Formal analysis of timeliness in the RaSTA protocol

Abstract

Formal reasoning about the correctness of safetycritical system properties is crucial since such systems may impact their environment when malfunctioning. The Rail Safe Transport Application (RaSTA) Protocol is a protocol for systems used in railway applications such as signaling. It claims to provide highly available and timely communication based on the application's demands. We investigate timeliness, i.e., the property that application data do not become obsolete.We analyze the protocol's specification and provide assumptions necessary to resolve imprecisions. Under the specified error model, we find that the deadlines proposed bound until messages are considered timely is too restrictive, disabling RaSTA's mechanisms to recover from lost messages in time. We formalize the specification of timeliness to provide a counterexample for the proposed bound and create an improved bound that does not lead to violated deadlines under the same assumptions and error model.