【文章內(nèi)容簡介】 1, VC3, and AU4, are explained in the table after the figure.At the lowest level, containers (C) are input to virtual containers (VC). The purpose of this function is to create a uniform VC payload by using bitstuffing to bring all inputs to a mon bitrate ready for synchronous multiplexing. Various containers (ranging from VC11 at Mbit/s to VC4 at Mbit/s) are covered by the SDH hierarchy. Next, VCs are aligned into tributary units (TUs), where pointer processing operations are implemented.These initial functions allow the payload to be multiplexed into TU groups (TUGs). As the figure illustrates, the xN label indicates the multiplexing integer used to multiplex the TUs to the TUGs. The next step is the multiplexing of the TUGs to higher level VCs, and TUG2 and TUG3 are multiplexed into VC3 (ANSI mappings) and VC4. These VCs are multiplexed with fixed bytestuffing to form administration units (AUs) which are finally multiplexed into the AU group (AUG). This payload then is multiplexed into the Synchronous Transport Module (STM).The information structure level SDH multiplexing step is called Synchronous Transport Module using STMN (Synchronous Transport, N = 14, 16, 64), in fourfold module, the basic module STM1. Four STM1 synchronous multiplexing constitute STM4, 16 個 four STM1 or STM4 synchronous multiplexing constitute STM16, the structure shown in Figure .Fig. Structure of SDH synchronous multiplexingSDH transmission network is posed of different types of network elements connected via fiberoptic cables posed of different network element SDH network to plete the transfer function: up / down operations, crossconnect services, such as selfhealing network failure.TM Terminal Multiplexer Terminal: terminal multiplexer used on the site of the network, such as the two endpoints of a chain which is a dualport device, shown in Fig. .Fig. Terminal MultiplexerADM Add / Drop Multiplexer: add / drop multiplexer for SDH transmission network adapter at the site, such as the chain of intermediate nodes, or SDH node on the ring is the most used online, the most important one network element, which is a threeport device, as shown in Figure . Add/drop multiplexerREG regenerative repeater: optical transmission network, there are two regenerative repeater, and a purely optical regenerative repeater, the main power amplifier to extend the optical distance of the optical transmission。 other is for pulse regeneration shaping the electric regenerative repeater, mainly through the optical / electrical conversion, sampling the electrical signal, reproduction judgment plastic, electrical / optical conversion, line noise does not accumulate in order to achieve and ensure transfer of the signal waveform on line integrity. After talking here is a regenerative repeater, REG is a twoport device, only two line ports W, E, shown in . Regenerative repeaterDXC digital crossconnect equipment: digital crossconnect equipment to plete the main crossconnect function STMN signal, it is a multiport device, it is actually equivalent to a crossmatrix, to plete the crossconnect between the various signals, such as Figure . Digital crossconnect equipment SDH equipment logic function blocksSDH equipment logic function blocks is shown as figure .SPI: SDH physical interface TTF: transfer terminal functions RST: regenerator section termination HOI: highlevel interfaces MST: multiplex section termination LOI: lowlevel interfaces MSP: MSP HOA: highlevel assembler MSA: multiplex section adaptation HPC: highend channel connection PPI: PDH Physical Interface OHA: overhead access function LPA: lowlevel channel adapter SEMF: synchronous equipment management function LPT: lowerorder channel terminal MCF: messaging feature LPC: lowlevel channel connection SETS: Synchronous Equipment Clock Source HPA: highend channel adapter SETPI: Synchronous Equipment Timing Physical Interface HPT: higherorder channel terminalFig. SDH equipment logic function blocks The basic network topology SDH network element SDH network is interconnected via optical cable from the device, the network node (NE) and the geometric arrangement of the transmission line on the configuration of the network topology. The effectiveness of the network (channel utilization) reliability and economy is largely related to its topology. The basic Fig. basic network topologyLinear structure: To make the point between two adjacent non connection function can be realized, which requires that all points should have the connection. This is an economical topology. Intermediate points should be used (ADM) drop multiplexer, both ends of the first and last use (TM) terminal multiplexers. Chain like structure: this network topology to all nodes in the network is one of the series, and both ends open. This topology is characterized by a more economical in the early SDH network used more, mainly for private networks (such as the railway network). Star structure: this is the network topology network element as a special node with other nodes connected to each network element, the other nodes in each network element disconnected, NE nodes of business to go through this particular node adapter. This network topology may be characterized by the unified management of a particular node to other network nodes, bandwidth allocation in favor。 cost, but there is a special security node processing capabilities and potential bottlenecks. The role of special nodes similar tandem switching network, this topology used for the local network (access network and user network). Tree structure: this can be seen as a bination of network topology chain topology and star topology, there are also potential bottlenecks special node security and processing capabilities.Ring: Ring topology is actually connected to the chain topology