Optical Transport
Optical Transport Network or OTN is a standard-based transmission protocol that uses optical networking techniques to address transmission requirements of service providers in transporting client signals. OTN uses Wavelength Division Multiplexing (WDM) and Synchronous Digital Hierarchy (SDH) or Synchronous Optical Networking (SONET) framing to provide flexible and robust transport of client signals.

Framing and Multiplexing in OTN
In OTN, client signals from various networking protocols like Ethernet, synchronous networks, packet over SONET/SDH (PoS), asynchronous transfer mode (ATM) etc. are mapped into Optical Channel Data Units (ODUs) as per their data rates. Lower order ODUs can then be mapped into higher order ODUs through multiplexing.

The standard ODU frame structures defined are ODU0 (1.25Gbps), ODU1 (2.5Gbps), ODU2 (10Gbps) and ODU3 (40Gbps/100Gbps). Multiple ODUk frames are further multiplexed into Optical Channel (OCh) frames as per the wavelength capacity. For example, 4x ODU2 frames can be multiplexed into a single OCh L (10Gbps x 4 = 40Gbps wavelength).

Service Transport in OTN
Optical Transport Network  provides transparent and adaptive transport of client signals end-to-end across the network. Client signals are terminated, processed and multiplexed only at the network edges while the core network serves as an optical "backbone" without any opto-electronic conversions.

The infrastructure is protocol and bit-rate transparent allowing legacy and future services to be transported together seamlessly. OTN also provides features like digital wrappers, forward error correction, OTU frame structure, timing/synchronization to ensure high reliability, error performance and quality of transmission.

Network Management and Fault Monitoring
OTN network elements have extensive management capabilities built-in as per the ITU-T draft recommendations. This includes network element or equipment management, connection or tunnel management and performance monitoring functions.

Key performance monitoring parameters like OTU/ODU frame delay, jitter, skew, errored frame count, unavailable time etc. are measured continuously to ensure service level agreements and quickly localize faults. A centralized network management system monitors the entire network and manages network elements, resources and restoration in case of failures.

Get more insights on Optical Transport Network