Hello,

you are probably just sending the BYE to the wrong contact. The 200 OK didn't come from your Kamailio but from the server where the request was dispatched to. So you have to use the URI from Contact header as your new Request URI. (This is true already for the ACK after the 200 OK was received.)

You have to change the sipp xml scenario file to
- extract the contact header and routes from the 200 OK
- include those information in every packet sent after the 200 OK.

Keywords: [next_url], [routes] and "rrs" attribute in the recv command.
Help: http://sipp.sourceforge.net/doc/reference.html#UAC

So the BYE should look like this:

      BYE [next_url] SIP/2.0
      [routes]
      Via: SIP/2.0/[transport] [local_ip]:[local_port];branch=[branch]
      From: sipp <sip:sipp@loicchabert.fr>;tag=[pid]SIPpTag00[call_number]
      To: sut <sip:[service]@[remote_ip]:[remote_port]>[peer_tag_param]
      Call-ID: [call_id]
      CSeq: 2 BYE
      Contact: sip:sipp@[local_ip]:[local_port]
      Max-Forwards: 70
      Subject: Performance Test
      Content-Length: 0

Hope that helps.

Best Regards,
Sebastian