WSN is an emerging technology which is deployed for monitoring and control applications. IEEE has introduced the 802.15.4 standard for a low rate, low power, low complexity and short range Wireless Personal Area Network (WPAN) in 2003. Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is defined as the basic access mechanism in the standard. It was noted that there is a problem of low throughput for short superframe duration due to the collision of packets at the start of the superframe. Hence in 2006, the standard was revised and the CSMA/CA algorithm was modified such that deferred transmission was assigned with another delay of random backoff periods before assessing the medium. In this paper, a simulation model of the CSMA/CA algorithm for IEEE 802.15.4/ 2006 using OPNET Modeler has been developed and the effect of deferments on the performance of WSN has been analyzed. It has been found that the deferment of packets to new superframe significantly affects the throughput, success probability and the average delay of WSN for a short superframe, while it has no effect on the performance of WSN for long superframe duration.