Voice and Voice Over IP

Today, the world has two separate and distinct public
networks. The public switched telephone network
(PSTN) has been in operation for well over a century. The
technological advances have been impressive, but the principle
is little changed from the days of manual switchboards. A
connection is switched from the caller to the sender by selecting
idle circuits from a pool and interconnecting them end-toend.
The connection is stable, exclusive to the parties, and
quality is so good that an intercontinental call can hardly be
distinguished from a local one.