[Serusers] SIP+B2BUA

Hi all, I installs vovida B2BUA on linux with proxy server SER. B2BUA and SER work fine.Here has a problem. I uses messenger 4.7 and kphone as sip client. I establishs session by B2BUA and SER.But why can't I see UDP packet pass through B2BUA. (1) (4) messenger 4.7 ---------------------> SER ---------------------------> kphone | | (2) | | (3) | | B2BUA Thanks.