ATM provides a connection oriented interface to attached hosts. To reach a remote destination over an ATM network, a host must establish a connection. ATM offers two kinds of connections. The first one is known as Switched Virtual Circuit ( SVC ) and the second one is known as Permanant Virtual Circuit.
A switched Virtual Circuit operates like a conventional voice telephone call. A host communicates with it's local ATM switch to request that the switch establish an SVC. The host specifies the complete address of a remote host computer and the quality of service required. The host then waits for the ATM network to creat a circuit. The ATM signalling system establishes a path from the originating stacross the ATM network, to remote host computer. The remote computer must agree to accept the virtual circuit.
In the case of Permanant Virtual Circuits , an administrator interacts with switches in an ATM network to configure virtual circuits by hand. The administrator specifies the source and destination of the circuit, the quality of service the circuit will receive, and the 24- bit identifiers each host uses to access the circuit.