epan/dissectors/packet-gsm_um.c

   1 /* packet-gsm_um.c
   2  * Routines for GSM Um packet disassembly
   3  * Duncan Salerno <duncan.salerno@googlemail.com>
   4  *
   5  * Wireshark - Network traffic analyzer
   6  * By Gerald Combs <gerald@wireshark.org>
   7  * Copyright 1998 Gerald Combs
   8  *
   9  * SPDX-License-Identifier: GPL-2.0-or-later
  10  */
  11
  12
  13 #include "config.h"
  14
  15 #include <epan/packet.h>
  16 #include <epan/prefs.h>
  17 #include <wiretap/wtap.h>
  18
  19 void proto_register_gsm_um(void);
  20 void proto_reg_handoff_gsm_um(void);
  21
  22 static int proto_gsm_um;
  23 static int hf_gsm_um_direction;
  24 static int hf_gsm_um_channel;
  25 static int hf_gsm_um_bsic;
  26 static int hf_gsm_um_arfcn;
  27 static int hf_gsm_um_band;
  28 static int hf_gsm_um_frequency;
  29 static int hf_gsm_um_frame;
  30 static int hf_gsm_um_error;
  31 static int hf_gsm_um_timeshift;
  32 static int hf_gsm_um_l2_pseudo_len;
  33
  34 static int ett_gsm_um;
  35
  36 static dissector_handle_t gsm_um_handle;
  37
  38 static dissector_handle_t lapdm_handle;
  39 static dissector_handle_t dtap_handle;
  40
  41 static bool dcs1800_gsm = true;
  42
  43 #define GSM_UM_L2_PSEUDO_LEN            0xfc
  44
  45
  46 static void
  47 decode_arfcn(uint16_t arfcn, const char **band, unsigned *uplink, unsigned *downlink)
  48 {
  49         /* Decode ARFCN to frequency using GSM 05.05 */
  50         if( arfcn >= 1 && arfcn <= 124 ) {
  51                 *band = "P-GSM 900";
  52                 *uplink = 890000 + 200 * arfcn;
  53                 *downlink = *uplink + 45000;
  54         }
  55         else if( arfcn == 0 ) {
  56                 *band = "E-GSM 900";
  57                 *uplink = 890000 + 200 * arfcn;
  58                 *downlink = *uplink + 45000;
  59         }
  60         else if( arfcn >= 975 && arfcn <= 1023 ) {
  61                 *band = "E-GSM 900";
  62                 *uplink = 890000 + 200 * (arfcn - 1024);
  63                 *downlink = *uplink + 45000;
  64         }
  65         else if( arfcn >= 955 && arfcn <= 974 ) {
  66                 *band = "R-GSM 900";
  67                 *uplink = 890000 + 200 * (arfcn - 1024);
  68                 *downlink = *uplink + 45000;
  69         }
  70         else if( arfcn >= 512 && arfcn <= 885 && dcs1800_gsm) {
  71                 *band = "DCS 1800";
  72                 *uplink = 1710200 + 200 * (arfcn - 512);
  73                 *downlink = *uplink + 95000;
  74         }
  75         else if( arfcn >= 512 && arfcn <= 810 && !dcs1800_gsm) {
  76                 *band = "PCS 1900";
  77                 *uplink = 1850200 + 200 * (arfcn - 512);
  78                 *downlink = *uplink + 80000;
  79         }
  80         else if( arfcn >= 259 && arfcn <= 293 ) {
  81                 *band = "GSM 450";
  82                 *uplink = 450600 + 200 * (arfcn - 259);
  83                 *downlink = *uplink + 10000;
  84         }
  85         else if( arfcn >= 306 && arfcn <= 340 ) {
  86                 *band = "GSM 480";
  87                 *uplink = 479000 + 200 * (arfcn - 306);
  88                 *downlink = *uplink + 10000;
  89         }
  90         else if( arfcn >= 128 && arfcn <= 251 ) {
  91                 *band = "GSM 850";
  92                 *uplink = 824200 + 200 * (arfcn - 128);
  93                 *downlink = *uplink + 45000;
  94         }
  95         else {
  96                 *band = "Unknown";
  97                 *uplink = *downlink = 0;
  98         }
  99 }
 100
 101
 102 static int
 103 dissect_gsm_um(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
 104 {
 105         proto_tree *gsm_um_tree = NULL;
 106         proto_item *ti;
 107
 108         col_set_str(pinfo->cinfo, COL_PROTOCOL, "GSM Um");
 109
 110         if (pinfo->pseudo_header->gsm_um.uplink) {
 111                 col_set_str(pinfo->cinfo, COL_RES_DL_DST, "BTS");
 112                 col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "MS");
 113         }
 114         else {
 115                 switch (pinfo->pseudo_header->gsm_um.channel) {
 116                         case GSM_UM_CHANNEL_BCCH:
 117                         case GSM_UM_CHANNEL_CCCH:
 118                         case GSM_UM_CHANNEL_PCH:
 119                         case GSM_UM_CHANNEL_AGCH:
 120                                 col_set_str(pinfo->cinfo, COL_RES_DL_DST, "Broadcast");
 121                                 break;
