mgcp/rtp: Fix RTP timestamps if enabled

This forces the output timing to fulfill
   dTS = dSegNo * fixedPacketDuration
where dSegNo = seqNo - lastSeqNo.

If timestamp patching is enabled, the output timestamp will be set
to lastTimestamp + dTS. This kind of relative updating is used to
handle seqNo- and timestamp-wraparounds properly.

The updating of timestamp and SSRC has been separated and the patch
field of mgcp_rtp_state has been renamed to patch_ssrc to reflect
it's semantics more closely. The offset fields are now used always
and will change the corresponding header field if they are != 0.

Ticket: OW#1065
Sponsored-by: On-Waves ehf

3 files changed, 68 insertions, 46 deletions

diff --git a/openbsc/include/openbsc/mgcp_internal.h b/openbsc/include/openbsc/mgcp_internal.h
index 255161f45..b6f4a0df1 100644
--- a/openbsc/include/openbsc/mgcp_internal.h
+++ b/openbsc/include/openbsc/mgcp_internal.h
@@ -50,7 +50,7 @@ struct mgcp_rtp_stream_state {
 
 struct mgcp_rtp_state {
 	int initialized;
-	int patch;
+	int patch_ssrc;
 
 	uint32_t orig_ssrc;
 
diff --git a/openbsc/src/libmgcp/mgcp_network.c b/openbsc/src/libmgcp/mgcp_network.c
index 79c9e1aba..6463ae0bb 100644
--- a/openbsc/src/libmgcp/mgcp_network.c
+++ b/openbsc/src/libmgcp/mgcp_network.c
@@ -278,7 +278,7 @@ void mgcp_patch_and_count(struct mgcp_endpoint *endp, struct mgcp_rtp_state *sta
 			state->timestamp_offset =
 				(state->out_stream.last_timestamp + tsdelta) -
 				timestamp;
-			state->patch = 1;
+			state->patch_ssrc = 1;
 			ssrc = state->orig_ssrc;
 			if (rtp_end->force_constant_ssrc != -1)
 				rtp_end->force_constant_ssrc -= 1;
@@ -300,7 +300,7 @@ void mgcp_patch_and_count(struct mgcp_endpoint *endp, struct mgcp_rtp_state *sta
 				    seq, timestamp, "input",
 				    &state->in_stream.last_tsdelta);
 
-		if (state->patch)
+		if (state->patch_ssrc)
 			ssrc = state->orig_ssrc;
 	}
 
@@ -308,16 +308,38 @@ void mgcp_patch_and_count(struct mgcp_endpoint *endp, struct mgcp_rtp_state *sta
 	state->in_stream.last_timestamp = timestamp;
 	state->in_stream.last_seq = seq;
 
-	/* apply the offset and store it back to the packet */
-	if (state->patch) {
-		seq += state->seq_offset;
-		rtp_hdr->sequence = htons(seq);
-		rtp_hdr->ssrc = htonl(ssrc);
+	if (rtp_end->force_constant_timing &&
+	    state->out_stream.ssrc == ssrc && state->packet_duration) {
+		int delta_seq = seq + state->seq_offset - state->out_stream.last_seq;
+		int timestamp_offset =
+			state->out_stream.last_timestamp - timestamp +
+			delta_seq * state->packet_duration;
+		if (state->timestamp_offset != timestamp_offset) {
+			state->timestamp_offset = timestamp_offset;
 
-		timestamp += state->timestamp_offset;
-		rtp_hdr->timestamp = htonl(timestamp);
+			LOGP(DMGCP, LOGL_NOTICE,
+			     "Timestamp patching enabled on 0x%x SSRC: %u "
+			     "SeqNo delta: %d, TS offset: %d, "
+			     "from %s:%d in %d\n",
+			     ENDPOINT_NUMBER(endp), state->in_stream.ssrc,
+			     delta_seq, state->timestamp_offset,
+			     inet_ntoa(addr->sin_addr), ntohs(addr->sin_port),
+			     endp->conn_mode);
+		}
 	}
 
