Abstract :
Switching system architectures have evolved to be responsive to the needs of the user. Their design has been constrained by the existing environment which treats terminals, transmission channels, and switching entities as separate "black boxes." Telephone switching circuits have used relatively expensive discrete components, and hence, system designers used common control techniques to minimize the system cost. This was done by providing the circuits in common whenever this was possible. Such common circuits were associated with a switched path for the period of time for which the functions of the circuit were required. This was followed by "one at a time" operation and by the use of stored program controls. The advent of low-cost electronic circuit components has resulted in the application of digital techniques to switching systems. For the first time, the combination of switching and transmission is possible. This is the near-term objective. The long-term objective, made possible by forecasts of low-cost memory and electronic gate circuits, is the combination of switching, transmission, and the terminals. This will result in much more complex terminals.
