An Optical Transport Network (OTN) is a standard-based transport technology that utilizes optics and wavelength division multiplexing (WDM) to allow the transmission of data from one place to another at high speeds over long distances. OTN provides reliable, flexible and scalable transport of packet and circuit-based client signals.

Working of an OTN

An OTN works by converting electrical signals carrying data into optical signals using lasers. The lasers emit light pulses to represent the ones and zeros of the digital data. The laser light is then transmitted through fiber optic cables. At the receiving end, photodetectors convert the light pulses back into electrical signals that can then be read as data by the destination network elements or devices.

OTNs utilize Dense Wavelength Division Multiplexing (DWDM) which allows multiple optical carrier signals to be sent simultaneously on the same optical fiber but on different wavelengths (colors) of laser light. Each wavelength can carry data at multi-Gbps rates independently, significantly increasing the overall capacity of the fiber. Modern DWDM systems can accommodate up to 200 channels on a single fiber with spacing as low as 50GHz.

The core Optical Transport Network frame structure that is used to transport client signals is organized into Optical Transport Units (OTUs). The various standards-defined OTU encodings allow interoperability at ever increasing data rates up to 400Gbit/s and beyond. OTN framing provides error monitoring functions to ensure highly reliable transport and fast protection switching if fiber cuts or equipment failures occur.

Client Signal Transport

OTNs support the transport of common client signals including SONET/SDH, Ethernet, Fibre Channel, InfiniBand and ODUflex. Client signals are mapped into Optical channel Payload Units (OPUs) which are then encapsulated into Optical channel Data Units (ODUs) along with overhead bytes for network monitoring and management.

The multiplexed ODUs are transmitted through the DWDM network using different carrier wavelengths. At the receiving end, the process is reversed and client signals are extracted and delivered to their intended destinations. This provides a transparent "pipe" for client services between two points without regard to protocol type or data rate.

Network Management Features

Advanced Network Management features are built into OTN transport to allow telecom carriers and network operators to effectively provision, monitor and maintain services delivered over the network.

Integration with Generalized Multiprotocol Label Switching (GMPLS) control plane protocols enables dynamic bandwidth allocation and restoration if problems occur. OTN elements support Connection Oriented (CO) switching of optical paths akin to SONET/SDH circuits for guaranteed service delivery.

Built-in Digital Diagnostic Monitoring (DDM) functions measure various optical layer parameters like optical power levels, signal quality and fiber impairments. This allows proactive network maintenance to fix issues before service outages. Remote fault management is also possible through standardized management protocol interfaces

Get more insights on Optical Transport Network