440 



THE BELL SYSTEM TECHNICAL JOURNAL; MARCH 1956 



tomer will not ordinarily need to hang up when NC is obtained. When 

 he himself dials, a second trial after a short wait following NC should 

 have a high probability of success. 



Not many situations will be as complex as shown in Fig. 8; commonly 

 several of the links between centers will be missing, the particular ones 

 retained having been chosen from suitable economic studies. A large 

 number of switching arrangements Avill be no more involved than the 

 illustrative one shown in Fig. 9(a), centering on the Toll Center of 

 Bloomsburg, Pennsylvania. The dashed lines indicate high usage groups 

 from Bloomsburg to surrounding toll centers; since Bloomsburg "homes" 

 on Scranton this is a final route as denoted by the solid line. As an exam- 

 ple of the operation, consider a call at Bloomsburg destined for Williams- 

 port. Upon finding all direct trunks busy, a second trial is made via 

 Harrisburg; and should no paths in the Harrisburg group be available, 

 a third and final trial is made through the Scranton group. 



In considering the traffic flow of a network such as illustrated at 

 Bloomsburg it is convenient to employ the conventional form of a two- 

 stage graded multiple having "legs" of varying sizes and traffic loads 

 individual to each, as shown in Fig. 9(b). Here only the circuits im- 

 mediately outgoing from the toll center are shown; the parcels of traffic 



(a) GEOGRAPHICAL LAYOUT 

 WILLIAMSPORT I 



SCRANTON 



BLOOMSBURG 

 HARRISBURG PA. 



(b) GRADED MULTIPLE SCHEMATIC 



FRACKVILLE 



HAZLETON 



WILKES- 

 BARRE 



PHILADELPHIA 



FINAL GROUP TO SCRANTON 



H.U. GROUP TO HARRISBURG 



.1 M t 



I 



NO. TRUNKS IN H.U. GROUPS I [T] [jF] [^ [A] [T] [28 1 rsl m 



LOAD TO AND FROM ^^^ .^. ^^ ^ 



DISTANT OFFICE (CCS) "^^^ '^' ^^ ^'^^ ^^' '^0 '^3 836 228 154 



DISTANT OFFICE SCRN HBG PTVL SHKN SNBY WMPT FKVL HZN WKSB PHLA 



Fig. 9 

 liiirg, Pa. 



Aulonialic ;ilU'riiaie routing for direct distance dialing at Blooms- 



