Juha Heinanen writes:
it does not have Supported: outbound, but there is ;ob param in contact.
this looks like bug in pjsip, because according to outbound rfc 5626:
4.3. Sending Non-REGISTER Requests
... UAs that support this specification SHOULD include the outbound option tag in a Supported header field in a request that is not a REGISTER request.
in my opinion, outbound module should check Supported: outbound and not just believe ;ob param.
perhaps there is another bug in pjsip, because it is not using the same flow for ack as it used for invite.
-- juha