ported by the i2CAT Foundation and the MCyT (Spanish Ministry of Science and Technology) under the projects TSI2005-06092 and TSI2007-66637-C02-01, which are partially funded by FEDER. C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security End-users need request, find and consume advanced media services, regard- less of terminal capabilities and location. SIP is an effective way to do this, not by providing services, but just primitives that can be used to implement them. Fundamentally, SIP is a control protocol that offers additional capacities such as user location, availability, and capabilities. SIP depends on relatively intelligent endpoints that require little or no interaction with servers. Each endpoint manages its own signaling, both to the user and to other endpoints. There is a separation between signaling and media-any kind of media sup- ported in next generation networks can be signaled, such as uncompressed high definition or 3D video application. But the real powerful advantage of SIP is that, with the help of companion protocols, it can provide an Internet-style plethora of continuous media, value- added services, such as conferencing, instant messaging, or even streaming and gaming. This concept is named SIP-CMI (SIP-based continuous media integration) [2]. On the other hand, the non-continuous media, value-added services can be provided by Service-Oriented Architecture (SOA) [3]. Furthermore, a combi- nation of SIP and Web services can fulfill all the needs of the current and future Internet user. Web services and SIP services are the paradigm of con- verged communication services [4]. Users demand personalized services that can be accessed from any terminal within any network. Therefore, service providers must deploy more advanced services with shorter time-to-market and development cycles in heterogeneous networks. SIP and SOA have characteristics that satisfy these criteria, and this is the main reason SIP has been selected by the Third Generation Part- nersh