Measures reported by NTPTimeServerTest
The absence of time synchronization between an NTP client and server can have serious repercussions on the performance and operations of the client - for instance, scheduled tasks such as virus scans or backup routines may not run on time on the client, SSL certificate validity checks may go awry, domain controllers may not be able to authenticate Windows clients, etc. If these adversities are to be avoided, administrators should be proactively alerted to a potential non-sync between the client's time and the server's time and should also receive a ‘heads-up’ on the probable reasons for the same. This is where the NTPTimeServerTest test helps!
This test periodically checks the accessibility and responsiveness of the NTP server from an external location, and also indicates how different the client's time is from the server's time. In the process, the test not only points to a time non-sync, but also reveals the probable reasons for the same - is it because the NTP server is down? Is it because the NTP server is slow in processing client requests? Or is it because the gap between the server's time and the client's time is very high?
The measures made by this test are as follows:
| Measurement |
Description |
Measurement Unit |
Interpretation |
| Availability |
Indicates whether/not the NTP server is available. |
Percent |
If this measure reports the value 100, it indicates that the NTP server is accessible. The value 0 on the other hand indicates that the NTP server cannot be connected to. |
| Delay |
Indicates the length of time it takes for a signal to be sent plus the length of time it takes for an acknowledgment of that signal to be received. This time delay therefore consists of the transmission times between the two points of a signal. |
Secs |
To synchronize its clock with a remote server, the client must compute the round-trip delay time and the offset. The round-trip delay δ is computed as:
δ = (t3-t0)-(t2-t1)
where
t0 is the client's timestamp of the request packet transmission, 100
t1 is the server's timestamp of the request packet reception, 150
t2 is the server's timestamp of the response packet transmission and 160
t3 is the client's timestamp of the response packet reception. 120
The shorter and more symmetric the round-trip time, the more accurate the estimate of the current time. |
| Offset |
Indicates the number of seconds the client must add to its time to synchronize with the server's time. |
Secs |
The offset θ is given by
A positive value indicates the server clock is higher. A negative value indicates the client clock is higher.
Normally, if the client offset exceeds NTP's default panic threshold of 1000 secs, NTP exits with a message to the system log. You can however, configure NTP to allow the time to be set to any value without restriction; but, this can happen only once. If the panic threshold is exceeded after that, NTP will exit with a message to the system log.
You can use the detailed diagnosis of this measure to know the client's time stamp, the server's time stamp, and the offset. |
| Time_direction |
Indicates whether the client is behind / ahead of the server in terms of time. |
|
If the client's clock is running faster than the server's, this measure will report the value Ahead. If the client's clock is running slower than the server's, this measure will report the value Behind.
The numeric values that correspond to these measure values are as follows:
| Measure Value |
Numeric Value |
| Ahead |
1 |
| Behind |
0 |
Note:
By default, this measure reports the Measure Values listed above to indicate whether client is ahead or behind the server. In the graph of this measure however, the same represented using the numeric equivalents. |
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