Ajay Agarwal

A REFERENCE BASED , TREE STRUCTURED TIME SYNCHRONIZATION APPROACH AND ITS ANALYSIS IN WSN

ABSTRACT Time synchronization for wireless sensor networks (WSNs) has been studied in recent years as a fundamental and significant research issue. Many applications based on these WSNs assume local clocks at each sensor node that need to be synchronized to a common notion of time. Time synchronization in a WSN is critical for accurate time stamping of events and fine-tuned coordination among the sensor nodes to reduce power consumption. This paper proposes a bidirectional, reference based, tree structured time synchronization service for WSNs along with network evaluation phase. This offers a push mechanism for (i) accurate and (ii) low overhead for global time synchronization. Analysis study of proposed approach shows that it is lightweight as the number of required broadcasting messages is constant in one broadcasting domain. KEYWORDS Ad Hoc Tree Structure; Clock synchronization; Wireless sensor networks, Hierarchical sensor network. 1. I NTRODUCTION Wireless sensor networks (WSNs) can be applied to a wide range of applications in domains as diverse as medical, industrial, military, environmental, scientific, and home networks [5]. Since the sensors in a WSN operate independently, their local clocks may not be synchronized with one another. This can cause difficulties when trying to integrate and interpret information sensed at different nodes. For instance, if a moving car is detected at two different times along a road, before we can even tell in what direction the car is going, the detection times have to be compared meaningfully. In addition, we must be able to transform the two time readings into a common frame of reference before estimating the speed of the vehicle. Estimating time differences across nodes accurately is also important in node localization. For example, many localization algorithms use ranging technologies to estimate inter-nodes distances; in these technologies, synchronization is needed for time-of-flight measurements that are then transformed into distances by multiplying with the medium propagation speed for the type of signal used such as radio frequency or ultrasonic. There are additional examples where cooperative sensing requires the nodes involved to agree on a common time frame such as configuring a beam-forming array and setting a TDMA (Time Division Multiple Access) radio schedule [6]. These situations mandate the necessity of one common notion of time in WSNs. Therefore, currently there is a huge research interest towards developing efficient clock synchronization protocols to provide a common notion of time. Time synchronization of WSNs is crucial to maintain data consistency, coordination, and perform other fundamental operations. Further, synchronization is considered a critical problem

An Approach towards Lightweight, Reference Based, Tree Structured Time Synchronization in WSN

Time synchronization for wireless sensor networks (WSNs) has been studied in recent years as a fundamental and significant research issue. Many applications based on these WSNs assume local clocks at each sensor node that need to be synchronized to a common notion of time. Time synchronization in a WSN is critical for accurate time stamping of events and fine-tuned coordination among the sensor nodes to reduce power consumption. This paper proposes a lightweight tree structured time synchronization approach for WSNs based on reference nodes. This offers a push mechanism for (i) accurate and (ii) low overhead for global time synchronization. Analysis and comparative study of proposed approach shows that it is lightweight as the number of required broadcasting messages is constant in one broadcasting domain.

An Approach towards Time Synchronization Based Secure Protocol for Wireless Sensor Network

Wireless sensor networks (WSN) have received a lot of attention recently due to their wide applications such as target tracking, environment monitoring, and scientific exploration in dangerous environments. Time synchronization is an important component of sensor networks to provide a common clock time in sensor nodes. Time synchronization protocols provide a mechanism for synchronizing the local clocks of the nodes in a sensor network. Some of the sensor nodes may be malicious, which can disrupt the normal operation of a sensor network. In this paper, we find out malicious nodes and propose time synchronization based secure protocol for a group of non-malicious nodes.

Generalized Grid Quorum Consensus for Replica Control Protocol

In distributed systems it is often necessary to provide coordination among the multiple concurrent processes to tolerate the contention, periods of asynchrony and a number of failures. Quorum systems provide a decentralized approach for such coordination. In this paper, we propose a replica control protocol by using a Generalized-grid quorum consensus, which is the generalization of a Read-one-write-all (ROWA), Grid quorum consensus, D-Space quorum consensus and Multi-dimensional-grid quorum consensus protocols. This protocol provides a very high read availability and read capacity while maintaining the reconfigurable levels of write availability and fault tolerance.

