When a site is connected to the network, new PVCs may be added when there is a demand for new sites, additional bandwidth, alternate routing, or when new applications require existing ports to talk to one another. Although the actual path taken through the network may vary from time to time, such as when automatic rerouting takes place, the beginning and end of the circuit will not change. PVCs are popular because they provide a cost-effective alternative to leased lines. Provisioning PVCs requires thorough planning, a knowledge of traffic patterns, and bandwidth utilization. There are fixed lead times for installation which limit the flexibility of adding service when required for short usage periods.
Users specify a destination address similar to a phone number.
Implementing SVCs in the network is more complex than using PVCs, but is transparent to end users. The network must quickly establish the connection and allocate bandwidth based on the user's requests. Finally, the network must track the calls and bill according to the amount of service provided. Although SVCs were defined in the initial frame relay specifications, they were not implemented by the first carriers or vendors of frame relay. Today, applications well-suited to SVCs are driving its deployment.