4.2.1 Mobile originating side – initiation of call setup

23.1723GPPRelease 17Stage 2Technical realization of Circuit Switched (CS) multimedia service UDI/RDI fallback and service modificationTS

By sending a SETUP message with a Repeat Indicator set to "support of service change and fallback", a multimedia BC-IE, and a speech BC-IE (see figure 4.1), a terminal may request a call to be set with the capability to fallback to either a speech only, a multimedia only call or to use service change later during the active state of the call (the first BC‑IE indicates the preferred service). If the terminal supports Network-initiated service upgrade to multimedia, then it shall also indicate this in the SETUP message with the "Enhanced Network-initiated ICM" (ENICM) Capability (see 3GPP TS 24.008[3]).

After checking the provisioning (see subclause 4.2.1.1), and verifying that the functionality is supported, the MSC replies in the CALL PROCEEDING message with either the two BCs in the same order (to indicate that it accepts the proposed settings – see figure 4.2), or with a single BC (multimedia or speech – see figure 4.3) unless the CALL PROCEEDING is delayed until the response from the terminating user and then it may also be sent with the BCs in reverse order (see clause 4.2.3).

In the case the MSC ignores the SETUP message if the presence of a reserved value for the Repeat Indicator is set, it sends a STATUS message back to the UE (see figure 4.4), with the Cause Value set to #100, "Conditional IE error" (see 3GPP TS 24.008 [3], clause 8.7.2). The UE then reacts as described in 3GPP TS 24.008 [3], clause 5.5.3.2.2, and may resend a new SETUP message with a single BC, or perform any appropriate action according to its implementation. This also applies in case the MSC returns instead a RELEASE COMPLETE message.

Figure 4.1: SETUP message towards the originating MSC

Figure 4.2: Normal case

Figure 4.3: Fallback case

NOTE: The sending of the STATUS message from the MSC and the second SETUP message from the UE are implementation dependent.

Figure 4.4: MSC not supporting the RI value

4.2.1.1 Subscription checking

The functional behaviour of the originating MSC and VLR is specified in 3GPP TS 23.018 [10]. The procedure specific to SCUDIF is specified in this subclause:

For mobile originated SCUDIF calls, the MSC shall convert both PLMN bearer capability 1 and PLMN bearer capability 2 to two individual Basic Service codes and send them in Send Info For Outgoing Call. The VLR shall check the subscription for those basic services, then indicates the availability of each basic service to the MSC by Complete Call. If both services are not provisioned, the VLR shall send Send Info For Outgoing Call negative response to the MSC. The MSC shall fall back to the allowed service if the availability of only one service is indicated. The MSC shall continue as a SCUDIF call if the availability of both services is indicated.

4.2.1.1.1 Send Info For Outgoing Call

Send Info For Outgoing Call contains the following SCUDIF specific information elements:

Information element name	Status	Description
Bearer service2	C	Bearer service 2 required for the MO call, derived from the PLMN bearer capability 2 information received in the set-up request from the MS. For a SCUDIF call, one of bearer service 2 or teleservice 2 shall be present.
Teleservice2	C	Teleservice 2 required for the MO call, derived from the PLMN bearer capability 2 information received in the set-up request from the MS. For a SCUDIF call, one of bearer service 2 or teleservice 2 shall be present.

4.2.1.1.2 Complete Call

Complete Call contains the following SCUDIF specific information elements:

Information element name	Status	Description
First service availability	C	Shall be present for a MO SCUDIF call if the Bearer service or Teleservice is allowed; otherwise shall be absent.
Second service availability	C	Shall be present for a MO SCUDIF call if the Bearer service 2 or Teleservice 2 is allowed; otherwise shall be absent.