I think you should not go for NS2 as most of the reputed journals do not accept its results in research papers. Also it has not been been updated from 2009. Better to use NS3 or OPNET
D. P. Sharma: please do not spread misinformation: no reputable journals would reject a paper based on the argument that "ns2 was used".
Reputable journals may reject a paper because simulation studies are inappropriate, or that inappropriate (typically, overreaching) conclusions are drawn based on simulations, etc.