[asterisk-dev] Jitter Buffer

[Martin Vít]

Slav Klenov wrote:
> Pavel Jerek, Martin Vit: The jitterbuffer should work for all cases, 
> however this doesn't stands for the IAX channel (from and to). The IAX 
> channel has its own jb (newjb by stevek). You can disable it setting 
> jitterbuffer=no in iax.conf, but in this case you will have the very 
> old iax2 jitterbuffer, which is hardcoded in chan_iax2.c and cannot be 
> disabled by configuration. Thats why I (and russell, when ported it to 
> trunk) omitted to include jb code in chan_iax2.c - you just can *not* 
> have jitterbuffer when doing [some chan <-> Asterisk <-> IAX chan] in 
> both directions! nor any generic jb (jbenable, jbforce, ...) 
> configuration properties are read from iax.conf - IAX cannot enable 
> the use of generic jb for its end and IAX cannot provide generic 
> timestamp information (in struct ast_frame) to be used for dejittering 
> on the other channel's end. This 
> http://bugs.digium.com/view.php?id=8189 bug report seems very strange 
> to me - it is not supposed the generic jb to work in this case at all 
> (no matter what settings you have).
I would clarify this bug (8189).
Consider this scenario (ilbc)SIP -> * -> ZAP. I've traced how 
translators are prepared for this: (ilbc)SIP -> ilbctoslin -> jitter 
buffer -> asterisk bridge -> write Zap (translation is done BEFORE 
dejjitering). The problem is when several frames come from SIP RTP very 
fast (because of delay followed by burst packets). If i understnad 
asterisk translator structures, there is one outbuffer used within this 
translator where translated frames are stored. but it is not clear to me 
if there is possible race condition and frames could overwrite this 
buffer or if incoming RTP packets are passed or not passed concurently 
to translator.

If I change translator path in ast_bridge to this: (ilbc)SIP -> jitter 
buffer -> asterisk bridge -> ilbctoslin write Zap everything is correct 
(translation is done AFTER dejittering)


>
> Slav
>
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-- 
Martin Vít
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http://www.vasesit.cz/
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