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. This creates an optical virtual private network for each client signal.

OTN—or Optical Transport Network—is a telecommunications industry standard protocol— defined in various ITU Recommendations, such as G.709 and G.798 —that provides an efficient way to transport, switch, and multiplex different services onto high-capacity wavelengths across the optical network.

Described in the ITU-T Recommendation G.709 (2003), OTN adds operations, administration, maintenance, and provisioning (OAM&P) functionality to optical carriers, specifically in a multi-wavelength system such as dense wavelength division multiplexing (DWDM).

for the Optical Transport Network (OTN)" G.872 defines an architecture that is composed of the Optical Channel (OCh), Optical Multiplex Section (OMS) and Optical Transmission Section (OTS).

The Optical Transport Network (OTN) is specified in several ITU-T Recommendations (G.872 on architecture (ITU-T, 2017), G.709 on frames and formats (ITU-T, 2009a), G.798 on atomic functions and processes (ITU-T, 2012a)). It is sometimes also called Optical Transport Hierarchy (OTH).