TY - CONF AB - 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. AU - Drees, Maximilian AU - Gmyr, Robert AU - Scheideler, Christian ID - 215 T2 - Proceedings of the 28th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA) TI - Churn- and DoS-resistant Overlay Networks Based on Network Reconfiguration ER - TY - JOUR AU - Schmid, Stefan AU - Avin, Chen AU - Scheideler, Christian AU - Borokhovich, Michael AU - Haeupler, Bernhard AU - Lotker, Zvi ID - 1835 IS - 3 JF - IEEE/ACM Trans. Netw. TI - SplayNet: Towards Locally Self-Adjusting Networks ER - TY - CONF AU - Derakhshandeh, Zahra AU - Gmyr, Robert AU - Porter, Alexandra AU - W. Richa, Andrea AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1836 T2 - DNA Computing and Molecular Programming - 22nd International Conference, DNA 22, Munich, Germany, September 4-8, 2016, Proceedings TI - On the Runtime of Universal Coating for Programmable Matter VL - 9818 ER - TY - CONF AU - Derakhshandeh, Zahra AU - Gmyr, Robert AU - W. Richa, Andrea AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1837 T2 - 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 TI - Universal Shape Formation for Programmable Matter ER - TY - CHAP AU - W. Richa, Andrea AU - Scheideler, Christian ID - 1845 T2 - Encyclopedia of Algorithms TI - Jamming-Resistant MAC Protocols for Wireless Networks ER - TY - CONF AB - 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. AU - Gmyr, Robert AU - Lefèvre, Jonas AU - Scheideler, Christian ID - 155 T2 - Proceedings of the 18th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS) TI - Self-stabilizing Metric Graphs ER - TY - CONF AB - 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. AU - Scheideler, Christian AU - Setzer, Alexander AU - Strothmann, Thim Frederik ID - 142 T2 - Proceedings of the 30th International Symposium on Distributed Computing (DISC) TI - Towards a Universal Approach for Monotonic Searchability in Self-stabilizing Overlay Networks ER - TY - JOUR AB - 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. AU - Ogierman, Adrian AU - Richa, Andrea AU - Scheideler, Christian AU - Schmid, Stefan AU - Zhang, Jin ID - 3872 IS - 3 JF - Distributed Computing SN - 0178-2770 TI - Sade: competitive MAC under adversarial SINR VL - 31 ER - TY - JOUR AU - Koutsopoulos, Andreas AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1812 JF - Inf. Comput. TI - Towards a universal approach for the finite departure problem in overlay networks ER - TY - JOUR AU - P. Fekete, Sandor AU - W. Richa, Andrea AU - Römer, Kay AU - Scheideler, Christian ID - 1813 IS - 2 JF - SIGACT News TI - Algorithmic Foundations of Programmable Matter Dagstuhl Seminar 16271 ER - TY - JOUR AU - Derakhshandeh, Zahra AU - Gmyr, Robert AU - W. Richa, Andrea AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1814 JF - Theor. Comput. Sci. TI - Universal coating for programmable matter ER - TY - CONF AU - J. Daymude, Joshua AU - Gmyr, Robert AU - W. Richa, Andrea AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1815 T2 - 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 TI - Improved Leader Election for Self-organizing Programmable Matter ER - TY - CONF AB - 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. AU - Gmyr, Robert AU - Hinnenthal, Kristian AU - Scheideler, Christian AU - Sohler, Christian ID - 105 T2 - Proceedings of the 44th International Colloquium on Automata, Languages, and Programming (ICALP) TI - Distributed Monitoring of Network Properties: The Power of Hybrid Networks ER - TY - CONF AB - 