Sie haben Javascript deaktiviert!
Sie haben versucht eine Funktion zu nutzen, die nur mit Javascript möglich ist. Um sämtliche Funktionalitäten unserer Internetseite zu nutzen, aktivieren Sie bitte Javascript in Ihrem Browser.

#### Prof. Dr. Christian Scheideler

Kontakt
Vita

Leiter - Professor

Telefon:
+49 5251 60-6728
Fax:
+49 5251 60-6697
Büro:
F2.326
Sprechzeiten:

Nach Vereinbarung. Bitte kontaktieren Sie das Sekretariat.

Web:
Besucher:
Fürstenallee 11

Mitglied - Professor - Teilprojektleiter

 03/2009 - heute Professor Professor im Institut für Informatik, Universität Paderborn 09/2005 - 02/2009 W2-Professor Technische Universität München 09/2000 - 08/2005 Assistant Professor Johns Hopkins University

# Lehr- und Forschungsschwerpunkte:

• Verteilte Algorithmen und Datenstrukturen
• Sicherheit in verteilten Systemen
• Randomisierte Algorithmen und stochastische Prozesse
• Netzwerktheorie
(insbesondere P2P Systeme, mobile ad-hoc Netzwerke und Sensor-Netzwerke)
• Diskrete Mathematik

# Weitere Funktionen

• Associate Editor des Journal of the ACM
• Associate Editor des Journal of Computer and System Sciences
• Managing Editor des Journal of Interconnection Networks
• Steering Committee der DISC
• Steering Committee der SIROCCO
• Stellvertretender Sprecher des Fachbereichs „Grundlagen der Informatik“ in der Gesellschaft für Informatik
• Local Arrangements Chair der SIROCCO 2022
• PC Chair des 36th Intl. Symposium on Distributed Computing (DISC 2022)
• Co-Organisator des 2nd Bertinoro Workshop on Distributed Geometric Algorithms (DIG 2022)
• PC Mitglied von Edu-Par 22, ICDCS 22, SAND 22, STACS 22, SOFSEM 23, UCNC 23
• Leiter des internationalen Dijkstra Preis Komitees 2022
• Co-Organisator der ICALP 2023

## Veröffentlichungen (RIS-DB)

Liste im Research Information System öffnen

## 2022

Coordinating Amoebots via Reconfigurable Circuits

M. Feldmann, A. Padalkin, C. Scheideler, S. Dolev, J. Comput. Biol. (2022), 29(4), pp. 317–343

The Structural Power of Reconfigurable Circuits in the Amoebot Model

A. Padalkin, C. Scheideler, D. Warner, in: 28th International Conference on DNA Computing and Molecular Programming (DNA 28), Schloss Dagstuhl – Leibniz-Zentrum für Informatik, 2022, pp. 8:1–8:22

Fault-Tolerant Shape Formation in the Amoebot Model

I. Kostitsyna, C. Scheideler, D. Warner, in: 28th International Conference on DNA Computing and Molecular Programming (DNA 28), Schloss Dagstuhl – Leibniz-Zentrum für Informatik, 2022, pp. 9:1–9:22

Local Mutual Exclusion for Dynamic, Anonymous, Bounded Memory Message Passing Systems

J.J. Daymude, A.W. Richa, C. Scheideler, in: 1st Symposium on Algorithmic Foundations of Dynamic Networks, SAND 2022, March 28-30, 2022, Virtual Conference, Schloss Dagstuhl - Leibniz-Zentrum für Informatik, 2022, pp. 12:1–12:19

Brief Announcement: The (Limited) Power of Multiple Identities: Asynchronous Byzantine Reliable Broadcast with Improved Resilience through Collusion

T. Götte, C. Scheideler, in: SPAA ’22: 34th ACM Symposium on Parallelism in Algorithms and Architectures, Philadelphia, PA, USA, July 11 - 14, 2022, ACM, 2022, pp. 99–101

## 2021

Logarithmic Time MIMO Based Self-Stabilizing Clock Synchronization

S. Dolev, R. Prasadh Narayanan, C. Scheideler, C. Schindelhauer, in: NANOCOM '21: The Eighth Annual ACM International Conference on Nanoscale Computing and Communication, Virtual Event, Italy, September 7 - 9, 2021, ACM, 2021, pp. 30:1-30:2

Beep-And-Sleep: Message and Energy Efficient Set Cover

T. Götte, C. Kolb, C. Scheideler, J. Werthmann, in: Algorithms for Sensor Systems (ALGOSENSORS '21), 2021

Coordinating Amoebots via Reconfigurable Circuits

M. Feldmann, A. Padalkin, C. Scheideler, S. Dolev, in: Stabilization, Safety, and Security of Distributed Systems - 23rd International Symposium, (SSS) 2021, Virtual Event, November 17-20, 2021, Proceedings, Springer, 2021, pp. 484-488

Logarithmic Time MIMO Based Self-Stabilizing Clock Synchronization

S. Dolev, R. Prasadh Narayanan, C. Scheideler, C. Schindelhauer, in: NANOCOM '21: The Eighth Annual ACM International Conference on Nanoscale Computing and Communication, Virtual Event, Italy, September 7 - 9, 2021, ACM, 2021, pp. 30:1-30:2

The Canonical Amoebot Model: Algorithms and Concurrency Control

J. J. Daymude, A. W. Richa, C. Scheideler, in: 35th International Symposium on Distributed Computing, DISC 2021, October 4-8, 2021, Freiburg, Germany (Virtual Conference), Schloss Dagstuhl - Leibniz-Zentrum für Informatik, 2021, pp. 20:1-20:19

A self-stabilizing Hashed Patricia Trie

T. Knollmann, C. Scheideler, Information and Computation (2021), 104697

While many research in distributed computing has covered solutions for self-stabilizing computing and topologies, there is far less work on self-stabilization for distributed data structures. However, when peers in peer-to-peer networks crash, a distributed data structure may not remain intact. We present a self-stabilizing protocol for a distributed data structure called the Hashed Patricia Trie (Kniesburges and Scheideler WALCOM'11) that enables efficient prefix search on a set of keys. The data structure has many applications while offering low overhead and efficient operations when embedded on top of a Distributed Hash Table. Especially, longest prefix matching for x can be done in O(log |x|) hash table read accesses. We show how to maintain the structure in a self-stabilizing way, while assuring a low overhead in a legal state and an asymptotically optimal memory demand of O(d) bits, where d is the number of bits needed for storing all keys.

Time-Optimal Construction of Overlays

T. Götte, K. Hinnenthal, C. Scheideler, J. Werthmann, in: Proc. of the 40th ACM Symposium on Principles of Distributed Computing (PODC '21), ACM, 2021

We show how to construct an overlay network of constant degree and diameter $O(\log n)$ in time $O(\log n)$ starting from an arbitrary weakly connected graph. We assume a synchronous communication network in which nodes can send messages to nodes they know the identifier of and establish new connections by sending node identifiers. If the initial network's graph is weakly connected and has constant degree, then our algorithm constructs the desired topology with each node sending and receiving only $O(\log n)$ messages in each round in time $O(\log n)$, w.h.p., which beats the currently best $O(\log^{3/2} n)$ time algorithm of [Götte et al., SIROCCO'19]. Since the problem cannot be solved faster than by using pointer jumping for $O(\log n)$ rounds (which would even require each node to communicate $\Omega(n)$ bits), our algorithm is asymptotically optimal. We achieve this speedup by using short random walks to repeatedly establish random connections between the nodes that quickly reduce the conductance of the graph using an observation of [Kwok and Lau, APPROX'14]. Additionally, we show how our algorithm can be used to efficiently solve graph problems in \emph{hybrid networks} [Augustine et al., SODA'20]. Motivated by the idea that nodes possess two different modes of communication, we assume that communication of the \emph{initial} edges is unrestricted. In contrast, only polylogarithmically many messages can be communicated over edges that have been established throughout an algorithm's execution. For an (undirected) graph $G$ with arbitrary degree, we show how to compute connected components, a spanning tree, and biconnected components in time $O(\log n)$, w.h.p. Furthermore, we show how to compute an MIS in time $O(\log d + \log \log n)$, w.h.p., where $d$ is the initial degree of $G$.

Near-Shortest Path Routing in Hybrid Communication Networks

S. Coy, A. Czumaj, M. Feldmann, K. Hinnenthal, F. Kuhn, C. Scheideler, P. Schneider, M. Struijs, in: 25th International Conference on Principles of Distributed Systems, OPODIS 2021, December 13-15, 2021, Strasbourg, France, Schloss Dagstuhl - Leibniz-Zentrum für Informatik, 2021, pp. 11:1–11:23

## 2020

Shortest Paths in a Hybrid Network Model

J. Augustine, K. Hinnenthal, F. Kuhn, C. Scheideler, P. Schneider, in: Proceedings of the 2020 ACM-SIAM Symposium on Discrete Algorithms, SODA 2020, Salt Lake City, UT, USA, January 5-8, 2020, SIAM, 2020, pp. 1280-1299

Forming tile shapes with simple robots

R. Gmyr, K. Hinnenthal, I. Kostitsyna, F. Kuhn, D. Rudolph, C. Scheideler, T. Strothmann, Nat. Comput. (2020), 19(2), pp. 375-390

Fast Hybrid Network Algorithms for Shortest Paths in Sparse Graphs

M. Feldmann, K. Hinnenthal, C. Scheideler, in: Proceedings of the 24th International Conference on Principles of Distributed Systems (OPODIS), Schloss Dagstuhl - Leibniz-Zentrum für Informatik, 2020

We consider the problem of computing shortest paths in \emph{hybrid networks}, in which nodes can make use of different communication modes. For example, mobile phones may use ad-hoc connections via Bluetooth or Wi-Fi in addition to the cellular network to solve tasks more efficiently. Like in this case, the different communication modes may differ considerably in range, bandwidth, and flexibility. We build upon the model of Augustine et al. [SODA '20], which captures these differences by a \emph{local} and a \emph{global} mode. Specifically, the local edges model a fixed communication network in which $O(1)$ messages of size $O(\log n)$ can be sent over every edge in each synchronous round. The global edges form a clique, but nodes are only allowed to send and receive a total of at most $O(\log n)$ messages over global edges, which restricts the nodes to use these edges only very sparsely. We demonstrate the power of hybrid networks by presenting algorithms to compute Single-Source Shortest Paths and the diameter very efficiently in \emph{sparse graphs}. Specifically, we present exact $O(\log n)$ time algorithms for cactus graphs (i.e., graphs in which each edge is contained in at most one cycle), and $3$-approximations for graphs that have at most $n + O(n^{1/3})$ edges and arboricity $O(\log n)$. For these graph classes, our algorithms provide exponentially faster solutions than the best known algorithms for general graphs in this model. Beyond shortest paths, we also provide a variety of useful tools and techniques for hybrid networks, which may be of independent interest.

Survey on Algorithms for Self-Stabilizing Overlay Networks

M. Feldmann, C. Scheideler, S. Schmid, ACM Computing Surveys (2020)

The maintenance of efficient and robust overlay networks is one of the most fundamental and reoccurring themes in networking. This paper presents a survey of state-of-the-art algorithms to design and repair overlay networks in a distributed manner. In particular, we discuss basic algorithmic primitives to preserve connectivity, review algorithms for the fundamental problem of graph linearization, and then survey self-stabilizing algorithms for metric and scalable topologies. We also identify open problems and avenues for future research.