Multi-dimensional Grid Quorum Consensus for High Capacity and Availability in a Replica Control Protocol

In distributed systems it is often necessary to provide coordination among the multiple concurrent processes to tolerate the contention, periods of asynchrony and a number of failures. Quorum systems provide a decentralized approach for such coordination. In this paper, we propose a replica control protocol by using a Multi-dimensional-grid-quorum-consensus, which is the generalization of a read-one-write-all (ROWA) protocol, Grid quorum consensus protocol and D-Space quorum consensus protocol. Provides very high read availability and read capacity while maintaining the reconfigurable levels of write availability and fault tolerance.

HT-Paxos: High Throughput State-Machine Replication Protocol for Large Clustered Data Centers

Paxos is a prominent theory of state-machine replication. Recent data intensive systems that implement state-machine replication generally require high throughput. Earlier versions of Paxos as few of them are classical Paxos, fast Paxos, and generalized Paxos have a major focus on fault tolerance and latency but lacking in terms of throughput and scalability. A major reason for this is the heavyweight leader. Through offloading the leader, we can further increase throughput of the system. Ring Paxos, Multiring Paxos, and S-Paxos are few prominent attempts in this direction for clustered data centers. In this paper, we are proposing HT-Paxos, a variant of Paxos that is the best suitable for any large clustered data center. HT-Paxos further offloads the leader very significantly and hence increases the throughput and scalability of the system, while at the same time, among high throughput state-machine replication protocols, it provides reasonably low latency and response time.

An approach for secure time synchronization in wireless sensor network

Wireless sensor networks (WSN) have received a lot of attention recently due to their wide applications such as target tracking, environment monitoring, and scientific exploration in dangerous environments. Secure time synchronization is a key service for wireless sensor networks (WSN). Time synchronization protocol synchronizes local clocks of group nodes to a common clock. In group, some of the sensor nodes may be malicious, which may disrupt the normal operation of a sensor network. In this paper a novel secure pair-wise and group-wise approaches for synchronizing the nodes in non-malicious environment are proposed.

Quantitative and Qualitative Comparison Study of Reference Based Time Synchronization Approach in Wireless Sensor Network

Time synchronization is an important research issue in wireless sensor networks (WSNs). Many applications based on these WSNs assume local clocks at each sensor node that need to be synchronized to a common notion of time. Some inherent properties of sensor networks such as limited energy, storage, computation, and bandwidth resources, combined with potentially high density of nodes make conventional synchronization methods unsuitable for these networks. Therefore, an increasing research focus on designing synchronization algorithms is required. In this paper we explore various time synchronization protocols and present theoretical analysis of protocols based on quantitative and qualitative criteria with the proposed Tree Structured Time Synchronization Protocol. The comparative study shows that it is an excellent conciliation among synchronization accuracy, computational complexity, and convergence time.

An Efficient Approach for Data Replication in Distributed Database Systems

To increase the availability of data and fault tolerance in distributed database, it is better to add a backup server for each primary server in the system. So, the primary server and backup server must be connected to each other. To connect these computers to each other when they are at a long distance, it is necessary to use a leased line which needs to be charged as data is transferred. When packets are transferred between primary and backup server, more money need to be paid for charging this line. So if number of transferred packets between these computers can be reduced, the company can economize in its expenditures. Moreover, the number of transactions which should be performed in the backup server reduces.

Tree Structured, Multi-hop Time Synchronization Approach in Wireless Sensor Networks

Time synchronization for wireless sensor networks (WSNs) has been studied in recent years as a fundamental and significant research issue. Time synchronization in a WSN is a critical for accurate time stamping of events and fine-tuned coordination among the sensor nodes to reduce power consumption. This paper proposes a reference based, tree structured multi-hop time synchronization service for WSNs in which sensor nodes synchronize by collecting reference points with reference to Root node of the logically constructed tree structure of the network. Proposed approach is lightweight as the number of required broadcasting messages is restricted to one broadcasting domain.