Session Initiation Protocol (SIP) is a standard protocol for initiating an interactive user session that involves controlling multimedia communication sessions such as video, voice, chat, gaming, and virtual reality. The protocol determines the messages that are sent between endpoints, which oversee establishment, termination and other essential elements of a call. SIP can be cast-off for creating, modifying and terminating sessions consisting of one or several media streams. SIP also provides five functions: user location, user availability, user capability, session setup, and session management. Like a public switched phone network, it sets up/establishes, ties together and tears down multimedia communications.