Circuit switching – a direct physical connection between two devices is created by space-division switches, time-division switches, or both. Circuit switching takes place at the physical layer. In circuit switching, the resources need to be reserved during the setup phase; the resources remain dedicated for the entire duration of data transfer until the teardown phase.
Packet switching – there is no resource allocation for a packet. This means that there is no reserved bandwidth on the links, and there is no scheduled processing time for each packet. Resources are allocated on demand. Packet switching uses either the virtual circuit approach or the datagram approach.
Message switching – has been phased out in general communications but still has networking applications.