ODU4

ODU4, or Optical Data Unit 4, is the Optical Data Unit level used in the Optical Transport Network (OTN) architecture. It provides a high-capacity transport container for carrying client signals across optical networks and is part of the ITU-T definitions that govern OTN framing, multiplexing, and management. ODU4 sits at the upper end of the original fixed-rate ODU hierarchy and is designed to support substantial payloads with accompanying overhead for network functions.

In practical terms, ODU4 supports payload data rates suitable for high-capacity traffic, including mappings of 40G and 100G Ethernet, Fibre Channel, and other client signals. It can be used in fixed mappings or via flexible payload schemes (ODUflex) to accommodate variable-rate traffic within the same architectural framework. The framing structure of ODU4 includes overhead and payload regions, with mechanisms for alignment and timing to maintain integrity over long-haul or metro networks. This structure enables efficient multiplexing, protection, and synchronization across the transport path.

ODU4 is typically transported over OTU4 (the corresponding optical channel), forming a core part of backbone and data center interconnect networks. It supports network features such as error monitoring, management, and protection switching, and can be combined with techniques like virtual concatenation to extend payload capacity beyond a single ODU4 container when needed. While newer flexible approaches exist, ODU4 remains a fundamental building block in many 100 Gbit/s class optical transport implementations and remains a reference point for high-capacity OTN deployments.