Confirmed Dialogs
When an SC UE is engaged in one or more ongoing IMS sessions, it will send a re-INVITE containing:
- An SDP offer, including the media characteristics used in the existing dialog, and
- A Reason header field containing the protocol SIP and reason parameters cause with the value 487 (as specified in RFC 3326 [57]), with reason text reading either Handover cancelled or Failure to transition to CS domain.
In all other ways, confirmed dialogs behave in accordance with TS 24.229 [2].