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List:       sems
Subject:    Re: [Sems] Sems strange-random PLC
From:       Stefan Sayer <stefan.sayer () iptego ! com>
Date:       2009-03-24 17:52:36
Message-ID: 49C91DE4.5050303 () iptego ! com
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Hello,


o ?????????? [03/18/09 17:07]:
> Greetings!
> 
> Recently there was a problem with voice through SEMS, as B2BUA. I'm
> using my own module for SEMS, but the problem is repeated in the original modules \
> SEMS (eg serviceline). The problem was that after some random time intervals and \
> not at each voice conversation arose artifacts: the phrase duplicated, sometimes in \
> that moment there was only one-sided audibility. Suspicion for the PLC, but the \
> channel is wide and stable ping to the server 1ms, and verified at the time of \
> voice distortion. Dedicated firewall was disabled, the scheme has been used only \
> sems, openser and two UA. An example of distortion, you can listen here: \
> http://www.voiptroubleshooter.com/sound_files/male1_2_sil_20ms_5.wav (or other \
> examples of this and similar problems \
> http://www.voiptroubleshooter.com/problems/plc.html). 
> I made various attempts to remedy the situation, disable all processing in the PLC \
> source sems, tried different modes of channels PLAYOUT_BUFFER. 
...
> It seems to me that the problem was to use various channels to `playout_buffer` \
> caller and the callee, but with `simple_playout` (which appears by default) the \
> problem was. Perhaps disable dtmf as assist. Other things to note that when using \
> jitter_buffer artifacts appear more frequently and consistently, but gently.
 >
 > It would like to know what is still the case, and in which direction 
to look. Thanks in advance!

simple_playout does not at all buffer the audio it receives. This means 
that when the audio for a packet that is to be sent is read and on the 
input audio for that exact time has not yet arrived, it sends empty 
audio. So for any application where the audio is to be sent through SEMS 
in realtime, you need to use a buffering playout_buffer. My 
recommendation is ADAPTIVE_PLAYOUT, because it minimizes the total 
delay, but if you know that you have only little jitter or a bounded 
amount of jitter, you may have better quality with JB_PLAYOUT.

Stefan





> 
> 
> 

-- 
Stefan Sayer
VoIP Services

stefan.sayer@iptego.com
www.iptego.com

IPTEGO GmbH
Wittenbergplatz 1
10789 Berlin
Germany

Amtsgericht Charlottenburg, HRB 101010
Geschaeftsfuehrer: Alexander Hoffmann
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