mgcp_network: translate payload type numbers in RTP packets

Since no transcoding is in place osmo-mgw forwards the incoming rtp
packets as they are (there may be minor modifications of the header) from
an ingress connection to an egress connection.

This works without problems as long as both connections use the same
payload type. For IANA defined fixed payload type numbers this is
usually the case, but for dynemic payload type numbers both ends may set
up the same codecs but with different payload type numbers.

When different payload type numbers are set up, and the packet is passed
through without modification, it will have the wrong payload type when
it is sent. The receiving end may then toss the packet since it expects
packets with the payload type it has configured.

The machanism, which is introduced with this patch looks up actual codec
inside the struct data of the ingress connection and then looks for the
matching codec in the struct data of the egress connection. When it
finds the codec there it looks up the payload type of this codec. The
header of the RTP packet is then patched with the correct payoad type.

- Add function mgcp_codec_pt_translate() to look up the payload type
- Add unit-test for function mgcp_codec_pt_translate()
- Add payload type translation to mgcp_network.c

Change-Id: I3a874e59fa07bcc2a67c376cafa197360036f539
Related: OS#2728
Related: OS#3384

1 files changed, 95 insertions, 0 deletions

diff --git a/tests/mgcp/mgcp_test.c b/tests/mgcp/mgcp_test.c
index 56d0ceef6..df6ea2fec 100644
--- a/tests/mgcp/mgcp_test.c
+++ b/tests/mgcp/mgcp_test.c
@@ -1616,6 +1616,100 @@ static void test_check_local_cx_options(void *ctx)
 	OSMO_ASSERT(check_local_cx_options(ctx, ",,,") == -1);
 }
 
+static void test_mgcp_codec_pt_translate_pars(struct mgcp_rtp_codec *c)
+{
+	c->rate = 8000;
+	c->channels = 1;
+	c->frame_duration_num = 23;
+	c->frame_duration_den = 42;
+}
+
+static void test_mgcp_codec_pt_translate(void)
+{
+	struct mgcp_conn_rtp conn_src;
+	struct mgcp_conn_rtp conn_dst;
+	int pt_dst;
+
+	/* Setup a realistic set of codec configurations on both
+	 * ends. AMR and HR will use different payload types. PCMU
+	 * must use 0 on both ends since this is not a dynamic payload
+	 * type */
+	test_mgcp_codec_pt_translate_pars(&conn_src.end.codecs[0]);
+	test_mgcp_codec_pt_translate_pars(&conn_dst.end.codecs[0]);
+	test_mgcp_codec_pt_translate_pars(&conn_src.end.codecs[1]);
+	test_mgcp_codec_pt_translate_pars(&conn_dst.end.codecs[1]);
+	test_mgcp_codec_pt_translate_pars(&conn_src.end.codecs[2]);
+	test_mgcp_codec_pt_translate_pars(&conn_dst.end.codecs[2]);
+	conn_src.end.codecs[0].payload_type = 112;
+	conn_dst.end.codecs[0].payload_type = 96;
+	conn_src.end.codecs[1].payload_type = 0;
+	conn_dst.end.codecs[1].payload_type = 0;
+	conn_src.end.codecs[2].payload_type = 111;
+	conn_dst.end.codecs[2].payload_type = 97;
+	conn_src.end.codecs[0].audio_name = "AMR/8000/1";
+	conn_dst.end.codecs[0].audio_name = "AMR/8000/1";
+	conn_src.end.codecs[1].audio_name = "PCMU/8000/1";
+	conn_dst.end.codecs[1].audio_name = "PCMU/8000/1";
+	conn_src.end.codecs[2].audio_name = "GSM-HR-08/8000/1";
+	conn_dst.end.codecs[2].audio_name = "GSM-HR-08/8000/1";
+	conn_src.end.codecs[0].subtype_name = "AMR";
+	conn_dst.end.codecs[0].subtype_name = "AMR";
+	conn_src.end.codecs[1].subtype_name = "PCMU";
+	conn_dst.end.codecs[1].subtype_name = "PCMU";
+	conn_src.end.codecs[2].subtype_name = "GSM-HR-08";
+	conn_dst.end.codecs[2].subtype_name = "GSM-HR-08";
+	conn_src.end.codecs_assigned = 3;
+	conn_dst.end.codecs_assigned = 3;
+
+	/* We expect the function to find the PT we must use when we send the
+	 * packet out to the destination. All we know is the context for both
+	 * connections and the payload type from the source packet */
+	pt_dst =
+	    mgcp_codec_pt_translate(&conn_src, &conn_dst,
+				    conn_src.end.codecs[0].payload_type);
+	OSMO_ASSERT(pt_dst == conn_dst.end.codecs[0].payload_type);
+	pt_dst =
+	    mgcp_codec_pt_translate(&conn_src, &conn_dst,
+				    conn_src.end.codecs[1].payload_type);
+	OSMO_ASSERT(pt_dst == conn_dst.end.codecs[1].payload_type);
+	pt_dst =
+	    mgcp_codec_pt_translate(&conn_src, &conn_dst,
+				    conn_src.end.codecs[2].payload_type);
+	OSMO_ASSERT(pt_dst == conn_dst.end.codecs[2].payload_type);
+
+	/* Try some constellations that must fail */
+	pt_dst = mgcp_codec_pt_translate(&conn_src, &conn_dst, 123);
+	OSMO_ASSERT(pt_dst == -EINVAL);
+	conn_src.end.codecs_assigned = 0;
+	conn_dst.end.codecs_assigned = 3;
+	pt_dst =
+	    mgcp_codec_pt_translate(&conn_src, &conn_dst,
+				    conn_src.end.codecs[0].payload_type);
+	OSMO_ASSERT(pt_dst == -EINVAL);
+	pt_dst =
+	    mgcp_codec_pt_translate(&conn_src, &conn_dst,
+				    conn_src.end.codecs[1].payload_type);
+	OSMO_ASSERT(pt_dst == -EINVAL);
+	pt_dst =
+	    mgcp_codec_pt_translate(&conn_src, &conn_dst,
+				    conn_src.end.codecs[2].payload_type);
+	OSMO_ASSERT(pt_dst == -EINVAL);
+	conn_src.end.codecs_assigned = 3;
+	conn_dst.end.codecs_assigned = 0;
+	pt_dst =
+	    mgcp_codec_pt_translate(&conn_src, &conn_dst,
+				    conn_src.end.codecs[0].payload_type);
+	OSMO_ASSERT(pt_dst == -EINVAL);
+	pt_dst =
+	    mgcp_codec_pt_translate(&conn_src, &conn_dst,
+				    conn_src.end.codecs[1].payload_type);
+	OSMO_ASSERT(pt_dst == -EINVAL);
+	pt_dst =
+	    mgcp_codec_pt_translate(&conn_src, &conn_dst,
+				    conn_src.end.codecs[2].payload_type);
+	OSMO_ASSERT(pt_dst == -EINVAL);
+}
+
 int main(int argc, char **argv)
 {
 	void *ctx = talloc_named_const(NULL, 0, "mgcp_test");
@@ -1639,6 +1733,7 @@ int main(int argc, char **argv)
 	test_osmux_cid();
 	test_get_lco_identifier();
 	test_check_local_cx_options(ctx);
+	test_mgcp_codec_pt_translate();
 
 	OSMO_ASSERT(talloc_total_size(msgb_ctx) == 0);
 	OSMO_ASSERT(talloc_total_blocks(msgb_ctx) == 1);