Patent GB-1449063-A (GB)
Title: Electronic time-division-multiplexed pabx telephone system
IPC: H04Q3/58
Filed: 1973-09-05
Abstract: 1449063 TDM PABX CHESTEL Inc 5 Sept 1973 [10 Oct 1972] 41783/73 Heading H4K In a TDM PABX in which an auxiliary conductor pair 22, 32, 25, Fig. 1, distributes clock pulses and wherein telephone sets 34, an attendant's position 27, trunk circuits 36 and single direction devices such as paging loudspeakers and bells are connected to a communication conductor pair 21, 30, 26 by appropriate interfaces in appliques 33, the send and receive legs of the two-way applique circuits are connected to spaced points on the communication conductor, sending being allocated a particular time slot in a frame the occurrance of which is determined by a counter 133, Fig. 8c, at the applique, and the receivers having all of the time slots applied to them to be available for controlled selective reception. Regenerators 40 are spaced along the transmission line. Frames of timing pulses (54 in the embodiment) are transmitted including fifty slots for the respective senders, two supervisory and signalling slots, and two synchronizing slots. The use of most forms of pulse modulation are said to be possible and pulse-width modulation is used in the embodiment. All stations are periodically addressed, bits of the address being transmitted in successive frames in the S and S slots of the communication conductor, and the state of an addressed channel is added at the station to the address code, for reception by any of the stations. Appliques may be arranged to be directly accessed or may be accessed only in conjunction with a transistor message. A fresh address is transmitted from the control station when the idle condition at the end of a composite S and S message is detected. Paging and ringing calls may be captured by a paged applique to establish a normal communication in response to the paging or ringing, and calls to a busy applique may be forwarded either to another predetermined station or to any free direct access station. The stations may be assigned priority classes which are indicated in their messages, and the classification may be used by an operator at the attendant position. Messages which may be either of general interest, or of pertinence to a particular station are successively applied to the S and S channel by a translator 43, and in the case of messages to particular stations, may include a trunk barring indication, or call forwarding instructions. These translator messages when returned to the central station may be used to monitor the appliques for malfunction. A message scheduler 46 which, by means of an address generator 41 sequentially initiates calls, may also connect a message from an applique received by receiver 51 to the pages by way of page transmitter 45. A message for paging being inserted by an applique into its signalling and supervision message. Appliques each use a standard master control unit 86 and have a feature selection unit 88 into which modules may be plugged for determining the features to be provided at that station, and its address. Incoming binary supervisory and control signals received from the communication line are distributed by 178 to master control unit 86 and to message assembler 170 the distributor having its own address supplied and sending a message send command to output or send mesage from the send message assembler 170, outgoing signalling and supervisory messages being generated in the master controller. Communication signals for the receiver are extracted at 92 and converted to voice signals by summing pulse width demodulator 95, under the control of audio gate 96 which selects the desired time slot or slots and may thus provide a conference facility. Audio gate 96 is controlled by a recirculating register 100 to gate the corresponding slot in successive frames in accordance with an address or number supplied over line 104 from the master controller and the occurrence of a corresponding frame count in counter 102. Outgoing signals on audio send line 85 are keyed in the appropriate time slot by audio gate 136 by the output of a digital comparator 133 in which the current timing pulse count of counter 33 is compared with the applique-address as determined by the module in the selection unit 88, and when inputs appear at both inputs of bit gate 142, a binary digital pulse is injected in the current time slot by bit generator 147. The applique master control unit 86 includes a memory 150 comprising six, fifty-bit registers and a register processor. Three of the registers are referred to as "call" registers and are designated "active" ,"camp-on" and "reserve" and in each of these one of the bit positions will be exclusively assigned by a "1" mark to another applique. The states of the other appliques indicated by their S and S messages are stored in another two of the registers and a final register comprises a disconnect signal store. The master control unit includes a hook status detector 124 which affects the call access to the three call registers, and a dial entry processor which delivers signals to the audio unit tone generator, e.g. dialling tone, busy tone, &c., and supplies to outgoing call processor 164 destination signals for a required call, and request signals for break-in or camp-on, the effectiveness of these being determined by plugged in modules in the feature selection unit. Trunk appliques are similar to other appliques but offer no "dial in" facility and give a caller access to a sequence of three call destinations the first of which may be the attendant's station if present, or a zone ringer. Access is not acknowledged to a calling exchange until a completed call is established. The applique includes an outpulser which sends dialling pulses in response to an applique call or in response to an S and S requirement and may further include a dial tone detector which suppresses audio transmission until outpulsing is completed, and circuitry for restricting predetermined out pulsing sequences. The trunk applique may also include a repertory dialler. The facilities provided and the steps necessary for their achievement are described with reference to flow diagrams.