Hii Aspirant.
Firstly, I didn't get your question. Like, Why do you think that you don't need to pay your fees. If you want admission in that college or want to learn there,  you are required to pay the fee, even though it is NIT, IIT or IIIT. If students do not pay fee, college administration will fail to run the college. But, if your question is in another way on the basis of category. Then, students belonging to SC/ST category are exempted from paying certain amount of fee. If I got the question wrong, please explain it.

Hii aspirant..

After getting admission seat at NIT and  IIIT you need to pay fees according to the college prospects. Usually the college fee and the hostel fee is taken semester wise by the respective colleges.

Although if you want some concession in your tuition fees and your college fees then you need to have tuition fee waiver tfw certificate and then you can separately apply for tuition fee waiver scholarship where they will provide you concession in your tuition fees and college fees.

 And if you do not belongs to tuition fee waiver category then there will be no concession in a fee and you have to pay the fee according to college policies.

Hope it helps. 

Best of luck.