402 BELL SYSTEM TECHNICAL JOURNAL 



order that they may complete person-to-person and other calls to 

 points within the tandem area over tandem trunks rather than over 

 the regular long distance circuits. Tandem systems in general make 

 use of common battery trunks and, since some of the older types of 

 toll switchboards either are not arranged to complete originating calls 

 over such trunks or are not equipped with the dialing arrangements 

 required for dialing through dial tandems, the application of this de- 

 sirable arrangement is somewhat limited. 



As indicated above, the only tandem operation involving ringdown 

 toll board circuits, at present, is for the purpose of making such 

 circuits accessible to operators at switchboard positions not having 

 a multiple appearance of the circuits. It is the belief of the author 

 that, with the further expansion of the long distance plant, the ring- 

 down circuits gradually will be replaced by through supervision cir- 

 cuits — that is, by circuits which, like the trunks used in local and 

 short-haul toll tandem operation, will give the originating operator 

 switchhook supervision from the called station. These new circuits, 

 no doubt, will be arranged for two-way and built-up circuit operation 

 and, incoming to dial areas from toll boards equipped with dials or 

 key sets, will be terminated directly on selectors. 



Although changing conditions may suggest better arrangements, it 

 seems probable that, from toll boards not equipped with dials or key 

 sets, the new circuits will be operated on a straightforward basis and 

 terminated on, or controlled at, operators' positions at the incoming 

 end. In the larger cities these positions may have equipment and 

 operating features quite similar to those in the panel sender tandem. 

 In such cities, it may well be that both straightforward and ringdown 

 incoming circuits will be terminated on switches but that the calls 

 will be received, and both terminal and through connections set up, 

 at the operators' positions, thus making use of the tandem type of 

 equipment for all switching purposes in the larger cities. Also, this 

 new inward and through toll offtce equipment may replace the present 

 type of toll office tandem equipment. In smaller cities, including 

 cities serving manual areas, the incoming circuits may be terminated 

 on equipment having features generally similar to those in the manual 

 straightforward system. 



The gradual extension of these arrangements would eventually dupli- 

 cate, in the long distance toll plant, tandem switching of the type 

 now so extensively used on the local and short-haul toll traffic, and 

 ultimately make the entire United States a super-tandem area. 



The scope of the present tandem systems has been determined 

 largely by economic considerations, although the desire to simplify 



