1. Configuration Guide
  2. IMS Support
  3. SRVCC PS-CS Access Transfer
  4. Early Dialogs

Early Dialogs

If the SC UE engages in a session which is in early dialog state, it will send a SIP UPDATE 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, early dialogs behave in accordance with TS 24.229 [2].

Call flow depicting SRVCC early dialog signaling.