Definition:
SIP is the real-time communication protocol for VoIP. SIP is a signaling protocol for Internet conferencing, telephony, presence, events notification (emergency calling) and instant messaging. SIP has been expanded to support video and instant-messaging applications. SIP uses a text-based programming language designed to perform basic call-control tasks, such as session call set up and tear down and signaling for features such as call hold, caller ID, conferencing and call transferring.