[Asterisk-Users] Weird IAX trunking/7960/ILBC quality issue

[Steve Totaro]

> 
> Greetings all,
> 
> I've been doing some testing with a new client's voicemail system from
my
> asterisk box at home. I'm using a 7960 (alaw/ulaw) then an IAX2 link
> between
> my server and the client's server.
> 
> I've configured IAX settings at both ends as follows: jitterbuffer
> enabled,
> trunking enabled, ILBC/GSM allowed in that order. When listening to
the
> voice prompts from VoicemailMain at the client's asterisk I hear about
one
> word in three, very similar to a GSM mobile on the border of its
coverage.
> Disabling trunking appears to make no difference. Disabling the jitter
> buffer appears to solve the problem, but with a connection that's
often
> used
> for other things, this is undesirable as a long-term solution.
> 
> When I make the same call from a SIP device (GXP2000), the issue
> disappears
> entirely. But the same problem does not occur from the 7960 to a PSTN
> gateway (also via IAX2 with exactly the same settings).
> 
> To summarize:
> 7960 -> remote (ILBC + jitterbuffer) = quality problem
> SIP -> remote (ILBC + jitterbuffer) = no problem
> 7960 -> remote (ILBC no jitterbuffer) = no problem
> 
> I'm not sure what's to blame here - the 7960 or my IAX settings, or
where
> to
> begin looking for solutions.
> 
> Any thoughts?
> 
> Regards,
> 
> Chris
> --
> C.M. Bagnall, Director, Minotaur I.T. Limited
> This email is made from 100% recycled electrons
> 
> 

Jitterbuffer is to blame.