2,492 research outputs found
More Bang For Your Buck: Quorum-Sensing Capabilities Improve the Efficacy of Suicidal Altruism
Within the context of evolution, an altruistic act that benefits the
receiving individual at the expense of the acting individual is a puzzling
phenomenon. An extreme form of altruism can be found in colicinogenic E. coli.
These suicidal altruists explode, releasing colicins that kill unrelated
individuals, which are not colicin resistant. By committing suicide, the
altruist makes it more likely that its kin will have less competition. The
benefits of this strategy rely on the number of competitors and kin nearby. If
the organism explodes at an inopportune time, the suicidal act may not harm any
competitors. Communication could enable organisms to act altruistically when
environmental conditions suggest that that strategy would be most beneficial.
Quorum sensing is a form of communication in which bacteria produce a protein
and gauge the amount of that protein around them. Quorum sensing is one means
by which bacteria sense the biotic factors around them and determine when to
produce products, such as antibiotics, that influence competition. Suicidal
altruists could use quorum sensing to determine when exploding is most
beneficial, but it is challenging to study the selective forces at work in
microbes. To address these challenges, we use digital evolution (a form of
experimental evolution that uses self-replicating computer programs as
organisms) to investigate the effects of enabling altruistic organisms to
communicate via quorum sensing. We found that quorum-sensing altruists killed a
greater number of competitors per explosion, winning competitions against
non-communicative altruists. These findings indicate that quorum sensing could
increase the beneficial effect of altruism and the suite of conditions under
which it will evolve.Comment: 8 pages, 8 figures, ALIFE '14 conferenc
Data Replication with 2D Mesh Protocol for Data Grid
Data replication is one of the widely approach to achieve high data availability and fault
tolerant of a system. Data replication in a large scale distributed and dynamic network
such as grid has effects the efficiency of data accessing and data consistency. Therefore a
mechanism that can maintain the consistency of the data and provide high data
availability is needed. This thesis discusses protocols and strategies of replicating data in
distributed database and grid environment where network and users are dynamic. There
are few protocols that have been implemented in distributed database and grid computing
which is discussed such as Read One-Write All (ROWA), Voting (VT), Tree Quorum
(TQ), Grid Configuration (GC), Three Dimensional Grid Structure (TDGS), Diagonal
Replication in Grid (DRG) and Neighbor Replication in Grid (NRG).
In this thesis, we introduce an enhanced replica control protocol, named Enhance
Diagonal Replication 2D Mesh (EDR2M) protocol for grid environment and compares its result of availability, and communication cost with the latest protocol TDGS (2001) and
NRG (2007). EDR2M proves data consistency by fulfilling the Quorum Intersection
Properties. Evaluations that is suitable and applicability for EDR2M protocol solutions
via analytical models and simulations.
