400 BELL SYSTEM TECHNICAL JOURNAL 



(Group II) are routed through one .t^^roup of repeaters reached from 

 the "O" level of the incoming 1st selectors, if destined for Long 

 Beach and Santa Monica; and through a different group of repeaters 

 reached from the 6th level of the incoming 1st selectors, if destined 

 for the Norwalk-Artesia-Beliflower exchange area. The transmission 

 gain of this second group of repeaters is higher than that of the first 

 group. 



Another arrangement is to use terminal repeaters in the tandem 

 trunks, and to provide pads in certain of the paths between the tandem 

 switches. The longer-haul connections are routed through the tandem 

 switches over paths not containing pads, while terminal and other 

 short-haul connections are routed over paths containing pads. This 

 arrangement is indicated in connection with the New Haven tandem 

 arrangements shown in Fig. 10, where the trunks to New London 

 appear on the 6th level of the tandem second selectors without pads, 

 and on the 7th level with pads. 



Still another means of obtaining transmission gain is to provide a 

 second group of trunks to the tandem office over which calls to the 

 more distant offices are routed. For convenience to the operators, 

 these trunks are sometimes designated as a separate tandem system 

 as, for example. Empire Tandem in New York City, which consists of 

 special, high-grade trunks to Suburban Tandem. In the Southern 

 New England System, two groups of trunks are provided between 

 certain of the tandem centers, as show^n in Fig. 9, the routing code 

 determining which group shall be used. 



Speed of Operation 

 As might be expected, the speed with which connections can be 

 made through tandem systems varies considerably, depending upon 

 the type of arrangement employed. Table II indicates the relative 

 theoretical speed of operation, in seconds, of some of the more common 

 tandem arrangements. Direct trunks frorn the tandem equipment 

 to the called office (distant city, in the case of toll office tandems) are 

 assumed; if sub-tandems are involved, a small amount of additional 

 time is required. Also a slight additional time is involved, in the 

 case of step-by-step tandems, if repeaters must be dialed in. 



Use of Tandem Systems in Toll Board Operation 



While tandem systems have been developed primarily for local and 



short-haul toll station-to-station traffic handled on manual or dial 



"A" boards, arrangements have been provided in a number of cities 



which give toll board operators access to existing tandem systems in 



