ernet Distant Midway Closer STB #1 STB #2 STB #3 Figure 2-7 Incorrectly Synchronized Signals on a Shared Media The receiver on the headend is going to struggle to decipher the corrupted transmissions on the cable because the signals are not arriving at the headend receiver at the correct time. In one case, the range to STB #1 has been measured incorrectly (too low a value) and SO the STB does not advance its transmissions enough to compensate for the delay on the cable, resulting in its transmissions ar- riving too late-at the time STB #2 has already started transmitting. Similarly, STB #2 has a phase alignment error that causes it to start transmitting too soon, talking over the tail end of the transmission from STB #3. One quick solution to this scenario would be to increase the width of the guard band, but that is simply consuming time on the cable that could be spent transmitting user data-and therefore a waste of money. 2.2 Use of Time Synchronization in Finance, Business, and Enterprise Synchronization, especially of time, has always been an important part of normal operations in IT systems and network elements. You are likely aware of the Network Time Protocol (NTP) that has been used for decades to coordinate the time on machines across a network. NTP uses a two-way time protocol to transfer Coordinated Universal Time (UTC) across a hierarchy of machines, as shown in Figure 2-8. The routers in the figure connected to the source of time (for example, GNSS or an atomic clock) are known as stratum 1, and every hop further away increases the stratum num- ber to indicate a reduction in the likely accuracy of the time on that node. Time source Servers Stratum 1 Peers Stratum 2 Stratum 3 Figure 2-8 NTP Time Distribution Network Hierarchy Besides being used for business processing (for example, logging the time a subscriber made a tele- phone call for billing purposes), NTP also has valuable operational uses, such as event correlation, fault isolation, and network-wide troubleshooting. The network engineer relies