IAX2 performance : Ring twice and hang-up

Hello,

I have configured a IAX2 to a VOIP provider. The VOIP provider seems to be far away because it takes a long time in order to start ringing.

The problem is that after start ringing, it just ring twice and then it hang up, then after a few seconds it redial again (we are using dial from a2billing with timeout of 100) and this time it works fine. Which one could be the reason of this hang-up after twice ringing? here is my IAX.CONF

[general]
bindport = 4569 ; Port to bind to (IAX is 4569)
bindaddr = 0.0.0.0 ; Address to bind to (all addresses on machine)

delayreject=yes

disallow=all
allow=ilbc

jitterbuffer=yes
maxjitterbuffer=800 ; Antes con maxjitterbuffer=1000
forcejitterbuffer=no
maxjitterinterps=10
resyncthreshold=-1

tos=throughput

Thanks
Jorge