INTERTOLL TRUNK CONCENTRATING EQUIPMENT 311 



Completion of Calls 



The basic circuit components of the intertoU trunk concentrating 

 equipment are shown in Fig. 4. Three incoming trunks in different groups 

 and from different switchboards are shown. Two outgoing trunks in 

 different groups are also shown. Assume that the controller is conditioned 

 to serve both incoming and outgoing trunks in the low to high order, 

 that a call is placed on incoming trunk 14 and a short time later on 

 incoming trunk 21, and that outgoing trunks 04 and 36 only are avail- 

 able for selection. Seizure of trunk 14 at the originating switchboard 

 causes the incoming trunk to place a ground on the start lead of incoming 

 trunk group 1. This ground indicates to the controller that a trunk in 

 incoming group 1 is calling for service. The controller then closes the 

 gate to all other ten groups, tests the select magnets associated with 

 horizontal 04 for crosses (since outgoing trunk 04 is first in order for 

 selection) and finding none operates the select magnets. It then tests 

 the hold magnets associated with vertical 14 and finding no crosses oper- 

 ates the hold magnets, thus closing the crosspoint whose coordinates are 

 (04, 14) connecting incoming trunk 14 to outgoing trunk 04. The outgo- 

 ing trunk transmits a seizure signal over the intertoll facilities to the 

 distant end which then transmits a signal back to incoming trunk 14, 

 which relays the information to the controller. The controller then re- 

 leases from that connection, opens the gates and admits the call waiting 

 on incoming trunk 21. It proceeds to complete this call to outgoing 

 trunk 36 which is next in order of selection in a similar manner. 



If in the assumed case outgoing trunk 36 was the last trunk then 

 a^'ailable for selection the controller would, at the completion of selection 

 of trunk 36, proceed as follows: 



(1) If any of the other outgoing trunks which had been locked out 

 were idle the controller would now make these trunks available for 

 selection. 



(2) If no trunks were idle the controller would wait, and cause a 

 signal to be transmitted to all associated outward switchboards. This 

 signal will prevent the lighting of idle trunk indicating lamps at each 

 switchboard. When one or more outgoing trunks become idle the con- 

 troller will make them available for selection and will permit the idle 

 trunk indicating lamps at the associated switchboards to light as an 

 indication that trunks arc available. 



Component Circuits of the Controller 



In the following paragraphs the component circuits of the controller 

 will be described individually. The descriptions of these circuits contain 

 the minimum of detail reciuired to understand how they function. 



