diff options
Diffstat (limited to 'src/codec/gsm610.c')
| -rw-r--r-- | src/codec/gsm610.c | 160 |
1 files changed, 143 insertions, 17 deletions
diff --git a/src/codec/gsm610.c b/src/codec/gsm610.c index a05eabab..5cc4f148 100644 --- a/src/codec/gsm610.c +++ b/src/codec/gsm610.c @@ -17,10 +17,6 @@ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * - * You should have received a copy of the GNU General Public License along - * with this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. - * */ #include <stdint.h> @@ -300,6 +296,35 @@ const uint16_t gsm610_bitorder[260] = { 29, /* LARc5:0 */ }; +/* + * Table 1 in section 6 of 3GPP TS 46.011 (substitution and muting of lost + * frames) specifies a silence frame in the form of GSM 06.10 parameters; + * the following const datum is this GSM 06.11 silence frame in GSM-FR + * RTP encoding. + */ +const uint8_t osmo_gsm611_silence_frame[GSM_FR_BYTES] = { + 0xDA, 0xA7, 0xAA, 0xA5, 0x1A, + 0x50, 0x20, 0x38, 0xE4, 0x6D, 0xB9, 0x1B, + 0x50, 0x20, 0x38, 0xE4, 0x6D, 0xB9, 0x1B, + 0x50, 0x20, 0x38, 0xE4, 0x6D, 0xB9, 0x1B, + 0x50, 0x20, 0x38, 0xE4, 0x6D, 0xB9, 0x1B, +}; + +static const uint16_t sid_code_word_bits[95] = { + /* bit numbers are relative to the RTP frame beginning, + * with signature bits included in the count. */ + 57, 58, 60, 61, 63, 64, 66, 67, 69, 70, 72, 73, + 75, 76, 78, 79, 81, 82, 84, 85, 87, 88, 90, 91, + 93, 94, 113, 114, 116, 117, 119, 120, 122, 123, + 125, 126, 128, 129, 131, 132, 134, 135, 137, + 138, 140, 141, 143, 144, 146, 147, 149, 150, + 169, 170, 172, 173, 175, 176, 178, 179, 181, + 182, 184, 185, 187, 188, 190, 191, 193, 194, + 196, 197, 199, 200, 202, 203, 205, 206, 225, + 226, 228, 229, 231, 232, 234, 235, 237, 240, + 243, 246, 249, 252, 255, 258, 261 +}; + /*! Check whether RTP frame contains FR SID code word according to * TS 101 318 §5.1.2 * \param[in] rtp_payload Buffer with RTP payload @@ -309,16 +334,7 @@ const uint16_t gsm610_bitorder[260] = { bool osmo_fr_check_sid(const uint8_t *rtp_payload, size_t payload_len) { struct bitvec bv; - uint16_t i, z_bits[] = { 57, 58, 60, 61, 63, 64, 66, 67, 69, 70, 72, 73, - 75, 76, 78, 79, 81, 82, 84, 85, 87, 88, 90, 91, - 93, 94, 113, 114, 116, 117, 119, 120, 122, 123, - 125, 126, 128, 129, 131, 132, 134, 135, 137, - 138, 140, 141, 143, 144, 146, 147, 149, 150, - 169, 170, 172, 173, 175, 176, 178, 179, 181, - 182, 184, 185, 187, 188, 190, 191, 193, 194, - 196, 197, 199, 200, 202, 203, 205, 206, 225, - 226, 228, 229, 231, 232, 234, 235, 237, 240, - 243, 246, 249, 252, 255, 258, 261 }; + uint16_t i; /* signature does not match Full Rate SID */ if ((rtp_payload[0] >> 4) != 0xD) @@ -327,10 +343,120 @@ bool osmo_fr_check_sid(const uint8_t *rtp_payload, size_t payload_len) bv.data = (uint8_t *) rtp_payload; bv.data_len = payload_len; - /* code word is all 0 at given bits, numbered from 1 */ - for (i = 0; i < ARRAY_SIZE(z_bits); i++) - if (bitvec_get_bit_pos(&bv, z_bits[i]) != ZERO) + /* code word is all 0 at given bits */ + for (i = 0; i < ARRAY_SIZE(sid_code_word_bits); i++) { + if (bitvec_get_bit_pos(&bv, sid_code_word_bits[i]) != ZERO) return false; + } return true; } + +/*! Classify potentially-SID FR codec frame in RTP format according + * to the rules of GSM 06.31 §6.1.1 + * \param[in] rtp_payload Buffer with RTP payload + * \returns enum osmo_gsm631_sid_class, with symbolic values + * OSMO_GSM631_SID_CLASS_SPEECH, OSMO_GSM631_SID_CLASS_INVALID or + * OSMO_GSM631_SID_CLASS_VALID corresponding to the 3 possible bit-counting + * classifications prescribed by the spec. + * + * Differences between the more familiar osmo_fr_check_sid() and