SDH transmission system in the world to have a unified standard for digital transmission rate of the frame structure and standard optical interface, allowing network management system interoperability, and therefore has good lateral compatibility, is fully compatible with existing PDH, and accommodate variety of new traffic signals, the formation of a unified global standard digital transmission system, improve the reliability of the network.

SDH (Synchronous Digital Hierarchy), defined according to ITU-T recommendations, is the transmission of digital signals at different speeds to provide information on the structure of the corresponding level, including the multiplexing method and mapping method, as well as the associated synchronization method consisting of a technical system.

OTN with WDM technology, large transmission capacity on the basis of the introduction of the SDH powerful operation, maintenance, management and assignment (OAM) capabilities, while addressing SDH function at the transport layer for lack of inadequate management and maintenance overhead. Using the embedded standard FEC, extensive maintenance and management overhead for large particles service access FEC error correction coding, improve the BER performance, increased light transmission span.

It should be said OTN and PTN are two completely different technologies, technically speaking we should say no contact.

PTN (Packet Transport Network) refers to an optical transport network architecture and specific technologies: IP traffic between the optical transmission medium and the underlying set a level for which the packet of bursty traffic statistical multiplexing and transmission requirements Designed to packet core business and supports multiple service provider, has a lower total cost of ownership (TCO), while inheriting traditional advantages of optical transmission, including high availability and reliability, efficient bandwidth management mechanisms and traffic engineering, convenient The OAM and network management, scalable, high security.

The main advantage of OTN is fully backward compatible, it can build on existing SONET / SDH management functions on the basis of not only the existence of a fully transparent communication protocol, but also for WDM-end connectivity and networking capabilities, It provides a light layer interconnect specification ROADM, and added sub-wavelength aggregation and grooming.

OTN is based on WDM technology, optical transport network layer in an organization's network, it is the next generation of backbone transmission network. OTN is the next generation through a series of ITU-T recommendation G.872, G.709, G.798, etc. norms "digital transmission system" and "optical transmission system" that will solve the traditional WDM networks without wavelength / sub-wavelength services poor scheduling, network capacity is weak, weak protection and other issues.

The rapid development of information technology, the popularity of network-based technology advances, prompting data center construction continues toward large-scale, high-density, high transfer rate, pluralism, virtualization, intelligent, green direction. At the same time, for faster data transfer rates, smaller footprint, lower energy consumption needs, making the data center physical infrastructure as an important part of the cabling system more and more people's attention. Fiber and copper cabling system in the data center are two basic transmission medium, compared with copper systems, fiber-optic network with greater bandwidth, faster transfer rates, longer distances, more slender volume, and stronger anti-interference ability and so on. Therefore, although limited by the high price factor optical fiber, optical fiber can be completely replaced by copper, but the data center construction "Light of Copper" trend is inevitable.

This article discusses the function of WDM technology OADM based systems, the node structure and its products and applications, and its drop multiplexing tributary signals in wavelengths, called optical channel. OADM node device is one of the key equipment of all-optical network.

In 1988, the United States launched the first of a digital transmission standard, the entire network clock synchronization levels are from a very precise master clock (using expensive cesium atomic clock, accuracy better than plus or minus 10 -11 th).