Patent GB-1238031-A (GB)
IPC: H04Q3/54
Filed: 1968-08-06
Abstract: 1,238,031. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. 6 Aug., 1968 [17 Aug., 1967], No. 37436/68. Heading H4K. In a system comprising two main offices which are permanently connected by direct junctions, additional semi permanent junctions via one or more tandem offices are made available in the event of overload. A semi permanent junction connection, also known as an augmentation connection, consists of a junction between each main office and the tandem office and a switching path interconnecting these junctions through the tandem, the path being held irrespective of whether or not a call is in existence. Such connections are set up under manual control from a main or a tandem office. General description Fig. 1. A call from subscriber 80 of office A to subscriber 70 of office B is normally set up over direct junction DT and the No. 5 cross-bar type switching frames associated with these offices. In the event that all direct junctions are busy an alternative route via an intermediate or tandem office IO is selected. A sender in the originating exchange A outpulses all the digits of the wanted subscriber's number to a register in IO whose own sender then outpulses the numerical portion of the number to the terminating office B when a switching path through IO and a junction to B have been seized. If the supervisor at A, say, decides that a semi-permanent route is required he seizes a free outgoing trunk circuit e.g. OT1 over lead Al and dials the number of a particular ring-trip bridge circuit TBC in B whereupon a path thereto is set up in the usual way. He holds this path, seizes another free outgoing trunk circuit e.g. OTn and dials a special code which results in a path being set up to a latching control access circuit 1 and thence to a latching control circuit 2 in the tandem office. The control circuit determines from the code that the held path between OT1 and TBC should be maintained and informs the incoming trunk circuit IT1 in this path accordingly. Thereafter the code control connection via OTn is released; the forward hold on the path through OT1 is removed; the appearance of OT1 on office A's switching network is changed (from AA to AB) to indicate to the marker that the route via OT1 is now effectively a direct route to B; and the part of the route between incoming trunk ITC in office B and the bridge circuit TBC is dropped. The unlatching of the "direct" route is effected by setting up another control connection and dialling another (different) special code. It is suggested that an augmentation connection can be set up under the control of a supervisor 3 at tandem but the necessary description as to how tandem signals the details of the connection to the offices A and B is not given. Particular description Figs. 2, 3.-The traffic manager 10 (Fig. 2) seizes a free outgoing trunk circuit OT1-OTn by closing switches SW1- SWn in turn until relay SN does not come up to a busy earth on the S lead 27 (SWB being in its 2 position and dialling pulse contact 41 being open) of the associated trunk circuit. When a free trunk is found, the loop on wires 28, 29 causes an associated tip and ring control circuit to seize the incoming trunk circuit IT1 at tandem. The manager dials, by pulsing contact 41, the number of a ring-trip bridge circuit in the wanted terminating exchange whereby the register (marker/sender in the tandem crossbar office (or the control circuits in a plurality of such offices if more than one tandem is necessary) causes a path to be set up through tandem's switching network to an outlet in the required direction and thence through the terminating offices switching network to the bridge circuit. The manager holds this path by closing contacts HLD1 and HLD2 and releases the particular switch SW1-SWn associated with the seized outgoing trunk circuit. He then hunts for another trunk circuit in similar manner to the above in order to set up a control connection to tandem by dialling a special code. Assuming trunk circuit OTn is seized, the digits of the special code are utilized by tandem's control circuit to set up a path to a latching control access circuit 1 and thence via a step-bystep selector 4 to a latch/unlatch control circuit associated individually with the incoming trunk IT1 in use for the existing connection to office B. Ringing current from the final selector bringsup relay LC in the latch/unlatch control (capacitor 59 blocks the D.C. battery superimposed when the ringing is tripped). Magnetic latching relay 2L follows to "permanently" busy the incoming trunk IT1. The manager upon hearing ringing tone in his receiver RCR opens the switch SWn so as to release the control connection. Thereafter he must busy the normal appearance AA of the outgoing trunk circuit and enable the appearance AB which denotes that this trunk is now effectively a direct junction to office B. This is effected by re-operating SW1, placing switches SWB and SWC in their position 1 and opening contact HLD2. SWC is now operated momentarily to bring up magnetic latching relay EX. (The latter is protected from negative transients on the sleeve lead by diode 11). Thereafter switch SW1 is opened to release 2S1 and thereby bring up relay 2T which places busy earth on the sleeve lead of appearance AA via contact 2T 1 and removes the earth on sleeve lead SA of appearance AB by opening contact 2T3. Finally the loop on leads 28, 29 is removed by opening contact HLD 1 whereby the final portion of the seized path viz. the path between the incoming trunk in office B and the ring trip bridge is released, the rest of the path being held however since earth is maintained on the sleeve lead SL in tandem by operated contact D1-1. In order to release the augmentation connection a new control path to tandem must be set up and an unlatch code signal transmitted thereto. The code signal steps the connector of selector 4 in tandem to its unlatch appearance T1 whereby ringing current brings up unlatch relay UC. Consequently 2L is unlatched by the discharge of capacitor 61 and therebythe "permanent" earthon thesleeve lead SL in tandem is removed. Since normal supervision is thus restored to the connection it will not release if call is in progress but will release thereafter. The reception of ringing tone in office A is interpreted as an O.K. signal whereupon the manager releases the control connection and re-operates SW1 to bring up 2S1. He then closes SWA to release EX followed by 2T at once if there is no call in progress through OT1 or at the end of such call. SW1 is opened to fully restore the system to normal.