On the effectiveness of IEEE 802.11e implementations in real hardware

Real-time multimedia traffic requires some minimum delivery guarantees to be effectively transmitted over packet-switched networks. This is even more necessary when interactive sessions (e.g., Voice-over-IP applications) are involved. Effective and timely packet delivery is sometimes achieved by overdimensioning network capacity. However, this is not the most practical and economic solution. Instead, providing a specific service to different traffic types may achieve better results without wasting network resources. Quality of Service (QoS) be implemented at different layers of the protocol stack, but tight control at the link layer is essential when the physical medium is shared among a number of devices. Wireless LANs are a typical example of that. The IEEE 802.11e amendment enhances the original version of the WiFi standard with new QoS functionalities. It maintains backward compatibility with legacy hardware, and this may cause the priority scheme to be ineffective in those deployments where non-QoS enabled hardware is present. In this paper, we analyze some widespread commercial 802.11 products to check the effectiveness of the QoS mechanisms. We show that all hardware under examination fails in providing effective QoS guarantees when legacy stations are present.