Impulse Noise Monitoring(INM) is not required for modem operation but is a capability for the measurement of Impulse Noise. The INM Profile includes the option to control an INM function on the receive direction in the xTU. A downstream Impulse Noise Monitor applies to the xTU-R; an upstream Impulse Noise Monitor applies to the xTU-C. If INM is not implemented, the relevant profile pointer within the xDSL Line Configuration Vector instance MUST be set to a null value(0). A default profile with an index of '1' will always exist and its parameters will be set to vendor-specific values, unless otherwise specified in this document. The index of this entry is hwVOPINMConfProfIndex.