Audio cant be heared

Hi

I have a problem in hearing voice from an extension

When i make the call from the extension audio cant be heared, but when i dial from asterisk itself audio is heared.
In both the sessions
sip sessions gets established

MY config files
in sip.conf file
[general]
nat = yes
externip=xxx.xxx.xxx.xxx
localip= 255.255.255.0

[ITSPprovider]
type= friend
fromuser=*********
fromdomain=***.**..***
secret=

disallow=all
allow = alaw
allow = ulaw
allow = ilbc
nat = yes
externip = ***.***.***.***(same as in general)

[222]
type = friend
fromuser=222
secret=***
disallow=all
allow = alaw
allow = ulaw
allow = ilbc
nat = yes
externip = ***.***.***.***(same as in general)

In extensions.conf
[provider]
exten => _0.,1,Dial(${EXTEN:1}@ITSPProvider,Ttr)

Please help

Regards
Dinesh