A connection that to the end-user behaves like a circuit but is actually realized in some other way, typically by the use of some form of packet switching system. A virtual circuit must be brought into existence or created before it can be used, and after use it will normally be dismantled or cleared. Usually this creation and clearing will be undertaken by the users of the system, by means of an appropriate protocol. A permanent virtual circuit (PVC) is created by the operator of the network system and cannot be cleared down by the user. The use of virtual circuits is usually associated with connection-oriented network services. Virtual circuits tend to be favoured by agencies that charge for the use of telecommunications systems, such as PTTs and PNOs, as the appropriate charging can be driven by the actions of creating and clearing the virtual circuit.