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About VoIP
VoIP and videoconferencing systems are increasingly becoming important and popular applications on the Internet. There are various approaches to such multimedia communication applications, among which H.323 [1], SIP [2], and Access Grid [3] are well-known. Most VoIP systems currently are designed to support relatively small size meetings. However new applications such as international scientific collaborations and real-time streams for monitoring require larger scale meetings which may have as many as hundreds of participating sites, and more sophisticated collaboration services such as video annotation and streaming visualization.

These emerging advanced distributed multimedia systems require a scalable, robust and adaptive service infrastructure. However, both the traditional telecommunication architecture based on client/server model and hardware multicast based Internet model have intrinsic limitations. Service-oriented architectures (SOA) have been developed for scalable Internet applications such as peer-to-peer computing, Grid and Web-Services computing and it is attractive to consider them for VoIP and videoconferencing systems. The architecture of the telecommunication monolithic service provision usually links the packet delivery, call control functions and service logic intelligence in the central hardware boxes. Service architectures suggest that one separates the MCU/Softswitch in VoIP into distinct services for media delivery, media processing and session management. These services can be distributed for large scale of conferencing and replicated for performance and fault tolerance. Further they can also be customized to support different client-side devices and application scenarios.

We propose a service-oriented VoIP conferencing framework which can interoperate with standards –based VoIP systems to forge an open software solution that will leverage existing conferencing resources. We define XGSP (XML based General Session Protocol) [4] as an interoperable control framework based on Web services technology for creating and controlling audio and videoconferences. XML is used to describe the XGSP protocol, similarly to the text messages in SIP, to enhance the interoperability with other Web based components. Based on this framework, we develop Global-MMCS (Global Multimedia Collaboration System) [5] to support scalable web-service based interoperable VoIP conferences and integrate multiple services including videoconferencing, instant messaging and streaming. Global-MMCS uses a unified, scalable, QoS aware “overlay” network – NaradaBrokering [6], to support medium and large size of real-time group communication over heterogeneous networking environments. Using XGSP schema, Global-MMCS specifies a distributed flexible conference management mechanism for integration of various VoIP conferencing services, and a common call signaling protocol for interactions between different conferencing endpoints.

The paper is organized in the following way. Section 2 introduces related work and our design principles. The system architecture is discussed in Section 3 while section 4 presents the implementation of the system and performance evaluation. Section 5 presents our conclusions and discusses future work