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Documents authored by Kumar, Manish

Document
DOI: 10.4230/LIPIcs.DISC.2025.9
Distributed Download from an External Data Source in Byzantine Majority Settings

Authors: John Augustine, Soumyottam Chatterjee, Valerie King, Manish Kumar, Shachar Meir, and David Peleg

Published in: LIPIcs, Volume 356, 39th International Symposium on Distributed Computing (DISC 2025)

Abstract
We consider the Download problem in the Data Retrieval Model, introduced in DISC'24, where a distributed set of peers, some of which may be Byzantine, seek to learn n bits of data stored at a trustworthy external data source. Each bit of data can be learned by a peer either through a direct and costly query of the source or through other peers that have already learned it; the goal is to design a collaborative protocol that reduces the query complexity defined as the maximum number of bits queried by any honest peer. We begin with a randomized protocol for the Download problem that achieves optimal query complexity, up to a logarithmic factor. For a stronger "dynamic" adversary that can change the set of Byzantine peers from one round to the next, we achieve optimality (within log factors) for both query complexity (in expectation) and time complexity, but with larger messages. In broadcast communication, where all peers (including Byzantine peers) are required to send the same message to all peers, we achieve (up to log factors) an optimal trade-off between query complexity, time complexity, and message size with the dynamic adversary. All of our protocols can tolerate any constant fraction β < 1 of Byzantine peers.
Cite as

John Augustine, Soumyottam Chatterjee, Valerie King, Manish Kumar, Shachar Meir, and David Peleg. Distributed Download from an External Data Source in Byzantine Majority Settings. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 9:1-9:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{augustine_et_al:LIPIcs.DISC.2025.9,
  author =	{Augustine, John and Chatterjee, Soumyottam and King, Valerie and Kumar, Manish and Meir, Shachar and Peleg, David},
  title =	{{Distributed Download from an External Data Source in Byzantine Majority Settings}},
  booktitle =	{39th International Symposium on Distributed Computing (DISC 2025)},
  pages =	{9:1--9:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-402-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{356},
  editor =	{Kowalski, Dariusz R.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.9},
  URN =		{urn:nbn:de:0030-drops-248262},
  doi =		{10.4230/LIPIcs.DISC.2025.9},
  annote =	{Keywords: Byzantine Fault Tolerance, Blockchain Oracle, Data Retrieval Model, Distributed Download}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2025.48
Brief Announcement: Distributed Download from an External Data Source in Asynchronous Faulty Settings

Authors: John Augustine, Soumyottam Chatterjee, Valerie King, Manish Kumar, Shachar Meir, and David Peleg

Published in: LIPIcs, Volume 356, 39th International Symposium on Distributed Computing (DISC 2025)

Abstract
The distributed Data Retrieval (DR) model consists of k peers connected by a complete peer-to-peer communication network, and a trusted external data source that stores an array X of n bits (n ≫ k). Up to β k of the peers might fail in any execution (for β ∈ [0, 1)). Peers can obtain the information either by inexpensive messages passed among themselves or through expensive queries to the source array X. In the DR model, we focus on designing protocols that minimize the number of queries performed by any nonfaulty peer (a measure referred to as query complexity) while maximizing the resilience parameter β. The Download problem requires each nonfaulty peer to correctly learn the entire array X. Earlier work on this problem focused on synchronous communication networks and established several deterministic and randomized upper and lower bounds. Our work is the first to extend the study of distributed data retrieval to asynchronous communication networks. We address the Download problem under both the Byzantine and crash failure models. We present query-optimal deterministic solutions in an asynchronous model that can tolerate any fixed fraction β < 1 of crash faults. In the Byzantine failure model, it is known that deterministic protocols incur a query complexity of Ω(n) per peer, even under synchrony. We extend this lower bound to randomized protocols in the asynchronous model for β ≥ 1/2, and further show that for β < 1/2, a randomized protocol exists with near-optimal query complexity. To the best of our knowledge, this is the first work to address the Download problem in asynchronous communication networks.
Cite as

