An analysis of the impact of the packetization interval for constant bit rate traffic is performed in the context of the IEEE 802.16 MAC layer (specifically in the context of IEEE 802.16d, Fixed WiMAX). Bandwidth used for overheads which include lower layer headers as well as retransmissions at the MAC layer is considered. An optimal packetization interval selection method for real-time delay-sensitive applications such as VoIP is proposed. Enhancements to the Unsolicited Grant Service retransmission strategy are proposed to further improve delay and minimize packet loss while making efficient use of the limited bandwidth resource.