|  | 2.1 | WAN Technology
| 2.1.3 | WAN virtual circuits
A virtual circuit is a logical circuit, as opposed to a point-to-point circuit, created to ensure reliable communication between two network devices. Two types of virtual circuits exist: switched virtual circuits (SVCs) and permanent virtual circuits (PVCs). SVCs are virtual circuits that are dynamically established on demand and terminated when transmission is complete. Communication over an SVC consists of three phases: circuit establishment, data transfer, and circuit termination. The establishment phase involves creating the virtual circuit between the source and destination devices. Data transfer involves transmitting data between the devices over the virtual circuit, and the circuit-termination phase involves tearing down the virtual circuit between the source and destination devices. SVCs are used in situations where data transmission between devices is sporadic. SVCs increase bandwidth used due to the circuit establishment and termination phases, but decrease the cost associated with constant virtual-circuit availability. A PVC is a permanently established virtual circuit that consists of one mode: data transfer. PVCs are used in situations where data transfer between devices is constant. PVCs decrease the bandwidth use associated with the establishment and termination of virtual circuits, but increase costs due to constant virtual-circuit availability.
| Threaded Case Study
Washington Project: WAN Technology Design
The WAN technology required for the Washington District WAN's link to the Internet is a Frame Relay PVC running at T1 speed.

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