A cable modem in communication with a cable modem termination system (CMTS) scans and tries to lock onto a primary channel, tries to receive a media access control domain description (MDD) message includes subsidiary channels from the CMTS if the primary channel is locked, and tries to lock onto the subsidiary channels in the received MDD message. The cable modem further retains the cable modem to work with the DOCSIS 3.0 standard upon the condition that the primary channel and the subsidiary channels are all locked or retains the cable modem to work with the DOCSIS 2.0 standard upon the condition that the MDD message is not received or the subsidiary channels are not successfully locked.