Time- and Space-Optimal Discrete Clock Synchronization in the Beeping Model

M. Feldmann, A. Khazraei, C. Scheideler, in: Proceedings of the 32nd ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), ACM, 2020

We consider the clock synchronization problem in the (discrete) beeping model: Given a network of $n$ nodes with each node having a clock value $\delta(v) \in \{0,\ldots T-1\}$, the goal is to synchronize the clock values of all nodes such that they have the same value in any round. As is standard in clock synchronization, we assume \emph{arbitrary activations} for all nodes, i.e., the nodes start their protocol at an arbitrary round (not limited to $\{0,\ldots,T-1\}$). We give an asymptotically optimal algorithm that runs in $4D + \Bigl\lfloor \frac{D}{\lfloor T/4 \rfloor} \Bigr \rfloor \cdot (T \mod 4) = O(D)$ rounds, where $D$ is the diameter of the network. Once all nodes are in sync, they beep at the same round every $T$ rounds. The algorithm drastically improves on the $O(T D)$-bound of \cite{firefly_sync} (where $T$ is required to be at least $4n$, so the bound is no better than $O(nD)$). Our algorithm is very simple as nodes only have to maintain $3$ bits in addition to the $\lceil \log T \rceil$ bits needed to maintain the clock. Furthermore we investigate the complexity of \emph{self-stabilizing} solutions for the clock synchronization problem: We first show lower bounds of $\Omega(\max\{T,n\})$ rounds on the runtime and $\Omega(\log(\max\{T,n\}))$ bits of memory required for any such protocol. Afterwards we present a protocol that runs in $O(\max\{T,n\})$ rounds using at most $O(\log(\max\{T,n\}))$ bits at each node, which is asymptotically optimal with regards to both, runtime and memory requirements.

A Bounding Box Overlay for Competitive Routing in Hybrid Communication Networks

J. Castenow, C. Kolb, C. Scheideler, in: Proceedings of the 21st International Conference on Distributed Computing and Networking (ICDCN), ACM, 2020

Convex Hull Formation for Programmable Matter

J.J. Daymude, R. Gmyr, K. Hinnenthal, I. Kostitsyna, C. Scheideler, A.W. Richa, in: Proceedings of the 21st International Conference on Distributed Computing and Networking, 2020

## 2019

MultiSkipGraph: A Self-stabilizing Overlay Network that Maintains Monotonic Searchability

L. Luo, C. Scheideler, T.F. Strothmann, in: Proceedings of the 2019 IEEE 33rd International Parallel and Distributed Processing Symposium (IPDPS '19), 2019

Self-stabilizing overlay networks have the advantage of being able to recover from illegal states and faults. However, the majority of these networks cannot give any guarantees on their functionality while the recovery process is going on. We are especially interested in searchability, i.e., the functionality that search messages for a specific node are answered successfully if a node exists in the network. In this paper we investigate overlay networks that ensure the maintenance of monotonic searchability while the self-stabilization is going on. More precisely, once a search message from node u to another node v is successfully delivered, all future search messages from u to v succeed as well. We extend the existing research by focusing on skip graphs and present a solution for two scenarios: (i) the goal topology is a super graph of the perfect skip graph and (ii) the goal topology is exactly the perfect skip graph.

Skeap & Seap: Scalable Distributed Priority Queues for Constant and Arbitrary Priorities

M. Feldmann, C. Scheideler, in: Proceedings of the 31st ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), ACM, 2019, pp. 287--296

We propose two protocols for distributed priority queues (denoted by 'heap' for simplicity in this paper) called SKEAP and SEAP. SKEAP realizes a distributed heap for a constant amount of priorities and SEAP one for an arbitrary amount. Both protocols build on an overlay, which induces an aggregation tree on which heap operations are aggregated in batches, ensuring that our protocols scale even for a high rate of incoming requests. As part of SEAP we provide a novel distributed protocol for the k-selection problem that runs in time O(log n) w.h.p. SKEAP guarantees sequential consistency for its heap operations, while SEAP guarantees serializability. SKEAP and SEAP provide logarithmic runtimes w.h.p. on all their operations. SKEAP and SEAP provide logarithmic runtimes w.h.p. on all their operations with SEAP having to use only O(log n) bit messages.

Distributed Computation in Node-Capacitated Networks

J. Augustine, M. Ghaffari, R. Gmyr, K. Hinnenthal, F. Kuhn, J. Li, C. Scheideler, in: Proceedings of the 31st ACM Symposium on Parallelism in Algorithms and Architectures, ACM, 2019, pp. 69--79

Computing by Programmable Particles

J.J. Daymude, K. Hinnenthal, A.W. Richa, C. Scheideler, in: Distributed Computing by Mobile Entities, Current Research in Moving and Computing., Springer, Cham, 2019, pp. 615-681

Always be Two Steps Ahead of Your Enemy - Maintaining a Routable Overlay under Massive Churn with an Almost Up-to-date Adversary

T. Götte, V.R. Vijayalakshmi, C. Scheideler, in: Proceedings of the 2019 IEEE 33rd International Parallel and Distributed Processing Symposium (IPDPS '19), IEEE, 2019

We investigate the maintenance of overlay networks under massive churn, i.e. nodes joining and leaving the network. We assume an adversary that may churn a constant fraction $\alpha n$ of nodes over the course of $\mathcal{O}(\log n)$ rounds. In particular, the adversary has an almost up-to-date information of the network topology as it can observe an only slightly outdated topology that is at least $2$ rounds old. Other than that, we only have the provably minimal restriction that new nodes can only join the network via nodes that have taken part in the network for at least one round. Our contributions are as follows: First, we show that it is impossible to maintain a connected topology if adversary has up-to-date information about the nodes' connections. Further, we show that our restriction concerning the join is also necessary. As our main result present an algorithm that constructs a new overlay- completely independent of all previous overlays - every $2$ rounds. Furthermore, each node sends and receives only $\mathcal{O}(\log^3 n)$ messages each round. As part of our solution we propose the Linearized DeBruijn Swarm (LDS), a highly churn resistant overlay, which will be maintained by the algorithm. However, our approaches can be transferred to a variety of classical P2P Topologies where nodes are mapped into the $[0,1)$-interval.

On the Complexity of Local Graph Transformations

C. Scheideler, A. Setzer, in: Proceedings of the 46th International Colloquium on Automata, Languages, and Programming, Dagstuhl Publishing, 2019, pp. 150:1--150:14

We consider the problem of transforming a given graph G_s into a desired graph G_t by applying a minimum number of primitives from a particular set of local graph transformation primitives. These primitives are local in the sense that each node can apply them based on local knowledge and by affecting only its 1-neighborhood. Although the specific set of primitives we consider makes it possible to transform any (weakly) connected graph into any other (weakly) connected graph consisting of the same nodes, they cannot disconnect the graph or introduce new nodes into the graph, making them ideal in the context of supervised overlay network transformations. We prove that computing a minimum sequence of primitive applications (even centralized) for arbitrary G_s and G_t is NP-hard, which we conjecture to hold for any set of local graph transformation primitives satisfying the aforementioned properties. On the other hand, we show that this problem admits a polynomial time algorithm with a constant approximation ratio.

Faster Construction of Overlay Networks

T. Götte, K. Hinnenthal, C. Scheideler, in: Structural Information and Communication Complexity, 2019

Shortest Paths in a Hybrid Network Model

J. Augustine, K. Hinnenthal, F. Kuhn, C. Scheideler, P. Schneider, in: Proceedings of the Fourteenth Annual ACM-SIAM Symposium on Discrete Algorithms, 2019, pp. 1280-1299

Self-Stabilizing Metric Graphs

R. Gmyr, J. Lefevre, C. Scheideler, Theory Comput. Syst. (2019), 63(2), pp. 177-199

A Bounding Box Overlay for Competitive Routing in Hybrid Communication Networks

J. Castenow, C. Kolb, C. Scheideler, in: Proceedings of the 26th International Colloquium on Structural Information and Communication Complexity (SIROCCO), 2019, pp. 345-348

A Loosely Self-stabilizing Protocol for Randomized Congestion Control with Logarithmic Memory

M. Feldmann, T. Götte, C. Scheideler, in: Proceedings of the 21st International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS), Springer, Cham, 2019, pp. 149-164

We consider congestion control in peer-to-peer distributed systems. The problem can be reduced to the following scenario: Consider a set $V$ of $n$ peers (called \emph{clients} in this paper) that want to send messages to a fixed common peer (called \emph{server} in this paper). We assume that each client $v \in V$ sends a message with probability $p(v) \in [0,1)$ and the server has a capacity of $\sigma \in \mathbb{N}$, i.e., it can recieve at most $\sigma$ messages per round and excess messages are dropped. The server can modify these probabilities when clients send messages. Ideally, we wish to converge to a state with $\sum p(v) = \sigma$ and $p(v) = p(w)$ for all $v,w \in V$. We propose a \emph{loosely} self-stabilizing protocol with a slightly relaxed legitimate state. Our protocol lets the system converge from \emph{any} initial state to a state where $\sum p(v) \in \left[\sigma \pm \epsilon\right]$ and $|p(v)-p(w)| \in O(\frac{1}{n})$. This property is then maintained for $\Omega(n^{\mathfrak{c}})$ rounds in expectation. In particular, the initial client probabilities and server variables are not necessarily well-defined, i.e., they may have arbitrary values. Our protocol uses only $O(W + \log n)$ bits of memory where $W$ is length of node identifiers, making it very lightweight. Finally we state a lower bound on the convergence time an see that our protocol performs asymptotically optimal (up to some polylogarithmic factor).

Fast Distributed Algorithms for LP-Type Problems of Low Dimension

K. Hinnenthal, C. Scheideler, M. Struijs, in: 33rd International Symposium on Distributed Computing (DISC 2019), 2019

## 2018

Breaking the $\tilde\Omega(\sqrt{n})$ Barrier: Fast Consensus under a Late Adversary

P. Robinson, C. Scheideler, A. Setzer, in: Proceedings of the 30th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), 2018

We study the consensus problem in a synchronous distributed system of n nodes under an adaptive adversary that has a slightly outdated view of the system and can block all incoming and outgoing communication of a constant fraction of the nodes in each round. Motivated by a result of Ben-Or and Bar-Joseph (1998), showing that any consensus algorithm that is resilient against a linear number of crash faults requires $\tilde \Omega(\sqrt n)$ rounds in an n-node network against an adaptive adversary, we consider a late adaptive adversary, who has full knowledge of the network state at the beginning of the previous round and unlimited computational power, but is oblivious to the current state of the nodes. Our main contributions are randomized distributed algorithms that achieve consensus with high probability among all except a small constant fraction of the nodes (i.e., "almost-everywhere'') against a late adaptive adversary who can block up to ε n$nodes in each round, for a small constant ε >0$. Our first protocol achieves binary almost-everywhere consensus and also guarantees a decision on the majority input value, thus ensuring plurality consensus. We also present an algorithm that achieves the same time complexity for multi-value consensus. Both of our algorithms succeed in $O(log n)$ rounds with high probability, thus showing an exponential gap to the $\tilde\Omega(\sqrt n)$ lower bound of Ben-Or and Bar-Joseph for strongly adaptive crash-failure adversaries, which can be strengthened to $\Omega(n)$ when allowing the adversary to block nodes instead of permanently crashing them. Our algorithms are scalable to large systems as each node contacts only an (amortized) constant number of peers in each communication round. We show that our algorithms are optimal up to constant (resp.\ sub-logarithmic) factors by proving that every almost-everywhere consensus protocol takes $\Omega(log_d n)$ rounds in the worst case, where d is an upper bound on the number of communication requests initiated per node in each round. We complement our theoretical results with an experimental evaluation of the binary almost-everywhere consensus protocol revealing a short convergence time even against an adversary blocking a large fraction of nodes.

