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T6 · T6-R16 · SIP and media

What SIP is for

Signaling and media are different jobs. SIP, in the RFC that opened, sets up the session. RTP, in RFC 3550, is the transport protocol for real-time applications. If you debug a dial tone by staring at an RTP port, you may be in the wrong job.

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Learn it in 5 minutes

  • 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.

Visual

What SIP is for Jobs. Teaching sketch. Confirm a live system. SIP Proxy Register RTP 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

Signaling and media are different jobs. SIP, in the RFC that opened, sets up the session. RTP, in RFC 3550, is the transport protocol for real-time applications. If you debug a dial tone by staring at an RTP port, you may be in the wrong job.

IANA's SIP parameter registry, last updated 2026-08-17 on the page that opened, lists header fields and says header field names are case-insensitive. Call-ID has the compact form i. Contact has the compact form m. A capture that hides compact forms will look like a different protocol.

This room does not invent timer values. If you need timer T1, open the RFC section and write the number you read. It is not repeated here because that section was not the part extracted.

Worked example

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.

Quiz

1. RFC 3261 describes SIP as creating, modifying, and terminating sessions.

2. Header names are case-sensitive, according to the IANA page.

Ecosystem

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

  • SIP — The Session Initiation Protocol, RFC 3261, for session signaling.
  • Compact form — A short header name. IANA lists i for Call-ID and m for Contact.

Config. On a study capture, expand compact headers before you compare two ladders.

Troubleshooting. Two Call-IDs can be two dialogs. Count them before you call it one failed call. A back-to-back agent can split them. Confirm the product's role on its own page.

Bridge. Zoom, Talkdesk, and Avaya can all sit on SIP trunks. The Wikipedia SIP trunking article splits a private domain and a public domain. The trunk is the interconnection.

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