Frame Relay is a Packet-Switching L2 protocol, it has no error recovery and only focus on speed. Higher level protocols can provide that if needed. PVC (Permanent Virtual Circuit): Always up, ready to transmit data. Form logical end-to-end links mapped over a physical network. SVC (Switched Virtual Circuit): Calls up when it needs to transmit data and closes the call when it is done. Uses DLCI (Data Link Connection Identifiers) to identify the virtual connection, this way the receiving end knows which connection an information frame belongs to.