In the area of network research, establishing a network in a real time scenario is very difficult. A single test bed takes a large amount of time and cost. Thus a network simulator tool helps the network developer to check whether the network is able to work in the real time. A simulator also saves a lot of time, money and makes the implementations easy. In this paper, we introduce the main features of different network simulator and consider their advantages and disadvantages. We hope this paper proves to be a good reference source for those people who feel difficult to select the appropriate network simulators for their research.