Harald Welte | 75bb820 | 2010-03-14 15:45:01 +0800 | [diff] [blame] | 1 | /* GPRS LLC protocol implementation as per 3GPP TS 04.64 */ |
| 2 | |
| 3 | /* (C) 2009 by Harald Welte <laforge@gnumonks.org> |
| 4 | * |
| 5 | * All Rights Reserved |
| 6 | * |
| 7 | * This program is free software; you can redistribute it and/or modify |
| 8 | * it under the terms of the GNU General Public License as published by |
| 9 | * the Free Software Foundation; either version 2 of the License, or |
| 10 | * (at your option) any later version. |
| 11 | * |
| 12 | * This program is distributed in the hope that it will be useful, |
| 13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 15 | * GNU General Public License for more details. |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License along |
| 18 | * with this program; if not, write to the Free Software Foundation, Inc., |
| 19 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | */ |
| 22 | |
| 23 | #include <errno.h> |
| 24 | |
| 25 | #include <openbsc/gsm_data.h> |
| 26 | #include <osmocore/msgb.h> |
| 27 | #include <openbsc/debug.h> |
| 28 | #include <osmocore/linuxlist.h> |
| 29 | #include <osmocore/timer.h> |
| 30 | #include <openbsc/gprs_bssgp.h> |
| 31 | #include <openbsc/gprs_llc.h> |
| 32 | #include <openbsc/crc24.h> |
| 33 | |
| 34 | /* Section 4.5.2 Logical Link States + Annex C.2 */ |
| 35 | enum gprs_llc_ll_state { |
| 36 | GPRS_LLS_UNASSIGNED = 1, /* No TLLI yet */ |
| 37 | GPRS_LLS_ASSIGNED_ADM = 2, /* TLLI assigned */ |
| 38 | GPRS_LLS_LOCAL_EST = 3, /* Local Establishment */ |
| 39 | GPRS_LLS_REMOTE_EST = 4, /* Remote Establishment */ |
| 40 | GPRS_LLS_ABM = 5, |
| 41 | GPRS_LLS_LOCAL_REL = 6, /* Local Release */ |
| 42 | GPRS_LLS_TIMER_REC = 7, /* Timer Recovery */ |
| 43 | }; |
| 44 | |
| 45 | /* Section 4.7.1: Logical Link Entity: One per DLCI (TLLI + SAPI) */ |
| 46 | struct gprs_llc_lle { |
| 47 | struct llist_head list; |
| 48 | struct timer_list t200; |
| 49 | struct timer_list t201; /* wait for acknowledgement */ |
| 50 | |
| 51 | enum gprs_llc_ll_state state; |
| 52 | |
| 53 | u_int32_t tlli; |
| 54 | u_int32_t sapi; |
| 55 | |
| 56 | u_int8_t v_sent; |
| 57 | u_int8_t v_ack; |
| 58 | u_int8_t v_recv; |
| 59 | |
| 60 | unsigned int n200; |
| 61 | unsigned int retrans_ctr; |
| 62 | }; |
| 63 | |
| 64 | enum gprs_llc_cmd { |
| 65 | GPRS_LLC_NULL, |
| 66 | GPRS_LLC_RR, |
| 67 | GPRS_LLC_ACK, |
| 68 | GPRS_LLC_RNR, |
| 69 | GPRS_LLC_SACK, |
| 70 | GPRS_LLC_DM, |
| 71 | GPRS_LLC_DISC, |
| 72 | GPRS_LLC_UA, |
| 73 | GPRS_LLC_SABM, |
| 74 | GPRS_LLC_FRMR, |
