Centralized Conferencing using SIP

Multiparty conferencing is an important telephony service, provided in the PSTN by conference bridges. Internet telephony can enhance this basic service by video conferencing and collaborative work. The Session Initiation Protocol (SIP) can support many different conferencing architectures, including the centralized conferencing server model. We describe design issues and challenges in implementing a SIP-based centralized conferencing server and discuss the architecture and performance of our implementation, sipconf. Keywords—Centralized conference server; dial-in conference bridge; SIP; RTP mixer; packet audio; packet video; Internet telephony; sipconf