Recommendation ITU-T J.224 defines the fifth generation of high-speed data-over-cable systems. The fifth-generation transmission systems introduce a number of new features that build upon what was present in previous ITU-T Recommendations namely ITU-T J.112, ITU-T J.122, ITU-T J.222.x-series, and ITU-T J.223.x-series. This Recommendation includes key new features for the physical (PHY) layer and defines full duplex data over cable service interface Specification (DOCSIS) mode of operation, including enhancements to the media access control (MAC) layer protocols as well as requirements for upper layer protocols such as Internet protocol (IP), dynamic host configuration protocol (DHCP), etc. The fifth-generation cable modem specifications fully incorporate the fourth generation specifications. NOTE - The structure and content of this Recommendation have been organized for ease of use through direct reference to the original source material, based on the recognition of CableLabs by ITU as an A.5 organization (https://www.itu.int/en/ITU-T/extcoop/Pages/sdo.aspx).