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Take into account Marker bit when patching RTP stream 

On a deployed osmo-mgw with RTP traffic coming from a thirdparty
RTP source, it was usual to see log messages like following one from
time to time:
"The input timestamp has an alignment error of 159 on SSRC"

Doing a quick traffic analysis showed that the above mentioned RTP
source was generating traffic from time to time containing RTP packets
with the Marker (M) bit.

Those messages were logged because the verification & patching funcions
in osmo-mgw were not Marker-bit aware. Hence, this patch implements
support for Marker bit when handling RTP packets.

The Marker bit is usually used as a start of a talkspurt, and has to be
considered a syncrhonization point, where timestamp and relation to real
time don't need to match with last received RTP packet in the stream.

Related: SYS#5498
Change-Id: I1fb449eda49e82607649122b9b9d983a9e5983fa
This commit is contained in:
Pau Espin 2021-07-07 13:41:19 +02:00 committed by pespin
parent d6769ea207
commit b066bd0c86
4 changed files with 90 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/osmocom/mgcp/mgcp_network.h
View File

@ -176,4 +176,4 @@ void mgcp_get_net_downlink_format_default(struct mgcp_endpoint *endp,
/* internal RTP Annex A counting */
void mgcp_rtp_annex_count(const struct mgcp_endpoint *endp, struct mgcp_rtp_state *state,
const uint16_t seq, const int32_t transit,
const uint32_t ssrc);
const uint32_t ssrc, const bool marker_bit);

55
src/libosmo-mgcp/mgcp_network.c
View File

@ -285,13 +285,21 @@ static int adjust_rtp_timestamp_offset(const struct mgcp_endpoint *endp,
struct mgcp_rtp_state *state,
const struct mgcp_rtp_end *rtp_end,
const struct osmo_sockaddr *addr,
int16_t delta_seq, uint32_t in_timestamp)
int16_t delta_seq, uint32_t in_timestamp,
bool marker_bit)
{
int32_t tsdelta = state->packet_duration;
int timestamp_offset;
uint32_t out_timestamp;
char ipbuf[INET6_ADDRSTRLEN];
if (marker_bit) {
/* If RTP pkt contains marker bit, the timestamps are not longer
* in sync, so we can erase timestamp offset patching. */
state->patch.timestamp_offset = 0;
return 0;
}
if (tsdelta == 0) {
tsdelta = state->out_stream.last_tsdelta;
if (tsdelta != 0) {
@ -335,13 +343,19 @@ static int align_rtp_timestamp_offset(const struct mgcp_endpoint *endp,
struct mgcp_rtp_state *state,
const struct mgcp_rtp_end *rtp_end,
const struct osmo_sockaddr *addr,
uint32_t timestamp)
uint32_t timestamp, bool marker_bit)
{
char ipbuf[INET6_ADDRSTRLEN];
int ts_error = 0;
int ts_check = 0;
int ptime = state->packet_duration;
if (marker_bit) {
/* If RTP pkt contains marker bit, the timestamps are not longer
* in sync, so no alignment is needed. */
return 0;
}
/* Align according to: T + Toffs - Tlast = k * Tptime */
ts_error = ts_alignment_error(&state->out_stream, ptime,
@ -414,12 +428,13 @@ void mgcp_get_net_downlink_format_default(struct mgcp_endpoint *endp,
void mgcp_rtp_annex_count(const struct mgcp_endpoint *endp,
struct mgcp_rtp_state *state, const uint16_t seq,
const int32_t transit, const uint32_t ssrc)
const int32_t transit, const uint32_t ssrc,
const bool marker_bit)
{
int32_t d;
/* initialize or re-initialize */
if (!state->stats.initialized || state->stats.ssrc != ssrc) {
if (!state->stats.initialized || state->stats.ssrc != ssrc || marker_bit) {
state->stats.initialized = 1;
state->stats.base_seq = seq;
state->stats.max_seq = seq - 1;
@ -503,6 +518,7 @@ void mgcp_patch_and_count(const struct mgcp_endpoint *endp,
int32_t transit;
uint16_t seq;
uint32_t timestamp, ssrc;
bool marker_bit;
struct rtp_hdr *rtp_hdr;
int payload = rtp_end->codec->payload_type;
unsigned int len = msgb_length(msg);
@ -515,9 +531,10 @@ void mgcp_patch_and_count(const struct mgcp_endpoint *endp,
timestamp = ntohl(rtp_hdr->timestamp);
arrival_time = get_current_ts(rtp_end->codec->rate);
ssrc = ntohl(rtp_hdr->ssrc);
marker_bit = !!rtp_hdr->marker;
transit = arrival_time - timestamp;
mgcp_rtp_annex_count(endp, state, seq, transit, ssrc);
mgcp_rtp_annex_count(endp, state, seq, transit, ssrc, marker_bit);
if (!state->initialized) {
state->initialized = 1;
@ -571,7 +588,7 @@ void mgcp_patch_and_count(const struct mgcp_endpoint *endp,
state->packet_duration;
adjust_rtp_timestamp_offset(endp, state, rtp_end, addr,
delta_seq, timestamp);
delta_seq, timestamp, marker_bit);
state->patch.patch_ssrc = true;
ssrc = state->patch.orig_ssrc;
@ -589,10 +606,14 @@ void mgcp_patch_and_count(const struct mgcp_endpoint *endp,
state->in_stream.last_tsdelta = 0;
} else {
/* Compute current per-packet timestamp delta */
check_rtp_timestamp(endp, state, &state->in_stream, rtp_end,
addr, seq, timestamp, "input",
&state->in_stream.last_tsdelta);
if (!marker_bit) {
/* Compute current per-packet timestamp delta */
check_rtp_timestamp(endp, state, &state->in_stream, rtp_end,
addr, seq, timestamp, "input",
&state->in_stream.last_tsdelta);
} else {
state->in_stream.last_tsdelta = 0;
}
if (state->patch.patch_ssrc)
ssrc = state->patch.orig_ssrc;
@ -607,7 +628,7 @@ void mgcp_patch_and_count(const struct mgcp_endpoint *endp,
state->out_stream.ssrc == ssrc && state->packet_duration)
/* Align the timestamp offset */
align_rtp_timestamp_offset(endp, state, rtp_end, addr,
timestamp);
timestamp, marker_bit);
/* Store the updated SSRC back to the packet */
if (state->patch.patch_ssrc)
@ -622,10 +643,14 @@ void mgcp_patch_and_count(const struct mgcp_endpoint *endp,
rtp_hdr->timestamp = htonl(timestamp);
/* Check again, whether the timestamps are still valid */
if (state->out_stream.ssrc == ssrc)
check_rtp_timestamp(endp, state, &state->out_stream, rtp_end,
addr, seq, timestamp, "output",
&state->out_stream.last_tsdelta);
if (!marker_bit) {
if (state->out_stream.ssrc == ssrc)
check_rtp_timestamp(endp, state, &state->out_stream, rtp_end,
addr, seq, timestamp, "output",
&state->out_stream.last_tsdelta);
} else {
state->out_stream.last_tsdelta = 0;
}
/* Save output values */
state->out_stream.last_seq = seq;

