ertain gap between each message. Ideally, this gap will be constant, but in reality, it will change a bit because of factors such as software scheduling. However, the slave can always determine the gap between the sending of consecutive Sync messages through the difference between the tl timestamps of those messages. On the slave side, the perceived gap between each mes- sage will be different, since the timestamping clock is not currently running at the correct tick rate. By comparing the perceived gap (from the t2 timestamps) with the actual gap Master Slave Slave uses t1 and t2 timestamp information to calculate on values. Average of on represents the Ab + db slave's "tick rate" error. Slave adjusts local oscillator to make on zero. Ac + Sc FIGURE 8-17 PTP syntonization process. PTP, Precision Time Protocol. 284 Open Radio Access Network (O-RAN) Systems Architecture and Design (from the tl timestamps), and averaging over many cycles to mitigate the effects of network variations, the error in the local tick rate can be determined and the rate adjusted. The first step of the slave synchronizing to the master involves the calculation of the round-trip delay, which is then divided by two to give the one-way (master to slave) delay. From Fig. 8-16, this round-trip delay is the time between the master sending the Sync mes- sage (t1) and the time it receives the Delay Request message (t4) minus the time it took the slave to send the Delay Request message after receiving the Sync message, which is t3 - t2. Therefore, round-trip delay = (t4 - t1) - (t3 - 12) or, by rearranging: round-trip delay = (t2 - t1) + (t4 - t3) and the one-way delay is half of this, SO: one-way delay = [(t2 - t1) + (t4 - t3)]/2 An important consideration in these calculations is that because the slave clock is not necessarily synchronized to the master clock yet-after all, that is what this whole process is being done to achieve-the value of t2 relative to tl, and of t4 relative to t3, could be way dif- ferent to the actual network delays, becau