rnal of Wireless Personal Communications 35(3): 269-87. [38] Jung, J.W., R. Mudumbai, D. Montgomery, and K. Hyun-Kook. 2003. Performance evaluation of two layered mobility management using mobile IP and session initiation protocol. GLOBECOM 3: 1190-94. [39] So, J.Y.H., W. Jidong, and D. Jones. 2005. SHIP Mobility Management hybrid SIP-HIP Scheme. Sixth International Conference on Software Engineering, Artificial Intelligence, Networking and Parallel/Distributed Computing, 2005 and First ACIS International Workshop on Self- Assembling Wireless Networks. SNPD/SAWN 2005, 226-30. [40] Banerjee, N., A. Acharya, and S.K. Das 2006. Seamless SIP-based mobility for multimedia applications. IEEE Network 20(2): 6-13. C 2009 by Taylor & Francis Group, LLC Part III SECURITY © 2009 by Taylor & Francis Group, LLC SIP Security: Threats, Vulnerabilities and Countermeasures Dimitris Geneiatakis, Georgios Kambourakis and Costas Lambrinoudakis University of the Aegean CONTENTS 18.1 Introduction 18.2 SIP Threats and Vulnerabilities 18.3 Attacks against the SIP 18.4 SIP Security Requirements 18.5 SIP Security Mechanisms and Services 18.6 Conclusions References 18.1 Introduction Until the early 1990s telecommunication providers were employing dedicated closed networks, like the Public Switch Telephone Network (PSTN), for trans- mitting voice. By this way the establishment of communication and voice transmission in PSTN was exploiting only 10-25% of the total available resources [1]. Even though significant effort has been devoted to improve resource utilization and to minimize the cost of the provided services, very little has been achieved to date. The Internet has supported the revolution in telecommunications and specifically in the provision of voice services, voice is transmitted over the Internet Protocol (VoIP) utilizing the Internet as a backbone network. Despite the fact that a plethora of novel, sophisticated, low-cost services can be offered in this way (e.g., conference rooms, click to dial etc), telecommunication providers