E.2.5 Service change

29.1633GPPInterworking between the IP Multimedia (IM) Core Network (CN) subsystem and Circuit Switched (CS) networksTS

E.2.5.2.1 SCUDIF

E.2.5.2.1.0 General

SCUDIF is standardised in 3GPPP 3GPP TS 23.172 [121].

E.2.5.2.1.1 IM CN subsystem originated change

E.2.5.2.1.1.1 Change from multimedia to speech

Figure E.2.5.2.1.1.1.1 shows an IM CN subsystem originated modification from multimedia to speech during an ongoing session when the CS leg supports BICC. The interworking node receives an INVITE message that indicates the dropping of the video media from the session, message 1. The interworking node can only accept the dropping of the media component and sends a corresponding codec modification request to the BICC network, message 2, and acknowledges the INVITE with a 200 OK message. The BICC network indicates a successful codec modification, message 5.

Figure E.2.5.2.1.1.1.1: IM CN subsystem originated modification
from multimedia to speech when the CS leg supports BICC

NOTE: Handling of a case, where a codec is received in BICC negotiation but not included in the available codec list negotiated previously, is not defined in the present release.

E.2.5.2.1.1.2 Change from speech to multimedia

Figure E.2.5.2.1.1.2.1 shows an IM CN subsystem originated modification from speech to multimedia during an ongoing session when the CS leg supports BICC. The interworking node receives an INVITE message that offers the adding of a video media to the ongoing speech session, message 1. The interworking node accepts the offer and sends a corresponding codec modification request to the BICC network, message 2. The BICC network indicates a successful codec modification, message 3. The interworking node acknowledges the INVITE with a 200 OK message after the MONA or H.245 in‑band negotiation in step 4 is completed.

If the codec modification is not successful in the BICC network, the interworking node responds to the INVITE message with the speech codec in the 200 OK message to retain the speech only session.

Figure E.2.5.2.1.1.2.1: IM CN subsystem originated modification
from speech to multimedia when the CS leg supports BICC

E.2.5.2.1.2 CS network originated change

E.2.5.2.1.2.1 Change from multimedia to speech

Figure E.2.5.2.1.2.1.1 shows a CS network originated modification from multimedia to speech during an ongoing session when the CS leg supports BICC. The interworking node receives a Modify Codec message that indicates the dropping of the video media from the session, message 1. The interworking node accepts the dropping of the video component and sends a corresponding INVITE message to the IM CN subsystem, message 2, and acknowledges the codec modification request to the BICC network, message 3. The IM CN subsystem acknowledges the INVITE dropping the video media with a 200 OK, message 4.

Figure E.2.5.2.1.2.1.1: CS network originated modification
from multimedia to speech when the CS leg supports BICC

E.2.5.2.1.2.2 Change from speech to multimedia

Figure E.2.5.2.1.2.2.1 shows a CS network originated modification from speech to multimedia during an ongoing session when the CS leg supports BICC. The interworking node receives a Modify Codec message that indicates the adding of a video media to the ongoing speech session, message 1. The interworking node accepts the offer and sends a corresponding INVITE message to the IM CN subsystem, message 2. The IM CN subsystem acknowledges the INVITE adding the video media with a 200 OK, message 3, and acknowledges the codec modification request to the BICC network, message 4. The interworking node may have to update the codecs, messages 7 and 8, after the MONA or H.245 in‑band negotiation in step 6.

If the IM CN subsystem does not accept the addition of the video media to the session, the interworking node rejects the modify codec request to retain the speech only session.

Figure E.2.5.2.1.2.2.1: CS network originated modification
from speech to multimedia when the CS leg supports BICC

E.2.5.2.2 Non-SCUDIF case (ISUP or BICC without SCUDIF)

E.2.5.2.2.1 Change from multimedia to audio

Figure E.2.5.2.2.1.1 shows an IM CN subsystem originated modification from multimedia to audio during an ongoing session when the CS leg supports ISUP or BICC without SCUDIF. The interworking node receives an INVITE message that indicates the dropping of the video media from the session, message 1. The interworking node can only accept the dropping of the media component and acknowledges the INVITE with a 200 OK, message 2. There are three alternative ways to handle the issue:

– The video component stays on in the CS leg. The interworking node may use the video component to send an announcement to the CS terminal to inform the user about the change of the end-to-end connection to audio only. Refer to figure E.2.5.2.2.1.1.

– The interworking node initiates an H.245 in‑band negotiation to close the video channel.

– The interworking node terminates the session.

Figure E.2.5.2.2.1.1: IM CN subsystem originated modification
from multimedia to speech when the CS leg supports ISUP or BICC without SCUDIF

E.2.5.2.2.2 Change from speech to multimedia

Figure E.2.5.2.2.2.1 shows an IM CN subsystem originated attempt to change from speech to multimedia during an ongoing session when the CS leg supports ISUP or BICC without SCUDIF. The interworking node receives an INVITE message that offers the adding of a video media to the ongoing speech session, message 1. The interworking node turns down the offer and responds to the INVITE message with the speech codec in the 200 OK message to retain the speech only session, message 2.

Figure E.2.5.2.2.2.1: IM CN subsystem originated modification
from speech to multimedia when the CS leg supports ISUP or BICC without SCUDIF