Hi, I run into a weird situation. My media gateay handle voice call with 2 different RTP ports for send & receive Here is what happened. (ps: both gateway and FS are all on public IP, no NAT involved) 1. Incoming call INVITE from gateway to FS Connection Information (c): IN IP4 100.100.100.100 (This is my media gateway IP address) Media Description, name and address (m): audio 5294 RTP/AVP 18 0 4 2. FS response with session progress with media information Connection Information (c): IN IP4 200.200.200.200 Media Description, name and address (m): audio 22428 RTP/AVP 0 3. I start to see some RTP traffic exchange between FS and GW from FS (22428) --> GW (5294) from GW (5292) --> FS (22428) please note: the GW use two DIFFERENT PORT for RTP, one for sending and one for receiving 4. For a while (about 5 secs, I think) The RTP flow change on FS side to become, (there is no RTCP packet during the time) from FS (22428) --> GW (5292) from GW (5292) --> FS (22428) In other word, the FS now sending RTP to 5292 instead of 5294 (which was intended in INVITE SDP message) And, of course, I cannot hear the voice on GW side after this. Anyone encounter this before? Are there any paramaters that might involved in this auto changing RTP port behavior of FS? Any direction for me is appreciated, I will play around with this, and post back my result to community. Dan Lan