s ahead of the master clock, SO the timestamps from each clock have that offset built in between them. The transparent clock has no concept of time, but it calculates the residence time using its own oscillator or frequency refer- ence. The mean transit time between GM and TC is 0.60 ns but there is 0.05 ns of asymmetry in the link, and similarly between TC and BC, the mean transit time is 0.70 ns with 0.20 ns of asymmetry. In contrast to the first hop, in the second hop the forward direction is shorter (0.70 compared with 0.90), which gives a negative value for asymmetry (-0.20). These asymmetry values are known beforehand and are configured on the port facing the upstream clock. These configured values are applied to the CF on both reception and transmission. Taking each step of the process in turn: 1. The timestamp for the origin of the Sync message is 144 S and 7.3 ns, which is represented as 144:7 in the originTimestamp field (which only holds seconds and nanoseconds) and 0.3 ns in the CF, which has the sub-nanosecond field. The combination of these two fields, when they ar- rive on the slave, will be used as t1. 2. The TC receives the message 0.65 ns later (must be a quick link!) and adds the measured resid- ence time of 207.4 ns to the 0.3 ns already in the CF. The TC is also configured with +0.05 ns of asymmetry for that link (positive being slower in the forward direction), which it also adds to the CF. So, the CF now contains 207.75 ns. 3. The BC receives the message 0.50 ns later, but that link has asymmetry (in the reverse direc- tion), SO the boundary clock adds that -0.20 ns of asymmetry to the incoming CF, SO it is now 207.55 ns. The t2 timestamp, however, comes from the BC clock and its value is 144:241.05 when the Sync message arrives. One could determine this by adding the original time from the master (144:7.3), the two (real, unadjusted) transit times, the TC residence time, and the clock offset of 25.2 ns (since the slave is ahead of the master) to arrive at the same value. The BC generates a