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REFER and Replaces

REFER asks another UA to send a request, and Replaces names the dialog that request should take over.

Learn in 5 minutes

  1. Read Refer-To and the 202 Accepted
  2. Follow progress in NOTIFY sipfrag bodies
  3. Match a Replaces dialog by Call-ID and both tags

Visual

REFER with Replaces · study drawing · cyphermonkeylabs.com TransferorTransfereeTarget REFER 202 INVITE NOTIFY 200

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REFER stays in the original dialog. The INVITE it causes is a new dialog that names the old one.

Worked example

Read Refer-To Find the Replaces parameter inside Refer-To. It is escaped.

  1. Dissect the REFER.
  2. Decode the idea of the Replaces parameter.
  3. Note that 202 has not happened yet in this message.

Fault

A tool closes the transfer when it sees 202 Accepted. The NOTIFY sipfrag later says SIP/2.0 486 Busy Here.

The subscription exists so the transferor can see failure as well as success.

Quiz

REFER is defined in


202 Accepted means


Replaces identifies a dialog by


The compact form of Refer-To is


A NOTIFY for this transfer carries


early-only on Replaces means


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.

Programmable communications APIs Twilio’s docs home is API reference, tutorials, and integration for Twilio products. Elastic SIP Trunking is the SIP-shaped product already cited in this lab. This page does not define the word CPaaS from an RFC. Read the vendor page before you copy a diagram that uses that word.

Glossary · Ecosystem map · Ports · Troubleshooting

Sources and go deeper