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Future multimedia networks will be a ubiquitous communication platform that allows users to enjoy continuous multimedia services in any location on any device. The user needs to be able to discover devices, discover services and capabilities, set up sessions, negotiate session characteristics, transmit data, adapt media, and modify sessions including seamless session handover, to enable best in class communication experience based on the context. A modular framework is needed to satisfy these requirements and to allow for independent evolution and development. Future multimedia communication will be based on Service Orientated Architecture (SOA) principles. Service composition will involve the collective use of multiple multimedia applications of different devices. To achieve this, it is necessary to “logically separate applications from the user’s network interface device” (Jones, 2007). The separation of base session signalling from applications means application developers do not need to be concerned with session signalling. The result is an ease of development and the deployment of new applications.
The use of the Internet for voice communication has increased significantly in recent years. Using IP will allow the convergence of video, voice and many new applications in a manner not possible on traditional networks. This will enable the provision of arbitrary, new applications and services to users. As users have become accustomed to high quality of service for voice communication, the same expectations will be demanded for multimedia communication over the internet. A multimedia communication system will be required to provide the platform for these services. The question that arises is whether a backward compatible approach with extensions based on SIP is that platform or if a clean slate approach like AMS is required.
SIP has been adopted by most telecommunication standards as the de facto signalling protocol for Voice over IP. It is an IETF standard and was designed to be a generic framework to set up and tear down multimedia sessions. SIP provides a number of principal functions including; user location, user availability, endpoint capabilities and session set up and session management. RFC 4485 clearly states that SIP was not designed to emulate telephony. However, due to the universal acceptance of SIP by telephony providers, voice has become the only real application of SIP, with video being used sparingly. Through use with other existing protocols it can currently handle many other types of multimedia communication, namely; white boarding (Xiaotao & Schulzrinne, 2004), desktop sharing (Xiaotao & Schulzrinne, 2004), file transfer (Xiaotao & Schulzrinne, 2004; Zhang, 2009), but use of SIP based solutions with these applications has been minimal. Support for these has evolved through industry, academia and the many working IETF working groups like SIP, MMUSIC, SIPPING, SIMPLE. Further technological advances are required for it to become the future, all embracing platform. Based on the extensibility of SIP such an approach is possible, but the ability to control complexity in supporting current and future applications is the fundamental challenge for SIP. The Session Description Protocol (SDP) (Handley & Jacobson, 1998) has been used in conjunction with SIP to describe multimedia sessions. To extend its initial scope and address issues viewed as limiting, like the ability to advertise capabilities, SDP has undergone significant changes in recent years..