The OC level is primarily used as a regional ISP backbone, and occasionally by very large hospitals, universities, or other major enterprises is OC-48.
OC-12 is a network line with communication speeds of up to 622.08 Mbit/s (payload: 601.344 Mbit/s; overhead: 20.736 Mbit/s). OC-12 lines are generally used by ISPs as wide area network (WAN) connections.
A data-link connection identifier (DLCI) determines the Frame Relay PVC. Frames are routed through one or more virtual circuits determined by DLCIs.
Each DLCI has a permanently configured switching path to a particular destination
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