TY - JOUR
AB - 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.
AU - Kolman, Petr
AU - Scheideler, Christian
ID - 476
IS - 2
JF - Theory of Computing Systems
TI - Towards Duality of Multicommodity Multiroute Cuts and Flows: Multilevel Ball-Growing
ER -
TY - CONF
AU - Derakhshandeh, Zahra
AU - Dolev, Shlomi
AU - Gmyr, Robert
AU - W. Richa, Andrea
AU - Scheideler, Christian
AU - Strothmann, Thim Frederik
ID - 1863
SN - 978-1-4503-2821-0
T2 - 26th ACM Symposium on Parallelism in Algorithms and Architectures, SPAA'14, Prague, Czech Republic - June 23 - 25, 2014
TI - Brief announcement: amoebot - a new model for programmable matter
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 - CONF
AB - 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.
AU - Ogierman, Adrian
AU - Richa, Andrea W.
AU - Scheideler, Christian
AU - Schmid, Stefan
AU - Zhang, Jin
ID - 446
T2 - Proceedings of the 33rd Annual IEEE International Conference on Computer Communications (INFOCOM)
TI - Competitive MAC under adversarial SINR
ER -
TY - CONF
AB - 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.
AU - Kniesburges, Sebastian
AU - Markarian, Christine
AU - Meyer auf der Heide, Friedhelm
AU - Scheideler, Christian
ID - 459
T2 - Proceedings of the 21st International Colloquium on Structural Information and Communication Complexity (SIROCCO)
TI - Algorithmic Aspects of Resource Management in the Cloud
ER -
TY - JOUR
AU - Jacob, Riko
AU - W. Richa, Andrea
AU - Scheideler, Christian
AU - Schmid, Stefan
AU - Täubig, Hanjo
ID - 1858
IS - 6
JF - J. ACM
TI - SKIP*: A Self-Stabilizing Skip Graph
ER -
TY - CONF
AB - 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.
AU - Feldotto, Matthias
AU - Scheideler, Christian
AU - Graffi, Kalman
ID - 412
T2 - Proceedings of the 14th IEEE International Conference on Peer-to-Peer Computing (P2P)
TI - HSkip+: A Self-Stabilizing Overlay Network for Nodes with Heterogeneous Bandwidths
ER -
TY - CONF
AB - 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.
AU - Scheideler, Christian
AU - Eikel, Martina
AU - Setzer, Alexander
ID - 397
T2 - Proceedings of the 12th Workshop on Approximation and Online Algorithms (WAOA)
TI - Minimum Linear Arrangement of Series-Parallel Graphs
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 - CONF
AB - 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.
AU - Foreback, Dianne
AU - Koutsopoulos, Andreas
AU - Nesterenko, Mikhail
AU - Scheideler, Christian
AU - Strothmann, Thim Frederik
ID - 393
T2 - Proceedings of the 16th International Symposium on Stabilization, Safety, and Security of Distributed Systems
TI - On Stabilizing Departures in Overlay Networks
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 -
TY - JOUR
AB - 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.
AU - Gall, Dominik
AU - Jacob, Riko
AU - Richa, Andrea W.
AU - Scheideler, Christian
AU - Schmid, Stefan
AU - Täubig, Hanjo
ID - 464
IS - 1
JF - Theory of Computing Systems
TI - A Note on the Parallel Runtime of Self-Stabilizing Graph Linearization
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 - 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(nlogn)O(nlogn)) 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
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
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 - JOUR
AB - 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.
AU - Eikel, Martina
AU - Scheideler, Christian
ID - 284
IS - 3
JF - Transactions on Parallel Computing
TI - IRIS: A Robust Information System Against Insider DoS Attacks
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 - 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 -