438 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 



at a T-40 grade of service and an occupancy of 0.81 would recjuire an 

 increase of 43 per cent (to 14.3 trunks), with a corresponding decrease 

 in occupancy to 0.57. The possible savings in toll lines with alternate 

 routing are therefore considerable in a system which must pro\'ide a 

 service level satisfactory for customer dialing. 



In order to take fullest advantage of the economies of alternate rout- 

 ing, present plans call for five classes of toll offices. There will be a large 

 number of so-called End Offices, a smaller number of Toll Centers, and 

 progressively fewer Primary Centers (about 150), Sectional Centers 

 (about 40) and Regional Centers (9), one of which will be the National 

 Center, to be used as the "home" switching point of the other eight 

 Regional Centers.* Primary and higher centers will be arranged to per- 

 form automatic alternate routing and are called Control Switching 

 Points (CSP's). Each class of office will "home" on a higher class of 

 office (not necessarily the next higher one) ; the toll paths between them 

 are called "final routes." As described in Section 4, these final routes will 

 be provided to give low delays, so that between each principal toll point 

 and ever}' other one there will be available a succession of approximatelj' 

 P.03 engineered trunk groups. Thus if the more direct and heavily loaded 

 interconnecting paths commonly provided are busj- there will still be a 

 good chance of making immediate connection over final routes. 



Fig. 8 illustrates the manner in which automatic alternate routing will 

 operate in comparison with present-day operator routing. On a call from 

 Syracuse, X. Y., to Miami, Florida, (a distance of some 1,250 miles), 

 under present-day operation, the Syracuse operator signals Albany, and 

 requests a trunk to Miami. With T-schedule operation the Syracuse- 

 Miami traffic might be expected to encounter as much as 25 per cent NC 

 during the busy hour, and approximately 4 per cent NC for the whole 

 day, producing perhaps a two-minute over-all speed of serA-ice in the 

 busy season. 



With the proposed automatic alternate routing plan, all points on the 

 chart will have automatic switching systems. f The customer (or the 

 operator until customer dialing arrangements are completed) will dial a 

 ten-digit code (three-digit area code 305 for Florida plus the listed 

 Miami seven-digit telephone number) into the Jiiachine at Syracuse. 

 The various routes which then might conceivably be tried automatically 



* Sec the hihlio^rajjliy ( i);irticulMily Pilliod and Truitt) for details of tlie 

 general trunkinji plan. 



t The notation uscmI on the diagram of Fig. 8 is: Opon firclo — Primary Center 

 (Syracuse, Miamij; Triangle — Sectional Center (All)an\-, Jacksonville); Sqviare 

 — Regional Center (White Plains, Atlanta, St. Louis; St. Louis is also the Na- 

 tional Center). 



