Issue No. 04 - October-December (2009 vol. 6)
DOI Bookmark: http://doi.ieeecomputersociety.org/10.1109/TDSC.2008.24
Martin Hutle , EPFL Vienna University of Technology, Vienna
Dahlia Malkhi , Microsoft Research
Ulrich Schmid , Vienna University of Technology, Vienna
Lidong Zhou , Microsoft Research
Aguilera et al. and Malkhi et al. presented two system models, which are weaker than all previously proposed models where the eventual leader election oracle Ω can be implemented, and thus, consensus can also be solved. The former model assumes unicast steps and at least one correct process with f outgoing eventually timely links, whereas the latter assumes broadcast steps and at least one correct process with f bidirectional but moving eventually timely links. Consequently, those models are incomparable. In this paper, we show that Ω can also be implemented in a system with at least one process with f outgoing moving eventually timely links, assuming either unicast or broadcast steps. It seems to be the weakest system model that allows to solve consensus via Ω-based algorithms known so far. We also provide matching lower bounds for the communication complexity of Ω in this model, which are based on an interesting “stabilization property” of infinite runs. Those results reveal a fairly high price to be paid for this further relaxation of synchrony properties.
Distributed systems, failure detectors, fault-tolerant distributed consensus, system modeling, partial synchrony.
U. Schmid, D. Malkhi, M. Hutle and L. Zhou, "Chasing the Weakest System Model for Implementing Ω and Consensus," in IEEE Transactions on Dependable and Secure Computing, vol. 6, no. , pp. 269-281, 2008.