Ns2 turorial

NS is simulator for networks. Using NS you can simulate all the existing networking, transport and application layer protocols. you can also embed your own protocol and simulate that as well. e.g You can simulate and compare the results between TCP and UDP protocols any kind of network topology that u want to generate.

Here is a link to a tutorial of NS by Marc Gries:: http://www.isi.edu/nsnam/ns/tutorial/.