ZTA LabFree University

T7 · T7-R19 · Call flows and routing

A ladder you are allowed to draw

The honest ladder for this lab has a caller, a SIP element that can proxy or register, and a called party. The arrows you can name from the pages that opened are the session setup and the registration function. Label anything else as a sketch and point at the RFC section you still need.

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Learn it in 5 minutes

  • A ladder is a drawing of messages between named boxes.
  • Draw a message only if a page you opened names that job.
  • SIP can create, modify, and terminate a session. Registration is a separate function in RFC 3261.
  • Early media, transfer, and conference methods are not copied here unless the section was read.
  • Vendor call-flow posters were not opened.

Visual

A ladder you are allowed to draw Ladder. Teaching sketch. Confirm a live system. Caller SIP Called 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

A ladder you are allowed to draw 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

The honest ladder for this lab has a caller, a SIP element that can proxy or register, and a called party. The arrows you can name from the pages that opened are the session setup and the registration function. Label anything else as a sketch and point at the RFC section you still need.

Zoom, Talkdesk, and Avaya each add product boxes around that ladder. The product box does not change the SIP job. It changes which admin page you open when the ladder is wrong.

A 200-class success is not two-way audio. Audio is RTP. The ladder should show both or admit it shows only signaling.

Worked example

Draw caller, SIP proxy, called party. Add one dashed RTP line that does not have to pass through the proxy. Title the drawing teaching sketch, not a packet capture.

Quiz

1. Registration and a phone call are the same SIP function.

2. A signaling ladder proves two-way audio.

Ecosystem

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

  • Ladder — A drawing of messages between named boxes.
  • Teaching sketch — A drawing this lab made to study. It is not a capture from a customer.

Config. Title every ladder with the pages it rests on.

Troubleshooting. If the picture has a box you cannot cite, delete the box.

Bridge. SIPREC later adds a recording session beside the communication session. Do not draw it on this first ladder.

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.

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