Last year at EXPO the concept of expanding Full-Duplex DOCSIS (FDX) beyond N+0 architectures was introduced using bi-directional echo canceling amplifiers. The expansion of FDX beyond N+0 architectures greatly expands the deployment potential of FDX and the symmetric gigabit services that it enables. As operators gather more experience in the building of N+0 plant, it has become apparent that construction time and costs are greater than initial estimates. This has resulted in more limited N+0 builds in targeted areas and a desire to pursue other methods to expand plant capacity, particularly upstream capacity. In response to this desire, the MSO community and CableLabs started two exploratory working groups, one on Extended Spectrum DOCSIS (ESD) and one on FDX amplifiers. The continuing work of these groups has led to the creation of DOCSIS 4.0, which will bring both FDX and ESD together in a single specification. This paper focuses on FDX and how it might be deployed in existing plant.