 122                         default:
 123                                 col_set_str(pinfo->cinfo, COL_RES_DL_DST, "MS");
 124                                 break;
 125                 }
 126                 col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "BTS");
 127         }
 128
 129         if (tree) {
 130                 const char *channel;
 131
 132                 ti = proto_tree_add_item(tree, proto_gsm_um, tvb, 0, 0, ENC_NA);
 133                 gsm_um_tree = proto_item_add_subtree(ti, ett_gsm_um);
 134
 135                 switch( pinfo->pseudo_header->gsm_um.channel ) {
 136                         case GSM_UM_CHANNEL_BCCH: channel = "BCCH"; break;
 137                         case GSM_UM_CHANNEL_CCCH: channel = "CCCH"; break;
 138                         case GSM_UM_CHANNEL_PCH: channel = "PCH"; break;
 139                         case GSM_UM_CHANNEL_AGCH: channel = "AGCH"; break;
 140                         case GSM_UM_CHANNEL_SACCH: channel = "SACCH"; break;
 141                         case GSM_UM_CHANNEL_FACCH: channel = "FACCH"; break;
 142                         case GSM_UM_CHANNEL_SDCCH: channel = "SDCCH"; break;
 143                         default: channel = "Unknown"; break;
 144                 }
 145
 146                 if( pinfo->pseudo_header->gsm_um.uplink ) {
 147                         proto_tree_add_string(gsm_um_tree, hf_gsm_um_direction, tvb, 0, 0, "Uplink");
 148                 }
 149                 else {
 150                         proto_tree_add_string(gsm_um_tree, hf_gsm_um_direction, tvb, 0, 0, "Downlink");
 151                 }
 152
 153                 proto_tree_add_string(gsm_um_tree, hf_gsm_um_channel, tvb, 0, 0, channel);
 154
 155                 /* Show the other fields, if we have them (ie. downlink, BTS->MS) */
 156                 if( !pinfo->pseudo_header->gsm_um.uplink ) {
 157                         const char *band;
 158                         unsigned downlink, uplink;
 159
 160                         decode_arfcn(pinfo->pseudo_header->gsm_um.arfcn, &band, &uplink, &downlink);
 161
 162                         proto_tree_add_uint(gsm_um_tree, hf_gsm_um_arfcn, tvb, 0, 0,
 163                                 pinfo->pseudo_header->gsm_um.arfcn);
 164                         proto_tree_add_string(gsm_um_tree, hf_gsm_um_band, tvb, 0, 0,
 165                                 band);
 166                         proto_tree_add_uint_format_value(gsm_um_tree, hf_gsm_um_frequency, tvb, 0, 0,
 167                                 downlink, "%u.%03uMHz", downlink / 1000, downlink % 1000);
 168                         proto_tree_add_uint(gsm_um_tree, hf_gsm_um_bsic, tvb, 0, 0,
 169                                 pinfo->pseudo_header->gsm_um.bsic);
 170                         proto_tree_add_uint(gsm_um_tree, hf_gsm_um_frame, tvb, 0, 0,
 171                                 pinfo->pseudo_header->gsm_um.tdma_frame);
 172                         proto_tree_add_uint(gsm_um_tree, hf_gsm_um_error, tvb, 0, 0,
 173                                 pinfo->pseudo_header->gsm_um.error);
 174                         proto_tree_add_uint(gsm_um_tree, hf_gsm_um_timeshift, tvb, 0, 0,
 175                                 pinfo->pseudo_header->gsm_um.timeshift);
 176                 }
 177         }
 178
 179         /* TODO: If CCCH downlink could work out of PCH or AGCH by peeking at next bytes, uplink is RACH */
 180
 181         switch( pinfo->pseudo_header->gsm_um.channel ) {
 182                 case GSM_UM_CHANNEL_BCCH:
 183                 case GSM_UM_CHANNEL_CCCH:
 184                 case GSM_UM_CHANNEL_PCH:
 185                 case GSM_UM_CHANNEL_AGCH:
 186                         if( !pinfo->pseudo_header->gsm_um.uplink ) {
 187                                 tvbuff_t *next_tvb;
 188                                 uint8_t pseudo_len, len_left, len_byte;
 189
 190                                 len_left = tvb_reported_length(tvb);
 191                                 len_byte = tvb_get_uint8(tvb, 0);
 192                                 pseudo_len = len_byte >> 2;
 193                                 next_tvb = tvb_new_subset_length_caplen(tvb, 1, MIN(len_left, pseudo_len), -1);
 194
 195                                 if (tree) {
 196                                         proto_tree_add_uint(gsm_um_tree, hf_gsm_um_l2_pseudo_len, tvb, 0, 1,
 197                                                 len_byte);
 198                                 }