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. AU - Feldmann, Michael AU - Scheideler, Christian ID - 125 SN - 978-3-319-69083-4 T2 - Proceedings of the 19th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS) TI - A Self-Stabilizing General De Bruijn Graph VL - 10616 ER - TY - CONF AB - 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. AU - Robinson, Peter AU - Scheideler, Christian AU - Setzer, Alexander ID - 3422 KW - distributed consensus KW - randomized algorithm KW - adaptive adversary KW - complexity lower bound SN - 978-1-4503-5799-9/18/07 T2 - Proceedings of the 30th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA) TI - Breaking the $\tilde\Omega(\sqrt{n})$ Barrier: Fast Consensus under a Late Adversary ER - TY - CONF AB - 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. AU - Feldmann, Michael AU - Kolb, Christina AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1163 KW - Topological Self-stabilization KW - Supervised Overlay KW - Publish-Subscribe System T2 - Proceedings of the 32nd IEEE International Parallel & Distributed Processing Symposium (IPDPS) TI - Self-Stabilizing Supervised Publish-Subscribe Systems ER - TY - CONF AB - 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. AU - Feldmann, Michael AU - Scheideler, Christian AU - Setzer, Alexander ID - 1164 T2 - Proceedings of the 32nd IEEE International Parallel & Distributed Processing Symposium (IPDPS) TI - Skueue: A Scalable and Sequentially Consistent Distributed Queue ER - TY - JOUR AU - J. Daymude, Joshua AU - Derakhshandeh, Zahra AU - Gmyr, Robert AU - Porter, Alexandra AU - W. Richa, Andrea AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1796 IS - 1 JF - Natural Computing TI - On the runtime of universal coating for programmable matter ER - TY - CONF AU - Gmyr, Robert AU - Hinnenthal, Kristian AU - Kostitsyna, Irina AU - Kuhn, Fabian AU - Rudolph, Dorian AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 5764 T2 - Proceedings of the 24th International Conference on DNA Computing and Molecular Programming TI - Forming Tile Shapes with Simple Robots ER - TY - GEN AB - 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. AU - Blömer, Johannes AU - Bobolz, Jan AU - Scheideler, Christian AU - Setzer, Alexander ID - 5820 TI - Provably Anonymous Communication Based on Trusted Execution Environments ER - TY - JOUR AU - Scheideler, Christian ID - 5984 JF - Theor. Comput. Sci. TI - Preface VL - 751 ER - TY - CONF AU - Scheideler, Christian ID - 5985 T2 - 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 TI - Relays: Towards a Link Layer for Robust and Secure Fog Computing ER - TY - CONF AU - Gmyr, Robert AU - Hinnenthal, Kristian AU - Kostitsyna, Irina AU - Kuhn, Fabian AU - Rudolph, Dorian AU - Scheideler, Christian ID - 5986 T2 - 43rd International Symposium on Mathematical Foundations of Computer Science, MFCS 2018, August 27-31, 2018, Liverpool, UK TI - Shape Recognition by a Finite Automaton Robot ER - TY - CONF AB - 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. AU - Knollmann, Till AU - Scheideler, Christian ED - Izumi, Taisuke ED - Kuznetsov, Petr ID - 4411 KW - Self-Stabilizing KW - Prefix Search KW - Distributed Data Structure T2 - Proceedings of the 20th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS) TI - A Self-Stabilizing Hashed Patricia Trie VL - 11201 ER - TY - CONF AB - 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. AU - Jung, Daniel AU - Kolb, Christina AU - Scheideler, Christian AU - Sundermeier, Jannik ID - 4563 KW - greedy routing KW - ad hoc networks KW - convex hulls KW - c-competitiveness T2 - Proceedings of the 14th International Symposium on Algorithms and Experiments for Wireless Networks (ALGOSENSORS) TI - Competitive Routing in Hybrid Communication Networks ER - TY - CONF AU - Jung, Daniel AU - Kolb, Christina AU - Scheideler, Christian AU - Sundermeier, Jannik ID - 4565 SN - 9781450357999 T2 - Proceedings of the 30th on Symposium on Parallelism in Algorithms and Architectures (SPAA) TI - Brief Announcement: Competitive Routing in Hybrid Communication Networks ER - TY - CONF AB - 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. AU - Feldmann, Michael AU - Kolb, Christina AU - Scheideler, Christian ID - 4351 T2 - Proceedings of the 20th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS) TI - Self-stabilizing Overlays for high-dimensional Monotonic Searchability VL - 11201 ER - TY - CONF AB - 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. AU - Scheideler, Christian AU - Setzer, Alexander ID - 5216 T2 - Proceedings of the 20th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS 2018) TI - Relays: A New Approach for the Finite Departure Problem in Overlay Networks ER - TY - CONF AB - 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. AU - Götte, Thorsten AU - Scheideler, Christian AU - Setzer, Alexander ID - 5222 T2 - Proceedings of the 20th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS 2018) TI - On Underlay-Aware Self-Stabilizing Overlay Networks VL - 11201 ER - TY - CONF AB - 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. AU - Luo, Linghui AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 7636 T2 - Proceedings of the 2019 IEEE 33rd International Parallel and Distributed Processing Symposium (IPDPS '19) TI - MultiSkipGraph: A Self-stabilizing Overlay Network that Maintains Monotonic Searchability ER - TY - CONF AB - 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. AU - Feldmann, Michael AU - Scheideler, Christian ID - 8534 T2 - Proceedings of the 31st ACM Symposium on Parallelism in Algorithms and Architectures (SPAA) TI - Skeap & Seap: Scalable Distributed Priority Queues for Constant and Arbitrary Priorities ER - TY - CONF AU - Augustine, John AU - Ghaffari, Mohsen AU - Gmyr, Robert AU - Hinnenthal, Kristian AU - Kuhn, Fabian AU - Li, Jason AU - Scheideler, Christian ID - 8871 T2 - Proceedings of the 31st ACM Symposium on Parallelism in Algorithms and Architectures TI - Distributed Computation in Node-Capacitated Networks ER - TY - CHAP AU - Daymude, Joshua J. AU - Hinnenthal, Kristian AU - Richa, Andréa W. AU - Scheideler, Christian ID - 9599 T2 - Distributed Computing by Mobile Entities, Current Research in Moving and Computing. TI - Computing by Programmable Particles ER - TY - CONF AB - 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. AU - Götte, Thorsten AU - Vijayalakshmi, Vipin Ravindran AU - Scheideler, Christian ID - 6976 T2 - Proceedings of the 2019 IEEE 33rd International Parallel and Distributed Processing Symposium (IPDPS '19) TI - Always be Two Steps Ahead of Your Enemy - Maintaining a Routable Overlay under Massive Churn with an Almost Up-to-date Adversary ER - TY - CONF AB - 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. AU - Scheideler, Christian AU - Setzer, Alexander ID - 10586 KW - Graphs transformations KW - NP-hardness KW - approximation algorithms T2 - Proceedings of the 46th International Colloquium on Automata, Languages, and Programming TI - On the Complexity of Local Graph Transformations VL - 132 ER - TY - CONF AU - Götte, Thorsten AU - Hinnenthal, Kristian