mgcp: add voice muxer support

This patch adds the voice muxer. You can use this to batch RTP
traffic to reduce bandwidth comsuption. Basically, osmux transforms
RTP flows to a compact batch format, that is later on decompacted
to its original form. Port UDP/1984 is used for the muxer traffic
between osmo-bsc_nat and osmo-bsc_mgcp (in the BSC side). This
feature depends on libosmo-netif, which contains the osmux core
support.

Osmux is requested on-demand via the MGCP CRCX/MDCX messages (using
the vendor-specific extension X-Osmux: on) coming from the BSC-NAT,
so you can selectively enable osmux per BSC from one the bsc-nat.cfg
file, so we have a centralized point to enable/disable osmux.

First thing you need to do is to accept requests to use Osmux,
this can be done from VTY interface of osmo-bsc_nat and
osmo-bsc_mgcp by adding the following line:

mgcp
  ...
  osmux on
  osmux batch-factor 4

This just initializes the osmux engine. You still have to specify
what BSC uses osmux from osmo-bsc_nat configuration file:

...
 bsc 1
  osmux on
 bsc 2
  ...
 bsc 3
  osmux on

In this case, bsc 1 and 3 should use osmux if possible, bsc 2 does
not have osmux enabled.

Thus, you can selectively enable osmux depending on the BSC, and
we have a centralized point for configuration from the bsc-nat to
enable osmux on demand, as suggested by Holger.

At this moment, this patch contains heavy debug logging for each
RTP packet that can be removed later to save cycles.

The RTP ssrc/seqnum/timestamp is randomly allocated for each MDCX that
is received to configure an endpoint.

1 files changed, 37 insertions, 5 deletions

diff --git a/openbsc/src/libmgcp/mgcp_protocol.c b/openbsc/src/libmgcp/mgcp_protocol.c
index 5c88c9dd3..1480acca3 100644
--- a/openbsc/src/libmgcp/mgcp_protocol.c
+++ b/openbsc/src/libmgcp/mgcp_protocol.c
@@ -236,7 +236,7 @@ static struct msgb *create_response_with_sdp(struct mgcp_endpoint *endp,
 		addr = endp->cfg->source_addr;
 
 	len = snprintf(sdp_record, sizeof(sdp_record) - 1,
-			"I: %u\n\n"
+			"I: %u%s\n\n"
 			"v=0\r\n"
 			"o=- %u 23 IN IP4 %s\r\n"
 			"c=IN IP4 %s\r\n"
@@ -244,7 +244,8 @@ static struct msgb *create_response_with_sdp(struct mgcp_endpoint *endp,
 			"m=audio %d RTP/AVP %d\r\n"
 			"a=rtpmap:%d %s\r\n"
 			"%s%s",
-			endp->ci, endp->ci, addr, addr,
+			endp->ci, endp->cfg->osmux && endp->osmux ? "\nX-Osmux: On" : "",
+			endp->ci, addr, addr,
 			endp->net_end.local_port, endp->bts_end.payload_type,
 			endp->bts_end.payload_type, endp->tcfg->audio_name,
 			fmtp_extra ? fmtp_extra : "", fmtp_extra ? "\r\n" : "");
@@ -759,6 +760,14 @@ static struct msgb *handle_create_con(struct mgcp_parse_data *p)
 		case 'M':
 			mode = (const char *) line + 3;
 			break;
+		case 'X':
+			if (strcmp("Osmux: on", line + 2) == 0 &&
+			    osmux_enable_endpoint(endp, OSMUX_ROLE_BSC) < 0) {
+				LOGP(DMGCP, LOGL_ERROR,
+				     "Could not activate osmux in endpoint %d\n",
+				     ENDPOINT_NUMBER(endp));
+			}
+			break;
 		case '\0':
 			have_sdp = 1;
 			goto mgcp_header_done;
@@ -859,8 +868,12 @@ mgcp_header_done:
 	if (p->cfg->change_cb)
 		p->cfg->change_cb(tcfg, ENDPOINT_NUMBER(endp), MGCP_ENDP_CRCX);
 
-	if (endp->conn_mode & MGCP_CONN_RECV_ONLY && tcfg->keepalive_interval != 0)
-		mgcp_send_dummy(endp);
+	if (endp->conn_mode & MGCP_CONN_RECV_ONLY && tcfg->keepalive_interval != 0) {
+		if (endp->osmux)
+			osmux_send_dummy(endp);
+		else
+			mgcp_send_dummy(endp);
+	}
 
 	create_transcoder(endp);
 	return create_response_with_sdp(endp, "CRCX", p->trans);
@@ -874,7 +887,7 @@ static struct msgb *handle_modify_con(struct mgcp_parse_data *p)
 {
 	struct mgcp_endpoint *endp = p->endp;
 	int error_code = 500;
-	int silent = 0;
+	int silent = 0, osmux = 0;
 	char *line;
 	const char *local_options = NULL;
 
@@ -909,6 +922,10 @@ static struct msgb *handle_modify_con(struct mgcp_parse_data *p)
 			}
 			endp->orig_mode = endp->conn_mode;
 			break;
+		case 'X':
+			if (strcmp("Osmux: on", line + 2) == 0)
+				osmux = 1;
+			break;
 		case 'Z':
 			silent = strcmp("noanswer", line + 3) == 0;
 			break;
@@ -926,6 +943,21 @@ static struct msgb *handle_modify_con(struct mgcp_parse_data *p)
 		}
 	}
 
+	/* Re-enable Osmux if we receive a MDCX, we have to set up a new
+	 * RTP flow: this generates a randomly allocated RTP SSRC and sequence
+	 * number.
+	 */
+	if (osmux) {
+		if (osmux_enable_endpoint(endp, OSMUX_ROLE_BSC) < 0) {
+			LOGP(DMGCP, LOGL_ERROR,
+			     "Could not update osmux in endpoint %d\n",
+			     ENDPOINT_NUMBER(endp));
+		}
+		LOGP(DMGCP, LOGL_NOTICE,
+		     "Re-enabling osmux in endpoint %d, we got updated\n",
+		     ENDPOINT_NUMBER(endp));
+	}
+
 	set_local_cx_options(endp->tcfg->endpoints, &endp->local_options,
 			     local_options);