TCP Connection Problem

Hi once more,

I 've done a little bit more investigation ,and i found out that the messagesa
are never send over TCP.I first realized that both requests and responses were
actually transported by udp.Then i tryed to create only a tcp provider but i
got the following exception:

javax.sip.TransactionUnavailableException: Could not resolve next hop or
listening point unavailable! 
	at
gov.nist.javax.sip.SipProviderImpl.getNewClientTransaction(SipProviderImpl.java:344)
	at sip_test.sendMessage(sip_test.java:228)
	at sip_test.main(sip_test.java:251)

So i can imagine that the requests were never transmitted over tcp ,but always
on udp.Is there a reason why this is happenning.It could be that something is
wrong with my systems settings and i cannot create tcp connections?

Thanks for your time , Michael