What is SIP and RTP, and how do they work?
SIP uses two protocols – The Session Initiation Protocol (SIP) is an industry-standard application-layer control protocol that can establish, modify and terminate multimedia sessions or calls. Examples of multimedia sessions include multimedia conferences, distance learning, and Internet telephony. SIP is used for the control messages – register with SIP server, initiate a phone call, negotiate the codec to use, etc. – and consists of text messages in a predefined but flexible format. SIP is fully specified in RFC 2543. With SIP, you join a SIP Registrar and configure your phone with the Registrars name and your username. Your SIP phone then keeps the SIP Registrar informed of your presence (whether you are online, and which IP address you can be contacted at). The Real-time Transport Protocol (RTP) provides end-to-end network transport functions suitable for applications transmitting real-time data such as audio, video or simulation data, over multicast or unicast network services. RT
