[asterisk-users] One way choppy sound

[Yelson Vivas]

Hi Guys
I'm conecting 2 astersk servers using this arquitecture

(Ext softphone)<==sip==>(asterisk 1)<====iax2 trunk====>(asterisk 2) 
<===alaw==>(pstn)

If i call from the Ext  to the asterisk 2 the sound is perfect, but  
if i call from Ext to the pstn, i can hear perfect but they tell me  
that sound really choppy, i tried using several codecs (same problem)  
but  i don't understand why the sound is bad in only one way.
Any sugestions to solve it more than welcome
Thanks
Yelson