Transparent Clocks vs. Enterprise Ethernet switches

Abstract

Precision Time Protocol (PTP) is a high-precision time synchronization protocol designed to operate over a local area network. PTP, typically referred to as 1588, is defined by the IEEE Standard 1588™-2008 and provides clock synchronization at the nanosecond level. Even though devices with support for 1588 are widely available, there have been few performance studies of such devices. This paper investigates the impact of latency and high bandwidth background traffic on 1588 clock synchronization in a network consisting of both 1588 and non-1588 aware switches. As expected, we found that 1588-aware switches provide higher precision time synchronization in smaller-scale networks. In larger networks with congestion, 1588-aware switches were unable to maintain high accuracy clock synchronization due to the lack of traffic prioritization. Our results also show that having cut-through Enterprise Ethernet switches with prioritization enabled is adequate for maintaining sub-microsecond synchronization.