17
tests/mgcp/mgcp_test.c
View File

@ -1282,6 +1282,15 @@ struct rtp_packet_info test_rtp_packets1[] = {
/* RTP: SeqNo=1002, TS=160320 */
{2.040000, 20, "\x80\x62\x03\xEA\x00\x02\x72\x40\x50\x60\x70\x80"
"\x01\x23\x45\x67\x89\xAB\xCD\xEF"},
/* RTP: SeqNo=1003, TS=180320, Marker */
{2.060000, 20, "\x80\xE2\x03\xEB\x00\x02\xC0\x60\x50\x60\x70\x80"
"\x01\x23\x45\x67\x89\xAB\xCD\xEF"},
/* RTP: SeqNo=1004, TS=180480 */
{2.080000, 20, "\x80\x62\x03\xEC\x00\x02\xC1\x00\x50\x60\x70\x80"
"\x01\x23\x45\x67\x89\xAB\xCD\xEF"},
/* RTP: SeqNo=1005, TS=180480, 10ms too late */
{2.110000, 20, "\x80\x62\x03\xED\x00\x02\xC1\xA0\x50\x60\x70\x80"
"\x01\x23\x45\x67\x89\xAB\xCD\xEF"},
};
static void test_packet_error_detection(int patch_ssrc, int patch_ts)
@ -1566,24 +1575,24 @@ static void test_no_cycle(void)
OSMO_ASSERT(conn->state.stats.initialized == 0);
mgcp_rtp_annex_count(endp, &conn->state, 0, 0, 2342);
mgcp_rtp_annex_count(endp, &conn->state, 0, 0, 2342, false);
OSMO_ASSERT(conn->state.stats.initialized == 1);
OSMO_ASSERT(conn->state.stats.cycles == 0);
OSMO_ASSERT(conn->state.stats.max_seq == 0);
mgcp_rtp_annex_count(endp, &conn->state, 1, 0, 2342);
mgcp_rtp_annex_count(endp, &conn->state, 1, 0, 2342, false);
OSMO_ASSERT(conn->state.stats.initialized == 1);
OSMO_ASSERT(conn->state.stats.cycles == 0);
OSMO_ASSERT(conn->state.stats.max_seq == 1);
/* now jump.. */
mgcp_rtp_annex_count(endp, &conn->state, UINT16_MAX, 0, 2342);
mgcp_rtp_annex_count(endp, &conn->state, UINT16_MAX, 0, 2342, false);
OSMO_ASSERT(conn->state.stats.initialized == 1);
OSMO_ASSERT(conn->state.stats.cycles == 0);
OSMO_ASSERT(conn->state.stats.max_seq == UINT16_MAX);
/* and wrap */
mgcp_rtp_annex_count(endp, &conn->state, 0, 0, 2342);
mgcp_rtp_annex_count(endp, &conn->state, 0, 0, 2342, false);
OSMO_ASSERT(conn->state.stats.initialized == 1);
OSMO_ASSERT(conn->state.stats.cycles == UINT16_MAX + 1);
OSMO_ASSERT(conn->state.stats.max_seq == 0);