| 75 | GPRS_LLC_XID, |
| 76 | }; |
| 77 | |
| 78 | struct gprs_llc_hdr_parsed { |
| 79 | u_int8_t sapi; |
| 80 | u_int8_t is_cmd:1, |
| 81 | ack_req:1, |
| 82 | is_encrypted:1; |
| 83 | u_int32_t seq_rx; |
| 84 | u_int32_t seq_tx; |
| 85 | u_int32_t fcs; |
| 86 | u_int32_t fcs_calc; |
| 87 | u_int8_t *data; |
| 88 | enum gprs_llc_cmd cmd; |
| 89 | }; |
| 90 | |
| 91 | #define LLC_ALLOC_SIZE 16384 |
| 92 | #define UI_HDR_LEN 3 |
| 93 | #define N202 4 |
| 94 | #define CRC24_LENGTH 3 |
| 95 | |
| 96 | static int gprs_llc_fcs(u_int8_t *data, unsigned int len) |
| 97 | { |
| 98 | u_int32_t fcs_calc; |
| 99 | |
| 100 | fcs_calc = crc24_calc(INIT_CRC24, data, len); |
| 101 | fcs_calc = ~fcs_calc; |
| 102 | fcs_calc &= 0xffffff; |
| 103 | |
| 104 | return fcs_calc; |
| 105 | } |
| 106 | |
| 107 | /* transmit a simple U frame */ |
| 108 | static int gprs_llc_tx_u() |
| 109 | { |
| 110 | struct msgb *msg = msgb_alloc(LLC_ALLOC_SIZE, "GPRS/LLC"); |
| 111 | |
| 112 | if (!msg) |
| 113 | return -ENOMEM; |
| 114 | |
| 115 | |
| 116 | |
| 117 | /* transmit the frame via BSSGP->NS->... */ |
| 118 | } |
| 119 | |
| 120 | static void t200_expired(void *data) |
| 121 | { |
| 122 | struct gprs_llc_lle *lle = data; |
| 123 | |
| 124 | /* 8.5.1.3: Expiry of T200 */ |
| 125 | |
| 126 | if (lle->retrans_ctr >= lle->n200) { |
| 127 | /* FIXME: LLGM-STATUS-IND, LL-RELEASE-IND/CNF */ |
| 128 | lle->state = GPRS_LLS_ASSIGNED_ADM; |
| 129 | } |
| 130 | |
| 131 | switch (lle->state) { |
| 132 | case GPRS_LLS_LOCAL_EST: |
| 133 | /* retransmit SABM */ |
| 134 | /* re-start T200 */ |
| 135 | lle->retrans_ctr++; |
| 136 | break; |
| 137 | case GPRS_LLS_LOCAL_REL: |
| 138 | /* retransmit DISC */ |
| 139 | /* re-start T200 */ |
| 140 | lle->retrans_ctr++; |
| 141 | break; |
| 142 | } |
| 143 | |
| 144 | } |
| 145 | |
| 146 | static void t201_expired(void *data) |
| 147 | { |
| 148 | struct gprs_llc_lle *lle = data; |
| 149 | |
| 150 | if (lle->retrans_ctr < lle->n200) { |
| 151 | /* transmit apropriate supervisory frame (8.6.4.1) */ |
| 152 | /* set timer T201 */ |
| 153 | lle->retrans_ctr++; |
| 154 | } |
| 155 | } |
| 156 | |
| 157 | /* Transmit a UI frame over the given SAPI */ |
| 158 | int gprs_llc_tx_ui(struct msgb *msg, u_int8_t sapi, int command) |
| 159 | { |
| 160 | u_int8_t *fcs, *llch; |
| 161 | u_int8_t addr, ctrl[2]; |
| 162 | u_int32_t fcs_calc; |
| 163 | u_int16_t nu = 0; |
| 164 | |
| 165 | /* Address Field */ |
| 166 | addr = sapi & 0xf; |
| 167 | if (command) |
| 168 | addr |= 0x40; |
| 169 | |
| 170 | /* Control Field */ |
