The SNR Margin per sub-carrier, expressing the ratio between the received signal power and received noise power per subscriber. It is an array of 512 octets, designed for supporting up to 512 (downstream) sub-carriers. The number of utilized octets on downstream direction depends on NSCds, and on upstream direction it depends on NSCus. This value is referred to here as NSC. Octet i (0 <= i < NSC) is set to a value in the range 0 to 254 to indicate that the respective downstream or upstream sub- carrier i has SNR of: (-32 + Adsl2SubcarrierSnr(i)/2) in dB (i.e., -32 to 95dB). The special value 255 means that no measurement could be done for the subcarrier because it is out of the PSD mask passband or that the noise PSD is out of range to be represented. Each value in this array is 8 bits wide.