# What SIP is for

Study notes. Not vendor documentation and not legal advice.

- RFC 3261 is an application-layer control protocol for creating, modifying, and terminating sessions.
- The abstract includes Internet telephone calls, multimedia distribution, and multimedia conferences.
- SIP invitations carry session descriptions so participants can agree on media types.
- Proxy servers help route requests, and SIP includes a registration function.
- Wikipedia describes SIP as signaling for sessions that involve voice, video, and messaging.

On a ladder, label the vertical lines as people or servers, and the arrows as SIP. Draw RTP as a separate dashed line. If you cannot name the SIP request you saw, do not draw it.