TANDEM OPERATION IN THE BELL SYSTEM 



399 



switches for giving local operators in Philadelphia access to a common 

 group of trunks terminating on the straightforward toll line tandem 

 in New York City. A more extensive use on intercity traffic is in 



PHILADELPHIA 

 TOLL BUILDING 



INCOMING STRAIGHTFORWARD 

 TRUNKS FROM PHILADELPHIA 

 DIAL SWITCHBOARDS 



116 CIRCUITS 



44 POINT TRUNK HUNTING 

 SWITCHES. ONE SWITCH 

 PER INCOMING TRUNK 



TO CORDS AND PLUGS IN CORD 



ENDED STRAIGHTFORWARD 



TOLL LINE TANDEM POSITIONS 



IN THE NEW YORK TOLL BUILDING 



40 CIRCUITS 



Fig. 13— Trunk hunting switch arrangement for Philadelphia to New York station- 

 to-station "A" board toll traffic. 



San Francisco and Oakland, California, chiefly for giving offices in 

 each of these cities direct access to offices in the other city. In San 

 Francisco, 62 incoming trunk groups containing 384 trunks are con- 

 centrated on 19 trunk groups and 239 trunks. In Oakland, 188 

 incoming trunk groups, containing 881 trunks, are concentrated on 

 25 trunk groups and ii?> trunks. 



Transmission Arrangements Affecting Traffic Operation 

 Tandem systems, unlike the general long distance system, operate 

 within definite areas and the associated trunks usually are designed 

 to give satisfactory transmission on connections between any two 

 offices in the tandem area. In some of the larger systems, however, 

 the tandem area is divided into transmission zones and the arrange- 

 ments provided for traffic between the different zones may require 

 the selection of the proper trunks or paths on the part of the operators. 

 One arrangement is to introduce telephone repeaters in certain of 

 the paths between the selectors in the tandem equipment, and to 

 route connections requiring repeater gain through these paths. Figure 

 14 shows schematically the Los Angeles long-haul step-by-step tandem 

 system, in which this arrangement is used. It will be noted, for 

 example, that connections from offices in the Metropolitan Area 

 (Group I) to Long Beach and Santa Monica use no repeaters at the 

 tandem office; and that connections from certain outlying offices 