John Augustine, Soumyottam Chatterjee, Valerie King, Manish Kumar, Shachar Meir, and David Peleg. Brief Announcement: Distributed Download from an External Data Source in Asynchronous Faulty Settings. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 48:1-48:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{augustine_et_al:LIPIcs.DISC.2025.48,
  author =	{Augustine, John and Chatterjee, Soumyottam and King, Valerie and Kumar, Manish and Meir, Shachar and Peleg, David},
  title =	{{Brief Announcement: Distributed Download from an External Data Source in Asynchronous Faulty Settings}},
  booktitle =	{39th International Symposium on Distributed Computing (DISC 2025)},
  pages =	{48:1--48:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-402-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{356},
  editor =	{Kowalski, Dariusz R.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.48},
  URN =		{urn:nbn:de:0030-drops-248646},
  doi =		{10.4230/LIPIcs.DISC.2025.48},
  annote =	{Keywords: Byzantine Fault Tolerance, Blockchain Oracle, Data Retrieval Model, Distributed Download}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2025.63
Brief Announcement: Optimal Dispersion Under Asynchrony

Authors: Debasish Pattanayak, Ajay D. Kshemkalyani, Manish Kumar, Anisur Rahaman Molla, and Gokarna Sharma

Published in: LIPIcs, Volume 356, 39th International Symposium on Distributed Computing (DISC 2025)

Abstract
We study the dispersion problem in anonymous port-labeled graphs: k ≤ n mobile agents, each with a unique ID and initially located arbitrarily on the nodes of an n-node graph with maximum degree Δ, must autonomously relocate so that no node hosts more than one agent. Dispersion serves as a fundamental task in the distributed computing of mobile agents, and its complexity stems from key challenges in local coordination under anonymity and limited memory. The goal is to minimize both the time to achieve dispersion and the memory required per agent. It is known that any algorithm requires Ω(k) time in the worst case, and Ω(log k) bits of memory per agent. A recent result [Kshemkalyani et al., 2025] gives an optimal O(k)-time algorithm in the synchronous setting and an O(k log k)-time algorithm in the asynchronous setting, both using O(log(k+Δ)) bits. We close the complexity gap in the asynchronous setting by presenting the first dispersion algorithm that runs in optimal O(k) time using O(log(k+Δ)) bits of memory per agent. Our solution relies on a novel technique for constructing a port-one tree in anonymous graphs, which may be of independent interest.
Cite as

Debasish Pattanayak, Ajay D. Kshemkalyani, Manish Kumar, Anisur Rahaman Molla, and Gokarna Sharma. Brief Announcement: Optimal Dispersion Under Asynchrony. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 63:1-63:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{pattanayak_et_al:LIPIcs.DISC.2025.63,
  author =	{Pattanayak, Debasish and Kshemkalyani, Ajay D. and Kumar, Manish and Molla, Anisur Rahaman and Sharma, Gokarna},
  title =	{{Brief Announcement: Optimal Dispersion Under Asynchrony}},
  booktitle =	{39th International Symposium on Distributed Computing (DISC 2025)},
  pages =	{63:1--63:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-402-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{356},
  editor =	{Kowalski, Dariusz R.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.63},
  URN =		{urn:nbn:de:0030-drops-248795},
  doi =		{10.4230/LIPIcs.DISC.2025.63},
  annote =	{Keywords: Distributed algorithms, mobile agents, local communication, dispersion, asynchrony, port-one tree, time and memory complexity}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2024.50
Brief Announcement: Agent-Based Leader Election, MST, and Beyond

Authors: Ajay D. Kshemkalyani, Manish Kumar, Anisur Rahaman Molla, and Gokarna Sharma

