By Marek Hajduczenia, PhD, Charter Communications; Glen Hardin, Charter Communications; John Chapman, Cisco Systems
Why RPHY go the distance? The answer to this question has a dramatic impact on the plant topology, network implementation, compute scaling and, most importantly, the operational performance of the overall system. One of the cost reduction opportunities is in the consolidation of HFC hub operations. HFC hubs can be consolidated, simplified, or even completely decommissioned by transitioning traditional integrated CMTS (iCMTS) platforms to virtualization solutions. This drives the opportunity for the complete hub-collapse and aggregating more customers into larger metro sites. Charter has been evaluating different technologies with Remote PHY (also referred to as R-PHY, R PHY, or simply RPHY) being one of those. Charter also examined the distance question of RPHY design in detail from a theoretical and practical perspective. While there are general statements to that effect, the relationship between specific distances and performance has not been identified to date. Spectrum Enterprise has been deploying vCMTS with subtended video cores and RPHY devices for years with many of its hospitality clients. The commercial application of RPHY has given Charter real-world data of actual deployments. This data is very relevant to the residential application for data services. Additionally, significant studies have been conducted using impairment generators in trial deployments, validating the impact of symmetric and asymmetric latency on the data throughput, video services, etc. This paper explains the challenge at hand, identifying key technical risks and limitations, and looks at the lessons learned from the existing video centric RPHY deployments within the Charter network. Details on the internal studies with impairment generator are also presented, exploring the limits of RPHY architecture performance, providing a much more positive picture of the system-level performance.