Sun, S., 2001. Establishing persistent identity using the handle system. Tenth International World Wide Web Conference. Hong Kong. May 1-5. [35] Franks, J., P. Hallam-Baker, J. Hostetler, S. Lawrence, P. Leach, A. Luotonen, and L. Stewart. 1999. HTTP authentication: Basic and digest access authentication. RFC 2617. http://www.fags.org/rfc/ rfc2617.html. Accessed July 25, 2008. [36] Jain-sip proxy (built on jain-sip 1.1 api). https://jain-sip-presence-proxy. dev.java.net/. Accessed July 25, 2008. [37] Rebahi, Y., D. Sisalem, J. Kuthan, A. Pelinescu-Onicicul, B. Iancu, J. Janak, and D. Mierla. The sip express router, an open source sip platform. http://www.iptel.org/ser. Accessed July 25, 2008. C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security [38] Sip-communicator 1.0. https://sip-communicator.dev.java.net/ Accessed July 25, 2008. [39] Huitema, C., and S. Weerahandi. 2000. Internet measurements: The rising tide and the dns snag. In Proceedings of the 13th ITC Specialist Seminar on IP Traffic Measurement Modeling and Management, IPseminar, Monterrey, CA, USA, ITC. September 18-20. © 2009 by Taylor & Francis Group, LLC SIP and Vertical Handoffs in Heterogeneous Wireless Networks Jie Zhang The University of British Columbia F. Richard Yu Carleton University Xiaolei Wang The University of British Columbia Henry C. B. Chan The Hong Kong Polytechnic University Victor C. M. Leung The University of British Columbia CONTENTS 11.1 Introduction 11.2 Vertical Handoff Management 11.3 Seamless Vertical Handoff Support Using SIP 11.4 Efficient Transport of SIP Traffic over SCTP 11.5 Conclusions References 11.1 Introduction With the widespread deployment of Internet services, it is expected that peo- ple will demand to access Internet service "anytime and anywhere." Third generation (3G) cellular mobile communication systems, which can provide very wide coverage, are contributing to the realization of this goal. However, the 384 kbps data transmission rate provided by current 3G systems is n