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T2 · T2-R04 · SIP, WebRTC, RTP

What SIP is for

Keep the jobs separate. SIP is the signaling. The Wikipedia article says the media is specified and carried by other protocols. RTP is the next room, not a paragraph you paste into a SIP trace and call finished.

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Counts on this page

4boxes
4opened sources
1confirm rows
5study lines

Opened sources

Confirm rows, no URL

Learn it in 5 minutes

  • Wikipedia says SIP initiates, maintains, modifies, and terminates communication sessions that involve voice, video, and messaging.
  • It says SIP is text-based and incorporates elements of HTTP and SMTP, and that a call may have multiple media streams.
  • It also says media type and setup are performed with the Session Description Protocol, and that SIP works with other protocols that carry the media.
  • RFC 3261, opened as SIP: Session Initiation Protocol, is the standards-track specification. The page notes that it obsoletes RFC 2543.
  • IANA's SIP parameters page says header field names are case-insensitive and points at RFC 3261. The page shows Last Updated 2026-08-17.

Visual

What SIP is for SIP. Teaching sketch. Confirm a live system. SIP HTTP-like SDP Media Names come from pages opened in 2026-10. A missing name stays confirm.

Count the boxes: 4. Each label is a name from a page or a study label marked on the drawing.

Flow

What SIP is for Caller SIP Called session setup session setup RTP, not required to hairpin Teaching sketch from RFC 3261 and RFC 3550. Not a packet capture.

What is going on

Keep the jobs separate. SIP is the signaling. The Wikipedia article says the media is specified and carried by other protocols. RTP is the next room, not a paragraph you paste into a SIP trace and call finished.

RFC 3261 is the document the IANA registry cites. The registry date 2026-08-17 is the date on the parameters page, not a new SIP version. Do not teach that date as a protocol release.

Worked example

On a ladder, label the setup arrows SIP and the dashed media arrow RTP. If someone writes the codec on the SIP arrow, move the codec to SDP, which is the next lesson.

Quiz

1. IANA's SIP parameters page cites RFC 3261 and shows Last Updated 2026-08-17.

2. SIP itself carries the voice packets.

Ecosystem

Sister pieces sit on the ecosystem page: the glossary, the mind map, the integration map, and the bridges.

  • SIP — The signaling protocol Wikipedia describes for starting, keeping, changing, and ending multimedia sessions.
  • SIP header field — A name in the IANA registry. The page says the names are case-insensitive.

Config. Record the RFC number and the IANA last-updated date as two different facts.

Troubleshooting. A call that sets up and has no audio is not a SIP failure yet. Move to RTP after the dialog exists.

Bridge. RFC 7092, also opened, says many deployments put entities in the signaling path that go beyond a proxy, and that RFC 3261's term for them is a back-to-back user agent.

Mind map, sister technologies, and future hooks live on the ecosystem page.

Sources and go deeper

Opened 2026-10. A row marked confirm has no link, because that page was not verified.

sources.json Markdown