We propose a timed reachability analysis method in order to generate system states of two classes of EFSM-based communication protocols; one class C1 consists of events such that the lower and upper bounds are all the same and the other class C2 consists of events such that they may be different. The proposed method enumerates only sequences of system states that are obtained through parallel execution of all possible events. Then, in order to evaluate the efficiency of the proposed method, we develop a verification tool based on the proposed method, and then apply the tool to a broadcasting protocol. The experimental results show that the total number of states generated by the proposed method is much less than that by the previous method.