The NTP tab of the Test Agent configuration dialog deals with NTP server settings.
Many of the performance tests and monitorings measure delay and/or jitter. These measurements are dependent on an accurate clock. By default, Test Agents will synchronize their internal clock to an NTP server provided by Netrounds (ntp.netrounds.com); you can however use any other NTP server (internal or external). In general, the closer the Test Agents are to the NTP server used, the more accurate the measurements will be.
Time offset: Current time offset to the configured NTP server.
The NTP sync is normally very fast and reliable, and typical time offsets are smaller than 1 ms. The conditions below will therefore be rare (but need to be mentioned):
- If the time offset is larger than 100 ms, the Test Agent is not allowed to perform any testing.
- UDP one-way delay measurements pose a stricter requirement on synchronization: the maximum time offset allowed is 4 ms. If this requirement is not met, a UDP test or monitoring will still start and will produce other measurements, but no one-way delay will be obtained.
- If a question mark "?" is shown for the time offset, this is because the Test Agent does not currently have a connection to the NTP server.
Clicking the Sync NTP button restarts and resets the Test Agent's NTP client. Doing this will not usually improve the synchronization, however. Normally, given an adequate connection, the NTP sync will be good enough for all kinds of testing. If it is not, check the connection.
Interface: The Test Agent network interface used for time synchronization.
Server: The domain name or IP address of the NTP server.
If you are using one Netrounds Test Agent as a proxy for your other Test Agents, you can have these other Test Agents synchronize their clocks using the proxy Test Agent. You then select the IP address of the proxy Test Agent as NTP server. The proxy Test Agent itself may for example synchronize to ntp.netrounds.com.