Dyson: An Architecture for Extensible Wireless LANs

Abstract

As wireless local area networks (WLANs) continue to evolve. the fundamental division of responsibility between the access point (AP) and the client has remained unchanged. In most cases, clients make independent decisions about associations and packet transmissions, using only locally available information. Furthermore, the IEEE 802.11 standard defines a very limited interface for transferring information between the APs and the clients. These factors impede customization of WLANs to meet site-specific challenges, and in a more general sense, impede rapid innovation to face challenges posed by new applications such as VoIP. This paper describes Dyson, an extensible architecture for WLANs, targeted primarily at enterprise scenarios. Our architecture is based on centralized, global management of channel resources. To provide extensibility, the interface between the infrastructure and clients is simple and relatively low-level, and can be controlled through a programmatic interface. Clients provide primitives that allow the central controller to control many aspects of client behavior. The controller can also instruct clients to gather and report information about channel conditions. We show that using these simple primitives, and by leveraging historical information, the network designer can easily customize many aspects of the WLAN behavior. We have built a prototype implementation of Dyson, which currently runs on a 23-node testbed distributed across one floor of a typical academic building. Using this testbed, we examine various aspects of the architecture in detail, including a range of policies for improving client-AP associations, providing user-specific airtime reservations, mitigating the effects of interference, and improving mobile handoffs. We show that Dyson is effective at providing greater efficiency while opening up the network to site-specific customizations.