Cellular Network Infrastructure » Core Network (CN) » OsmoMSC

An example dissection of a CC Setup:

Note that further above, there is a Bearer Capabilities listing of codecs, while further below there also is the Supported Codec List, with separate information for UMTS and GSM.

3GPP TS 24.008 says that "This information element shall be included for speech calls, if the mobile station supports UMTS radio access." (I interpret this so that UMTS doesn't imply 3G, but means R99 and is also used on 2G).
The Supported Codecs are only present in the MO CC Setup (not in MT, where the CN sends the CC Setup), but is also contained in the CC Call Confirmed message (which in MT the MS sends to the CN).

GSM A-I/F DTAP - Setup
    Protocol Discriminator: Call Control; call related SS messages (3)
        .... 0011 = Protocol discriminator: Call Control; call related SS messages (0x3)
        0... .... = TI flag: allocated by sender
        .000 .... = TIO: 0
    10.. .... = Sequence number: 2
    ..00 0101 = DTAP Call Control Message Type: Setup (0x05)
    Bearer Capability 1 - (MS supports at least full rate speech version 1 and half rate speech version 1. MS has a greater preference for full rate speech version 1 than for half rate speech version 1)
        Element ID: 0x04
        Length: 6
        Octet 3
            0... .... = Extension: Extended
            .11. .... = Radio channel requirement: MS supports at least full rate speech version 1 and half rate speech version 1. MS has a greater preference for full rate speech version 1 than for half rate speech version 1
            ...0 .... = Coding standard: GSM standardized coding
            .... 0... = Transfer mode: circuit
            .... .000 = Information transfer capability: Speech (0x0)
        Octets 3a - Speech Versions
            0... .... = Extension: Extended
            .0.. .... = Coding: octet used for extension of information transfer capability
            ..00 .... = Spare bit(s): 0
            .... 0100 = Speech version indication: GSM full rate speech version 3(FR AMR) (0x4)
            0... .... = Extension: Extended
            .0.. .... = Coding: octet used for extension of information transfer capability
            ..00 .... = Spare bit(s): 0
            .... 0010 = Speech version indication: GSM full rate speech version 2(GSM EFR) (0x2)
            0... .... = Extension: Extended
            .0.. .... = Coding: octet used for extension of information transfer capability
            ..00 .... = Spare bit(s): 0
            .... 0000 = Speech version indication: GSM full rate speech version 1(GSM FR) (0x0)
            0... .... = Extension: Extended
            .0.. .... = Coding: octet used for extension of information transfer capability
            ..00 .... = Spare bit(s): 0
            .... 0101 = Speech version indication: GSM half rate speech version 3(HR AMR) (0x5)
            1... .... = Extension: No Extension
            .0.. .... = Coding: octet used for extension of information transfer capability
            ..00 .... = Spare bit(s): 0
            .... 0001 = Speech version indication: GSM half rate speech version 1(GSM HR) (0x1)
    Called Party BCD Number - (2002)
        Element ID: 0x5e
        Length: 3
        1... .... = Extension: No Extension
        .000 .... = Type of number: unknown (0x0)
        .... 0001 = Numbering plan identification: ISDN/Telephony Numbering (ITU-T Rec. E.164 / ITU-T Rec. E.163) (0x1)
        Called Party BCD Number: 2002
    Call Control Capabilities
        Element ID: 0x15
        Length: 2
        0000 .... = Maximum number of supported bearers: 1
        .... 0... = MCAT: The mobile station does not support Multimedia CAT
        .... .0.. = ENICM: The mobile station does not support the Enhanced Network-initiated In-Call Modification procedure
        .... ..0. = Prolonged Clearing Procedure: Not supported
        .... ...1 = DTMF: the mobile station supports DTMF as specified in subclause 5.5.7 of TS 24.008
        0000 .... = Spare bit(s): 0
        .... 0000 = Maximum number of speech bearers: 0
    Supported Codec List
        Element ID: 0x40
        Length: 8
        System Identification (SysID): UMTS (0x04)
        Bitmap Length: 2
        Codec Bitmap for SysID 1
            0... .... = TDMA EFR: False
            .1.. .... = UMTS AMR 2: True
            ..1. .... = UMTS AMR: True
            ...0 .... = HR AMR: False
            .... 0... = FR AMR: False
            .... .0.. = GSM EFR: False
            .... ..0. = GSM HR: False
            .... ...0 = GSM FR: False
            00.. .... = Spare bit(s): 0
            ..0. .... = OHR AMR-WB: False
            ...0 .... = OFR AMR-WB: False
            .... 0... = OHR AMR: False
            .... .1.. = UMTS AMR-WB: True
            .... ..0. = FR AMR-WB: False
            .... ...0 = PDC EFR: False
        System Identification (SysID): GSM (0x00)
        Bitmap Length: 2
        Codec Bitmap for SysID 2
            0... .... = TDMA EFR: False
            .0.. .... = UMTS AMR 2: False
            ..0. .... = UMTS AMR: False
            ...1 .... = HR AMR: True
            .... 1... = FR AMR: True
            .... .1.. = GSM EFR: True
            .... ..1. = GSM HR: True
            .... ...1 = GSM FR: True
            00.. .... = Spare bit(s): 0
            ..0. .... = OHR AMR-WB: False
            ...0 .... = OFR AMR-WB: False
            .... 0... = OHR AMR: False
            .... .0.. = UMTS AMR-WB: False
            .... ..0. = FR AMR-WB: False
            .... ...0 = PDC EFR: False

Related:

24.008 5.2.1 Mobile originating call establishment:
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.

24.008 5.2.2.3.2 Receipt of CALL CONFIRMED and ALERTING by the network:
For speech calls, if the CALL CONFIRMED message contains a Supported Codec List information element, the
network shall use this list to select the codec for UTRAN. If no Supported Codec List information element is received,
then for UTRAN the network shall select the default UMTS speech codec according to subclause 5.2.1.11.
Codecs for GERAN shall be selected from the codecs indicated in the Supported Codec List information element or in
the Bearer Capability information element. If neither a Supported Codec List information element nor a Bearer
Capability information element is received, then for GERAN the network shall select GSM full rate speech version 1.