Patent GB-711318-A (GB)
Title: Improvements in or relating to circuit arrangements for telecommunication installations having relay switches
Inventor: SPIECKER FRIEDRICK
IPC: H04Q3/00
Filed: 1952-07-16
Abstract: 711,318. Automatic exchange systems. SIEMENS & HALSKE AKT.-GES. July, 16, 1952, No. 18043/52. Class 40 (4)  In a relay system in which a number of first lines (e.g. subscribers' lines) can be coupled to a number of second lines (e.g. intermediate lines) which are allocated in turn in an allotter, the latter contains a set of relays, one for each first line, which on operation initiates a coupling operation and means which, on the operation of one of said coupling initiating relays, disables the remainder of these relays until the required coupling operation is completed. Trunking scheme.-A calling line, say in group Tn Gr 1, Fig. 1, has access over relays LK1 to any one of ten first intermediate lines 1ZL. Each of these has access over relays VZK1 to two second intermediate lines 2ZL each of which has access over relays VNK to three sets of selection relays WR. Dialled digits set a marker LEF which marks a called line say in group Tn Gr 2 and a connection is established between the selection relays WR and the called line over intermediate lines via a number of relay switches of which only EZK2 is shown, intermediate lines, xZL, and relay switch LK2. It is to be noted that the intermediate lines xZL used for outgoing calls are identical with intermediate lines 1.ZL used for incoming calls and that the relay switches LK may be used for both. Detailed description.-A calling subscriber's over line Tn1 operates line relay AR1 which brings up, in a series circuit, a coupling initiating relay Ka1 individual to the line, a relay R indicating that the call is an incoming one and a relay An common to the group of subscribers to which the calling subscriber belongs. If one of the sets of selection relays WR1 ... 6 is free then the first relay Qv1 of the chain Qv1 ... n comes up in series with G and locks. If however all of WR1 ... 6 are busy or if the second .intermediate line to which ZL1 has access are busy, relays C11, C12, are up and C1 operates to step the chain to the next Qv relay and so on. Assuming however that WR1 is free QV1 operates and brings up D1 and Plo in series. D1 brings up C11 to busy the appropriate second intermediate line. Plo brings up C1 which busies the first intermediate line and also relay Q1 designating this intermediate line. Q1 operates the coupling relay K, in series with a common guard relay Ug. Plo causes the following relays to operate in series: the coupling relays K11, K21 and the relay C21. individual to the set of selecting relays WR1. The line Tnl is thus connected to the selecting relay set WR1 a holding circuit for the coupling and busying relays being completed over the third wire in which the subscriber's cut-off relay TR1 and the busy relay O1 of WB1 also operate. TR1 releases Ka1 which is followed by the slow-to-release guard relay Ug. Relay C21 effects the coupling of the circuit WR1 with the register ZE whereupon G1 operates. The register receives the dialled digits and sets the marker LEF which marks, say, marking wire tn2. When all the digits have been received the register cuts a resistance out of the circuit of G1 to cause N1 to operate. A marking and test circuit is then completed in which, if the wanted line is free, relay Pwrl in WR1, relay Ka2 in the subscriber's line circuit and An in the allotter circuit of the appropriate group of lines all operate. Since the call is an outgoing one R does not operate. The second intermediate lines are taken into use for outgoing traffic in the opposite order to that for the incoming traffic by the chain Qen ... Qe1 Assuming that Qe2 represents the first free line in this sequence, this relay is operated in series with G, by the operation of An. Negative marking potential is thus applied to lead 97 to designate the second intermediate line and this in conjunction with markings from the register ZE causes the coupling of the relay set WR1 with this second intermediate line in the coupler EZK. Qe2 brings up busy relay C2 and also Q2, the last bringing up the coupling relay K2 in series with Ug and the connection between the relay set WR1, and the subscriber's line Tn2 is completed. The connection is held over the third wire 98 over which the line and cut-off relays AR2, TR2 also operate. TR2 releases Ka2 by inserting resistance 101 in its circuit. Preventing double connections (including case of subscriber busy).-Relay An (which operates both for an incoming and outgoing call) in operating, connects into the circuit of the Ka relays a resistance 121, sufficiently low to hold a Ka relay already operated, but sufficiently high to prevent the operation of a further Ka relay. Thus only one connection between a subscriber and a first stage intermediate line can be established whilst relay An is operated whether the connection be incoming or outgoing. The slow-release relay Ug which operates on the setting up of the connection and thereupon opens the circuit of all the Ka relays remains up sufficiently long after the Ka relay releases to ensure restoration of the allotter circuit before the acceptance of another call. Moreover relay Ug (and also G) connects negative potential to lead 105 so that if any incoming call occurs while Ug (or G) is up, the TR relay comes up, disconnects the AR relay and locks itself over the calling loop in a circuit having busy tone connected in series. If a call is attempted to a busy line, relay Pwr fails to operate in the marking circuit either because the AR relay is operated to open the circuit or because the TR relay has inserted a resistance such as 101 into the circuit. Relay G1, being short circuited, releases followed by 021 whose winding (ii) is also short-circuited. The opening of the holding circuit thus releases AR1 in the calling subscriber's line circuit but TR1 holds over the calling subscriber's loop and reverts busy tone. In a modification Fig. 4, the Ka relay in operating short circuits its high resistance winding, thereby preventing the operation of a further Ka relay in a parallel circuit.