Telephone Communications Control System Having a Plurality of Remote Switching Units

This invention relates to a communications line control system and more specifically relates to a control system for controlling and recording the use of long-distance communication circuits.

In the past the control and recordation of long-distance telephone calls was performed by a PABX or CENTREX operator who selected the outgoing long-distance lines over which a call was to be placed either by selecting bulk rate lines, such as WATS lines, foreign exchange lines or tie lines, or in the alternative, if these lines were not available, selected a local trunk line. This method of controlling and recording telephone calls has proved to be costly and inefficient and accordingly, attempts have been made to control the placing of telephone calls and the recordation thereof on a more efficiently controlled basis. Thus, for example, with respect to the recordation of telephone calls, a number of systems have been developed for recording the use of long-distance telephone communication circuits. Baichtal, et al. disclosed in U.S. Pat. No. 3,825,689 an automatic message metering and storage system. Each of a plurality of subscriber lines is scanned in sequence with each subscriber line having an associated unique location in a memory unit. This system records information resulting from long-distance, toll and other type of telephone services. However, it does not provide any means for selectively connecting long-distance lines so as to minimize the cost of the telephone call. Along somewhat the same technological lines as the Baichtal et al development, LeStrat et al. developed, as disclosed in U.S. Pat. No. 3,651,269, a telephone accounting system wherein each of a plurality of toll junctures associated with each of a plurality of trunk lines is scanned by command of a computer. Predetermined storage areas in the computer are allotted to each trunk line wherein data regarding the time of transfer of the long-distance call is stored in the memory location associated with the line being scanned, with this information being utilized later to generate a bill to the calling party. The system is located in a toll exchange so that centralized charging of each of the subscribers using the long-distance lines can be achieved.

Caithmaer, et al. provided a central telephone message accounting system as disclosed in U.S. Pat. No. 3,829,617 which has a central processing unit for receiving data with respect to the identity of a calling party, the nature of the call and the duration of the call. Thus, a juncture is positioned on each of a plurality of trunk lines with the junctures being scanned for telephone calls being placed. When a telephone call is detected, the call is connected via a branch line to a data receiver. The data is stored and then re-sent to a remote toll office where the call is completed. Other systems have been developed for recording the use of long-distance trunk lines on an automatic basis to thereby provide information to a central processing unit for preparing telephone bills as disclosed in Joel U.S. Pat. No. 3,760,110 and Woolf, et al. U.S. Pat. No. 3,806,652. However, none of these systems discloses a switching system wherein telephone calls are switched at remote satellite locations such that the cost of any particular call is minimized.

Telephone metering systems have been combined with private automatic branch exchanges to provide a combined switching and metering function. Thus, Gayler, et al. disclosed in U.S. Pat. No. 3,870,823 a metering system for use with a PABX in connection with direct distance dialed, WATS and extended area service telephone communications lines. The system includes both a PABX and a central processing unit with switching matrices and detecting circuits for addressing each of a plurality of long-distance trunk lines with sample addresses synchronous with the addressing of receivers within the metering system so that the receiver can sample and analyze the information on the trunk line. As in the case of the aforementioned traffic metering developments, this system does not provide a method or apparatus for switching long-distance communications lines in order to minimize the cost of long-distance telephone calls.

Of even greater importance to telephone subscribers is the fact that the hardware for controlling the connection of long-distance telephone lines in accordance with any criteria, such as line availability, is expensive. To control the connection of long-distance lines in accordance with the criterion that the least expensive available line will be connected first, wherein the least expensive line may vary with many parameters such as, the line type, restricted use and position in a rotary, results in even additional expenses. Accordingly, in the past it has not been commercially feasible to provide at each PABX or CENTREX unit, a switching system having computerized control so as to connect long-distance lines in order to minimize the cost of long-distance telephone calls except through the provision of dedicated costly computerized switching equipment. Steps have been taken in the art, as exemplified by Gebhardt, et al. U.S. Pat. No. 3,225,144, Vigliante, et al. U.S. Pat. No. 3,268,669 and Joel U.S. Pat. No. 3,731,000 for controlling the interconnection of telephone lines between a local office and a toll office by means of a remotely positioned central processing unit. The advantage of such a system is that only one computer is required to control a plurality of remote switching circuits. Thus, the cost of the computer per switching circuit is substantially reduced. None of the systems disclosed in the aforementioned patents, however, teaches or suggests an arrangement wherein an efficient and inexpensive means is provided for controlling and monitoring the connection of long-distance telephone circuits for the purpose of minimizing the cost of the long-distance telephone calls connected through the switching systems between the customer's location(s) and one or more local or central toll offices.

