[sip-comm] OK response not received



I am using the Sip-Communicator with an asterisk server. Everything works
fine except that sometimes (quite randomly) the registration hangs in a
"TRYING" state until the application timeouts and goes to the "unregistered"

I checked out the logs from Asterisk and the final "OK" response is sent.
However after scanning my computer port I could see that the last message
that I receive is the "TRYING" response. So somehow the OK response never
reach my machine.

Has somebody experienced the same problem (and would have a way to solve
this) ?

Can it be dued to the fact that we are using the UDP protocol ?

An easy way to test this matter is to set the "REGISTRATION_EXPIRATION" to 2
seconds for example. Usually after a few minutes the Sip-Communicator

Thanks for your help.