Toronto Networking Seminar

Understanding Congestion and Flash Crowds in WLANS

Elizabeth Belding
Department of Computer Science
University of California, Santa Barbara

Date:  Friday, March 30,  2pm
Location: BA1220 (Bahen Center)


Flash crowds and high concentrations of users in wireless LANs (WLANs) cause significant interference problems and unsustainable load at access points. This leads to poor connectivity for users, severe performance degradation, and possible WLAN collapse.  To validate this claim, we will discuss two case studies of large, heavily loaded operational WLANs. These studies provide significant insight into the degraded performance and collapse of a WLAN during heavy use. To address these problems, we present IQU, a practical queue-based user association management system for heavily loaded WLANs. IQU grants users fair opportunities to access the WLAN while maintaining high overall throughput, even when the WLAN is heavily loaded. The basic premise of IQU is to control user associations with the WLAN through request queues and work period allocations.  Through a prototype implementation, we demonstrate that IQU significantly improves network throughput under heavy load; the tradeoff is that users have to wait for network access.  We explore the impact of IQU parameters on system performance, and validate the robustness of IQU under heavy load conditions. Through IQU, WLANs can be utilized efficiently and network collapse prevented.


Elizabeth M. Belding is an Associate Professor in the Department of Computer Science at the University of California, Santa Barbara.  Elizabeth's research focuses on mobile networking, specifically mesh networks, multimedia, monitoring, and advanced service support.  She is the founder of the Mobility Management and Networking (MOMENT) Laboratory ( at UCSB.  Elizabeth is the author of over 50 papers related to mobile networking and has served on over 40 program committees for networking conferences.  Elizabeth served as the TPC Co-Chair of ACM MobiCom 2005 and IEEE SECON 2005, and is currently the TPC Co-Chair of ACM MobiHoc 2007.  She also serves on the editorial board for the IEEE Transactions on Mobile Computing.  Elizabeth is the recipient of an NSF CAREER award, and a 2002 Technology Review 100 award, awarded to the world's top young investigators.  See for further details.