 199
 200                                 /* Only dissect non-empty frames */
 201                                 if( tvb_reported_length(next_tvb) ) {
 202                                         call_dissector(dtap_handle, next_tvb, pinfo, tree);
 203                                 }
 204                         }
 205                         else {
 206                                 /* Either RACH, or something invalid */
 207                                 call_data_dissector(tvb, pinfo, tree);
 208                         }
 209                         break;
 210                 case GSM_UM_CHANNEL_SACCH:
 211                 case GSM_UM_CHANNEL_FACCH:
 212                 case GSM_UM_CHANNEL_SDCCH:
 213                         call_dissector(lapdm_handle, tvb, pinfo, tree);
 214                         break;
 215                 default:
 216                         call_data_dissector(tvb, pinfo, tree);
 217                         break;
 218         }
 219         return tvb_captured_length(tvb);
 220 }
 221
 222 void
 223 proto_register_gsm_um(void)
 224 {
 225         static hf_register_info hf[] = {
 226                 { &hf_gsm_um_direction,
 227                 { "Direction",  "gsm_um.direction", FT_STRINGZ, BASE_NONE,
 228                   NULL, 0x0, NULL, HFILL }},
 229
 230                 { &hf_gsm_um_channel,
 231                 { "Channel",    "gsm_um.channel", FT_STRINGZ, BASE_NONE,
 232                   NULL, 0x0, NULL, HFILL }},
 233
 234                 { &hf_gsm_um_bsic,
 235                 { "BSIC",       "gsm_um.bsic", FT_UINT8, BASE_DEC,
 236                   NULL, 0x0, "Base station identity code", HFILL }},
 237
 238                 { &hf_gsm_um_arfcn,
 239                 { "ARFCN",      "gsm_um.arfcn", FT_UINT16, BASE_DEC,
 240                   NULL, 0x0, "Absolute radio frequency channel number", HFILL }},
 241
 242                 { &hf_gsm_um_band,
 243                 { "Band",       "gsm_um.band", FT_STRING, BASE_NONE,
 244                   NULL, 0x0, NULL, HFILL }},
 245
 246                 { &hf_gsm_um_frequency,
 247                 { "Frequency",  "gsm_um.frequency", FT_UINT32, BASE_DEC,
 248                   NULL, 0x0, NULL, HFILL }},
 249
 250                 { &hf_gsm_um_frame,
 251                 { "TDMA Frame", "gsm_um.frame", FT_UINT32, BASE_DEC,
 252                   NULL, 0x0, NULL, HFILL }},
 253
 254                 { &hf_gsm_um_error,
 255                 { "Error",      "gsm_um.error", FT_UINT8, BASE_DEC,
 256                   NULL, 0x0, NULL, HFILL }},
 257
 258                 { &hf_gsm_um_timeshift,
 259                 { "Timeshift",  "gsm_um.timeshift", FT_UINT16, BASE_DEC,
 260                   NULL, 0x0, NULL, HFILL }},
 261
 262                 { &hf_gsm_um_l2_pseudo_len,
 263                 { "L2 Pseudo Length",   "gsm_um.l2_pseudo_len", FT_UINT8, BASE_DEC,
 264                   NULL, GSM_UM_L2_PSEUDO_LEN, NULL, HFILL }}
 265
 266         };
 267         static int *ett[] = {
 268                 &ett_gsm_um
 269         };
 270         module_t *gsm_um_module;
 271
 272         proto_gsm_um = proto_register_protocol("GSM Um Interface", "GSM Um", "gsm_um");
 273         proto_register_field_array(proto_gsm_um, hf, array_length(hf));
 274         proto_register_subtree_array(ett, array_length(ett));
 275
 276         gsm_um_module = prefs_register_protocol(proto_gsm_um, NULL);
 277         prefs_register_bool_preference(gsm_um_module, "dcs1800",
 278                                    "Treat ARFCN 512-810 as DCS 1800 rather than PCS 1900",
 279                                    "Treat ARFCN 512-810 as DCS 1800 rather than PCS 1900",
 280                                    &dcs1800_gsm);
 281
 282         gsm_um_handle = register_dissector("gsm_um", dissect_gsm_um, proto_gsm_um);
 283 }
 284
 285 void
 286 proto_reg_handoff_gsm_um(void)
 287 {
 288         lapdm_handle = find_dissector_add_dependency("lapdm", proto_gsm_um);
 289         dtap_handle = find_dissector_add_dependency("gsm_a_dtap", proto_gsm_um);
 290
 291         dissector_add_uint("wtap_encap", WTAP_ENCAP_GSM_UM, gsm_um_handle);
 292 }
 293
 294 /*
 295  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 296  *
 297  * Local variables:
 298  * c-basic-offset: 8
 299  * tab-width: 8
 300  * indent-tabs-mode: t
 301  * End:
 302  *
 303  * vi: set shiftwidth=8 tabstop=8 noexpandtab:
 304  * :indentSize=8:tabSize=8:noTabs=false:
 305  */