dmtAlDslNetworkProfile-MarginConfig-RaDownshiftMarginDown 1.3.6.1.4.1.529.23.10.1.1.48

Valid ONLY in rate-adapt-mode = DYNAMIC. In dB. If current down stream noise margin is below this parameter for more than ra-downshift-int-down sec, modem shall attemp to rate adapt (bitrate down).