[OpenSIPS-Users] https://datatracker.ietf.org/doc/html/rfc3261#section-13.3.1.1

[Johan De Clercq]

Question,

I always believed that fr_inv_timer should trigger when an invite is not
finished in due time.
This seems however to contradict the link in the title

 If the UAS is not able to answer the invitation immediately, it can
   choose to indicate some kind of progress to the UAC (for example, an
   indication that a phone is ringing).  This is accomplished with a
   provisional response between 101 and 199.  These provisional
   responses establish early dialogs and therefore follow the procedures
   of Section 12.1.1
<https://datatracker.ietf.org/doc/html/rfc3261#section-12.1.1> in
addition to those of Section 8.2.6
<https://datatracker.ietf.org/doc/html/rfc3261#section-8.2.6>.  A UAS
MAY
   send as many provisional responses as it likes.  Each of these MUST
   indicate the same dialog ID.  However, these will not be delivered
   reliably.

   If the UAS desires an extended period of time to answer the INVITE,
   it will need to ask for an "extension" in order to prevent proxies
   from canceling the transaction.  A proxy has the option of canceling
   a transaction when there is a gap of 3 minutes between responses in a
   transaction.  To prevent cancellation, the UAS MUST send a non-100
   provisional response at every minute, to handle the possibility of
   lost provisional responses.

      An INVITE transaction can go on for extended durations when the
      user is placed on hold, or when interworking with PSTN systems
      which allow communications to take place without answering the
      call.  The latter is common in Interactive Voice Response (IVR)
      systems.


Can somebody please comment on this ?

BR, Johan.
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