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THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1953 



RANDOM 



PREFERENCE 



CIRCUIT 



MONITOR 



Fig. 17 — Originating position — right side. 



Line pegs are removed from the array while they are occupied on a 

 call. The jack thus remains empty during the busy interval. The origi- 

 nating operator utilizes a hne peg and a call slip in originating each dial 

 tone call. 



The incoming trunk and register arrays are located on the left column 

 at this position as shown on Fig. 16. The incoming trunk array consists 

 of pegs and jacks arranged in accordance with the trunk groups. The 

 primary horizontal grouping is assigned a route number which is used 

 only for identification purposes. The horizontal rows within a route rep- 

 resent the number of the trunk link frame switch on which the trunk is 

 located. Vertical rows represent trunk link frames. Provision is made 

 for a maximum of 400 incoming trunks. Trunk identification is a four- 



