SDH its obvious superiority transmission network has become the mainstream of development. SDH technology and some advanced technology, such as optical wavelength division multiplexing (WDM), ATM technology, Internet technology (Packet over SDH), so that the role of SDH network is growing. SDH has been included in various countries in the 21st century high-speed communications network application project is the development direction of the telecommunications industry recognized digital transmission network, with great commercial prospects.