Patent GB-1489217-A (GB)
Title: Traffic monitoring device for groups of inter-city circuits
IPC: H04M3/36
Filed: 1974-10-25
Abstract: 1489217 Automatic exchange systems J M BERNARD L LABBOZ and D VESQUE 25 Oct 1974 [25 Oct 1973] 46338/74 Heading H4K A traffic recorder for a group of interexchange trunks includes a scanning arrangement which couples the trunks to equipment including both decadic pulse and multifrequency tone receivers.The recorder obtains the number of the called party, and the time of occurrence of each of the various stages of a call. No means are disclosed for determining the calling subscriber's identity. The recorder (Fig. 5) is coupled to analogue interexchange trunks 1 0 -1 19 , as shown in Fig. 4, the trunks comprising in addition to either two trunks 1 0 -1 18  or four (trunk 1 19 ) speech wires a pair of signalling wires T and R. In operation the T and R wires are sequentially scanned at 100 Hz for a change in potential therebetween. When a trunk is seized by exchange 1 a 100 ms. pulse is transmitted on the T wire and this pulse is detected by the recorder which records the time of occurrence, HO, of the pulse as a trunk seizure time. The subsequent operation is dependent on whether decadic or multifrequency tone signalling is to be used between exchanges. It is not disclosed how the recorder determines which type of signalling is to follow. Decadic signalling.-The called exchange responds to the trunk seizure pulse with a 100 ms. proceed to send pulse on the R wire, the time of occurrence of which, H 1 , is recorded as the commencement of signalling time. Exchange 1 proceeds to send the digits of the called subscriber in decadic form on wire T, and these are recorded. The time of occurrence of a called subscriber free signal (two 100 ms. pulses) or a called subscriber busy signal (one 100 ms. pulse) on wire R is then recorded as a termination of signalling time, H 2 , and in the case where the subscriber is free the time of occurrence, H 3 , of a 100 ms. called subscriber answering pulse on wire R is then recorded. Finally the time of occurrence, H 4 , of a 500 ms. release pulse on wire T is recorded. Multifrequency signalling.-A 2 out of 6 inband code is used with the frequencies ranging from 700-1700 Hz in 200 Hz steps, the signalling taking place on the speech wires. Subsequent to the detection of the 100 ms. seizing pulse, a multifrequency receiver is allocated to the trunk and is coupled to the speech wires, via a switching network 16 and a respective one of the coupling units 5 0 -5 19 , each time the trunk is scanned. The called exchange responds with a proceed to send signal in multifrequency form and the time of occurrence, H 1 , of this tone is recorded followed by a recording of the called subscriber identity. All the following signals are then in decadic form as for the decadic signalling case except that no called subscriber free or busy signal is remitted. It is therefore necessary to detect the end of signalling time by other means and hence the recorder includes a translation arrangement whereby it can determine from the proceed to send tone and the initial tones of the called subscriber identity how many more tones are to be signalled. It takes account of the fact that the calling exchange sends only an initial section of the called number and then awaits a further proceed to send signal. The initial section may then be repeated if the receiving exchange is only to act as a tandem exchange for the call. Using the translation arrangement (table 2, not shown), the final multifrequency tone can be recognized, the time of occurrence H2, thereof recorded and the multifrequency receiver released. The times H 3 , H 4  are then detected exactly as for decadic signalling. The computer section of the recorder is illustrated in Fig. 6 (not shown), and includes a programmer (111). The recorder outputs recorded information on a teleprinter, printer or fast punching unit.