Circuit switching is a networking paradigm
that involves the creation of persistant circuits, or paths, between two nodes in the network. One good example of a circuit-switched network is the public telephone
In circuit switched networks, when one node wants to send information to another, it "calls" the other node. A circuit is then established between the two nodes. In traditional circuit switching, as with the telephone network, this circuit uses a fixed amount of bandwidth (digital or analog), regardless of whether data is being sent. This can be wasteful, but provides assurance that the entire bandwidth of the connection will be available at any time while it is open.
Circuit switching has been around for a long time. The first telephone networks were circuit switched networks, even though human operators did the switching. As time marched on, mechanical, and then later, electronic machines did the switching.
Modern circuit switching, such as with ATM, can vary the amount of bandwidth allocated to a circuit dynamically, so an idle circuit does not consume bandwidth. This provides the flexibility of circuit switching without the waste of bandwidth in idle circuits.
Contrast packet switching, where there are no "connections", just individual packets with source and destination information that compete for available bandwidth.