OC3

OC-3, or Optical Carrier level 3, is a standard interface in the SONET/SDH telecommunications hierarchy that carries data at a nominal rate of 155.52 megabits per second. In SONET terminology it corresponds to STS-3, and in SDH terms to STM-1. OC-3 is formed by multiplexing three STS-1 signals into a single OC-3 signal, providing a higher-capacity backbone link suitable for metro and long-haul networks.

Technically, an OC-3 frame includes overhead for transport, section, line, and path management, along with a payload for user data. The payload can carry a variety of service types, such as DS-3, Ethernet, or ATM, using established mapping and multiplexing techniques. The optical signal is usually transmitted over fiber and can use standard telecom wavelengths around 1310 or 1550 nanometers, with the option to carry multiple OC-3 channels over a single fiber via wavelength-division multiplexing.

Deployment and use have historically been widespread in North American telecom networks since the 1990s as a standard rate for access and backbone links. OC-3 remains in service in some networks for legacy equipment and cost reasons, but many operators have migrated to higher-rate OC-n systems (such as OC-12 or OC-48) or to packet-based Ethernet transport as part of network modernization.

See also: SONET, SDH, OC-n, STS-1, STM-1, DS-3.