possible ways to expedite routing and handle resolution are possible future research paths. We intend to leverage the scalable resolution, security, and administration services of the Handle System and use it to replace the DNS system within the SIP protocol. According to RFC 3263, the main reason SIP needs to use DNS is to enable the originator domain proxy to locate the SIP proxy in the destination domain (IP, port and transport protocol). The other need for DNS in SIP is for the terminating proxy to identify a backup for the originating proxy in the case the latter fails. Replacing the DNS within SIP requires carefully examining all the DNS resolutions performed by UA clients and proxy servers according to RFC 3263 and formalizing the fields to be resolved within the handles. Besides, we envision the future Handle Sys- tem to be completely decentralized and to be based on concepts like dis- tributed hash tables, where a particular identifier is not necessarily required to be located under a domain hierarchy. Finally, part of our current research is to focus on implementing a structured peer-to-peer form of the Handle System to expedite lookups and resolutions, and eliminate single points of failure. 10.6 Conclusion In this paper, we outlined the use of an indirection architecture based on the Handle System to address SIP inter-domain mobility. Our approach not only enables roaming controlled by the users rather than organizations, but also provides a faster implementation than traditional approaches currently deployed. Through our work, users are able to dynamically enable their own mobility and benefit from the advantages of a secure distributed persistent identifier network. By disassociating users from DNS domains, while still pro- viding the means to interact with traditional SIP systems, we provide a scal- able interchangeable enhancement to the SIP infrastructure. C 2009 by Taylor & Francis Group, LLC SIP Mobility Technologies and the Use of Persistent Identifiers Acknowledgements We would like to thank 