osmux: Set Marker bit on osmux frame loss detected

Until this patch, we didn't notify in any way to the RTP reader when an
Osmux frame was lost. Instead, we updated the seq&timestamp as if there
was no lost, and as a result the RTP reader would only see a steady
increase of delay every time an osmux frame was lost.

As the batch_factor for the lost packet is unknown, we cannot assume any
number of amr payloads lost, and thus we cannot simply increment seq and
timestamp for a specific amount. Instead, the only viable solution seems
to set the M marker bit in the first rtp packet generated after a
non-consecutive osmux frame is received.

The implementation may act differently with the first generated RTP
packet based on the first osmux seq number used for the stream. In case
0 it's used as first osmux seq number, M will be set depending on
request from original RTP packet having the M bit set. If it's not 0,
the first RTP packer will unconditionally have the M bit. That's not an
issue because it's anyway expect for receiver to sync on the first
packet.

Related: OS#3185

Change-Id: I2efed6d726a1b8e77e686c7a5fe1940d3f4901a7

1 files changed, 1 insertions, 0 deletions

diff --git a/include/osmocom/netif/osmux.h b/include/osmocom/netif/osmux.h
index e8e2c67..dfed66a 100644
--- a/include/osmocom/netif/osmux.h
+++ b/include/osmocom/netif/osmux.h
@@ -80,6 +80,7 @@ struct osmux_out_handle {
 	uint16_t rtp_seq;
 	uint32_t rtp_timestamp;
 	uint32_t rtp_ssrc;
+	uint8_t osmux_seq_ack; /* Latest received seq num */
 	struct osmo_timer_list	timer;
 	struct llist_head list;
 	void (*tx_cb)(struct msgb *msg, void *data); /* Used defined rtp tx callback */