The future European Train Control System (ETCS) will be based on mobile communication and overcome fixed blocks in order to increase track utilization and interoperability throughout Europe. Data processing on board the train and in radio block centers as well as the radio communication link are crucial factors for the safe and efficient operation. Their real-time behavior under inevitable link failures needs to be modeled and evaluated. The paper presents a first simplified model of communication failure and recover behavior as well as safety-critical data exchange. Performance evaluation of the stochastic Petri net model shows that the official quality of service specifications may lead to a bad utilization.