CROSSBAR DIAL TELEPHONE SWITCHING SYSTEM 113 



bulb angle iron sections with a sheet metal base. The bulb angle 

 construction provides a framework which is light in weight and has 

 the required strength, and permits an equipment mounting arrange- 

 ment which conserves space and facilitates the wiring of the apparatus. 

 The frames are welded and incorporate such features as sanitary base 

 construction, guards to protect the apparatus and wiring against 

 damage from the rolling ladders located between the rows of frames, 

 and a cable duct or runway for the A.-C. power service cables with 

 plug receptacle outlets for use with electric soldering irons, portable 

 lights, etc. 



These frame equipments are built in standardized units, which 

 provide the required flexibility to satisfy the variations in telephone 

 traffic and classes of service encountered in the different telephone 

 areas. Where it has been necessary to divide an equipment assembly 

 into several units, due to the limitations of handling, shipping and to 

 care for different classes of service, the equipments have been designed 

 so that the installation effort required for interconnecting such units 

 has been reduced to a minimum. 



The bays of equipment located at the right, in Fig. 16, equipped 

 with crossbar switches, are the primary line link bays. The vertical 

 units of these crossbar switches are wired to the subscriber lines. 

 These primary bays are made available in units of 100 and 200-line 

 capacities. As discussed previously the number of primary bays 

 provided in a line link frame may be varied to fit the traffic load of 

 the subscriber lines. The left-hand bay of this frame contains the 

 vertical file of crossbar switches, known as the secondary switches and 

 the vertical units of these switches are wired to district junctors and 

 line junctors. The line link control circuit apparatus, which is 

 common to the frame, is located at the bottom of this bay. 



Figure 17 shows a group of three frame units, namely, the sub- 

 scriber sender link, the district junctor and the district link frames, 

 which are closely associated in the trunking network and have been 

 designed as a fixed equipment group. However, for shipping reasons 

 the group is divided into three separate equipment units. The 

 district junctor circuits, consisting primarily of relays, are mounted in 

 groups on the middle frame. These groups are provided in stand- 

 ardized units of various types, such as those required to serve coin and 

 non-coin subscribers lines. A similar arrangement of frames is used 

 for the combination of terminating sender link, the incoming trunk, 

 and the incoming link frames. 



Figure 18 shows a row of subscriber sender frames and a frame of 

 "A" operator senders located at the extreme right. These frames 



