Development of The Strowger System
The commercial version of the Strowger switch, as developed by the Strowger Automatic Telephone Exchange Company, used a rotary dial for signalling to the exchange. The original final selector (connector) switch which connected to 100 customers was supplemented by preceding group selector stages, as the "cascading" enabled connection to many more customers, and to customers at other exchanges. Another requirement for commercial systems was a circuit to detect a busy connection (line) and return a busy signal to the calling subscriber.
Instead of dedicating an expensive first-stage selector switch to each customer as in the first exchange, the customer was given access to the first-stage switch of a telephone network, often by a linefinder which searched "backward" for the calling line; so requiring only a few relays for the equipment required for each customer line.
Later Strowger (SXS) exchanges often used a subscriber uniselector as part of the line equipment individual to each line, which searched "forward" for a first selector. This was more economic for higher calling-rate domestic or business customers, and had the advantage that access to additional switches could readily be added if the traffic increased (the number of linefinders serving a group of was limited by the wiring multiple installed). Hence exchanges with subscriber uniselectors were usually used at British exchanges with a high proportion of business customers eg director exchanges, or in New Zealand where the provision of local free calling meant that residential customers had a relatively high calling rate.
The fundamental modularity of the system combined with its step-by-step (hence the alternative name) selection process and an almost unlimited potential for expansion that gives the Strowger system its technical advantage. Previous systems had all been designed for a fixed number of subscribers to be switched directly to each other in a mesh arrangement. This became quadratically more complex as each new customer was added, as each new customer needed a switch to connect to every other customer. In modern terminology, the previous systems were not "scalable".
Read more about this topic: SXS
Famous quotes containing the words development of the, development of, development and/or system:
“There are two things which cannot be attacked in front: ignorance and narrow-mindedness. They can only be shaken by the simple development of the contrary qualities. They will not bear discussion.”
—John Emerich Edward Dalberg, 1st Baron Acton (1834–1902)
“Creativity seems to emerge from multiple experiences, coupled with a well-supported development of personal resources, including a sense of freedom to venture beyond the known.”
—Loris Malaguzzi (20th century)
“Ultimately, it is the receiving of the child and hearing what he or she has to say that develops the child’s mind and personhood.... Parents who enter into a dialogue with their children, who draw out and respect their opinions, are more likely to have children whose intellectual and ethical development proceeds rapidly and surely.”
—Mary Field Belenky (20th century)
“Few white citizens are acquainted with blacks other than those projected by the media and the so—called educational system, which is nothing more than a system of rewards and punishments based upon one’s ability to pledge loyalty oaths to Anglo culture. The media and the “educational system” are the prime sources of racism in the United States.”
—Ishmael Reed (b. 1938)