ce model that potentially eliminates the need for service level agreements (SLAs) between domains. Instead, the local domain proxy will directly challenge the user and grant her trust provided sufficient credentials exist within the user's persistent identifier. These credentials can include financial information as well as trust information that the actual server can validate before allowing the user to route traffic through. 10.4 Implementation 10.4.1 Testbed We have implemented the functionality described in this paper as an extension to two open source SIP servers, the JAIN-SIP proxy [36] and the SIP express router (SER) [37]. The JAIN-SIP proxy server is an open source JAVA-based SIP proxy built on top of the JAIN-SIP-1.1 API. SER is an open-source, configurable SIP server that is widely deployed in the research community. We have implemented a JAVA-based H-SIP API that can be easily called from both proxy servers to expose the H-SIP interface operations. The operations mainly enable inter-domain authentication, registration, and call routing using handles. All the results depicted hereafter are based on the JAIN-SIP proxy. Our testbed is a realization of the framework depicted in Figure 10.1. We are running three modified SIP servers on three separate domains: 1. ece.unm.edu located at the University of New Mexico, Albuquerque, New Mexico [Server IP: 129.24.24.106 cnri.reston.va.us located in Reston, Virginia [Server IP: 132.151.9.104 3. istec.org located in Panama [Server IP: 168.77.202.59 A roaming user is allowed to move across the domains while establishing connectivity within each domain using the respective local server. The three servers are running Fedora Core 4 kernels and are identical in terms of work- load and processing speed (AMD Athlon 1.1 GHz processors). We have used the terms persistent identifier and handle interchangeably throughout this paper since our current implementation of the persistent identifier is the handle. C 2009 by Taylor & Francis Group, LLC SIP Mobility Technologies and t