Self-Stabilizing Supervised Publish-Subscribe Systems

M. Feldmann, C. Kolb, C. Scheideler, T.F. Strothmann, in: Proceedings of the 32nd IEEE International Parallel & Distributed Processing Symposium (IPDPS), IEEE, 2018

In this paper we present two major results: First, we introduce the first self-stabilizing version of a supervised overlay network (as introduced in~\cite{DBLP:conf/ispan/KothapalliS05}) by presenting a self-stabilizing supervised skip ring. Secondly, we show how to use the self-stabilizing supervised skip ring to construct an efficient self-stabilizing publish-subscribe system. That is, in addition to stabilizing the overlay network, every subscriber of a topic will eventually know all of the publications that have been issued so far for that topic. The communication work needed to processes a subscribe or unsubscribe operation is just a constant in a legitimate state, and the communication work of checking whether the system is still in a legitimate state is just a constant on expectation for the supervisor as well as any process in the system.

Skueue: A Scalable and Sequentially Consistent Distributed Queue

M. Feldmann, C. Scheideler, A. Setzer, in: Proceedings of the 32nd IEEE International Parallel & Distributed Processing Symposium (IPDPS), IEEE, 2018

We propose a distributed protocol for a queue, called Skueue, which spreads its data fairly onto multiple processes, avoiding bottlenecks in high throughput scenarios. Skueuecan be used in highly dynamic environments, through the addition of join and leave requests to the standard queue operations enqueue and dequeue. Furthermore Skueue satisfies sequential consistency in the asynchronous message passing model. Scalability is achieved by aggregating multiple requests to a batch, which can then be processed in a distributed fashion without hurting the queue semantics. Operations in Skueue need a logarithmic number of rounds w.h.p. until they are processed, even under a high rate of incoming requests.

On the runtime of universal coating for programmable matter

J. J. Daymude, Z. Derakhshandeh, R. Gmyr, A. Porter, A. W. Richa, C. Scheideler, T.F. Strothmann, Natural Computing (2018)(1), pp. 81--96

Forming Tile Shapes with Simple Robots

R. Gmyr, K. Hinnenthal, I. Kostitsyna, F. Kuhn, D. Rudolph, C. Scheideler, T.F. Strothmann, in: Proceedings of the 24th International Conference on DNA Computing and Molecular Programming, Springer International Publishing, 2018, pp. 122-138

Provably Anonymous Communication Based on Trusted Execution Environments

J. Blömer, J. Bobolz, C. Scheideler, A. Setzer, 2018

In this paper, we investigate the use of trusted execution environments (TEEs, such as Intel's SGX) for an anonymous communication infrastructure over untrusted networks. For this, we present the general idea of exploiting trusted execution environments for the purpose of anonymous communication, including a continuous-time security framework that models strong anonymity guarantees in the presence of an adversary that observes all network traffic and can adaptively corrupt a constant fraction of participating nodes. In our framework, a participating node can generate a number of unlinkable pseudonyms. Messages are sent from and to pseudonyms, allowing both senders and receivers of messages to remain anonymous. We introduce a concrete construction, which shows viability of our TEE-based approach to anonymous communication. The construction draws from techniques from cryptography and overlay networks. Our techniques are very general and can be used as a basis for future constructions with similar goals.

Preface

C. Scheideler, Theor. Comput. Sci. (2018), 751, pp. 1

Relays: Towards a Link Layer for Robust and Secure Fog Computing

C. Scheideler, in: Proceedings of the 2018 Workshop on Theory and Practice for Integrated Cloud, Fog and Edge Computing Paradigms, TOPIC@PODC 2018, Egham, United Kingdom, July 27, 2018, 2018, pp. 1-2

Shape Recognition by a Finite Automaton Robot

R. Gmyr, K. Hinnenthal, I. Kostitsyna, F. Kuhn, D. Rudolph, C. Scheideler, in: 43rd International Symposium on Mathematical Foundations of Computer Science, MFCS 2018, August 27-31, 2018, Liverpool, UK, 2018, pp. 52:1-52:15

A Self-Stabilizing Hashed Patricia Trie

T. Knollmann, C. Scheideler, in: Proceedings of the 20th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS), Springer, Cham, 2018

While a lot of research in distributed computing has covered solutions for self-stabilizing computing and topologies, there is far less work on self-stabilization for distributed data structures. Considering crashing peers in peer-to-peer networks, it should not be taken for granted that a distributed data structure remains intact. In this work, we present a self-stabilizing protocol for a distributed data structure called the hashed Patricia Trie (Kniesburges and Scheideler WALCOM'11) that enables efficient prefix search on a set of keys. The data structure has a wide area of applications including string matching problems while offering low overhead and efficient operations when embedded on top of a distributed hash table. Especially, longest prefix matching for $x$ can be done in $\mathcal{O}(\log |x|)$ hash table read accesses. We show how to maintain the structure in a self-stabilizing way. Our protocol assures low overhead in a legal state and a total (asymptotically optimal) memory demand of $\Theta(d)$ bits, where $d$ is the number of bits needed for storing all keys.

Competitive Routing in Hybrid Communication Networks

D. Jung, C. Kolb, C. Scheideler, J. Sundermeier, in: Proceedings of the 14th International Symposium on Algorithms and Experiments for Wireless Networks (ALGOSENSORS) , Springer, 2018

Routing is a challenging problem for wireless ad hoc networks, especially when the nodes are mobile and spread so widely that in most cases multiple hops are needed to route a message from one node to another. In fact, it is known that any online routing protocol has a poor performance in the worst case, in a sense that there is a distribution of nodes resulting in bad routing paths for that protocol, even if the nodes know their geographic positions and the geographic position of the destination of a message is known. The reason for that is that radio holes in the ad hoc network may require messages to take long detours in order to get to a destination, which are hard to find in an online fashion. In this paper, we assume that the wireless ad hoc network can make limited use of long-range links provided by a global communication infrastructure like a cellular infrastructure or a satellite in order to compute an abstraction of the wireless ad hoc network that allows the messages to be sent along near-shortest paths in the ad hoc network. We present distributed algorithms that compute an abstraction of the ad hoc network in $\mathcal{O}\left(\log ^2 n\right)$ time using long-range links, which results in $c$-competitive routing paths between any two nodes of the ad hoc network for some constant $c$ if the convex hulls of the radio holes do not intersect. We also show that the storage needed for the abstraction just depends on the number and size of the radio holes in the wireless ad hoc network and is independent on the total number of nodes, and this information just has to be known to a few nodes for the routing to work.

Brief Announcement: Competitive Routing in Hybrid Communication Networks

D. Jung, C. Kolb, C. Scheideler, J. Sundermeier, in: Proceedings of the 30th on Symposium on Parallelism in Algorithms and Architectures (SPAA), ACM Press, 2018

Self-stabilizing Overlays for high-dimensional Monotonic Searchability

M. Feldmann, C. Kolb, C. Scheideler, in: Proceedings of the 20th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS), Springer, Cham, 2018, pp. 16-31

We extend the concept of monotonic searchability~\cite{DBLP:conf/opodis/ScheidelerSS15}~\cite{DBLP:conf/wdag/ScheidelerSS16} for self-stabilizing systems from one to multiple dimensions. A system is self-stabilizing if it can recover to a legitimate state from any initial illegal state. These kind of systems are most often used in distributed applications. Monotonic searchability provides guarantees when searching for nodes while the recovery process is going on. More precisely, if a search request started at some node $u$ succeeds in reaching its destination $v$, then all future search requests from $u$ to $v$ succeed as well. Although there already exists a self-stabilizing protocol for a two-dimensional topology~\cite{DBLP:journals/tcs/JacobRSS12} and an universal approach for monotonic searchability~\cite{DBLP:conf/wdag/ScheidelerSS16}, it is not clear how both of these concepts fit together effectively. The latter concept even comes with some restrictive assumptions on messages, which is not the case for our protocol. We propose a simple novel protocol for a self-stabilizing two-dimensional quadtree that satisfies monotonic searchability. Our protocol can easily be extended to higher dimensions and offers routing in $\mathcal O(\log n)$ hops for any search request.

Relays: A New Approach for the Finite Departure Problem in Overlay Networks

C. Scheideler, A. Setzer, in: Proceedings of the 20th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS 2018), 2018

A fundamental problem for overlay networks is to safely exclude leaving nodes, i.e., the nodes requesting to leave the overlay network are excluded from it without affecting its connectivity. To rigorously study self-stabilizing solutions to this problem, the Finite Departure Problem (FDP) has been proposed [9]. In the FDP we are given a network of processes in an arbitrary state, and the goal is to eventually arrive at (and stay in) a state in which all leaving processes irrevocably decided to leave the system while for all weakly-connected components in the initial overlay network, all staying processes in that component will still form a weakly connected component. In the standard interconnection model, the FDP is known to be unsolvable by local control protocols, so oracles have been investigated that allow the problem to be solved [9]. To avoid the use of oracles, we introduce a new interconnection model based on relays. Despite the relay model appearing to be rather restrictive, we show that it is universal, i.e., it is possible to transform any weakly-connected topology into any other weakly-connected topology, which is important for being a useful interconnection model for overlay networks. Apart from this, our model allows processes to grant and revoke access rights, which is why we believe it to be of interest beyond the scope of this paper. We show how to implement the relay layer in a self-stabilizing way and identify properties protocols need to satisfy so that the relay layer can recover while serving protocol requests.

On Underlay-Aware Self-Stabilizing Overlay Networks

T. Götte, C. Scheideler, A. Setzer, in: Proceedings of the 20th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS 2018), Springer, 2018, pp. 50-64

We present a self-stabilizing protocol for an overlay network that constructs the Minimum Spanning Tree (MST) for an underlay that is modeled by a weighted tree. The weight of an overlay edge between two nodes is the weighted length of their shortest path in the tree. We rigorously prove that our protocol works correctly under asynchronous and non-FIFO message delivery. Further, the protocol stabilizes after O(N^2) asynchronous rounds where N is the number of nodes in the overlay.

## 2017

A. Ogierman, A. Richa, C. Scheideler, S. Schmid, J. Zhang, Distributed Computing (2017), 31(3), pp. 241-254

This paper considers the problem of how to efficiently share a wireless medium which is subject to harsh external interference or even jamming. So far, this problem is understood only in simplistic single-hop or unit disk graph models. We in this paper initiate the study of MAC protocols for the SINR interference model (a.k.a. physical model). This paper makes two contributions. First, we introduce a new adversarial SINR model which captures a wide range of interference phenomena. Concretely, we consider a powerful, adaptive adversary which can jam nodes at arbitrary times and which is only limited by some energy budget. Our second contribution is a distributed MAC protocol called Sade which provably achieves a constant competitive throughput in this environment: we show that, with high probability, the protocol ensures that a constant fraction of the non-blocked time periods is used for successful transmissions.

