3. Frequency, Phase, and Time Deployment Options 4. Mid-haul and Front-haul Timing 5. Timing Security and MACsec Chapter 12. Operating and Verifying Timing Solutions 1. Hardware and Software Solution Requirements 2. Writing a Request for Proposal 3. Testing Timing 4. Automation and Assurance 5. Troubleshooting and Field Testing References Further Reading Abbreviations Foreword The distribution of synchronization across telecommunications networks has been a requirement since the emergence of digital networks back in the 1970s. Initially, frequency synchronization was required for the transfer of voice calls. Over the years, multiple generations of equipment standards increased the requirement for frequency synchronization. In the relatively recent past, the require- ment was expanded to include time or, more precisely, phase synchronization. This need is princip- ally driven by mobile base stations requiring phase alignment with other base stations to support overlapping radio footprints. One of the main issues when dealing with network synchronization is that when synchronization goes wrong, it initially doesn't look like a synchronization problem! I started my engineering career as a digital designer, and one of the first lessons I learned when doing printed circuit board (PCB) layout design was to always do the clock distribution plans first and make them as robust as pos- sible. This was, and still is, best practice, because on PCB assemblies, when clocking issues occur, they manifest as logic design issues, not as clocking issues, making these types of problems very challenging to debug. Networks are just the same. Synchronization issues in networks lead to sporadic outages and/or data loss events, often hours or days apart, which can appear to be traffic loading/management issues and thus are very challenging to track down. This is why network architects have always taken great care to design quality into their synchronization networks to ensure the synchronization is distrib- uted robustly by design, not b