|--- SCHC ACK Header --|- W=w1 -|...|---- W=wi -----|
         |--T-|---M--|-1-|        |...|---M--|        |---M--|
  +------+----+------+---+--------+...+------+--------+------+~~~~~+
  |RuleID|DTag| W=w1 |C=0| Bitmap |...| W=wi | Bitmap |00..00| pad |
  +------+----+------+---+--------+...+------+--------+------+~~~~~+
                            next L2 Word boundary ->|<-- L2 Word ->|