Towards a universal approach for the finite departure problem in overlay networks

A. Koutsopoulos, C. Scheideler, T.F. Strothmann, Inf. Comput. (2017), pp. 408--424

Algorithmic Foundations of Programmable Matter Dagstuhl Seminar 16271

S. P. Fekete, A. W. Richa, K. Römer, C. Scheideler, SIGACT News (2017)(2), pp. 87--94

Universal coating for programmable matter

Z. Derakhshandeh, R. Gmyr, A. W. Richa, C. Scheideler, T.F. Strothmann, Theor. Comput. Sci. (2017), pp. 56--68

Improved Leader Election for Self-organizing Programmable Matter

J. J. Daymude, R. Gmyr, A. W. Richa, C. Scheideler, T.F. Strothmann, in: Algorithms for Sensor Systems - 13th International Symposium on Algorithms and Experiments for Wireless Sensor Networks, ALGOSENSORS 2017, Vienna, Austria, September 7-8, 2017, Revised Selected Papers, 2017, pp. 127--140

Distributed Monitoring of Network Properties: The Power of Hybrid Networks

R. Gmyr, K. Hinnenthal, C. Scheideler, C. Sohler, in: Proceedings of the 44th International Colloquium on Automata, Languages, and Programming (ICALP), 2017, pp. 137:1--137:15

We initiate the study of network monitoring algorithms in a class of hybrid networks in which the nodes are connected by an external network and an internal network (as a short form for externally and internally controlled network). While the external network lies outside of the control of the nodes (or in our case, the monitoring protocol running in them) and might be exposed to continuous changes, the internal network is fully under the control of the nodes. As an example, consider a group of users with mobile devices having access to the cell phone infrastructure. While the network formed by the WiFi connections of the devices is an external network (as its structure is not necessarily under the control of the monitoring protocol), the connections between the devices via the cell phone infrastructure represent an internal network (as it can be controlled by the monitoring protocol). Our goal is to continuously monitor properties of the external network with the help of the internal network. We present scalable distributed algorithms that efficiently monitor the number of edges, the average node degree, the clustering coefficient, the bipartiteness, and the weight of a minimum spanning tree. Their performance bounds demonstrate that monitoring the external network state with the help of an internal network can be done much more efficiently than just using the external network, as is usually done in the literature.

A Self-Stabilizing General De Bruijn Graph

M. Feldmann, C. Scheideler, in: Proceedings of the 19th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS), Springer, Cham, 2017, pp. 250-264

Searching for other participants is one of the most important operations in a distributed system.We are interested in topologies in which it is possible to route a packet in a fixed number of hops until it arrives at its destination.Given a constant $d$, this paper introduces a new self-stabilizing protocol for the $q$-ary $d$-dimensional de Bruijn graph ($q = \sqrt[d]{n}$) that is able to route any search request in at most $d$ hops w.h.p., while significantly lowering the node degree compared to the clique: We require nodes to have a degree of $\mathcal O(\sqrt[d]{n})$, which is asymptotically optimal for a fixed diameter $d$.The protocol keeps the expected amount of edge redirections per node in $\mathcal O(\sqrt[d]{n})$, when the number of nodes in the system increases by factor $2^d$.The number of messages that are periodically sent out by nodes is constant.

## 2016

Churn- and DoS-resistant Overlay Networks Based on Network Reconfiguration

M. Drees, R. Gmyr, C. Scheideler, in: Proceedings of the 28th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), 2016, pp. 417--427

We present three robust overlay networks: First, we present a network that organizes the nodes into an expander and is resistant to even massive adversarial churn. Second, we develop a network based on the hypercube that maintains connectivity under adversarial DoS-attacks. For the DoS-attacks we use the notion of a Omega(log log n)-late adversary which only has access to topological information that is at least Omega(log log n) rounds old. Finally, we develop a network that combines both churn- and DoS-resistance. The networks gain their robustness through constant network reconfiguration, i.e., the topology of the networks changes constantly. Our reconguration algorithms are based on node sampling primitives for expanders and hypercubes that allow each node to sample a logarithmic number of nodes uniformly at random in O(log log n) communication rounds. These primitives are specific to overlay networks and their optimal runtime represents an exponential improvement over known techniques. Our results have a wide range of applications, for example in the area of scalable and robust peer-to-peer systems.

S. Schmid, C. Avin, C. Scheideler, M. Borokhovich, B. Haeupler, Z. Lotker, IEEE/ACM Trans. Netw. (2016)(3), pp. 1421--1433

On the Runtime of Universal Coating for Programmable Matter

Z. Derakhshandeh, R. Gmyr, A. Porter, A. W. Richa, C. Scheideler, T.F. Strothmann, in: DNA Computing and Molecular Programming - 22nd International Conference, DNA 22, Munich, Germany, September 4-8, 2016, Proceedings, 2016, pp. 148--164

Universal Shape Formation for Programmable Matter

Z. Derakhshandeh, R. Gmyr, A. W. Richa, C. Scheideler, T.F. Strothmann, in: Proceedings of the 28th ACM Symposium on Parallelism in Algorithms and Architectures, SPAA 2016, Asilomar State Beach/Pacific Grove, CA, USA, July 11-13, 2016, ACM, 2016, pp. 289--299

Jamming-Resistant MAC Protocols for Wireless Networks

A. W. Richa, C. Scheideler, in: Encyclopedia of Algorithms, 2016, pp. 999--1002

Self-stabilizing Metric Graphs

R. Gmyr, J. Lefèvre, C. Scheideler, in: Proceedings of the 18th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS), 2016, pp. 248--262

We present a self-stabilizing algorithm for overlay networks that, for an arbitrary metric given by a distance oracle, constructs the graph representing that metric. The graph representing a metric is the unique minimal undirected graph such that for any pair of nodes the length of a shortest path between the nodes corresponds to the distance between the nodes according to the metric. The algorithm works under both an asynchronous and a synchronous daemon. In the synchronous case, the algorithm stablizes in time O(n) and it is almost silent in that after stabilization a node sends and receives a constant number of messages per round.

Towards a Universal Approach for Monotonic Searchability in Self-stabilizing Overlay Networks

C. Scheideler, A. Setzer, T.F. Strothmann, in: Proceedings of the 30th International Symposium on Distributed Computing (DISC), 2016, pp. 71--84

For overlay networks, the ability to recover from a variety of problems like membership changes or faults is a key element to preserve their functionality. In recent years, various self-stabilizing overlay networks have been proposed that have the advantage of being able to recover from any illegal state. However, the vast majority of these networks cannot give any guarantees on its functionality while the recovery process is going on. We are especially interested in searchability, i.e., the functionality that search messages for a specific identifier are answered successfully if a node with that identifier exists in the network. We investigate overlay networks that are not only self-stabilizing but that also ensure that monotonic searchability is maintained while the recovery process is going on, as long as there are no corrupted messages in the system. More precisely, once a search message from node u to another node v is successfully delivered, all future search messages from u to v succeed as well. Monotonic searchability was recently introduced in OPODIS 2015, in which the authors provide a solution for a simple line topology.We present the first universal approach to maintain monotonic searchability that is applicable to a wide range of topologies. As the base for our approach, we introduce a set of primitives for manipulating overlay networks that allows us to maintain searchability and show how existing protocols can be transformed to use theses primitives.We complement this result with a generic search protocol that together with the use of our primitives guarantees monotonic searchability.As an additional feature, searching existing nodes with the generic search protocol is as fast as searching a node with any other fixed routing protocol once the topology has stabilized.

## 2015

IRIS: A Robust Information System Against Insider DoS Attacks

M. Eikel, C. Scheideler, Transactions on Parallel Computing (2015)(3), pp. 18:1--18:33

In this work, we present the first scalable distributed information system, that is, a system with low storage overhead, that is provably robust against denial-of-service (DoS) attacks by a current insider. We allow a current insider to have complete knowledge about the information system and to have the power to block any ϵ-fraction of its servers by a DoS attack, where ϵ can be chosen up to a constant. The task of the system is to serve any collection of lookup requests with at most one per nonblocked server in an efficient way despite this attack. Previously, scalable solutions were only known for DoS attacks of past insiders, where a past insider only has complete knowledge about some past time point t0 of the information system. Scheideler et al. [Awerbuch and Scheideler 2007; Baumgart et al. 2009] showed that in this case, it is possible to design an information system so that any information that was inserted or last updated after t0 is safe against a DoS attack. But their constructions would not work at all for a current insider. The key idea behind our IRIS system is to make extensive use of coding. More precisely, we present two alternative distributed coding strategies with an at most logarithmic storage overhead that can handle up to a constant fraction of blocked servers.

Towards Establishing Monotonic Searchability in Self-Stabilizing Data Structures

C. Scheideler, A. Setzer, T.F. Strothmann, in: Proceedings of the 19th International Conference on Principles of Distributed Systems (OPODIS), 2015

Distributed applications are commonly based on overlay networks interconnecting their sites so that they can exchange information. For these overlay networks to preserve their functionality, they should be able to recover from various problems like membership changes or faults. Various self-stabilizing overlay networks have already been proposed in recent years, which have the advantage of being able to recover from any illegal state, but none of these networks can give any guarantees on its functionality while the recovery process is going on. We initiate research on overlay networks that are not only self-stabilizing but that also ensure that searchability is maintained while the recovery process is going on, as long as there are no corrupted messages in the system. More precisely, once a search message from node u to another node v is successfully delivered, all future search messages from u to v succeed as well. We call this property monotonic searchability. We show that in general it is impossible to provide monotonic searchability if corrupted messages are present in the system, which justifies the restriction to system states without corrupted messages. Furthermore, we provide a self-stabilizing protocol for the line for which we can also show monotonic searchability. It turns out that even for the line it is non-trivial to achieve this property. Additionally, we extend our protocol to deal with node departures in terms of the Finite Departure Problem of Foreback et. al (SSS 2014). This makes our protocol even capable of handling node dynamics.

Towards a Universal Approach for the Finite Departure Problem in Overlay Networks

A. Koutsopoulos, C. Scheideler, T.F. Strothmann, in: Proceedings of the 17th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS), 2015, pp. 201-216

A fundamental problem for overlay networks is to safely exclude leaving nodes, i.e., the nodes requesting to leave the overlay network are excluded from it without affecting its connectivity. There are a number of studies for safe node exclusion if the overlay is in a well-defined state, but almost no formal results are known for the case in which the overlay network is in an arbitrary initial state, i.e., when looking for a self-stabilizing solution for excluding leaving nodes. We study this problem in two variants: the Finite Departure Problem (FDP) and the Finite Sleep Problem (FSP). In the FDP the leaving nodes have to irrevocably decide when it is safe to leave the network, whereas in the FSP, this leaving decision does not have to be final: the nodes may resume computation when woken up by an incoming message. We are the first to present a self-stabilizing protocol for the FDP and the FSP that can be combined with a large class of overlay maintenance protocols so that these are then guaranteed to safely exclude leaving nodes from the system from any initial state while operating as specified for the staying nodes. In order to formally define the properties these overlay maintenance protocols have to satisfy, we identify four basic primitives for manipulating edges in an overlay network that might be of independent interest.

