OSF DCE Administration Guide--Core Components
OSF DCE Administration Guide—Core Components
In addition to eliminating large inaccuracy values during synchronization, DTS also
discards intervals that are received from faulty clocks (t2 in the figure). DTS detects and
rejects clock intervals that do not intersect with the majority of the intervals. When DTS
detects a faulty interval, it notifies the system manager by displaying an event message,
identifying the server that sent the faulty value.
A server that has a high-drift clock or is far away in the network submits its time to the
DTS entity (t1 in the figure), but the large time interval is ignored since more accurate
times are available. Note that, in Figure 23-2, the endpoints of correct time (t1) are
further from the computed time midpoint than those of the interval that is declared faulty
(t2).
Figure 23-2. Computed Time
Time
CT
Intersection of
correct intervals
(computed time)
UTC
t1
t2
t3
t4
During the synchronization process, servers with the greatest accuracy have the most
influence in determining new system times throughout the network. In the previous
figure, the server that submitted time value t3 has the smallest correct interval and is
therefore the closest to the computed time. Server systems with external time-providers
are usually the servers with the most accurate times. Beyond TP servers, those servers
with the highest quality clocks and best communications links tend to influence the time
on other systems to the greatest degree.
The synchronization process also reduces the skew between systems. The computed
time interval is often smaller than the interval that is supplied by any single clock. Note
that the computed time in the previous figure is a smaller interval than any of the source
intervals. As the synchronization procedure is constantly repeated on each network
system, the skew between systems is reduced and they are more closely synchronized.
However, if a time-provider is absent from the network, the clocks may collectively drift
away from UTC.
23 − 8 Tandem Computers Incorporated 124243