In one example, a Cable Modem Termination System (CMTS) sends first bandwidth allocation messages to a first upstream transmit interface on a cable modem and send second bandwidth allocation messages to a second upstream transmit interface on the cable modem. The bandwidth allocation messages indicate transmit windows for the cable modem to range over the interfaces. The transmit windows included in the first bandwidth allocation messages are spaced based on receipt of ranging requests from the second upstream transmit interface, and the transmit windows included in the second bandwidth allocation messages are spaced based on receipt of ranging requests from the first upstream transmit interface.