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Documents authored by Khan, Muhammad Samir

Document
DOI: 10.4230/LIPIcs.DISC.2021.26
Byzantine Consensus with Local Multicast Channels

Authors: Muhammad Samir Khan and Nitin H. Vaidya

Published in: LIPIcs, Volume 209, 35th International Symposium on Distributed Computing (DISC 2021)

Abstract
Byzantine consensus is a classical problem in distributed computing. Each node in a synchronous system starts with a binary input. The goal is to reach agreement in the presence of Byzantine faulty nodes. We consider the setting where communication between nodes is modelled via an undirected communication graph. In the classical point-to-point communication model all messages sent on an edge are private between the two endpoints of the edge. This allows a faulty node to equivocate, i.e., lie differently to its different neighbors. Different models have been proposed in the literature that weaken equivocation. In the local broadcast model, every message transmitted by a node is received identically and correctly by all of its neighbors. In the hypergraph model, every message transmitted by a node on a hyperedge is received identically and correctly by all nodes on the hyperedge. Tight network conditions are known for each of the three cases. We introduce a more general model that encompasses all three of these models. In the local multicast model, each node u has one or more local multicast channels. Each channel consists of multiple neighbors of u in the communication graph. When node u sends a message on a channel, it is received identically by all of its neighbors on the channel. For this model, we identify tight network conditions for consensus. We observe how the local multicast model reduces to each of the three models above under specific conditions. In each of the three cases, we relate our network condition to the corresponding known tight conditions. The local multicast model also encompasses other practical network models of interest that have not been explored previously, as elaborated in the paper.
Cite as

Muhammad Samir Khan and Nitin H. Vaidya. Byzantine Consensus with Local Multicast Channels. In 35th International Symposium on Distributed Computing (DISC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 209, pp. 26:1-26:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{khan_et_al:LIPIcs.DISC.2021.26,
  author =	{Khan, Muhammad Samir and Vaidya, Nitin H.},
  title =	{{Byzantine Consensus with Local Multicast Channels}},
  booktitle =	{35th International Symposium on Distributed Computing (DISC 2021)},
  pages =	{26:1--26:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-210-5},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{209},
  editor =	{Gilbert, Seth},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2021.26},
  URN =		{urn:nbn:de:0030-drops-148285},
  doi =		{10.4230/LIPIcs.DISC.2021.26},
  annote =	{Keywords: Byzantine fault, distributed algorithm, consensus, broadcast, multicast}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2019.30
Exact Byzantine Consensus on Arbitrary Directed Graphs Under Local Broadcast Model

Authors: Muhammad Samir Khan, Lewis Tseng, and Nitin H. Vaidya

Published in: LIPIcs, Volume 153, 23rd International Conference on Principles of Distributed Systems (OPODIS 2019)

Abstract
We consider Byzantine consensus in a synchronous system where nodes are connected by a network modeled as a directed graph, i.e., communication links between neighboring nodes are not necessarily bi-directional. The directed graph model is motivated by wireless networks wherein asymmetric communication links can occur. In the classical point-to-point communication model, a message sent on a communication link is private between the two nodes on the link. This allows a Byzantine faulty node to equivocate, i.e., send inconsistent information to its neighbors. This paper considers the local broadcast model of communication, wherein transmission by a node is received identically by all of its outgoing neighbors, effectively depriving the faulty nodes of the ability to equivocate. Prior work has obtained sufficient and necessary conditions on undirected graphs to be able to achieve Byzantine consensus under the local broadcast model. In this paper, we obtain tight conditions on directed graphs to be able to achieve Byzantine consensus with binary inputs under the local broadcast model. The results obtained in the paper provide insights into the trade-off between directionality of communication links and the ability to achieve consensus.
Cite as

Muhammad Samir Khan, Lewis Tseng, and Nitin H. Vaidya. Exact Byzantine Consensus on Arbitrary Directed Graphs Under Local Broadcast Model. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 30:1-30:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{khan_et_al:LIPIcs.OPODIS.2019.30,
  author =	{Khan, Muhammad Samir and Tseng, Lewis and Vaidya, Nitin H.},
  title =	{{Exact Byzantine Consensus on Arbitrary Directed Graphs Under Local Broadcast Model}},
  booktitle =	{23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
  pages =	{30:1--30:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-133-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{153},
  editor =	{Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.30},
  URN =		{urn:nbn:de:0030-drops-118161},
  doi =		{10.4230/LIPIcs.OPODIS.2019.30},
  annote =	{Keywords: complexity and impossibility results for distributed computing, fault-tolerance, reliability}
}
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