AU - Scheideler, Christian ID - 12944 T2 - Structural Information and Communication Complexity TI - Faster Construction of Overlay Networks ER - TY - CONF AU - Augustine, John AU - Hinnenthal, Kristian AU - Kuhn, Fabian AU - Scheideler, Christian AU - Schneider, Philipp ID - 15627 SN - 9781611975994 T2 - Proceedings of the Fourteenth Annual ACM-SIAM Symposium on Discrete Algorithms TI - Shortest Paths in a Hybrid Network Model ER - TY - JOUR AU - Gmyr, Robert AU - Lefevre, Jonas AU - Scheideler, Christian ID - 14830 IS - 2 JF - Theory Comput. Syst. TI - Self-Stabilizing Metric Graphs VL - 63 ER - TY - CONF AU - Castenow, Jannik AU - Kolb, Christina AU - Scheideler, Christian ID - 14539 T2 - Proceedings of the 26th International Colloquium on Structural Information and Communication Complexity (SIROCCO) TI - A Bounding Box Overlay for Competitive Routing in Hybrid Communication Networks ER - TY - CONF AB - 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). AU - Feldmann, Michael AU - Götte, Thorsten AU - Scheideler, Christian ID - 13182 T2 - Proceedings of the 21st International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS) TI - A Loosely Self-stabilizing Protocol for Randomized Congestion Control with Logarithmic Memory ER - TY - CONF AU - Hinnenthal, Kristian AU - Scheideler, Christian AU - Struijs, Martijn ID - 13652 T2 - 33rd International Symposium on Distributed Computing (DISC 2019) TI - Fast Distributed Algorithms for LP-Type Problems of Low Dimension ER - TY - CONF AU - Augustine, John AU - Hinnenthal, Kristian AU - Kuhn, Fabian AU - Scheideler, Christian AU - Schneider, Philipp ED - Chawla, Shuchi ID - 27051 T2 - Proceedings of the 2020 ACM-SIAM Symposium on Discrete Algorithms, SODA 2020, Salt Lake City, UT, USA, January 5-8, 2020 TI - Shortest Paths in a Hybrid Network Model ER - TY - JOUR AU - Gmyr, Robert AU - Hinnenthal, Kristian AU - Kostitsyna, Irina AU - Kuhn, Fabian AU - Rudolph, Dorian AU - Scheideler, Christian AU - Strothmann, Thim ID - 17808 IS - 2 JF - Nat. Comput. TI - Forming tile shapes with simple robots VL - 19 ER - TY - CONF AB - 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. AU - Feldmann, Michael AU - Hinnenthal, Kristian AU - Scheideler, Christian ID - 20755 T2 - Proceedings of the 24th International Conference on Principles of Distributed Systems (OPODIS) TI - Fast Hybrid Network Algorithms for Shortest Paths in Sparse Graphs ER - TY - JOUR AB - 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. AU - Feldmann, Michael AU - Scheideler, Christian AU - Schmid, Stefan ID - 16902 JF - ACM Computing Surveys TI - Survey on Algorithms for Self-Stabilizing Overlay Networks ER - TY - CONF AB - 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. AU - Feldmann, Michael AU - Khazraei, Ardalan AU - Scheideler, Christian ID - 16903 T2 - Proceedings of the 32nd ACM Symposium on Parallelism in Algorithms and Architectures (SPAA) TI - Time- and Space-Optimal Discrete Clock Synchronization in the Beeping Model ER - TY - CONF AU - Castenow, Jannik AU - Kolb, Christina AU - Scheideler, Christian ID - 15169 T2 - Proceedings of the 21st International Conference on Distributed Computing and Networking (ICDCN) TI - A Bounding Box Overlay for Competitive Routing in Hybrid Communication Networks ER - TY - CONF AU - Daymude, Joshua J. AU - Gmyr, Robert AU - Hinnenthal, Kristian AU - Kostitsyna, Irina AU - Scheideler, Christian AU - Richa, Andréa W. ID - 16346 SN - 9781450377515 T2 - Proceedings of the 21st International Conference on Distributed Computing