Performance evaluation of IEEE 802.11 infrastructure mode with intra-cell UDP traffic

IEEE 802.11-based Wireless LANs have become ubiquitous in coffee shops, office buildings, and hundreds of millions of residential homes. Access points, or APs, have been playing an important role in infrastructure Wireless LANs. An AP provides lots of services including cell identification, synchronization, authentication, distribution service, etc. Another important functionality of AP is to relay messages among wireless stations inside the same wireless cell. In current implementations, an AP needs to compete for the wireless channel with all other wireless stations using DCF protocol. Our objective in this paper is to design systematic and reproducible experiments to show that, with uncontrolled UDP traffic in the network, the AP becomes the system bottleneck and the system goodput could drop to an unacceptable level, mainly due to buffer overflow at the AP. E.g., in an 802.11g wireless network operating at 54Mbps, the saturation UDP goodput can be as low as only several Mbps, and TCP connections can be easily choked by UDP traffic for a long duration. We think this observation is important because UDP traffic volume is growing rapidly with the widely-deployed Voice over WiFi, wireless surveillance system, digital games, multimedia streaming applications, etc.