WDM and SDH difference?

SDH, called "digital synchronization sequence", mainly used for drop multiplexing E1 (2M), E3, T3, STM-1 ~ STM-64 and other ranking data transmitted. And it can be various types of data such as: ATM, E1, FE, GE and other types of data transmission unified package, compatibility strong;WDM, called wavelength division multiplexing system with DWDM and CWDM points, primarily distinguished by the frequency of the light wave signals of different channels used to transmit signals, which can carry include transmission SDH, FCOM, GE and other large particles of business, Mainly used for inter-provincial and provincial transport network.