On Flat Lossy Channel Machines

Author Philippe Schnoebelen

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Philippe Schnoebelen
  • LSV, CNRS, ENS Paris-Saclay, Université Paris-Saclay


We thank A. Finkel who raised the issue of flatness in lossy channel systems. We also thank J. Leroux and S. Halfon for useful comments that helped improve this paper.

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Philippe Schnoebelen. On Flat Lossy Channel Machines. In 29th EACSL Annual Conference on Computer Science Logic (CSL 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 183, pp. 37:1-37:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)


We show that reachability, repeated reachability, nontermination and unboundedness are NP-complete for Lossy Channel Machines that are flat, i.e., with no nested cycles in the control graph. The upper complexity bound relies on a fine analysis of iterations of lossy channel actions and uses compressed word techniques for efficiently reasoning with paths of exponential lengths. The lower bounds already apply to acyclic or single-path machines.

Subject Classification

ACM Subject Classification
  • Theory of computation → Logic and verification
  • Infinite state systems
  • Automated verification
  • Flat systems
  • Lossy channels


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