ircuits within a path, and paths accommodating two or more circuits or connections. Switched virtual circuit (SVC) means the user pays a fee to gain access to the network, usually a fixed monthly charge based on port capacity and any local loop or access line cost. The user also pays an additional fee each time the network is used, similar to the long distance phone call model. Sometimes called bandwidth on demand, the service is billed according to amount of bandwidth, class of service, and time used. It can be very cost effective within a range of practical, day-to-day content transport needs. A permanent virtual circuit (PVC) means that the carrier or service provider configures the network to provide service between two or more locations on a permanent basis. Depending on the way the service is ordered and configured, it can be flexible and complex to use, or rigid and easy to use. If the service is configured as a perman- PRACTICAL IP AND TELECOM FOR BROADCAST ENGINEERING AND OPERATIONS ent virtual path (PVP), this means the user can configure multiple circuits aggregating up to the maximum amount of bandwidth avail- able on the path. If that's one circuit on one path, SO be it. If that's X number of circuits with equal or unequal amounts of bandwidth, that works too. On the other hand, if the carrier configures PVC service, it can't be changed by the user, but only by the carrier after an order for changed or new service is issued. This has economic and operational implications, which may be significant or insignificant. For example, if the circuit is in use 24/7, as might be the case with a studio-to- transmitter link (STL), it may be necessary to go off air to make changes. If that is not acceptable, then establishing a new set of access and transport facilities and then moving the traffic to the new facility, followed by decommission of the other facility in previous use. Both PVC and SVC have configuration parameters that should be considered carefully when specifying and commencing use of ATM transport