# What is SIP (Session Initiation Protocol)?

> 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.

- Canonical URL: https://www.broadnet.me/answers/what-is-sip
- Language: en
- Last reviewed: 2026-07-22
- Publisher: BroadNet (https://www.broadnet.me)

## Related

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- [What is IMS (IP Multimedia Subsystem)?](https://www.broadnet.me/answers/what-is-ims)
- [What is RTP (Real-time Transport Protocol)?](https://www.broadnet.me/answers/what-is-rtp)
- [What is SDP (Session Description Protocol)?](https://www.broadnet.me/answers/what-is-sdp)
- [What is an SBC (Session Border Controller)?](https://www.broadnet.me/answers/what-is-sbc)
- [How does a voice API and SIP trunking work?](https://www.broadnet.me/answers/voice-api-sip-trunking)
- [What is WebRTC?](https://www.broadnet.me/answers/what-is-webrtc)
- [Voice](https://www.broadnet.me/products/voice)