Networking Principles for SDH Optical Transmission Equipment
Raytrans has developed various SDH optical transmission equipment based on the SDH system, which can fundamentally solve the issues of capacity, quality, network management, and security faced in networks. Due to the advantages of diverse types, flexible circuit scheduling and management, and strong network management capabilities of SDH optical transmission equipment, we have more options in network organization. We must consider from the perspective of the entire network, organize the network rationally, and fully leverage the superiority of SDH optical transmission equipment to ensure the uniformity, integrity, and advancement of network construction.
SDH optical transmission equipment can be divided into Terminal Multiplexer (TM), Regenerative Repeater (REG), Add-Drop Multiplexer (ADM), and Digital Cross-Connect (DXC) equipment based on their types. During network organization, attention should be paid to the rational configuration of various interfaces of the equipment and the appropriate application of the equipment in the network. Among the four types of equipment mentioned above, ADM is an important device that embodies the characteristics of SDH. ADM can be used to form links, suitable for environments where there are add/drop circuit requirements at nodes along the route, and can also be used in access networks. If the TMs at both ends of a link are replaced with ADMs and connected end-to-end to form a ring, an SDH self-healing ring with automatic protection switching can be formed. This method is suitable for use in local networks and has also been extended to secondary trunk networks in recent years. With the rapid development of SDH technology, most current ADM equipment has the capability of tributary-to-multiplex section, multiplex section-to-multiplex section, and tributary-to-tributary cross-connection, making add/drop circuits quite flexible. Functionally, it is equivalent to a small DXC. The network structures of self-healing rings can be mainly divided into the following four types: Unidirectional Path Switched Ring (1+1), Bidirectional Path Switched Ring (1:1), Two-fiber Bidirectional Multiplex Section Shared Protection Ring, and Four-fiber Bidirectional Multiplex Section Shared Protection Ring. An important indicator for measuring the performance of a self-healing network is the protection/restoration time. Many critical services can only tolerate extremely short service protection/restoration times, approximately within 50ms. In this regard, self-healing networks based on DXC routing require several minutes, while self-healing rings generally perform better, achieving (50-200)ms. With the continuous improvement of SDH technology, the protection/restoration time of self-healing rings will be reduced to within 50ms. DXC is a device that can cross-connect all or part of the timeslots of a digital signal from one port to any other port. Common DXCs include DXC4/4 and DXC4/1, with the lowest cross-connection rates being VC4 and VC12 respectively, and port types including 2Mbit/s, 34Mbit/s, 140Mbit/s, 155Mbit/s, etc. The former is mainly used at trunk network nodes, while the latter is mainly used in local networks. DXC equipment works in conjunction with the corresponding network management system. When a fault occurs in the network, it can find a pre-configured alternative route in a short time to restore interrupted services. It should be noted here that, apart from traffic classification and improving the fill level within STM-N, a single DXC device cannot deliver other benefits. The role of each DXC is only evident when used in an environment with circuit groups in at least three directions. The characteristic of DXC application is its networking capability.
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