A cable modem system and method is provided for supporting data transfer protocols that extend beyond standard protocols used in conventional data over cable systems. A cable modem in accordance with the invention determines, during registration, whether a CMTS with which it communicates is capable of supporting an extended protocol, and if it is, transfers data to the CMTS in accordance with the extended protocol. Additionally, a CMTS in accordance with the invention is notified during registration whether or not a cable modem supports an extended protocol and stores this information. When a request for transmission opportunity is subsequently received from the cable modem, the CMTS accesses the stored information to determine if the cable modem supports the extended protocol. If the cable modem supports the extended protocol, the CMTS processes data received from the cable modem during the transmission opportunity in accordance with that protocol.