packet-h261.c

   1 /* packet-h261.c
   2  *
   3  * Routines for ITU-T Recommendation H.261 dissection
   4  *
   5  * $Id: packet-h261.c,v 1.17 2002/08/28 21:00:15 jmayer Exp $
   6  *
   7  * Copyright 2000, Philips Electronics N.V.
   8  * Andreas Sikkema <andreas.sikkema@philips.com>
   9  *
  10  * Ethereal - Network traffic analyzer
  11  * By Gerald Combs <gerald@ethereal.com>
  12  * Copyright 1998 Gerald Combs
  13  *
  14  * This program is free software; you can redistribute it and/or
  15  * modify it under the terms of the GNU General Public License
  16  * as published by the Free Software Foundation; either version 2
  17  * of the License, or (at your option) any later version.
  18  *
  19  * This program is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU General Public License
  25  * along with this program; if not, write to the Free Software
  26  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  27  */
  28
  29 /*
  30  * This dissector tries to dissect the H.261 protocol according to Annex C
  31  * of ITU-T Recommendation H.225.0 (02/98)
  32  *
  33  * This dissector is called by the RTP dissector
  34  */
  35
  36
  37 #ifdef HAVE_CONFIG_H
  38 # include "config.h"
  39 #endif
  40
  41 #include <glib.h>
  42 #include <epan/packet.h>
  43
  44 #include <stdio.h>
  45 #include <string.h>
  46
  47 /* H.261 header fields             */
  48 static int proto_h261          = -1;
  49 static int hf_h261_sbit        = -1;
  50 static int hf_h261_ebit        = -1;
  51 static int hf_h261_ibit        = -1;
  52 static int hf_h261_vbit        = -1;
  53 static int hf_h261_gobn        = -1;
  54 static int hf_h261_mbap        = -1;
  55 static int hf_h261_quant       = -1;
  56 static int hf_h261_hmvd        = -1; /* Mislabeled in a figure in section C.3.1 as HMDV */
  57 static int hf_h261_vmvd        = -1;
  58 static int hf_h261_data        = -1;
  59
  60 /* H.261 fields defining a sub tree */
  61 static gint ett_h261           = -1;
  62
  63 static void
  64 dissect_h261( tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree )
  65 {
  66         proto_item *ti            = NULL;
  67         proto_tree *h261_tree     = NULL;
  68         unsigned int offset       = 0;
  69
  70         if ( check_col( pinfo->cinfo, COL_PROTOCOL ) )   {
  71                 col_set_str( pinfo->cinfo, COL_PROTOCOL, "H.261" );
  72         }
  73
  74         if ( check_col( pinfo->cinfo, COL_INFO) ) {
  75                 col_set_str( pinfo->cinfo, COL_INFO, "H.261 message");
  76         }
  77
  78         if ( tree ) {
  79                 ti = proto_tree_add_item( tree, proto_h261, tvb, offset, -1, FALSE );
  80                 h261_tree = proto_item_add_subtree( ti, ett_h261 );
  81                 /* SBIT 1st octet, 3 bits */
  82                 proto_tree_add_uint( h261_tree, hf_h261_sbit, tvb, offset, 1, tvb_get_guint8( tvb, offset ) >> 5 );
  83                 /* EBIT 1st octet, 3 bits */
  84                 proto_tree_add_uint( h261_tree, hf_h261_ebit, tvb, offset, 1, ( tvb_get_guint8( tvb, offset )  << 3 ) >> 5 );
  85                 /* I flag, 1 bit */
  86                 proto_tree_add_boolean( h261_tree, hf_h261_ibit, tvb, offset, 1, tvb_get_guint8( tvb, offset ) & 2 );
  87                 /* V flag, 1 bit */
  88                 proto_tree_add_boolean( h261_tree, hf_h261_vbit, tvb, offset, 1, tvb_get_guint8( tvb, offset ) & 1 );
  89                 offset++;
  90
  91                 /* GOBN 2nd octet, 4 bits */
  92                 proto_tree_add_uint( h261_tree, hf_h261_gobn, tvb, offset, 1, tvb_get_guint8( tvb, offset ) >> 4 );
  93                 /* MBAP 2nd octet, 4 bits, 3rd octet 1 bit */
  94                 proto_tree_add_uint( h261_tree, hf_h261_mbap, tvb, offset, 1,
  95                     ( tvb_get_guint8( tvb, offset ) & 15 )
  96                     + ( tvb_get_guint8( tvb, offset + 1 ) >> 7 ) );
  97                 offset++;
  98
  99                 /* QUANT 3rd octet, 5 bits (starting at bit 2!) */
 100                 proto_tree_add_uint( h261_tree, hf_h261_quant, tvb, offset, 1, tvb_get_guint8( tvb, offset ) & 124 );
 101                 /* HMVD 3rd octet 2 bits, 4th octet 3 bits */
 102                 proto_tree_add_uint( h261_tree, hf_h261_hmvd, tvb, offset, 1,
 103                     ( ( tvb_get_guint8( tvb, offset ) << 4) >> 4 )
 104                      + ( tvb_get_guint8( tvb, offset ) >> 5 ) );
 105                 offset++;
 106
 107                 /* VMVD 4th octet, last 5 bits */
 108                 proto_tree_add_uint( h261_tree, hf_h261_vmvd, tvb, offset, 1, tvb_get_guint8( tvb, offset ) & 31 );
 109                 offset++;
 110
 111                 /* The rest of the packet is the H.261 stream */
 112                 proto_tree_add_item( h261_tree, hf_h261_data, tvb, offset, -1, FALSE );
 113         }
 114 }
 115
 116 void
 117 proto_register_h261(void)
 118 {
 119         static hf_register_info hf[] =
 120         {
 121                 {
 122                         &hf_h261_sbit,
 123                         {
 124                                 "Start bit position",
