Transmission Design of Intertoll Telephone Trunks

S E P T E M B E R 1953 19BS, American Telephone and Telegraph Company Copyright, Transmission Design of Intertoll Telephone Trunks By H. R. HUNTLEY (Manuscript received June 12, 1953) At the 1952 Minneapolis summer meeting of the A.I.E.E. a symposium* on the nationwide toll switching plan went into such features as the fundamental plant layout, numbering plan, toll switching and automatic accounting equipments. The present paper is intended to round out this coverage of the plan with a further discussion of the transmission features. THE PROBLEM In the new nationwide toll switching plan using switching machines the layouts of toll circuits and the routings of traffic will be quite different from that of the earlier plans which were based on manual switching. Individual calls can be switched so fast and cheaply that switching is no longer a limiting factor and circuits can be laid out and used in such a way as to obtain maximum economy with few, if any, limitations from the switching standpoint. An example of these changes is given in Fig. 1 which shows in (a) the circuit groups which would be used to handle a given (assumed) flow of traffic on a manual basis and in (b) the groups which would be used to handle the same traffic on a dial basis. In (a) there are 44 different * Trans. A.I.E.E., 71, Part I, Sept., 1952. 1019 1020 T H E B E L L SYSTEM TECHNICAL J O U R N A L , S E P T E M B E R , 1953 (a) RINGDOWN OPERATION · REGIONAL CENTER -PRIMARY O U T L E T TOLL CENTER ( b ) NATIONWIDE TOLL DIALING F I N A L GROUPS c