A simulation of EDR2M protocol is developed and the performance metrics evaluated
are data availability, and communication cost. By getting the sufficient number of
quorum, number of nodes in each quorum, and selecting the middle node of the diagonal
sites to have the copy of the data file have improved the availability and communication
cost for read and write operation compared to the latest protocol, TDGS (2001) and NRG
(2007). Thus, the experiment has showed scientifically that EDR2M is the adequate
protocol to achieve high data availability in a low communication cost by providing
replica control protocol for a dynamic network such as grid environmen
An assessment of blockchain consensus protocols for the Internet of Things
In a few short years the Internet of Things has become an intrinsic part of everyday life, with connected devices included in products created for homes, cars and even medical equipment. But its rapid growth has created several security problems, with respect to the transmission and storage of vast amounts of customers data, across an insecure heterogeneous collection of networks. The Internet of Things is therefore creating a unique set of risk and problems that will affect most households. From breaches in confidentiality, which could allow users to be snooped on, through to failures in integrity, which could lead to consumer data being compromised; devices are presenting many security challenges to which consumers are ill equipped to protect themselves from. Moreover, when this is coupled with the heterogeneous nature of the industry, and the interoperable and scalability problems it becomes apparent that the Internet of Things has created an increased attack surface from which security vulnerabilities may be easily exploited. However, it has been conjectured that blockchain may provide a solution to the Internet of Things security and scalability problems. Because of blockchain’s immutability, integrity and scalability, it is possible that its architecture could be used for the storage and transfer of Internet of Things data. Within this paper a cross section of blockchain consensus protocols have been assessed against a requirement framework, to establish each consensus protocols strengths and weaknesses with respect to their potential implementation in an Internet of Things blockchain environment
Survey on replication techniques for distributed system
Distributed systems mainly provide access to a large amount of data and computational resources through a wide range of interfaces. Besides its dynamic nature, which means that resources may enter and leave the environment at any time, many distributed systems applications will be running in an environment where faults are more likely to occur due to their ever-increasing scales and the complexity. Due to diverse faults and failures conditions, fault tolerance has become a critical element for distributed computing in order for the system to perform its function correctly even in the present of faults. Replication techniques primarily concentrate on the two fault tolerance manners precisely masking the failures as well as reconfigure the system in response. This paper presents a brief survey on different replication techniques such as Read One Write All (ROWA), Quorum Consensus (QC), Tree Quorum (TQ) Protocol, Grid Configuration (GC) Protocol, Two-Replica Distribution Techniques (TRDT), Neighbour Replica Triangular Grid (NRTG) and Neighbour Replication Distributed Techniques (NRDT). These techniques have its own redeeming features and shortcoming which forms the subject matter of this survey
Novelty circular neighboring technique using reactive fault tolerance method
The availability of the data in a distributed system can be increase by implementing fault tolerance mechanism in the system. Reactive method in fault tolerance mechanism deals with restarting the failed services, placing redundant copies of data in multiple nodes across network, in other words data replication and migrating the data for recovery. Even if the idea of data replication is solid, the challenge is to choose the right replication technique that able to provide better data availability as well as consistency that involves read and write operations on the redundant copies. Circular Neighboring Replication (CNR) technique exploits neighboring policy in replicating the data items in the system performs well with regards to lower copies needed to maintain the system availability at the highest. In a performance analysis with existing techniques, results show that CNR improves system availability by average 37% by offering only two replicas needed to maintain data availability and consistency. The study demonstrates the possibility of the proposed technique and the potential of deploying in larger and complex environment
Supporting disconnected operations in mobile computing
Mobile computing has enabled users to seamlessly access databases even when they are on the move. However, in the absence of readily available high-quality communication, users are often forced to operate disconnected from the network. As a result, software applications have to be redesigned to take advantage of this environment while accommodating the new challenges posed by mobility. In particular, there is a need for replication and synchronization services in order to guarantee availability of data and functionality, (including updates) in disconnected mode. To this end we propose a scalable and highly available data replication and management service. The proposed replication technique is compared with a baseline replication technique and shown to exhibit high availability, fault tolerance and minimal access times of the data and services, which are very important in an environment with low-quality communication links.<br /
Server Placement with Shared Backups for Disaster-Resilient Clouds
A key strategy to build disaster-resilient clouds is to employ backups of
virtual machines in a geo-distributed infrastructure. Today, the continuous and
acknowledged replication of virtual machines in different servers is a service
provided by different hypervisors. This strategy guarantees that the virtual
machines will have no loss of disk and memory content if a disaster occurs, at
a cost of strict bandwidth and latency requirements. Considering this kind of
service, in this work, we propose an optimization problem to place servers in a
wide area network. The goal is to guarantee that backup machines do not fail at
the same time as their primary counterparts. In addition, by using
virtualization, we also aim to reduce the amount of backup servers required.
The optimal results, achieved in real topologies, reduce the number of backup
servers by at least 40%. Moreover, this work highlights several characteristics
of the backup service according to the employed network, such as the
fulfillment of latency requirements.Comment: Computer Networks 201
- …