le back-haul networks are present in the power industry, SO there are obviously lessons we can share. Generally, many of the tools and deployment lessons used in one industry are directly applicable to other industries. In the power industry there is an increasing focus on improving the robustness and stability of the power distribution network, or "the grid," especially as it needs to cope with the challenges of inter- mittent power sources such as that from renewable sources. You might hear the term "smart grid" to describe any one of several programs to increase the "intelligence" of the grid through digitalization. One of these efforts to improve the grid in the United States is the North American Synchro Phasor Initiative (NASPI), which requires the placement of monitoring devices called phasor measure- ment units (PMUs) around the grid. These devices measure synchrophasorsprecise measure- ments of the magnitude and phase of the sine waves carrying the electrical power. These measure- ments are taken at high speed (> 30 measurements per second) and each measurement is timestamped according to a common time reference, allowing correlation of these measurements across the whole grid. Synchronization of the PMU equipment is generally done using an industry-specific profile of PTP, called the "Power Profile," with a local GPS receiver as the source of the common time reference. There are numerous applications in the power substation that use synchronization, with a range of required accuracies. Some of these applications, such as supervisory control and data acquisition (SCADA), are similarly deployed by other industries, such as monitoring the power grid in an elec- tric railway track network. The current issue facing grid operators is to how to be prepared in the case of an outage of the local GPS system, such as that caused by a jamming event. The solution is to carry a backup source of time from a remote location over the data transport network (see Figure 2-12). The obvious choice for the solution is again 