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DVB-S2-BB: Add preference for default mode adaptation format 

DVB Baseband Frames have four possible mode adaptation formats, and
the check to distinguish them depends on only a CRC-8, so it's possible
to have ambiguity, particularly in a large capture. Add a preference to
for preferred format, defaulting to the SatLabs L.3 mode, since that's
the most common format I've seen in captures or in datasheets for
BBFrames over UDP or RTP. Also make L.3 the second highest preference
when something else is set to the default.
This commit is contained in:
John Thacker 2021-05-26 21:57:05 -04:00
parent 17f2fc32f7
commit 1513237d10
1 changed files with 47 additions and 15 deletions
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62
epan/dissectors/packet-dvb-s2-bb.c
View File

@ -46,6 +46,7 @@
#include <epan/reassemble.h>
#include <epan/conversation.h>
#include <epan/proto_data.h>
#include <wsutil/bits_count_ones.h>
#define BIT_IS_SET(var, bit) ((var) & (1 << (bit)))
#define BIT_IS_CLEAR(var, bit) !BIT_IS_SET(var, bit)
@ -63,6 +64,13 @@
#define DVB_S2_MODEADAPT_L3SIZE 4
#define DVB_S2_MODEADAPT_L4SIZE 3
static const int dvb_s2_modeadapt_sizes[] = {
[DVB_S2_MODEADAPT_TYPE_L1] = DVB_S2_MODEADAPT_L1SIZE,
[DVB_S2_MODEADAPT_TYPE_L2] = DVB_S2_MODEADAPT_L2SIZE,
[DVB_S2_MODEADAPT_TYPE_L3] = DVB_S2_MODEADAPT_L3SIZE,
[DVB_S2_MODEADAPT_TYPE_L4] = DVB_S2_MODEADAPT_L4SIZE,
};
/* CRC table crc-8, poly=0xD5 */
static guint8 crc8_table[256] = {
@ -98,8 +106,17 @@ void proto_reg_handoff_dvb_s2_modeadapt(void);
#define DVB_S2_RCS_TABLE_DECODING 0
#define DVB_S2_RCS2_TABLE_DECODING 1
static const enum_val_t dvb_s2_modeadapt_enum[] = {
{"l1", "L.1 (0 bytes)", DVB_S2_MODEADAPT_TYPE_L1},
{"l2", "L.2 (2 bytes including sync)", DVB_S2_MODEADAPT_TYPE_L2},
{"l3", "L.3 (4 bytes including sync)", DVB_S2_MODEADAPT_TYPE_L3},
{"l4", "L.4 (3 bytes)", DVB_S2_MODEADAPT_TYPE_L4},
{NULL, NULL, -1}
};
static gboolean dvb_s2_full_dissection = FALSE;
static gboolean dvb_s2_df_dissection = FALSE;
static gint dvb_s2_default_modeadapt = DVB_S2_MODEADAPT_TYPE_L3;
/* Initialize the protocol and registered fields */
static int proto_dvb_s2_modeadapt = -1;
@ -1525,32 +1542,32 @@ static int dissect_dvb_s2_modeadapt(tvbuff_t *tvb, packet_info *pinfo, proto_tre
check for ambiguity and report it. */
/* Try L.1 format: no header. */
if (test_dvb_s2_crc(tvb, DVB_S2_MODEADAPT_L1SIZE)) {
matched_headers++;
matched_headers |= (1 << DVB_S2_MODEADAPT_TYPE_L1);
modeadapt_type = DVB_S2_MODEADAPT_TYPE_L1;
modeadapt_len = DVB_S2_MODEADAPT_L1SIZE;
}
/* Try L.2 format: header includes sync byte */
if ((tvb_get_guint8(tvb, DVB_S2_MODEADAPT_OFFS_SYNCBYTE) == DVB_S2_MODEADAPT_SYNCBYTE) &&
test_dvb_s2_crc(tvb, DVB_S2_MODEADAPT_L2SIZE)) {
matched_headers++;
matched_headers |= (1 << DVB_S2_MODEADAPT_TYPE_L2);
modeadapt_type = DVB_S2_MODEADAPT_TYPE_L2;
modeadapt_len = DVB_S2_MODEADAPT_L2SIZE;
}
/* Try L.3 format: header includes sync byte */
if ((tvb_get_guint8(tvb, DVB_S2_MODEADAPT_OFFS_SYNCBYTE) == DVB_S2_MODEADAPT_SYNCBYTE) &&
test_dvb_s2_crc(tvb, DVB_S2_MODEADAPT_L3SIZE)) {
matched_headers++;
modeadapt_type = DVB_S2_MODEADAPT_TYPE_L3;
modeadapt_len = DVB_S2_MODEADAPT_L3SIZE;
}
/* Try L.4 format: header does not include sync byte */
if (test_dvb_s2_crc(tvb, DVB_S2_MODEADAPT_L4SIZE)) {
matched_headers++;
matched_headers |= (1 << DVB_S2_MODEADAPT_TYPE_L4);
modeadapt_type = DVB_S2_MODEADAPT_TYPE_L4;
modeadapt_len = DVB_S2_MODEADAPT_L4SIZE;
}
/* In my experience and in product data sheets, L.3 format is the most
* common for outputting over UDP or RTP, so give it highest priority
* (or second highest if another is set to default) by trying it last.
