TY - CONF AB - 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. AU - Scheideler, Christian AU - Setzer, Alexander AU - Strothmann, Thim Frederik ID - 241 T2 - Proceedings of the 19th International Conference on Principles of Distributed Systems (OPODIS) TI - Towards Establishing Monotonic Searchability in Self-Stabilizing Data Structures 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. 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. AU - Koutsopoulos, Andreas AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 242 T2 - Proceedings of the 17th International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS) TI - Towards a Universal Approach for the Finite Departure Problem in Overlay Networks ER - TY - JOUR AB - 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. AU - Kniesburges, Sebastian AU - Koutsopoulos, Andreas AU - Scheideler, Christian ID - 327 JF - Theoretical Computer Science TI - A deterministic worst-case message complexity optimal solution for resource discovery ER - TY - CONF AU - Derakhshandeh, Zahra AU - Gmyr, Robert AU - Strothmann, Thim Frederik AU - A. Bazzi, Rida AU - W. Richa, Andrea AU - Scheideler, Christian ID - 1850 SN - 978-3-319-21998-1 T2 - DNA Computing and Molecular Programming - 21st International Conference, DNA 21, Boston and Cambridge, MA, USA, August 17-21, 2015. Proceedings TI - Leader Election and Shape Formation with Self-organizing Programmable Matter VL - 9211 ER - TY - CONF AU - Derakhshandeh, Zahra AU - Gmyr, Robert AU - W. Richa, Andrea AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1851 SN - 978-1-4503-3674-1 T2 - Proceedings of the Second Annual International Conference on Nanoscale Computing and Communication, NANOCOM' 15, Boston, MA, USA, September 21-22, 2015 TI - An Algorithmic Framework for Shape Formation Problems in Self-Organizing Particle Systems ER - TY - CONF AU - Derakhshandeh, Zahra AU - Gmyr, Robert AU - Strothmann, Thim Frederik AU - A. Bazzi, Rida AU - W. Richa, Andrea AU - Scheideler, Christian ID - 1852 SN - 978-1-4503-3617-8 T2 - Proceedings of the 2015 ACM Symposium on Principles of Distributed Computing, PODC 2015, Donostia-San Sebasti{\'{a}}n, Spain, July 21 - 23, 2015 TI - Brief Announcement: On the Feasibility of Leader Election and Shape Formation with Self-Organizing Programmable Matter ER - TY - CONF AU - Koutsopoulos, Andreas AU - Scheideler, Christian AU - Strothmann, Thim Frederik ID - 1853 SN - 978-1-4503-3588-1 T2 - Proceedings of the 27th ACM on Symposium on Parallelism in Algorithms and Architectures, SPAA 2015, Portland, OR, USA, June 13-15, 2015 TI - Brief Announcement: Towards a Universal Approach for the Finite Departure Problem in Overlay Networks ER - TY - CONF AB - 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. AU - Scheideler, Christian AU - Setzer, Alexander AU - Eikel, Martina ID - 371 T2 - Proceedings of the 18th International Conference on Principles of Distributed Systems (OPODIS) TI - RoBuSt: A Crash-Failure-Resistant Distributed Storage System ER - TY - JOUR AB - 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. AU - Kniesburges, Sebastian AU - Koutsopoulos, Andreas AU - Scheideler, Christian ID - 378 IS - 3 JF - Theory of Computing Systems TI - Re-Chord: A Self-stabilizing Chord Overlay Network ER - TY - JOUR AB - This article studies the design of medium access control (MAC) protocols for wireless networks that are provably robust against arbitrary and unpredictable disruptions (e.g., due to unintentional external interference from co-existing networks or due to jamming). We consider a wireless network consisting of a set of n honest and reliable nodes within transmission (and interference) range of each other, and we model the external disruptions with a powerful adaptive adversary. This adversary may know the protocol and its entire history and can use this knowledge to jam the wireless channel at will at any time. It is allowed to jam a (1 − )-fraction of the timesteps, for an arbitrary constant > 0 unknown to the nodes. The nodes cannot distinguish between the adversarial jamming or a collision of two or more messages that are sent at the same time. We demonstrate, for the first time, that there is a local-control MAC protocol requiring only very limited knowledge about the adversary and the network that achieves a constant (asymptotically optimal) throughput for the nonjammed time periods under any of the aforementioned adversarial strategies. The derived principles are also useful to build robust applications on top of the MAC layer, and we present an exemplary study for leader election, one of the most fundamental tasks in distributed computing. AU - Awerbuch, Baruch AU - Richa, Andrea W. AU - Scheideler, Christian AU - Schmid, Stefan AU - Zhang, Jin ID - 387 IS - 4 JF - Transactions on Algorithms TI - Principles of Robust Medium Access and an Application to Leader Election ER -