Analysis of Clock Synchronization Approaches for Residential Ethernet

Residential Ethernet (ResE) is a new standardization activity in IEEE 802 that is considering extensions to Ethernet to allow the transport of time-sensitive traffic. Applications that ResE is expected to carry will include digital video, high-fidelity digital audio, and gaming traffic, as well as traditional non-time-sensitive traffic (e.g., data traffic). One goal of ResE is to allow a single network infrastructure in the residence to carry both timesensitive and non-time-sensitive applications. The Audio/Video (A/V) applications for ResE have tight jitter and wander requirements; in addition, applications where A/V content is delivered to multiple locations (e.g., gaming, digital stereo speakers) may have tight time synchronization requirements. To meet the jitter, wander, and time synchronization requirements for the applications, time synchronization must be provided to the ResE endpoints. Several approaches for providing time synchronization, all of which are based on principles used in IEEE 1588 and employ time stamps, are being considered. However, a number of algorithms for using the time stamp information have been suggested, e.g., instantaneous phase adjustments, instantaneous phase adjustments and less frequent instantaneous frequency adjustments, phase adjustments and possibly less frequent frequency adjustments with filtering, phase and frequency adjustments using phase-locked loops (PLLs), and use of transparent clocks. The jitter and wander performance and delivered time accuracy of each scheme will depend on the rate of phase and, if appropriate, frequency adjustments (which is limited by the rate at which time stamp information is transported), bandwidth and gain-peaking of the various filters and/or PLLs, quality of the node clocks (frequency tolerance, phase noise level and characteristics, etc.), and size of the network. This paper develops simulation models to analyze several of the approaches (the remaining approaches will be considered in future work). Simulation results are obtained and compared with each other and with end-to-end application jitter and wander requirements. While this is initial work, the eventual goal is to provide input for deciding which approach is best for Residential Ethernet.