844 research outputs found
Fast and Compact Distributed Verification and Self-Stabilization of a DFS Tree
We present algorithms for distributed verification and silent-stabilization
of a DFS(Depth First Search) spanning tree of a connected network. Computing
and maintaining such a DFS tree is an important task, e.g., for constructing
efficient routing schemes. Our algorithm improves upon previous work in various
ways. Comparable previous work has space and time complexities of bits per node and respectively, where is the highest
degree of a node, is the number of nodes and is the diameter of the
network. In contrast, our algorithm has a space complexity of bits
per node, which is optimal for silent-stabilizing spanning trees and runs in
time. In addition, our solution is modular since it utilizes the
distributed verification algorithm as an independent subtask of the overall
solution. It is possible to use the verification algorithm as a stand alone
task or as a subtask in another algorithm. To demonstrate the simplicity of
constructing efficient DFS algorithms using the modular approach, We also
present a (non-sielnt) self-stabilizing DFS token circulation algorithm for
general networks based on our silent-stabilizing DFS tree. The complexities of
this token circulation algorithm are comparable to the known ones
Self-stabilizing interval routing algorithm with low stretch factor
A compact routing scheme is a routing strategy which suggests routing tables that are space efficient compared to traditional all-pairs shortest path routing algorithms. An Interval Routing algorithm is a compact routing algorithm which uses a routing table at every node in which a set of destination addresses that use the same output port are grouped into intervals of consecutive addresses. Self-stabilization is a property by which a system is guaranteed to reach a legitimate state in a finite number of steps starting from any arbitrary state. A self-stabilizing Pivot Interval Routing (PIR) algorithm is proposed in this work. The PIR strategy allows routing along paths whose stretch factor is at most five, and whose average stretch factor is at most three with routing tables of size O(n3/2log 23/2n) bits in total, where n is the number of nodes in the network. Stretch factor is the maximum ratio taken over all source-destination pairs between the length of the paths computed by the routing algorithm and the distance between the source and the destination. PIR is also an Interval Routing Scheme (IRS) using at most 2n( 1+lnn)1/2 intervals per link for the weighted graphs and 3n(1+ lnn)1/2 intervals per link for the unweighted graphs. The preprocessing stage of the PIR algorithm consists of nodelabeling and arc-labeling functions. The nodelabeling function re-labels the nodes with unique integers so as to facilitate fewer number of intervals per arc. The arc-labeling is done in such a fashion that the message delivery protocol takes an optimal path if both the source and the destination are located within a particular range from each other and takes a near-optimal path if they are farther from each other
Self-stabilizing protocol for anonymous oriented bi-directional rings under unfair distributed schedulers with a leader
We propose a self-stabilizing protocol for anonymous oriented bi-directional rings of any size under unfair distributed schedulers with a leader. The protocol is a randomized self-stabilizing, meaning that starting from an arbitrary configuration it converges (with probability 1) in finite time to a legitimate configuration (i.e. global system state) without the need for explicit exception handler of backward recovery. A fault may throw the system into an illegitimate configuration, but the system will autonomously resume a legitimate configuration, by regarding the current illegitimate configuration as an initial configuration, if the fault is transient. A self-stabilizing system thus tolerates any kind and any finite number of transient faults. The protocol can be used to implement an unfair distributed mutual exclusion in any ring topology network; Keywords: self-stabilizing protocol, anonymous oriented bi-directional ring, unfair distributed schedulers. Ring topology network, non-uniform and anonymous network, self-stabilization, fault tolerance, legitimate configuration
Self-Stabilization in the Distributed Systems of Finite State Machines
The notion of self-stabilization was first proposed by Dijkstra in 1974 in his classic paper. The paper defines a system as self-stabilizing if, starting at any, possibly illegitimate, state the system can automatically adjust itself to eventually converge to a legitimate state in finite amount of time and once in a legitimate state it will remain so unless it incurs a subsequent transient fault. Dijkstra limited his attention to a ring of finite-state machines and provided its solution for self-stabilization. In the years following his introduction, very few papers were published in this area. Once his proposal was recognized as a milestone in work on fault tolerance, the notion propagated among the researchers rapidly and many researchers in the distributed systems diverted their attention to it. The investigation and use of self-stabilization as an approach to fault-tolerant behavior under a model of transient failures for distributed systems is now undergoing a renaissance. A good number of works pertaining to self-stabilization in the distributed systems were proposed in the yesteryears most of which are very recent. This report surveys all previous works available in the literature of self-stabilizing systems
A Taxonomy of Daemons in Self-stabilization
We survey existing scheduling hypotheses made in the literature in
self-stabilization, commonly referred to under the notion of daemon. We show
that four main characteristics (distribution, fairness, boundedness, and
enabledness) are enough to encapsulate the various differences presented in
existing work. Our naming scheme makes it easy to compare daemons of particular
classes, and to extend existing possibility or impossibility results to new
daemons. We further examine existing daemon transformer schemes and provide the
exact transformed characteristics of those transformers in our taxonomy.Comment: 26 page
Asynchronous neighborhood task synchronization
