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