 125                                 "h261.sbit",
 126                                 FT_UINT8,
 127                                 BASE_DEC,
 128                                 NULL,
 129                                 0x0,
 130                                 "", HFILL
 131                         }
 132                 },
 133                 {
 134                         &hf_h261_ebit,
 135                         {
 136                                 "End bit position",
 137                                 "h261.ebit",
 138                                 FT_UINT8,
 139                                 BASE_DEC,
 140                                 NULL,
 141                                 0x0,
 142                                 "", HFILL
 143                         }
 144                 },
 145                 {
 146                         &hf_h261_ibit,
 147                         {
 148                                 "Intra frame encoded data flag",
 149                                 "h261.i",
 150                                 FT_BOOLEAN,
 151                                 BASE_NONE,
 152                                 NULL,
 153                                 0x0,
 154                                 "", HFILL
 155                         }
 156                 },
 157                 {
 158                         &hf_h261_vbit,
 159                         {
 160                                 "Motion vector flag",
 161                                 "h261.v",
 162                                 FT_BOOLEAN,
 163                                 BASE_NONE,
 164                                 NULL,
 165                                 0x0,
 166                                 "", HFILL
 167                         }
 168                 },
 169                 {
 170                         &hf_h261_gobn,
 171                         {
 172                                 "GOB Number",
 173                                 "h261.gobn",
 174                                 FT_UINT8,
 175                                 BASE_DEC,
 176                                 NULL,
 177                                 0x0,
 178                                 "", HFILL
 179                         }
 180                 },
 181                 {
 182                         &hf_h261_mbap,
 183                         {
 184                                 "Macroblock address predictor",
 185                                 "h261.mbap",
 186                                 FT_UINT8,
 187                                 BASE_DEC,
 188                                 NULL,
 189                                 0x0,
 190                                 "", HFILL
 191                         }
 192                 },
 193                 {
 194                         &hf_h261_quant,
 195                         {
 196                                 "Quantizer",
 197                                 "h261.quant",
 198                                 FT_UINT8,
 199                                 BASE_DEC,
 200                                 NULL,
 201                                 0x0,
 202                                 "", HFILL
 203                         }
 204                 },
 205                 {
 206                         &hf_h261_hmvd,
 207                         {
 208                                 "Horizontal motion vector data",
 209                                 "h261.hmvd",
 210                                 FT_UINT8,
 211                                 BASE_DEC,
 212                                 NULL,
 213                                 0x0,
 214                                 "", HFILL
 215                         }
 216                 },
 217                 {
 218                         &hf_h261_vmvd,
 219                         {
 220                                 "Vertical motion vector data",
 221                                 "h261.vmvd",
 222                                 FT_UINT8,
 223                                 BASE_DEC,
 224                                 NULL,
 225                                 0x0,
 226                                 "", HFILL
 227                         }
 228                 },
 229                 {
 230                         &hf_h261_data,
 231                         {
 232                                 "H.261 stream",
 233                                 "h261.stream",
 234                                 FT_BYTES,
 235                                 BASE_NONE,
 236                                 NULL,
 237                                 0x0,
 238                                 "", HFILL
 239                         }
 240                 },
 241 };
 242
 243         static gint *ett[] =
 244         {
 245                 &ett_h261,
 246         };
 247
 248
 249         proto_h261 = proto_register_protocol("ITU-T Recommendation H.261",
 250             "H.261", "h261");
 251         proto_register_field_array(proto_h261, hf, array_length(hf));
 252         proto_register_subtree_array(ett, array_length(ett));
 253
 254         register_dissector("h261", dissect_h261, proto_h261);
 255 }