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CANCEL, BYE, and re-INVITE

CANCEL abandons an unanswered INVITE, BYE ends a confirmed dialog, and re-INVITE changes a dialog that already exists.

Learn in 5 minutes

  1. Pair 200 OK for CANCEL with 487 for the INVITE
  2. Use BYE only on a confirmed dialog
  3. Treat a mid-dialog INVITE as a re-INVITE and a possible target refresh

Visual

CANCEL, then 487 · study drawing · cyphermonkeylabs.com UAPeer INVITE 100 180 CANCEL 200 487 ACK

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The dialog state decides the method. The branch decides whether CANCEL matches.

Worked example

Dissect a BYE This BYE assumes the dialog already exists. Find the CSeq and the To tag.

  1. Dissect the BYE.
  2. Confirm both tags are present.
  3. Read the CSeq number.

Fault

The 200 OK and the CANCEL crossed. The caller sends no BYE. The callee stays off hook and RTP continues.

A late CANCEL does not unwind a 200 OK. The UAS may answer 200 to the CANCEL and leave the dialog up.

Quiz

CANCEL uses


After a successful cancel, the INVITE completes with


BYE is appropriate when


If 200 OK and CANCEL cross


A re-INVITE is


491 Request Pending means


Ecosystem

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

AI omni-channel agents A voice bot still needs a session. SIP creates, modifies, and ends sessions. Omni-channel, in the contact-center sense, means the same contact can also live on chat or another digital channel. Those channels do not replace the voice session. On Amazon Connect the platform owns the managed PSTN voice channel. Bridging an outside carrier into Connect with a Chime Voice Connector is not a supported pattern unless AWS reviews it. When an SBC forks the voice leg to a recorder, that fork is SIPREC, a different plane from the customer dialog.

AI agents A voice bot still needs a session. On Amazon Connect the platform owns the managed PSTN voice channel. Bridging an outside carrier into Connect with a Chime Voice Connector is not a supported pattern unless AWS reviews it. The FreeSWITCH manual page also describes SignalWire, founded by the FreeSWITCH team, as a hosted platform with AI agents behind REST APIs and SWML.

Glossary · Ecosystem map · Ports · Troubleshooting

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