The switching introduction of electronics for switching

A purely manual switching system couldn't be kept in use for a long time because the necessary personnel rapidly increases with the number of subscribers. For example, it was calculated that a Graham Bell type system having all the subscribers of today connected to it will require the whole population of the United States as its personnel. The development of telephone required more economical methods and fewer persons. So were born the rotary selector switches ("Stroger", "Rotary", "R5") one along with the other. To find out the number calling, these systems conducted a sequential search of the subscribers states ; using a sequential search as well, the connection with the called number was established. These systems allowed the development of local automatic telephone. But the sequential search could not make the International Automatic Switching Feasible. This problem was solved by the invention of the "multi-selectors", this was the "CROSSBAR".