Although enhanced distributed coordination function EDCF mechanism brings service differentiation between different access categories, Quality of service is not guaranteed for delay sensitive applications such as voice unless further open parameters of the amendment may be supported in the implementation phase. Among these parameters we focus in this paper on packet bursting scheme. We examine Packet Bursting scheme impact on service differentiation in IEEE 802.11e enhanced distributed channel access EDCF using SPN model. Performance analysis of throughput and mean access delay versus virtual load are investigated. Numerical results investigated show how packet bursting scheme can counteract the inherent QoS limitation of service differentiation by bringing efficiency improvement. Additionally results show advantages and limitations of Packet Bursting scheme with respect to virtual load in wireless varying environment characterized by a slow Rayleigh fading.