It accordingly is an object of this invention to provide an improved system for controlling and monitoring the connection of long-distance telecommunications lines for the purpose of minimizing the cost of long-distance telephone communications.

It is another object of this invention to provide an improved method and apparatus for remotely controlling the connection of long distance telecommunications lines on the basis of a least cost routing.

Accordingly, this invention relates to a method and apparatus for switching long-distance telecommunications circuits wherein a central processing system is coupled to each of a plurality of remote satellite switching units. Each remote satellite switching unit includes a circuit routing matrix for connecting a local station to a selected long-distance line which may, for example, be a local trunk line, bulk rate lines such as WATS, foreign exchange or tie lines or lines between remote units. The remote satellite switching unit also includes a microcomputer system for detecting the status of outgoing lines from a PABX or CENTREX and the destination of a requested call. This information is transmitted to the central processing system which in turn selects the least expensive line at any given time for transmitting the long-distance call. This information is transmitted back to the microcomputer system which provides command signals to the circuit routing matrix to connect the requested call to the selected outgoing long distance line. The central processing system compiles a record of the party placing the call, the long-distance line used, the time duration of the call, and line utilization of the system as well as observes the status of the remote unit, etc., to compute a periodic account statement for the subscriber. The system is capable of providing camp-on call-back services as well as providing a decision making function of selecting which of a plurality of call requests are connected first and determines the time interval during which the calling party must await the availability of a less expensive long-distance line before the call is placed over a more expensive line.

Other objects, features and advantages of the present invention will become more fully apparent with reference to the following detailed description of the preferred embodiment, the appended claims and the accompanying drawings in which:

FIG. 1 is a simplified diagram of the system configuration of the present invention;

FIG. 2 is a schematic block diagram of the central processing system of the present invention;

FIG. 3 is a block diagram of the remote satellite unit of the present invention;

FIG. 4 through FIG. 10 are more detailed schematic illustrations of the components employed in the remote satellite unit.

At the outset, a general overview of the operation and advantages of the system of the present invention will be presented, followed by a detailed description of the preferred embodiment thereof.

The present invention achieves cost reduction in long-distance telecommunications calls through the highly efficient use of bulk-rate communications facilities including WATS, foreign exchange (FX) and tie lines. Because a business organization pays a fixed monthly amount for each such facility, the higher the traffic load or usage per facility, the lower the cost of long-distance telephone calls on a per minute basis. Thus, in operation the present system determines from the area code of the number being called whether the subscriber or calling party has an FX or tie line terminated in that area. If not, or if these lines are presently in use, a determination is made as to the lowest cost WATS line available. If the appropriate bulk facility is not available, the user is given an indication of this and enters his extension into the system in order to be called back. The user is placed in the appropriate queue for the particular bulk facility and the system continues to process calls, keeping the user in the queue for a preselected interval, e.g. ten minutes if necessary, and calls back the user when the line becomes available. Thus, the present invention achieves effective utilization of bulk communications lines which may approach a 95% time utilization during peak hours. The availability of local lines insures that no call will wait longer than the predetermined selected interval.

To achieve this, a central processing system communicates with a substantial plurality of remote satellite switching units via telephone lines or other communication links such as, for example, satellite communications links. In the preferred embodiment, data is transferred between the central processing system and the satellite switching units in block mode using a suitable variable length message format such as ASCII. The central processing unit controls all switching functions and records the necessary data required for billing, generating traffic statistics, etc. from the remote satellite switching unit.

Three classes of trunk lines serve as an input to the satellite switching units, namely, rotary dial or tone dial branch trunks which pass from a subscriber's CENTREX or PBX system, standard local lines, and incoming WATS service lines. The output trunks from the satellite switching units also fall into three classes, that is, bulk rate lines including outgoing WATS line, tie lines and/or foreign exchange (FX) lines, local trunk lines and lines to recording devices. The present invention is capable of detecting either tone or rotary dial from the input telephone circuits thereto and addresses the output telecommunication circuit, by means of tone or rotary dial signalling.