and Networking TI - Convex Hull Formation for Programmable Matter ER - TY - CONF AU - Dolev, Shlomi AU - Prasadh Narayanan, Ram AU - Scheideler, Christian AU - Schindelhauer, Christian ED - Galluccio, Laura ED - Mitra, Urbashi ED - Magarini, Maurizio ED - Abada, Sergi ED - Taynnan Barros, Michael ED - Krishnaswamy, Bhuvana ID - 25105 T2 - NANOCOM '21: The Eighth Annual ACM International Conference on Nanoscale Computing and Communication, Virtual Event, Italy, September 7 - 9, 2021 TI - Logarithmic Time MIMO Based Self-Stabilizing Clock Synchronization ER - TY - CONF AU - Feldmann, Michael AU - Padalkin, Andreas AU - Scheideler, Christian AU - Dolev, Shlomi ED - Johnen, Colette ED - Michael Schiller, Elad ED - Schmid, Stefan ID - 28917 T2 - Stabilization, Safety, and Security of Distributed Systems - 23rd International Symposium, (SSS) 2021, Virtual Event, November 17-20, 2021, Proceedings TI - Coordinating Amoebots via Reconfigurable Circuits VL - 13046 ER - TY - CONF AU - Dolev, Shlomi AU - Prasadh Narayanan, Ram AU - Scheideler, Christian AU - Schindelhauer, Christian ED - Galluccio, Laura ED - Mitra, Urbashi ED - Magarini, Maurizio ED - Abada, Sergi ED - Taynnan Barros, Michael ED - Krishnaswamy, Bhuvana ID - 27048 T2 - NANOCOM '21: The Eighth Annual ACM International Conference on Nanoscale Computing and Communication, Virtual Event, Italy, September 7 - 9, 2021 TI - Logarithmic Time MIMO Based Self-Stabilizing Clock Synchronization ER - TY - CONF AU - J. Daymude, Joshua AU - W. Richa, Andrea AU - Scheideler, Christian ED - Gilbert, Seth ID - 27050 T2 - 35th International Symposium on Distributed Computing, DISC 2021, October 4-8, 2021, Freiburg, Germany (Virtual Conference) TI - The Canonical Amoebot Model: Algorithms and Concurrency Control VL - 209 ER - TY - CONF AB - 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 $G$. AU - Götte, Thorsten AU - Hinnenthal, Kristian AU - Scheideler, Christian AU - Werthmann, Julian ED - Censor-Hillel, Keren ID - 22283 T2 - Proc. of the 40th ACM Symposium on Principles of Distributed Computing (PODC '21) TI - Time-Optimal Construction of Overlays ER - TY - CONF AU - Coy, Sam AU - Czumaj, Artur AU - Feldmann, Michael AU - Hinnenthal, Kristian AU - Kuhn, Fabian AU - Scheideler, Christian AU - Schneider, Philipp AU - Struijs, Martijn ED - Bramas, Quentin ED - Gramoli, Vincent ED - Milani, Alessia ID - 30217 T2 - 25th International Conference on Principles of Distributed Systems, OPODIS 2021, December 13-15, 2021, Strasbourg, France TI - Near-Shortest Path Routing in Hybrid Communication Networks VL - 217 ER - TY - CHAP AU - Götte, Thorsten AU - Kolb, Christina AU - Scheideler, Christian AU - Werthmann, Julian ID - 26888 SN - 0302-9743 T2 - Algorithms for Sensor Systems (ALGOSENSORS '21) TI - Beep-And-Sleep: Message and Energy Efficient Set Cover ER - TY - JOUR AU - Feldmann, Michael AU - Padalkin, Andreas AU - Scheideler, Christian AU - Dolev, Shlomi ID - 31060 IS - 4 JF - J. Comput. Biol. TI - Coordinating Amoebots via Reconfigurable Circuits VL - 29 ER - TY - CONF AU - Padalkin, Andreas AU - Scheideler, Christian AU - Warner, Daniel ED - Ouldridge, Thomas E. ED - Wickham, Shelley F. J. ID - 32602 SN - 1868-8969 T2 - 28th International Conference on DNA Computing and Molecular Programming (DNA 28) TI - The Structural Power of Reconfigurable Circuits in the Amoebot Model VL - 238 ER - TY - CONF AU - Kostitsyna, Irina AU - Scheideler, Christian AU - Warner, Daniel ED - Ouldridge, Thomas E. ED - Wickham, Shelley F. J. ID - 32603 SN - 1868-8969 T2 - 