 IEEE 1588-2019 (PTPv2.1): Introduces the newest edition of the PTP standard and explains how it differs from the previous versions. Up until this point, you have explored the basic concepts required to understand the sources of time and the distribution of synchronization using physical systems and methods (such as cables and wires). Now the focus moves onto another popular method to carry timing information, one based upon packet transport. This chapter covers the details of one commonly used packet distribution method, namely the precision time protocol (PTP). "Chapter 9. PTP Deployment Considerations", will cover other methods of transporting synchronization using packets. Network engineers imple- menting high-precision timing solutions increasingly deploy PTP to replace the dedicated time dis- tribution circuits used in older technologies. 7.1 History and Overview of PTP In 2002, the Institute of Electrical and Electronics Engineers (IEEE) defined the first version of a packet-based protocol, known as PTP, to accurately carry time. The IEEE designed PTP chiefly for industrial applications over short-distance communications-such as a local-area network (LAN). The protocol proposed in this standard specifically addressed the following needs of measurement and control systems: Spatially localized (meaning situated close to each other) Microsecond to sub-microsecond accuracy and precision Administration-free operation Accessible for both high-end devices and low-cost, low-end devices The standard was assigned the number 1588, and most people refer to the first version of the stand- ard as IEEE 1588-2002, or more colloquially, PTPv1, named after the version of the protocol. The IEEE updated the PTP standard in 2008 to version 2 of the protocol (PTPv2). Members of nu- merous industries, including the industrial, utility, and telecommunications sectors, who use PTP to provide high-accuracy time between machines or radio base stations, supported the revision. The update added features such as the ability to support 