Add rtcp-mux support

This commit adds support for RFC 5761: Multiplexing RTP Data and Control
Packets on a Single Port. Specifically, it enables the feature when
using chan_pjsip.

A new option, "rtcp_mux" has been added to endpoint configuration in
pjsip.conf. If set, then Asterisk will attempt to use rtcp-mux with
whatever it communicates with. Asterisk follows the rules set forth in
RFC 5761 with regards to falling back to standard RTCP behavior if the
far end does not indicate support for rtcp-mux.

The lion's share of the changes in this commit are in
res_rtp_asterisk.c. This is because it was pretty much hard wired to
have an RTP and an RTCP transport. The strategy used here is that when
rtcp-mux is enabled, the current RTCP transport and its trappings (such
as DTLS SSL session) are freed, and the RTCP session instead just
mooches off the RTP session. This leads to a lot of specialized if
statements throughout.

ASTERISK-26732 #close
Reported by Dan Jenkins

Change-Id: If46a93ba1282418d2803e3fd7869374da8b77ab5

1 files changed, 66 insertions, 2 deletions

diff --git a/res/res_pjsip_sdp_rtp.c b/res/res_pjsip_sdp_rtp.c
index e32d2b65f..9f39256e5 100644
--- a/res/res_pjsip_sdp_rtp.c
+++ b/res/res_pjsip_sdp_rtp.c
@@ -169,6 +169,23 @@ static int rtp_check_timeout(const void *data)
 	return 0;
 }
 
+/*!
+ * \brief Enable RTCP on an RTP session.
+ */
+static void enable_rtcp(struct ast_sip_session *session, struct ast_sip_session_media *session_media,
+	const struct pjmedia_sdp_media *remote_media)
+{
+	enum ast_rtp_instance_rtcp rtcp_type;
+
+	if (session->endpoint->media.rtcp_mux && session_media->remote_rtcp_mux) {
+		rtcp_type = AST_RTP_INSTANCE_RTCP_MUX;
+	} else {
+		rtcp_type = AST_RTP_INSTANCE_RTCP_STANDARD;
+	}
+
+	ast_rtp_instance_set_prop(session_media->rtp, AST_RTP_PROPERTY_RTCP, rtcp_type);
+}
+
 /*! \brief Internal function which creates an RTP instance */
 static int create_rtp(struct ast_sip_session *session, struct ast_sip_session_media *session_media)
 {
@@ -186,7 +203,6 @@ static int create_rtp(struct ast_sip_session *session, struct ast_sip_session_me
 		return -1;
 	}
 
-	ast_rtp_instance_set_prop(session_media->rtp, AST_RTP_PROPERTY_RTCP, 1);
 	ast_rtp_instance_set_prop(session_media->rtp, AST_RTP_PROPERTY_NAT, session->endpoint->media.rtp.symmetric);
 
 	if (!session->endpoint->media.rtp.ice_support && (ice = ast_rtp_instance_get_ice(session_media->rtp))) {
@@ -569,6 +585,13 @@ static void process_ice_attributes(struct ast_sip_session *session, struct ast_s
 			continue;
 		}
 
+		if (session->endpoint->media.rtcp_mux && session_media->remote_rtcp_mux && candidate.id > 1) {
+			/* Remote side may have offered RTP and RTCP candidates. However, if we're using RTCP MUX,
+			 * then we should ignore RTCP candidates.
+			 */
+			continue;
+		}
+
 		candidate.foundation = foundation;
 		candidate.transport = transport;
 
@@ -865,6 +888,26 @@ static int setup_media_encryption(struct ast_sip_session *session,
 	return 0;
 }
 
