Patent GB-1417654-A (GB)
Title: Telephone accounting equipment
IPC: H04M15/04
Filed: 1973-04-30
Abstract: 1417654 Automatic exchange systems INTERNATIONAL STANDARD ELECTRIC CORP 30 April 1973 [8 May 1972] 20367/73 Heading H4K Centralized call accounting equipment includes a core store into which the numbers of a calling and called subscriber are read in conjugation with other information needed to bill the call and the conformation in the call store is transferred to magnetic tape when the core store becomes full. General.-The equipment comprises two identical subsystems A, B and a control/display panel 4 which are linked via an interface (which is not described) to a telephone switching system having C.A.M.A./L.A.M.A. capabilities, e.g. a common control cross-bar switchings system. Only one subsystem is on-line at a time and a changeover is effected either by manual operation at the panel 4 or in the event of an alarm in the on-line system. A format control FC, Fig. 2, receives the data pertaining to a call in parallel 10-bit binary coded decimal (BCD) form and acts in response to one of four demand signals to check the data and cause it to be read into core memory CM. Detailed description.-Three pieces of information are stored in respect of each call, each piece including the identity of the trunk being used because each piece of information is stored in the core store and eventually on tape independently of the others and the three pieces of information must finally be collated. The three pieces of information comprise (a) an initial entry (IE) including the numbers of the calling and called subscribers and the trunk identification, this entry being made at the commencement of a toll call; (b) an answer entry (A) including the trunk identification and the time in seconds; (C) a disconnect entry (D) including the trunk identification and the time in seconds. In addition to these entries made as a result of demands from the switching system a minute entry (MIN) is made every minute giving the time in minutes for reference purposes. With reference to Figs. 2 and 3, in response to a demand signal received over terminals 30, 32 or 1150 and if core memory control is idle, format control sequentially scans 20 sets of 10 interface units 1/0 to gate each set of 10 parallel bits to parallel to series gates P3 from which the data is fed to data check DC where the parity of the data is checked, one bit of the 10-bit data signal indicating the parity. In response to a positive check the data is scanned again and transferred under the control of write command control WCC and core memory control CMC to core memory CM. All parity failures are counted and compared with the number of demands. If a predetermined ratio is exceeded an alarm is set to cause the on- and off-line systems to interchange. In the event that the core memory control is busy the demand signal is held until it can be processed or the circuit times out and drops off for a second trial or for operator handling. All demands are delayed slightly to allow for relay bounce. Once the data is stored in the core memory the demand is removed by a release signal to the telephone system. When the core memory contains a full block of data, the tape unit is energized and the data transferred. The data transferred is checked with that in the core store and a second transfer takes place if an error is detected. All time information is derived from a digital clock CL1 and from a master clock CL2 in the respective A or B system. The master clock also transfers the time from the digital clock through the TSC master clock encoder and buffer CL3 to operator positions coupled to the telephone system. The clocks are kept in a specified tolerance by comparator clock CL4 and if any of the digital clocks drift out of a specified tolerance an alarm is generated for the system containing the incorrect clock. The magnetic tape control serves as an interface between the magnetic tape unit and the core control enabling either 7 or 9 track tape units to be used at any standard or non-standard density or transfer rate after only minor changes in this one circuit.