Section: 5.2.2.3.1 Response to SETUP
Content: Having entered the "call present state" the call control entity of the mobile station shall - with the exception of the cases described below - acknowledge the SETUP message by a CALL CONFIRMED message, and enter the "mobile terminating call confirmed" state. If the mobile station supports multicall, it shall include the Stream Identifier (SI) information element in the CALL CONFIRMED message. If the mobile station is located in the network supporting multicall, it shall never include the SI that is in use and shall include with either of the following two values: - SI="no bearer"; - SI=new value (not used by any of the existing bearers). If the mobile station supporting multicall is located in the network not supporting multicall, it shall include the SI with value 1. The call control entity of the mobile station may include in the CALL CONFIRMED message to the network one or two bearer capability information elements to the network, either preselected in the mobile station or corresponding to a service dependent directory number (see 3GPP TS 29.007[ General requirements on interworking between the Public Land Mobile Network (PLMN) and the Integrated Services Digital Network (ISDN) or Public Switched Telephone Network (PSTN) ]  [38]). The mobile station may also use the backup bearer capability IE, if provided by the network, to deduce the requested service (see 3GPP TS 27.001[ General on Terminal Adaptation Functions (TAF) for Mobile Stations (MS) ]  [36], subclause 8.3.3.1). The mobile station may also include one or two bearer capabilities in the CALL CONFIRMED message to define the radio channel requirements. In any case the rules specified in subclause 9.3.2.2 shall be followed. NOTE: The possibility of alternative responses (e.g., in connection with supplementary services) is for further study. For speech calls the mobile station 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 MS supports the enhanced network-initiated in-call modification procedure as specified in subclause 5.3.4.3, the MS shall indicate this in the Call Control Capabilities IE in the CALL CONFIRMED message. A busy MS which satisfies the compatibility requirements indicated in the SETUP message shall respond either with a CALL CONFIRMED message if the call setup is allowed to continue or a RELEASE COMPLETE message if the call setup is not allowed to continue, both with cause #17 "user busy". If the mobile user wishes to refuse the call, a RELEASE COMPLETE message shall be sent with the cause #21 "call rejected". In the cases where the mobile station responds to a SETUP message with RELEASE COMPLETE message the mobile station shall release the MM connection and enter the "null" state after sending the RELEASE COMPLETE message. The network shall process the RELEASE COMPLETE message in accordance with subclause 5.4.