the present + * function are: + * + * 1. osmo_fr_check_sid() returns true only if the SID frame is absolutely + * perfect, with all 95 bits of the SID code word zeroed. However, the + * rules of GSM 06.31 §6.1.1 allow up to one bit to be in error, + * and the frame is still accepted as valid SID. + * + * 2. The third possible state of invalid SID is not handled at all by the + * simpler osmo_fr_check_sid() function. + * + * 3. osmo_fr_check_sid() includes a check for 0xD RTP signature, and returns + * false if that signature nibble is wrong. That check is not included + * in the present version because there is no place for it in the + * ETSI-prescribed classification, it is neither speech nor SID. The + * assumption is that this function is used to classify the bit content + * of received codec frames, not their RTP encoding - the latter needs + * to be validated beforehand. + * + * Which function should one use? The answer depends on the specific + * circumstances, and needs to be addressed on a case-by-case basis. + */ +enum osmo_gsm631_sid_class osmo_fr_sid_classify(const uint8_t *rtp_payload) +{ + struct bitvec bv; + uint16_t i, n; + + bv.data = (uint8_t *) rtp_payload; + bv.data_len = GSM_FR_BYTES; + + /* count not-SID-matching bits per the spec */ + n = 0; + for (i = 0; i < ARRAY_SIZE(sid_code_word_bits); i++) { + if (bitvec_get_bit_pos(&bv, sid_code_word_bits[i]) != ZERO) + n++; + if (n >= 16) + return OSMO_GSM631_SID_CLASS_SPEECH; + } + if (n >= 2) + return OSMO_GSM631_SID_CLASS_INVALID; + else + return OSMO_GSM631_SID_CLASS_VALID; +} + +/*! Reset the SID field and the unused bits of a potentially corrupted, + * but still valid GSM-FR SID frame in RTP encoding to their pristine state. + * \param[in] rtp_payload Buffer with RTP payload - must be writable! + * + * Per GSM 06.12 section 5.2, a freshly minted SID frame carries 60 bits + * of comfort noise parameters (LARc and 4 times Xmaxc), while the remaining + * 200 bits are all zeros; the latter 200 all-0 bits further break down into + * 95 bits of SID field (checked by receivers to detect SID) and 105 unused + * bits which receivers are told to ignore. Network elements that receive + * SID frames from call leg A uplink and need to retransmit them on leg B + * downlink should "rejuvenate" received SID frames prior to retransmission; + * this function does the job. + */ +void osmo_fr_sid_reset(uint8_t *rtp_payload) +{ + uint8_t *p, sub; + + p = rtp_payload + 5; /* skip magic+LARc */ + for (sub = 0; sub < 4; sub++) { + *p++ = 0; + *p++ &= 0x1F; /* upper 5 bits of Xmaxc field */ + *p++ &= 0x80; /* and the lsb spilling into the next byte */ + *p++ = 0; + *p++ = 0; + *p++ = 0; + *p++ = 0; + } +} + +/*! Preen potentially-SID FR codec frame in RTP format, ensuring that it is + * either a speech frame or a valid SID, and if the latter, making it a + * perfect, error-free SID frame. + * \param[in] rtp_payload Buffer with RTP payload - must be writable! + * \returns true if the frame is good, false otherwise + */ +bool osmo_fr_sid_preen(uint8_t *rtp_payload) +{ + enum osmo_gsm631_sid_class sidc; + + sidc = osmo_fr_sid_classify(rtp_payload); + switch (sidc) { + case OSMO_GSM631_SID_CLASS_SPEECH: + return true; + case OSMO_GSM631_SID_CLASS_INVALID: + return false; + case OSMO_GSM631_SID_CLASS_VALID: + /* "Rejuvenate" this SID frame, correcting any errors */ + osmo_fr_sid_reset(rtp_payload); + return true; + default: + /* There are only 3 possible SID classifications per GSM 06.31 + * section 6.1.1, thus any other return value is a grave error + * in the code. */ + OSMO_ASSERT(0); + } +} |