Hello Aspirant,

CSAB stands for Central Seat Allocation Board. It is responsible for counselling for admission in some of the AICTE approved engineering institutions located in North Eastern states and Union Territories and also for admission to supernumerary seats for NITs situated in Union Territories along with some Self Financed Technical Institutions. The counselling and admission is done solely on the basis of JEE-Main and this counselling starts after the completion of JOSAA counselling. If you want to sit in CSAB Counselling and want to get seat in any of the Union Territory or any North-Eastern state's college then you should have domicile of that region. But as mentioned in the question, you are seeking admission in NIT in Andhra Pradesh which is not in the region of CSAB Counselling so you can get NIT in Andhra Pradesh only through JOSAA counselling.

You can check out previous year's cut-off for NIT Andhra Pradesh from the link given below :-

https://engineering.careers360.com/articles/jee-main-cutoff-for-nit-andhra-pradesh

However I would recommend you to use JEE-Main College Predictor to predict the chances of your admission in different colleges  based upon your percentile and category :-

https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer

I hope this information helps you.

Good Luck!!