12.2A SC UE procedures for PS to CS access transfer, vSRVCC
24.2373GPPIP Multimedia (IM) Core Network (CN) subsystem IP Multimedia Subsystem (IMS) service continuityRelease 17Stage 3TS
12.2A.1 General
The SC UE may be engaged in one or more ongoing sessions before vSRVCC access transfer is performed. By an ongoing session, it is meant a session for which the response to the initial SIP INVITE request to establish this session has been sent or received.
In the vSRVCC session continuity procedures the SC UE shall consider only sessions where the following applies:
1. the SIP dialog contains speech and video media components supporting a real time video session synchronized with speech as defined in 3GPP TS 22.173 [24], which includes the codecs for speech and video as specified in 3GPP TS 26.114 [68]; and
2. the speech media is carried over a PS bearer with QCI=1 as specified in 3GPP TS 23.203 [65];
for access transfer. Sessions considered for vSRVCC procedures are regarded as full-duplex.
12.2A.2 ICS-based
If:
– SC using ICS is enabled;
– the Gm reference point is retained upon PS handover procedure;
NOTE 1: The SC UE knows that the Gm reference point is retained upon PS handover if, following handover, the SC UE has a "dedicated PDP context for SIP signalling" or has a "general-purpose PDP context" to carry the IM CN subsystem-related signalling, as described in 3GPP TS 24.229 subclause B.2.2.1.
– the SC UE is using ICS capabilities as defined in 3GPP TS 24.292 [4]; and
– vSRVCC procedures (as described in 3GPP TS 24.008 [8]) have been completed;
then the SC UE, in order to add Gm control for the newly established CS session, shall:
– send a SIP re-INVITE request for each session with only speech media component or with both speech and video media components to be transferred starting with the session with active speech and video media components that was most recently made active;
– within the SDP offer for sessions with speech and video media components, indicate the media lines for the speech and video media components as speech and video media components over circuit switched bearer in accordance with 3GPP TS 24.292 [4]. If the precondition mechanism is used, the SC UE shall indicate the related local preconditions as met; and
– within the SDP offer for sessions with only speech media component, indicate the media lines for the speech media component as speech media component over circuit switched bearer in accordance with 3GPP TS 24.292 [4]. If the precondition mechanism is used, the SC UE shall indicate the related local preconditions as met;
NOTE 2: The SIP dialog established over the source PS access network stays the same after vSRVCC procedures, e.g. the IP address of the UE, the Call-ID or the P-CSCF do not change. Therefore in this case a SIP re-INVITE request needs to be sent to add ICS-control for the CS bearer.
12.2A.3 Not based on ICS
After successful vSRVCC procedures (as described in 3GPP TS 24.008 [8]) have been completed, if the SC UE is not using ICS capabilities, the SC UE shall replace the session with active speech and video media components which was most recently made active with the newly established CS voice/video call.
NOTE 1: In the case when ICS is not supported or used, only the ongoing session with active speech and video media components which was most recently made active is transferred from PS to CS.
In addition, if:
– the Gm reference point is retained upon PS handover; and
NOTE 2: The SC UE knows that the Gm reference point is retained upon PS handover if, following handover, the SC UE has a dedicated PDP context for SIP signalling or has a general-purpose PDP context to carry the IM CN subsystem-related signalling, as described in 3GPP TS 24.229 [2] subclause B.2.2.1.
– there are one or more remaining media component(s) in the IMS session other than the speech and the video media components which were transferred to the CS Target Access Leg;
the SC UE shall:
– send a SIP re-INVITE request to the SCC AS as specified for media removal in subclause 13.2.1; and
– indicate in the SDP offer the speech and video media components as being removed.
NOTE 3: The SC UE can still send a SIP re-INVITE request if there are no remaining media components in the IMS session.
12.2A.4 Void
12.2A.5 Call in alerting phase
If the conditions in subclause 12.2.3B.1 for the application of subclause 12.2.3B.3 are satisfied for a session with active speech media component and active video media component prior to the successful completion of the vSRVCC procedures (as described in 3GPP TS 24.008 [8]), then after the successful completion of the vSRVCC handover procedures, the SC UE shall apply the procedures specified in subclause 12.2.3B.3
12.2A.5A Call in pre-alerting phase
If the SC UE supports the PS to CS SRVCC for originating calls in pre-alerting phase and the conditions in subclause 12.2.3B.1 for the application of subclause 12.2.3B.3.3 are satisfied for a session with active speech media component and active video media component prior to the successful completion of the vSRVCC procedures (as described in 3GPP TS 24.008 [8]), then after the successful completion of the vSRVCC handover procedures, the SC UE shall apply the procedures specified in subclause 12.2.3B.3.3.
If the SC UE supports the PS to CS SRVCC for terminating calls in pre-alerting phase and the conditions in subclause 12.2.3B.1 for the application of subclause 12.2.3B.3.4 are satisfied for a session with active speech media component and active video media component prior to the successful completion of the vSRVCC procedures (as described in 3GPP TS 24.008 [8]), then after the successful completion of the vSRVCC handover procedures, the SC UE shall apply the procedures specified in subclause 12.2.3B.3.4.
12.2A.6 Abnormal cases
If the SC UE:
– receives a NOTIFICATION message containing an "SRVCC handover cancelled, IMS session re-establishment required" as described in 3GPP TS 24.301 [52] or receives an event notification containing an "SRVCC handover cancelled, IMS session re-establishment required" indicator from the lower layers as described in 3GPP TS 24.501 [98] depending on the access in use; or
– does not successfully transition to UTRAN after it receives the handover command (as described in 3GPP TS 36.331 [62]);
then:
– if the SC UE is engaged in one or more ongoing IMS sessions, the SC UE shall send a SIP re-INVITE request in accordance with subclause 12.2.4.1; and
– if the SC UE is engaged in a session in early dialog state, the SC UE shall send a SIP UPDATE request, in accordance with subclause 12.2.4.2.