Used to specify the speed of fiber optic networks. The base rate (OC-1) is 51.84 Mbps. OC-2 runs at twice the base rate, OC-3 at three times the base rate (155.52 Mbps), etc. Common rates are: OC-1, OC-3, OC-12, OC-24, and OC-48. Below is a table of theoretical throughput (approximate) for various OC levels.