Manual
ibaClock
56
Issue 1.4
Figure 21: NTP time stamp exchange
The client (peer A) sends the time stamp T1 to the server (peer B). Then the server sends
the client a message containing the time stamp T1 (sending time from the client), T2
(receiving time at the server) and T3 (sending time from the server). As soon as the client
has received this message, the time stamp T4 (receiving time at the client’s location) is
also set and the offset as well as the round-trip delay can be calculated as follows.
𝑅𝑜𝑢𝑛𝑑 − 𝑡𝑟𝑖𝑝 𝑑𝑒𝑙𝑎𝑦 = (𝑇
4
− 𝑇
1
) − (𝑇
3
− 𝑇
2
)
𝑂𝑓𝑓𝑠𝑒𝑡 =
1
2
∙ [(𝑇
2
+ 𝑇
3
) − (𝑇
1
+ 𝑇
4
)]
However, this offset calculation only provides an exact value if the run-times in both di-
rections are identical.
To keep the error in the time synchronization as small as possible, the time stamp ex-
change
𝑇
1
to
𝑇
4
takes place a total of 4 times.
The network components involved do not make any additional corrections to the NTP
packets, as is the case with PTP for example.
