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 - 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 - 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
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
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 - 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
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 - 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
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 - 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
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
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 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 - 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 - 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 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 - 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 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 -