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
Leader election is one of the fundamental and well-studied problems in distributed computing. In this paper, we initiate the study of leader election using mobile agents. Suppose n agents are positioned initially arbitrarily on the nodes of an arbitrary, anonymous, n-node, m-edge graph G. The agents relocate themselves autonomously on the nodes of G and elect an agent as a leader such that the leader agent knows it is a leader and the other agents know they are not leaders. The objective is to minimize time and memory requirements. Following the literature, we consider the synchronous setting in which each agent performs its operations synchronously with others and hence the time complexity can be measured in rounds. The quest in this paper is to provide solutions without agents knowing any graph parameter, such as n, a priori. We first establish that, without agents knowing any graph parameter a priori, there exists a deterministic algorithm to elect an agent as a leader in O(m) rounds with O(nlog n) bits at each agent. Using this leader election result, we develop a deterministic algorithm for agents to construct a minimum spanning tree of G in O(m+nlog n) rounds using O(n log n) bits memory at each agent, without agents knowing any graph parameter a priori. Finally, using the same leader election result, we provide improved time/memory results for other fundamental distributed graph problems, namely, gathering, maximal independent set, and minimal dominating sets, removing the assumptions on agents knowing graph parameters a priori.
Cite as

Ajay D. Kshemkalyani, Manish Kumar, Anisur Rahaman Molla, and Gokarna Sharma. Brief Announcement: Agent-Based Leader Election, MST, and Beyond. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 50:1-50:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{kshemkalyani_et_al:LIPIcs.DISC.2024.50,
  author =	{Kshemkalyani, Ajay D. and Kumar, Manish and Molla, Anisur Rahaman and Sharma, Gokarna},
  title =	{{Brief Announcement: Agent-Based Leader Election, MST, and Beyond}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{50:1--50:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.50},
  URN =		{urn:nbn:de:0030-drops-212782},
  doi =		{10.4230/LIPIcs.DISC.2024.50},
  annote =	{Keywords: Distributed algorithms, mobile agents, local communication, leader election, MST, MIS, gathering, minimal dominating sets, time and memory complexity, graph parameters}
}
Document
DOI: 10.4230/LIPIcs.SAND.2024.18
Reconfiguration and Locomotion with Joint Movements in the Amoebot Model

Authors: Andreas Padalkin, Manish Kumar, and Christian Scheideler

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

Abstract
We are considering the geometric amoebot model where a set of n amoebots is placed on the triangular grid. An amoebot is able to send information to its neighbors, and to move via expansions and contractions. Since amoebots and information can only travel node by node, most problems have a natural lower bound of Ω(D) where D denotes the diameter of the structure. Inspired by the nervous and muscular system, Feldmann et al. have proposed the reconfigurable circuit extension and the joint movement extension of the amoebot model with the goal of breaking this lower bound. In the joint movement extension, the way amoebots move is altered. Amoebots become able to push and pull other amoebots. Feldmann et al. demonstrated the power of joint movements by transforming a line of amoebots into a rhombus within O(log n) rounds. However, they left the details of the extension open. The goal of this paper is therefore to formalize the joint movement extension. In order to provide a proof of concept for the extension, we consider two fundamental problems of modular robot systems: reconfiguration and locomotion. We approach these problems by defining meta-modules of rhombical and hexagonal shapes, respectively. The meta-modules are capable of movement primitives like sliding, rotating, and tunneling. This allows us to simulate reconfiguration algorithms of various modular robot systems. Finally, we construct three amoebot structures capable of locomotion by rolling, crawling, and walking, respectively.
Cite as

Andreas Padalkin, Manish Kumar, and Christian Scheideler. Reconfiguration and Locomotion with Joint Movements in the Amoebot Model. In 3rd Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 292, pp. 18:1-18:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{padalkin_et_al:LIPIcs.SAND.2024.18,
  author =	{Padalkin, Andreas and Kumar, Manish and Scheideler, Christian},
  title =	{{Reconfiguration and Locomotion with Joint Movements in the Amoebot Model}},
  booktitle =	{3rd Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2024)},
  pages =	{18:1--18:20},
  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.2024.18},
  URN =		{urn:nbn:de:0030-drops-198963},
  doi =		{10.4230/LIPIcs.SAND.2024.18},
  annote =	{Keywords: programmable matter, modular robot system, reconfiguration, locomotion}
}
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