Exploring the Wonders of OTN - Optical Transport Network

Updated on May 25, 2023 by

With the explosion of digital traffic and the ever-growing array of bandwidth-hungry applications, Optical Transport Network (OTN) evolves from point-to-point DWDM remedies to scalable and robust optical networking applications that cater to a wide variety of client signals with equally-varied service requirements. Carriers are also placing a particular emphasis on OTN in the Metro area, where it is shifted rapidly from SONET/SDH to Wavelength Division Multiplexing (WDM). With the goal of boosting bandwidth and increasing network functionality, OTN provides a way to support different traffic types in a more cost-effective manner than by using SONET/SDH networks.

What Is OTN Network?

Defined by the ITU Telecommunication Standardization Sector (ITU-T), OTN is a digital wrapper technology that provides an efficient and globally accepted way to multiplex different services onto optical light paths. The OTN technology or digital wrapper technology provides a network-wide framework that adds SONET/SDH-like features to WDM equipment. It creates a transparent, hierarchical network designed for use on both WDM and TDM devices. (More information about WDM and TDM systems is available in Optical Wavelength Bands Evolution.)

OTN integrates functions of transporting, multiplexing, routing, management, and supervision, and builds OTN client (e.g. SONET/SDH, IP, ATM) connections in the Metro and Core networks. Nowadays, it is widely deployed in the metro, regional, and long-haul DWDM packet-optical transport networks.

OTN (Optical Transport Network)

What Is OTN Information Structure?

The information structure of OTN is a meticulously designed framework that governs the organization and transmission of data within optical networks. At its core, the OTN information structure comprises several key components, one being the OTM (Optical Transport Module) and the other being OTU (Optical Transport Unit), collaboratively achieving efficient data transport and management.

  • Optical Transport Module (OTM)

The Optical Transport Module is composed of two components: a digital structure and an optical structure. It serves as an information structure transmitted through the optical interface.Within the Optical Channel Payload Unit (OPU), the payload frames are housed, and the payload area of the OPU structure incorporates end-user services like IP, Ethernet, or any other protocol. The OPU overhead is intricately linked to the mapping of client data into the payload area. Furthermore, the Optical Channel Data Unit (ODU) encompasses both the OPU overhead and payload area, along with additional overhead components such as BIP8, GCC1/2, Tandem Connection Monitoring (TCM), and more. The ODU signifies the representation of the OTN path service within an OTN network.

  • Optical Transport Unit (OTU)

The Optical Transport Unit (OTU), as an independent component, encompasses the overhead and payload of ODU. Its functions include providing segment-level overhead, such as BIP8, and supporting General Communication Channel (GCC) bytes for overhead communication between network nodes. In addition, OTU plays a crucial role in the OTN, ensuring the integrity and reliability of data transmission. By encapsulating the overhead and payload of the ODU, the OTU contributes to enhancing the overall robustness of the network.


What Are the Advantages of OTN Networks?

In the OTN network, the seamless integration of optical transmission and electrical processing provides transparent end-to-end connections with enhanced efficiency and ample capacity, suitable for long-distance transmission. This strategic integration is widely deployed by network providers, covering fundamental functions in metropolitan and core networks, thereby enhancing overall performance and reliability. It highlights the synergistic relationship between otn systems and advanced technology, bringing benefits such as increased resilience and simplified operations.

      • Standard Hierarchy

OTN standards include a standard multiplexing hierarchy, defining exactly how the lower-rate signals ascend into the higher-rate payloads. This allows the WDM platform to shift lower-rate services within 10Gbps, 40Gbps, or 100Gbps wavelengths, without the need for external wavelength demultiplexing and manual interconnects.

      • Transport Capacity Expansion

OTN networks provide the underlying high-capacity infrastructure for core interoffice, metropolitan interoffice, and broadband business-access networks. Carriers deploy OTN to support the greatest number of services on the least amount of infrastructure.

      • Reduced Cost

With multiple clients transported on a single wavelength and their specific requirements preserved, the OTN network reduces the overall cost of transport and ensures efficient bandwidth utilization.

      • Transport Flexibility

Network operators can employ the technologies needed to support current transport demands, while also enabling future adoption of new technologies as business needs dictate. It can easily scale ring networks, end-to-end networks, and mesh networks.

      • Timing Transparency

Timing transparency is important for offering wholesale services to third-party providers. The transparency of OTN enables the networks to carry any service, including Ethernet, storage, and digital video, as well as SONET/SDH without interfering with the client timing.

Optical Transmission Network Solutions

FS Data Center Interconnection Solution

FS's interconnection solution for small and medium-sized data centers utilizes WDM equipment, not only significantly reducing bare fiber usage and operational costs but also seamlessly integrating OTN technology. The solution supports a 1+1 backup configuration, ensuring the secure and reliable operation of critical modules such as controllers and power modules, as well as the reliability of business operations and link monitoring. Through the integration of high-performance Erbium-Doped Fiber Amplifier (EDFA) technology, it effectively ensures stable long-distance transmission. This comprehensive solution not only provides a reliable communication infrastructure but also accelerates digital transformation, helping businesses better adapt to the changing demands of the market.

Optical Transport Equipment in OTN Networks

In the intricate landscape of OTN, key components play a pivotal role in ensuring seamless and efficient data transmission. WDM MUX/DEMUX, EDFA, WDM Transponder/Multiplexer, and more constitute the backbone of optical transport equipment.

The following list highlights some common FS OTN-based products along with their functions, providing you with a comprehensive understanding of the versatility of optical transport equipment.

Item Function
WDM MUX/DEMUX Provide high-performance signal division and multiplex
DCM Compensate for the dispersion of the transmitting fiber to maintain the original shape of the signal pulse in long distance transmission.
OADM Add/drop the selected wavelengths in one or multiple channels
EDFA Extend the power budget over long distances
WDM Transponder/Muxponder Provide functions such as electrical and optical signals conversions and wavelength conversion/additional functionality of multiplexing
OLP Optical line protection for optical power monitoring and automatic switching
VOA Variable optical attenuator for optical power management

Key Considerations for Successful OTN Network Deployment

      • What's your fiber type and the link loss (typical 0.25dB/KM)?

OTN solutions offered by solution suppliers can be tailored to both dual and single fiber types. And link loss is necessary for collocating the most appropriate optical transceivers and some active components such as EDFA amplifiers.

      • How many spans do you have, and what is the distance between each of them?

The specific distance your network transports will determine the fundamental equipment needed in the OTN system. Specifically, the transmission distance between each span will indicate whether the Dispersion Compensation Module (DCM) would be needed to compensate in the fiber optical link.

      • What's the data rate between each span? And how many businesses do you plan to transmit?

To make clear, the data rate and capacity for each span in your network are conducive to choosing the most practical types of MUX or OADM for your current OTN infrastructure. And a good acquisition of the number of businesses you are to deploy can pave the way for future network expansion.

      • Do you have plans to expand the network capacity in the future?

The question of future network capacity expansion and scalability is crucial because it ensures that the network architecture can seamlessly adapt and grow in tandem with evolving requirements.


In conclusion, OTN technology not only signifies a significant advancement in optical networking beyond SONET/SDH but also presents a lucrative business opportunity for both carriers and service providers. As we navigate the era of data/transport convergence, OTN networks stand out for providing carriers with unparalleled architectural flexibility, client-protocol independence, and the ability to differentiate services. The maturity of OTN networks is evident, and their evolution is certain to persist in response to the escalating demands of network traffic.

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