Initiator                                                   Responder
---------------------------------------------------------------------
          <new TCP connection is established by Initiator>

Stream Prefix|Length|non-ESP marker|IKE message -->
                                <-- Length|non-ESP marker|IKE message
Length|non-ESP marker|IKE message -->
                                <-- Length|non-ESP marker|IKE message

                                [...]
Length|ESP packet ->
                                                 <- Length|ESP packet