ODUs

ODU stands for Optical Data Unit, a fundamental data container used in the Optical Transport Network (OTN) defined by ITU-T standards. An ODU carries client payloads through an optical transport system and is carried inside an Optical Transport Unit (OTU), which provides the framing, overhead, and error management required for long-haul transmission. The ODU is designed to multiplex a variety of client signals, such as Ethernet, Fibre Channel, PDH/SDH, or other data streams, into a standard transport format while enabling performance monitoring and protection mechanisms.

The ODU family includes several fixed-rate types and a flexible option. Common variants are ODU0, ODU1, ODU2, ODU3, and ODU4, each supporting different payload capacities to match the bandwidth needs of the transported client signals. In addition, ODUflex provides a flexible bandwidth option that can carry varying payloads up to a maximum nominal rate, enabling more efficient use of available capacity for bursty or variable traffic. An ODU is encapsulated within an OTUk frame (the optical transport unit) for transmission, with forward error correction (FEC) and overhead to ensure signal integrity and alignment across the network.

Operation and management in an OTN context include multiplexing and demultiplexing of ODUs, as well as supervisory functions and performance monitoring at the ODU and OTU layers. ODUs enable scalable, architecture-neutral transport across heterogeneous networks and are central to the efficiency and resilience of modern optical networks.

See also: Optical Transport Network, OTU, OTN standards (ITU-T G.709, G.872).