Patent GB-781622-A (GB)
Title: Improvements in or relating to time assignment signal interpolation systems
IPC: H04J3/17
Filed: 1955-05-13
Abstract: 781,622. Multiplex systems. WESTERN ELECTRIC CO., Inc. May 13, 1955 [May 17, 1954], No. 13882/55. Class 40 (4). In a multiplex system, transmission of a number of one-way speeches larger than the number of system channels is made possible by a switching system in which the audio input circuits are continuously sequentially monitored to ascertain whether or not the talker is speaking and the channels are allocated accordingly. The transmitter and receiver talkerchannel switching arrangements are controlled by pulses from blocking oscillators 1102 and 1407 respectively which are fed by 768 kc/s. oscillators 1101 and 1406 which are not necessarily synchronized. In the transmitter, audio lines 1-31, Figs. 12, 13, found to be active by logic circuit 901 when sequentially sampled 1000 times per second by the appearance of their identifying codes on the activity sampling matrix 1204, are connected to transmission channels A-L, Fig. 11, through audio sampler gates 1221, 1222 ... which are controlled by talker-identity codes on matrix 1022 from a memory 702 rotating at 64,000 revs. per sec., and a distributer 1115 driven at the same speed by codes on wiring matrix 1125 produced by counter 1104. A talker is thus associated with an allocated channel by the position of bis identity code in the identity memory and the association is retained until such time as the channel becomes the longest inactive, when the code in the corresponding channel slot in a " channel availability " memory 701 which rotates and is synchronized with the identity memory is changed to indicate that the channel is next for service. The identity of the associated talker is then removed from its channel slot in the memory. In memory 701 channel slots in which the talker is active are marked " 0 " and assigned channels which have become inactive are given an availability number 15, 14, 13, 12 ... according to the duration of their inactivity. At the receiver, Figs. 14-19, channels A-L are connected sequentially to a time-separation multiplex bus 1421 by gates 1411-A-1411-L which are opened by channel codes in binary produced on wiring matrix 1401 by collector control counter 1408, and distributer gates 1711, 1712..., connect the bus 1421 to audio outlets 1-31 in accordance with talker identity codes applied successively to distribution wiring matrix 1903 by a memory 1801 which is set by tone signals with talkeridentity codes corresponding channel for channel with those in the combined transmitter memory. The transmitter memories are rotated twice during the activity sampling of each audio input, once for searching or questioning and once for effecting the operations shown to be necessary by the search. The " search " and " entry " are controlled by channel clock pips generated by the blocking oscillator 1102 at 1.3 microsecond intervals, alternate groups of twelve pips being switched to terminals 1107 or 1108 by gate 1106 under the control of counter 1105. The search is conducted by three logic circuits:- Question 1. Is this talker active (901) ? Question 2. Is this talker assigned to a channel (1211) ? and Question 3. Is the assigned channel marked active (602) ? When a talker becomes active his activity is detected when his identity code on matrix 1204 establishes a connection to Question 1 circuit 901 which is an on-off device termed a " slicer " which changes state at a predetermined input and the pulse sample is regenerated as a gating pip by circuit 901 to make the TASI (time assignment speech interpolation) control bistable multivibrator 902 " active." " Enable entry " gate 703, " hold gate 903, and " reactivate " gate 904 are as a result, partially enabled, the latter through disable entry switch 601. Further enabling pulses to " enable entry " gate 703 are derived from the circulating memories, through " use next recognizer " 706 which is operated by the appearance in the memory of the longest inactive channel marked 1111 and "disconnect code recognizer " 707 when 00000 is present. When thus enabled a clock pip at 708 passes through to trigger switch control 711, which changes over entry switches 712 to " write " the code on activity sampling matrix 1204 into the memory. Switches 712 also inject a pulse into " check position " memory 713 to control the transmission of the talker's identity code. When a talker is thus assigned, codes are regenerated in unit 705 at each appearance at the memory output and returned to the input. The assignment is held during later searches whilst the assignee is still active by " hold " gate 903, which gates search clock pip to return TASI control 902 to " idle " after any possibility of operating " release " gate 907 has passed. When a talker becomes idle release gate 907 is enabled by the idle condition of TASI control 902 and pulses from logic circuits 1211 and 602, gate the search clock pip to " release switch " control 1007. The channel active code 0000 is erased and a code number which is a function of the queue position of the channel determined by " assigned channel counter " 1012 during the previous entry interval, is inserted by the transfer of release switches 1008 from read to write. The counter is reset to 0011 by way of terminal 1013 at the beginning of each entry interval. Availability numbers are advanced towards the end of the queue by add 0001 circuit 603 each time an idle channel is put back into service. When TASI control 902 is not reset to " idle " at the start of an entry interval add 0001 circuit operates from the beginning of the entry interval a pulse through " start addition " gate 604 triggering " addition control " multi-vibrator 605 which provides one pulse to " add " gate 606. An entry clock pip triggers add circuit 603 unless gate 606 is inhibited by logic circuit 602. " Add " gate 606 is also controlled by " smaller than recogniser " circuit 912 which compares the code in availability code storer reactivated channel 913 with the code in the availability loop so that the code numbers of channels lower in the queue than the channel to be reactivated are advanced one to fill the gap. Reactivation occurs when the talker has an identity code in the memory and an availability code other than 0000. " Reactivate " gate 904 is enabled by TASI control 902 active and logic circuit 602, and operation occurs when a code identical to the talker's code appears in a channel slot. A search clock pip triggers " reactivate control " 915 which resets TASI control 901 and operates " reactivate switches " 916 to send channel availability code to store 913 and write 0000 in memory 701.. When an idle channel is stepped to 1111 in the channel availability memory it operates " use next recogniser " 706 on its next appearance to provide an input to " disconnect " gate 716 and since " disconnect code recogniser " 707 which inhibits disconnect gate when the disconnect code 00000 is recognised is not operated due to the presence of an. identity code the entry clock pip triggers " switch control " multivibrator 717 to erase the talker identity code and insert the disconnect code by changing over switches 714. The disconnect code operates disconnect code sampler 1305 and the output of disconnect tone filter 1031 is connected via multiplex bus 1301 to the channel from which the previous talker has been disconnected. The channel is not assigned to a new talker until 5 milliseconds have elapsed in order that the disconnect tone may be effective at the receiver. This is done by disconnect switch 717 and " minimum disconnect interval " multivibrator 611 which opens " disable entry " switch 601 blocking any new assignments and preventing clipping of previous " talkspurt." Idle channels may be marked in the memory during disconnection but because 1111 exists in the memory they are accorded a lower availability number. Disconnect code circulates and tone is transmitted until the next assignment to a newly active talker when the pulse injected in the " check position " memory 713 controls the transmission of tones representing in code the talker's identity. Tones a.re developed in pulser 1307 and filters 1041-1045 are tuned to the 2nd, 5th, 8th, 11th and 14th harmonics for the 1st-5th digits respectively. The 18th harmonic is used for disconnect tone. Pulses of tone pass through summing resistors 1061-1065 and 1070, according to the code on matrix 1022, and appear as an amplitude modulated pulse representative of the talker's identity. The pulse is applied to the appropriate channel by " send control " switch 801 through " sample and hold " gate 802, the check position memory pulse passing through " send connect " gate 803 and " or " gate 804 to actuate " send code " multi-vibrator 805. The tones are sent for 5 milliseconds under the control of minimum identity interval control 807 which is operated by " entry switches" control 711 at the time of talker assignment. The return of control 807 disables gate 803 so that " send code " control 805 cannot be triggered for a further 5 millisecs. The check pulse is stepped sequentially from channel to channel at the end of each cycle by erase and inject check pulse equipment 719,720 under the control of transfer counter 815 and gate 817 to check each channel. In the receiver the pulse produced by a channel gate 1411A-1411L when its code appears on matrix 1401 is also employed to operate its "disconnect connector " switch 1414A-1414L so that a pulse from slicer 1413 in response to the receipt of " disconnect tone " through filter 1412 triggers disconnect control 1501 to write 00000 in the appropriate channel slot of memory 1801 by means of switches 1802. When talker-identity tones replace disconnect tones they are fed over bus 1417 and are converted after 5 milli-seconds to a binary marking code by filters and slicers 1601-1610. The trailing edge of the disconnect pulse in slicer 1612 triggers " minimum interval " multivibrator 1502 to