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Documents authored by Goswami, Pritam

Document
DOI: 10.4230/LIPIcs.OPODIS.2024.17
Perpetual Exploration of a Ring in Presence of Byzantine Black Hole

Authors: Pritam Goswami, Adri Bhattacharya, Raja Das, and Partha Sarathi Mandal

Published in: LIPIcs, Volume 324, 28th International Conference on Principles of Distributed Systems (OPODIS 2024)

Abstract
Perpetual exploration stands as a fundamental problem in the domain of distributed mobile agent algorithms, where the objective is to ensure that each node within a graph is visited by at least one agent infinitely often. While this issue has received significant attention, particularly concerning ring topologies, the presence of malicious nodes, referred to as black holes, adds more complexity. A black hole can destroy any incoming agent without leaving any trace of its existence. In [Bampas et al., 2015; Královič and Miklík, 2010], the authors have considered this problem in the context of periodic data retrieval. They introduced a variant of a black hole called gray hole (where the adversary chooses whether to destroy an agent or let it pass) among other variants, and showed that 4 asynchronous and co-located agents are necessary and sufficient to solve the periodic data retrieval problem (hence perpetual exploration) in the presence of such a gray hole if each of the nodes of the ring has a whiteboard. This paper investigates the exploration of a ring by introducing a realistic variant of a gray hole, called a "Byzantine black hole". In addition to the usual capabilities of a gray hole, the adversary can also choose whether to erase any previously stored information on that node. Note that in [Bampas et al., 2015; Královič and Miklík, 2010], this problem was considered with only one particular initial scenario (i.e., agents are initially co-located) and one specific communication model (i.e., whiteboard). Now, there can be many other initial scenarios where all agents might not be co-located (i.e., they may be scattered). Also, there are many weaker communications models such as Face-to-Face and Pebble, where this perpetual exploration problem is yet to be investigated in the presence of a Byzantine black hole. The main results of our paper focus on minimizing the number of agents while guaranteeing that they perform the perpetual exploration on a ring even in the presence of a Byzantine black hole under different communication models and for different starting scenarios. On the positive side, as a byproduct of our work, we achieved a better upper and lower bound result (i.e., 3 agents) for perpetual exploration in the presence of a Byzantine black hole (which is a more generalized version of a gray hole), by trading-off the scheduler capability, when the agents are initially co-located, and each node contains a whiteboard.
Cite as

Pritam Goswami, Adri Bhattacharya, Raja Das, and Partha Sarathi Mandal. Perpetual Exploration of a Ring in Presence of Byzantine Black Hole. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 17:1-17:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{goswami_et_al:LIPIcs.OPODIS.2024.17,
  author =	{Goswami, Pritam and Bhattacharya, Adri and Das, Raja and Mandal, Partha Sarathi},
  title =	{{Perpetual Exploration of a Ring in Presence of Byzantine Black Hole}},
  booktitle =	{28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
  pages =	{17:1--17:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-360-7},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{324},
  editor =	{Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.17},
  URN =		{urn:nbn:de:0030-drops-225532},
  doi =		{10.4230/LIPIcs.OPODIS.2024.17},
  annote =	{Keywords: Mobile Agents, Exploration, Ring, Black Hole, Malicious host, Byzantine Fault}
}
Document
DOI: 10.4230/LIPIcs.SAND.2024.20
Space and Move-Optimal Arbitrary Pattern Formation on Infinite Rectangular Grid by Oblivious Robot Swarm

Authors: Avisek Sharma, Satakshi Ghosh, Pritam Goswami, and Buddhadeb Sau

Published in: LIPIcs, Volume 292, 3rd Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2024)

Abstract
Arbitrary Pattern Formation (APF) is a fundamental coordination problem in swarm robotics. It requires a set of autonomous robots (mobile computing units) to form an arbitrary pattern (given as input) starting from any initial pattern. This problem has been extensively investigated in continuous and discrete scenarios, with this study focusing on the discrete variant. A set of robots is placed on the nodes of an infinite rectangular grid graph embedded in the euclidean plane. The movements of each robot is restricted to one of the four neighboring grid nodes from its current position. The robots are autonomous, anonymous, identical, and homogeneous, and operate Look-Compute-Move cycles. In this work, we adopt the classical OBLOT robot model, meaning the robots have no persistent memory or explicit communication methods, yet they possess full and unobstructed visibility. This work proposes an algorithm that solves the APF problem in a fully asynchronous scheduler assuming the initial configuration is asymmetric. The considered performance measures of the algorithm are space and number of moves required for the robots. The algorithm is asymptotically move-optimal. Here, we provide a definition of space complexity that takes the visibility issue into consideration. We observe an obvious lower bound 𝒟 of the space complexity and show that the proposed algorithm has the space complexity 𝒟+4. On comparing with previous related works, we show that this is the first proposed algorithm considering OBLOT robot model that is asymptotically move-optimal and has the least space complexity which is almost optimal.
Cite as

Avisek Sharma, Satakshi Ghosh, Pritam Goswami, and Buddhadeb Sau. Space and Move-Optimal Arbitrary Pattern Formation on Infinite Rectangular Grid by Oblivious Robot Swarm. In 3rd Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 292, pp. 20:1-20:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{sharma_et_al:LIPIcs.SAND.2024.20,
  author =	{Sharma, Avisek and Ghosh, Satakshi and Goswami, Pritam and Sau, Buddhadeb},
  title =	{{Space and Move-Optimal Arbitrary Pattern Formation on Infinite Rectangular Grid by Oblivious Robot Swarm}},
  booktitle =	{3rd Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2024)},
  pages =	{20:1--20:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-315-7},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{292},
  editor =	{Casteigts, Arnaud and Kuhn, Fabian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SAND.2024.20},
  URN =		{urn:nbn:de:0030-drops-198989},
  doi =		{10.4230/LIPIcs.SAND.2024.20},
  annote =	{Keywords: Distributed algorithms, Oblivious robots, Optimal algorithms, Swarm robotics, Space optimization, and Rectangular grid}
}
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