To place a long-distance call, a subscriber dials a special access number via the PABX or CENTREX unit. The satellite switching unit responds with a first dial tone. The subscriber then enters a one to seven digit account number. The satellite acknowledges the number with a second dial tone if the account number is valid or with an error signal if the number is invalid. In the case of an invalid number, the first dial tone is reconnected after providing an error tone, thus permitting a second try. After a second invalid attempt, the subscriber is disconnected and the central processing system flags that attempt. If valid, a second dial tone is heard by the subscriber who then dials the desired long-distance number. In response thereto, if no usable trunks are available, the system returns a busy signal, e.g., three tone bursts, and then returns a dial tone to the subscriber. The subscriber may then hange up or may enter his call-back number which is up to seven digits. This call-back number is generally the telephone extension of the subscriber but may be an access code plus the extension of the subscriber. Assuming that a number of subscribers have encountered busy bulk rate lines and have requested the system to call them back when a line becomes available, the system preferably has three queues. Subscribers are called back in the descending order of queues depending upon their respective positions within the queues. The number of subscribers that can use the first or second queues is limited so that those in the highest priority queues can have their calls connected to long distance lines first. When an appropriate trunk is available for the subscriber who is waiting for a call-back, the subscriber is called back. When the subscriber goes off-hook, the tone signalling is transmitted into the network and at the same time is fed back to the subscriber's telephone unit so that the subscriber knows the call has been placed.

When the subscriber is called back, the unit will allow three rings to occur before aborting the call-back. If the subscriber's extension is busy, the system will recognize this and place the call-back in the appropriate queue. If the subscriber desired to cancel the call, he may go back on-hook at any time after hearing the transmission of the tone signalling.

If desired, a special account number can be utilized on long-distance calls in order that a particular account can be billed for the call. Thus, the subscriber enters his subaccount number and upon receipt of the second dial tone, the #key on the telephone tone keyboard and any number up to ten digits followed by a second # key is keyed into the system. The system records the number and returns the dial tone after which the subscriber then dials the desired long-distance telephone number.

An abbreviated dial number can be keyed into the system in order to simplify the calling procedure on the part of a subscriber. Thus, for example, if there is a group of numbers which are used most frequently, these numbers can be coded into a two-digit number and utilized in lieu of dialing or keying an entire number. To use an abbreviated dial number, upon receipt of the second dial tone, the subscriber enters an *, a two-digit number corresponding to the number desired to be dialed followed by the entry of a #. From rotary phones two digits are entered but the second digit cannot be a zero or one. The system then automatically retrieves the full number from storage and places the call to the desired party. To enter an abbreviated dial number into the system, the subscriber first enters his account number and upon hearing the second dial tone, enters an *, any two digits followed by an * and then a ten-digit telephone number. The system signals its acceptance of the telephone number with a single tone burst or signals its rejection with a two tone burst. In connection with the aforementioned, it should be understood that the specific format for placing an abbreviated dial number call, etc., can be varied in keeping with the invention by simply changing the logic, i.e., the algorithm, in the central processing system and in the remote satellite unit.

Refer now to FIG. 1, where there is disclosed, in simplified block diagram form the preferred embodiment of the communications switching system of the present invention. The switching system of the present invention includes central processing system 11 of conventional design known in the art and a plurality of remote satellite switching units 13. As contemplated in the preferred embodiment, the central processing system 11 can provide control signals for controlling multiple satellite switching units separately and in tandem. Each satellite switching unit 13 has a plurality of input lines connected thereto from voice connecting arrangements 15. The voice connecting arrangement 15 provides isolation between the output lines of a PABX or CENTREX unit 17 and the satellite switching unit 13. Also connected to the input of the satellite switch 13 are local telephone lines 21 which are connected to the switch 13 via the voice connecting arrangement 15. If desired, an INWATS line can be connected to the satellite switching unit 13.

At the output of the switching unit, a plurality of bulk rate and DDD telephone circuits 26 are coupled to an output voice connecting arrangement 27. As illustrated, the bulk rate lines typically include OUTWATS lines, foreign exchange lines, and tie lines. In order to assure the availability of long-distance lines, the output of the switch 13 is also connected to conventional business DDD lines which can be utilized to convey long-distance communications, as desired.

The satellite switch 13 is operated in accordance with command signals from the central processing unit 11. These signals are coupled to the satellite switching unit 13 via a private data line 34 of conventional arrangement known in the art. Should for any reason the private date line become unusable, an alternative data line interconnect is obtained by automatic dial up via the DDD network in a conventional manner known in the art.

It should be understood that information signals containing, in coded form, information with respect to the party called, the calling party, the status of lines, etc., are conveyed via the data line switch 34 to the Central Processing System 11 to provide the Central Processing System with information by which a decision can be made as to which output lines should be connected, disconnected, etc. It should also be understood that while a private data line is used in the preferred embodiment of the present invention, other data circuit methods for transmitting command signals to the satellite switches and information from the switches to the Central Processing System 11 can be utilized.

