he industry. If readers are interested in third generation wireless networks, they can read the reference documents. 5.6.1.1 IP Multimedia Subsystem (IMS) of 3GPP IMS [8]: In 1998, the mobile world realized that migration to all-IP would help to globalize the telecommunication market and the 3GPP effort was launched. In 2000, 3GPP made SIP part of the all-IP mobile standard under © 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security the name IMS-Internet multimedia subsystem. The IP Multimedia Subsystem (IMS) is an architectural framework for delivering IP multimedia to mobile users. In order to achieve access independence and to maintain a smooth interop- eration with wireline terminals across the Internet, the IP multimedia subsys- tem attempts to be conformant to IETF "Internet standards." Therefore, the interfaces specified conform as far as possible to IETF "Internet standards" for the cases where an IETF protocol has been selected, e.g., SIP. The SIP application server may host and execute services. The SIP applica- tion server can influence and impact the SIP session on behalf of the services and it uses the ISC interface (IP Multimedia Subsystem Service Control Inter- face) to communicate with components of the IMS core network. The Third Generation Partnership Project (3GPP) [8]: The 3GPP is collaboration agreement that was established in December 1998. The collabo- ration agreement brings together a number of telecommunications standards bodies that are known as organizational partners. The original scope of 3GPP was to produce globally applicable technical specifications and technical reports for a Third Generation Mobile System based on evolved GSM core networks and the radio access technologies that they support (i.e., Universal Terrestrial Radio Access (UTRA) both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes). The scope was subsequently amended to include the maintenance and development of the Global System for Mobile communication (GSM) tec