The Joint Seat Allocation Authority (JoSAA) is a counselling procedure for candidates who have cleared both JEE Mains and JEE Advance. On the other hand the Central Seat Allocation Board (CSAB) is a special counselling which is conducted following JOSAA admission procedure is over. It is done in order to fill the vacant seats (if ay) in IIITs, NITs and GFTIs, CSAB counselling is conducted. It depends, if you have got a seat through JOSAA, you do not need to take part in CSAB.