A deterministic worst-case message complexity optimal solution for resource discovery

S. Kniesburges, A. Koutsopoulos, C. Scheideler, Theoretical Computer Science (2015), pp. 67-79

We consider the problem of resource discovery in distributed systems. In particular we give an algorithm, such that each node in a network discovers the address of any other node in the network. We model the knowledge of the nodes as a virtual overlay network given by a directed graph such that complete knowledge of all nodes corresponds to a complete graph in the overlay network. Although there are several solutions for resource discovery, our solution is the first that achieves worst-case optimal work for each node, i.e. the number of addresses (O(n)O(n)) or bits (O(nlog⁡n)O(nlog⁡n)) a node receives or sends coincides with the lower bound, while ensuring only a linear runtime (O(n)O(n)) on the number of rounds.

Leader Election and Shape Formation with Self-organizing Programmable Matter

Z. Derakhshandeh, R. Gmyr, T.F. Strothmann, R. A. Bazzi, A. W. Richa, C. Scheideler, in: DNA Computing and Molecular Programming - 21st International Conference, DNA 21, Boston and Cambridge, MA, USA, August 17-21, 2015. Proceedings, 2015, pp. 117--132

An Algorithmic Framework for Shape Formation Problems in Self-Organizing Particle Systems

Z. Derakhshandeh, R. Gmyr, A. W. Richa, C. Scheideler, T.F. Strothmann, in: Proceedings of the Second Annual International Conference on Nanoscale Computing and Communication, NANOCOM' 15, Boston, MA, USA, September 21-22, 2015, ACM, 2015, pp. 21:1--21:2

Brief Announcement: On the Feasibility of Leader Election and Shape Formation with Self-Organizing Programmable Matter

Z. Derakhshandeh, R. Gmyr, T.F. Strothmann, R. A. Bazzi, A. W. Richa, C. Scheideler, in: Proceedings of the 2015 ACM Symposium on Principles of Distributed Computing, PODC 2015, Donostia-San Sebasti{\'{a}}n, Spain, July 21 - 23, 2015, ACM, 2015, pp. 67--69

Brief Announcement: Towards a Universal Approach for the Finite Departure Problem in Overlay Networks

A. Koutsopoulos, C. Scheideler, T.F. Strothmann, in: Proceedings of the 27th ACM on Symposium on Parallelism in Algorithms and Architectures, SPAA 2015, Portland, OR, USA, June 13-15, 2015, ACM, 2015, pp. 77--79

## 2014

RoBuSt: A Crash-Failure-Resistant Distributed Storage System

C. Scheideler, A. Setzer, M. Eikel, in: Proceedings of the 18th International Conference on Principles of Distributed Systems (OPODIS), 2014, pp. 107--122

In this work we present the first distributed storage system that is provably robust against crash failures issued by an adaptive adversary, i.e., for each batch of requests the adversary can decide based on the entire system state which servers will be unavailable for that batch of requests. Despite up to \gamma n^{1/\log\log n} crashed servers, with \gamma>0 constant and n denoting the number of servers, our system can correctly process any batch of lookup and write requests (with at most a polylogarithmic number of requests issued at each non-crashed server) in at most a polylogarithmic number of communication rounds, with at most polylogarithmic time and work at each server and only a logarithmic storage overhead. Our system is based on previous work by Eikel and Scheideler (SPAA 2013), who presented IRIS, a distributed information system that is provably robust against the same kind of crash failures. However, IRIS is only able to serve lookup requests. Handling both lookup and write requests has turned out to require major changes in the design of IRIS.

Re-Chord: A Self-stabilizing Chord Overlay Network

S. Kniesburges, A. Koutsopoulos, C. Scheideler, Theory of Computing Systems (2014)(3), pp. 591-612

The Chord peer-to-peer system is considered, together with CAN, Tapestry and Pastry, as one of the pioneering works on peer-to-peer distributed hash tables (DHT) that inspired a large volume of papers and projects on DHTs as well as peer-to-peer systems in general. Chord, in particular, has been studied thoroughly, and many variants of Chord have been presented that optimize various criteria. Also, several implementations of Chord are available on various platforms. Though Chord is known to be very efficient and scalable and it can handle churn quite well, no protocol is known yet that guarantees that Chord is self-stabilizing, i.e., the Chord network can be recovered from any initial state in which the network is still weakly connected. This is not too surprising since it is known that the Chord network is not locally checkable for its current topology. We present a slight extension of the Chord network, called Re-Chord (reactive Chord), that turns out to be locally checkable, and we present a self-stabilizing distributed protocol for it that can recover the Re-Chord network from any initial state, in which the n peers are weakly connected, in O(nlogn) communication rounds. We also show that our protocol allows a new peer to join or an old peer to leave an already stable Re-Chord network so that within O(logn)^2) communication rounds the Re-Chord network is stable again.

Principles of Robust Medium Access and an Application to Leader Election

B. Awerbuch, A.W. Richa, C. Scheideler, S. Schmid, J. Zhang, Transactions on Algorithms (2014)(4)

SKIP*: A Self-Stabilizing Skip Graph

R. Jacob, A. W. Richa, C. Scheideler, S. Schmid, H. Täubig, J. ACM (2014)(6), pp. 36:1--36:26

Brief announcement: amoebot - a new model for programmable matter

Z. Derakhshandeh, S. Dolev, R. Gmyr, A. W. Richa, C. Scheideler, T.F. Strothmann, in: 26th ACM Symposium on Parallelism in Algorithms and Architectures, SPAA'14, Prague, Czech Republic - June 23 - 25, 2014, ACM, 2014, pp. 220--222

A. Ogierman, A.W. Richa, C. Scheideler, S. Schmid, J. Zhang, in: Proceedings of the 33rd Annual IEEE International Conference on Computer Communications (INFOCOM), 2014, pp. 2751--2759

This paper considers the problem of how to efficiently share a wireless medium which is subject to harsh external interference or even jamming. While this problem has already been studied intensively for simplistic single-hop or unit disk graph models, we make a leap forward and study MAC protocols for the SINR interference model (a.k.a. the physical model). We make two contributions. First, we introduce a new adversarial SINR model which captures a wide range of interference phenomena. Concretely, we consider a powerful, adaptive adversary which can jam nodes at arbitrary times and which is only limited by some energy budget. The second contribution of this paper is a distributed MAC protocol which provably achieves a constant competitive throughput in this environment: we show that, with high probability, the protocol ensures that a constant fraction of the non-blocked time periods is used for successful transmissions.

Algorithmic Aspects of Resource Management in the Cloud

S. Kniesburges, C. Markarian, F. Meyer auf der Heide, C. Scheideler, in: Proceedings of the 21st International Colloquium on Structural Information and Communication Complexity (SIROCCO), 2014, pp. 1-13

In this survey article, we discuss two algorithmic research areas that emerge from problems that arise when resources are offered in the cloud. The first area, online leasing, captures problems arising from the fact that resources in the cloud are not bought, but leased by cloud vendors. The second area, Distributed Storage Systems, deals with problems arising from so-called cloud federations, i.e., when several cloud providers are needed to fulfill a given task.

A Note on the Parallel Runtime of Self-Stabilizing Graph Linearization

D. Gall, R. Jacob, A.W. Richa, C. Scheideler, S. Schmid, H.. Täubig, Theory of Computing Systems (2014)(1), pp. 110-135

Topological self-stabilization is an important concept to build robust open distributed systems (such as peer-to-peer systems) where nodes can organize themselves into meaningful network topologies. The goal is to devise distributed algorithms where nodes forward, insert, and delete links to neighboring nodes, and that converge quickly to such a desirable topology, independently of the initial network configuration. This article proposes a new model to study the parallel convergence time. Our model sheds light on the achievable parallelism by avoiding bottlenecks of existing models that can yield a distorted picture. As a case study, we consider local graph linearization—i.e., how to build a sorted list of the nodes of a connected graph in a distributed and self-stabilizing manner. In order to study the main structure and properties of our model, we propose two variants of a most simple local linearization algorithm. For each of these variants, we present analyses of the worst-case and bestcase parallel time complexities, as well as the performance under a greedy selection of the actions to be executed. It turns out that the analysis is non-trivial despite the simple setting, and to complement our formal insights we report on our experiments which indicate that the runtimes may be better in the average case.

On Stabilizing Departures in Overlay Networks

D. Foreback, A. Koutsopoulos, M. Nesterenko, C. Scheideler, T.F. Strothmann, in: Proceedings of the 16th International Symposium on Stabilization, Safety, and Security of Distributed Systems, 2014, pp. 48--62

A fundamental problem for peer-to-peer systems is to maintain connectivity while nodes are leaving, i.e., the nodes requesting to leave the peer-to-peer system are excluded from the overlay network without affecting its connectivity. There are a number of studies for safe node exclusion if the overlay is in a well-defined state initially. Surprisingly, the problem is not formally studied yet for the case in which the overlay network is in an arbitrary initial state, i.e., when looking for a self-stabilizing solution for excluding leaving nodes. We study this problem in two variants: the Finite Departure Problem (FDP) ) and the Finite Sleep Problem (FSP). In the FDP the leaving nodes have to irrevocably decide when it is safe to leave the network, whereas in the FSP, this leaving decision does not have to be final: the nodes may resume computation if necessary. We show that there is no self-stabilizing distributed algorithm for the FDP, even in a synchronous message passing model. To allow a solution, we introduce an oracle called NIDEC and show that it is sufficient even for the asynchronous message passing model by proposing an algorithm that can solve the FDP using NIDEC. We also show that a solution to the FSP does not require an oracle.

Minimum Linear Arrangement of Series-Parallel Graphs

C. Scheideler, M. Eikel, A. Setzer, in: Proceedings of the 12th Workshop on Approximation and Online Algorithms (WAOA), 2014, pp. 168--180

We present a factor $14D^2$ approximation algorithm for the minimum linear arrangement problem on series-parallel graphs, where $D$ is the maximum degree in the graph. Given a suitable decomposition of the graph, our algorithm runs in time $O(|E|)$ and is very easy to implement. Its divide-and-conquer approach allows for an effective parallelization. Note that a suitable decomposition can also be computed in time $O(|E|\log{|E|})$ (or even $O(\log{|E|}\log^*{|E|})$ on an EREW PRAM using $O(|E|)$ processors). For the proof of the approximation ratio, we use a sophisticated charging method that uses techniques similar to amortized analysis in advanced data structures. On general graphs, the minimum linear arrangement problem is known to be NP-hard. To the best of our knowledge, the minimum linear arrangement problem on series-parallel graphs has not been studied before.

HSkip+: A Self-Stabilizing Overlay Network for Nodes with Heterogeneous Bandwidths

M. Feldotto, C. Scheideler, K. Graffi, in: Proceedings of the 14th IEEE International Conference on Peer-to-Peer Computing (P2P), 2014, pp. 1-10

In this paper we present and analyze HSkip+, a self-stabilizing overlay network for nodes with arbitrary heterogeneous bandwidths. HSkip+ has the same topology as the Skip+ graph proposed by Jacob et al. [PODC 2009] but its self-stabilization mechanism significantly outperforms the self-stabilization mechanism proposed for Skip+. Also, the nodes are now ordered according to their bandwidths and not according to their identifiers. Various other solutions have already been proposed for overlay networks with heterogeneous bandwidths, but they are not self-stabilizing. In addition to HSkip+ being self-stabilizing, its performance is on par with the best previous bounds on the time and work for joining or leaving a network of peers of logarithmic diameter and degree and arbitrary bandwidths. Also, the dilation and congestion for routing messages is on par with the best previous bounds for such networks, so that HSkip+ combines the advantages of both worlds. Our theoretical investigations are backed by simulations demonstrating that HSkip+ is indeed performing much better than Skip+ and working correctly under high churn rates.

