1. Introduction
Developing network security protocols in mobile ad hoc networks (MANETs) has design challenges due to high security vulnerabilities and unique characteristics of MANET environments such as open medium, dynamic changing network topology, decentralized decision-making and cooperation, lack of centralized authority, lack of resources in mobile devices (e.g., bandwidth, memory, computational power), and no clear line of defense [7]. Under these environmental constraints, intrusion detection mechanisms are used as a second line of defense and have become essential for systems with the goal of high-survivability in the presence of inside attackers.