28th International Conference on DNA Computing and Molecular Programming (DNA 28) TI - Fault-Tolerant Shape Formation in the Amoebot Model VL - 238 ER - TY - CONF AU - Daymude, Joshua J. AU - Richa, Andréa W. AU - Scheideler, Christian ED - Aspnes, James ED - Michail, Othon ID - 33230 T2 - 1st Symposium on Algorithmic Foundations of Dynamic Networks, SAND 2022, March 28-30, 2022, Virtual Conference TI - Local Mutual Exclusion for Dynamic, Anonymous, Bounded Memory Message Passing Systems VL - 221 ER - TY - CONF AU - Götte, Thorsten AU - Scheideler, Christian ED - Agrawal, Kunal ED - Lee, I-Ting Angelina ID - 33240 T2 - SPAA ’22: 34th ACM Symposium on Parallelism in Algorithms and Architectures, Philadelphia, PA, USA, July 11 - 14, 2022 TI - Brief Announcement: The (Limited) Power of Multiple Identities: Asynchronous Byzantine Reliable Broadcast with Improved Resilience through Collusion ER - TY - CONF AU - Kostitsyna, Irina AU - Scheideler, Christian AU - Warner, Daniel ED - Aspnes, James ED - Michail, Othon ID - 30987 SN - 1868-8969 T2 - 1st Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2022) TI - Brief Announcement: Fault-Tolerant Shape Formation in the Amoebot Model VL - 221 ER - TY - CONF AU - Aguiliera, Marcos AU - Richa, Andréa W. AU - Schwarzmann, Alexander A. AU - Panconesi, Alessandro AU - Scheideler, Christian AU - Woelfel, Philipp ED - Milani, Alessia ED - Woelfel, Philipp ID - 33967 T2 - PODC ’22: ACM Symposium on Principles of Distributed Computing, Salerno, Italy, July 25 - 29, 2022 TI - 2022 Edsger W. Dijkstra Prize in Distributed Computing ER - TY - JOUR AB - 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. AU - Knollmann, Till AU - Scheideler, Christian ID - 21096 JF - Information and Computation SN - 0890-5401 TI - A self-stabilizing Hashed Patricia Trie ER - TY - JOUR AU - Götte, Thorsten AU - Kolb, Christina AU - Scheideler, Christian AU - Werthmann, Julian ID - 43109 JF - Theor. Comput. Sci. TI - Beep-and-Sleep: Message and Energy Efficient Set Cover VL - 950 ER - TY - CONF AU - Werthmann, Julian AU - Scheideler, Christian AU - Coy, Sam AU - Czumaj, Artur AU - Schneider, Philipp ID - 45188 TI - Routing Schemes for Hybrid Communication Networks ER - TY - CONF AU - Dou, Jinfeng AU - Götte, Thorsten AU - Hillebrandt, Henning AU - Scheideler, Christian AU - Werthmann, Julian ID - 45193 T2 - Proc. of the 42nd ACM Symposium on Principles of Distributed Computing (PODC '23) TI - Brief Announcement: Distributed Construction of Near-Optimal Compact Routing Schemes for Planar Graphs ER - TY - JOUR AU - Götte, Thorsten AU - Hinnenthal, Kristian AU - Scheideler, Christian AU - Werthmann, Julian ID - 45192 JF - Distributed Computing TI - Time-Optimal Construction of Overlays ER - TY - CHAP AU - Götte, Thorsten AU - Knollmann, Till AU - Meyer auf der Heide, Friedhelm AU - Scheideler, Christian AU - Werthmann, Julian ED - Haake, Claus-Jochen ED - Meyer auf der Heide, Friedhelm ED - Platzner, Marco ED - Wachsmuth, Henning ED - Wehrheim, Heike ID - 45875 T2 - On-The-Fly Computing -- Individualized IT-services in dynamic markets TI - Capabilities and Limitations of Local Strategies in Dynamic Networks VL - 412 ER - TY - CHAP AU - Blömer, Johannes AU - Eidens, Fabian AU - Jager, Tibor AU - Niehues, David AU - Scheideler, Christian ED - Haake, Claus-Jochen ED - Meyer auf der Heide, Friedhelm ED - Platzner, Marco ED - Wachsmuth, Henning ED - Wehrheim, Heike ID - 45891 T2 - On-The-Fly Computing -- Individualized IT-services in dynamic markets TI - Robustness and Security VL - 412 ER -