A bandwidth allocation and monitoring method may divide available bandwidth on a shared communication medium into a plurality of discrete tones that can be individually allocated to modems on an as-needed basis. The effective modulation rate that a particular modem can use for each discrete tone can be monitored over time using a schedule of pilot tones transmitted from the modems on different tones at different times. The schedule may define representative pilot tones, in which case effective modulation rates for neighboring tones may be inferred from a determined effective modulation rate of a pilot tone.