International Journal of Computer Applications (0975 – 8887) Volume 36– No.11, December 2011 13 A Comparative study of Time Synchronization Protocols in Wireless Sensor Network Amit Nayyer Shoolini University Solan, H.P, India Meenakshi Nayyer Baddi University Solan, H.P, India Lalit Kr. Awasthi NIT Hamirpur H.P, India ABSTRACT Wireless sensors network is a type of the ad-hoc network. It is comprised of many sensors which are interlinked with each other for performing the same function collectively such as monitoring the weather conditions, temperature, different kind of vibrations and sound etc. Any distributed system requires time synchronization. In particular, time Synchronization is extremely important for Wireless sensor network applications e.g. for data fusion, TDMA schedules, synchronizes sleep periods, etc. In this paper, we study different time synchronization protocols available for sensor networks, like Reference Broadcast Synchronization (RBS), Flooding Time Synchronization Protocol (FTSP) and Time Synchronization Protocol for Sensor networks (TPSN). Network Time Protocol (NTP) which is very famous in the computer network is also considered. The simulations of these different protocols are performed on the sensor network with the help of a simulator. The effects of these protocols on different parameters are studied and results obtained are compared. Keywords Time synchronization, clock synchronization, wireless sensor network. 1. INTRODUCTION New advancement towards the minimization, reducing the cost and power requirements have motivated the researchers towards wireless sensor network [1]. The aim of many researchers is to create an environment that is rich of sensors. The deployment of sensor can be very helpful in detecting the different conditions of the environment like sound, temperature and movement of objects [6]. There are a wide range of applications envisioned for such sensor networks, including micro-climate studies, groundwater contaminant monitoring, precision agriculture, condition-based maintenance of machinery in complex environments, urban disaster prevention and response, and military interests etc. These applications are not fulfilled by the traditional and existing architecture. In many scenarios, deploying wired sensors in large areas is impractical due to requirement of infrastructure. Putting manual observation in fields such as environmental monitoring is not only time consuming but also it require a lot of man power to cover a large area. Moreover the events in such type of environment are low enough that sometime even a few occurs in a day. Deploying a large number of sensors in such area makes sure that all the area is covered well. Generally, the sensors are thrown rather than manually deployed to cover the area. In sensor networks, different factors demands flexible and robust time synchronization, while simultaneously is making it more difficult to achieve as compared to computer networks [8]. Some sensors are so battery constrained that they only wake up occasionally, take a reading, transmit it and return to sleep [10]. To notify the time of events that occur in the environment is the basic requirement for nodes. For example, accurate time is needed to measure the time-of-flight of sound; distribute an acoustic beam forming array; form a low- power TDMA radio schedule [17]; integrate a time series of proximity detections into a velocity estimate; or suppress redundant messages by recognizing duplicate detections of the same event by different sensors. In this research work, we compare the existing time synchronization protocols and show the results based on different parameters selected. We try to show that the particular protocol is better in a particular situation and need of the application. We consider the various uses of time synchronization in detail, and describe the axes along which these applications can be characterized. Based on our experience exploring this problem space, we propose several general guidelines for the use of time synchronization protocols in sensor networks. No single synchronization scheme can be optimal on all axes (e.g., precision, lifetime, scope, energy, availability), but many applications do not require best performance on all the above mention axes. A range of schemes should be available to system designers, such that the synchronization that is provided matches what is needed. An ideal synchronization system will minimize its energy use by providing service that is exactly necessary and sufficient for the needs of the application. Tunable parameters can allow synchronization modes to be matched more closely to the requirements of the application. Most existing time synchronization schemes make a common assumption: that their goal is to keep the clock synchronized all the time. Applications assume that they can query the clock at any time, and it will be synchronized. Another approach is to let clocks at sensors to run at their natural rate, and when any event of interest occur the node time stamp the event with the clock of the cluster head [18]. This has many advantages; for example, it enables post-facto synchronization, peer-to-peer synchronization, and participation in multiple timescales. The outline of the paper is as follows: In section II, we briefly review literature survey in clock synchronization. It also describes various challenges that should be considered during the design of time synchronization protocol for sensor networks. Section III reviews related work in clock synchronization. This chapter discusses the results of related research which compare time synchronization protocols. We explore a number of metrics that have found relevant for evaluating time synchronization in the sensor network domain in this related research. In Section IV, we show the comparison results of our simulation of the time synchronization protocols. Finally, in Section V, we present our conclusions and describe directions for future research in this area.