asterisk users - Dec 2006 - asterisk -1.4 with sip communicator

Hi all,
Thanks for your reply,
I'm using sip communicator(in java that is intergrated with one ERP ) and
asterisk is interfaced with this.
i'm able to make calls between pingtel and Voip user,
and also i can able to make call from Sip communicator to pingtel or Voip
phone.
but now i'm can't make calls between 2 sip communicator.. it mean i can
able to make a call and receive.. but i can't hear the  other person voice.
but my voice he can able to hear...
some times i can't able to make (Between 2 sip comm.)call also...

I'm using asterisk 1.4 versoin...

could u tell me any suggestions..

Regards,
nsthi
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