In crucial times, such as natural disasters like Earthquakes, Floods, military attack, rescue and emergency operations, etc., it is not possible to maintain an infrastructure. In these situations, wireless Mobile Ad-Hoc networks can be an alternative to wired networks. In our thesis, due to the importance of MANET (Mobile Ad-hoc Network) applications, we do research on MANET and its subtype IMANET (Internet based Mobile Ad-hoc Network). In MANETs, finding an optimum path among nodes is not a simple issue due to the random mobility of nodes and topology changes frequently. Simple routing algorithms like Shortest Path, Dijksta‟s and Link State fail to find route in such dynamic scenarios. A number of ad-hoc protocols (Proactive, Reactive, Hybrid and Position based) have been developed for MANETs. In this thesis, we have designed an IMANET in OPNET 14.5 and tested the performance of three different routing protocols namely OLSR (Optimum Link State Routing), TORA (Temporarily Ordered Routing Algorithm) and AODV (Ad-hoc On-demand Distance Vector) in different scenarios by varying the number of nodes and the size of the area. The experimental results demonstrate that among the three protocols, none of the routing protocol can ensure good quality HTTP and voice communication in all our considered scenarios.