On Wed, Apr 6, 2011 at 2:15 PM, Mark Sobkow <m.sobkow@marketelsystems.com> wrote:

We've tried several different softphones: Phoner (SIPPER stack), X-Lite,
and our internal M-Phone (I forget what SIP stack implementation that
uses, as I didn't write it.) All exhibit the same problem.

Our network admin insists it's not a network problem. As we hadn't had
this problem previously, I can't argue with him over it.

I'm a little unclear about what is supposed to be sending the ACK -- the
softphone, FreeSwitch, or our application code.

This is typical SIP traffic, so the UA sending the INVITE should be ACKing the appropriate responses from FS. In your case, FreeSWITCH sends a 200 OK several times, indicating that the phone has answered the INVITE. However, FS is not receiving the required ACK from the UA so it gives up and sends a BYE.

So, what Tony said is correct - for *some* reason the ACK is not making it back to FreeSWITCH. This is *not* a problem with FreeSWITCH, it's a problem on the network or with the originating UA.

Are you able to confirm that the UA is seeing the 200 OK from FreeSWITCH? That sounds like a reasonable first place to troubleshoot.

-MC