state rank is considered for admission into colleges in your state, you know that.....
there is 50% reservation in general group for the natives of the state where the nit is. the other 50% of all nits is added and is distributed to other states considering population.
now i am from kerala nit calicut is where we have 50% reservation. my air is 1910 and state 43. if i apply to other nit, say trichy for ece, and it so happens dat too many applied for da same 50% all india seats, then my all india rank comes into play. ie, if some one with a state rank below mine(from a diffrent state), but better air also applies, he may get and i may not.....
i hope i am clear.....u can nudge me any time......