152 research outputs found
Self-Stabilizing TDMA Algorithms for Dynamic Wireless Ad-hoc Networks
In dynamic wireless ad-hoc networks (DynWANs), autonomous computing devices
set up a network for the communication needs of the moment. These networks
require the implementation of a medium access control (MAC) layer. We consider
MAC protocols for DynWANs that need to be autonomous and robust as well as have
high bandwidth utilization, high predictability degree of bandwidth allocation,
and low communication delay in the presence of frequent topological changes to
the communication network. Recent studies have shown that existing
implementations cannot guarantee the necessary satisfaction of these timing
requirements. We propose a self-stabilizing MAC algorithm for DynWANs that
guarantees a short convergence period, and by that, it can facilitate the
satisfaction of severe timing requirements, such as the above. Besides the
contribution in the algorithmic front of research, we expect that our proposal
can enable quicker adoption by practitioners and faster deployment of DynWANs
that are subject changes in the network topology
Self-stabilizing TDMA Algorithms for Wireless Ad-hoc Networks without External Reference
Time division multiple access (TDMA) is a method for sharing communication
media. In wireless communications, TDMA algorithms often divide the radio time
into timeslots of uniform size, , and then combine them into frames of
uniform size, . We consider TDMA algorithms that allocate at least one
timeslot in every frame to every node. Given a maximal node degree, ,
and no access to external references for collision detection, time or position,
we consider the problem of collision-free self-stabilizing TDMA algorithms that
use constant frame size.
We demonstrate that this problem has no solution when the frame size is , where is the chromatic number for
distance- vertex coloring. As a complement to this lower bound, we focus on
proving the existence of collision-free self-stabilizing TDMA algorithms that
use constant frame size of . We consider basic settings (no hardware
support for collision detection and no prior clock synchronization), and the
collision of concurrent transmissions from transmitters that are at most two
hops apart. In the context of self-stabilizing systems that have no external
reference, we are the first to study this problem (to the best of our
knowledge), and use simulations to show convergence even with computation time
uncertainties
Shared-object System Equilibria: Delay and Throughput Analysis
We consider shared-object systems that require their threads to fulfill the
system jobs by first acquiring sequentially the objects needed for the jobs and
then holding on to them until the job completion. Such systems are in the core
of a variety of shared-resource allocation and synchronization systems. This
work opens a new perspective to study the expected job delay and throughput
analytically, given the possible set of jobs that may join the system
dynamically.
We identify the system dependencies that cause contention among the threads
as they try to acquire the job objects. We use these observations to define the
shared-object system equilibria. We note that the system is in equilibrium
whenever the rate in which jobs arrive at the system matches the job completion
rate. These equilibria consider not only the job delay but also the job
throughput, as well as the time in which each thread blocks other threads in
order to complete its job. We then further study in detail the thread work
cycles and, by using a graph representation of the problem, we are able to
propose procedures for finding and estimating equilibria, i.e., discovering the
job delay and throughput, as well as the blocking time.
To the best of our knowledge, this is a new perspective, that can provide
better analytical tools for the problem, in order to estimate performance
measures similar to ones that can be acquired through experimentation on
working systems and simulations, e.g., as job delay and throughput in
(distributed) shared-object systems
Alien Registration- Korak, Betha (Portland, Cumberland County)
https://digitalmaine.com/alien_docs/32178/thumbnail.jp
Self-Stabilizing and Private Distributed Shared Atomic Memory in Seldomly Fair Message Passing Networks
We study the problem of privately emulating shared memory in message-passing networks. The system includes clients that store and retrieve replicated information on N servers, out of which e are data-corrupting malicious. When a client accesses a data-corrupting malicious server, the data field of that server response might be different from the value it originally stored. However, all other control variables in the server reply and protocol actions are according to the server algorithm. For the coded atomic storage algorithms by Cadambe et al., we present an enhancement that ensures no information leakage and data-corrupting malicious fault-tolerance. We also consider recovery after the occurrence of transient faults that violate the assumptions according to which the system was designed to operate. After their last occurrence, transient faults leave the system in an arbitrary state (while the program code stays intact). We present a self-stabilizing algorithm, which recovers after the occurrence of transient faults. This addition to Cadambe et al. considers asynchronous settings as long as no transient faults occur. The recovery from transient faults that bring the system counters (close) to their maximal values may include the use of a global reset procedure, which requires the system run to be controlled by a fair scheduler. After the recovery period, the safety properties are provided for asynchronous system runs that are not necessarily controlled by fair schedulers. Since the recovery period is bounded and the occurrence of transient faults is extremely rare, we call this design criteria self-stabilization in the presence of seldom fairness. Our self-stabilizing algorithm uses a bounded amount of storage during asynchronous executions (that are not necessarily controlled by fair schedulers). To the best of our knowledge, we are the first to address privacy, data-corrupting malicious behavior, and self-stabilization in the context of emulating atomic shared memory in message-passing systems
Self-stabilizing Byzantine Multivalued Consensus
Consensus, abstracting a myriad of problems in which processes have to agree
on a single value, is one of the most celebrated problems of fault-tolerant
distributed computing. Consensus applications include fundamental services for
the environments of the Cloud and Blockchain, and in such challenging
environments, malicious behaviors are often modeled as adversarial Byzantine
faults.
At OPODIS 2010, Mostefaoui and Raynal (in short MR) presented a
Byzantine-tolerant solution to consensus in which the decided value cannot be a
value proposed only by Byzantine processes. MR has optimal resilience coping
with up to t < n/3 Byzantine nodes over n processes. MR provides this
multivalued consensus object (which accepts proposals taken from a finite set
of values) assuming the availability of a single Binary consensus object (which
accepts proposals taken from the set {0,1}).
This work, which focuses on multivalued consensus, aims at the design of an
even more robust solution than MR. Our proposal expands MR's fault-model with
self-stabilization, a vigorous notion of fault-tolerance. In addition to
tolerating Byzantine, self-stabilizing systems can automatically recover after
the occurrence of arbitrary transient-faults. These faults represent any
violation of the assumptions according to which the system was designed to
operate (provided that the algorithm code remains intact).
To the best of our knowledge, we propose the first self-stabilizing solution
for intrusion-tolerant multivalued consensus for asynchronous message-passing
systems prone to Byzantine failures. Our solution has a O(t) stabilization time
from arbitrary transient faults.Comment: arXiv admin note: text overlap with arXiv:2110.0859
How to Stop Disagreeing and Start Cooperatingin the Presence of Asymmetric Packet Loss
We consider the design of a disagreement correction protocol in multi-vehicle systems. Vehicles broadcast in real-time vital information such as position, direction, speed, acceleration, intention, etc. This information is then used to identify the risks and adapt their trajectory to maintain the highest performance without compromising the safety. To minimize the risk due to the use of inconsistent information, all cooperating vehicles must agree whether to use the exchanged information to operate in a cooperative mode or use the only local information to operate in an autonomous mode. However, since wireless communications are prone to failures, it is impossible to deterministically reach an agreement. Therefore, any protocol will exhibit necessary disagreement periods. In this paper, we investigate whether vehicles can still cooperate despite communication failures even in the scenario where communication is suddenly not available. We present a deterministic protocol that allows all participants to either operate a cooperative mode when vehicles can exchange all the information in a timely manner or operate in autonomous mode when messages are lost. We show formally that the disagreement time is bounded by the time that the communication channel requires to deliver messages and validate our protocol using NS-3 simulations. We explain how the proposed solution can be used in vehicular platooning to attain high performance and still guarantee high safety standards despite communication failures
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