mgcp/rtp: Fix output timing error counter

The tsdelta computation and error detection didn't handle the
intialisation phase properly.

This patches fixes this by skipping the output timing validation
when the SSRCs don't match.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/libmgcp/mgcp_network.c b/openbsc/src/libmgcp/mgcp_network.c
index 75d39c1..53f1a20 100644
--- a/openbsc/src/libmgcp/mgcp_network.c
+++ b/openbsc/src/libmgcp/mgcp_network.c
@@ -237,6 +237,16 @@
 		state->jitter = 0;
 		state->transit = arrival_time - timestamp;
 		state->out_stream = state->in_stream;
+		state->out_stream.last_timestamp = timestamp;
+		/* force output SSRC change */
+		state->out_stream.ssrc = rtp_hdr->ssrc - 1;
+		LOGP(DMGCP, LOGL_INFO,
+			"Initializing stream on 0x%x SSRC: %u timestamp: %u "
+			"from %s:%d in %d\n",
+			ENDPOINT_NUMBER(endp), state->in_stream.ssrc,
+			state->seq_offset,
+			inet_ntoa(addr->sin_addr), ntohs(addr->sin_port),
+			endp->conn_mode);
 	} else if (state->in_stream.ssrc != rtp_hdr->ssrc) {
 		int32_t tsdelta = state->out_stream.last_tsdelta;
 		if (tsdelta == 0) {
@@ -286,9 +296,10 @@
 	}
 
 	/* Check again, whether the timestamps are still valid */
-	check_rtp_timestamp(endp, &state->out_stream, rtp_end, addr,
-			    seq, timestamp, "output",
-			    &state->out_stream.last_tsdelta);
+	if (state->out_stream.ssrc == rtp_hdr->ssrc)
+		check_rtp_timestamp(endp, &state->out_stream, rtp_end, addr,
+				    seq, timestamp, "output",
+				    &state->out_stream.last_tsdelta);
 
 	/*
 	 * The below takes the shape of the validation from Appendix A. Check
diff --git a/openbsc/tests/mgcp/mgcp_test.ok b/openbsc/tests/mgcp/mgcp_test.ok
index 57d3bfb..4d3caac 100644
--- a/openbsc/tests/mgcp/mgcp_test.ok
+++ b/openbsc/tests/mgcp/mgcp_test.ok
@@ -80,15 +80,15 @@
 TS: 1560, dTS: 160, TS Errs: in 5, out 5
 TS: 1720, dTS: 160, TS Errs: in 5, out 5
 Output SSRC changed to 10203040
-TS: 34688, dTS: 32968, TS Errs: in 5, out 6
-TS: 34848, dTS: 160, TS Errs: in 5, out 7
-TS: 35008, dTS: 160, TS Errs: in 5, out 7
-TS: 35128, dTS: 120, TS Errs: in 6, out 8
-TS: 35288, dTS: 160, TS Errs: in 7, out 9
-TS: 35448, dTS: 160, TS Errs: in 7, out 9
-TS: 35768, dTS: 160, TS Errs: in 7, out 9
-TS: 35928, dTS: 160, TS Errs: in 7, out 9
-TS: 36088, dTS: 160, TS Errs: in 8, out 10
+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
 Testing packet error detection, patch timestamps.
 Output SSRC changed to 11223344
 TS: 0, dTS: 0, TS Errs: in 0, out 0
@@ -104,15 +104,15 @@
 TS: 1560, dTS: 160, TS Errs: in 5, out 5
 TS: 1720, dTS: 160, TS Errs: in 5, out 5
 Output SSRC changed to 10203040
-TS: 34688, dTS: 32968, TS Errs: in 5, out 6
-TS: 34848, dTS: 160, TS Errs: in 5, out 7
-TS: 35008, dTS: 160, TS Errs: in 5, out 7
-TS: 35128, dTS: 120, TS Errs: in 6, out 8
-TS: 35288, dTS: 160, TS Errs: in 7, out 9
-TS: 35448, dTS: 160, TS Errs: in 7, out 9
-TS: 35768, dTS: 160, TS Errs: in 7, out 9
-TS: 35928, dTS: 160, TS Errs: in 7, out 9
-TS: 36088, dTS: 160, TS Errs: in 8, out 10
+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
 Testing packet error detection, patch SSRC, patch timestamps.
 Output SSRC changed to 11223344
 TS: 0, dTS: 0, TS Errs: in 0, out 0