Alert: If you HATE long posts, stop reading and click here . The Session Initiation Protocol, a VoIP protocol, used for originating and termination of media sessions like voice, video, IM, presence etc. Before we enter into the more technical details of SIP, let's refresh our basic telecom VoIP skills. I'd like to insist here that SIP is a signalling protocol, its NOT a media protocol -- which means it is a set of rules use to control the signaling part of a media session. It doesn't have any control on media. So let's not wait to start the basic call flow of SIP. Key terms: It is important to familiarize with these terms in order to understand basic SIP call flow. Here are few of them: Call flow : It's a flow diagram of SIP messages -- shows an ideal way how a media session carried over two endpoints. Its a must know thing and will be useful for your troubleshooting as well. Endpoint: Any device which is used to originate and terminate ...