Optical transport networks are a type of modern telecommunications networks, which use fibers as major trasnmission media. An optical transport network consists of multiple optical network nodes interconnected by multiple optical fiber links.

To increase the network transmission capacity, WDM transmission technology is used in fiber links. And different node architecture is implemented for nodes. The simplest node architecture can be an optical terminal multiplexer/demultiplexer to multiplex or demultiplex optical channels; a more advanced node architecture can be a reconfigurable optical add/drop multiplexer (ROADM), which has the flexibility of adding/dropping optical channels at the node. ROADMs are generally implemented with a ring topology. Finally, the most advanced optical nodes are optical cross-connects (OXCs). Such a type of nodes have the capability of switching wavelength channels from one input interface to another output interface. In addition, if wavelength converters are deployed in the node, wavelength conversion is allowed as well.