asterisk users - Dec 2005 - IAX Jitterbuffer and trunking

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?

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.

Thanks,

Richard

Hi!
> 2) PolycomSIP -> *1 ->IAX-> *3 -> Zap TDM400 Analog
> 3) H323 Gateway -> *2 ->IAX-> *3 -> Zap TDM400 Analog
Here is what you want to enable jb for ZAP:
http://bugs.digium.com/view.php?id=3854

Cheers, Philipp

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