The optical transport network (OTN) is an optical network standardized by the International Telecommunication Union ( ITU) in which carriers transmit customer data by means of a transport service. It is a consistent further development of the synchronous digitalhierarchy( SDH) and dense wavelength division multiplexing( DWDM).
The optical transport network is based on the Optical Transport Hierarchy( OTH), is a technology for core networks and consists of three layers. The lowest layer, the Optical Transmission Section( OTS), describes the optical fiber path between two optical system components. These can be optical amplifiers( OA), optical add/drop multiplexers( OADM) or optical cross splitters( OXC). The layer above, the Optical Multiplex Section( OMS) comprises the multiplexing functions of a DWDM link between two network nodes. The top layer is the Optical Channel Layer( OCh) and refers to the optical channel between two nodes.
The optical transport network can carry 10- Gigabit Ethernet at full bandwidth from Ethernet switches and routers. Transport is via Optical Transport Units( OTU) with nominal transfer rates of 2.5 Gbit/s, 10 Gbit/s, 40 Gbit/s and in the future 100 Gbit/s. In conjunction with DWDM technology, data rates of several terabits are achieved, which has led to the name 100 Gigabit Ethernet or Terabit Ethernet. A variant of DWDM technology is IP over DWDM( IPoDWDM), which offers a flexible, more manageable network configuration.
ITU Recommendation G.709 specifies the data rates for optical transport units (OTU), which include ATM, SDH, Ethernet and Fibre Channel( FC) payloads. This standard also defines the Network Node Interface( NNI) to the optical transport network.