System. Over the next fifteen years, this more than quadrupled to over one trillion. A increasing fraction of this traffic was for the long-haul routes in the network, between the largest cities in the nation and via the transcontinental routes. As a consequence, the build-out of long-haul plant was emphasized in investments, resulting in better quality circuits for long-haul transmissions. Due to the investments in the plant, the average speed of establishing connections was steadily decreasing throughout the 1920s, AT&T was able to effect several rate cuts in long-distance service in just a few years. However, the growth also caused major construction problems in the layout of the cable plant. By 1930, the long-haul business was handled by about 2,500 toll centers, out of 6,400 central offices in the United States and eastern Canada. The long-haul build-out in the United States was paralleled by the construction of the Trans-Canada Telephone System, having been planned immediately after the formation of the Telephone Association of Canada in 1921. A systematic approach was needed to limit the number of intermediate toll offices that relayed the calls across the country, to further reduce set-up time, and to establish technical parameters for interchange points to assure a certain level of circuit quality. In 1929, the results of this research outlined a new fundamental layout of the toll plant (circuit) and the routing of toll calls. This first continental toll switching system became known as the General Toll Switching Plan''. Hierarchical interconnections During the growth of telephone service since the first installations of telephone exchanges and the development of advanced manual and automatic switching systems, approximately 2,500 switching systems had been established in the nation that had trunks for connecting to other communities. The systems were designated as toll centers to which all local calls were routed that had to be connected to another toll center closer to the destination of each long distance call. The technological improvements since the transcontinental transmission line of 1914 required a new methodology and plan of managing the traffic. The purpose of this plan was to provide systematically a basic layout of the plant compatible with the highest practicable standards of service achievable within given economic goals. The layout of cabling and major toll centers needed optimization in the number of switching steps required along a given route to connect any two telephones on the continent. The General Toll Switching