1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +--------------------------------------------------------------+
  |                                                              |
  |                Data Sequence Number (8 octets)               |
  |                                                              |
  +--------------------------------------------------------------+
  |              Subflow Sequence Number (4 octets)              |
  +-------------------------------+------------------------------+
  |  Data-Level Length (2 octets) |        Zeros (2 octets)      |
  +-------------------------------+------------------------------+