Patent GB-1208258-A (GB)
Title: A self-steering switching network
IPC: H04Q3/00
Filed: 1969-05-30
Abstract: 1,208,258. Automatic exchange systems. NORTHERN ELECTRIC CO. Ltd. 30 May, 1969 [7 June, 1968], No. 27566/69. Heading H4K. In a self-steering cross-bar switching network, unnecessary seizure of links leading to switches having no idle outlets is prevented by marking such links as busy. The marking of such links emanating from one stage is effected by the operation of a relay whose operating circuit includes off-normal contacts of all the bridge magnets pertaining to the switches in the succeeding stage on which the links terminate. During a path search, one of the select magnets 1S33-1S11, say 1S11 (Fig. 1) in one stage of the network is brought up by earth extended from a previous stage or a line circuit. Via the contacts 1S11-1, an earth is extended over back contacts 2L1-1 . . . 2L3-1 to the first free link, viz. one not having an operated hold magnet 1H11 . . . 1H13, which extends to the select magnets 2S33 . . . 2S11 of the next stage. Thus, if 1H11 is back, the earth is effective to bring up 2S11 viz. the first select magnet in the first switch of the second stage, whereas if 1H11 and 1H12 are both energized the earth brings up select magnet 2S31, viz. the first select magnet in the third switch of the second stage. (The first suffix digit associated with the select and hold magnets indicates the order number of the switch to which it pertains.) Via off-normal contact 2S11-1 say, a relay 2L1 is then brought up to prevent any other path searches being made until the present one is complete and a path is switched through, 2L1 and 2S11, both holding to the earth provided by off-normal contacts 1S11-1 of the first operated select magnet. It should also be noted that the relay 2L1 and its'counterparts prevent any shuffling of select magnets in the event that busy hold magnets release during a path search. Furthermore, 2L1, at its contacts 2L1-2, extends the earth on 1S11-1 through to the links emanating from the second stage, the particular select magnet thereby energized in a third stage or the junctor chosen if the second stage is the last, being dependent on which of the hold magnets 2H11 . . . 2H13 (in this case) is not operated. The above procedure repeats at each stage until the junctor circuits are reached, whereupon the hold magnets pertaining to the chosen select magnets are brought-up backwardly from the junction in well-known manner, cf. for example Specification 739,905, and the select magnets are restored. All switch outlets busy.-In this case all of the switch's hold magnets are operative, e.g. magnets 2H11 . . . 2H13 of the first switch in the second stage (Fig. 2). Consequently earth is extended over the contact chain 2H11-2 . . . 2H13-2, to a switch busy relay 2B1 in the first stage. The contacts 2B1-1, 2B1-3, 2B1-5 therefore prevent earth markings over operated first stage select magnet contacts, e.g. 1S11, from being extended to the select magnets 2S11 . . . 2S13 of the first switch in the second stage. The marking is diverted to the second hold magnets' link marking leads irrespective of the condition of the first hold magnets' conditions, whereby only the select magnets of the second (or higher order number) switch in the second stage can be considered during the path search. Similar relays 3B1 . . . 3B3 are provided in the second stage. Contacts of these relays are included in another chain, e.g. 3B1-2, 3B2-2, 3B3-2 so as to prevent seizure of any link whose ultimate termination (i.e. after one, two or more stages) is blocked, thus ensuring that at no time is a select magnet energized (except in the first stage) unless at least one path through the network is accessible thereto.