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In this paper, we show that the protocol complex of a Byzantine synchronous system can remain (k-1)-connected for up to ceil(t/k) rounds, where t is the maximum number of Byzantine processes, and t >= k >= 1. This topological property implies that ceil(t/k) + 1 rounds are necessary to solve k-set agreement in Byzantine synchronous systems, compared to floor(t/k) + 1 rounds in synchronous crash-failure systems. We also show that our connectivity bound is tight as we indicate solutions to Byzantine k-set agreement in exactly ceil(t/k) + 1 synchronous rounds, at least when n is suitably large compared to t. In conclusion, we see how Byzantine failures can potentially require one extra round to solve k-set agreement, and, for n suitably large compared to t, at most that.
@InProceedings{mendes_et_al:LIPIcs.DISC.2017.35,
author = {Mendes, Hammurabi and Herlihy, Maurice},
title = {{Tight Bounds for Connectivity and Set Agreement in Byzantine Synchronous Systems}},
booktitle = {31st International Symposium on Distributed Computing (DISC 2017)},
pages = {35:1--35:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-053-8},
ISSN = {1868-8969},
year = {2017},
volume = {91},
editor = {Richa, Andr\'{e}a},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2017.35},
URN = {urn:nbn:de:0030-drops-79930},
doi = {10.4230/LIPIcs.DISC.2017.35},
annote = {Keywords: Byzantine, synchronous, k-set agreement, topology, connectivity}
}