lock recovery servo in the slave-the software function that processes the timestamps to achieve syntonization and synchronization-has to use smart techniques that allow it to try and gauge the PDV and the effect it has had on each message received and use advanced algorithms to filter out the effects of PDV. How well this can be done depends on a number of factors-internal ones to the slave, basically how smart the boffins who developed the servo are, and external ones such as both the amount and nature of the PDV. Often, a leading-edge servo implementation can achieve PDV filtering of a couple of orders of magnitude. In other words, if the PDV experience by the event messages is 100 us, the recovered time will be accurate to 1 us. As we shall see, this might be acceptable for some applications but not others. The second way of handling PDV is to do whatever can be done to eliminate it. If there is little PDV affecting the event messages, there is not SO much to have to filter out. This is where we come back to FTS, PTS, and the value of boundary clocks. Consider the three net- works shown in Fig. 8-22. PTP Unaware Network Generic Generic Generic Generic Generic Generic Non-PTP Non-PTP Non-PTP Non-PTP Non-PTP Switch Switch Switch Switch Switch Full Timing Support (FTS) G.8275.1 G.8275.1 G.8275.1 G.8275.1 G.8275.1 G.8275.1 G.8273.2 G.8273.2 G.8273.2 G.8273.2 G.8273.2 Partial Timing Support (PTS) G.8275.2 G.8275.2 G.8275.2 G.8275.2 G.8275.2 G.8275.2 T-BC-P T-BC-P G.8273.4 G.8273.4 FIGURE 8-22 PTP network types. PTP, Precision Time Protocol. Chapter 8 Synchronization in open radio access networks Each of these networks has a PTP master providing time to a PTP slave through a net- work of five switches. This difference between these three is whether those switches also act as PTP boundary clocks. In the first network, none of the switches act as boundary clocks, meaning that the PTP event messages have to pass through each switch in exactly the same way as any other data packet would-this is a PTP-unaware network, si