The core technology behind the public switched telephone network, i.e., the voice services offered by telephone companies.
In this type of network, a "permanent" circuit is set up between the originating and destination point for the duration of the call or transmission. This is in contrast to packet switched networks in which pieces of an individual message or transmission could - and likely do, take numerous paths from beginning to end.
A key advantage to circuit-switched networks is reliability.
A key disadvantage is capacity - it can be expensive to add additional resources, which puts such networks at a disadvantage in an era of rapdily expanding use of data networks, such as the Internet. According to Lucent, the average duration, or "holding time," of a voice call is three minutes, while an Internet session could easily last several hours. In addition, data streams are limited to 64k bits/sec (or multiples of that).
Because of such issues, carriers in recent years have begun either moving to packet networks or using devices such as softswitches to offload data traffic onto dedicated packet networks.
