Performance Comparison of R-PHY and R-MACPHY Modular Cable Access Network Architectures

Abstract

Emerging modular cable network architectures distribute some cable headend functions to remote nodes that are located close to the broadcast cable links reaching the cable modems (CMs) in the subscriber homes and businesses. In the remote-PHY (R-PHY) architecture, an R-PHY device conducts the physical layer processing for the analog cable transmissions, while the headend runs the data over cable service interface specification (DOCSIS) medium access control (MAC) for the upstream transmissions of the distributed CMs over the shared cable link. In contrast, in the remote MACPHY (R-MACPHY) architecture, an R-MACPHY device (RMD) conducts both the physical and MAC layer processing. In this paper, we conduct a comprehensive performance comparison of the R-PHY and R-MACPHY architectures. We first develop analytical delay models for the polling-based MAC with gated bandwidth allocation of Poisson traffic in the R-PHY and R-MACPHY architectures. We then conduct extensive simulations to assess the accuracy of the analytical model and to evaluate the delay-throughput performance of the R-PHY and R-MACPHY architectures for a wide range of deployment and operating scenarios. Our evaluations include long converged interconnect network (CIN) distances between remote nodes and headend, bursty self-similar traffic, and double-phase polling to mask long CIN propagation distances. We find that for long CIN distances above 100 miles, the R-MACPHY architecture achieves significantly shorter mean upstream packet delays than the R-PHY architecture, especially for bursty traffic. Our extensive comparative R-PHY and R-MACPHY evaluation can serve as a basis for the planning of modular broadcast cable based access networks.