36
tests/mgcp/mgcp_test.ok
View File

@ -792,6 +792,15 @@ Stats: Jitter = 0, Transit = -144000
In TS: 160320, dTS: 160, Seq: 1002
Out TS change: 160, dTS: 160, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 0, Transit = -144000
In TS: 180320, dTS: 0, Seq: 1003
Out TS change: 20000, dTS: 0, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 0, Transit = -163840
In TS: 180480, dTS: 160, Seq: 1004
Out TS change: 160, dTS: 160, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 0, Transit = -163840
In TS: 180640, dTS: 160, Seq: 1005
Out TS change: 160, dTS: 160, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 5, Transit = -163760
Testing packet error detection.
Output SSRC changed to 11223344
In TS: 0, dTS: 0, Seq: 0
@ -886,6 +895,15 @@ Stats: Jitter = 0, Transit = -144000
In TS: 160320, dTS: 160, Seq: 1002
Out TS change: 160, dTS: 160, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 0, Transit = -144000
In TS: 180320, dTS: 0, Seq: 1003
Out TS change: 20000, dTS: 0, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 0, Transit = -163840
In TS: 180480, dTS: 160, Seq: 1004
Out TS change: 160, dTS: 160, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 0, Transit = -163840
In TS: 180640, dTS: 160, Seq: 1005
Out TS change: 160, dTS: 160, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 5, Transit = -163760
Testing packet error detection, patch timestamps.
Output SSRC changed to 11223344
In TS: 0, dTS: 0, Seq: 0
@ -980,6 +998,15 @@ Stats: Jitter = 0, Transit = -144000
In TS: 160320, dTS: 160, Seq: 1002
Out TS change: 160, dTS: 160, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 0, Transit = -144000
In TS: 180320, dTS: 0, Seq: 1003
Out TS change: 20000, dTS: 0, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 0, Transit = -163840
In TS: 180480, dTS: 160, Seq: 1004
Out TS change: 160, dTS: 160, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 0, Transit = -163840
In TS: 180640, dTS: 160, Seq: 1005
Out TS change: 160, dTS: 160, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 5, Transit = -163760
Testing packet error detection, patch SSRC, patch timestamps.
Output SSRC changed to 11223344
In TS: 0, dTS: 0, Seq: 0
@ -1072,6 +1099,15 @@ Stats: Jitter = 0, Transit = -144000
In TS: 160320, dTS: 160, Seq: 1002
Out TS change: 160, dTS: 160, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 0, Transit = -144000
In TS: 180320, dTS: 0, Seq: 1003
Out TS change: 20000, dTS: 0, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 0, Transit = -163840
In TS: 180480, dTS: 160, Seq: 1004
Out TS change: 160, dTS: 160, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 0, Transit = -163840
In TS: 180640, dTS: 160, Seq: 1005
Out TS change: 160, dTS: 160, Seq change: 1, TS Err change: in +0, out +0
Stats: Jitter = 5, Transit = -163760
Testing multiple payload types
creating message from statically defined input:
---------8<---------