Section: 5.2.1.11 Speech Codec Selection
Content: For speech calls, a mobile station implementing this version of the protocol shall indicate all codecs that it supports for UTRAN in the Supported Codec List information element. Codecs for GERAN shall be indicated in the Bearer Capability information element, if this information element is included. Additionally, if the mobile station supports codecs for GERAN and UTRAN, it shall indicate the codecs for GERAN also in the Supported Codec List information element. If the network does not receive a Supported Codec List information element then for speech calls in UTRAN it shall select the default UMTS speech codec. For speech calls in GERAN, if the network does not receive a Supported Codec List information element nor a Bearer Capability information element, the network shall select GSM full rate speech version 1. The network shall determine the default UMTS speech codec by the following: i) If no GSM Speech Version codepoints are received in the Supported Codec List IE or in octet 3a etc. of the Bearer Capabilities IE then a "UMTS only" terminal is assumed and the default UMTS speech codec shall be UMTS_AMR. ii) If at least one GSM Speech Version codepoint is received in the Supported Codec List IE or in octet 3a etc. of the Bearer Capabilities IE then the ME supports GSM and UMTS and the default UMTS speech codec shall be UMTS_AMR_2. NOTE 1: In case (ii), if the call is set up in A/Gb or GERAN Iu mode by a R99 ME, call control in the core network may treat the ME as a "GSM only" ME. The default UMTS speech codec will only become relevant when an intersystem handover to UTRAN Iu mode is initiated by the radio access network, and can be determined when this procedure is started. If the Supported Codec List IE is received, then the network shall use this list to select the codec for Iu mode and indicate the selected codec to the ME via RANAP and RRC protocol in the NAS Synchronisation Indicator IE. See 3GPP TS 25.413[ UTRAN Iu interface Radio Access Network Application Part (RANAP) signalling ]  [19c], 3GPP TS 25.331[ None ]  [23c] and 3GPP TS 44.118[ None ]  [111]. The NAS Synchronisation Indicator IE shall be coded as the 4 least significant bits of the selected codec type (CoID) defined in 3GPP TS 26.103[ Speech codec list for GSM and UMTS ]  [83], subclause 6.3. The network shall determine the preference for the selected codec type; codec type prioritisation is not provided by the ME. The ME shall activate the codec type received in the NAS Synchronisation Indicator IE. If the mobile station does not receive the NAS Synchronisation Indicator IE (RRC protocol) - during setup of a speech call; - during inter-system handover of a speech call from A/Gb or GERAN Iu mode to UTRAN Iu mode; - during an in-call modification from data to speech; - during a SRVCC handover to UTRAN Iu mode; or - during a 5G-SRVCC handover from NG-RAN to UTRAN Iu mode, then it shall select the UMTS_AMR_2 speech codec. NOTE 2: If the network does not support UMTS_AMR_2, it may activate the UMTS_AMR codec and indicate to the mobile station that it shall select UMTS_AMR_2. According to 3GPP TS 26.103[ Speech codec list for GSM and UMTS ]  [83], subclause 5.4, no interworking problem will occur in this case. If the mobile station has selected a speech codec for UTRAN Iu mode, it shall keep this codec until - a new codec is requested by the network by sending a NAS Synchronisation Indicator IE (RRC protocol); - a new codec is requested by the network during inter-system handover from UTRAN Iu mode to A/Gb or GERAN Iu mode; or - an in-call modification from speech to data is performed. For adaptive multirate codec types no indication of subsets of modes is supported in this protocol, from the mobile station or to the mobile station. It is a pre-condition that the support of such codec types by the mobile station implicitly includes all modes defined for that codec type.