Richard Scobie wrote:
Is there a way to configure the IAX jitterbuffer to get the benefit of
trunktimestamps, while not having any jitterbuffering (reducing delay)?
My SVN asterisk systems use the following topologies:
1) PolycomSIP -> *1 ->IAX-> *2 -> H323 Gateway
2) PolycomSIP -> *1 ->IAX-> *3 -> Zap TDM400 Analog
3) H323 Gateway -> *2 ->IAX-> *3 -> Zap TDM400 Analog
In all the above, the primary jitter path is the IAX one and the codec
is Alaw all the way.
In an effort to reduce path delay and multiple jitterbuffering I have
configured the following:
On the basis that the Polycom IP500 phones have a decent jitterbuffer
built in, Asterisk 1 has jitterbuffer=no in iax.conf.
Asterisk 2 has the same setting as the H323 GW has it's own jitterbuffer.
Asterisk 3 has jitterbuffer=yes in iax.conf, to buffer the Zap
interface and provide PLC. I notice that zapata.conf has an entry
jitterbuffers=4 by default - is this a different one in which case
should it be turned off or is it setting parameters for the IAX JB?
There's a few points in here so far:
1) the new jitterbuffer and trunktimestamps are independent settings,
and have independent effect. You get the same effect with
trunktimestamps (correct pass-through of frame timestamps), whether you
use the jb or not.
2) The IAX jitterbuffer is disabled _by default_ (unless you use
"forcejitterbuffer"), when a call is bridged from an IAX channel to
another VoIP channel. So, you don't need to forcibly disable the jb in
your case, it should automatically be disabled: In your cases, it would
only ever be enabled on box "*3", when a call comes in from IAX, and
goes to zap.
3) Yes, the setting in zapata.conf is for 4 very small buffers, which
are different than than the IAX jb.
Looking at README.jitterbuffer:
"If you don't use trunktimestamps, there's lots of ways the
jitterbuffer can get confused because timestamps aren't necessarily
sent through the trunk correctly."
This presumably means that if I want to use IAX trunking effectively,
I have to enable the IAX JB on all Asterisks.
No, you don't need to enable the jitterbuffers anywhere except on the
last machine that's receiving VoIP (in your cases above, *3). I would
expect trunktimestamps would help you if you're using trunking for the
IAX links between your boxes.
-SteveK
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