diff options
Diffstat (limited to 'src/common/csd_v110.c')
| -rw-r--r-- | src/common/csd_v110.c | 188 |
1 files changed, 188 insertions, 0 deletions
diff --git a/src/common/csd_v110.c b/src/common/csd_v110.c new file mode 100644 index 00000000..d6c00b03 --- /dev/null +++ b/src/common/csd_v110.c @@ -0,0 +1,188 @@ +/* + * (C) 2023 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de> + * Author: Vadim Yanitskiy <vyanitskiy@sysmocom.de> + * + * All Rights Reserved + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU Affero General Public License as published by + * the Free Software Foundation; either version 3 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU Affero General Public License for more details. + * + * You should have received a copy of the GNU Affero General Public License + * along with this program. If not, see <http://www.gnu.org/licenses/>. + * + */ + +#include <stdint.h> +#include <errno.h> + +#include <osmocom/core/bits.h> +#include <osmocom/core/utils.h> +#include <osmocom/gsm/gsm44021.h> +#include <osmocom/gsm/gsm_utils.h> +#include <osmocom/gsm/protocol/gsm_04_08.h> +#include <osmocom/isdn/v110.h> + +#include <osmo-bts/csd_v110.h> +#include <osmo-bts/lchan.h> + +/* key is enum gsm48_chan_mode, so assuming a value in range 0..255 */ +const struct csd_v110_lchan_desc csd_v110_lchan_desc[256] = { +#if 0 + [GSM48_CMODE_DATA_14k5] = { + /* TCH/F14.4: 290 bits every 20 ms (14.5 kbit/s) */ + .fr = { .num_blocks = 1, .num_bits = 290 }, + }, +#endif + [GSM48_CMODE_DATA_12k0] = { + /* TCH/F9.6: 4 * 60 bits every 20 ms (12.0 kbit/s) */ + .fr = { .num_blocks = 4, .num_bits = 60 }, + }, + [GSM48_CMODE_DATA_6k0] = { + /* TCH/F4.8: 2 * 60 bits every 20 ms (6.0 kbit/s) */ + .fr = { .num_blocks = 2, .num_bits = 60 }, + /* TCH/H4.8: 4 * 60 bits every 40 ms (6.0 kbit/s) */ + .hr = { .num_blocks = 4, .num_bits = 60 }, + }, + [GSM48_CMODE_DATA_3k6] = { + /* TCH/F2.4: 2 * 36 bits every 20 ms (3.6 kbit/s) */ + .fr = { .num_blocks = 2, .num_bits = 36 }, + /* TCH/H2.4: 4 * 36 bits every 40 ms (3.6 kbit/s) */ + .hr = { .num_blocks = 4, .num_bits = 36 }, + }, +}; + +/* 3GPP TS 44.021, Figure 4: Coding of data rates (E1/E2/E3 bits) */ +static const uint8_t e1e2e3_map[_LCHAN_CSD_M_NUM][3] = { + [LCHAN_CSD_M_T_600] = { 1, 0, 0 }, + [LCHAN_CSD_M_T_1200] = { 0, 1, 0 }, + [LCHAN_CSD_M_T_2400] = { 1, 1, 0 }, + [LCHAN_CSD_M_T_4800] = { 0, 1, 1 }, + [LCHAN_CSD_M_T_9600] = { 0, 1, 1 }, +#if 0 + [LCHAN_CSD_M_T_19200] = { 0, 1, 1 }, + [LCHAN_CSD_M_T_38400] = { 0, 1, 1 }, + [LCHAN_CSD_M_T_14400] = { 1, 0, 1 }, + [LCHAN_CSD_M_T_28800] = { 1, 0, 1 }, +#endif +}; + +int csd_v110_rtp_encode(const struct gsm_lchan *lchan, uint8_t *rtp, + const uint8_t *data, size_t data_len) +{ + const struct csd_v110_frame_desc *desc; + ubit_t ra_bits[80 * 4]; + + OSMO_ASSERT(lchan->tch_mode < ARRAY_SIZE(csd_v110_lchan_desc)); + if (lchan->type == GSM_LCHAN_TCH_F) + desc = &csd_v110_lchan_desc[lchan->tch_mode].fr; + else + desc = &csd_v110_lchan_desc[lchan->tch_mode].hr; + if (OSMO_UNLIKELY(desc->num_blocks == 0)) + return -ENOTSUP; + + /* handle empty/incomplete Uplink frames gracefully */ + if (OSMO_UNLIKELY(data_len < (desc->num_blocks * desc->num_bits))) { + /* encode N idle frames as per 3GPP TS 44.021, section 8.1.6 */ + memset(&ra_bits[0], 0x01, sizeof(ra_bits)); + for (unsigned int i = 0; i < desc->num_blocks; i++) + memset(&ra_bits[i * 80], 0x00, 8); /* alignment pattern */ + goto ra1_ra2; + } + + /* RA1'/RA1: convert from radio rate to an intermediate data rate */ + for (unsigned int i = 0; i < desc->num_blocks; i++) { + struct osmo_v110_decoded_frame df; + + /* convert a V.110 36-/60-bit frame to a V.110 80-bit frame */ + if (desc->num_bits == 60) + osmo_csd_12k_6k_decode_frame(&df, &data[i * 60], 60); + else /* desc->num_bits == 36 */ + osmo_csd_3k6_decode_frame(&df, &data[i * 36], 36); + + /* E1 .. E3 must set by out-of-band knowledge */ + if (lchan->csd_mode == LCHAN_CSD_M_NT) { + /* non-transparent: as per 3GPP TS 48.020, Table 7 */ + df.e_bits[0] = 0; /* E1: as per 15.1.2, shall be set to 0 (for BSS-MSC) */ + df.e_bits[1] = (i >> 1) & 0x01; /* E2: 0 for Q1/Q2, 1 for Q3/Q4 */ + df.e_bits[2] = (i >> 0) & 0x01; /* E3: 0 for Q1/Q3, 1 for Q2/Q4 */ + } else { + /* transparent: as per 3GPP TS 44.021, Figure 4 */ + df.e_bits[0] = e1e2e3_map[lchan->csd_mode][0]; /* E1 */ + df.e_bits[1] = e1e2e3_map[lchan->csd_mode][1]; /* E2 */ + df.e_bits[2] = e1e2e3_map[lchan->csd_mode][2]; /* E3 */ + } + + osmo_v110_encode_frame(&ra_bits[i * 80], 80, &df); + } + +ra1_ra2: + /* RA1/RA2: convert from an intermediate rate to 64 kbit/s */ + if (desc->num_blocks == 4) { + /* 4 * 80 bits (16 kbit/s) => 2 bits per octet */ + for (unsigned int i = 0, j = 0; i < RFC4040_RTP_PLEN; i++) { + rtp[i] = (0xff >> 2); + rtp[i] |= (ra_bits[j++] << 7); + rtp[i] |= (ra_bits[j++] << 6); + } + } else { + /* 2 * 80 bits (8 kbit/s) => 1 bit per octet */ + for (unsigned int i = 0; i < RFC4040_RTP_PLEN; i++) { + rtp[i] = (0xff >> 1); + rtp[i] |= (ra_bits[i] << 7); + } + } + + return RFC4040_RTP_PLEN; +} + +int csd_v110_rtp_decode(const struct gsm_lchan *lchan, uint8_t *data, + const uint8_t *rtp, size_t rtp_len) +{ + const struct csd_v110_frame_desc *desc; + ubit_t ra_bits[80 * 4]; + + OSMO_ASSERT(lchan->tch_mode < ARRAY_SIZE(csd_v110_lchan_desc)); + if (lchan->type == GSM_LCHAN_TCH_F) + desc = &csd_v110_lchan_desc[lchan->tch_mode].fr; + else + desc = &csd_v110_lchan_desc[lchan->tch_mode].hr; + if (OSMO_UNLIKELY(desc->num_blocks == 0)) + return -ENOTSUP; + + if (OSMO_UNLIKELY(rtp_len != RFC4040_RTP_PLEN)) + return -EINVAL; + + /* RA1/RA2: convert from 64 kbit/s to an intermediate rate */ + if (desc->num_blocks == 4) { + /* 4 * 80 bits (16 kbit/s) => 2 bits per octet */ + for (unsigned int i = 0, j = 0; i < RFC4040_RTP_PLEN; i++) { + ra_bits[j++] = (rtp[i] >> 7); + ra_bits[j++] = (rtp[i] >> 6) & 0x01; + } + } else { + /* 2 * 80 bits (8 kbit/s) => 1 bit per octet */ + for (unsigned int i = 0; i < RFC4040_RTP_PLEN; i++) + ra_bits[i] = (rtp[i] >> 7); + } + + /* RA1'/RA1: convert from an intermediate rate to radio rate */ + for (unsigned int i = 0; i < desc->num_blocks; i++) { + struct osmo_v110_decoded_frame df; + + /* convert a V.110 80-bit frame to a V.110 36-/60-bit frame */ + osmo_v110_decode_frame(&df, &ra_bits[i * 80], 80); + if (desc->num_bits == 60) + osmo_csd_12k_6k_encode_frame(&data[i * 60], 60, &df); + else /* desc->num_bits == 36 */ + osmo_csd_3k6_encode_frame(&data[i * 36], 36, &df); + } + + return desc->num_blocks * desc->num_bits; +} |