**1.1.2 Hybrid networks**

The proliferation of computer laptops, personal digital assistants (PDA), and mobile phones, coupled with the nearly universal availability of wireless communication services is enabling the goal of ubiquitous wireless communications (Beigy & Meybodi, 2003); (Ramjee et al., 1997); (Leong & Zhuang, 2002); (Guerin, 1988). Unfortunately, to realize the benefits of omni-present connectivity, users must contend with the challenges of a confusing array of incompatible services, devices, and wireless technologies. Rice University, USA, is developing RENÉ (Rice Everywhere NEtwork) (Aazhang & Cavallaro, 2001), a system that enables ubiquitous and seamless communication services. The key innovations are a first-of-its-kind multi-tier network interface card, intelligent proxies that enable a new level of graceful adaptation in unmodified applications, and a novel approach to hierarchical and coarse-grained quality of service provisioning. The design of RENÉ requires a coordinated, collaborative effort across traditional layers and across different time scales of the system to maintain uninterrupted user connectivity.
