FR & EFR: support TW-TS-001 output via rtp fr-efr-format vty optionfalconia/rtp_traulike

Themyscira Wireless Technical Specification TW-TS-001 defines
an alternative RTP payload format for FR and EFR codecs specifically
for use within a GSM RAN, replicating the full functionality and
semantics of T1/E1 Abis.  Add support for emitting this RTP format
instead of standard TS 101 318 by way of a vty config option.

Change-Id: I8536256101ca669ab416d4f2e91b576430c930fc

4 files changed, 71 insertions, 5 deletions

diff --git a/include/osmo-bts/bts.h b/include/osmo-bts/bts.h
index 62017d78..00fbdf3b 100644
--- a/include/osmo-bts/bts.h
+++ b/include/osmo-bts/bts.h
@@ -301,6 +301,7 @@ struct gsm_bts {
 
 	bool rtp_nogaps_mode;		/* emit RTP stream without any gaps */
 	bool use_ul_ecu;		/* "rtp internal-uplink-ecu" option */
+	bool emit_fr_twts001;
 	bool emit_hr_rfc5993;
 
 	struct {
diff --git a/src/common/l1sap.c b/src/common/l1sap.c
index 7f61f2cd..0e3b9f23 100644
--- a/src/common/l1sap.c
+++ b/src/common/l1sap.c
@@ -1813,21 +1813,64 @@ static void send_rtp_rfc5993(struct gsm_lchan *lchan, uint32_t fn,
 	send_ul_rtp_packet(lchan, fn, msg->data, msg->len);
 }
 
+/* a helper function for emitting FR/EFR UL in TW-TS-001 format */
+static void send_rtp_twts001(struct gsm_lchan *lchan, uint32_t fn,
+			     struct msgb *msg, bool good_frame)
+{
+	uint8_t teh;
+	bool send_frame;
+
+	if (msg->len == GSM_FR_BYTES || msg->len == GSM_EFR_BYTES) {
+		if (good_frame)
+			teh = 0xE0;
+		else
+			teh = 0xE2;
+		send_frame = true;
+	} else {
+		teh = 0xE6;
+		send_frame = false;
+	}
+	/* always set DTXd and TAF bits */
+	if (lchan->ts->trx->bts->dtxd)
+		teh |= 0x08;
+	if (fn % 104 == 52)
+		teh |= 0x01;
+	if (send_frame) {
+		msgb_push_u8(msg, teh);
+		send_ul_rtp_packet(lchan, fn, msg->data, msg->len);
+	} else {
+		send_ul_rtp_packet(lchan, fn, &teh, 1);
+	}
+}
+
 /* A helper function for l1sap_tch_ind(): handling BFI
  *
- * Please note that we pass the msgb to this function, even though it is
- * currently not used.  This msgb passing is a provision for adding
- * support for TRAU-UL-like RTP payload formats like TW-TS-001 that allow
- * indicating BFI along with deemed-bad frame data bits, just like
+ * Please note that the msgb passed to this function is used only when
+ * the BTS is configured to emit FR & EFR UL in TW-TS-001 format,
+ * indicating BFI along with deemed-bad frame data bits just like
  * GSM 08.60 and 08.61 TRAU-UL frames.
  */
 static void tch_ul_bfi_handler(struct gsm_lchan *lchan,
 			       const struct gsm_time *g_time, struct msgb *msg)
 {
+	struct gsm_bts *bts = lchan->ts->trx->bts;
 	uint32_t fn = g_time->fn;
 	uint8_t ecu_out[GSM_FR_BYTES];
 	int rc;
 
+	/* Are we on TCH/FS or TCH/EFS, configured to emit TW-TS-001 extended
+	 * RTP format?  If so, emit BFI per that spec.  The placement of
+	 * this check before the ECU is intentional: the modes of TW-TS-001
+	 * UL output (closely replicating the classic GSM architecture in which
+	 * a BTS never applies an ECU to its UL output) and internal UL ECU
+	 * are mutually exclusive. */
+	if (bts->emit_fr_twts001 && lchan->type == GSM_LCHAN_TCH_F &&
+	    (lchan->tch_mode == GSM48_CMODE_SPEECH_V1 ||
+	     lchan->tch_mode == GSM48_CMODE_SPEECH_EFR)) {
+		send_rtp_twts001(lchan, fn, msg, false);
+		return;
+	}
+
 	/* Are we applying an ECU to this uplink, and are we in a state
 	 * (not DTX pause) where we emit ECU output? */
 	if (lchan->ecu_state && !osmo_ecu_is_dtx_pause(lchan->ecu_state)) {
@@ -1842,7 +1885,7 @@ static void tch_ul_bfi_handler(struct gsm_lchan *lchan,
 