| 171 | ctrl[0] = 0xc0; |
| 172 | ctrl[0] |= nu >> 6; |
| 173 | ctrl[1] = (nu << 2) & 0xfc; |
| 174 | ctrl[1] |= 0x01; /* Protected Mode */ |
| 175 | |
| 176 | /* prepend LLC UI header */ |
| 177 | llch = msgb_push(msg, 3); |
| 178 | llch[0] = addr; |
| 179 | llch[1] = ctrl[0]; |
| 180 | llch[2] = ctrl[1]; |
| 181 | |
| 182 | /* append FCS to end of frame */ |
| 183 | fcs = msgb_put(msg, 3); |
| 184 | fcs_calc = gprs_llc_fcs(llch, fcs - llch); |
| 185 | fcs[0] = fcs_calc & 0xff; |
| 186 | fcs[1] = (fcs_calc >> 8) & 0xff; |
| 187 | fcs[2] = (fcs_calc >> 16) & 0xff; |
| 188 | |
| 189 | return gprs_bssgp_tx_dl_ud(msg); |
| 190 | } |
| 191 | |
| 192 | static int gprs_llc_hdr_dump(struct gprs_llc_hdr_parsed *gph) |
| 193 | { |
| 194 | DEBUGP(DGPRS, "LLC SAPI=%u %c %c FCS=0x%06x(%s) ", |
| 195 | gph->sapi, gph->is_cmd ? 'C' : 'R', gph->ack_req ? 'A' : ' ', |
| 196 | gph->fcs, gph->fcs_calc == gph->fcs ? "correct" : "WRONG"); |
| 197 | |
| 198 | if (gph->cmd) |
| 199 | DEBUGPC(DGPRS, "CMD=%u ", gph->cmd); |
| 200 | |
| 201 | if (gph->data) |
| 202 | DEBUGPC(DGPRS, "DATA "); |
| 203 | |
| 204 | DEBUGPC(DGPRS, "\n"); |
| 205 | } |
| 206 | static int gprs_llc_hdr_rx(struct gprs_llc_hdr_parsed *gph, |
| 207 | struct gprs_llc_lle *lle) |
| 208 | { |
| 209 | switch (gph->cmd) { |
| 210 | case GPRS_LLC_SABM: /* Section 6.4.1.1 */ |
| 211 | lle->v_sent = lle->v_ack = lle->v_recv = 0; |
| 212 | if (lle->state == GPRS_LLS_ASSIGNED_ADM) { |
| 213 | /* start re-establishment (8.7.1) */ |
| 214 | } |
| 215 | lle->state = GPRS_LLS_REMOTE_EST; |
| 216 | /* FIXME: Send UA */ |
| 217 | lle->state = GPRS_LLS_ABM; |
| 218 | /* FIXME: process data */ |
| 219 | break; |
| 220 | case GPRS_LLC_DISC: /* Section 6.4.1.2 */ |
| 221 | /* FIXME: Send UA */ |
| 222 | /* terminate ABM */ |
| 223 | lle->state = GPRS_LLS_ASSIGNED_ADM; |
| 224 | break; |
| 225 | case GPRS_LLC_UA: /* Section 6.4.1.3 */ |
| 226 | if (lle->state == GPRS_LLS_LOCAL_EST) |
| 227 | lle->state = GPRS_LLS_ABM; |
| 228 | break; |
| 229 | case GPRS_LLC_DM: /* Section 6.4.1.4: ABM cannot be performed */ |
| 230 | if (lle->state == GPRS_LLS_LOCAL_EST) |
| 231 | lle->state = GPRS_LLS_ASSIGNED_ADM; |
| 232 | break; |
| 233 | case GPRS_LLC_FRMR: /* Section 6.4.1.5 */ |
| 234 | break; |
| 235 | case GPRS_LLC_XID: /* Section 6.4.1.6 */ |
| 236 | break; |
| 237 | } |
| 238 | |
| 239 | return 0; |
| 240 | } |
| 241 | |
| 242 | /* parse a GPRS LLC header, also check for invalid frames */ |
| 243 | static int gprs_llc_hdr_parse(struct gprs_llc_hdr_parsed *ghp, |
| 244 | const u_int8_t *llc_hdr, int len) |
