OC-1, OC-3, OC-12, OC-24, OC-48
Optical Carrier transmission speeds, used in fiber optic networks conforming to SONET standard.
OC-1 is 51.85 Mbps.
Higher levels are multiples of that speed (i.e. OC-3 transmits 155,000,000 bits per second ,which equals 3 x 51.84 Mbps).