This is the receive-direction counterpart to cvdslMCMConfProfileTxBandStart, defining the low end of a frequency band this VDSL line uses for receiving rather than transmitting, since VDSL uses different tone allocations for upstream and downstream in frequency-division schemes. Because upstream and downstream typically use non-overlapping tone ranges in VDSL's FDD-style plans, mixing up transmit and receive band definitions here would misallocate spectrum and degrade or prevent proper operation in one direction. Confirming the receive band range doesn't overlap the transmit band range for the same profile is a basic sanity check before activating a custom spectrum plan.