An outline of the trunking aspect of automatic telephony

After an introduction defining the scope of trunking, the ideas ¿traffic unit¿ and ¿grade of service¿ are investigated in some detail. The history of trunking is touched on briefly, this Section terminating with a description of the means provided in modern exchanges for connecting one rank of switches with another. The traffic-carrying capacity of switches under the ¿ full availability¿ condition leads to a consideration of the possible methods of trunking when the availability is ¿limited.¿ The particular method called ¿grading¿ is described in detail and the traffic capacity of various grading arrangements is investigated. The effect of changes in the distribution of traffic is next considered, and then information is collected regarding the design curves used by the Post Office. The paper closes with a description of the methods adopted in the Post Office for measuring traffic and traffic overflows, and of the use made of these measurements.