Patent GB-1049475-A (GB)
Title: Improvements in or relating to trunk dialling telecommunication systems
IPC: H04Q3/00
Filed: 1964-09-29
Abstract: 1,049,475. Automatic exchange systems. SIEMENS & HALSKE A.G. Sept. 29, 1964 [Sept. 30, 1963], No. 39542/64. Heading H4K. To increase their availability, registers employed in the various exchanges involved in setting up a trunk connection are released if the routing digits from the originating trunk exchange do not arrive promptly, it being necessary to take registers into use again if further digits appear. Until the destination is reached and the final trunk exchange signals back the condition of the wanted line, it is not known how many digits are involved in any call. Since the establishment of line condition is relatively slow the registers release and the terminating trunk exchange seizes a register and reverts a seize signal to the originating exchange which forwards a ready code on receipt of which the ready signal can be sent. Should the registers not be released when the line condition is determined the condition signal, a multi-frequency code, is sent following a normally existing acknowledgment signal reverted from the terminating trunk exchange. The condition code is reverted continuously until a forward acknowledgment is picked up. The exchanges may be provided with different classes of register depending on whether they serve local calls, national network calls, or calls over an international network. An originating trunk exchange is reached and an appropriate register put in service in response to a " trunk call required " digit. As soon as the register has sufficient digits to proceed it obtains a link and sends a 50 c/s. seize signal to put a register into service in the first transit trunk exchange. This seize signal continues until a " digit request " signal is reverted whereupon it is replaced by a multi-frequency 2-out-of-6 code giving the first digit. The first digit continues to be transmitted until its reception at the transit exchange quenches the " digit request " signal which is promptly resumed to obtain the next digit. When the first transit exchange has sufficient digits to extend the connection it does not revert the " digit request " signal but sets up a link to the next trunk exchange. The absence of " digit request" signal at the originating trunk exchange causes it to send a further seize signal to put a register into service in the second transit exchange. Instead of indicating its action by silence, the retiring register in the first transit exchange may revert a " last required digit received " signal. Alternatively the originating exchange may send digits one after the other in response to a send digits signal which is reverted continuously until the requesting exchange has sufficient digits or the originating exchange runs out of digits. As a further alternative the digits may be sent as multi-frequency bursts of a specific length in response to a digit send signal which is interrupted for as long as a digit in each burst is received. The digits may be sent without reference to restorations of this digit send signal or may be sent in response to the restorations. Release of the registers, in the absence of further digits within a given time, is governed by that trunk exchange register currently at the end of the connection. Instead of remaining silent when it has no further digits on hand for transmission the originating exchange may send a signal forward to precipitate release. When the originating register remains silent there is the chance that the forward register will release and before its reverted digit request signal expires at the originating exchange further digits may be received and transmitted. Since no digit request signal follows the first such digit it will be known that the forward register has retired and a new seize signal is called for. Where both registers have released, the arrival of further digits causes reseizure of an originating exchange register which issues a seizure demand for a register in the forward exchange. In the context of time assigned speech interpolation techniques, the continuous transmission of a digit code until reception of an acknowledgment which continues until a further digit is sent, enables a channel to be held. If the digit codes are sent as pulses a continuous audio signal is employed to hold the channel. Transitions between one type of digit transmission and another must be recorded at an exchange so that, if a register is released during an idle time, the appropriate signalling will be put into service when re-seizure is effected.