Patent GB-970160-A (GB)
Title: Improvements in or relating to telephone line concentrator systems
IPC: H04Q3/00
Filed: 1960-12-07
Abstract: 970,160. Automatic telephone exchange systems. WESTERN ELECTRIC CO. Inc. Dec. 7, 1960 [Dec. 24, 1959], No. 42101/60. Heading H4K. In a system utilizing line concentrator means for connecting, under the control of a central office, a number of subscriber lines to a lesser number of office links extending to the central office, a calling line is initially connected to a called line over a path through the central office including office links, and thereafter the two lines are connected via a local link within the concentrator means under control of the central office. If the calling and called parties are served by the same concentrator the local link used is one within that concentrator; if they are served by different concentrators the local link used is one between the two concentrators concerned. Call between two subscribers served by the same primary concentrator, Fig. 1.-The subscribers served by the primary concentrator shown are assumed to be subscribers of a PBX. When such a subscriber dials outside the PBX the call is handled as described in Specification 957,052. On an intra-PBX call, however, the central office participates conventionally only until the called party answers, whereupon the links to the central office are released and a local connection is set up within the primary concentrator. Incoming calls to the PBX may be dialled directly as each PBX extension is terminated in the same manner as an ordinary line. The primary concentrator includes a full access switching network for connecting a maximum of fifty-eight subscribers to ten links, such as 19, extending to the secondary concentrator, which includes a partial access switching network for selectively connecting up to two hundred links to a maximum of one hundred trunks, such as 20, to the central office. The concentrator switching networks consist of onewire switches employing PNPN transistor crosspoints, talking battery being supplied at the primary concentrator and cross-point holding power locally. When subscriber 11 goes offhook, the line scanner 71 notes the service request and repeats it to the central office where the line number, primary concentrator and secondary concentrator concerned are recorded. A connection is then set up between the calling station and a digit detector (not shown) at the central office, crosspoints such as 15 and 18 being operated by line mark selector 13 and link mark selector 14, and link mark selector 16 and trunk mark selector 17, respectively. On receipt of dial tone the caller dials the wanted number which is, translated into the station equipment number of the called station, say station 12. The link mark selector is then advanced to the called line and if this is idle an idle link and trunk to the primary concentrator are selected and crosspoint 21 is operated. In the secondary concentrator link mark selector 16 and trunk mark selector 17 energize crosspoint 22 to complete the path, and the called party is then rung. When he replies the link scanner 25 indicates this to the central office, when trips the ringing. Since the equipment numbers of stations 11 and 12 indicatethat they are connected to the same primary concentrator; the remote concentrator control therefore releases the operated crosspoints (as described in Specification 957,052) and causes the skew link mark selector 28 and line mark selector 13 to energize crosspoints 29 and 30 to complete the local connection between stations 11 and 12. When either party hangs up, the skew link scanner 33 signals this to the remote concentrator control at the central office and the relevant crosspoint is released. - Calls between subscribers served by different primary concentrators.-In these calls operation is basically similar but the local links are interprimary links. The procedure is described in detail with reference to Figs. 2, 3 and 4 (not shown).