|--- SCHC ACK Header ----|--------      Bitmap     --------|
         |-- T --|-M-| 1 |
+-- ... -+- ... -+---+---+---------------------------------+
| RuleID |  DTag | W |C=0|1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1|
+-- ... -+- ... -+---+---+---------------------------------+
       next L2 Word boundary ->|