## 2013

Competitive throughput in multi-hop wireless networks despite adaptive jamming

A. W. Richa, C. Scheideler, S. Schmid, J. Zhang, Distributed Computing (2013)(3), pp. 159--171

Corona: A stabilizing deterministic message-passing skip list

R. Mohd Nor, M. Nesterenko, C. Scheideler, Theor. Comput. Sci. (2013), pp. 119--129

An Efficient and Fair MAC Protocol Robust to Reactive Interference

A. W. Richa, C. Scheideler, S. Schmid, J. Zhang, IEEE/ACM Trans. Netw. (2013)(3), pp. 760--771

Towards Duality of Multicommodity Multiroute Cuts and Flows: Multilevel Ball-Growing

P. Kolman, C. Scheideler, Theory of Computing Systems (2013)(2), pp. 341-363

An elementary h-route ow, for an integer h 1, is a set of h edge- disjoint paths between a source and a sink, each path carrying a unit of ow, and an h-route ow is a non-negative linear combination of elementary h-routeows. An h-route cut is a set of edges whose removal decreases the maximum h-route ow between a given source-sink pair (or between every source-sink pair in the multicommodity setting) to zero. The main result of this paper is an approximate duality theorem for multicommodity h-route cuts and ows, for h 3: The size of a minimum h-route cut is at least f=h and at most O(log4 k f) where f is the size of the maximum h-routeow and k is the number of commodities. The main step towards the proof of this duality is the design and analysis of a polynomial-time approximation algorithm for the minimum h-route cut problem for h = 3 that has an approximation ratio of O(log4 k). Previously, polylogarithmic approximation was known only for h-route cuts for h 2. A key ingredient of our algorithm is a novel rounding technique that we call multilevel ball-growing. Though the proof of the duality relies on this algorithm, it is not a straightforward corollary of it as in the case of classical multicommodity ows and cuts. Similar results are shown also for the sparsest multiroute cut problem.

C. Avin, B. Häupler, Z. Lotker, C. Scheideler, S. Schmid, in: Proceedings of the 27th IEEE International Parallel and Distributed Processing Symposium (IPDPS), 2013, pp. 395-406

This paper initiates the study of self-adjusting networks (or distributed data structures) whose topologies dynamically adapt to a communication pattern $\sigma$. We present a fully decentralized self-adjusting solution called SplayNet. A SplayNet is a distributed generalization of the classic splay tree concept. It ensures short paths (which can be found using local-greedy routing) between communication partners while minimizing topological rearrangements. We derive an upper bound for the amortized communication cost of a SplayNet based on empirical entropies of $\sigma$, and show that SplayNets have several interesting convergence properties. For instance, SplayNets features a provable online optimality under special requests scenarios. We also investigate the optimal static network and prove different lower bounds for the average communication cost based on graph cuts and on the empirical entropy of the communication pattern $\sigma$. From these lower bounds it follows, e.g., that SplayNets are optimal in scenarios where the requests follow a product distribution as well. Finally, this paper shows that in contrast to the Minimum Linear Arrangement problem which is generally NP-hard, the optimal static tree network can be computed in polynomial time for any guest graph, despite the exponentially large graph family. We complement our formal analysis with a small simulation study on a Facebook graph.

IRIS: A Robust Information System Against Insider DoS-Attacks

M. Eikel, C. Scheideler, in: Proceedings of the 25th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), 2013, pp. 119-129

In this work we present the first scalable distributed information system,i.e., a system with low storage overhead, that is provably robust againstDenial-of-Service (DoS) attacks by a current insider. We allow acurrent insider to have complete knowledge about the information systemand to have the power to block any \epsilon-fraction of its serversby a DoS-attack, where \epsilon can be chosen up to a constant. The taskof the system is to serve any collection of lookup requests with at most oneper non-blocked server in an efficient way despite this attack. Previously,scalable solutions were only known for DoS-attacks of past insiders, where apast insider only has complete knowledge about some past time pointt_0 of the information system. Scheideler et al. (DISC 2007, SPAA 2009) showedthat in this case it is possible to design an information system so that anyinformation that was inserted or last updated after t_0 is safe against a DoS-attack. But their constructions would not work at all for a current insider. The key idea behindour IRIS system is to make extensive use of coding. More precisely, we presenttwo alternative distributed coding strategies with an at most logarithmicstorage overhead that can handle up to a constant fraction of blocked servers.

CONE-DHT: A distributed self-stabilizing algorithm for a heterogeneous storage system

S. Kniesburges, A. Koutsopoulos, C. Scheideler, in: Proceedings of the 27th International Symposium on Distributed Computing (DISC), 2013, pp. 537-549

We consider the problem of managing a dynamic heterogeneous storagesystem in a distributed way so that the amount of data assigned to a hostin that system is related to its capacity. Two central problems have to be solvedfor this: (1) organizing the hosts in an overlay network with low degree and diameterso that one can efficiently check the correct distribution of the data androute between any two hosts, and (2) distributing the data among the hosts so thatthe distribution respects the capacities of the hosts and can easily be adapted asthe set of hosts or their capacities change. We present distributed protocols forthese problems that are self-stabilizing and that do not need any global knowledgeabout the system such as the number of nodes or the overall capacity of thesystem. Prior to this work no solution was known satisfying these properties.

A Deterministic Worst-Case Message Complexity Optimal Solution for Resource Discovery

S. Kniesburges, A. Koutsopoulos, C. Scheideler, in: Proceedings of 20th International Colloqium on Structural Information and Communication Complexity (SIROCCO), 2013, pp. 165-176

We consider the problem of resource discovery in distributed systems. In particular we give an algorithm, such that each node in a network discovers the add ress of any other node in the network. We model the knowledge of the nodes as a virtual overlay network given by a directed graph such that complete knowledge of all nodes corresponds to a complete graph in the overlay network. Although there are several solutions for resource discovery, our solution is the first that achieves worst-case optimal work for each node, i.e. the number of addresses (O(n)) or bits (O(nlogn)) a node receives or sendscoincides with the lower bound, while ensuring only a linearruntime (O(n)) on the number of rounds.

## 2012

Editorial for Algorithmic Aspects of Wireless Sensor Networks

S. Dolev, C. Scheideler, Theor. Comput. Sci. (2012), pp. 1

Selfish Distributed Optimization

B. Monien, C. Scheideler, in: Euro-Par 2012 Parallel Processing - 18th International Conference, Euro-Par 2012, Rhodes Island, Greece, August 27-31, 2012. Proceedings, Springer, 2012, pp. 1--2

Towards higher-dimensional topological self-stabilization: A distributed algorithm for Delaunay graphs

R. Jacob, S. Ritscher, C. Scheideler, S. Schmid, Theoretical Computer Science (2012), pp. 137-148

This article studies the construction of self-stabilizing topologies for distributed systems. While recent research has focused on chain topologies where nodes need to be linearized with respect to their identiers, we explore a natural and relevant 2-dimensional generalization. In particular, we present a local self-stabilizing algorithm DStab which is based on the concept of \local Delaunay graphs" and which forwards temporary edges in greedy fashion reminiscent of compass routing. DStab constructs a Delaunay graph from any initial connected topology and in a distributed manner in time O(n3) in the worst-case; if the initial network contains the Delaunay graph, the convergence time is only O(n) rounds. DStab also ensures that individual node joins and leaves aect a small part of the network only. Such self-stabilizing Delaunay networks have interesting applications and our construction gives insights into the necessary geometric reasoning that is required for higherdimensional linearization problems.Keywords: Distributed Algorithms, Topology Control, Social Networks

Tiara: A self-stabilizing deterministic skip list and skip graph

T. Clouser, M. Nesterenko, C. Scheideler, Theoretical Computer Science (2012), pp. 18-35

We present Tiara — a self-stabilizing peer-to-peer network maintenance algorithm. Tiara is truly deterministic which allows it to achieve exact performance bounds. Tiara allows logarithmic searches and topology updates. It is based on a novel sparse 0-1 skip list. We then describe its extension to a ringed structure and to a skip-graph.Key words: Peer-to-peer networks, overlay networks, self-stabilization.

Smoothed analysis of left-to-right maxima with applications

V. Damerow, B. Manthey, F. Meyer auf der Heide, H. Räcke, C. Scheideler, C. Sohler, T. Tantau, Transactions on Algorithms (2012)(3), pp. 30

A left-to-right maximum in a sequence of n numbers s_1, …, s_n is a number that is strictly larger than all preceding numbers. In this article we present a smoothed analysis of the number of left-to-right maxima in the presence of additive random noise. We show that for every sequence of n numbers s_i ∈ [0,1] that are perturbed by uniform noise from the interval [-ε,ε], the expected number of left-to-right maxima is Θ(&sqrt;n/ε + log n) for ε>1/n. For Gaussian noise with standard deviation σ we obtain a bound of O((log3/2 n)/σ + log n).We apply our results to the analysis of the smoothed height of binary search trees and the smoothed number of comparisons in the quicksort algorithm and prove bounds of Θ(&sqrt;n/ε + log n) and Θ(n/ε+1&sqrt;n/ε + n log n), respectively, for uniform random noise from the interval [-ε,ε]. Our results can also be applied to bound the smoothed number of points on a convex hull of points in the two-dimensional plane and to smoothed motion complexity, a concept we describe in this article. We bound how often one needs to update a data structure storing the smallest axis-aligned box enclosing a set of points moving in d-dimensional space.

Self-Organizing Particle Systems

M. Drees, M. Hüllmann (married name: Eikel), A. Koutsopoulos, C. Scheideler, in: Proceedings of the 26th IEEE International Parallel and Distributed Processing Symposium (IPDPS), 2012, pp. 1272-1283

Nanoparticles are getting more and more in the focus of the scientic community since the potential for the development of very small particles interacting with each other and completing medical and other tasks is getting bigger year by year. In this work we introduce a distributed local algorithm for arranging a set of nanoparticles on the discrete plane into specic geometric shapes, for instance a rectangle. The concept of a particle we use can be seen as a simple mobile robot with the following restrictions: it can only view the state of robots it is physically connected to, is anonymous, has only a constant size memory, can only move by using other particles as an anchor point on which it pulls itself alongside, and it operates in Look-Compute-Move cycles. The main result of this work is the presentation of a random distributed local algorithm which transforms any given connected set of particles into a particular geometric shape. As an example we provide a version of this algorithm for forming a rectangle with an arbitrary predened aspect ratio. To the best of our knowledge this is the rst work that considers arrangement problems for these types of robots.

Competitive and fair throughput for co-existing networks under adversarial interference

A.W. Richa, C. Scheideler, S. Schmid, J.. Zhang, in: Proceedings of the 31st Annual ACM SIGACT-SIGOPS Symposium on Principles and Distributed Computing (PODC), 2012, pp. 291-300

This paper initiates the formal study of a fundamental problem: How to efficiently allocate a shared communication medium among a set of K co-existing networks in the presence of arbitrary external interference? While most literature on medium access focuses on how to share a medium among nodes, these approaches are often either not directly applicable to co-existing networks as they would violate the independence requirement, or they yield a low throughput if applied to multiple networks. We present the randomized medium access (MAC) protocol COMAC which guarantees that a given communication channel is shared fairly among competing and independent networks, and that the available bandwidth is used efficiently. These performance guarantees hold in the presence of arbitrary external interference or even under adversarial jamming. Concretely, we show that the co-existing networks can use a Ω(ε2 min{ε, 1/poly(K)})-fraction of the non-jammed time steps for successful message transmissions, where ε is the (arbitrarily distributed) fraction of time which is not jammed.

