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OTN system technology is a networking technology for transport networks based on existing optoelectronic technologies, which has been proposed in the context of some key technologies of the all-optical networking (such as optical buffering, optical timing regeneration, optical digital performance monitoring, and wavelength conversion) being immature. OTN conducts full optical processing within the subnet and conducts optoelectronic mixed processing at the subnet boundary. However, the ultimate goal is still all-optical networking. Therefore, the current stage of OTN can be regarded as a transitional stage of all-optical networking.
According to the network layering of OTN system technology, it can be divided into three layers: the optical channel layer, the optical multiplex section layer, and the optical transmission section layer. In addition, in order to solve the problem of digital monitoring of customer signals, the optical channel layer is further divided into two sub-layers: the optical channel transport unit and the optical channel data unit, similar to the segment layer and the channel layer of SDH technology.
Therefore, technically speaking, OTN system technology has effectively inherited and combined the traditional advantages of existing SDH and WDM technologies, while expanding the network functions that are compatible with business transmission requirements. From the perspective of equipment types, OTN equipment can be regarded as a fusion of SDH and WDM equipment, which expands the advantages and functions of the original equipment types.
With the vigorous promotion of broadband data services and the increasing maturity of OTN technology, it is a natural result of OTN technology to construct more efficient and reliable transport networks using OTN technology. The existing SDH networks in the metropolitan core layer and backbone layer are mainly suitable for TDM services, while the main increase in recent times are data services with statistical characteristics. Therefore, large-scale new construction of SDH networks is not possible for the subsequent network construction at these network layers. However, the scale construction and expansion of WDM networks are inevitable. IP services uploaded directly to the existing WDM networks through POS or Ethernet interfaces will face deficiencies in network organization, protection, and maintenance management.
Therefore, based on the existing WDM system networks, when the conditions permit, they can be gradually upgraded to support the maintenance management functions with G.709 overheads according to the needs. For the new or expanded transport networks of existing WDM systems, after eliminating the SDH network layer, they should at least support the maintenance management functions based on G.709 overheads and the protection switching functions based on the optical layer. That is to say, OTN system networks replace the corresponding functions of SDH networks.
As the transmission network evolves towards high capacity, OTN will gradually be applied to the network. ASON technology will also gradually be transplanted into the transmission network based on ODUk and optical wavelengths. OTN system technology includes the complete system architecture of the optical and electrical layers, both of which have network survival mechanisms. Introducing ASON technology based on OTN mainly needs to consider the implementation of the control plane in network resource automatic discovery technology, routing technology, signaling technology, and network protection and recovery technology.
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