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Building Telephony Systems with OpenSIPS 1.6 by Flavio E. Goncalves

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Call forwarding

Now we are going to work with call forwarding. There are usually three kinds of call forwarding. This forwarding is important for voicemail operations.

  • Blind call forwarding: All INVITE requests sent to this phone number will be redirected immediately to the phone stored in the user_preferences table. The SIP router will fork the call, creating a new leg to the new destination. The phone with call forward configured won't even ring, whether it's registered or not.
  • Forward on busy: In this case, we will use the failure_route feature to intercept the "486 Busy" message and create a new leg by sending the INVITE request to the final destination.
  • Forward on no answer: If a phone replies to an INVITE request with a "480 Temporarily unavailable" ...

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