The Consultative Committee for Space Data Systems (CCSDS) File Delivery Protocol (CFDP) is a new international standard developed by the space agencypsilas to meet the growing space communication need for effective transfer of information in a wide variety of mission configurations of inter-planetary space links. The performance of CFDP in the deferred NAK mode has been evaluated in a theoretical manner. The delivery latency mainly depended on timer used in both sender and receiver. In this paper we have proposed a dynamic NAK timer algorithm for CFDP in deferred NAK mode under bandwidth constrain. Then we have implemented and validated the algorithm in NS and also presented its performance results and analysis