Refer now to FIG. 2, where there is disclosed a more detailed schematic block diagram of the Central Processing System 11. The central processing system employs a minicomputer system which includes a digital computer for performing the processing of the data from the remote satellite units. In the preferred embodiment, the minicomputer system is an assembly of standard components from the Interdata, Inc., Model 7/32 Computer System; however, it should be understood that a number of other systems in the industry meet the application requirements of the invention. Interdata standard components are used in the operation of the Central Processing, and include both hardware and software packages as identified in the appendix A. Further, the application program package used in the interoperation of the remote satellite unit 13 is also appendixed in its entirety as appendix B.

The interoperation with the remote satellite unit is via data communication circuits as aforementioned. The data communication circuits include private line facilities and alternately can employ the switched network on a dial-up basis. The interface with these facilities are commercially available and, for example, are provided by the Bell Telephone System and other independent companies. By convention, the interface between the Minicomputer System and the telephone circuit includes a data modem which, in the preferred embodiment, employs a Bell 103 type unit or equivalent. Further, the interface with the DDD network employs data access arrangements (DAA) which, in the preferred embodiment are commercially available CBS data couplers.

Finally, as illustrated in FIG. 2, the central processing unit is redundant with 100% duplication of the minicomputer system and related peripheral components for the purpose of reliability. Interconnection between either system and the data channel's modem hardware is via the Fall Back Switch arrangement, which in the preferred embodiment, employs a commercially available Spectron Corporation Model FBS 1224.

Refer now to FIG. 3, where there is disclosed a more detailed schematic block diagram of the remote satellite switching unit 13. Trunk lines from one or more inlet exchanges are connected to a line control unit 41 of the switching satellite unit 13 via the voice connecting arrangements 15. Trunk lines to the outlet exchanges are connected from the circuit routing matrix 51 via voice connecting arrangements 27.

The line control units 41 have the function of providing detection and control of analog and DC signals on the trunk lines by means of a stored program in the microcomputer system 49. The line control units 41 interconnect directly with the inlet voice connecting arrangements 15 and with outlet voice connecting arrangements 27 via the circuit routing matrix 51. The voice connecting arrangements typically employed for interposition with Bell facilities are Bell VCA - CDQ2W for tie trunks interconnect and CDH for any of the other aforementioned interconnects.

Each inlet voice connecting arrangement 15 is assigned to a line control unit 41 and the associated inlet port on the circuit routing matrix 51. Each outlet voice connecting arrangement 27 is assigned to an outlet port on the circuit routing matrix. The voice connecting arrangements include six interface leads per circuit which are conventionally identified as CT/CR, CS/CG, and CBS1/CBS2. The CTR and CR leads carry voice transmission, tone address signalling and call progress signalling as is known in the art. The CS/CG lines carry service request, answer/disconnect and DC dial pulsing information. Finally, the CBS1/CBS2 lines carry line status indication, seize/release and DC dial pulsing information. In the preferred embodiment, two of these leads, that is, the CG and CBS2 leads, are used as signal ground return for both of the voice connecting arrangements 15 and 27 and the remote switching unit 13. These leads are bonded to a common ground electrode. Accordingly, a four lead interface per circuit is employed in the present invention and the circuit routing matrix 51 is of the four pole type.

The output of each line control unit 41 is connected to the matrix switch assembly 51 which, as will be more fully explained hereinbelow, includes a matrix switching arrangement together with decoders and drivers therefor. The circuit routing matrix 51 has the function of providing an interconnect for the voice and signalling path between the line control units 41 and the 2-of-8 tone transceiver 55 and the trunk lines to the outlet exchanges. The circuit routing matrix is controlled by means of control signals from the microcomputer system 49.

The 2-of-8 tone transceivers 55 have the function of providing detection of touch-tone signals keyed into the system from a local subscriber telephone unit. These signals are converted to binary digital signals which are coupled to the central processing unit via the data line. In addition, the push button tone transceivers 55 transmit 2-of-8 tone signals via the circuit routing matrix 51 to outlet exchanges under the control of the microcomputer system 49.