 	/* Are we in rtp continuous-streaming special mode? If so, send out
 	 * a BFI packet as zero-length RTP payload. */
-	if (lchan->ts->trx->bts->rtp_nogaps_mode) {
+	if (bts->rtp_nogaps_mode) {
 		send_ul_rtp_packet(lchan, fn, NULL, 0);
 		return;
 	}
@@ -1903,6 +1946,11 @@ static int l1sap_tch_ind(struct gsm_bts_trx *trx, struct osmo_phsap_prim *l1sap,
 		if (bts->emit_hr_rfc5993 && lchan->type == GSM_LCHAN_TCH_H &&
 		    lchan->tch_mode == GSM48_CMODE_SPEECH_V1)
 			send_rtp_rfc5993(lchan, fn, msg);
+		else if (bts->emit_fr_twts001 &&
+			 lchan->type == GSM_LCHAN_TCH_F &&
+			 (lchan->tch_mode == GSM48_CMODE_SPEECH_V1 ||
+			  lchan->tch_mode == GSM48_CMODE_SPEECH_EFR))
+			send_rtp_twts001(lchan, fn, msg, true);
 		else
 			send_ul_rtp_packet(lchan, fn, msg->data, msg->len);
 		/* if loopback is enabled, also queue received RTP data */
diff --git a/src/common/vty.c b/src/common/vty.c
index 0fc9007d..3dae2e09 100644
--- a/src/common/vty.c
+++ b/src/common/vty.c
@@ -420,6 +420,8 @@ static void config_write_bts_single(struct vty *vty, const struct gsm_bts *bts)
 		vty_out(vty, " rtp continuous-streaming%s", VTY_NEWLINE);
 	vty_out(vty, " %srtp internal-uplink-ecu%s",
 		bts->use_ul_ecu ? "" : "no ", VTY_NEWLINE);
+	vty_out(vty, " rtp fr-efr-format %s%s",
+		bts->emit_fr_twts001 ? "tw-ts-001" : "ts101318", VTY_NEWLINE);
 	vty_out(vty, " rtp hr-format %s%s",
 		bts->emit_hr_rfc5993 ? "rfc5993" : "ts101318", VTY_NEWLINE);
 	vty_out(vty, " paging queue-size %u%s", paging_get_queue_max(bts->paging_state),
@@ -823,6 +825,19 @@ DEFUN(cfg_bts_no_rtp_int_ul_ecu,
 	return CMD_SUCCESS;
 }
 
+DEFUN_ATTR(cfg_bts_rtp_fr_format,
+	   cfg_bts_rtp_fr_format_cmd,
+	   "rtp fr-efr-format (ts101318|tw-ts-001)",
+	   RTP_STR "FR & EFR output format\n"
+	   "TS 101 318 (standard)\n" "TW-TS-001 (non-standard)\n",
+	   CMD_ATTR_IMMEDIATE)
+{
+	struct gsm_bts *bts = vty->index;
+
+	bts->emit_fr_twts001 = !strcmp(argv[0], "tw-ts-001");
+	return CMD_SUCCESS;
+}
+
 DEFUN_ATTR(cfg_bts_rtp_hr_format,
 	   cfg_bts_rtp_hr_format_cmd,
 	   "rtp hr-format (rfc5993|ts101318)",
@@ -2726,6 +2741,7 @@ int bts_vty_init(void *ctx)
 	install_element(BTS_NODE, &cfg_bts_no_rtp_cont_stream_cmd);
 	install_element(BTS_NODE, &cfg_bts_rtp_int_ul_ecu_cmd);
 	install_element(BTS_NODE, &cfg_bts_no_rtp_int_ul_ecu_cmd);
+	install_element(BTS_NODE, &cfg_bts_rtp_fr_format_cmd);
 	install_element(BTS_NODE, &cfg_bts_rtp_hr_format_cmd);
 	install_element(BTS_NODE, &cfg_bts_band_cmd);
 	install_element(BTS_NODE, &cfg_description_cmd);
diff --git a/tests/osmo-bts.vty b/tests/osmo-bts.vty
index c4732344..86f140e1 100644
--- a/tests/osmo-bts.vty
+++ b/tests/osmo-bts.vty
@@ -237,6 +237,7 @@ OsmoBTS(bts)# list
   no rtp continuous-streaming
   rtp internal-uplink-ecu
   no rtp internal-uplink-ecu
+  rtp fr-efr-format (ts101318|tw-ts-001)
   rtp hr-format (rfc5993|ts101318)
   band (450|GSM450|480|GSM480|750|GSM750|810|GSM810|850|GSM850|900|GSM900|1800|DCS1800|1900|PCS1900)
   description .TEXT