Patent GB-1471984-A (GB)
Title: Apparatus for supervising operation of a multiplex system
IPC: H04J3/14
Filed: 1974-07-01
Abstract: 1471984 Supervising multiplex operation COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT ALCATEL 1 July 1974 [3 July 1973] 29082/74 Heading H4M In an apparatus for supervising the operation of both multiplexer and demultiplexer in a binary data multiplex transmission system (either between the high speed output and slower inputs of a multiplexer or between the high speed input and slower outputs of a demultiplexer), a word of q bits is sampled from a slow train (i.e. input data before multiplexing or output data after demultiplexing) and held in a memory, and is compared with a q bit word passing through a register and sampled from a high speed train at the high speed multiplex bit rate divided by K. K is such that the high speed bit rates in the system are slightly greater than K times any of the slow speed bit rates. This sampling and comparing operation is carried out in a first part of a selection period. The timing of the divided bit rate is regulated in accordance with the number of non-coincidences at the comparator output. In a second part of the selection period, the system changes to operate in an error control mode and any errors detected in the comparison are used to set off an alarm. Four slow speed non-synchronous signals M1-M4 to be multiplexed and four signals N1-N4 obtained after demultiplexing are applied to a selector 5a where they are sampled in accordance with timing pulses S1-S8. Each successively selected pulse train Mi is passed via a shift register delay 9 to a shift register memory 10 which is advanced in accordance with the clock appropriate to Mi when the gate 11 is open by a signal p. This opening occurs for half of a minor cycle of 8 clock pulses. Slow speed signals Ni obtained after demultiplexing are applied to the register 10 but are not passed through the delay 9 which is provided to compensate for the time taken in multiplexing the signals Mi. The high speed output from the multiplexer is applied to a shift register 13 which is advanced by reference to the high speed clock F divided by 4. The constants of registers 10 and 12 are compared by digital comparator 14, and lack of equality causes the logic circuit 15 to deliver a 1 at its output X. This output is applied to a modulo 3 counter 16 (Fig. 1b) which may be reset by pulses from another modulo 3 counter 17 receiving input clock pulses S, one per minor cycle. If the counter 16 counts two lacks of coincidence during three minor cycles, faulty timing of the divided clock pulses F4 is indicated and a signal R is emitted which triggers a shift order in the clock pulse divider. The procedure continues in successive minor cycles until correct timing is established.  The output from the counter 17 is applied to a modulo 6 counter 18 which will be reset by the pulses R. When 18 does provide an output (indicating 12 minor cycles without error and thus correct timing of the clock), the flip-flop 20 is reset to zero and the switch K changes its position (to b). If an error is then detected a counter 22 is activated and this triggers a differentiator 23 to reset the flip-flop 20 and effect a new timing check. If this is satisfactory and a further error is passed to counter 22, the alarm selector 26 is activated. This has eight outputs L1-L8 corresponding to the eight inputs to the selector 5a and each is connected via a resettable memory flip-flop 27 to an indicator 28 for each input output time. Illumination of any particular line indicates faulty multiplexing for the particular input/output. If the multiplexer or demultiplexer behaves so that synchronism cannot be established in the first part of operation, the count in the counter 18 will never reach 5 and the switch K will not be changed from the a position. To ensure that an alarm is given in this condition, the Q output of the flip-flop 20 is used to set a D type flip-flop 30 which is interrogated (by pulse Y) at the end of each supervisory cycle. If an output is provided, the alarm circuit 26 is triggered.