Private and Switch Network Data Arrangement 61 provides transmission of signals on the data line linking the central processing system 11 with the microcomputer system 49. The arrangement for passing low speed data signals is of conventional design for the purpose of converting the digital signals from the microcomputer 49 to appropriate analog signals for transmission over the data link and for receiving analog signals over the data link and converting these signals to digital signals for processing by the microcomputer system 49. In the preferred embodiment, a dedicated line 56 is provided so that access between the central processing system 11 and the microcomputer 49 is on a continuous basis. Should the private line for some reason be out of order, a backup line, which preferably is a direct dial line, is also connected to the data transceiver. The use of a DDD network for data communications is a conventional technique employing Bell Data Access Arrangement CBS.

The operation of the line control unit 41, the switch matrix assembly 51 and the push button tone transceivers 55 is controlled by the microcomputer system 49 which includes a central processing unit and memory. Conventional control logic known in the art is employed in interfacing the microcomputer system 49 with the line control unit 41, the circuit routing matrix 51, the push button tone transceivers 55 and the data transceivers 61. Finally, a progress tone signal generator 58 is provided for generating busy signals, error signals, etc., to advise the local subscriber of the status of the telephone call being placed. The progress tone signal generator accordingly is a conventional audio signal generator which is connected to the line control unit through a matrix to be explained more fully hereinbelow.

FIGS. 4-10 and the following description thereof is a more detailed description and schematic presentation of the remote satellite unit. The unit is a hardware assembly of modules manufactured specifically for performing the aforementioned control of communications circuits. The hardware assembly is referred to in the preferred embodiment as a SST-1 Satellite Switch Terminal. As depicted in FIG. 3, it is composed of a Microcomputer System 49, a Line Control Group 41, a Circuit Routing Matrix 51, a Tone Transceiver Group 55, a Tone Generator Group 58, and a Private and Switch Network Data Line Arrangement 61. A detailed disclosure of each of these equipments is given hereinbelow. Although one embodiment will be described, it is to be understood that various changes and modifications may be made by those skilled in the art without departing from the spirit of the invention.

Refer now to FIG. 4, which is a detailed schematic illustration of the microcomputer system 49. The microcomputer system 49 is used in the preferred embodiment as UP-607 Processor and SI-609 Scanner/Interrupt and consists of commercially available components and elements that interface with one another in an industry conventional configuration as shown in FIG. 4. The microcomputer system controls and communicates with external components and equipment 41, 51, 55 and 61, in software selectable modes by industry conventional methods through a system bus 90.

The basic central processing unit is a group of Large Scale Integration (LSI) elements, which define the characteristics of the bus 90 and are a part of the Intel Corp. MCS-80 Microcomputer System. These elements are a C8080A CPU 491, a D8224 Clock Generator and Driver 492, a C8228 System Controller 493 and a P8214 Priority Interrupt Control Unit 494. In addition, the 8T95 and 8216 Interface Elements 492 and 494, respectively, provide requisite bus buffer/driver capability.

An industry standard configuration of memory elements is employed in the Microcomputer System and, as illustrated in FIG. 4, includes commercially available C2708 UV Erasable Programmable Read-Only Memorys (PROM) 495 and P2102 Read Alternate Memorys (RAM) 496. The stored program contained in the PROM which is used in the remote satellite unit is in appendix B and is presented in its entirety in the assembly language of the MCS-80 Microcomputer System. Software select logic used in addressing memory and other hardware elements throughout the remote satellite unit employ conventional Small Scale Integration (SSI) and Medium Scale Integration (MSI) logic elements. The specific decode function is accomplished using 74LS138 MSI logic elements 496.

The Microcomputer System provides a conventional serial data interface for linking to the central computer system using a commercially available LSI element Universal Asynchronous Receiver/Transmitter (UAR/T) 497, such as a Western Digital Corporation TR1602B or equivalent.

Refer now to FIG. 5, which is a more detailed schematic illustration of the line control group 41. The line control group 41 is an assembly of line control units, as previously depicted in FIG. 3, each unit providing the requisite control between an inlet telephone circuit and an outlet telephone circuit via the circuit routing matrix 51. As aforementioned, the control is performed by a microcomputer system 49, via a system bus 90, in software selectable modes.

The line control unit is referred to in the preferred embodiment of the present invention as an LT-610 Line Terminator. The unit consists of an assembly of elements for the detection and control of analog and DC signals on the trunk line. As aforementioned, the analog signals appear across telephone circuit interface leads CT/CR; and the DC signals appear between CBS1/CS and a signal common electrode.

