OTUk

OTUk, in the context of optical networking, denotes the Optical Transport Unit with a variable level k, a family of frame structures used within an Optical Transport Network (OTN). The term is defined in ITU-T recommendations that specify how high‑capacity traffic is carried, multiplexed, and managed. OTUk serves as the transport layer that encapsulates client signals and provides mechanisms for routing, protection switching, and performance monitoring across long‑haul fiber links.

An OTUk frame comprises overhead and payload. The overhead carries control, management, and synchronization information, enabling interoperability among equipment from different vendors. The payload carries an Optical Data Unit (ODUk) or other higher‑order data, depending on the network configuration. The OTU layer also incorporates forward error correction (FEC) to improve signal integrity over noisy or long routes, which is a key feature of operational optical transport networks.

Multiple levels exist, commonly referred to as OTU0, OTU1, OTU2, and OTU3, with additional variants in some specifications. Each level corresponds to a nominal data‑rate tier, ranging from a few gigabits per second to tens or hundreds of gigabits per second, depending on the particular OTUk family implementation. The exact rates and coding schemes are defined by ITU‑T standards and may evolve with new revisions.

OTUk is widely used in backbone networks, data‑center interconnects, and telecom services to multiplex diverse client signals into a single high‑capacity optical channel while maintaining interoperability and robust network management.

See also: OTN, OTU, ODU, ITU-T G.709, ITU-T G.798.