Examination of time and frequency control across wide area networks using IEEE-1588v2 unicast transmissions

The IEEE 1588–2008 Precision Time Protocol (PTP) version 2 (IEEE 1588v2) can be used to synchronize a slave clock to a grandmaster clock over a wide area network (WAN). However, many of the algorithms the slaves use to steer to the master are optimized for a scenario where both devices are on the same subnet or local area network (LAN). This paper is a study of existing PTP hardware from a number of different manufacturers in unicast mode. We characterize the performance of the equipment, beginning with the timing outputs of the masters that are locked to their built-in Global Positioning System (GPS) receivers. Next, we compare the results of steering unicast clients to their masters through a LAN versus several wider-area network configurations such as virtual-LANs and the public Internet. Analysis of the results will show how clients of different manufacture handle the various network paths. It is our hope that these comparisons will instigate changes to clock steering and synchronization algorithms, which may help improve the overall capabilities of PTP for telecom and other networking environments. As network synchronization techniques improve, the quality of the PTP masters will become more significant. Therefore, the performance and calibration of PTP masters with respect to UTC(NIST) is also discussed.