This draft new Recommendation 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 Recommendations [ITU-T J.112], [ITU-T J.122], [ITU-T J.222], and [ITU-T J.223]. This Recommendation includes key new features for the physical (PHY) layer and defines Full Duplex DOCSIS® Mode of operation, including enhancements to the media access control (MAC) layer protocols as well as requirements for upper layer protocols (e.g., IP, DHCP, etc.). Also, security specification and Operations Support System Interface (OSSI) specifications for cable modem and CCAP are in scope. The fifth-generation high-speed data-over-cable systems specifications are also known as DOCSIS 3.1 specifications (DOCSIS 3.1 Full-Duplex). This work item plans to endorse as ITU-T Recommendation the following CableLabs standards: [DOCSIS MULPIv3.1], [DOCSIS PHYv3.1], [DOCSIS CM-OSSIv3.1], [DOCSIS SECv3.1] and [DOCSIS CCAP-OSSIv3.1].