Patent GB-1446047-A (GB)
Title: Message metering system
IPC: H04M15/04
Filed: 1973-10-02
Abstract: 1446047 Automatic exchange systems; metering VIDAR CORP 2 Oct 1973 [6 Oct 1972] 46018/73 Heading H4K In a C.A.M.A. system wherein the voltage on a metering wire associated with a subscriber is repeatedly scanned and converted to digital form, metering pulses indicating the charging rate for the call appear on the wire only at the commencement of a call and the total number of pulses is stored in a memory uniquely associated with the subscriber, the C.A.M.A. equipment further reacting to a voltage level indicating both calling and called subscribers are off-hook to cause an accumulator store of said subscriber memory to be fed with pulses at a fixed rate independent of the call charging rate. The system is applied to a No. 1 crossbar exchange and the wires scanned are the "M" wires (Fig. 6) on which wires one of five voltage levels can be present, the only negative level being used to indicate pulses associated with the call charging rate for a call just established. Metering pulses are not supplied to the C.A.M.A. equipment by the exchange equipment during a call but after a call to a particular zone has been established, the zone circuit (Fig. 6) applies to the M wire a number of - 48 v pulses by the operation of relay MR, which number is stored in a 4 bit zone count memory of the subscriber's memory to indicate the zone to which the call is established. During a call a + 9 v level is present on the M wire and causes 1 second pulses produced in the C.A.M.A. equipment to be counted by an accumulator store forming part of the subscriber's memory. On termination of the call all stored information in the subscriber's memory is transferred to a magnetic tape. C.A.M.A. equipment (Fig. 1).-The subscribers are arranged in groups of 1000 lines, the M wires of a group being scanned four at a time by a scanner bank 8 (detailed in Fig. 2, not shown) and the voltage levels on these 4 lines are simultaneously translated into 2 bit binary code by four A/D converters contained in the scanner bank, the codes being transferred in parallel over wires 33 to a scanner bank adapter 10 (detailed in Fig. 3, not shown). Each of the wires 33 may have a transmitter and receiver at respective ends to enable the scanner bank and the adapter to be separated by a relatively long distance, the receivers utilizing LED's and photo-transistors to achieve good electrical isolation. The information received for the four subscribers simultaneously is sequentially read into a 10 bit 1024-stage register forming a control memory, for each stage of which there is a corresponding stage of a 9 bit 1024 stage register forming a lower order accumulator memory and of a 12 bit 1024 stage register forming an 8 bit higher order accumulator memory and a 4 bit zone pulse memory. The equipment uses two clock rates, a first for addressing the memory stages in synchronism with the scanning of the respective subscribers M wires and a second slower rate for reading out information to one of two duplicate tape storage units over a respective data path A or B. For a detailed description of how the zone pulses and the 1 second metering pulses come to be stored attention is direction to the Specification. At the termination of a call a data message comprising 8 eight, eight bit, bytes is transferred over a data path to output and control unit 14, where bits indicating the time are inserted before the information is recorded on to the storage tape. Byte 0 includes a call termination flag to indicate that 7 more bytes are to occur, together with parity bits, other bit parities being indicative of various failures. Bytes 1 and 2 form a 16 bit BCD indication of the four higher order digits of the subscriber's directory number as determined from a directory strap circuit (85, Fig. 3, not shown). Byte 3 and bit positions 2 and 3 of byte 4 are used to signal the lower order digits in binary code as determined by the position of a counter driving the scanner. Bit positions 4-7 of byte 4 signal the number of zone indicating pulses received, and bit positions 1 and 2 are unused. Bytes 5 and 6 signal the higher order and lower order digits corresponding to the accumulated number of 1 second metering pulses counted. Byte 7 includes flags in bits 0-3, but 4 and 5 indicate that it is the last byte of the message and bits 6 and 7 are unused. The 8 bytes are stored in an eight byte buffer in the output control unit OCU and the time indication is inserted into the vacant bit positions of bytes 4 and 7. If a test call is involved an indication is inserted in bits 4 and 5 of byte 7. Further the binary coded lower order subscriber digits in bytes 3 and 4 are converted into BCD form. The modified bytes are then transferred to a tape unit for registration on a magnetic tape.