Brief Announcement: SplayNets - Towards Self-Adjusting Distributed Data Structures

S. Schmid, C. Avin, C. Scheideler, B. Häupler, Z. Lotker, in: Proceedings of the 26th International Symposium on Distributed Computing (DISC), 2012, pp. 439-440

This paper initiates the study of self-adjusting distributed data structures for networks. In particular, we present SplayNets: a binary search tree based network that is self-adjusting to routing request.We derive entropy bounds on the amortized routing cost and show that our splaying algorithm has some interesting properties.

Brief Announcement: Hashed Predecessor Patricia Trie - A Data Structure for Efficient Predecessor Queries in Peer-to-Peer Systems

S. Kniesburges, C. Scheideler, in: Proceedings of the 26th International Symposium on Distributed Computing (DISC), 2012, pp. 435-436

The design of ecient search structures for peer-to-peer systems has attracted a lot of attention in recent years. In this announcement we address the problem of nding the predecessor in a key set and present an ecient data structure called hashed Predecessor Patricia trie. Our hashed Predecessor Patricia trie supports PredecessorSearch(x) and Insert(x) and Delete(x) in O(log log u) hash table accesses when u is the size of the universe of the keys. That is the costs only depend on u and not the size of the data structure. One feature of our approach is that it only uses the lookup interface of the hash table and therefore hash table accesses may be realized by any distributed hash table (DHT).

Approximate Duality of Multicommodity Multiroute Flows and Cuts: Single Source Case

P. Kolman, C. Scheideler, in: Proceedings of the 23th ACM SIAM Symposium on Discrete Algorithms (SODA), 2012, pp. 800-810

Given an integer h, a graph G = (V;E) with arbitrary positive edge capacities and k pairs of vertices (s1; t1); (s2; t2); : : : ; (sk; tk), called terminals, an h-route cut is a set F µ E of edges such that after the removal of the edges in F no pair si ¡ ti is connected by h edge-disjoint paths (i.e., the connectivity of every si ¡ ti pair is at most h ¡ 1 in (V;E n F)). The h-route cut is a natural generalization of the classical cut problem for multicommodity °ows (take h = 1). The main result of this paper is an O(h722h log2 k)-approximation algorithm for the minimum h-route cut problem in the case that s1 = s2 = ¢ ¢ ¢ = sk, called the single source case. As a corollary of it we obtain an approximate duality theorem for multiroute multicom-modity °ows and cuts with a single source. This partially answers an open question posted in several previous papers dealing with cuts for multicommodity multiroute problems.

A Self-Stabilization Process for Small-World Networks

S. Kniesburges, A. Koutsopoulos, C. Scheideler, in: Proceedings of the 26th IEEE International Parallel and Distributed Processing Symposium (IPDPS), 2012, pp. 1261--1271

Small-world networks have received significant attention because of their potential as models for the interaction networks of complex systems. Specifically, neither random networks nor regular lattices seem to be an adequate framework within which to study real-world complex systems such as chemical-reaction networks, neural networks, food webs, social networks, scientific-collaboration networks, and computer networks. Small-world networks provide some desired properties like an expected polylogarithmic distance between two processes in the network, which allows routing in polylogarithmic hops by simple greedy routing, and robustness against attacks or failures. By these properties, small-world networks are possible solutions for large overlay networks comparable to structured overlay networks like CAN, Pastry, Chord, which also provide polylogarithmic routing, but due to their uniform structure, structured overlay networks are more vulnerable to attacks or failures. In this paper we bring together a randomized process converging to a small-world network and a self-stabilization process so that a small-world network is formed out of any weakly connected initial state. To the best of our knowledge this is the first distributed self-stabilization process for building a small-world network.

## 2011

Competitive and Fair Medium Access Despite Reactive Jamming

A. W. Richa, C. Scheideler, S. Schmid, J. Zhang, in: 2011 International Conference on Distributed Computing Systems, ICDCS 2011, Minneapolis, Minnesota, USA, June 20-24, 2011, IEEE Computer Society, 2011, pp. 507--516

Towards jamming-resistant and competitive medium access in the SINR model

A. W. Richa, C. Scheideler, S. Schmid, J. Zhang, in: Proceedings of the 3rd ACM workshop on Wireless of the students, by the students, for the students, S3@MOBICOM 2011, Las Vegas, NV, USA, September 19 - 23, 2011, ACM, 2011, pp. 33--36

Self-stabilizing leader election for single-hop wireless networks despite jamming

A. W. Richa, C. Scheideler, S. Schmid, J. Zhang, in: Proceedings of the 12th ACM Interational Symposium on Mobile Ad Hoc Networking and Computing, MobiHoc 2011, Paris, France, May 16-20, 2011, ACM, 2011, pp. 15

Re-Chord: a self-stabilizing chord overlay network

S. Kniesburges, A. Koutsopoulos, C. Scheideler, in: SPAA 2011: Proceedings of the 23rd Annual ACM Symposium on Parallelism in Algorithms and Architectures, San Jose, CA, USA, June 4-6, 2011 (Co-located with FCRC 2011), 2011, pp. 235--244

Hashed Patricia Trie: Efficient Longest Prefix Matching in Peer-to-Peer Systems

S. Kniesburges, C. Scheideler, in: WALCOM: Algorithms and Computation - 5th International Workshop, WALCOM 2011, New Delhi, India, February 18-20, 2011. Proceedings, Springer, 2011, pp. 170--181

Programming for Distributed Computing: From Physical to Logical Networks

C. Scheideler, K. Graffi, in: Computer Science, The Hardware, Software and Heart of It, Springer, 2011, pp. 155--168

Broadcasting - How Can I Quickly Disseminate Information?

C. Scheideler, in: Algorithms Unplugged, Springer, 2011, pp. 223--229

Towards Duality of Multicommodity Multiroute Cuts and Flows: Multilevel Ball-Growing

P. Kolman, C. Scheideler, in: 28th International Symposium on Theoretical Aspects of Computer Science, STACS 2011, March 10-12, 2011, Dortmund, Germany, 2011, pp. 129--140

Stabilizing consensus with the power of two choices

B. Doerr, L.A. Goldberg, L. Minder, T. Sauerwald, C. Scheideler, in: Proceedings of the 23rd ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), 2011, pp. 149-158

In the standard consensus problem there are n processes with possibly di®erent input values and the goal is to eventually reach a point at which all processes commit to exactly one of these values. We are studying a slight variant of the consensus problem called the stabilizing consensus problem [2]. In this problem, we do not require that each process commits to a ¯nal value at some point, but that eventually they arrive at a common, stable value without necessarily being aware of that. This should work irrespective of the states in which the processes are starting. Our main result is a simple randomized algorithm called median rule that, with high probability, just needs O(logmlog log n + log n) time and work per process to arrive at an almost stable consensus for any set of m legal values as long as an adversary can corrupt the states of at most p n processes at any time. Without adversarial involvement, just O(log n) time and work is needed for a stable consensus, with high probability. As a by-product, we obtain a simple distributed algorithm for approximating the median of n numbers in time O(logmlog log n + log n) under adversarial presence.

Self-Stabilizing DeBruijn Networks

A.W. Richa, C. Scheideler, in: Proceedings of the 13th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS), 2011, pp. 416-430

This paper presents a dynamic overlay network based on the De Bruijn graph which we call Linearized De Bruijn (LDB) network. The LDB network has the advantage that it has a guaranteed constant node degree and that the routing between any two nodes takes at most O(log n) hops with high probability. Also, we show that there is a simple local-control algorithm that can recover the LDB network from any network topology that is weakly connected.

Corona: A Stabilizing Deterministic Message-Passing Skip List

M. Nesterenko, R. Mohd, C. Scheideler, in: Proceedings of the 13th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS), 2011, pp. 356--370

We present Corona, a deterministic self-stabilizing algorithm for skip list construction in structured overlay networks. Corona operates in the low-atomicity message-passing asynchronous system model. Corona requires constant process memory space for its operation and, therefore, scales well. We prove the general necessary conditions limiting the initial states from which a self-stabilizing structured overlay network in message-passing system can be constructed. The conditions require that initial state information has to form a weakly connected graph and it should only contain identiers that are present in the system. We formally describe Corona and rigorously prove that it stabilizes from an arbitrary initial state subject to the necessary conditions. We extend Corona to construct a skip graph.

## 2010

Algorithmische Grundlagen verteilter Speichersysteme

F. Meyer auf der Heide, C. Scheideler, Informatik Spektrum (2010)(5), pp. 468--474

Foreword

C. Gavoille, B. Patt-Shamir, C. Scheideler, Theory of Computing Systems (2010)(4), pp. 809--810

Time Complexity of Distributed Topological Self-stabilization: The Case of Graph Linearization

D. Gall, R. Jacob, A. W. Richa, C. Scheideler, S. Schmid, H. Täubig, in: LATIN 2010: Theoretical Informatics, 9th Latin American Symposium, Oaxaca, Mexico, April 19-23, 2010. Proceedings, Springer, 2010, pp. 294--305

Brief announcement: towards robust medium access in multi-hop networks

A.W. Richa, J. Zhang, C. Scheideler, S. Schmid, in: Proceedings of the 29th Annual ACM Symposium on Principles of Distributed Computing, PODC 2010, Zurich, Switzerland, July 25-28, 2010, ACM, 2010, pp. 114--115

A Jamming-Resistant MAC Protocol for Multi-Hop Wireless Networks

A.W. Richa, C. Scheideler, S. Schmid, J. Zhang, in: Distributed Computing, 24th International Symposium, DISC 2010, Cambridge, MA, USA, September 13-15, 2010. Proceedings, Springer, 2010, pp. 179--193

Brief Announcement: Stabilizing Consensus with the Power of Two Choices

B. Doerr, L. Ann Goldberg, L. Minder, T. Sauerwald, C. Scheideler, in: Distributed Computing, 24th International Symposium, DISC 2010, Cambridge, MA, USA, September 13-15, 2010. Proceedings, Springer, 2010, pp. 528--530

## 2009

Foreword

R. D. Kleinberg, C. Scheideler, Theory Comput. Syst. (2009)(2), pp. 187

Towards a Scalable and Robust DHT

B. Awerbuch, C. Scheideler, Theory Comput. Syst. (2009)(2), pp. 234--260

Robust random number generation for peer-to-peer systems

B. Awerbuch, C. Scheideler, Theor. Comput. Sci. (2009)(6-7), pp. 453--466

A Distributed and Oblivious Heap

C. Scheideler, S. Schmid, in: Automata, Languages and Programming, 36th Internatilonal Colloquium, ICALP 2009, Rhodes, Greece, July 5-12, 2009, Proceedings, Part II, Springer, 2009, pp. 571--582

A Self-stabilizing and Local Delaunay Graph Construction

R. Jacob, S. Ritscher, C. Scheideler, S. Schmid, in: Algorithms and Computation, 20th International Symposium, ISAAC 2009, Honolulu, Hawaii, USA, December 16-18, 2009. Proceedings, Springer, 2009, pp. 771--780

