Before a computer on an ATM network can send any data, it must first establish a virtual circuit connecting it to the destination. Virtual circuits are point to point and bi-directional. Virtual circuits are established within virtual paths. A series of virtual paths can be connected to form a virtual circuit. Many circuits can be supported by one virtual path.
Many virtual paths can exist over a single transmission path.
ATM switches perform the routing in an ATM network. The Virtual Circuit Identifier and the Virtual Path Identifier in the ATM cell header indicate to the ATM switch how a packet should be routed. Virtual paths can be permanent or switched. A permanent virtual path is established by the network manager and exists for a long period of time, often for the life of the network. Virtual circuits can be routed over the existing permanent virtual circuits.