With the rapid development of the Internet, the number of Internet users is rapidly increased in the number of geometries, and the comparable bits of data-based communications in communication services have risen rapidly, and the Internet business has become a multimedia communication industry. The most rapid and competitive areas. At the same time, whether it is from the number of users from data or from a single user needs, it is much larger than the past. In particular, the latter, its growth will directly need the bandwidth of the system to grow in order of order. Therefore, how to improve the performance of the communication system, increase system bandwidth, to meet growing business needs, becoming a focus of concern. The fiber has the advantages of high bandwidth and transmission distance, which has become the main physical connection medium of broadband integrated digital service network, but if only a simple fiber optic cable is connected, it is not possible to constitute a transmission network that is responsible for the various complex applications. The backbone transmission needs to be supported by a complex transport protocol, and by means of the fiber as a physical medium. The concept of the SDH transfer network was initially proposed in 1985, as proposed by the US Bell Communications Research, Synchronous Optical Network, Sonet. It is composed of a standard transmission structure of a single set of points, suitable for a variety of adaptive processing (i.e., part of the network node interface bitstream can be used for telecommunications services) in physical media such as fiber, microwave, satellite, etc. Uploaded. This standard has become a new standard for US digital system in 1986. International Telecommunication Alliance Standard Ministry (ITU-T) Received Sonet Concept in 1988, and reached an agreement with the US Standard Association (ANSI), renamed SONET modified as synchronous digital series ( Synchronous Digital Hierarchy, SDH) makes it adapt to the general technical system of optical fiber, microwave, and satellite transmission. The SDH network is a revolution on the original PLESIOCHRONOS DIGITAL HIERARCHY Synchronization Series. The PDH is asynchronous to copy, and the access to the low-speed branch signal on any network node is reproduced on that node, the code transform, the code speed adjustment, timing, disturbance code, the descent code, etc., and PDH only The electrical interface is specified, and there is no uniform provision for the line system and optical interface, and the establishment of the global information network cannot be achieved. As the SDH technology introduces, the transmission system not only has the function of providing a signal propagation, but also provides functions of processing, monitoring of signals, and monitoring. SDH is defined by a variety of container C and virtual container VC and the definition of a cascaded complex frame, such as a variety of circuit layers, such as the asynchronous digital series, DQDB, FDDI, ATM, etc. of the variety of rates, and possibly possible A variety of new business that appears. A large number of spare channels in segment overhead enhances the scalability of the SDH network. Through software control, the method of manually changing the wiring in the original PDH implements cross-connect and points, providing flexible upper / down circuit capabilities, and makes network topology varies, enhances network adaptive business development. Flexibility and security, the optimization utilization of circuit protection, height, and communication capabilities can be implemented in a larger geometric range, thereby laid the foundation for enhancement network capabilities, and can be renewed in a few seconds. In particular, the SDH is self-healing ring, and it can be quickly recovered in tens of milliseconds after the circuit has failed. These advantages of SDH make it a basic transmission network for broadband service digital network. The original radio movie and TV Department has been clearly stated in the development of national cable TV networks in 1995. The national ministries and provincial trunks have adopted SDH transmission technology. The data stream has a transmission rate of 2.5Gb / s, which is STM-16.
Nowadays, my country's cable television network uses an SDH transport system in the province and outside the province. The SDH network of cable television networks plays a role in the public physical transmission platform. On this platform, part of the bandwidth is used to transmit broadcast TV programs, the other The data stream used to directly transmit user data or converge from ATM, IP switches. This article only discusses the transmission of IP data streams using the SDH network using cable TV networks. First, the basic constituent SDH transport network is composed of some SDH network units, synchronous information transmission, finishing, transfer, and exchange functions in optical fibers, microwaves, or satellites, integrated by unified network management operations. Information network. Network effective management, dynamic network maintenance, functional monitoring of business performance can effectively improve the utilization of network resources. SDH has a unified network node (NNI), which simplifies the interoperability of the signal and the signal transmission, multiplexing, cross-connect, and exchange process. It has a standardized information structure level, called synchronous transport module (Synchronous Transport Module) ), STM-N. When N = 1, 4, 16, its most basic module is STM-1, STM-4, and STM-16, and has a block-like frame structure, allowing extensive overhead bits (ie, interface bits in network node). The remainder of the net load after the stream is used for the operation, management, and maintenance of the network (OAM). Its basic network unit has synchronous fiber optic line systems or SDH microwave transfer systems, synchronous multiplexers (SM), slot multiplexer (ADM), and synchronous digital cross-connect devices (SDXC), and more. The two most important network elements of the SDH Transfer Network are terminal multiplexers and slot multiplexuses. Taking STM-1 as an example, the main task of the terminal multiplexer is to incorporate low speed branch signals and 155MB / s electrical signals into the STM-1 frame structure, and then enter the microwave transfer system after converting the CMI (symbol inversion code). The reversal is just the opposite. Separation multiplexers, integrating synchronous multiplexing and digital cross-connect functions, with flexible interpolation of any branch signal, and has great flexibility in network design. A typical network application consisting of these two basic network units has a variety of forms, a bit of point applications, linear applications, constituting a hub, constituting a ring web, and a mesh-shaped application. Second, the transmission principle of SDH technology is used to carry information, and a block frame structure is composed of a longitudinal 9 row and a lateral 270 × n column byte, each byte containing 8B (BIT). The entire frame structure consists of three parts: section overhead area, net load area, and management unit pointer zone. The section overhead areas are mainly used for the operation, management, maintenance and assignment of the network to ensure that the information can be transmitted normally, and the management unit pointer is used to indicate the information in the net load area in the STM-N intra. Accurate Location to separate the net load properly when receiving. The net load area is used to store bits and small amounts of information services for information services for channel overhead bytes for channel maintenance management. When the frame transfer of the SDH, press the left right and right, and the serial stream is arranged in a small to large. The transmission time per frame is 125μs, transmits 1/125 × 106 = 8000 frames per second. For STM-1, the number of bits that can be transmitted per frame is 8 × (270 × 9 × 1) = 19940b, the transmission rate of STM-1 is 19440 × 8000 = 155.52 Mb / s, and STM-4 is 622.080MB. / S, STM-16 is 2488.320Mb / s. The frame structure of various business signals into the SDH must pass three steps, namely mapping, positioning, and multiplexing. The mapping is to adjust the signal of the various incoming rates, and then load the corresponding standard container C while adding the channel overhead POH to form a virtual container VC. The positioning is the information receiving a branch unit or a management unit that generates a deviation of the frame phase, which is implemented by the function of the branch unit pointer or the management unit pointer. The multiplexing is the process of adjusting the plurality of low-order channel layer signals into high-order channels or adjusting the plurality of high-order channel layer signals through the code velocity to enter the multiplexed layer. These three steps are described as an example of a 139.264MB / S signal to STM-1.