As presented in FIG. 5, the interconnect between the inlet and outlet telephone circuit is on the line control unit via a line relay group 411, and then via the circuit routing matrix 51, as previously mentioned. The line relay group 411 employs complementary - MOS (CMOS) analog switches and dry reed relays for signal control. The CMOS elements used in the preferred embodiment are commercially available RCA CD4016 units. They are employed in the multiplexing of analog signals from the call progress tone sources via audible tone amplifiers 412 and from other analog inputs from the circuit routing matrix via split bypass amplifier 413. The dry reed relays employed in the preferred embodiment are commercially available Struthers-Dunn MRRN Series units. They are employed in the splitting of the analog signal line between the analog multiplex bus and the inlet signal pair CT/CR; in the splitting of the analog signal line between the circuit routing matrix inlet and the inlet signal pair CT/CR; and in the individual breaking of the DC signal leads interconnected between the circuit routing matrix inlet and the inlet DC signalling pair CBS1/CS.

Further presented in FIG. 5 are the line control unit elements for the detection of analog and DC signals on the trunk line. These signals are detected by sampling, via the micro-computer system application program, the converted output of the audible tone receiver 420 and the DC signalling buffer 419. The audible tone receiver is an AM Detector, as is well known in the art, and is designed for the detection of telephone network type audible tone signals with protection against interference from voice currents or other tone signalling systems; and the DC signalling buffer 419 provides high to low level voltage conversion between the trunk line interface CBS1/CS and the IC logic element interface.

The logic elements requisite to the software selectable line control unit operation by the microcomputer system via the system bus 90, includes standard MSI, SSI and discrete units interconnected in a conventional manner. As shown in FIG. 5, in the preferred embodiment, the decode function 414 employs 74LS138 MSI logic elements; the output data bus interface 415 uses F9334PC MSI logic elements and the input data base interface 418 uses 74LS251 MSI logic elements. In addition, to support the duration of inputted audible tones, a cadence generator 416 makes use of a 74123 MSI logic element. Further, in the preferred embodiment, a conventional analog application of operational amplifiers employing Motorola MC1458V is used for the previously described amplifiers and receivers, 412, 413 and 420.

Refer now to FIG. 6, which is a detailed schematic illustration of the circuit routing matrix 51. The circuit routing matrix 51 provides switching between an inlet telephone circuit via a unit in the line control group 41 and an outlet telephone circuit; between an inlet telephone circuit via a unit in the line control group 41 and a unit in the tone transceiver group 55; or between an inlet telephone circuit via a unit in the line control group 41 and both the outlet telephone circuit and a unit in the tone transceiver group 55. As aforementioned, the switching is performed by the microcomputer system 49, via the system bus 90, in software selectable modes.

The circuit routing matrix 51 is referred to in the preferred embodiment of the present invention as an assembly of RY-612 Matrix and a BD-611 Buffer Decoder. The matrix unit consists of a sub-array, related axis drivers and ordinate decoders. The buffer decoder unit consists of array decoders, a switching timing circuit and the requisite logic interface with the system bus 90 for the control by the microcomputer system 49.

As presented in FIG. 6, the previously described interconnect is by way of a 4-pole non-blocking array 511. The defined array is obtained by cascading standard units of commercially available matrices. The matrix unit used in the preferred embodiment is a C.P. Clare Mini Memory Matrix 969A48A4B. A 4-pole crosspoint in the matrix is switched by axis drivers 512 which employ power transistor circuitry. FIG. 6A provides a discrete component schematic illustration of the circuitry used in the preferred embodiment to operate with the Clare Matrix, specifically identifying the commercially available drive and power transistor employed.

The logic elements requisite to the software selectable circuit routing matrix operation by the microcomputer system, via the system bus 90, consists of standard MSI and SSI units interconnected in a conventional manner. As shown in FIG. 6, for the preferred embodiment, the output data bus interface 514 uses 75LS174 MSI logic elements and the switching pulse duration timing circuit 515 makes use of a 74123 MSI logic element.

Refer now to FIG. 7, which is a detailed schematic illustration of the tone transceiver group 55. The tone transceived group 55 is an assembly of transceiver units, as previously depicted in FIG. 3. A transceiver unit is used in the activation of the interconnect between an inlet telephone circuit and an outlet telephone circuit via the circuit routing matrix 51. As aforementioned, the control is performed by the microcomputer system 49, via the system bus 90, in software selectable modes.

The transceiver unit is referred to in the preferred embodiment of the present invention as an RS-618 Register/Sender. The unit consists of an assembly of elements for the receiving and transmission of 2-of-8 tone signals on the telephone circuit and the control of a dial tone on the telephone circuit.

