[Linphone-users] get_current_send_ts and get_current_recv_ts goes out of sync

[Erno Szabados]

Hi,

I try to transfer packets using get_current_send_ts and get_current_recv_ts 
but the thing goes out of sync after a short while. 

I send packetized audio data and telephone events (not only DTMF), but the 
telephone events have no timestamp so I create a timestamp by 
rtp_session_get_current_send_ts. To receive these I use the timestamp created 
by get_current_recv_ts. ortp is set to scheduled and nonblocking mode. For 
testing purposes I also try to create audio packet timestamps by 
get_current_send. 

The receiver gets packets OK, but then the answer sent back (event packets) 
are discarded because the timestamp returned by get_current_send_ts (by 
receiver) is too old for the initiator. (sender)

I also try to transfer audio packets using get_current functions but after a 
while (from few secs to few minutes)
- the packet queue gets full (even though I read it) and old packets get 
discarded and/or
- the receiver starts to find packets too old and discards them.

Sometimes the receiver gets back to sync and returns packets again but
then later it loses sync again, and finally a fatal situation escalates:
the scheduler asks for too old packets which it cannot get because the message 
queue gets full and old packets are dropped.

I noticed that the size of the jitter buffer affects the time the packets 
start to lose. 0 ms means instant packet timing failure, 5 ms on my 1GHz 
Celeron sometimes make it for a few minutes, but increasing the jitter buffer 
size further does not guarantee safe packet arrival - only latency increases.
The network I use is of good quality w. 100 Mbit bandwidth and monitoring the 
UDP TX shows packet flow is OK with negligible packet loss.

TIA for any useful information on how to solve this.

Erno Szabados.

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