Description: Downstream subcarriers mask. A bitmap of 512 bits that allows masking up to 512 downstream subcarriers. If bit i (0 <= i < NSCds) is set to '1', the respective downstream subcarrier is masked, and if set to '0', the respective subcarrier is unmasked. Note that there should always be unmasked subcarriers (i.e.,this object cannot be all 1's). Also note that if NSCds < 512, all bits i(NSCds < i <= 512) should be set to '1'.

NSCds is the highest subcarrier index that can be transmitted in the downstream direction. For G.992.3, G.992.4, and G.992.5, it is defined in the corresponding Recommendations. For G.992.1, NSCds = 256 and for G.992.2, NSCds = 128.