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Signaling drill with the cited answer

Each signaling answer is written here, with the RFC, before the quiz asks it.

Learn in 5 minutes

  1. Match a dialog with Call-ID, CSeq, branch, and To tag
  2. Place both kinds of ACK
  3. Say what 487 follows

Visual

The ladder the interview is about · study drawing · cyphermonkeylabs.com AliceSBCBob INVITE 100 INVITE 180 180 200 200 ACK

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The quiz repeats these rows. It does not introduce a new fact.

Worked example

Say the ACK kind The last hop follows 200 OK. What kind of ACK is it?

  1. Press Play.
  2. Step until the hop named in the question.
  3. Inspect that message and answer the check.

Fault

The ladder shows 487 and the ticket looks for an end-to-end ACK with a new branch. The hop-by-hop ACK on z9hG4bK7766as01 is present and was ignored.

The lesson states both ACK rules. This final is non-2xx.

Quiz

You tie the dialog with


The Via branch identifies


ACK after 200 OK


ACK after 487


100 Trying means


487 follows


Ecosystem

Glossary, sister systems, and the integration seam for this room.

Workforce management WFM forecasts volume and builds schedules. It consumes contact-center events. It does not parse Via headers. When a forecast is wrong, the SIP symptom is usually queue delay and 480 or carrier congestion, not a broken dialog ID.

Glossary · Ecosystem map · Ports · Troubleshooting

Sources and go deeper