Patent GB-1086737-A (GB)
Title: Telephone switching systems
Inventor: KROM MYRON E
IPC: H04M3/42
Filed: 1964-10-21
Abstract: 1,086,737. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. Oct. 21, 1964 [Oct. 22, 1963], No. 42848/64. Heading H4K. In an exchange system, certain privileged subscribers are provided with two appearances on the switching network whereby an incoming call may be diverted to the second appearance in the event that the subscriber is busy on his first appearance. When a call is diverted in this manner, a burst of tone is sent to the subscriber so as to apprise him of the waiting call and when he has finished his existing call he merely flashes his switch-hook so as to connect himself to the second appearance. The existing call need not be released and an interim or triangular call may be set up. It is suggested that conference calls may also be set up but details of this are not given. It is stated that the switching network may utilize crossbars. The details regarding the exchange operations required for the diversion are described in U.S.A. Specification 3,278,692. Operation. Subscriber S1 initiates a call.-On closing the loop a relay S, having its windings in series with the line wires, and a line relay L in the first (regular) line circuit 101 come up. Relays SR2, D and SR3 follow and a connection via the network (not shown) to a register is set up whereafter an earth on sleeve S brings up relay RS. Relay SR1 follows and dial tone from a source not shown is reverted. At the end of dialling RS is caused to fall back temporarily whereby D and SR3 release whereafter RS restores and a connection to the wanted party is set up. Waiting call on second appearance.-Such a call cannot intrude until S1 has finished dialling i.e. until D relapses but at such time an earth on the auxiliary (second) appearance brings up AS. The latter causes SR1 to fall back slowly during which time a tone from source 102 is sent to S, the loop on the regular appearance is shunted by a resistor 107 and a tone burst from another source (120) is sent to the waiting party. Accepting call on second appearance.-S flashes his switch hook whereby SR falls back temporarily to bring up TR1, H1 and H2. A retard coil 110/111 is thus connected in shunt with the first appearance and, when SR restores, relay TRA energizes so as to complete the transfer of the connection from the first to the second appearance and to supply batteryfeed to S1. Revert from second to first appearance.-Again subscriber S1 flashes his hook switch whereby S and hence TR fall. The restoration of S brings down TRA and H1 whereby the original connection is restored and the loop on the second appearance is held over resistor 115. Release.-If party B on the first appearance releases while S 1 is connected to party C on the second appearance, relay RS followed by H1 falls and D comes up. If now a new incoming call occurs it is diverted to the first appearance so that RS comes up to be followed by SR1. Consequently D falls back to bring down SR1 but during its slow release a burst of tone is again sent to S1. The latter by flashing his switch hook can connect himself to the new call as mentioned above. However, if no new call occurs, flashing by S has no effect and the circuit is not released until he holds down his hook for a period longer than that defined by a delayed release timer 114. In the latter case S fell as soon as the loop was broken whereby TR and H1 came up. When SR2 falls back after the delay, TR, H1 and AS all restore. Subscriber S1 may initiate a call, while a caller is waiting on the second appearance, by releasing the circuit as just mentioned and then setting up a call as described above, a burst of tone being reverted to S1 when AS comes up and SR1 falls back at the end of dialling. If C releases while S1 is connected to B, AS falls followed by H2 while SR1 comes up so as to restore the initial circuit conditions. Incoming call.-Relay RS responds to earth on the sleeve and ringing current from an unspecified source is sent to S1. When he answers relays S, SR1 and SR2 come up but D remains back. Simultaneous incoming calls.-The call on the second appearance cannot be dealt with in any way until S1 connects through to that on the first appearance and a burst of tone is reverted. Triangular call.-Assuming that S1 is connected to B and that S1's second appearance is free, then S1 gains access to the second appearance by flashing his switchhook whereby he is connected to a register and relay RS is transferred from the regular to the auxiliary sleeve. In addition relays TR, H1, TRA and L in line circuit 126 operate as do D and H2. With the register connected, RS comes up followed by SR1, and S1 commences dialling as described above. When the third party replies, RS and D having fallen back meanwhile, a triangular connection via capacitors 112 and 113 is obtained. If S1 again flashes, the auxiliary appearance is released by the relapse of TR and TRA. Party lines.-Whenever the tip party takes part in a call a relay PT (Fig. 3, not shown) comes up. When e.g. tip ringing occurs on the auxiliary appearance a discharge tube (GT) and relay (T) are operative so as to connect a burst of tone to the tip party to inform him that another call is awaiting him. However, if the ring party is talking the PT relay is back so that tip ringing causes a busy tone source to be connected up. Similarly busy tone is connected up in response to " ring ringing " if the tip party is in conversation.