INTERTOLL TRUNK CONCEXTKA'llXi; IXjUll'MENT 309 



are made a part of th(^ incominjj; dunk circuits rather than a part of the 

 less numerous out.t>;oint>; trunks to which th(\v may l)e switched. Swilchinfj; 

 Ix'twccii inconiiiiii' ;ind outgoinu; trunks is thci'efore jjerformcd on a four- 

 wire basis. 



Controller CircuH 



The controUcM' circuit is the control element of the trunk concent I'ating 

 ecjuipmeiit. Its primary function is to select the incoming and outgoing 

 trunks to be interconnected and to operate the proper select and hold 

 magnets of the associated switches to close the required crosspoint. 

 Since the controller circuit is described in some detail latei-, only the 

 general principles of it will be dealt wdth at this time. 



The controller divides the incoming trunks into ten groups, (0 to 9), 

 of ten trunks each. When idle it admits calls for a very short interval 

 and then closes gates which exclude all other groups until calls recog- 

 nized, within the gate, have been served. The controller serves the groups 

 and trunks within the gate in one of two orders depending upon the 

 direction of selection existing at the time. In one case selection will 

 start with the lowest numbered trunk in the lowest numbered group 

 and progress to the highest numbered trunk in the highest numbered 

 group. In the other case the order will be reversed starting with the 

 highest numbered trunk in the highest numbered group and progressing 

 to the lowest numbered trunk in the lowest numbered group 



The controller also divides the outgoing trunks into four groups, (0 

 to 3), of ten. The outgoing trunks are served in order, either from low 

 numbered to high numbered trunks or vice-versa. Once selected, the 

 outgoing trunk remains locked out, after use, until all triuiks have been 

 used, or until a trouble condition causes a reversal of the direction of 

 selection of the outgoing trunks. 



To avoid comiecting an incoming trunk to two outgoing trunks or 

 connecting two incoming trunks to an outgoing trunk the controller 

 tests both the select and hold magnets for possible trouble conditions, 

 such as crosses, before operating them. 



Each intertoll trunk concentrating equipment has but one controller. 

 If the controller ceased to function the entire concentrating ecjuipment 

 would be out of service. To insure reliability the philosophy was adopted 

 in the design that no single trouble should disable the controller. This 

 accounts for some of the features, the reasons for which otherwise are 

 not obvious. 



