Circuit-switching

Circuit-switching was the approach used in the first generations of communication networks; they create a 'circuit' from one party to the other, with each switch along the path knowing about each circuit passing through them.

In the early circuit-switched networks, such as the early telephone network, the 'circuits' were actual analog physical circuits (hence the name).

Later on, networks used for data tranmission used so-called 'virtual circuits'; in these networks, the switches that formed them knew about the virtual circuits passing through them.

This is fundamentally different from a reliable byte stream in a packet-switching network, where the switches (routers) have no idea about the byte streams which may be passing through them.