Manual Switch – In the telephone exchange all subscribers are
connected to a central switch and it is manually operated by an operator. If a
person want to call another person first he or she should call to telephone
exchange. There is a person who can connect the two subscribers together by
plugging in the exchange.
Strowger Switch - Every subscriber line ended at the Strowger switch with a
relay, referred to as line relay. This switch had stepping relays that worked
according to the dial pulses. Upon completing one digit,
the first stepping relay would activate another stepping relay. Complete
connection was achieved by serial activation of several stepping relays. The
line relays were connected to an electromechanical device called line finder.
Crossbar switch - Crossbar switch employed centralized common control
equipment which encompassed a group of equipment engaged in establishing call
set up. The
equipment was released and was available for setting up other calls once
setting up phase of a call was over. Crossbar switch replaced the line finder
with line scanner, to check when a telephone line connected to a line link
frame was off hook.
SPC switch – after the evolution of electronics, especially the
invention of the transistor, SPC switches came into use. The SPC switch
entirely replaced the electromechanical common control equipment of the cross
bar switch with electronic circuits, while retaining the same switching matrixes.
These systems employ memories based on RAM (Random Access Memory) technology,
tape and disk storage. SPC switching system was space division switching
systems.
