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comparison Speech-codec-selection @ 99:c28a1518d268
Speech-codec-selection: document AT%SPVER
| author | Mychaela Falconia <falcon@freecalypso.org> |
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| date | Tue, 06 Jun 2023 03:54:53 +0000 |
| parents | 915ff61137ee |
| children |
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| 98:915ff61137ee | 99:c28a1518d268 |
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| 163 | 163 |
| 164 Step 1: set AT%MSCAP to the standard config for your currently running firmware | 164 Step 1: set AT%MSCAP to the standard config for your currently running firmware |
| 165 version, usually AT%MSCAP=37,00,00 or AT%MSCAP=B7,C7,00. | 165 version, usually AT%MSCAP=37,00,00 or AT%MSCAP=B7,C7,00. |
| 166 | 166 |
| 167 Step 2: execute 'rm /pcm/MSCAP' in fc-fsio, deleting the file from FFS. | 167 Step 2: execute 'rm /pcm/MSCAP' in fc-fsio, deleting the file from FFS. |
| 168 | |
| 169 Speech version preference list | |
| 170 ============================== | |
| 171 | |
| 172 Whenever a GSM MS supports any additional speech codecs beyond the always- | |
| 173 required FRv1, it needs to indicate this support to the network in the Bearer | |
| 174 capability IE. However, the encoding of the relevant bits in this IE indicates | |
| 175 not only which codecs the MS supports, but also their order of preference. | |
| 176 Indicating the order of preference between supported codecs is not optional: | |
| 177 the MS always has to transmit _some_ order-of-preference list toward the | |
| 178 network. (For GSM MS supporting FRv1 and HRv1 but no others, there is an | |
| 179 abbreviated version of the Bearer capability IE with octet 3a list omitted, but | |
| 180 even then the order of preference between the two supported codecs is still | |
| 181 indicated via the two radio channel requirement bits.) | |
| 182 | |
| 183 Our current FreeCalypso TCS2/TCS3 hybrid firmware indicates the following order | |
| 184 of preference to the network, between the 5 potentially supported codecs: | |
| 185 | |
| 186 AMR-FR > AMR-HR > EFR > FRv1 > HRv1 | |
| 187 | |
| 188 (The '>' character in the above line indicates that the codec on the left is | |
| 189 preferred over the codec on the right.) | |
| 190 | |
| 191 The actual Bearer capability IE is constructed by first masking off each of the | |
| 192 5 possible codecs as supported or not-supported per EF_MSCAP (see previous | |
| 193 section), but those codecs that remain in the supported set are sent to the | |
| 194 network in the order of preference following the above diagram. | |
| 195 | |
| 196 It appears that most GSM networks ignore the speech version preference order | |
| 197 indicated by the MS, treating the MS-provided speech version list as an | |
| 198 unordered checklist of supported or non-supported, and impose their own | |
| 199 preference order set by network policy. Such behavior is implemented in Osmocom | |
| 200 CNI software, and is also observed on the legacy GSM network of T-Mobile USA as | |
| 201 of this writing. However, the world as a whole is big, there are many different | |
| 202 GSM networks in different countries, and I (Mother Mychaela) deem it valuable to | |
| 203 provide a mechanism whereby FreeCalypso-equipped GSM community members can test | |
| 204 experimentally how their countries' GSM networks react to different speech | |
| 205 version lists indicated by the MS, including peculiar preference orders. | |
| 206 | |
| 207 To facilitate such testing, FreeCalypso Tourmaline firmware provides a private | |
| 208 debug-oriented AT command controlling the speech version list: AT%SPVER. This | |
| 209 command takes the following forms: | |
| 210 | |
| 211 AT%SPVER=0 -- restore standard behavior | |
| 212 AT%SPVER=1,sv1[,sv2[,sv3[,sv4[,sv5]]]]] -- set custom speech version list | |
| 213 AT%SPVER? -- query current setting | |
| 214 | |
| 215 In the second listed form of AT%SPVER command, arguments sv1 through sv5 are | |
| 216 speech version codes as transmitted over the air in the Bearer capability IE, | |
| 217 as given in Table 10.5.103/3GPP TS 24.008: | |
| 218 | |
| 219 0 = FRv1 | |
| 220 1 = HRv1 | |
| 221 2 = EFR | |
| 222 4 = AMR-FR | |
| 223 5 = AMR-HR | |
| 224 | |
| 225 The speech version list sent to the network will be exactly as given in the | |
| 226 AT%SPVER command, in that order. You can list just one speech version, or all | |
| 227 5 of them, or any intermediate subset - but FRv1 (sv code 0) must always be | |
| 228 included, or the AT%SPVER command will be rejected. Some examples: | |
| 229 | |
| 230 AT%SPVER=1,0 -- declare support for FRv1 only | |
| 231 AT%SPVER=1,2,0,1 -- declare support for EFR, FRv1 and HRv1 in this order | |
| 232 AT%SPVER=1,1,0 -- prefer HRv1 over FRv1 | |
| 233 | |
| 234 Unlike AT%MSCAP, the setting made with AT%SPVER is volatile: it is not saved | |
| 235 anywhere in FFS, and thus does not persist across firmware boot cycles. | |
| 236 | |
| 237 In order to affect the Bearer capability IE in the Call confirmed message for | |
| 238 MT calls, the AT%SPVER command needs to be given before the MT Setup message | |
| 239 arrives from the network. For MO call testing, it is sufficient to set AT%SPVER | |
| 240 before dialing the MO call with ATD command. |