[Asterisk-Dev] IAX2 Jitter Buffer questions

Andrew Kohlsmith akohlsmith-asterisk at benshaw.com
Tue Jan 20 08:07:41 MST 2004

This is going to be a kind of meandering email, it's mostly a brain dump of 
trying to understand what's going on.  I have been trying to help fix a 
problem with my one asterisk server.  Calls through Voicepulse are mostly 
fine but sometimes the jitter on my line causes the GSM call to sound like 
absolute shit.

My jitter buffer settings, from iax.conf:


(Old settings were dropcount=3 and maxexcessbuffer=100)

Now from reading the chan_iax2.c file it seems that the "jitterbuffer" 
command needs to be boolean yes/no/true/false/etc.  Other examples I've 
seen where it was set to a value must be incorrect since the funciton 
ast_true() is used to parse that particular parameter.

chan_iax2.c is rather confusing.  Two variables in particular: 
maxjitterbuffer and max_jitter_buffer.  it seems that the latter is the 
maximum excess jitter buffer.  Would a patch cleaning this up be 

Now back to the jitter buffer -- it seems that if jitterbuffer=yes that 
chan_iax2 will keep a running tab of the latency (I'm guessing through use 
of the undocumented pingtime parameter (and probably the undocumented 
lagrqtime parameter for trunked lines) -- is this right?)  and adjusting 
the delay in sending packets.

There is another undocumented parameter called lagrqtime that seems to only 
be used with trunked connections -- can anyone shed some light on these 

In the meantime I have set pingtime=1 in iax.conf (ping every 1s?) -- I'm 
unsure what else I can do try and keep the quality as high as possible.  My 
connection is pretty much unloaded (512kbps on a full T1) and I do have LLQ 
set up on *my* end of the T1...  I know it's not ideal but it's about as 
best I can do at this point.

How's my aim with the iax2 jitter buffer settings and attempt at 


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