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Content for  TS 23.172  Word version:  18.0.0

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4.3.3.1a GMSC Handling at Terminating Side  4.3.3.2 Terminating MSC Handling 
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4.3.3.1a  GMSC Handling at Terminating Side |R6|  p. 36

Depending on operator policy, the GMSC may remove the 3G-324.M2 codec from the list of supported codec types if the call is received from selected other PLMNs.

4.3.3.2  Terminating MSC Handling  p. 36

The terminating MSC receives the list of supported codec types, including the 3G-324.M codec and possibly the 3G-324.M2 codec. It shall then send a SETUP message towards the terminating UE including a Repeat Indicator with the value "service change and fallback" and two BC-IEs, according to the following rule:
  • if the 3G-324.M codec is the first (preferred) codec in the list of supported codecs, then the first BC-IE in the SETUP message is the multimedia BC-IE, and the second BC-IE is the speech BC-IE (see Figure 4.17);
  • if the 3G-324.M codec is in the list of supported codec types, but not in the first position, then the first BC-IE in the SETUP message is the speech BC-IE, and the second BC-IE is the multimedia BC-IE (see Figure 4.18).
The terminating UE answers according to its capabilities in the CALL CONFIRMED message. The terminating MSC shall determine the Selected Codec and construct the list of available codecs according to the following rules:
  • If no Repeat Indicator is included, and only a speech BC-IE is received, the MSC shall choose a speech codec as the Selected Codec according to the normal mechanism, and no 3G-324.M codec shall be inserted in the list of available codecs (see Figure 4.19).
  • If no Repeat Indicator is included, and only a multimedia BC-IE is received, the MSC shall choose the 3G 324.M codec as the Selected Codec, and only the 3G-324.M codec shall be inserted in the list of available codecs (see Figure 4.20).
  • If the Repeat Indicator is included, and the speech BC_IE is the first BC-IE and the multimedia BC-IE is the second BC-IE, the MSC shall choose a speech codec as the Selected Codec according to the normal mechanism, and both the 3G-324.M codec and speech codecs shall be inserted in the list of available codecs (see Figure 4.21) If the terminating MSC supports incoming requests for a network-initiated service change from speech to multimedia and was offered the 3G-324.M2 codec and the terminal had indicated in the CALL CONFIRMED message with the"Enhanced Network-initiated ICM" (ENICM) Capability for the support of Network-initiated service upgrade to multimedia, the 3G-324.M codec shall be the last but one codec in the list and the 3G-324.M2 codec shall be the last codec in the list.
  • If the Repeat Indicator is included, and the multimedia BC-IE is the first BC-IE and the speech BC-IE is the second BC-IE, the Selected Codec shall be the 3G-324.M codec, and both the 3G-324.M codec and speech codecs shall be inserted in the list of available codecs (see Figure 4.22). If the terminating MSC supports incoming requests for a network-initiated service change from speech to multimedia and was offered the 3G-324.M2 codec and the terminal had indicated in the CALL CONFIRMED message with the"Enhanced Network-initiated ICM" (ENICM) Capability for the support of Network-initiated service upgrade to multimedia, the terminating MSC it shall include the 3G-324.M2 codec as second codec in the list of available codecs.
The Selected Codec and the list of available codecs shall be sent back to the originating MSC according to the normal codec negotiation procedure.
Copy of original 3GPP image for 3GPP TS 23.172, Fig. 4.17: 3G-324M codec first
Figure 4.17: 3G-324M codec first
(⇒ copy of original 3GPP image)
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Copy of original 3GPP image for 3GPP TS 23.172, Fig. 4.18: Speech codec first
Figure 4.18: Speech codec first
(⇒ copy of original 3GPP image)
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Copy of original 3GPP image for 3GPP TS 23.172, Fig. 4.19: Speech only
Figure 4.19: Speech only
(⇒ copy of original 3GPP image)
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Copy of original 3GPP image for 3GPP TS 23.172, Fig. 4.20: Multimedia only
Figure 4.20: Multimedia only
(⇒ copy of original 3GPP image)
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Copy of original 3GPP image for 3GPP TS 23.172, Fig. 4.21: Speech preferred
Figure 4.21: Speech preferred
(⇒ copy of original 3GPP image)
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Copy of original 3GPP image for 3GPP TS 23.172, Fig. 4.22: Multimedia preferred
Figure 4.22: Multimedia preferred
(⇒ copy of original 3GPP image)
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