Android developer

A  SIP server  is the main component of an IP PBX, dealing with the setup of all SIP calls in the network. A SIP server is also referred to as a  SIP Proxy  or a Registrar. Although the SIP server is the most important part of the SIP based phone system, it only handles call setup and call tear down. It does not actually transmit or receive any audio. This is done by the media server in RTP. An example of a SIP server is  3CX Phone System  - a  Windows-based SIP server

The calling phone sends out an invite The called phone sends an information response 100 – Trying – back. When the called phone starts ringing a response 180 – Ringing – is sent back When the caller picks up the phone, the called phone sends a response 200 – OK The calling phone responds with ACK – acknowledgement Now the actual conversation is transmitted as data via RTP When the person calling hangs up, a BYE request is sent to the calling phone The calling phone responds with a 200 – OK.