Reo is a channel-based exogenous coordination model wherein complex coordinators are compositionally built out of basic channel types (like synchronous or FIFO channels) and connectors. In this talk, first we will briefly explain the semantics of Reo based on languages of Timed Data Streams and an operational semantics based on so called Constraint Automata. Then, we continue with different issues in modeling Reo circuits by constraint automata and discuss some examples. We finally report on the-state-of-the-art and future work for developing an integrated tool for visualizing, simulating and model checking Reo circuits and constraint automata.