Protocols BroadNet answer

What is SIP (Session Initiation Protocol)?

Last reviewed July 22, 20261 min readReviewed by BroadNet engineering

Quick answer

SIP (Session Initiation Protocol, RFC 3261) is the signaling protocol that sets up, modifies, and tears down real-time voice and video sessions over IP. It handles the call control — inviting, ringing, answering, and hanging up — while the actual audio travels separately as RTP media negotiated through an SDP offer/answer inside the SIP messages. SIP is the backbone of VoIP, SIP trunking, and programmable voice. See /answers/what-is-rtp, /answers/what-is-sdp, and /answers/voice-api-sip-trunking.

Plain-language definitionVendor-neutralReviewed July 22, 2026

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