OC3 line – Optical Carrier with 3x the Speed of an OC1
An OC3 line is a leased line transmitting at 155.52Mbit/s. It has a payload of 148.608Mbit/s, and an overhead of 6.912Mbit/s.
OC stands for Optical Carrier. The '3' refers to the speed: an OC3 line is three times as fast as an OC1 line.
The 'optical' bit refers to a Synchronous Optical Networking (SONET) fiber optic network.