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, 44 insertions, 0 deletions

diff --git a/openbsc/src/libmgcp/mgcp_vty.c b/openbsc/src/libmgcp/mgcp_vty.c
index 953d34b67..e9b7d1227 100644
--- a/openbsc/src/libmgcp/mgcp_vty.c
+++ b/openbsc/src/libmgcp/mgcp_vty.c
@@ -129,6 +129,10 @@ static int config_write_mgcp(struct vty *vty)
 		vty_out(vty, "  rtp transcoder-range %u %u%s",
 			g_cfg->transcoder_ports.range_start, g_cfg->transcoder_ports.range_end, VTY_NEWLINE);
 	vty_out(vty, "  transcoder-remote-base %u%s", g_cfg->transcoder_remote_base, VTY_NEWLINE);
+	vty_out(vty, "  osmux %s%s",
+		g_cfg->osmux == 1 ? "on" : "off", VTY_NEWLINE);
+	vty_out(vty, "  osmux batch-factor %d%s",
+		g_cfg->osmux_batch, VTY_NEWLINE);
 
 	return CMD_SUCCESS;
 }
@@ -434,6 +438,10 @@ DEFUN(cfg_mgcp_loop,
       "Loop audio for all endpoints on main trunk\n"
       "Don't Loop\n" "Loop\n")
 {
+	if (g_cfg->osmux) {
+		vty_out(vty, "Cannot use `loop' with `osmux'.%s", VTY_NEWLINE);
+		return CMD_WARNING;
+	}
 	g_cfg->trunk.audio_loop = atoi(argv[0]);
 	return CMD_SUCCESS;
 }
@@ -726,6 +734,10 @@ DEFUN(cfg_trunk_loop,
 {
 	struct mgcp_trunk_config *trunk = vty->index;
 
+	if (g_cfg->osmux) {
+		vty_out(vty, "Cannot use `loop' with `osmux'.%s", VTY_NEWLINE);
+		return CMD_WARNING;
+	}
 	trunk->audio_loop = atoi(argv[0]);
 	return CMD_SUCCESS;
 }
@@ -1056,6 +1068,33 @@ DEFUN(reset_all_endp, reset_all_endp_cmd,
 	return CMD_SUCCESS;
 }
 
+#define OSMUX_STR "RTP multiplexing"
+DEFUN(cfg_mgcp_osmux,
+      cfg_mgcp_osmux_cmd,
+      "osmux (on|off)",
+       OSMUX_STR "Enable OSMUX\n" "Disable OSMUX\n")
+{
+	if (strcmp(argv[0], "on") == 0) {
+		g_cfg->osmux = 1;
+		if (g_cfg->trunk.audio_loop) {
+			vty_out(vty, "Cannot use `loop' with `osmux'.%s",
+				VTY_NEWLINE);
+			return CMD_WARNING;
+		}
+	} else if (strcmp(argv[0], "off") == 0)
+		g_cfg->osmux = 0;
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_mgcp_osmux_batch_factor,
+      cfg_mgcp_osmux_batch_factor_cmd,
+      "osmux batch-factor <1-4>",
+      OSMUX_STR "Batching factor\n" "Number of messages in the batch\n")
+{
+	g_cfg->osmux_batch = atoi(argv[0]);
+	return CMD_SUCCESS;
+}
 
 int mgcp_vty_init(void)
 {
@@ -1108,6 +1147,8 @@ int mgcp_vty_init(void)
 	install_element(MGCP_NODE, &cfg_mgcp_sdp_fmtp_extra_cmd);
 	install_element(MGCP_NODE, &cfg_mgcp_sdp_payload_send_ptime_cmd);
 	install_element(MGCP_NODE, &cfg_mgcp_no_sdp_payload_send_ptime_cmd);
+	install_element(MGCP_NODE, &cfg_mgcp_osmux_cmd);
+	install_element(MGCP_NODE, &cfg_mgcp_osmux_batch_factor_cmd);
 
 	install_element(MGCP_NODE, &cfg_mgcp_trunk_cmd);
 	install_node(&trunk_node, config_write_trunk);
@@ -1203,6 +1244,9 @@ int mgcp_parse_config(const char *config_file, struct mgcp_config *cfg,
 	int rc;
 	struct mgcp_trunk_config *trunk;
 
+	/* Default to 4 messages */
+	cfg->osmux_batch = 4;
+
 	g_cfg = cfg;
 	rc = vty_read_config_file(config_file, NULL);
 	if (rc < 0) {