In this paper we generate conformance test cases for a communication protocol modeled in an EFSM(Extended Finite State Machine) by a fault coverage analysis. For the analysis model, we choose the expanded EFSM to resolve the inter-dependency problem between control and data flows within an EFSM. An expanded EFSM has several useful properties and makes it easy to generate test cases. For test case generation, at first we define data elements in the expanded EFSM. With the definition, we define some probable fault models in edges of the expanded EFSM and discuss what test cases to be needed for satisfying each fault model. The analysis shows that control flow test cases with full fault coverage and data flow test cases satisfying 'all-du-paths' criterion are needed to guarantee high fault coverage in the expanded EFSM. A mass of generated test cases by high fault coverage is optimized through some steps. The result of a simple protocol shows the efficacy of this method.