SDH( Synchronous Digital Hierarchy)is known as synchronous digital system. It standardizes the frame structure of digital signals, multiplexing, transmission rate levels, interface code type characteristics, providing an international support framework, based on which a flexible, reliable, easy to manage the world's telecommunication transmission network has been developed and built. This kind of transmission network is easy to expand, suitable for the development of new telecommunication services, and the interoperability of equipment produced by different manufacturers has become possible, which is exactly the goal that network builders have been pursuing for a long time.

SDH technical characteristics:

SDH wascreatedto overcomethe shortcomings of thequasi-synchronous digital systemPDH, the processis the opposite ofPDH, it is the existing goals and then set specifications, and finally develop equipment. This maximizes the optimal way to define systems and equipment that meet the requirements of future telecommunication networks. Its specific technical features include the following.

SDH enables theharmonization ofthree regional standards in North America, Japan, and Europe at theSTM-1level and above. Digital signals Digital signals no longer need to be converted to another standard when communicating across national boundaries, and for the first time, a truly worldwide standard on digital transmission regimes has been realized.

Because of the unified standard optical interface, it is possible to achieve horizontal compatibility on basic optical cable segments, i.e., to allow equipment from different manufacturers to interoperate on the optical path and to meet the requirements of a multi-vendor environment. 　

The SDH frame structure is rich in overhead bits, which account for about5% of the entire signal, and can be processed by software, thus greatly enhancing the operation, management and maintenance of the network.

SDH network is fully compatible with the existing network, i.e.,SDH is compatible withvarious rates of theexistingPDH , so thatSDH can support the already establishedPDH network, and at the same time, it is also favorable for thesmooth transition fromPDH toSDH .At the same time,SDH network can also accommodatevarious new service signals suchasATM signals, that is,SDH has complete backward and forward compatibility.

SDH adopts synchronous multiplexing and flexible multiplexing mapping structure, where different levels of code streams are arranged regularly within the net load of the frame structure, and the net load is synchronized with the network, which makes it possible to make high-speed signals divide low-speed branch signals directly at one time by using software, which is also known as the so-called one-step multiplexing feature. For example,after adoptingthe ADM ofSDH , the software can be used to directly divide the2Mbit/s branch signalsat one time, avoiding the process of re-multiplexing all the high-speed signals after breaking them down step by step and eliminating the need for a full set of back-to-back multiplexing equipment.Therefore,the up and down services ofSDH are very easy, the network structure and equipment are greatly simplified, and the realization of digital cross-connections is also relatively easy.

SDH uses a large number of software for network configuration and control, making configuration more flexible and scheduling more convenient.

From the viewpoint ofOSImodel,SDHbelongs to the lowest physical layer, and there is no strict restriction on its higher layer, which facilitatesthe adoption of various network technologies onSDHto supportATMorIPtransmission.

SDH is strictly synchronous and specifiesthe class ofSynchronous Transport Module (STM)signals.The rate class ofSDHsignals is denoted asSTM-N, whereNis an integer.CurrentlySDHcan only supportfourNvalues,STM-1,STM-4,STM-16, andSTM-64.The most basic and important modular signal isSTM-1, whose rate is 155.520 Mbit/s. The higher levelSTM-Nsignal isobtained by interpolatingthe basic modular signalSTM-1bytes.

The technical information in this chapter and the related SDH equipment troubleshooting procedures are provided by Shenzhen Optical Transmission Network Technology Co. Huawei SDH optical transmission equipment, SDH transmission equipment sales phone: 13430988088 Welcome to telephone consultation!