OTN Optical Transport Network Hierarchical Structure and Technical Features

Optical Transport Network (OTN) technology is a compromise between electric networks and all-optical networks, which incorporates the SDH's strong and comprehensive OAM&P concept and functionality into WDM optical networks. It effectively addresses the shortcomings of existing WDM systems in performance monitoring and maintenance management. OTN optical transport network technology can support the transparent transmission, high-bandwidth multiplexing and switching, and configuration of client signals. It has strong cost support capabilities, provides powerful OAM functionality, supports multilayer nested concatenation monitoring (TCM) function, and has forward error correction (FEC) support capabilities.

The hierarchical structure of optical transport network products

Optical transport network products conform to the general model of specified transport networks, following their hierarchy, information definition, customer relationships, network topology, and functional definition. According to the International Telecommunication Union's ITU-T regulations, OTN is divided into seven layers: client signal layer, optical channel data unit, optical channel transport unit, optical channel layer, optical multiplex section layer, and optical transmission section layer.

Technical characteristics of optical transport network products

As a new type of networking technology, the main advantages of OTN optical transport network products relative to existing transport networking technologies are as follows:

• Multiple client signal encapsulation and transparent transmission. Based on the ITU-T G.709 OTN frame structure, multiple client signals can be mapped and transparently transmitted, such as SDH, ATM, Ethernet, and so on.

• Large-grain bandwidth multiplexing, cross-connecting, and configuring. The electrical layer bandwidth granule defined by OTN is the optical channel data unit, and the optical layer bandwidth granule is the wavelength. Its multiplexing, cross-connecting, and configuring granularity is much larger, which greatly improves the adaptation and transmission efficiency of high-bandwidth data customer services.

• Strong cost and maintenance management capabilities. OTN provides cost management capabilities similar to SDH, and the OTN frame structure of the OTN optical channel layer greatly enhances the digital monitoring capabilities of the OCh layer. OTN also provides a 6-layer nested concatenation monitoring (TCM) function, making it possible to perform performance monitoring simultaneously in an end-to-end and multiple-segment manner when forming OTN networks.

• Enhanced networking and protection capabilities. Through the introduction of the OTN frame structure, ODUk cross-connect, and multidimensional reconfigurable optical add-drop multiplexer (ROADM), the networking capability of the optical transport network has been greatly enhanced, changing the current status quo of using SDH VC-12/VC-4 scheduling bandwidth and WDM point-to-point to provide large-capacity transmission bandwidth. By using forward error correction (FEC) technology, the transmission distance of the optical layer is significantly increased. In addition, OTN will provide more flexible electric and optical layer-based business protection functionality.

OTN not only provides "pipelines" but also has networking capabilities. At the same time, the application of OTN optical transport network products increases network configuration flexibility and can provide network protection and enhance security. In addition to reducing network construction costs, the introduction of OTN can also improve the manageability and quick fault location of WDM equipment, provide business protection, enable rapid business development, network fragment consolidation, reduce the number of spare parts, investment protection, and all-business support capabilities. Whether it is optical or electrical cross-connect, there will be larger-capacity OTN equipment available in the coming years. While adapting to the development of all services, its powerful network support capabilities will also play a strong driving role in the development of data services. We will see that OTN, which can provide large-grain bandwidth scheduling and management, is no longer a point-to-point pipeline but a new generation of flexible scheduling and protection recovery-enabled optical networks.