In reality, design and planning of wave-length routed WDM mesh networks cannot ignore the inside constraints posed by each Optical Add/Drop Multiplexer (OADM), e.g. connectivity among ports and links, allowed colors at each port. Nevertheless, existing simulators fail to address these issues. Hence, the paper proposes a flexible and easy-to-use simulator called SimuON. It adopts a novel approach to encode the insides of heterogeneous OADMs in a generalized and efficient way, and it couples those interior constraints into routing and wavelength assignment.