[Asterisk-Users] iaxtel and jitterbuffer

[Andrew Kohlsmith]

On Saturday 28 August 2004 23:01, Michael George wrote:
> It's a PII 266 (okay, not the fatest system) with 192MB RAM.  X is not
> running and the Framebuffer has been turned off in /boot/grum/menu.lst.  I
> have disabled all the servers except for sshd.  I have the latest source
> from CVS HEAD as of about 30min ago.

Should be fine.  I ran * on a P90 for a while; it did everything I needed 
except iLBC.  :-)

> There is no Zap card in this sytem.  The only phone on it is a SIP phone.
> With it I dial in to digium's 1-700 number.  The audio is better, but still
> choppy and unacceptible.

Is your SIP phone doing any kind of silence suppression?  It must be turned 
off because asterisk takes its timing from the RTP stream and if the phone's 
not transmitting frames continuously you'll get shitty audio.

Note that latest CVS HEAD looks like they're making provisions for self-timing 
but without a stable clock source it's unlikely to help you.  There are 
ztdummy modules which use the RTC or certain brands of USB controller to 
provide adequate timing but ideally you want some kind of Zaptel hardware in 
there providing a 1000Hz interrupt.

Also -- make sure your uplink is acceptable.  First test: make sure there is 
nothing plugged into your upstream except for your asterisk box and the 
phone.  Some routers are known to play silly bugger with your packets which 
naturally wreaks havoc with asterisk.  :-)

> So even with X11 eliminated the sound is still bad to Digium.  I tried
> another's 1700 number, and it sounded the same, so it's not something
> unique to digium and me.

Perhaps something to do with your upstream or connection to IAXtel.  That's 
why I'm recommending having nothing but asterisk and the phone on the 
connection, at least until we nail down what the poor audio's being caused 
by.

> Would IAX/GSM be so sensitive to half-duplex that I cannot expect it to
> work with my ISP only giving me 1/2 duplex service?

It has nothing to do with IAX or GSM. Stop blaming them.  My upstream is half 
duplex as well (pretty much anyone on DSL or cable is on a half duplex 
connection whether they realize it or not).  

There are many, many people using asterisk every day for long distance and in 
environments where audio quality is crucial.  Let's stop blaming asterisk and 
take a good hard look at what's happenning, shall we?

-A.