Available and safe message freshness detection algorithm Online publication date: Thu, 04-Nov-2010
by Andrea Bondavalli, Lorenzo Falai, Stefano Porcarelli, Salvatore Sabina, Fabrizio Zanini
International Journal of Critical Computer-Based Systems (IJCCBS), Vol. 1, No. 4, 2010
Abstract: The detection of messages delayed more than a given threshold – called 'message freshness detection' – is an important requirement in many distributed critical real-time systems. In this paper, a solution for addressing this requirement is described and deeply analysed. Our solution, the 'available and safe freshness detection algorithm (ASFDA)', was proposed for a distributed infrastructure for railway control, but it fits also to different systems with similar characteristics. ASFDA allows the detection of 'old' messages: violations of real-time requirements. ASFDA is based on round trip time estimation technique, a well known method used in distributed systems with real-time requirements. In the paper, we demonstrate that ASFDA can detect all the messages older than allowed; we also demonstrate, through an availability analysis performed by simulation, that the availability penalty reached by the proposed freshness detection algorithm is practically negligible if compared with its theoretical limits.
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