The Open Access Research Test-bed for Wireless Networks (ORBIT) is a collaborative project involving industry and academia that is funded by the National Science Foundation (NSF). There are two components to the ORBIT test-bed. One is an indoor lab test-bed of a grid of wireless fidelity (WiFi) access points (APs); the other, a campus-wide field-trial outdoor network that attempts to create a hybrid network of wireless networks by combining third-generation (3G), fixed 802.11, and ad-hoc 802.11 networks. This paper focuses on the outdoor network and describes the various components of the hybrid network architecture. Because wireless clients do not normally have interfaces for disparate access technologies, the network uses mobile wireless gateways (MWGs) that serve as gateways for the mobile clients. These MWGs are able to backhaul traffic over multiple wireless access technologies (e.g., 3G and 802.11a/g/e). The mobile clients communicate with the MWGs using 802.11b links. The MWGs can communicate with the Internet over either the 3G or the fixed 802.11 network. All-Internet Protocol (IP) connectivity is provided to the MWG to access the 3G network using IP base stations (IP-BSs). We discuss various relevant handoff issues—including IP-BS to IP-BS (P-P) handoff within the 3G network, 3G to 802.11 network handoff, and handoff between different subnets within the 802.11 network—and present efficient mechanisms for all three handoff scenarios. © 2005 Lucent Technologies Inc.