1 Introduction
SDH technology has been a mature and standard technology so far. Using the advantages of SDH synchronous multiplexing, standardized optical interfaces, strong network management capabilities, flexible network topology capabilities and high reliability, the multi-service transmission platform MSTP implements TDM, ATM, Ethernet and other services based on traditional SDH Access, processing, and transmission provide multi-service nodes for unified network management. The functional model is shown in Figure 1.
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MSTP can introduce an intelligent intermediate adaptation layer such as RPR and MPLS technology between Ethernet and SDH, and combine multiple technologies to improve the data processing and QoS support capabilities of the device, and complete the Ethernet frame to the SDH virtual container through the GFP protocol Encapsulation mapping, while using virtual cascade and LCAS technology to enhance the flexibility and efficiency of virtual container bandwidth allocation.
2 Core technology of MSTP in metropolitan area network
MSTP retains the traditional advantages of SDH and is constantly updating its technology. Since its development in 2001, it has experienced three major leaps. Below is a brief introduction to its current core technology.
2.1 VC cascade
The concept of VC concatenation is defined in ITU-T G.7070, and is divided into two types: continuous concatenation and virtual concatenation. Continuous cascading is to combine several connected containers into a large container and transmit it through the SDH system. Each VC is continuous in the SDH frame structure and shares the same channel overhead (POH). Sometimes it is also simply referred to as a tier. United [3, 4].
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In addition, he can enable operators to effectively adjust transmission capacity according to user business needs. Using VC virtual cascade technology can also achieve multi-path transmission. The characteristic of VC virtual concatenation is that the discontinuous SDH synchronous payload (data) is cascaded to form a virtual concatenated signal group (VCG) for transmission to achieve the purpose of matching service bandwidth. In the SDH network, the implementation of VC virtual concatenation is relatively simple. The only thing to pay attention to is to ensure the transmission of the serial number SQ of the virtual container participating in VCAT, and to ensure that the VC of the transmitted signal can be correctly queued and reassembled at the receiving end of the system.
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