This specification defines the PHY, MAC, LINK and CONVERGENCE protocol stack layers for the G.9954.X system providing the following features: " Operation over Phoneline or/and over Coax. " PHY-layer payload transmission rates of 4 - 320 Mbit/sec. " Rate adaptive transceivers that optimize data rates and packet error rates for dynamically varying channel conditions on a per-packet basis. " QAM modulation technique for communication over phone wire or coaxial cabling. " Spectrum notching over Phoneline for compatibility with Amateur Radio services. " Synchronous MAC protocol controlled by a dynamically elected master employing a collision avoidance media access strategy. " Support for constant and variable bit-rate data services. " Peer-to-Peer communication within a master-controlled network. " Packet aggregation (packetization) performed within the G.9954.X protocol stack layer up to latency limits of the service flow and available transmission bandwidth. " Quality of Service guarantees for bandwidth, jitter, latency and BER. " QoS support for services with explicit traffic and rate specifications providing a link layer that is well suited for streaming audio and video. " Protocol-specific convergence layers. " Backward Compatible with G.9951/G.9952 in mode A over phoneline using G.9951/G.9952 asynchronous MAC protocol. " Coexistence and interoperability between G.9954 and G.9954.X devices in a mixed network. " Compatibility with other phoneline services such as POTS, V.90, ISDN and G.992.1, G.992.2, G.992.3, and G.992.4. " Compatibility with other coaxial services such as VDSL, VDSL2 and Cable-TV channels. " Interoperability between Phone and Coax PHY layers using spectral modes A & B thus allowing a mixed phoneline/coaxial network. " Local and remote management of G.9954.X devices. " Provisions for future security extensions.