Time settings

Generic

Time settings

The Allegro Network Multimeter can be configured to use a time synchronization service. NTP is supported for all variants of the Allegro Network Multimeter. PTP service may be used if management interface supports hardware time stamping. If a GNSS/GPS-capable extension card is available, GNSS/GPS time synchronization is available and the antenna cable delay in nanoseconds can be configured.

To enable a time service, switch to the desired type in the dropdown box. The time service field will show whether the selected service is running or not.

NTP - For active NTP time retrieval, you can specify and edit dedicated NTP servers the Allegro Network Multimeter should communicate with. If you do not specify a NTP server, a set of predefined NTP servers will be automatically selected.

NTP from data plane - For passive time retrieval, NTP from data plane can be used to retrieve the time to be synchronized passively from NTP packets within the traffic that is analyzed. The IP address of a desired NTP server must be set. As soon as a NTP server packet is seen, the system time of the Allegro Network Multimeter will be set. The wait period field can be used to set a time period where subsequent updates are ignored. If set to 0, every time packet of that server will be used. NTP from data plane is ideal in situation where the Allegro Network Multimeter MGT interface can not or may not actively connect to the network.

PTP - For PTP time retrieval, the PTP grandmaster clock identity is shown. This is usually an EUI-64 address. The first and last set of octets of the identity represent the (EUI-48) MAC address of the grandmaster.

The following settings are possible for PTP and should match the settings of the PTP grandmaster:

• Delay mechanism: Use end-to-end (E2E), peer-to-peer (P2P) or automatic delay measurement. In case automatic measurement is selected, E2E is used at the beginning and switched to P2P when a peer delay request is received. Default is Auto.
• Network transport: Use UDPv4, UDPv6 or Layer 2 as network transport. Default is UDPv4.
• Domain number: The domain number of the grandmaster. This is used to define logical groups of synchronized clocks.

GNSS/GPS - The GNSS/GPS time synchronization option will become available when a GNSS/GPS-capable extension card is installed in the Allegro Network Multimeter.

If no time synchronization mechanism is selected the date and time of the device can be manually configured by entering a properly formatted date and time description. Below the time synchronization settings, the time zone used by the device can be configured. The drop-down list provides a list of cities grouped by world regions to select the appropriate time zone.

When a nanosecond-resolution capture card with support for PPS-synchronization is installed, the toggle Enable PPS synchronization can be used to enable this type of synchronization. It is only shown when the time service chosen is not GPS as those two modes cannot be used simultaneously. The time offset in nanoseconds is also configurable allowing to compensate for the PPS connection cable length. This feature should only be enabled when it is made sure that a proper PPS signal is provided to the network adapter. Otherwise the packet timestamps may be incorrect.

To make any of the above changes take effect, click on the Save settings button at the bottom of the page. To reload the stored settings, click on Reload settings.

Changes of the system time and packet timestamping

The packet processing uses a monotonically increasing time for software packet timestamping and statistics calculation (see Hardware packet timestamping in Global settings for information about packet timestamps on interfaces with hardware packet timestamping enabled) . If the clock for some reason jumps forward in time (e.g. changing the time synchronization method or manually changing the time) the same will happen with the statistics and the packet timestamps and there may be a gap in the statistics. If the system clock jumps backwards in time the packet processing cannot jump back. In this case a warning "problematic change of system time detected (core restart recommended)" is displayed. While the packet processing time is ahead of the system clock the packet processing time will run at a speed of 75% of real-time so that the system clock will eventually catch up. This can e.g. lead to statistics that show higher traffic bandwidth than there actually is. A restart of the packet processing is always recommended in this case.

Time discrepancy

If the clocks of the multimeter and the browser accessing the web interface are not synchronized, the displayed results may appear to be unexpected or wrong (due to the results being timestamped using the multimeter's clock, but some calculations being done in the browser using the browser's clock). The web interface can detect when these two clocks are not in sync and can generate a warning when it happens. The number of seconds the clocks need to drift apart before a warning is displayed can be configured here. The default value is 60 seconds

Time profiles

Time profiles are used to configure the time frame during which certain rules (e.g. incidents, ringbuffer filters) in the multimeter should be applied. Each profile consists of a name and a set of timespans that dictate when the profile is active. Multiple timespans can be configured for each weekday.