Transparent Clocks vs. Enterprise Ethernet switches

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.

[1]  Pedro Moreira,et al.  White rabbit: Sub-nanosecond timing distribution over ethernet , 2009, 2009 International Symposium on Precision Clock Synchronization for Measurement, Control and Communication.

[2]  Radim Bartos,et al.  The impact of network latency on the synchronization of real-world IEEE 1588-2008 devices , 2010, 2010 IEEE International Symposium on Precision Clock Synchronization for Measurement, Control and Communication.

[3]  Kang Lee,et al.  Object-oriented Model for IEEE 1588 Standard , 2007, 2007 IEEE International Symposium on Precision Clock Synchronization for Measurement, Control and Communication.

[4]  Kang Lee,et al.  IEEE 1588 standard for a precision clock synchronization protocol for networked measurement and control systems , 2002, 2nd ISA/IEEE Sensors for Industry Conference,.

[5]  Dragan Obradovic,et al.  Synchronization performance of the Precision Time Protocol in the face of slave clock frequency drift , 2008, 2008 IEEE International Conference on Automation Science and Engineering.

[6]  David L. Mills,et al.  Network Time Protocol (Version 3) Specification, Implementation and Analysis , 1992, RFC.

[7]  J.C. Eidson,et al.  Spider transparent clock , 2008, 2008 IEEE International Symposium on Precision Clock Synchronization for Measurement, Control and Communication.

[8]  Deog-Kyoon Jeong,et al.  Practical considerations in the design and implementation of time synchronization systems using IEEE 1588 , 2009, IEEE Communications Magazine.

[9]  Jeff Burch,et al.  Verifying the performance of transparent clocks in PTP systems , 2009, 2009 International Symposium on Precision Clock Synchronization for Measurement, Control and Communication.