Patent GB-945354-A (GB)
Title: Improvements in or relating to destination coded signal transmission systems
IPC: H04J3/17
Filed: 1960-04-22
Abstract: 945,354. Telephone transmission systems. WESTERN ELECTRIC CO. Inc. April 22, 1960 [May 25, 1959], No. 14193/60. Heading H4R. In a system in which signals sent over a transmission channel are preceded by a destination indicating signal which is inserted in a store at the receiver and in which subsequent signals, such as disconnect signals or errorconnecting signals are also sent, means is provided for detecting disparities between the contents of the store and said subsequent signals and for giving an indication if the number of such disparities becomes excessive. The invention is applied to a so-called TASI system of the type described in Specification 891,993, in which a disparity is recorded if a disconnect signal or an error-correcting signal is received in respect of a channel whose store is empty, i.e. is disconnected at that time. Receipt of such a signal indicates that a previously transmitted connect signal has failed to be received and that therefore the channel was faulty at that time. Fig. 2 illustrates the storage devices at the receiver in which the receiver memory stores on a time division basis the identities in binary form of all destinations at present connected to channels, each time slot corresponding to a channel. The storage device comprises a plurality of circulating systems such as 100 one for each binary digit. Correct signals or error-correction signals comprise the binary identity of the destination applied to leads 102 or 109 together with a write pulse applied to lead 103 or 110 in the time slot associated with the channel. The binary digits are inserted into the delay line via the gate 107 opened by the write pulse which also inhibits gate 114 to remove any identity previously circulating in this time position. Disconnect signals applied to lead 116 in the appropriate time position also inhibit gate 114. Identities circulating in the store are received by leads 118 to control connection of the channels to their destined lines as described in Specification 891,993. The outputs from the store are also inverted in amplifiers 122, 123 . . . so that if a time slot is empty, i.e. contains all " 0 's then all the amplifiers feed " 1 "s to the gate 125. If a disconnect signal is received on lead 116 the last input to gate 125 receives a " 1 " and the gate emits a disparity signal on lead 126. Likewise, if an error correction code (other than all zero) gate 119 passes an output via gate 120 to this last input of gate 126 which similarly emits a signal on lead 126. Pulses on lead 126 thus indicate disparities on the channel associated with the time slot of the pulse. These pulses are counted simultaneously for all channels on a time division basis by the two circulating systems 130, 131 on a " reflected binary " basis. When the fourth disparity signal is received, gate 147 is opened to pass a pulse to distributer 150, running in synchronism with the channel pulses so that one of the leads 151 indicative of the channel is pulsed to initiate an alarm and the removal of the channel from service. Any count is destroyed when a connection signal is received, by the application of a pulse from lead 103 to inhibit gates 136, 138. This guards against premature removal from service, due to minor interruptions.