(9) The supervisory to be held in such a manner that it can be released immediately whilst under the control of the register.

(10) The receipt of a signal from Call Control when the supervisory is required to perform the following functions:-

• (i) Receive the called party's class of service (X, Y or DDI).

• (ii) Operate the D-switch access relays and mark the switch outlet.

• (iii) Release the forward path in preparation for a second attempt at switching to the called line.

(11) Holding the switch path and the K relay in the called subscriber line circuit.

(12) A transformer-type speech bridge.

(13) The following facilities on calls to non-DDI subscribers:

• (i) The register to release and the supervisory to hold to the caller's loop.

• (ii) Connection of interrupted ringing, and ring-return battery to the called line.

• (iii) The return of ring tone to the caller.

• (iv) Disconnection of interrupted ringing, ring-return battery and ring tone when the called line answers.

(14) The following facilities on calls to DDI subscribers:

• (i) The Register to release and the Supervisory to hold to the caller's loop.

• (ii) A loop to be forwarded to seize an incoming selector at the PABX.

• (iii) further dialled digits to be repeated to the PABX.

• (iv) A metallic loop to be extended to the PABX during the dialling of a digit.

• (v) A reversal of line polarity to be detected as the 'called extension-answer' signal. 

(15) Positive-battery phased metering to take place as followsz- 

• (i) The first meter pulse to be applied when a called subscriber or extension 'answer• signal has persisted for at leaat 200ms. 

• (ii) The second meter pulse to be applied efter an interval of between 10 and 11 tenths of the call-charge period. 

• (iii) Subsequent meter pulses to be applied after an interval of 11 tenths of the call-charge period. 

• (iv) The timing to continue if the caller fails to clear after the called party has cleared. One more meter pulse is applied followed by an interval equal to 11 tenths of the call-charge period, after which the caller is 'parked' and supervisory is released. 

(16) The supervisory to be prevented from releasing whilst a meter pulse is being applied to the subscriber's meter.

(17) The supervisory to be force-released and busied against further calls, should a permanent metering signal be applied. 

(18) 'Answer' and 'clear' supervision.

(19) Lighting a SUPERVISORY ALARM lamp and giving a Deferred alarm, under the control of the ALARM EXTENSION key, should:-

• (i) The ratchet relay fail to restore to normal.

• (ii) A permanent metering condition be applied to the P wire.

(20) A call to continue without metering in the absence of the class-of-service signal of the caller.

(21) Applying call trace to the originating or terminating connection,

(22) Traffic recording.

(23) Working with a line loop of 1.3K-ohm (including the telephone instrument) and a minimum leak resistance of 50K-ohms.

(24) In a double-unit exchange, also connecting the supervisory to the switch network of either unit in order to terminate the call in either unit. (Sea section 3.7). 

3.1 Mode of Working: Own-Exchange Supervisory is Primary Choice 

Note: If the initial ('code') digits indicate that the call is to be routed out of the exchange, the own-exchange supervisory is released and the required type of outgoing supervisory is connected to the caller. The register releases. 

To connect a caller to an own-exchange supervisory relay set, Call Control interrogates all of them by extending negative battery on the OER(A) or OER(B) lead via Route Selectors {or in Mk1 and 2 exchanges, Route Relays 1). 

This causes transistor VT14 to conduct. 

If the Supervisory is free, there is a negative potential on the base of transistor VT15; therefore when transistor VT14 turns on, so does VT15. Hence an earth signal is extended via the C lead to the C-switch selector. 

The C-switch selector now selects a C switch with a free own-exchange supervisory connected to it. Negative battery is extended on the S(A)/S(B) lead to all the supervisory relay sets associated with the chosen C switch.

 This causes transistor VT16 to switch on and operate the OER relays in the free own-exchange supervisories associated with the chosen C switch. 

LN3 inhibits the operation of LR ( line reverse polarity) 

RA3 prepares a 680 ohm shunt for the speech pair.

RA4 short circuits relay E

RB1 - Operates relay BC and holds relay LN independently of MKA3

RB2 -

RB3 - busies the relay set against further calls and releases OER

RB4 allows either relay XM or YM or TIM  to operate 

(XM may operate if as a result of decoding the caller's number, an X-party COS is generated, a signal on lead X from the COS Amplifiers )

YM may operate if as a result of decoding the caller's number, an Y-party COS is generated, a signal on lead Y from the COS Amplifiers )

Relay BC opersating :-

earths the P wire and operates relay K in the calling subscriber line circuit. The resultant earth on the Call-Control KT lead gives a 'switching complete' signal to Call Control, which releases the selectors. The release of the supervisory selector releases relay MK. Contact BC1 also operates relay HA. Relay OER releasing, removes the 'free' signal to the supervisory selector. If, as a result of decoding the caller's number, an X-party COS is generated, a signal on lead X from the COS Amplifiers operates relay XM.