International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 03 Issue: 01 | Jan-2016 www.irjet.net p-ISSN: 2395-0072 © 2016, IRJET | Impact Factor value: 4.45 | ISO 9001:2008 Certified Journal | Page 622 A Comparative Review on Reliability and Fault Tolerance Enhancement Protocols in Wireless Sensor Networks Abhinav Sharma 1 , Sandeep Sharma 2 1 M.Tech Scholar, Computer Engineering and Technology Department, Guru Nanak Dev University, Punjab, India 2 Asst Prof, Computer Engineering and Technology Department, Guru Nanak Dev University, Punjab, India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - Fault Tolerance of Wireless Sensor Networks (WSN) is a very significant and central issue in current research topics related to WSN. It is of critical importance because these nodes are deployed in harsh environmental conditions which make them prone to failure and simultaneously their sensed data is very precious for various applications and hence it is desired to lose this precious data because of fatal failures. Since the working environment of WSN is Presented with many challenges and deployment issues that affect the operation of WSN so a need for a fault tolerant technique becomes essential for good quality sensor data since the quality of sensed data is proportional to the amount data sensed and a number of sensing nodes. The fault tolerant technique should satisfy all the characteristics of WSN operations and must have minimum deployment and operational overheads because node’s energy and computation power of nodes are the scarcest resources of any WSN which should be kept in mind while designing a fault tolerant technique for the WSN. In this paper, we recapitulate and compared some of the existing and widely used fault tolerant techniques and protocols of WSN for encountering faults. The paper compares the various characteristics of some existing techniques and provides us a picture for the comparative analysis of various recent fault tolerance protocols and techniques. From the findings of the comparison we highlighted the issues challenges and faced in achieving fault tolerance and give some description for systematic investigation in order to provide enhancement to fault tolerance and reliability techniques. Key Words: Wireless sensor network, Fault tolerance, reliability protocols. 1. INTRODUCTION WSN consists of interconnected Sensor nodes (SNs) which are deployed in a very large number and are capable of sensing, gathering, processing and transmitting the data. SNs collect data by sensing the target surroundings and send the sensed data to base station (BS) by using wireless transmission techniques. Key Characteristics of Wireless Sensor Networks are:  Limited Power constraints for nodes because of usage of either batteries or energy harvesting  Mobility of nodes  Ability to withstand after node failures  Network topologyǯs dynamic nature  Ability to cope with Communication failures  Deployment Scalability to large scale and wide geographical area  Ease of use  Ability to resist failure in harsh environmental conditions  Continuous operation  Power consumption  Heterogeneity of nodes The communication topology and geographical positions of nodes of an SN must be in such a way that all the above characteristics of the WSN are satisfied. During operation SN can be down for several reasons and most common of them are, running out of energy, harsh environmental conditions and sometimes the activities of any intruder can also be the cause of failure. In the case of failure of SNǯs, naturally, the overall quality of the sensor network suffers, as the nodes which are down are not able to contribute their sensed data to provide the overall accurate picture of the environment. The sensing quality also diminishes proportionally with the increasing number of down nodes. Since there is an enormous number of an event which can lead to failure of a WSN so a fault tolerance mechanism must be employed so that system can meet all the above characteristics.