• Permanent Virtual Circuits (PVC) - a hard coded connection defined link by link by the system administrator.  There are no rerouting capabilities if any link fails.


• Switched Virtual Circuits (SVC) - Uses edge devices which have ATM End Station Addresses (AESA) consisting of 40 hexadecimal characters (20 bytes).  A target switch received a User-Network Interface (UNI) signal and tries to set up an SVC by finding a path between two edge devices by using one of two routing protocols:

• Interim Inter-Switch Protocol (IISP) is an older protocol that is a statistically created routing algorithm that is not easily scalable.


• Private Network-to-Node Inferface (P-NNI) is a scalable, dynamic routing algorithm.

Using one of the protocols, the signal request is routed through the network and a path is determined between two edge devices.  Once the SVC is set up, data is then switched and transmitted between the devices.