SIP trunking enables the end point’s PBX (Phone Exchange System) to send and receive calls via Internet. As SIP is applied for the signalling protocol for multiple real-time application, SIP trunk is able to control voice, video and messaging applications. It is also a voice over Internet Protocol (VoIP) technology and streaming media service based on the Session Initiation Protocol (SIP) by which Internet telephony service providers (ITSPs) deliver telephone services and unified communications to customers equipped with SIP-based IP PBX and unified communications facilities. Most unified communications applications provide voice, video, and other streaming media applications such as desktop sharing, web conferencing, and shared whiteboard.