This identifies the tone index for which a maximum allowed transmit PSD ceiling, as opposed to the target PSD in the plain TxPSD table, is being specified, serving as the key for the paired cvdslMCMConfProfileMaxTxPSDPSD value. The distinction between target PSD and max PSD matters because the max value defines a hard regulatory or safety ceiling the modem must never exceed at that tone, even if adaptive power control would otherwise push higher. This table is what enforces spectral compatibility rules, like protecting amateur radio bands, as a strict cap rather than just a suggested operating point.