3 * Routines for ITU-T Recommendation H.261 dissection
5 * $Id: packet-h261.c,v 1.19 2003/08/23 06:36:46 guy Exp $
7 * Copyright 2000, Philips Electronics N.V.
8 * Andreas Sikkema <andreas.sikkema@philips.com>
10 * Ethereal - Network traffic analyzer
11 * By Gerald Combs <gerald@ethereal.com>
12 * Copyright 1998 Gerald Combs
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.
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.
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.
30 * This dissector tries to dissect the H.261 protocol according to Annex C
31 * of ITU-T Recommendation H.225.0 (02/98)
40 #include <epan/packet.h>
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;
60 /* H.261 fields defining a sub tree */
61 static gint ett_h261 = -1;
64 dissect_h261( tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree )
66 proto_item *ti = NULL;
67 proto_tree *h261_tree = NULL;
68 unsigned int offset = 0;
70 if ( check_col( pinfo->cinfo, COL_PROTOCOL ) ) {
71 col_set_str( pinfo->cinfo, COL_PROTOCOL, "H.261" );
74 if ( check_col( pinfo->cinfo, COL_INFO) ) {
75 col_set_str( pinfo->cinfo, COL_INFO, "H.261 message");
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 );
86 proto_tree_add_boolean( h261_tree, hf_h261_ibit, tvb, offset, 1, tvb_get_guint8( tvb, offset ) & 2 );
88 proto_tree_add_boolean( h261_tree, hf_h261_vbit, tvb, offset, 1, tvb_get_guint8( tvb, offset ) & 1 );
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 ) );
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 );
102 /* HMVD 3rd octet 2 bits, 4th octet 3 bits */
103 proto_tree_add_uint( h261_tree, hf_h261_hmvd, tvb, offset, 2,
104 ( ( tvb_get_guint8( tvb, offset ) & 0x03 ) << 3 )
105 + ( tvb_get_guint8( tvb, offset+1 ) >> 5 ) );
108 /* VMVD 4th octet, last 5 bits */
109 proto_tree_add_uint( h261_tree, hf_h261_vmvd, tvb, offset, 1, tvb_get_guint8( tvb, offset ) & 31 );
112 /* The rest of the packet is the H.261 stream */
113 proto_tree_add_item( h261_tree, hf_h261_data, tvb, offset, -1, FALSE );
118 proto_register_h261(void)
120 static hf_register_info hf[] =
125 "Start bit position",
149 "Intra frame encoded data flag",
161 "Motion vector flag",
185 "Macroblock address predictor",
209 "Horizontal motion vector data",
221 "Vertical motion vector data",
250 proto_h261 = proto_register_protocol("ITU-T Recommendation H.261",
252 proto_register_field_array(proto_h261, hf, array_length(hf));
253 proto_register_subtree_array(ett, array_length(ett));
257 proto_reg_handoff_h261(void)
259 dissector_handle_t h261_handle;
261 h261_handle = create_dissector_handle(dissect_h261, proto_h261);
262 dissector_add("rtp.pt", PT_H261, h261_handle);