1. Configuration Guide
  2. IMS Support
  3. SRVCC PS-CS Access Transfer
  4. Early Dialogs
  5. SRVCC Handover Support in Alerting Phase

SRVCC Handover Support in Alerting Phase

The SBC supports handovers between Packet-Switched (PS) and Circuit-Switched(CS) networks for calls in an alerting phase; that is, a 180 ringing response for the initial INVITE has been sent or received and the SIP final response has not been sent or received.

The behavior of the two anchoring points, ATCF and ATGW, is defined by 3GPP in Release 12 of Technical Specification TS 24.237. Oracle Communications developed these functional entities based on the initial version of TS 24.237 Release 10, and has added the sip-feature-caps configuration element to align with Release 12.

To ensure that calls in an alerting phase are transferred between PS and CS networks, set the sip-feature-caps value as follows:

  • Set state to “enabled”
  • Set atcf-management-uri to "management" or "psi"
  • Set atcf-alerting to "enabled"

For information on the results of these settings, refer to the SIP Feature Capabilities section.

The diagram below shows an incoming call session during the alerting phase.

Depicts an incoming call session during the alerting phase.

This diagram shows an outgoing call session during the alerting phase.

Depicts an outgoing call session during the alerting phase.