A distributed polylogarithmic time algorithm for self-stabilizing skip graphs

R. Jacob, A. W. Richa, C. Scheideler, S. Schmid, H. Täubig, in: Proceedings of the 28th Annual ACM Symposium on Principles of Distributed Computing, PODC 2009, Calgary, Alberta, Canada, August 10-12, 2009, 2009, pp. 131--140

A DoS-resilient information system for dynamic data management

M. Baumgart, C. Scheideler, S. Schmid, in: SPAA 2009: Proceedings of the 21st Annual ACM Symposium on Parallelism in Algorithms and Architectures, Calgary, Alberta, Canada, August 11-13, 2009, 2009, pp. 300--309

Brief Announcement: On the Time Complexity of Distributed Topological Self-stabilization

D. Gall, R. Jacob, A. W. Richa, C. Scheideler, S. Schmid, H. Täubig, in: Stabilization, Safety, and Security of Distributed Systems, 11th International Symposium, SSS 2009, Lyon, France, November 3-6, 2009. Proceedings, Springer, 2009, pp. 781--782

Stabilizing Consensus with the Power of Two Choices

B. Doerr, L. Ann Goldberg, L. Minder, T. Sauerwald, C. Scheideler, in: Algorithmic Methods for Distributed Cooperative Systems, 06.09. - 11.09.2009, Schloss Dagstuhl - Leibniz-Zentrum für Informatik, Germany, 2009

## 2008

Algorithms for Overlay Networks

C. Scheideler, Bulletin of the EATCS (2008), pp. 130--152

A jamming-resistant MAC protocol for single-hop wireless networks

B. Awerbuch, A. W. Richa, C. Scheideler, in: Proceedings of the Twenty-Seventh Annual ACM Symposium on Principles of Distributed Computing, PODC 2008, Toronto, Canada, August 18-21, 2008, ACM, 2008, pp. 45--54

SPREAD: an adaptive scheme for redundant and fair storage in dynamic heterogeneous storage systems

M. Mense, C. Scheideler, in: Proceedings of the Nineteenth Annual ACM-SIAM Symposium on Discrete Algorithms, SODA 2008, San Francisco, California, USA, January 20-22, 2008, SIAM, 2008, pp. 1135--1144

Tiara: A Self-stabilizing Deterministic Skip List

T. Clouser, M. Nesterenko, C. Scheideler, in: Stabilization, Safety, and Security of Distributed Systems, 10th International Symposium, SSS 2008, Detroit, MI, USA, November 21-23, 2008. Proceedings, Springer, 2008, pp. 124--140

Broadcasting: Wie verbreite ich schnell Informationen?

C. Scheideler, in: Taschenbuch der Algorithmen, Springer, 2008, pp. 229--236

## 2007

Algorithms for Fault-Tolerant Routing in Circuit-Switched Networks

A. Bagchi, A. Chaudhary, C. Scheideler, P. Kolman, SIAM J. Discrete Math. (2007)(1), pp. 141--157

Linearization: Locally Self-Stabilizing Sorting in Graphs

M. Onus, A. W. Richa, C. Scheideler, in: Proceedings of the Nine Workshop on Algorithm Engineering and Experiments, ALENEX 2007, New Orleans, Louisiana, USA, January 6, 2007, 2007

Towards Scalable and Robust Overlay Networks

B. Awerbuch, C. Scheideler, in: 6th International workshop on Peer-To-Peer Systems, IPTPS 2007, Bellevue, WA, USA, February 26-27, 2007, 2007

A denial-of-service resistant DHT

B. Awerbuch, C. Scheideler, in: Proceedings of the Twenty-Sixth Annual ACM Symposium on Principles of Distributed Computing, PODC 2007, Portland, Oregon, USA, August 12-15, 2007, ACM, 2007, pp. 370--371

A Denial-of-Service Resistant DHT

B. Awerbuch, C. Scheideler, in: Distributed Computing, 21st International Symposium, DISC 2007, Lemesos, Cyprus, September 24-26, 2007, Proceedings, Springer, 2007, pp. 33--47

Overlay Networks for Peer-to-Peer Networks

A. W. Richa, C. Scheideler, in: Handbook of Approximation Algorithms and Metaheuristics., 2007

Dynamic and redundant data placement

A. Brinkmann, S. Effert, F. Meyer auf der Heide, C. Scheideler, in: IEEE International Conference on Distributed Computing Systems (ICDCS), 2007

We present a randomized block-level storage virtualization for arbitrary heterogeneous storage systems that can distribute data in a fair and redundant way and can adapt this distribution in an efficient way as storage devices enter or leave the system. More precisely, our virtualization strategies can distribute a set of data blocks among a set of storage devices of arbitrary non-uniform capacities so that a storage device representing x% of the capacity in the system will get x% of the data (as long as this is in principle possible) and the different copies of each data block are stored so that no two copies of a data block are located in the same device. Achieving these two properties is not easy, and no virtualization strategy has been presented so far that has been formally shown to satisfy fairness and redundancy while being time- and space-eflcient and allowing an efficient adaptation to a changing set of devices.

Can ISPs and P2P users cooperate for improved performance?

V. Aggarwal, A. Feldmann, C. Scheideler, ACM Computer Commucation Review (2007)

## 2006

Improved bounds for the unsplittable flow problem

P. Kolman, C. Scheideler, J. Algorithms (2006), 61(1), pp. 20--44

Survivable Monitoring in Dynamic Networks

G. Ateniese, C. Riley, C. Scheideler, IEEE Trans. Mob. Comput. (2006)(9), pp. 1242--1254

Distributed coloring in O/spl tilde/(/spl radic/(log n)) bit rounds

K. Kothapalli, C. Scheideler, M. Onus, C. Schindelhauer, in: IPDPS, 2006

Robust Random Number Generation for Peer-to-Peer Systems

B. Awerbuch, C. Scheideler, in: OPODIS, 2006, pp. 275--289

Towards a scalable and robust DHT

B. Awerbuch, C. Scheideler, in: SPAA, 2006, pp. 318--327

The Effect of Faults on Network Expansion

A. Bagchi, A. Bhargava, A. Chaudhary, D. Eppstein, C. Scheideler, Theory Comput. Syst. (2006)(6), pp. 903--928

Towards a paradigm for robust distributed algorithms and data structures

C. Scheideler, in: 6th International HNI Symposium on New Trends in Parallel and Distributed Computing, 2006

## 2005

Transparent Data Structures, or How to Make Search Trees Robust in a Distributed Environment

M. Korzeniowski, C. Scheideler, in: ISPAN, 2005, pp. 182--187

Supervised Peer-to-Peer Systems

K. Kothapalli, C. Scheideler, in: ISPAN, 2005, pp. 188--193

M. Onus, A. W. Richa, K. Kothapalli, C. Scheideler, in: ISPAN, 2005, pp. 346--351

Constant density spanners for wireless ad-hoc networks

K. Kothapalli, C. Scheideler, M. Onus, A. W. Richa, in: SPAA, 2005, pp. 116--125

C. Scheideler, in: STOC, 2005, pp. 704--713

Overlay networks for wireless ad hoc networks

C. Scheideler, in: IMA Workshop on Wireless Communications, 2005

## 2004

Simple On-Line Algorithms for the Maximum Disjoint Paths Problem

P. Kolman, C. Scheideler, Algorithmica (2004)(3), pp. 209--233

Group Spreading: A Protocol for Provably Secure Distributed Name Service

B. Awerbuch, C. Scheideler, in: ICALP, 2004, pp. 183--195

A Distributed Hash Table for Computational Grids

C. Riley, C. Scheideler, in: IPDPS, 2004

Robust Distributed Name Service

B. Awerbuch, C. Scheideler, in: IPTPS, 2004, pp. 237--249

Survivable Monitoring in Dynamic Networks

G. Ateniese, C. Riley, C. Scheideler, in: IWIA, 2004, pp. 33--47

Consistent and compact data management in distributed storage systems

B. Awerbuch, C. Scheideler, in: SPAA, 2004, pp. 44--53

Pagoda: a dynamic overlay network for routing, data management, and multicasting

A. Bhargava, K. Kothapalli, C. Riley, C. Scheideler, M. Thober, in: SPAA, 2004, pp. 170--179

The effect of faults on network expansion

A. Bagchi, A. Bhargava, A. Chaudhary, D. Eppstein, C. Scheideler, in: SPAA, ACM, 2004, pp. 286--293

## 2003

Storage Management as Means to cope with Exponential Information Growth

C. Scheideler, K. Salzwedel, F. Meyer auf der Heide, A. Brinkmann, M. Vodisek, U. Rückert, in: Proceedings of SSGRR 2003, 2003

The advances in Internet technology have led to tremendous improvements in business, education, and science and have changed the way we think, live, and communicate. Information exchange has become ubiquitous by the possibilities offered through modern technologies. We are able to offer information 24 hours a day through our web sites and can leave messages every time and from anywhere in the world. This change in communication has led to new challenges. Enterprises have to deal with an information amount that doubles every year. The technological foundation to cope with this information explosion is given by Storage Area Networks (SANs), which are able to connect a great number of storage systems over a fast interconnection network. However, to be able to use the benefits of a SAN, an easy-to-use and efficient management support has to be given to the storage administrator. In this paper, we will suggest new storage management concepts and we will introduce a new management environment that is able to significantly reduce management costs and increases the performance and resource utilization of the given SAN infrastructure.

Smoothed Motion Complexity

V. Damerow, F. Meyer auf der Heide, H. Räcke, C. Scheideler, C. Sohler, in: ESA, Springer, 2003, pp. 161--171

B. Awerbuch, A. Brinkmann, C. Scheideler, in: ICALP, Springer, 2003, pp. 1153--1168

Peer-to-peer systems for prefix search

B. Awerbuch, C. Scheideler, in: PODC, ACM, 2003, pp. 123--132

Perfectly Balanced Allocation

A. Czumaj, C. Riley, C. Scheideler, in: RANDOM-APPROX, Springer, 2003, pp. 240--251

On local algorithms for topology control and routing in ad hoc networks

L. Jia, R. Rajaraman, C. Scheideler, in: SPAA, ACM, 2003, pp. 220--229

Information gathering in adversarial systems: lines and cycles

K. Kothapalli, C. Scheideler, in: SPAA, ACM, 2003, pp. 333--342

## 2002

Improved Bounds for Acyclic Job Shop Scheduling

U. Feige, C. Scheideler, Combinatorica (2002)(3), pp. 361--399

Improved bounds for the unsplittable flow problem

P. Kolman, C. Scheideler, in: SODA, ACM/SIAM, 2002, pp. 184--193

Compact, adaptive placement schemes for non-uniform requirements

A. Brinkmann, K. Salzwedel, C. Scheideler, in: SPAA, 2002, pp. 53--62

Algorithms for fault-tolerant routing in circuit switched networks

A. Bagchi, A. Chaudhary, C. Scheideler, P. Kolman, in: SPAA, 2002, pp. 265--274

Models and Techniques for Communication in Dynamic Networks

C. Scheideler, in: STACS, Springer, 2002, pp. 27--49

Liste im Research Information System öffnen

##### SIROCCO 2022

29th International Colloquium on Structural Information
and Communication Complexity