As aforementioned, the tone signals appear across telephone circuit interface leads CT/CR and are transmitted to and from the transceiver unit via the line control unit and the circuit routing matrix.

As presented in FIG. 7, the tone signals across the interface signal pair between the transceiver unit and the circuit routing matrix are passed to a 2-of-8 tone receiver 556 via input amplifier 551 and dial tone reject filter 553. Further, tones are passed to the interface signal pair from the 2-of-8 tone encoder 557 via low pass filter 554 and output amplifier 552 or are passed from the dial tone bus via switch 555, and output amplifier 552. The receiver 556 detects the presence of valid high and low band sine waves used in tone dialing in the telephone network. The filter 553 permits the detection of the 2-of-8 tones in the presence of a conventional dial tone as is known in the art. The encoder 557 digitally synthesizes the high and low band sine waves from an inputed 2-of-8 code. The filter 554 removes unwanted frequency components from the signal generated in the digital synthesization. The input amplifier 551, output amplifier 552 and low pass filter 554 are of conventional analog design using operational amplifiers and in the preferred embodiment employs commercially available Motorola MC1458V amplifiers. The dial tone bus switch is a CMOS Analog Switch and in the preferred embodiment employs a commercially available RCA 14016 CD. The dial tone filter 553 is a manufacturing application of hybrid technology as is known in the art and in the preferred embodiment employs a commercially available KTI F853 filter. The 2-of-8 tone receiver 557, also a hybrid package, is a Mitel CM 8822. The 2-of-8 tone encoder is of CMOS construction and, in the preferred embodiment, is an application of a Motorola MC 1441OP device.

The logic elements employed in the interface with the system bus 90 for the transceiver unit operation by the microcomputer system consists of standard MSI and SSI units interconnected in a conventional manner. As shown in FIG. 7, for the preferred embodiment, the software select function 561 employs a 74LS138 MSI logic element; the output register function for the 2-of-8 code 560 employs a P8212 MSI logic element; the output register function for the dial tone switch state 558 employs a 74LS74 MSI logic element, and the input 2-of-8 code data bus interface 559 employs a 74368 MSI logic element.

Refer now to FIG. 8, which is a more detailed schematic illustration of the progress tone generator group 58. The Progress Tone Generator Group is an assembly of tone sources used in generating audible tone signals by the tone transceiver group 55, as previously described, and by the line control group 41, as previously described. The signals are employed to give information to system users about the progress or disposition of the telephone call.

The progress tone generator group 58, in the preferred embodiment of the present invention, is a single unit referred to as a MO-619 Master Oscillator. As identified in FIG. 8, the unit employs, for the basic tone source, circuits which are typical semi-conductor applications of commercially available components.

Each of the tones are generated from circuit variations in the application of a Motorola MC14410 tone encoder. The output of each of the tone encoders is one or a pair of digitally synthesized sine waves, and is coupled to the related tone bus via an active filter and output amplifier. The active filter is employed to attenuate unwanted frequency components created in the digital synthesization of the sinewaves. The filters and amplifiers are conventional applications of the Motorola MC1458V operational amplifier.

The MC14410 tone encoder accepts digital coded inputs for the tones. The digital coded inputs control an external clocked frequency generator. The dial tone from generator 581 and the beep tone from generator 582 are single frequencies and are generated from a fixed code which is continuously applied to the encoder, and a crystal clock input.

The error tone from generator 583 is a varying single frequency and is generated from a fixed code for the center frequency which is continuously applied to the encoder and a varying clock input. The varying clock input is from a voltage controlled oscillator (VCO) circuit which, in the preferred embodiment, is a conventional application of the Motorola Mc14046CP Phase-Locked Loop CMOS Integrated Circuit. The control voltage input to the VCO, in effect the frequency modulation of the sweep input, is from a single frequency oscillator output at the sweep frequency. The sweep oscillator circuit is a conventional operational amplifier circuit design employing in the preferred embodiment Motorola MC1458V units.

The no circuit tone from generator 584 is an interrupted single frequency pair and is generated from a fixed code, which is continuously gated to the input of the encoder at the interruption rate and from a crystal clock unit. The gate control, in effect the amplitude modulation of the cadence input, is supplied from a conventional timer circuit design, which in the preferred embodiment, employs as the basic element the Signetics NE556 unit.

