2 seconds delay lync freepbx

Dear all,
I have a strange issue. I have connected lync 2013 and freepbx 4.211.64-4 with sip trunk. I have an issue when i call from
freepbx extension to lync extension. While the lync etension answer the call in freepbx extension is still ringing for about 2 seconds and after 2 seconds the call is ok and both sides can hear each other. If i call from lync to freepbx everything is ok. If i select no nat in sip settings then the delay is more about 4 seconds, if i select route in sip settings then the delay is 2 seconds. I tried almost everything in trunk configuration in sip settings but i cannot fix this problem. Any help please?

reagrds
pantos

Finaly i found the problem by myself and resolve it. It was dns issue