Title: Available and safe message freshness detection algorithm

Authors: Andrea Bondavalli, Lorenzo Falai, Stefano Porcarelli, Salvatore Sabina, Fabrizio Zanini

Addresses: DSI, University of Florence, Viale Morgagni 65, Firenze 50134 Italy. ' ResilTech S.r.l., Via Bagnoli, 2, Pontedera (Pi) 56025 Italy. ' Engineering Ingegneria Informatica S.p.A., Via Nazionale per Teramo,14, Mosciano Sant'Angelo (Te) 64023 Italy. ' Ansaldo-STS S.p.A., Via Paolo Mantovani 3-5, Genova 16151 Italy. ' Ansaldo-STS S.p.A., Via Paolo Mantovani 3-5, Genova 16151 Italy

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.

Keywords: railway control systems; safety; availability; critical systems; distributed systems; real-time systems; message freshness detection; railways; simulation; message delay.

DOI: 10.1504/IJCCBS.2010.036604

International Journal of Critical Computer-Based Systems, 2010 Vol.1 No.4, pp.336 - 363

Published online: 04 Nov 2010 *

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