Description: The SNR Margin per sub-carrier group, expressing the ratio between the received signal power and received noise power per sub-scriber group. It is an array of 512 octets, designed for supporting up to 512 (downstream) sub-carriers groups and can be retrieved in a single segment. The number of utilized octets on downstream direction depends on NSds, and on upstream direction it depends on NSus. This value is referred here as NS. Octet i (0 <= i < NS) is set to a value in the range 0 to 254 to indicate that the respective downstream or upstream sub- carrier group i has SNR of: (-32 + Xdsl2SubcarrierSnr(i)/2) in dB (i.e., -32 to 95dB). The special value 255 means that no measurement could be done for the sub-carrier group 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. This table is from draft-ietf-adslmib-vdsl2-01.txt.