[PATCH 5/9] Add handling of BFI (Bad Frame Indicatior) of received TRAU frames

[Andreas Eversberg]

If a bad TRAU frame is received, it is forwarded to MNCC application
as GSM_BAD_FRAME. The application can now handle the GAP of missing
audio. (e.g. by extrapolation)

If TRAU frames are forwarded via RTP, bad frames are dropped, but frame
counter and timestamp of RTP sender state is incremented.
---
 openbsc/src/libtrau/rtp_proxy.c | 15 ++++++++++++++-
 openbsc/src/libtrau/trau_mux.c  |  5 ++++-
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/openbsc/src/libtrau/rtp_proxy.c b/openbsc/src/libtrau/rtp_proxy.c
index 9c16a95..22d135c 100644
--- a/openbsc/src/libtrau/rtp_proxy.c
+++ b/openbsc/src/libtrau/rtp_proxy.c
@@ -245,7 +245,7 @@ int rtp_send_frame(struct rtp_socket *rs, struct gsm_data_frame *frame)
 	int payload_type;
 	int payload_len;
 	int duration; /* in samples */
-	int is_amr = 0;
+	int is_amr = 0, is_bfi = 0;
 
 	if (rs->tx_action != RTP_SEND_DOWNSTREAM) {
 		/* initialize sequences */
@@ -277,6 +277,12 @@ int rtp_send_frame(struct rtp_socket *rs, struct gsm_data_frame *frame)
 		duration = RTP_GSM_DURATION;
 		is_amr = 1;
 		break;
+	case GSM_BAD_FRAME:
+		payload_type = 0;
+		payload_len = 0;
+		duration = RTP_GSM_DURATION;
+		is_bfi = 1;
+		break;
 	default:
 		DEBUGPC(DLMUX, "unsupported message type %d\n",
 			frame->msg_type);
@@ -304,6 +310,13 @@ int rtp_send_frame(struct rtp_socket *rs, struct gsm_data_frame *frame)
 		}
 	}
 
+	if (is_bfi) {
+		/* In case of a bad frame, just count and drop packt. */
+		rs->transmit.timestamp += duration;
+		rs->transmit.sequence++;
+		return 0;
+	}
+
 	msg = msgb_alloc(sizeof(struct rtp_hdr) + payload_len, "RTP-GSM-FULL");
 	if (!msg)
 		return -ENOMEM;
diff --git a/openbsc/src/libtrau/trau_mux.c b/openbsc/src/libtrau/trau_mux.c
index fd1895f..bb513cc 100644
--- a/openbsc/src/libtrau/trau_mux.c
+++ b/openbsc/src/libtrau/trau_mux.c
@@ -242,7 +242,10 @@ struct msgb *trau_decode_fr(uint32_t callref,
 		i++;
 		j++;
 	}
-	frame->msg_type = GSM_TCHF_FRAME;
+	if (tf->c_bits[11]) /* BFI */
+		frame->msg_type = GSM_BAD_FRAME;
+	else
+		frame->msg_type = GSM_TCHF_FRAME;
 	frame->callref = callref;
 	msgb_put(msg, sizeof(struct gsm_data_frame) + 33);
 
-- 
1.8.1.5