OCx - Optical Carrier levels:

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.

OC-1 = 51.84 Mbps
OC-3 = 155.52 Mbps
OC-9 = 466.56 Mbps
OC-12 = 622.08 Mbps
OC-24 = 1.244 Gbps
OC-36 = 1.866 Gbps
OC-48 = 2.488 Gbps
OC-96 = 4.976 Gbps
OC-192 = 9.953 Gbps
OC-255 = 13.219 Gbps