| 摘要 |
1395413 Automatic exchange systems SIEMENS AG 20 July 1972 [9 Sept 1971] 34008/72 Heading H4K In a telecommunication system, signals between data substations and the exchange in one or other direction are acknowledged by the receiving end only after a delay and the transmitting end is arranged to indicate that a double or undesirable connection has occured if an acknowledgement is received too quickly. The invention deals with avoiding errors that can occur when the exchange employs the same tone for "calling tone" and for "proceed to send" tone and the substations if idle automatically respond to an incoming call if ready to receive and employ a single tone for "waiting to transmit" (in connection with an outgoing call), and for "ready to receive" (in connection with an incoming call), the transmission delays being such that transmission of calling tone may be initiated after a substation has initiated a call but before that call has been detected at the exchange, or a call may be initiated after the exchange has initiated transmission of a calling signal and before that calling signal has reached the substation, the signals in the two directions in each case relating to different calls but being interpreted as relating to the same call. The substations may be directly connected to the exchange or connected thereto by one or more concentrators. The figure shows a substation signalling circuit DSt connected to an exchange circuit EDs. As shown the acknowledgement delay is effected at the subscriber end DSt, delay t having a value at least equal to the difference between the maximum and minimum transmission time between any substation and the exchange. If the substation goes off-hook inputs K6 and K8 go to "1" potential and if it is ready to receive or transmit input K7 goes to "0" poential. If no signal is being received at E2, the other input to NAND gate G6 is zero and NAND gate G8 enables S2 to transmit calling tone to receiver El. As a counter Z is at zero count at this time providing a "1" output at a2 gate G5 responds producing a new call "0" potential at K5. If prior to such new call detection a new incoming call is detected for the subscriber, calling tone is transmitted from S1 to E2 and a counter Z is started. If the substation is free and ready to receive then after the delay determined by t, acknowledgement tone is transmitted from S2 to El. The lower counts of the counter enable a line a1 and if a tone is received at this time it cannot be a ready to receive tone and the output of NAND gate G4 goes to zero indicating that signals from two separate calls are involved, the exchange responding by sending engaged tone to the distant station and accepting the outgoing call. The upper counts of the counter enable a line a2 and if a tone is received at this time the output of NAND gate G4 goes to zero indicating that the substation is free and ready to receive. |
