Network Simulator 2 is a popular open source discrete event simulator that substantial support for simulation of TCP, routing, and multicast protocols over wired and wireless networks. NS-2 mainly find its application in the networking research to simulate wired and wireless networks. The provides overview of NS2 and NS2 Installation, Working with simple examples - wired and wireless scenario, Working with existing protocols, Simulation and interpretation of trace file, Trace file analysis using AWK scripts, working with NAM, simulation and evaluation of routing protocols for mobile adhoc networks and Mannasim a popular wireless sensor network simulator.