*/
/* Try L.3 format: header includes sync byte */
if ((tvb_get_guint8(tvb, DVB_S2_MODEADAPT_OFFS_SYNCBYTE) == DVB_S2_MODEADAPT_SYNCBYTE) &&
test_dvb_s2_crc(tvb, DVB_S2_MODEADAPT_L3SIZE)) {
matched_headers |= (1 << DVB_S2_MODEADAPT_TYPE_L3);
modeadapt_type = DVB_S2_MODEADAPT_TYPE_L3;
}
if (matched_headers == 0) {
@ -1560,6 +1577,11 @@ static int dissect_dvb_s2_modeadapt(tvbuff_t *tvb, packet_info *pinfo, proto_tre
return 0;
}
if (matched_headers & (1 << dvb_s2_default_modeadapt)) {
modeadapt_type = dvb_s2_default_modeadapt;
}
modeadapt_len = dvb_s2_modeadapt_sizes[modeadapt_type];
col_set_str(pinfo->cinfo, COL_PROTOCOL, "DVB-S2 ");
col_set_str(pinfo->cinfo, COL_INFO, "DVB-S2 ");
@ -1570,7 +1592,7 @@ static int dissect_dvb_s2_modeadapt(tvbuff_t *tvb, packet_info *pinfo, proto_tre
"DVB-S2 Mode Adaptation Header L.%d", modeadapt_type);
dvb_s2_modeadapt_tree = proto_item_add_subtree(ti, ett_dvb_s2_modeadapt);
if (matched_headers > 1) {
if (ws_count_ones(matched_headers) > 1) {
expert_add_info_format(pinfo, ti, &ei_dvb_s2_bb_header_ambiguous,
"Mode adaptation header format is ambiguous. Assuming L.%d", modeadapt_type);
}
@ -1617,6 +1639,11 @@ static int dissect_dvb_s2_modeadapt(tvbuff_t *tvb, packet_info *pinfo, proto_tre
proto_tree_add_item(dvb_s2_modeadapt_tree, hf_dvb_s2_modeadapt_frameno, tvb, cur_off, 1, ENC_BIG_ENDIAN);
cur_off++;
}
} else {
/* Warn if ambiguity exists even when no subtree (i.e. L.1 / length 0) */
if (ws_count_ones(matched_headers) > 1) {
proto_tree_add_expert_format(tree, pinfo, &ei_dvb_s2_bb_header_ambiguous, tvb, 0, 0, "Mode adaptation header format is ambiguous. Assuming L.%d", modeadapt_type);
}
}
/* start DVB-BB dissector */
@ -1989,6 +2016,11 @@ void proto_register_dvb_s2_modeadapt(void)
"Check this to enable full protocol dissection of data above GSE Layer",
&dvb_s2_full_dissection);
prefs_register_enum_preference(dvb_s2_modeadapt_module, "default_modeadapt",
"Preferred Mode Adaptation Interface",
"The preferred Mode Adaptation Interface in the case of ambiguity",
&dvb_s2_default_modeadapt, dvb_s2_modeadapt_enum, FALSE);
register_init_routine(dvbs2_defragment_init);
}