Telephone Switching System

1,170,250. Automatic exchange systems. HITACHI Ltd., and NIPPON TELEGRAM R. TELEPHONE PUBLIC CORP. 17 Nov., 1966, No. 51612/66. Heading H4K. In a marker controlled local exchange connected by trunks L R to a parent exchange, a calling subscriber is initially connected to a register R which automatically seizes one of the trunks via a switch train RL separate from the main speech switch train LLF and repeats further digits over the separate switch train until such time as the main speech train is completed, whereafter further digits are repeated over this train and the register and separate train are released. If the initially dialled digits signify a local call, the trunk and 'the connection thereto are released and the register and marker complete the call in the normal manner (link IOT). If the first digit is O, a toll trunk LT is seized over the separate switch train and digits are repeated to this trunk in a manner similar to the above, the trunk to the parent exchange being released. Incoming trunks ICT are connected via the switch train RL to a register. In this case if the iitial digit which is suppressed signifies a tandem call, the register is connected via a relay selector TC (Fig. 5, not shown) to a both-way trunk BWTR leading to the wanted sub-exchange LE and digits are repeated over this path. When digit repeating is completed, the incoming trunk is connected via switches LLF to BWTR and the path via TC is dropped. For such tandem calls, ringing at the sub-exchange is controlled by relays in the trunk circuit of BWTR (Fig. 6, not shown). The switches LLF and RL comprise cross-bars, the operation of the latter in response to seizure of a register being described with reference to Figs. .3 and 4 (not shown). The initial digit(s) discriminator comprises a contact tree having relays connected to the relevant outlets for controlling the various kinds of call (Fig. 3, not shown). The subexchange LE is of the step-by-step type.