initiator                                                    listener
    |                                                           |
    |    S  0(20) <MP_CAPABLE>, <TFO cookie>                    |
    | --------------------------------------------------------> |
    |                                                           |
    |    S. 0(0) ack 21 <MP_CAPABLE>                            |
    | <-------------------------------------------------------- |
    |                                                           |
    |    .  1(100) ack 21 <DSS ack=1 seq=1 ssn=1 dlen=100>      |
    | <-------------------------------------------------------- |
    |                                                           |
    |    .  21(0) ack 1 <MP_CAPABLE>                            |
    | --------------------------------------------------------> |
    |                                                           |
    |    .  21(20) ack 101 <DSS ack=101 seq=1 ssn=1 dlen=20>    |
    | --------------------------------------------------------> |
    |                                                           |