+	/* Store the updated SSRC back to the packet */
+	if (state->patch_ssrc)
+		rtp_hdr->ssrc = htonl(ssrc);
+
+	/* Apply the offset and store it back to the packet.
+	 * This won't change anything if the offset is 0, so the conditional is
+	 * omitted. */
+	seq += state->seq_offset;
+	rtp_hdr->sequence = htons(seq);
+	timestamp += state->timestamp_offset;
+	rtp_hdr->timestamp = htonl(timestamp);
+
 	/* Check again, whether the timestamps are still valid */
 	if (state->out_stream.ssrc == ssrc)
 		check_rtp_timestamp(endp, &state->out_stream, rtp_end, addr,
diff --git a/openbsc/tests/mgcp/mgcp_test.ok b/openbsc/tests/mgcp/mgcp_test.ok
index 4d3caacb5..3beeb5970 100644
--- a/openbsc/tests/mgcp/mgcp_test.ok
+++ b/openbsc/tests/mgcp/mgcp_test.ok
@@ -94,46 +94,46 @@ Output SSRC changed to 11223344
 TS: 0, dTS: 0, TS Errs: in 0, out 0
 TS: 160, dTS: 160, TS Errs: in 0, out 0
 TS: 320, dTS: 160, TS Errs: in 0, out 0
-TS: 320, dTS: 160, TS Errs: in 1, out 1
-TS: 480, dTS: 160, TS Errs: in 1, out 1
-TS: 640, dTS: 160, TS Errs: in 1, out 1
-TS: 960, dTS: 320, TS Errs: in 2, out 2
-TS: 1120, dTS: 160, TS Errs: in 3, out 3
-TS: 1280, dTS: 160, TS Errs: in 3, out 3
-TS: 1400, dTS: 120, TS Errs: in 4, out 4
-TS: 1560, dTS: 160, TS Errs: in 5, out 5
-TS: 1720, dTS: 160, TS Errs: in 5, out 5
+TS: 480, dTS: 160, TS Errs: in 1, out 0
+TS: 640, dTS: 160, TS Errs: in 1, out 0
+TS: 800, dTS: 160, TS Errs: in 1, out 0
+TS: 960, dTS: 160, TS Errs: in 2, out 0
+TS: 1120, dTS: 160, TS Errs: in 3, out 0
+TS: 1280, dTS: 160, TS Errs: in 3, out 0
+TS: 1440, dTS: 160, TS Errs: in 4, out 0
+TS: 1600, dTS: 160, TS Errs: in 5, out 0
+TS: 1760, dTS: 160, TS Errs: in 5, out 0
 Output SSRC changed to 10203040
-TS: 34688, dTS: 160, TS Errs: in 5, out 5
-TS: 34848, dTS: 160, TS Errs: in 5, out 5
-TS: 35008, dTS: 160, TS Errs: in 5, out 5
-TS: 35128, dTS: 120, TS Errs: in 6, out 6
-TS: 35288, dTS: 160, TS Errs: in 7, out 7
-TS: 35448, dTS: 160, TS Errs: in 7, out 7
-TS: 35768, dTS: 160, TS Errs: in 7, out 7
-TS: 35928, dTS: 160, TS Errs: in 7, out 7
-TS: 36088, dTS: 160, TS Errs: in 8, out 8
+TS: 34728, dTS: 160, TS Errs: in 5, out 0
+TS: 34888, dTS: 160, TS Errs: in 5, out 0
+TS: 35048, dTS: 160, TS Errs: in 5, out 0
+TS: 35208, dTS: 160, TS Errs: in 6, out 0
+TS: 35368, dTS: 160, TS Errs: in 7, out 0
+TS: 35528, dTS: 160, TS Errs: in 7, out 0
+TS: 35848, dTS: 160, TS Errs: in 7, out 0
+TS: 36008, dTS: 160, TS Errs: in 7, out 0
+TS: 36008, dTS: 160, TS Errs: in 8, out 0
 Testing packet error detection, patch SSRC, patch timestamps.
 Output SSRC changed to 11223344
 TS: 0, dTS: 0, TS Errs: in 0, out 0
 TS: 160, dTS: 160, TS Errs: in 0, out 0
 TS: 320, dTS: 160, TS Errs: in 0, out 0
-TS: 320, dTS: 160, TS Errs: in 1, out 1
-TS: 480, dTS: 160, TS Errs: in 1, out 1
-TS: 640, dTS: 160, TS Errs: in 1, out 1
-TS: 960, dTS: 320, TS Errs: in 2, out 2
-TS: 1120, dTS: 160, TS Errs: in 3, out 3
-TS: 1280, dTS: 160, TS Errs: in 3, out 3
-TS: 1400, dTS: 120, TS Errs: in 4, out 4
-TS: 1560, dTS: 160, TS Errs: in 5, out 5
-TS: 1720, dTS: 160, TS Errs: in 5, out 5
-TS: 1880, dTS: 160, TS Errs: in 5, out 5
-TS: 2040, dTS: 160, TS Errs: in 5, out 5
-TS: 2200, dTS: 160, TS Errs: in 5, out 5
-TS: 2320, dTS: 120, TS Errs: in 6, out 6
-TS: 2480, dTS: 160, TS Errs: in 7, out 7
-TS: 2640, dTS: 160, TS Errs: in 7, out 7
-TS: 2960, dTS: 160, TS Errs: in 7, out 7
-TS: 3120, dTS: 160, TS Errs: in 7, out 7
-TS: 3280, dTS: 160, TS Errs: in 8, out 8
+TS: 480, dTS: 160, TS Errs: in 1, out 0
+TS: 640, dTS: 160, TS Errs: in 1, out 0
+TS: 800, dTS: 160, TS Errs: in 1, out 0
+TS: 960, dTS: 160, TS Errs: in 2, out 0
+TS: 1120, dTS: 160, TS Errs: in 3, out 0
+TS: 1280, dTS: 160, TS Errs: in 3, out 0
+TS: 1440, dTS: 160, TS Errs: in 4, out 0
+TS: 1600, dTS: 160, TS Errs: in 5, out 0
+TS: 1760, dTS: 160, TS Errs: in 5, out 0
+TS: 1920, dTS: 160, TS Errs: in 5, out 0
+TS: 2080, dTS: 160, TS Errs: in 5, out 0
+TS: 2240, dTS: 160, TS Errs: in 5, out 0
+TS: 2400, dTS: 160, TS Errs: in 6, out 0
+TS: 2560, dTS: 160, TS Errs: in 7, out 0
+TS: 2720, dTS: 160, TS Errs: in 7, out 0
+TS: 3040, dTS: 160, TS Errs: in 7, out 0
+TS: 3200, dTS: 160, TS Errs: in 7, out 0
+TS: 3200, dTS: 160, TS Errs: in 8, out 0
 Done