ese documents in day-to-day operations-most often only when initially deploying, doing ac- ceptance testing, fixing interoperability issues, or something goes awry (hopefully rarely). 8.1.1 Reading the Recommendations As outlined in Table 8-1, the following sections group each of the recommendations into the follow- ing major categories: Physical and TDM timing Frequency in packet networks (SyncE) Packet-based timing distribution (of frequency, phase, and time) The section for each category includes a summary outline of each of the important recommenda- tions belonging to that category. The goal for these sections is to enable the reader to navigate to where further information can be found on topics of interest and to provide a summary of what can be found there. Each of these recommendations is available for download (for free!) in PDF format from the web- site https://www.itu.int. With a decent understanding of the concepts contained in this book, you should be able to understand these documents and put them into the overall solution context. This is not to say that you will understand all of it, but you should understand it well enough for 99% of what you need to do. 8.2 ITU-T Physical and TDM Timing Recommendations The first section of the recommendations to address is that related to frequency transfer using phys- ical and TDM methods. These recommendations include many that specify the historical methods of frequency synchronization, although these techniques were (and still are) widely used in the older 2G/3G radio base stations for mobile networks. They also are still relevant to more modern techniques, such as SyncE, because it was designed with similar goals to the existing legacy meth- ods that came from SDH and SONET. The first section will categorize the different types of recommendations and how they fit into the overall picture. Subsequent sections will address each category in turn and outline a summary of the recommendations that apply for that category. 8.2.1 Types of Standards for Physical Syn