Session Initiation Protocol
This is used for telephony and video conferencing.
SIP messages sent from initiator to responder via servers
- Determine location of responder
- Discover NAT bindings
- Negotiate parameters and options for the call An offer/answer exchange using SDP to describe the session being created
- Alert the responding user – make phone ring! – and agree to setup a call
- NAT binding discovery and connection probing takes place while alerting
This runs with SDP, which then makes the P2P connection at which point the users switch to RTP
WebRTC is an alternative