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From Wiki-FL

OC-3 - See optical carrier 3.
ONU - See optical network unit.
optical carrier 3 (OC-3) - An fiber optic line carrying 155 megabits per second; a U.S. designation generally recognized throughout the telecommunications community worldwide.
optical network unit (ONU) - A form of access node that converts optical signals transmitted via fiber to electrical signals that can be transmitted via coaxial cable or twisted pair copper wiring to individual subscribers. (See hybrid fiber/coax.)