| 245 | { |
| 246 | u_int8_t *ctrl = llc_hdr+1; |
| 247 | int is_sack = 0; |
| 248 | unsigned int crc_length; |
| 249 | u_int32_t fcs_calc; |
| 250 | |
| 251 | if (len <= CRC24_LENGTH) |
| 252 | return -EIO; |
| 253 | |
| 254 | crc_length = len - CRC24_LENGTH; |
| 255 | |
| 256 | ghp->ack_req = 0; |
| 257 | |
| 258 | /* Section 5.5: FCS */ |
| 259 | ghp->fcs = *(llc_hdr + len - 3); |
| 260 | ghp->fcs |= *(llc_hdr + len - 2) << 8; |
| 261 | ghp->fcs |= *(llc_hdr + len - 1) << 16; |
| 262 | |
| 263 | /* Section 6.2.1: invalid PD field */ |
| 264 | if (llc_hdr[0] & 0x80) |
| 265 | return -EIO; |
| 266 | |
| 267 | /* This only works for the MS->SGSN direction */ |
| 268 | if (llc_hdr[0] & 0x40) |
| 269 | ghp->is_cmd = 0; |
| 270 | else |
| 271 | ghp->is_cmd = 1; |
| 272 | |
| 273 | ghp->sapi = llc_hdr[0] & 0xf; |
| 274 | |
| 275 | /* Section 6.2.3: check for reserved SAPI */ |
| 276 | switch (ghp->sapi) { |
| 277 | case 0: |
| 278 | case 4: |
| 279 | case 6: |
| 280 | case 0xa: |
| 281 | case 0xc: |
| 282 | case 0xd: |
| 283 | case 0xf: |
| 284 | return -EINVAL; |
| 285 | } |
| 286 | |
| 287 | if ((ctrl[0] & 0x80) == 0) { |
| 288 | /* I (Information transfer + Supervisory) format */ |
| 289 | u_int8_t k; |
| 290 | |
| 291 | ghp->data = ctrl + 3; |
| 292 | |
| 293 | if (ctrl[0] & 0x40) |
| 294 | ghp->ack_req = 1; |
| 295 | |
| 296 | ghp->seq_tx = (ctrl[0] & 0x1f) << 4; |
| 297 | ghp->seq_tx |= (ctrl[1] >> 4); |
| 298 | |
| 299 | ghp->seq_rx = (ctrl[1] & 0x7) << 6; |
| 300 | ghp->seq_rx |= (ctrl[2] >> 2); |
| 301 | |
| 302 | switch (ctrl[2] & 0x03) { |
| 303 | case 0: |
| 304 | ghp->cmd = GPRS_LLC_RR; |
| 305 | break; |
| 306 | case 1: |
| 307 | ghp->cmd = GPRS_LLC_ACK; |
| 308 | break; |
| 309 | case 2: |
| 310 | ghp->cmd = GPRS_LLC_RNR; |
| 311 | break; |
| 312 | case 3: |
| 313 | ghp->cmd = GPRS_LLC_SACK; |
| 314 | k = ctrl[3] & 0x1f; |
| 315 | ghp->data += 1 + k; |
| 316 | break; |
| 317 | } |
| 318 | } else if ((ctrl[0] & 0xc0) == 0x80) { |
| 319 | /* S (Supervisory) format */ |
| 320 | ghp->data = NULL; |
| 321 | |
| 322 | if (ctrl[0] & 0x20) |
| 323 | ghp->ack_req = 1; |
| 324 | ghp->seq_rx = (ctrl[0] & 0x7) << 6; |
| 325 | ghp->seq_rx |= (ctrl[1] >> 2); |
| 326 | |
| 327 | switch (ctrl[1] & 0x03) { |
| 328 | case 0: |
| 329 | ghp->cmd = GPRS_LLC_RR; |
| 330 | break; |
| 331 | case 1: |
| 332 | ghp->cmd = GPRS_LLC_ACK; |
| 333 | break; |
| 334 | case 2: |
| 335 | ghp->cmd = GPRS_LLC_RNR; |
| 336 | break; |
| 337 | case 3: |
| 338 | ghp->cmd = GPRS_LLC_SACK; |
| 339 | break; |
| 340 | } |
