Patent GB-1211479-A (GB)
Title: Improvements in or relating to automatic telephone exchanges
Inventor: MURRAY LAWRENCE JOHN
IPC: H04Q3/00
Filed: 1968-05-08
Abstract: 1,211,479. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. 24 March, 1969 [8 May, 1968], No. 21680/68. Heading H4K. In an exchange employing register senders and a succession of group selecting switching stages, each having a plurality of inlets with selective access to a plurality of levels of outlets, one or more levels of the first stage are provided for routing of outgoing junction calls, the outlets of each said one or more levels are divided into two sets connected to different second group selecting stages and the outlets of one set and then the other are interrogated for possible use each time that level is nominated, the order in which the two sets are interrogated being alternated for successive seizures of the first switching stage. The invention enables the number of outgoing junction routes to be doubled without increasing the number of group selecting stages and while retaining full access between inlets and outlets. Less than double the number may be provided in which case an attempt is made to connect to some junction routes twice during a single seizure attempt, or more than double the number may be provided if full access is not essential . In the embodiment shown each group selector is generally similar to that described in Specification 1,131,367 which employs two stages of reed relay switching matrices and has 48 inlets and 10 levels of 20 outlets, the outlets of some levels being split for the purposes of the present invention into two groups of ten. The group selecting stages are controlled by programme controlled apparatus. As shown the subscribers SUB are connected via non-numerical selectors NNS to register access relays sets RARS which can connect one at a time to selected ones of a small group of registers REG, can hold a connection after the register has been released and can on instruction cause busy tone to be returned to a caller. The registers are register translators which receive dial pulses in loop disconnect form and transmit digits which may be requested by "proceed to send" signals in high speed coded form. Busy tone is returned if a first seizure attempt fails to find a group selector of the first group selection stage which has a free outlet at the required level as designated by the first dialled digit or if such a free outlet is found in a split level and a selector of the second stage and having a free outlet corresponding to the second dialled digit is not found during two successive seizure attempts. Two attempts are made in the later case as two sets SC, SX and SC, SY of second group selectors are provided and are associated with different halves X and Y of a split level such as the level "3" to a first selector such as FCSI. A bi-stable common to all levels or a bi-stable individual to that level switched for each seizure attempt or for each established connection using that selector or that level, nominates one or other of the halves X and Y to be interrogated first. Normally during a first attempt one of the sets SC, SX and SC, SY is taken into use and in the second attempt the other set is taken into use, the two sets being connected to different trunks and thus double the number of trunks to another exchange can be provided.