Faults are likely to occur in distributed systems. The motivation for designing self-stabilizing system is to be able to automatically recover from a faulty state. As per Dijkstra\u27s definition, a system is self-stabilizing if it converges to a desired state from an arbitrary state in a finite number of steps. The paradigm of self-stabilization is considered to be the most unified approach to designing fault-tolerant systems. Any type of faults, e.g., transient, process crashes and restart, link failures and recoveries, and byzantine faults, can be handled by a self-stabilizing system; Many applications in distributed systems involve multiple phases. Solving these applications require some degree of synchronization of phases. In this thesis research, we introduce a new problem, called asynchronous neighborhood task synchronization ( NTS ). In this problem, processes execute infinite instances of tasks, where a task consists of a set of steps. There are several requirements for this problem. Simultaneous execution of steps by the neighbors is allowed only if the steps are different. Every neighborhood is synchronized in the sense that all neighboring processes execute the same instance of a task. Although the NTS problem is applicable in nonfaulty environments, it is more challenging to solve this problem considering various types of faults. In this research, we will present a self-stabilizing solution to the NTS problem. The proposed solution is space optimal, fault containing, fully localized, and fully distributed. One of the most desirable properties of our algorithm is that it works under any (including unfair) daemon. We will discuss various applications of the NTS problem
Self-stabilizing routing protocols
In systems made up of processors and links connecting the processors, the global state of the system is defined by the local variables of the individual processors. The set of global states can be defined as being either legal or illegal. A self-stabilizing system is one that forces a system from an illegal state to a global legal state without external interference, using a finite number of steps. This thesis will concentrate on application of self-stabilization to routing problems, in particular path identification, connectivity and methods involved in destinational routing. Traditional methods for creation of rooted paths to multiple destinations in a computer network involve the creation of spanning trees, and broadcasting information on the tree to be picked up by the individual nodes on the tree. The information for the creation of the tree are all sourced at the root, and the individual nodes update information from the centralized source. The self-stabilization model for networks allows the decision for a creation of a tree and message checking to occur automatically, locally, and more important, in contrast to traditional networks, asynchronously. The creation, message passing occur with a node and its immediate neighbor, and the tree, path is created based on this communicated data. In addition, the self-stabilization model eliminates the requisite initialization of traditional networks, i.e. given any arbitrary initial state the system (a given network) is guaranteed to stabilize to a legal global state, in the case of a broadcast network, a minimal spanning tree rooted at a source
On the Limits and Practice of Automatically Designing Self-Stabilization
A protocol is said to be self-stabilizing when the distributed system executing it is guaranteed to recover from any fault that does not cause permanent damage. Designing such protocols is hard since they must recover from all possible states, therefore we investigate how feasible it is to synthesize them automatically. We show that synthesizing stabilization on a fixed topology is NP-complete in the number of system states. When a solution is found, we further show that verifying its correctness on a general topology (with any number of processes) is undecidable, even for very simple unidirectional rings. Despite these negative results, we develop an algorithm to synthesize a self-stabilizing protocol given its desired topology, legitimate states, and behavior. By analogy to shadow puppetry, where a puppeteer may design a complex puppet to cast a desired shadow, a protocol may need to be designed in a complex way that does not even resemble its specification. Our shadow/puppet synthesis algorithm addresses this concern and, using a complete backtracking search, has automatically designed 4 new self-stabilizing protocols with minimal process space requirements: 2-state maximal matching on bidirectional rings, 5-state token passing on unidirectional rings, 3-state token passing on bidirectional chains, and 4-state orientation on daisy chains
Design and analysis of distributed primitives for mobile ad hoc networks
This dissertation focuses on the design and analysis of distributed primitives for
mobile ad hoc networks, in which mobile hosts are free to move arbitrarily. Arbitrary
mobility adds unpredictability to the topology changes experienced by the network, which
poses a serious challenge for the design and analysis of reliable protocols. In this work,
three different approaches are used to handle mobility. The first part of the dissertation
employs the simple technique of ignoring the mobility and showing a lower bound for the
static case, which also holds in the mobile case. In particular, a lower bound on the worstcase
running time of a previously known token circulation algorithm is proved. In the
second part of the dissertation, a self-stabilizing mutual exclusion algorithm is proposed
for mobile ad hoc networks, which is based on dynamic virtual rings formed by circulating
tokens. The difficulties resulting from mobility are dealt with in the analysis by showing
which properties hold for several kinds of mobile behavior; in particular, it is shown that
mutual exclusion always holds and different levels of progress hold depending on how
the mobility affects the token circulation. The third part of the dissertation presents two
broadcasting protocols which propagate a message from a source node to all of the nodes in
the network. Instead of relying on the frequently changing topology, the protocols depend
on a less frequently changing and more stable characteristic â the distribution of mobile
hosts. Constraints on distribution and mobility of mobile nodes are given which guarantee
that all the nodes receive the broadcast data
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