Description: This attribute defines the bit mask which is used in combination with the PhsField to define which bytes in header must be suppressed/restored by the sending or receiving device. Each bit of this bit mask corresponds to a byte in the PhsField, with the least significant bit corresponding to the first byte of the PhsField. Each bit of the bit mask specifies whether or not the corresponding byte should be suppressed in the packet. A bit value of '1' indicates that the byte should be suppressed by the sending device and restored by the receiving device. A bit value of '0' indicates that the byte should not be suppressed by the sending device or restored by the receiving device. If the bit mask does not contain a bit for each byte in the PhsField then the bit mask is extended with bit values of '1' to be the necessary length.