Optical Carrier Series of physical protocols (OC-1, OC-2, OC-3, and so on) defined for SONET optical signal transmissions OC signal levels put STS frames onto multimode fiber-optic line at a variety of speeds The base rate is 51 84 Mbps (OC-1); each signal level thereafter operates at a speed divisible by that number (thus, OC-3 runs at 155 52 Mbps) See also SONET and STS-3c