Patent GB-1075042-A (GB)
Abstract: 1,075,042. Automatic exchanges. AUTOMATIC TELEPHONE & ELECTRIC CO. Jan. 17, 1966, No. 2130/66. Heading H4K. In a subscriber trunk dialling network classof-caller signals are sent to a trunk switching centre over the GO channel of a carrier link by means of a signalling system in which initiation of a trunk call causes an out-band vf seizing signal to be sent forward to the switching centre followed by a sustained in-band vf prefix signal, receipt of a sustained out-band backward acknowledgment signal causing the prefix signal to be replaced by an in-band classof-caller signal, digits being sent as out-band vf signals whether the class-of-caller signalling is in progress or not. The classes of caller involved are ordinary subscriber, coin-box and operator and the signalling is in 2 out of 6 vf code. The incoming relay set at the trunk switching centre responds to the seize signal by calling an idle register which in turn applies for the use of a common vf receiver, the backward acknowledgment signal not being sent until the common receiver is connected. When the class-of-caller code is received and checked it is set up in the incoming relay set where it provides an input direct to a common translator which determines with reference to the route required the rate at which meter pulses are to be sent or the number of such pulses at fixed intervals. Meter pulses are received as outband signals. A calling subscriber gains access to an outgoing relay set OGRS in the exchange after dialling the access digit and the calling loop applied to + and - conductors brings up relay A and slow to release relay B, which provides earth on the P-wire over B1. By means not shown earth is applied briefly to lead M of the terminal signalling equipment TA which transmits a brief outband seize signal to the receive equipment RB at the trunk switching centre to provide earth on the E-wire which effects seizure of the incoming relay set ICRS. At the exchange a class-of-caller potential is placed on the D wire via the caller's meter coil, namely earth for an ordinary subscriber and negative battery for a coin-box subscriber: for an operator calling there is no potential and no meter. Slow to operate relay CP connects the D-wire in turn, as it operates, to the operating windings of relays AO and ACB which are connected to earth and positive battery respectively. Either one or neither of these relays operates to thereby indicate the class of caller. Relay CP which has operated over contact B1 connects the GO channel of the trunk to a relay contact tree leading from frequencies W to Z. In the unoperated condition of relay PF the frequencies V and U are transmitted on the forward inband prefix signal. Upon seizure of the incoming relay set ICRS a relay BB (not shown) operates and via contact BB2 operates relay K which via contacts K4 to K9 connects the register connector RC to a register-connector uniselector RS which provides access to the outgoing trunk lines TLC. Also an idle register STDR is taken into use over the register connector RC. Earth is now applied over contact K3 to the element TE in the selected register which allows relay MC to operate, if the common v.f. register is idle as evidenced by battery upon the T lead, and so extend the register STDR to MFR over contacts MC1 to MC6. Relay CPB now operates. The prefix signal being transmitted from the exchange now passes over contacts BO2, BCB2, OP2 and BO1, BCB1 OP1 and via RC6, RC7 to the in-channel of the receiving unit RSU in the v.f. register and by means not shown relay SG operates to operate relay BCB which via the contact BCB9 apply earth marking to the M wire of the terminal equipment TB. An out-band signal is thereby transmitted in acknowledgment of the prefix signal. Receipt of the out-band signal at RA provides earth on the E-wire to operate relay PF whose contacts PF4, PF5 and PF7 in the contact tree leading from the frequency generators remove the prefix signal u-v and replace it by the class-ofcaller signal as determined by the operated states of relays AO and ACB, giving W-Y for operators, W-V for coin-boxes and W-U for ordinary subscribers. The class-of-caller signal on arrival in register MFR brings up a pair of signal relays RU to RZ and a relay OK is operated over a signal validity checking circuit (not shown). Dependent upon the class of caller earth is extended over one of contacts RU1, RV1, RY1 to operate one of relays BO (ordinary subscriber), BCB (coin-box), OP (operator), which self hold. Any one one of these relays removes earth from the M-wire (via OP6, BCB6, BO6) and closes a contact (BO7, BCB7, OP8) in a class-of-caller lead to a translator. The removal of the backward out-band signal signifies the setting up of the class of caller condition at the switching centre and is effective at the exchange, by dropping relay CP, in replacing the go channel on to the hybrid transformer HYP and so removing the class-ofcall signal. The signal relays RU to RZ accordingly release followed by OK and BCP, so disconnecting the go channel (via BO2, BCB2, OP2 &c.) from the register MFR which is released as contact BCP7 drops relays CPB and MC. Regardless of whether the common register MFR has been connected to the selected register STDR (it may be in use for another call) dialling may take place. Dialling impulses reaching the outgoing relay set OCRS release relay A in correspondence which via contact A1 placing earth on the SZ-wire causes digit out-band signals to be transmitted to the terminal equipment RB. Corresponding D.C. signals on the E-wire are registered in STDR; the first digit signal may be registered in the incoming relay sets to avoid mutilation due to a delay in seizing STDR (means not shown). At an appropriate point in the registration a translator TRANS is seized and some or all the digits are transferred. Contacts TX1 to TX6 operate and earth over contact TX1 operates relay TA which via contact TA1 communicates the class of caller to information on one of leads LOS, LCB, LOP to the translator (assuming by this time the common register MFR has been taken into use). Upon the basis of this information and the routing digits the translator prepares for a selected meter pulse source for connection to the MP wire (by means not shown), which operates on the regular or variable-time interval principle, and further controls the route selector RS and initiater STDR into taking into use the v.f. register MFR for forward transmission of digits. When register STDR has finished its above operation a signal on lead ST operates relay H so dropping relay K via H1. Contact H2 extends an end of dialling signal to the trunk route TLC on lead DL and contacts K4 to K9 extend the speech path to the trunk route and connect a supervisory relay DB to wire PS. Register STDR is now free for other calls. A replying called party returns earth on wire DL to operate relay DB. For an operator call (relay or operated) contacts DB1 extend earth to the M lead and the resulting outband signal in the outing relay set operates relay D. Since neither relay AO or ACB is operated, relay DD is operated over contact D1. The ensuing reversal of line polarity at DD1 and DD2 signals the reply to the operator. For ordinary subscriber and coin-box calls relay OP in the incoming relay set is not operated and relay DB by means not shown connects the meter pulse source to lead MP and out-band signals operate relay D in the outgoing relay set. Since either relay AO or ACB is operated relay DD is unaffected and for each meter pulse either earth or battery is applied to the D lead and hence to the meter coil.