asterisk users - Dec 2005 - provu 2100 videophone and asterisk

Hi,
   I'm trying the provu 2100 videophone for videocalling. Point-to-point
they are wonderful.
Now I'm trying to use Asterisk 1.0.9 with them. The audio call is working
but I'm unable to do a correct video call. My configuration is:
	VideoPhone -- Asterisk -- IAX2 -- Asterisk -- VideoPhone

I tried with H216 and H263. This is my sip.conf file:

[Provu] 
type=friend 
context=default             
callerid=Provukkk        
username=Provu23      
videosupport=yes
secret=test                
host=dynamic
nat=no                             
canreinvite=yes                 
dtmfmode=rfc2833         
incominglimit=1                 
mailbox=411@default     
disallow=all                     
allow=alaw
allow=h261
allow=h263
allow=g723.1                   

regards
gianrico fichera