Refer now to FIG. 9, which is a more detailed schematic illustration of the private and switched network data arrangement 61. As previously depicted in FIG. 3 and here in FIG. 9, the data arrangement is that element of the remote satellite unit which provides the interface with a private line facility and alternately the switched network for the data communication between the microcomputer system and the central computer system. As aforementioned, the selection of which data communications path is to be employed is performed by the microcomputer system 49 via system bus 90 in software selectable modes.

As illustrated in FIG. 9, the private and switched network data arrangement 61 is a data access interface which includes two modems 611 and 612, one for the primary path (Private Wire) and one for the alternative path (DDD Network), an automatic dialer 613; and an interface with the system bus 90 for software control. In the preferred embodiment, the modem is referred to as an MM-620 Modem Module and the autodialer and system bus interface as a DB-621 Dial Back Up Unit.

The FSK Modem 611 and 612 provide 2 wire full duplex operation in support of 300BPS frequency shift keying (FSK) data transmission and is commonly referred to in the art by Bell hardware model numbers 103/113. The unit used in the preferred embodiment is Universal Data System, Model UDS103ARC. As identified, the carrier detect signal output from both modems are inputs to the microcomputer interface logic and are used in the software selection of the communication path. Further as shown, the communications path selected is interconnected with microcomputer System serial data interface 617 by a software output command, which enables the appropriate path in the data port switch 618.

The autodialer 613, upon software command, provides a fully automatic dial up operation into the DDD network. Signals from the microcomputer System via the system bus interface logic are, as identified, an Enable (Auto Dial Enabler), Done (Last Digit), and a Reset/Retry (Clear/Redial). The autodialer performs all other functions requisite to automatic calling through the network via a Bell provided Data Access Arrangement (DAA) which, by standard Bell reference designation, is data coupler CBS.

The logic elements requisite to the software selectable private and switch data arrangement by the microcomputer system via the system bus 90, consists of standard MSI and SSI units interconnected in a conventional manner. As shown in FIG. 9, for the preferred embodiment, the select function 614 employs a 74LS 138MSI logic element; the output register function for the command data 615 employs a 74LS175 MSI logic element; and the input data bus interface 616 employs a 74366 MSI logic element.

Refer now to FIG. 10, which details the autodialer 613 circuitry. Identified is the CBS data coupler control lead interface as required for call originations consisting of OH, DA and CCT, as known by Bell reference. The autodialer is a sequence controller operating in accordance with Dial Pulse Origination sequence criteria, as established for operations in the DDD network.

The sequence controller employs conventional SSI and MSI logic elements in standard applications. As shown, the time delay requirements of Redial Wait, Dial Tone Wait, and Interdigit Wait make use of a commercially available general purpose timer as referenced. The more critical timing needs for dial pulse accuracy are obtained from a clock input which is CPU crystal sourced. The final dial pulse make/break rates derive from up counts of 10 ms. The count sequence for the make/break ratio, dial pulse count, and digit count employ MSI counter logic elements as referenced. Dial number programmability is by BCD switch control of a diode array employing a general purpose diode as referenced, with digit selection achieved with MSI decoder logic element as referenced. The referenced full adder MSI logic element, as part of the digit counter, is used to decrement the loaded number by one, for subsequent correct count. The remaining controller logic is standard application of SSI elements.

While the present invention has been described in connection with a single remote switching circuit, it should be understood that the central computer 11 can be utilized to control in tandem a plurality of such remote switching units. Thus, for example, assume that a caller wishes to place a call to a long-distance city, but the cheapest bulk rate lines available are through one or more other remote switching units. In this case, the central processing unit, after determining the area code of the party being called, interrogates a number of other remote switching units to determine whether bulk rate lines are available for transmitting the call to the remote party. If such lines are available, the central processing unit provides command signals to the respective remote switching units to route the call therethrough to the remote telephone unit being called.

While the present invention has been disclosed with respect to a preferred embodiment thereof, it should be understood that there may be other embodiments which fall within the spirit and scope of the invention as defined by the appended claims.

Appendix A is a printout of the program for controlling the operation in the central processing system by the minicomputer system. The minicomputer system is of conventional design known in the art; however, included in Annex A to the Appendix is the structure of the computer as set out in the preferred embodiment. The attached program listing will enable those skilled in the art to implement the present invention to achieve the functions set out hereinabove.

Appendix B is a printout of the program for carrying out the various operations in the remote satellite unit by the microcomputer of the present invention. The remote satellite unit hardware structure, including the microcomputer system, is an assembly of modules interconnected specifically to meet the requirements set forth herein. The modules, as incorporated in the assembly, are as illustrated in FIG. 4.