International Journal of Wireless & Mobile Networks (IJWMN) Vol. 3, No. 5, October 2011 DOI : 10.5121/ijwmn.2011.3519 245             Himadri Nath Saha # 1 , Dr. Debika Bhattacharyya # 2 , Dr. P. K.Banerjee * 3 Assistant Professor # 1 , Professor # 2 , Professor * 3 Department of Computer Science and Engineering, Institute of Engineering & Management, West Bengal, India # 1, # 2 Department of Electronics and Tele Communication Engineering, Jadavpur university, West Bengal, India * 3 him_shree_2004@yahoo.com #1 , bdebika@yahoo.com #2 Abstract: Currently the mobile wireless technology is experiencing rapid growth. However the major challenge for deployment of this technology with its special characteristics is securing the existing and future vulnerabilities. The lack of static infrastructure causes several issues in mobile Ad hoc network (MANET) environment, such as node authentication and secure routing. In this paper we propose a new approach for secure routing of data packets in MANET. This approach will reduce the computational overhead to a lot extent. The scheme is based on a specific criterion of the nodes called “fidelity Index” .Data packets are routed based on this fidelity index. Simulation results show our proposed scheme is simple yet robust under some scenarios. Keywords: fidelity; delay; fidelity index; sequence number; hop destination; flooding attack; black hole attack; co-operative black hole attack;routing. I. INTRODUCTION Mobile Ad-hoc Network (MANET) is a collection of wireless mobile hosts without fixed network [1] infrastructure and centralized administration (Figure-1). Communication in MANET [2] is done via multi-hop paths. MANET contains diverse resources; Nodes operate in shared wireless medium; [3] Network topology changes unpredictably and very dynamically; Radio link [4] fidelity is necessary; connection breaks are pretty frequent. Moreover, density of nodes, number of nodes and mobility of these hosts may vary in different applications. There is no stationary infrastructure. Each node in MANET [5] acts a router that forwards data packets to other nodes. Therefore selection of effective, suitable, adaptive and robust routing scheme is of utmost importance .Our proposed scheme that is fidelity based on demand (FBOD)routing is a secure routing scheme based on fidelity index. FBOD is a robust, effective, suitable, adaptive and cost effective scheme. .