Structured modules from fiber basics to 400G coherent. In-depth coverage of DWDM, OTN, coherent optics, network design, and more — written by field engineers. Glossaries, troubleshooting guides, optical formulas, 80+ infographics, and ITU-T standards references. Optical. An optical transport network (OTN) is a digital wrapper that encapsulates frames of data, to allow multiple data sources to be sent on the same channel. Aggregate size can scale in steps. OTN—or Optical Transport Network—is a telecommunications industry standard protocol— defined in various ITU Recommendations, such as G.