not match, an error signal is generated (block 159), while if there is a match block 164), the call is consummated as a local call, which may or may not be chargeable. If the length is determined to be greater than 7, depending upon the country in which the system is used, then the number is checked to see if it is a long distance call, which is done by testing the first two digits of the phone number (block -66). If, for example, the first two digits are each less than or equal to 2 (block 168), then such would be indicative of a local call (block 170), upon which a match look-up would be generated (block 172), and if a match is found in the "look-up" table of the EPROM, then the call progresses (block 164), while if there is no match, then the call terminates (block 160). If the first two digits are greater than 2, then such would be indicative of a long-distance call (block 174) and it would further investigate to see if there was a match in the "look-up" table (block 176). If there is match, then the long-distance flag would be set for that call. It is, of course, emphasized that such is shown only by way of example, and the length of the dialed telephone number that is checked will of course vary from country to country, as well as the determination as to which constitutes a local call, a free call or a long distance call.

The following is a listing of the source code for controlling microprocessor 30, for carrying out the above-described operations. The programming language is PL/M. ##SPC1##

While a specific embodiment of the invention has been shown and described, it is to be understood that numerous changes and modifications may be made therein without departing from the scope, spirit and intent of the invention as set forth in the appended claims.