+static void set_ice_components(struct ast_sip_session *session, struct ast_sip_session_media *session_media)
+{
+	struct ast_rtp_engine_ice *ice;
+
+	ast_assert(session_media->rtp != NULL);
+
+	ice = ast_rtp_instance_get_ice(session_media->rtp);
+	if (!session->endpoint->media.rtp.ice_support || !ice) {
+		return;
+	}
+
+	if (session->endpoint->media.rtcp_mux && session_media->remote_rtcp_mux) {
+		/* We both support RTCP mux. Only one ICE component necessary */
+		ice->change_components(session_media->rtp, 1);
+	} else {
+		/* They either don't support RTCP mux or we don't know if they do yet. */
+		ice->change_components(session_media->rtp, 2);
+	}
+}
+
 /*! \brief Function which negotiates an incoming media stream */
 static int negotiate_incoming_sdp_stream(struct ast_sip_session *session, struct ast_sip_session_media *session_media,
 					 const struct pjmedia_sdp_session *sdp, const struct pjmedia_sdp_media *stream)
@@ -909,6 +952,11 @@ static int negotiate_incoming_sdp_stream(struct ast_sip_session *session, struct
 		return -1;
 	}
 
+	session_media->remote_rtcp_mux = (pjmedia_sdp_media_find_attr2(stream, "rtcp-mux", NULL) != NULL);
+	set_ice_components(session, session_media);
+
+	enable_rtcp(session, session_media, stream);
+
 	res = setup_media_encryption(session, session_media, sdp, stream);
 	if (res) {
 		if (!session->endpoint->media.rtp.encryption_optimistic ||
@@ -1087,6 +1135,9 @@ static int create_outgoing_sdp_stream(struct ast_sip_session *session, struct as
 		return -1;
 	}
 
+	set_ice_components(session, session_media);
+	enable_rtcp(session, session_media, NULL);
+
 	if (!(media = pj_pool_zalloc(pool, sizeof(struct pjmedia_sdp_media))) ||
 		!(media->conn = pj_pool_zalloc(pool, sizeof(struct pjmedia_sdp_conn)))) {
 		return -1;
@@ -1250,6 +1301,12 @@ static int create_outgoing_sdp_stream(struct ast_sip_session *session, struct as
 	attr->name = !session_media->locally_held ? STR_SENDRECV : STR_SENDONLY;
 	media->attr[media->attr_count++] = attr;
 
+	/* If we've got rtcp-mux enabled, just unconditionally offer it in all SDPs */
+	if (session->endpoint->media.rtcp_mux) {
+		attr = pjmedia_sdp_attr_create(pool, "rtcp-mux", NULL);
+		pjmedia_sdp_attr_add(&media->attr_count, media->attr, attr);
+	}
+
 	/* Add the media stream to the SDP */
 	sdp->media[sdp->media_count++] = media;
 
@@ -1284,6 +1341,11 @@ static int apply_negotiated_sdp_stream(struct ast_sip_session *session, struct a
 		return -1;
 	}
 
+	session_media->remote_rtcp_mux = (pjmedia_sdp_media_find_attr2(remote_stream, "rtcp-mux", NULL) != NULL);
+	set_ice_components(session, session_media);
+
+	enable_rtcp(session, session_media, remote_stream);
+
 	res = setup_media_encryption(session, session_media, remote, remote_stream);
 	if (!session->endpoint->media.rtp.encryption_optimistic && res) {
 		/* If optimistic encryption is disabled and crypto should have been enabled but was not
@@ -1315,7 +1377,9 @@ static int apply_negotiated_sdp_stream(struct ast_sip_session *session, struct a
 		return -1;
 	}
 	ast_channel_set_fd(session->channel, fdno, ast_rtp_instance_fd(session_media->rtp, 0));
-	ast_channel_set_fd(session->channel, fdno + 1, ast_rtp_instance_fd(session_media->rtp, 1));
+	if (!session->endpoint->media.rtcp_mux || !session_media->remote_rtcp_mux) {
+		ast_channel_set_fd(session->channel, fdno + 1, ast_rtp_instance_fd(session_media->rtp, 1));
+	}
 
 	/* If ICE support is enabled find all the needed attributes */
 	process_ice_attributes(session, session_media, remote, remote_stream);