[SR-Users] Keep requests order

Greetings, I'm having some problems with keeping the order of the messages in Kamailio. In some cases i'm receiving an ACK for the first INVITE and immediately after that a RE-INVITE is sent by the client. What is happening is that the the ACK took double the time of the RE-INVITE to process and as a consequence, the RE-INVITE was relayed before the ACK. I have two questions : 1 - Is there a way to keep the order of the messages in a dialog, and if so, what are the downsides to it? 2 - The machine wasn't in a load state (only one concurrent call) and the ACK and the RE-INVITE should go roughly through the same processing methods and should take took the same time to be be relayed. What can be the reason for this? Best Regards, Duarte Rocha