According to the wordage of network evolution of three paradigms (FDM
STM & ATM)
this paper clarifies briefly the status of STM network and the new concepts of Asynchronous Transfer Mode of ATM networ(?). It emphatically points out the characteristics of SDH and its position in the STM & ATM networks
and specifies the significance of network frequency and plesiochronous operation
The author wishes to correct the falseness of "mistaking ADH for PDH".