Patent GB-1040254-A (GB)
Title: Improvements in and relating to time division communication systems
IPC: H04Q11/04
Filed: 1963-04-04
Abstract: 1,040,254. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. April 4, 1963 [April 24, 1962], No. 13335/63. Heading H4K. In a time division communicator system comprising a central office having a plurality of lines connectable thereto by gate circuits over a common transmission channel in distinct time slots of a repetitive cycle for transmitting coded information and control signals, originating in the lines, over the transmission channel, the information and control signals each producing a characteristic number of code signals during a predetermined time interval, the central office comprises means connected to receive signals over the common channel for distinguishing between various types of coded signals, said means including a plurality of timing means each having distinct time delay, said time delays being of duration having values corresponding to those intervals wherein tests are made to ascertain whether the number of code signals received correspond to the characteristic number required to indicate that a particular coded signal is being received. The coded signals distinguished are dial makes and breaks and long makes and breaks such as occur at the end of a dial train, and clear-down respectively. Connection of calling line to register.-The subscriber's lines are scanned cyclically the scanning pulse for each line having a duration of five frames. If the calling number is not present in the line store, then a pulse in the next free time-slot is inserted in the line store in delay line combinations indicative of the calling line and at the same time the call progress state of that time slot is changed from CP0 to CP1. When the line is next scanned if the off hook condition is still present the call state advances to CP2. If, however, the off-hook condition is absent then the state reverts to CP0 which deletes the pulse from the line store. The pulses in the line store gate the calling subscribing signals on to a SEND multiplex highway, whence they enter gate 510 of the signal detector, Fig. 6. At the same time the calling line pulse is inserted into a combination of delay lines indicative of a free register, and the call state advanced to CP3. The pulse so stored is used to gate signals from the signal detector into the counting circuitry of the register concerned. In the CP3 state, delta-modulated dial tone signals are fed to the receive highway in this phase. Operation of signal detector.-Pulses received from the SEND highway are inserted in 20 Ásec. (one frame) delay line 501 and recirculated. Every 25 frames (i.e. ¢ m.sec.) a pulse on lead m inhibits the circulation, and gates the pulse into the 500 Ásec. delay line 502. Circulation in 25 frame delay line 502 is permitted provided gate 517 emits a pulse every time, and after 4 circulations (in 2 m.sec.) gate 525 emits a channel pulse, indicative of a loop condition. It is seen that a loop condition is only recognized as such provided it lasts for 2 m.secs. In the call progress state CP3, the output from 525 is inserted in 2 m.sec. delay line 503 via 530. At ten millisecond intervals mnk inhibits circulation at 533, and if during the succeeding interval no loop condition is received 503 has no circulating pulses so that when the mnk signal next appears, gate 534 emits a pulse on Sb indicating a break in the loop. This signal is used to charge the call progress state to CP4 and closed loop condition are now tested for. Thus an output from 525 is gated in by mnk and circulation is maintained at 536 by the continued output from 525. After 10 m.secs. mnk and CP4 enable 538 to emit a " make " signal Sm. This signal causes the call progress state to advance to CP5 to permit detection of the next dial break and so on. The circuit of delay line 503 is arranged (by means not shown) to respond to CP5 (and CP6) in the same way as to CP3 (and CP4). Circuit 53 is used to detect long makes (between dial pulse trains) and long breaks (at disconnection). The end of a dial break causes a pulse to be inserted in delay line 504 via gate 540, and the end of a dial make causes a pulse to be inserted via gate 542. The circulation is deleted by the mnkl pulse every 160 ms. If no pulse is inserted between successive mnkl pulses then the flip-flop below 504 emits a pulse from its - output which is gated out of 543 or 544 by CP4 or CP3 to indicate a long break or long make. Completion of connection.-The called line's digits are read out and compared with the numbers in the line store. If the called line is free, the first free pulse (state CP0) is emitted by the marker and gated into the called lines store combination. The pulse also is set to state CP9 in the call progress memory. A flipflop in the marker is also set by the calling line pulse and reset by the called line pulse. This signal is fed to a pulse shift memory in which a counter counts the number of time slots between the two pulses. This number is inserted in pulse shifter memory stores in the time position of the called line and the complement is inserted in the time position of the called line. These outputs are then fed to corresponding gates in a tapped delay line whose input is connected to the SEND highway, the gates being connected to the RECEIVE highway so that transposition of the information between the time slots is effected. At CP9, a delta-modulated ringing signal is sent to the SEND and RECEIVE highways for transmission to the two subscribers. When a long make is detected in this position indicating that the called subscriber has answered the calling line pulse goes to state CP12 in which conversation takes place and the register is released (not described in detail). Busy conditions.-If the called line is already present in the line number store the marker changes the calling line state from CP8 to CPB which causes delta-modulated busy tone to be gated to the receive highway. Likewise if there is no free channel the pulse shift counter steps to its last position and this similarly changes CP8 to CPB.