orting timing information. The latter part of this chapter explained the different elements of this network chain and the variations that can be seen in these chains. Even though it is recommended to keep the network chain as short as pos- sible, ITU-T G.803 defines the maximum number of nodes that can exist in such chains and ex- plains the restrictions based on different clock types belonging to different stratum levels. As discussed in this chapter, there can be deployments where NEs are connected into different topo- logies and are often configured into ring topologies. If not designed properly for frequency distribu- tion, such deployments can suffer from a degraded synchronization signal, where frequency is looped back through the network SO that all nodes get synchronized to the delayed version of their own clock-a timing loop. The chapter discussed an example of NEs connected in a ring topology and explained the formation of timing loops, which could cause critical issues for timing networks. The goal of this chapter was to explain the technology, deployments, and restrictions of frequency distribution via the physical layer, which is one of the main aspects of timing networks. "Chapter 7. Precision Time Protocol", focuses in detail on the protocols and exact mechanism of distributing timing information using packets. Chapter 7. Precision Time Protocol In this chapter, you will learn the following: History and overview of PTP: Explains how PTP originated and provides an overview of the imperatives that led to its development. PTP Versus NTP: Compares these commonly used time protocols. IEEE 1588-2008 (PTPv2): Examines the many features of the standard and the principal mech- anisms of its operation. PTP clocks: Examines the types of clocks defined in IEEE 1588 and the characteristics of each clock type. Profiles: Provides details of the three telecom profiles and the other major industry profiles. PTP security: Describes how security has been handled in PTP and explores future develop- ments on the topic.