398 BRLL SYSTEM TECHNICAL JOURNAL 



It may be mentioned, in passing, that the Connecticut tandem system 

 shown on Fig. 10 does not make use of any step-by-step "B" board 

 equipments. 



An arrangement using intermediate dialing or intermediate key 

 pulsing circuits is used in a few cases, in lieu of the " B " board arrange- 

 ment, as a sub-tandem for completing calls incoming to step-by-step 

 central offices from a manual straightforward tandem system in a 

 nearby large city, such as to dial subscribers in Trenton, New Jersey, 

 from the Newark manual tandem system. Straightforward trunks 

 from the manual tandem switchboard terminate on step-by-step 

 selectors, and on multipled line lamps and answering jacks in the 

 regular switchboard at the incoming end of the trunk, with an auxiliary 

 circuit for lighting the line lamps on an incoming call. When the 

 inward operator plugs into an answering jack in response to a lamp 

 signal, an order tone automatically is sent back over the trunk to the 

 originating operator, who thereupon passes the called number. On 

 key pulsing switchboards, the inward operator sets up on her key 

 set, the desired number, and disconnects from the trunk. On dialing 

 boards, the inward operator dials the called number over a dialing 

 jack associated with the trunk, using a second cord, and disconnects 

 both cords. Release of the connection at the tandem and called offices 

 is under the control of the originating operator. 



When used in conjunction with a step-by-step tandem, the inter- 

 mediate dialing or key pulsing arrangement serves the same purpose, 

 for a limited amount of traffic, as the step-by-step " B " board arrange- 

 ment described above. 



Trunk Concentratmg Tandems 



Where small volumes of traffic to the same terminating point origi- 

 nate at a number of offices which are closely associated, geographically, 

 trunk costs frequently may be reduced through the use of trunk con- 

 centrating switches. Both direct trunks and trunks to a tandem 

 system are treated in this manner. 



While different types of switches are used under the various con- 

 ditions encountered in practice, all function automatically to select a 

 trunk in a common trunk group, or the switches are permanently 

 associated with the common trunks and operate to find the incoming 

 trunk on which a call is waiting. No dial pulses are required to cause 

 the connection between the trunks to be made, and to switchboard 

 operators the outgoing trunks are practically the equi\alent of direct 

 trunks to the called office, or to the tandem office, as the case may be. 



Figure L^ shows schematicalh- the use of trunk concentrating 



