|--- SCHC ACK Header ---|- W=w1 -|...|----- W=wi ------|
+------+--------+-------+--------+...+--------+--------+------+-------+
|RuleID| W=b'w1 | C=b'0 | Bitmap |...| W=b'wi | Bitmap | b'00 |b'0-pad|
+------+--------+-------+--------+...+--------+--------+------+-------+
|3 bits| 2 bits | 1 bit | 7 bits |...| 2 bits | 7 bits |2 bits|