Network services

SIP

Also called session initiation protocol, VoIP, voice over IP, port 5060, INVITE, RTP, SDP, user agent, softphone, PBX, signaling

The signaling that sets up a VoIP call on port 5060: INVITE, ringing, 200 OK, ACK — then the audio flows separately over RTP.

SIP (Session Initiation Protocol, UDP or TCP 5060, or 5061 with TLS) sets up, changes and ends VoIP calls. It is readable text, like HTTP: a caller sends INVITE, gets 100 Trying, 180 Ringing and 200 OK, and replies ACK — a three-way setup — then BYE to hang up. SIP only does signaling; the voice itself travels in a separate RTP media stream on its own UDP ports, which the SDP body inside the SIP messages negotiates (the codec and the port). So one call is two flows: SIP on 5060 to set it up, RTP elsewhere to carry the audio.

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