Timeline
SIP concept proposed
Mark Handley, Henning Schulzrinne, Eve Schooler, and Jonathan Rosenberg began work on SIP at Columbia University.
RFC 2543 published
First version of SIP standardized by IETF. Defined basic session initiation, INVITE, BYE, REGISTER methods.
3GPP adopts SIP
3GPP selects SIP for IP Multimedia Subsystem (IMS), making it the standard for next-gen mobile networks.
RFC 3261 published
Major revision replacing RFC 2543. Added detailed transaction handling, improved security, and clarified ambiguities. Still the current base standard.
SIP becomes widely deployed
Major VoIP services like Vonage and Skype begin large-scale deployments using SIP or SIP-derived protocols.
SIP Extensions for Presence
RFC 3856, 3903 — Added presence and instant messaging capabilities to SIP.
SIP Outbound (RFC 5626)
Specified how user agents maintain persistent connections to handle NAT traversal.
WebRTC emerges
Introduces browser-based real-time communication, often using SIP over WebSocket for signaling.
SIP on WebRTC
RFC 7118 — SIP over WebSockets for browser-based voice/video.
LTE VoLTE deployment
Voice over LTE using SIP/IMS becomes widely deployed in mobile networks worldwide.
STIR/SHAKEN
RFC 8224 — Framework to authenticate caller ID and prevent robocalling/spoofing.
5G VoNR
Voice over New Radio (5G) continues to use SIP/IMS for voice services.
AI-powered SIP
Integration of AI for call analytics, transcription, translation, and automated fraud detection in SIP calls.
SIP Creators
Mark Handley
Co-creator of SIP
Network researcher who co-invented SIP while at USC/ISI. Now a professor at UCL, London.
Henning Schulzrinne
Co-creator of SIP
Professor at Columbia University. Also co-created RTP (Real-time Transport Protocol) and RTSP.
Jonathan Rosenberg
Primary author of RFC 3261
Former CTO at Cisco's Collaboration unit. One of the most prolific IETF authors in the VoIP space.
Eve Schooler
Early SIP contributor
Researcher at Intel and Imperial College. Co-author of the first SIP RFC.
SIP vs H.323
| Feature | SIP | H.323 |
|---|---|---|
| Complexity | Text-based, simple | Binary ASN.1, complex |
| Extensibility | Easy to extend | Rigid |
| Firewall/NAT | Challenging, needs SBC/STUN | Similar challenges |
| Call Setup | Faster (fewer RTTs) | Slower |
| Adoption | Dominant (IMS, VoLTE, 5G) | Legacy video conferencing |
| Codecs | Negotiated via SDP | Negotiated via H.245 |
Key RFCs
- RFC 2543 (1999) — Original SIP specification
- RFC 3261 (2002) — SIP v2, current base standard
- RFC 3262 — Reliability of Provisional Responses
- RFC 3263 — Locating SIP Servers
- RFC 3264 — SDP Offer/Answer Model
- RFC 3311 — UPDATE Method
- RFC 3515 — REFER Method (call transfer)
- RFC 3856 — Presence Event Package
- RFC 4028 — Session Timers
- RFC 5626 — SIP Outbound (NAT traversal)
- RFC 7118 — SIP over WebSockets
- RFC 8224 — STIR/SHAKEN caller ID auth