| 341 | } else if ((ctrl[0] & 0xe0) == 0xc0) { |
| 342 | /* UI (Unconfirmed Inforamtion) format */ |
| 343 | ghp->data = ctrl + 2; |
| 344 | |
| 345 | ghp->seq_tx = (ctrl[0] & 0x7) << 6; |
| 346 | ghp->seq_tx |= (ctrl[1] >> 2); |
| 347 | if (ctrl[1] & 0x02) { |
| 348 | ghp->is_encrypted = 1; |
| 349 | /* FIXME: encryption */ |
| 350 | } |
| 351 | if (ctrl[1] & 0x01) { |
| 352 | /* FCS over hdr + all inf fields */ |
| 353 | } else { |
| 354 | /* FCS over hdr + N202 octets (4) */ |
| 355 | if (crc_length > UI_HDR_LEN + N202) |
| 356 | crc_length = UI_HDR_LEN + N202; |
| 357 | } |
| 358 | } else { |
| 359 | /* U (Unnumbered) format: 1 1 1 P/F M4 M3 M2 M1 */ |
| 360 | ghp->data = NULL; |
| 361 | |
| 362 | switch (ctrl[0] & 0xf) { |
| 363 | case 0: |
| 364 | ghp->cmd = GPRS_LLC_NULL; |
| 365 | break; |
| 366 | case 0x1: |
| 367 | ghp->cmd = GPRS_LLC_DM; |
| 368 | break; |
| 369 | case 0x4: |
| 370 | ghp->cmd = GPRS_LLC_DISC; |
| 371 | break; |
| 372 | case 0x6: |
| 373 | ghp->cmd = GPRS_LLC_UA; |
| 374 | break; |
| 375 | case 0x7: |
| 376 | ghp->cmd = GPRS_LLC_SABM; |
| 377 | break; |
| 378 | case 0x8: |
| 379 | ghp->cmd = GPRS_LLC_FRMR; |
| 380 | break; |
| 381 | case 0xb: |
| 382 | ghp->cmd = GPRS_LLC_XID; |
| 383 | break; |
| 384 | default: |
| 385 | return -EIO; |
| 386 | } |
| 387 | } |
| 388 | |
| 389 | /* calculate what FCS we expect */ |
| 390 | ghp->fcs_calc = gprs_llc_fcs(llc_hdr, crc_length); |
| 391 | |
| 392 | /* FIXME: parse sack frame */ |
| 393 | } |
| 394 | |
| 395 | /* receive an incoming LLC PDU */ |
| 396 | int gprs_llc_rcvmsg(struct msgb *msg, struct tlv_parsed *tv) |
| 397 | { |
| 398 | struct bssgp_ud_hdr *udh = (struct bssgp_ud_hdr *) msg->l3h; |
Harald Welte | cf3c414 | 2010-04-30 16:33:12 +0200 | [diff] [blame] | 399 | struct gprs_llc_hdr *lh = msgb_llch(msg); |
Harald Welte | 75bb820 | 2010-03-14 15:45:01 +0800 | [diff] [blame] | 400 | struct gprs_llc_hdr_parsed llhp; |
| 401 | struct gprs_llc_entity *lle; |
| 402 | int rc; |
| 403 | |
| 404 | rc = gprs_llc_hdr_parse(&llhp, lh, TLVP_LEN(tv, BSSGP_IE_LLC_PDU)); |
| 405 | |
| 406 | /* FIXME: find LLC Entity */ |
| 407 | |
| 408 | gprs_llc_hdr_dump(&llhp); |
| 409 | rc = gprs_llc_hdr_rx(&llhp, lle); |
| 410 | |
| 411 | if (llhp.data) { |
Harald Welte | cf3c414 | 2010-04-30 16:33:12 +0200 | [diff] [blame] | 412 | msgb_gmmh(msg) = llhp.data; |
Harald Welte | 75bb820 | 2010-03-14 15:45:01 +0800 | [diff] [blame] | 413 | switch (llhp.sapi) { |
| 414 | case GPRS_SAPI_GMM: |
| 415 | rc = gsm0408_gprs_rcvmsg(msg); |
| 416 | } |
| 417 | } |
| 418 | |
| 419 | return 0; |
| 420 | } |