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THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1954 



meat to the same destination form a single group of trunks in the switch- 

 board multiple. 



The use of idle triuik indicating lamps is required with such a group 

 for the following reasons: 



1. To force the traffic onto the direct trunks, if these are provided, 

 when one or more of these trunks is idle. The direct circuits are first 

 choice and calls should be routed to them when available to prevent 

 overloading the outgoing trunks from the concentrator which might 

 block traffic from other switchboards. 



2. To make all trunks to the concentrator busy to operators when all 

 intertoll trunks outgoing from the concentrator are in use. Fig. 13 is a 

 simplified schematic of the idle indicating chain used in an outward 

 switchboard for a group of trunks containing both direct and concen- 

 trator trunks. The arrangement shown is for a group consisting of direct 

 trunks and trunks to a single concentrator. The idle indicating facilities 

 are flexible and any desired grouping arrangement is attainable. A few of 

 these arrangements are indicated by showing the relations of the jacks 

 in the switchboard multiple. 



USE OF THE INTERTOLL TRUNK CONCENTRATING EQUIPMENT IN AN OP- 

 ERATOR ALTERNATE ROUTING ARRANGEMENT 



The intertoll trunk concentrating equipment as previously stated is 

 an independent system and its use and location are therefore flexible. 



ORIGINATING TOLL CENTER 



OUTWARD TOLL 

 SWITCHBOARDS 



DIRECT 



CIRCUITS 



7 OR 8 DIGITS 



CONCENTRATOR 



CIRCUITS 



7 OR 8 DIGITS 



TANDEM TRUNK 



CIRCUITS 



NO. 4 TYPE 



TOLL OFFICE 



10 OR n DIGITS 



TERMINATING 

 TOLL CENTER 



NO. 4 TYPE 



TOLL OFFICE 



OR 



CROSSBAR 



TANDEM 

 OFFICE 



Fig. 14 — Use of concentrating equipment in an operator alternate routing 

 arrangement. 



