 implement services with high complexity using collaborative services or an orchestration of services (e.g., in the form of a BPEL process [18]). They can be implemented in different environments, programming languages, and platforms and can be located in different service providers. In the case of advance media services, it takes advantage of the power of SOA and SIP convergence, because of the SOA. This paradigm can be applied with Web service orchestration, transparent integration with other services and integration with continuous media services such as session and stream control, multimedia services composition, and call signaling, as shown in Figure 2.8. SIP works as an application layer signaling protocol and media control in parallel with SOAP in the data plane, as depicted in Figure 2.9. In the specific case of the Web services, the service provider develops their application and provides a Web Service Description Language (WDSL) inter- face that describes the capabilities of the service. The location of the service is stored in a Universal Description Discovery Integration (UDDI) repository that manages the publication, search, and discovery of services. C 2009 by Taylor & Francis Group, LLC SIP: Advanced Media Integration BYE Il 408 Input/ Condition transition WS-Init 200ok WS-User accepted WS-InviteUser WS-AddUser 200ok 200ok 200ok 200ok/condition 1 create conference Collaboration FIGURE 2.8 SIP/Web services collaboration. Data plane Signaling plane HTTP/WS Stack TCP / UDP FIGURE 2.9 Data plane and control plane. C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security 2.4 MPEG-21/SIP-Based Cross-Layer In recent years, network connections are becoming ubiquitous and, there- fore, people expect to access multimedia content anywhere and anytime. One approach to solve this requirement is to use a technique known as session mobility, which allows a user to maintain a media session even while chang- ing terminals. For example, upon entering the office, a person may want to c